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Limitations of Existing Scheduling Tools in Planning Utility Line Construction Projects

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Title:
Limitations of Existing Scheduling Tools in Planning Utility Line Construction Projects
Creator:
CHENG, BIN ( Author, Primary )
Copyright Date:
2008

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Subjects / Keywords:
Assembly lines ( jstor )
Charts ( jstor )
Drainage water ( jstor )
Geometric lines ( jstor )
Irrigation water ( jstor )
Linear scheduling ( jstor )
Manholes ( jstor )
Sanitary sewers ( jstor )
Scheduling ( jstor )
Stormwater sewer systems ( jstor )

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Source Institution:
University of Florida
Holding Location:
University of Florida
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Copyright Bin Cheng. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Embargo Date:
12/31/2006
Resource Identifier:
496174532 ( OCLC )

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LIMITATIONS OF EXISTING SCHEDULING TOOLS IN PLANNING UTILITY LINE CONSTRUCTION PROJECTS By BIN CHENG A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN BUILDING CONSTRUCTION UNIVERSITY OF FLORIDA 2005

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Copyright 2005 by Bin Cheng

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This dissertation is dedicated to my wife, my son, and my parents.

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ACKNOWLEDGMENTS First I would like to thank to those individuals who without their guidance, encouragement, and assistance this thesis would not have been possible. I am especially thankful for the time and energy Dr. R. Raymond Issa and Dr. Ian Flood devoted to leading me in the right direction and helping me prepare my thesis. I will be forever grateful for Dr. Ian Flood’s fantastic scheduling class. I would also like to thank Dr. Robert Cox for serving on my committee. Last but definitely not least, I really appreciate the help of Mr. Charles D. Bell and all my former colleagues with Hamlet Construction who gave me valuable information and support. I owe special thanks to my wife and my parents for their support, and for their understanding and encouragement throughout the entire process. I would be lost without their unconditional patience and love. iv

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TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................iv ABSTRACT .......................................................................................................................xi CHAPTER 1 INTRODUCTION............................................................................................................1 Study Motivation..........................................................................................................1 Organization of this Study............................................................................................2 2 LITERATURE REVIEW.................................................................................................4 Gantt (Bar) Chart Scheduling Method..........................................................................5 Advantages of Bar Charts......................................................................................5 Limitation..............................................................................................................6 Network Scheduling Methods......................................................................................6 Advantages of Network Scheduling Methods.......................................................7 Limitation of Network Scheduling Methods.........................................................7 Time-Scaled Logic Diagrams: A Variation of CPM....................................................8 Linear Scheduling Method (LSM)..............................................................................10 Benefits and Limitations......................................................................................12 Barriers to Implementing LSM...........................................................................13 Commercial LOB Software Packages.................................................................13 Summary.....................................................................................................................14 3 RESEARCH OBJECTIVES...........................................................................................16 4 MODIFIED LINEAR SCHEDULE METHOD.............................................................18 5 CASE STUDY PROJECT OPERATION MODEL...................................................22 Introduction.................................................................................................................22 Quantity Estimates for the Project..............................................................................24 Estimate Project Duration...........................................................................................28 Estimate Equipment Production Rate..................................................................29 Estimate the Production Rate for Each Crew from the Time Sheet....................30 Project Monitoring and Control..................................................................................38 v

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HCC’s Scheduling Problem........................................................................................42 Summary.....................................................................................................................43 6 CASE STUDAY...............................................................................44 Unit 97 Project............................................................................................................44 Estimating Construction Duration for the Utility Lines.............................................46 Estimation of Sewer Line Construction Duration...............................................46 Estimate of Storm Drainage Line Construction Duration...................................49 Potable Water Line and Irrigation/Fire Water Line............................................51 Linked Bar Chart and Linear Scheduling for Unit 97................................................52 Application of the Modified Linear Schedule Method on Florence Path...................55 Identify Intersection Location.............................................................................55 Linear Scheduling on Florence Path....................................................................58 Adjusted Linear Scheduling for Florence Path...................................................59 Summary.....................................................................................................................60 7 CONCLUSIONS AND RECOMMENDATIONS........................................................62 Conclusions.................................................................................................................62 Recommendations for Future Research......................................................................63 LIST OF REFERENCES...................................................................................................65 BIOGRAPHICAL SKETCH.............................................................................................67 vi

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LIST OF TABLES Table page 2.1 Comparison of Linked Bar Chart and Linear Scheduling Method..........................15 4.1 Surveying Data from Engineering Drawing.............................................................18 4.2 Estimated Construction Duration.............................................................................20 5.1. Equipment List and Rate for one typical Sewer Crew.............................................27 5.2. Rate of a Typical Crew for H Company..................................................................27 5.3 Cycle Times for Tracked Excavator.........................................................................29 5.4 Production Rate for Laying 8” PVC Sewer Lines for HCC.....................................33 5.5 Production Rate of Installing Manholes for H Company.........................................33 5.6 Production Rates of Laying Storm Drainage Pipe...................................................34 5.7 Production Rate from Historical Project..................................................................35 6.1 Summary of Project Information..............................................................................46 6.2 Estimated Duration of Main Sewer Line..................................................................47 6.3 Predicted Duration of Manhole Construction..........................................................48 6.4 Predicted Duration of Installing Service Line..........................................................49 6.5 Predicted Duration of Laying Main Storm Drainage Line.......................................50 6.6 Predicted Duration of Storm Drainage Manhole Installation...................................51 6.7 Predicted Duration of Potable Water Line and Irrigation/Fire Water Line..............52 6.8 Summary of Unit 97 Utility Lines............................................................................52 6.9 Coordinates of Storm Drainage Stations and Sanitary Sewer Stations....................56 6.10 Production Rate and Duration for Each Section of Storm Drainage Line...............58 vii

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6.11 Production Rate and Duration for Each Section of Sanitary Sewer Line................59 6.12 Comparison of Schedule Tools Over the Project – Florence Path...........................61 viii

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LIST OF FIGURES Figure page 2.1 Bar Chart for Placing a Slab on a Grade (Mubarak, 2003)........................................5 2.2 Time-Scaled Logic Diagram (Flood, 2003)...............................................................9 2.3 Time-Scaled Logic Diagram....................................................................................10 2.4 Balanced Production Curves for Repetitive Processes............................................12 2.5 Non-balanced Production Curves for Repetitive Processes.....................................12 4.1 Linear Equations for Line 1 and Line 2...................................................................19 4.2 Interference Location and Time of Line 1 and Line 2.............................................21 5.1 Organizational Structure of HCC Utility Company.................................................23 5.2 HCC Operation Flow Chart......................................................................................24 5.3 Estimating Take-off Spreadsheet for Sanitary Sewer Pipe......................................26 5.4 A Sample Bid Sheet for H Company, March 2004..................................................28 5.5 Superintendent’s Daily Report Sheet.......................................................................32 5.6 Production Rate of Sanitary Sewer Line Based on Pipe Depth...............................34 5.7 Multiple-Level Schedule System.............................................................................39 5.8 Gantt Chart of Multiple Project Scheduled by MS-Project —— Company Level..40 5.9 Crew Tracking Table................................................................................................41 6.1 Aerial Photo of The Villages Project.......................................................................44 6.2 Linked Bar Chart Schedule for the Florence Path....................................................53 6.3 Linear Schedule diagram for the Unit 97 Project on Project Level.........................54 6.4 Florence Path Plan and Profile.................................................................................57 ix

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6.5 Storm Drainage Line and Sanitary Sewer Line in X-Y Coordinate System............58 6.6 Linear Scheduling and Adjusted Linear Scheduling for Storm Drainage Line and Sanitary Sewer Line.................................................................................................59 x

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science in Building Construction LIMITATIONS OF EXISTING SCHEDULING TOOLS IN PLANNING UTILITY LINE CONSTRUCTION PROJECTS By Bin Cheng December 2005 Chair: Ian Flood Cochair: R. Raymond Issa Major Department: Building Construction Although the popular scheduling methods, such as the Gantt chart and its variations the Linked Gantt chart and the critical path method (CPM), are really beneficial to the construction industry, these methods are inadequate when applied to scheduling linear construction projects. The line of balance (LOB) and its variations are more appropriate for linear construction because of their presentation of productivity and project progress corresponding to true location. However, most of LOB studies focus on the activities of a linear project. The LOB and its variations have not been used to study the scheduling problems associated with multiple utility lines. These utility lines intersect with each other at certain locations as designed. Each line at the intersection location has its own elevation. Crews are assigned to work on each line. These crews may arrive at the intersection location simultaneously which causes work space conflicts. The current LOB method and its variations do not show the interference locations, predict the interference time, or show how to avoid work space conflicts in order to keep crews working continuously. This study develops the modified LOB method which uses a group of xi

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linear equations to identify the construction interference locations of utility lines. The method allows the user to estimate the interference time of two or more utility lines based on the historical production rate data which take into consideration many factors (pipe size, pipe depth, soil conditions, city or countryside). Based on the results of this analysis the construction schedule can be adjusted to satisfy the construction constraints. A case study on an actual project that the author has worked on is used to illustrate how the modified LOB methodology works and how it helps avoid construction interruption, keep the continuity of crew work, and avoid the often resulting construction delays and cost overruns. xii

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CHAPTER 1 INTRODUCTION Study Motivation Due to an increasingly competitive environment, construction companies are forced to be more efficient in order to achieve competitive operational advantage. Companies are always looking for improvements in equipment features, communication tools, efficient management techniques, and training their human resources. Construction companies are also narrowing their focus, becoming specialists in certain types of construction projects. This specialization requires more focused project planning and controlling techniques that prove to be better for certain type of projects while providing specialized construction services. The benefits of the effective planning, scheduling and control of construction projects are: reduced construction time, reduced cost overruns and the minimization of disputes. These benefits accrue to the contractors, owners, suppliers and workers in the form of improvements in productivity, quality and resource utilization. (Mattila and Abraham, 1998) The Gantt chart and critical path method (CPM) scheduling technique are popular in construction projects due to easy-to-use software packages, such as Primavera Project Planner. The Critical Path Method (CPM) was originally applied to industrial processed and later on it was introduced for use on construction projects. The technique has also been applied to highway construction projects by the transportation departments in most states. The adequacy of using CPM for these kinds of projects is questionable. The Line of Balance (LOB) and its variations were developed to search for a better solution for 1

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2 highway type projects, such as tunnel construction, high rise building, pipe line projects, and even utility projects. The application of LOB and Linear scheduling techniques to utility projects has been questioned by industrial professionals (REF). For the underground utility project, the layouts of several utility lines are diverged. But on some locations, these utility lines intersect with each other, one over another. The construction of each utility line must be sequenced in this situation to avoid workspace conflicts, or lines with lower elevation are constructed ahead of the ones with higher elevation, and to provide work continuity for crews or resources. This study will focus on the comparison of construction scheduling techniques, such as the Gantt chart, CPM, the Linked Bar Chart, and the LOB or Linear Schedule Method (LSM), when used on utility projects. It will list the advantages and disadvantages of each technique, propose a modified LSM method, apply this proposed method and Linked Bar Chart in the context of a utility project case study, and it will make recommendations for future research on utility projects. Organization of this Study This introduction of the study is the first of seven chapters. It depicts the research motivation, and addresses the different parts of this study. The literature review in Chapter 2 presents in detail the currently popular scheduling methods used in the construction industry and it describes their application to linear construction projects. The LSM method which is used in scheduling linear construction projects and it capabilities and shortfall will also be discussed. Chapter 2 also discusses the advantage, limitations, relationships, and application of each scheduling method in linear construction projects. Chapter 3 describes research objectives and research significance. Chapter 4 presents a modified LSM method to solve the interference problems while scheduling multiple

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3 utility line constructions. Chapter 5 introduces the background of the company and project operation model. It also describes the problems faced by management personnel. Chapter 6 illustrates the implementation of the modified LSM method and Linked Bar Chart on the case study project. Chapter 7 states the conclusions that have been drawn based on the results of the research and it lists areas for future research.

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CHAPTER 2 LITERATURE REVIEW The most common scheduling method used in the construction industry is the Gantt chart (Bar chart) and the Critical Path Method (CPM). The Gantt chart (Bar chart) has gained wide acceptance and popularity because of its simplicity and ease of preparation and understanding. No “theory” or complicated calculations are involved. The CPM network can show the logical dependencies of activities, and estimate and predict the completion date of a project based on mathematical calculations. But both the Gantt chart and CPM are unable to accurately model the repetitive nature of linear construction. This includes the inability of CPM to provide work continuity for crews or resources, to plan the large number of activities necessary to represent a repetitive or linear project (Harris, 1996), and the inability of Gantt chart (Bar chart) and CPM to indicate rates of progress, and to accurately reflect actual conditions (Mattila and Abraham, 1998). The consequence of this is that there have been many attempts to find an effective scheduling technique for linear construction. These include, but are not limited to, the Line of Balance (LOB), the vertical production method (VPM), the linear scheduling method, the repetitive project modeling (RPM), the linear scheduling model (LSM), and the repetitive scheduling method (RSM) (Mattila and Abraham,1998). All of these concepts and methods are the variations of LOB, which was originally developed for the manufacturing industry. This chapter discusses the popular scheduling methods in the construction industry, such as the Gantt Chart and CPM. It also reviews current 4

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5 applications of LOB and its variations, and it describes the inability of LOB in solving the construction interferences of two or more utility lines. Gantt (Bar) Chart Scheduling Method The Bar chart is a time-scaled graphic representation of project activities. It is popular in construction industry because of its ability to graphically represent a project’s activities on a time scale. A bar chart has become a vehicle for representing many pieces of a project’s information. A project must be broken into smaller, usually homogeneous components, each of which is called an activity or task. Bar charts basically use the x-axis to depict time, and the y-axis is used to represent individual activities (see Figure 2.1). Figure 2.1 Bar Chart for Placing a Slab on a Grade (Mubarak, 2003) Advantages of Bar Charts Bar charts have gained wide acceptance and popularity mainly because of their simplicity and ease of preparation and understanding. No “theory” or complicated calculations are involved. Anyone can understand them. Bar charts particularly appeal to persons who do not have a technical background. For example, some clients and upper

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6 level managers may better understand the plan for carrying out a construction project by looking at a bar chart than by looking at a schematic of logic network. Despite the advent of CPM and the evolution of powerful computers, Bar chart did not disappear or lose their importance. Instead, they evolved to a different supporting role that made them more valuable and popular (Mubarak, 2003). The advantages of using a Bar chart are: Bar charts are time scaled, the length of the activity bar represents the time duration of the activity). Both the node, in the node networks, and the arrow, in the arrow networks, are not time-scaled. Bar charts are simple to prepare Bar charts are easy to understand Bar charts are acceptable for presentation, especially for field people and people who are unfamiliar with the CPM Bar charts can be loaded with more information, such as cash-flow diagrams and man-hours. This advantage is partially a by-product of being time scaled. Limitation The main limitation of the Bar chart is its lack of logical representation. Bar charts do not reveal the entity relationships. Although some software programmers have tried to depict logical relationships on bar charts, the result have not always been clear. The logic lines would get tangled, and unlike networks, Bar charts do not allow the length of the bars to be changed or moved around to make items clearer or look better (Mubarak, 2003). When applying the bar chart to a linear construction project, a huge diagram would repeat n times in scheduling linear and repetitive projects. In addition, the bar chart is unable to indicate progress rate and actual location. Network Scheduling Methods One of the major network scheduling methods which have been used in the construction industry is CPM. This method involves the use of a geometric representation

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7 of a flow chart which depicts the precedence between activities. CPM is a duration-driven technique in which the basic inputs are project activities, their durations, and dependence relationships. Activity durations are functions of the resources required (rather than available) to complete each activity. The CPM formulation assumes that resources are not restricted in any sense (Ammar and Mohieldin, 2002). The use of network techniques and CPM by construction companies has reached a steady level after the enthusiastic boom of the early 1960’s. Computer programs eliminate the need to prepare a network, but the network notation provides an easily understood output format for management personnel. (Lutz and Hijazi,1993) Advantages of Network Scheduling Methods Network scheduling methods have the following over bar charts (Mubarak, 2003): Networks show logic, the relationships among the activities. Bar charts do not Networks can better represent large and complicated projects. Networks can estimate, or predict, the completion date of the project, or other dates, on the basis of mathematical calculations of the CPM Limitation of Network Scheduling Methods Compared to bar charts, network scheduling is not time scaled. It requires practitioners to be trained to understand the CPM. Its presentation is not as acceptable to field personnel as bar charts and resource information can not be loaded in CPM. Some scheduling software vendors have tried to take the advantage of the time-scaled feature of Bar chart and impose it on networks. This resulted in what some persons have called time-scaled logic diagrams (REF). On the other hand, there is evidence that contractors do not use network scheduling in highly repetitive jobs because of their belief that high repetition would reduce the

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8 chances of successful scheduling and control by networks (Arditi and Albulak, 1986). For example, the network method presents complications in projects of repetitive nature such as high rise building construction. CPM-based techniques have been criticized widely in the literature for their inability to model repetitive projects (Russell and Wong, 1993). The first problem is the sheer size of the network. In a repetitive project of n units, the network prepared for one unit has to be repeated n times and linked to the others which results in a huge network that is difficult to manage. This may cause difficulties in communication among the members of the construction management team. The second problem is that the CPM algorithm is designed primarily for optimizing project duration rather than dealing adequately with the special resource constraints of repetitive projects. The CPM algorithm has no capability that would ensure a smooth procession of crews from unit to unit with no conflict and no idle time for workers and equipment. This leads to hiring and procurement problems in the flow of labor and material during construction (Arditi, Sikangwan, and Tokdemir, 2002). Time-Scaled Logic Diagrams: A Variation of CPM Time-scaled logic diagram overcomes some of the disadvantages of CPM. It depicts all logical relationships among the activities and presents these dependencies of activities on time-based axis. The result looks like spaghetti. It shows critical relationships (Figure 2-2). In some simple cases, this method may work as good and acceptable solution(Mubarak, 2005). However, the presentation of time-scaled logic diagram to field personnel is not as good as bar chart. In addition, it has the same shortcomings as basic CPM in scheduling repetitive projects.

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9 Figure 2.2 Time-Scaled Logic Diagram (Flood, 2005) Linked Bar Chart: A Mingle of CPM and Bar Chart Linked Bar Chart is currently popular in the construction industry for its easily understood presentation. It is time-based diagram. The bar charts are linked based on their logical relationships. Critical relationships are highlighted through CPM computation. (Figure 2-3). It even shows the project progress on the bar charts. However, there is still no indication of production rates in linked bar chart, this situation could not be anticipated by the scheduler during the development of the linked bar chart. It has no capability that would ensure a smooth procession of crews from unit to unit with no conflict and no idle time for workers and equipment. This leads to hiring and procurement problems in the flow of labor and material during construction (Arditi, Sikangwan, and Tokdemir, 2002). Another problem of the linked bar chart is when scheduling repetitive projects such as pipe line is the enormous size of the network. In a pipe line project of n sections, the bar chart prepared for one section has to be repeated n times and linked to the others; this results in a huge linked bar chart that is difficult to manage and cause difficulties in communication among the members of the construction management team. A new format was developed for work of a repetitive nature, such as work on floors in a high-rise project, or work on sections in underground pipe line or utility line project.

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10 In the pipe line or utility line instance, the uses of linked bar chart, basic CPM, and time-scaled logic diagram, were laborious; the input for work on a typical section was duplicative and tedious. Further, once the schedule had reached the typical section, it was impossible to predict a result through basic arithmetic without the use of a computer. This suggested that there were ways of graphing the result other than network presentation. This realization resulted in the development of some methods for use in linear and repetitive projects. The Line of Balance (LOB), Linear Scheduling Method (LSM) are ones of them. Basically the LOB and LSM are solving the scheduling problems in repetitive projects in the same way but are called in different terms. They are classified as LSM. Figure 2.3 Time-Scaled Logic Diagram (Flood, 2005) Linear Scheduling Method (LSM) A common characteristic of LSM and LOB techniques is the typical unit network. Representative construction projects that fit into this category are a repetitive housing project or a high-rise building. (Lutz and Hijazi, 1993) Typical process production or flow line curves are depicted in Figure 2.4 and Figure 2.5. Figures 2.4 and 2.5 show the balanced and unbalanced production flow lines for a high rise building. For example, the sequence of processes for a high rise building construction project may include form

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11 erection, steel installation, concrete placement, form removal, curtain wall installation, and glazing. The production curves for activities are plotted as a function of time. The production rate for a process can be determined from its slope. The horizontal distance between the production curves for two consecutive activities at given location indicates the time buffer. The difference between the cumulative number of production quantities delivered and the quantity at any given time is termed the “criticality”. The negative criticality indicates the actual progress is less than the production forecast. The LSM and LOB are quantity-time diagrams. They focus on the required delivery of completed quantities. Linear construction projects often consist of repetitive processes which have different production rates. This phenomenon of production rate imbalance has the potential for negatively impacting project performance by causing work stoppages, inefficient utilization of allocated resources, and excessive costs. Production rate imbalance occurs when the production curves of leading processes intersect the curves of following process because of different production rates and insufficient lag between start times of processes. The LSM and LOB can determine at any time (Lumsden, 1968): 1. Shortage of delivered materials which may impact production; 2. Materials which are being delivered in excess which may cause additional material handling or require additional storage space; 3. The jobs or processes which are falling behind and the required rate of acceleration to satisfy the required quantities; 4. The jobs or processes which are ahead of schedule which may be placing heavier demands on operating capital than necessary, and

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12 Figure 2.4 Balanced Production Curves for Repetitive Processes (Source: Lutz and Hijazi,1993) Figure 2.5 Non-balanced Production Curves for Repetitive Processes (Source: Lutz and Hijazi,1993) 5. A forecast of partially completed production units by job, work station, or process to support the delivery schedule of finished units. Benefits and Limitations The major benefit of the LSM and LOB methodology is that it provides production rate and duration information in the form of an easily interpreted graphical format. LSM plot for a linear construction project can be easily constructed, it can show at a glance

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13 what is wrong with the progress of project, and it allows for the detection of potential future bottlenecks. Although the LSM methodology can be used to aid in the planning and control of any type of project it is better suited for application to repetitive projects as opposed to non-repetitive projects. A limitation of this methodology is that it assumes that production rates are linear. Due to the stochastic nature of construction processes, the assumption that production rates of construction projects and processes are linear may be erroneous. Barriers to Implementing LSM The application of the LSM methodology by the US construction industry has been very limited. Some barriers to the implementation of the LOB methodology include the following (REF): 1. There is a lack of awareness among practitioners in the US construction industry that the LSM methodology exists. 2. Owners and contractors began adopting network techniques as planning tools at about the same time that the LSM methodology was originated and developed. These entities are reluctant to adopt new planning tools which are not being used by their counterparts or competitors. 3. Computerized tools employing network techniques are widely available whereas computerized tools employing the LSM methodology are not currently commercially available. Due to the popularity of the relatively inexpensive computer in the US construction industry, there is a resistance to change to a planning method which is currently not supported by computer. Commercial LOB Software Packages Arditi (2002) and his colleagues developed a computerized system Chriss which uses the LOB method to schedule high-rise building construction. The system consists of

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14 five main processing modules: the Construction Knowledge Input module, the Project-Information Input module, the Expert System module, the Construction Planning module, and the LOB Scheduling module. Chriss has been tested using different scenarios. It is a prototype, a proof of the LOB concept that is operational. Its purpose is to assist users with scheduling decisions in a repetitive environment. It can be further developed by adding more capabilities. Summary This chapter has reviewed scheduling methods in construction, such as the Gantt chart, basic CPM, time-scaled logic diagram, and linked bar chart. Currently, linked bar chart is the most popular scheduling method in the construction industry for its overwhelming advantages over other scheduling methods. However the applications of these scheduling methods do have problems in scheduling linear construction projects, even with the linked bar chart The LSM and its variations are beneficial to linear construction. However, their application in construction industry has been limited. Table 2-1 shows a comparison of the linked bar chart and LSM in scheduling repetitive projects. From the comparison, it obviously shows that LSM has more benefits than the linked bar chart method. However, the existing LSM method and its variations have not solved the location interference problems in the underground utility project. For the underground utility project, the layouts of several utility lines are diverged. But on some locations, these utility lines intersect with each other, one over another. The construction of each utility line must be sequenced in this situation to avoid workspace conflicts, or lines with higher elevation are constructed ahead of the ones with lower elevation, and to provide work continuity for crews or resources. The next chapter will introduce a method for

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15 sequencing the construction process in order to avoid interference between crews working on the same utility project. Table 2.1 Comparison of Linked Bar Chart and Linear Scheduling Method Linked Bar Chart Linear Schedule Method Time-based chart Space-based chart Time buffer Space buffer Identification of project progress Sort of. Without identifying the exact location Production rate Flow of Labor Different production rates indicate the flow of labor Space Conflicts

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CHAPTER 3 RESEARCH OBJECTIVES The popular scheduling methods, such as Gantt chart and its variation (linked Gantt chart) and CPM, are really beneficial to the construction industry. The Gantt chart and its variations are popular because of their easily understood presentation. The CPM network is strong in analyzing logic relationships among activities. However these methods are criticized while applied to scheduling linear construction projects. The line of balance (LOB) concept is borrowed from the manufacturing industry to solve the scheduling problems in linear construction projects. LOB and its variations, such as linear scheduling method (LSM), are beneficial to linear construction in its presentation on productivity and project progress corresponding to true location. Time buffer and space buffer concepts are introduced while developing LOB application in the construction industry. Most of the linear scheduling method studies (REF) have focused on the activities of a linear project. The current linear scheduling method and its variations have not addressed the scheduling problems associated with multiple utility lines. An underground utility construction company usually undertakes construction of several utility lines of a project, such as storm drainage line, sanitary sewer line, potable water line, gas line, etc. These utility lines may intersect with each other at some locations as designed. Each line at the intersected location has its own elevation. Crews are assigned to work on each line. These crews may arrive in the intersected location simultaneously which cause work space conflicts. The current linear scheduling method and its variations do not indicate the interference location, predict the interference time, and help in avoiding work space 16

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17 conflicts to keep crews working continuously without interruptions. The objectives of this study are comparing the existing scheduling tools using for planning the utility line construction projects, find the limitations and explore a method to: indicate the interference locations for projects with two or more utility lines predict the interference time of these utility lines avoid the work space conflicts This study has practical significance. By applying the proposed modified linear scheduling methodology, the crews will avoid construction interference and project delays, improve crew productivity, and prevent projects from experiencing cost overruns.

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CHAPTER 4 MODIFIED LINER SCHEDULE METHOD The objective of this methodology is to overcome the main challenges in scheduling construction of two or more utility lines with different line layouts; to identify construction interference locations; to predict the interference time; and to adjust the project schedule. The methodology depicts two utility lines with interferences. Suppose there are two utility lines, line 1 and line 2. Line 1 and line 2 intersect at one location. The engineering drawings require the elevation of line 2 is below the elevation of line 1 at the intersected point. This requires the construction of line 2 at the intersection point has to be two days ahead of the construction of line 1. The following steps describe the modified LSM: 1. Extract surveying data of each utility line from the engineering drawings. List the linear equation of each utility line and compute the intersected points. For example, as shown in Table 4.1, two groups of survey data are extracted from the engineering drawings for line 1 and line 2 respectively. Table 4.1 Surveying Data from Engineering Drawing Line 1 x y Line 2 x y Sta. L1-1 500 -5.00 Sta. L2-1 600 -15.00 Sta. L1-2 2800 9.00 Sta. L2-2 2400 10.00 The linear equations about the two lines can be calculated by inserting these two data sets in the following equations: (Equation 4-1) 0435.80061.01xy 18

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19 (Equation 4-2) 333.230139.022xy The intersection location (1960.19, 3.91) can be identified accurately by obtaining a solution for these two linear equations. Figure 4.1 Linear Equations for Line 1 and Line 2 2. Estimate the interference time of these two lines. Table 4.2 lists the production rate and length for each line. The construction duration for each line can be computed by dividing the line length by its production rate. The linear equations for drafting the LOB diagrams of these two lines are: (Equation 4-3) 2004.011x t (Equation 4-4) 20033.022xt Figure4.2 depicts the LOB schedule for line 1 and line 2. At the location x = 1960.19 L.F., the corresponding time for line 1 is 5.84 days and for line 2 it is 4.53 days. Since

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20 the elevation of line 2 at the intersection location is lower than the elevation of line 1, the construction of line 2 must be two days ahead of line 1. However, the time buffer between these lines at this point is only 1.33 days (5.84 4.53 = 1.33 days). This requires the construction management personnel to adjust the schedule. Table 4.2 Estimated Construction Duration Line 1 L.F. Productivity (L.F./Day) Duration (Days) Line 2 L.F. Productivity (L.F./Day) Duration (Days) Sta. L1-1 0 250 0 Sta. L2-1 0 300 0 Sta. L1-2 2300 250 9.2 Sta. L2-2 1800 300 6 3. Adjust the original schedule. In order to satisfy the construction constraints, the construction of line 1 must delayed at the intersection point. That means the construction time at the intersection point for line 1 is 6.53 days (2 + 4.53 = 6.53 days). In addition, construction companies usually want to keep the crew work continuous in order to keep the production rate constant and to avoid setup time and learning time. The solution is move line 1 along the time axis to make it go through point (1960.19, 6.53) with production rate 250 L.F./Day. The adjusted LSM linear equation for line 1 is: (Equation 4-5) 3068.1004.011aaxt The adjusted schedule for line 1 is also shown in Figure 4.2.

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21 Line1: t = 0.004x -2Line2: t = 0.0033x 20.001.002.003.004.005.006.007.008.009.0010.000100200300400500600700800900100011001200130014001500160017001800190020002100220023002400250026002700280029003000FeetDay (1960.19, 4.53)(1960.19, 5.84)(1960.19, 6.53)Adjusted Line 1: t = 0.004x 1.3068 Figure 4.2 Interference Location and Time of Line 1 and Line 2 Summary This chapter describes the modified LOB method for use in solving construction interference in laying two or more utility lines. The three steps used represent extracting data from engineering drawings; identifying the interference locations; drawing the original LOB, and adjusting the original LOB to satisfy construction constraints. The next chapter presents a case study. It describes the problems faced by the company and how the modified LOB is applied to solve the problems.

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CHAPTER 5 CASE STUDYPROJECT OPERATION MODEL Introduction HCC is one of the largest utility contractors in the North Florida area. It was founded in 1974. Most of the company’s work comes from either private developers or public-funded municipal projects. In the private sector, the company performs underground utilities services for buildings, plants, subdivisions and other facilities. Land developers award contracts to HCC for street construction and utility installation. Public projects include work like installing new utilities and replacing old utilities in existing cities or developments. HCC performs a variety of infrastructure projects in the public sector, including the construction and maintenance of sewer systems, storm water systems, water distribution systems, gas systems and power conduit systems. The company’s participation in both the public and private sectors and its diverse mix of project types and sizes have contributed to the Company's revenue growth and profitability in changing economic environments. In 2002, the company reported revenues of $22 million. The annual revenue rose to $30 million in revenues in 2003, a 36% growth in gross revenues. Usually HCC splits an awarded contract into its several parts: sanitary sewer system, storm drainage system, potable water system, fire and irrigation system, power sleeve line, and gas line. HCC has several types of crews to perform these separated jobs. Each type of crew has expertise experience on its work. Figure 5.1 shows the organization structure of HCC and its crews’ expertise. 22

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23 President Supervisor Superintendent Superintendent Superintendent OfficeManager ProjectEngineer ChiefEstimator Estimator Estimator AccountPayable AccountReceivable Payroll ChiefMechanic Mechanic Mechanic Foreman Main Operator Second Operator Lead Man Tail Man Backman Labors Water & Sewage Crew Foreman Labors Labors Miscilleous Crew Foreman Operator Labor Labors Gas Crew Book keeper Figure 5.1 Organizational Structure of HCC Utility Company The water and sewer crews have been labeled as the “main line crew”, because they have the most productive operators and equipment and they perform the most complicated tasks related to the sanitary sewer system, storm drainage system, and water distribution pipe installation. Gas crews are relative small in size and their tasks are also relative simply, because the depth of gas line usually does not vary along its length. The miscellaneous crews mainly perform supplementary tasks such as painting manholes, cleaning up, and putting sod after compaction, etc. The mechanics maintain all equipment and drive the fuel truck to job sites to refill the equipment. The estimators do quantity taking off for the projects, and after it is checked by the project engineer they call suppliers for quotations. The bookkeeper maintains the as-built drawing using the daily report from superintendents for pay-app purposes as well as other paper work such as change orders if the as-built quantity is not same as planned. The accounting department

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24 takes care of all the accounts payable and receivable with the help of the front desk receptionist. Figure 5.2 shows the operation flow chart for the H Construction Company. Project Manager Field Personnel Estimating Scheduling Project Monitoring and Control Billing Accountant Client H Company Information System1. Labor cost2. Equipment cost3. Material cost4. Subcontract quote1. Labor productivity2. Equipment productivity3. Crew productivityBudget SummerySchedule for project Monitor and control1. Daily site record2. Weekly progress1. Weekly performance2. Weekly progress report3. Daily site record PaymentBilling statementPaycheck1. Weekly performance report2. Weekly cost report3. Labor performance report4. Equipment performance report5. Subcontractor performance report6. Material report Figure 5.2 HCC Operation Flow Chart Quantity Estimates for the Project The basics of a successful construction business are to win a bid and provide the construction service on time and within budget. Winning a bid with reasonable profit

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25 margin and keeping the crews busy cover the home office overhead and makes money for the company. The company uses the unit-price contract type. The following are regular bid items: Storm Drainage Sanitary sewer Water distribution (potable water) Fire and irrigation (non-potable water) Roadway sleeve Utility trenching After review the engineering drawing, the estimator takes off the quantity of each type of bid item. The drainage and sewer pipes are usually gravity pipes; they must be kept at a certain slope to let the waste water flow under gravity. The depth of the storm drainage and the sanitary sewer pipes varies from several feet to 40-50 feet. On the other hand, the water distribution pipes (both potable and non-potable) are pressure pipes and they have lift stations installed. The installation of the pressure pipes is based on the specifications and engineering drawings, for example “at least 48 inches deep”. For utility projects, one of the most important jobs is to estimate the quantities of soil to be moved and backfilled. For this strenuous job, the H Construction C ompany has developed a spreadsheet for making this job easy. Figure 5.3 shows an example of the spreadsheets which is used by the estimator to input the information of structure from the Down Hill (Column A to C) to Up Hill (Columns H to J) and pipe information (Columns E and F) and service line information (Columns N and O). The spreadsheet will calculate the “total soil moved (CY)” “Pipe length for different depth” “manhole numbers and depth distribution” “Average Pipe depth” “number for both single and double services”

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26 Figure 5.3 Estimating Take-off Spreadsheet for Sanitary Sewer Pipe Besides the information from spreadsheet in Figure 5.3, the cost information needed for estimating are: Hourly cost of ownership and operation of the machinery Hourly cost of labor, operators Fringe benefits Subcontractor cost. Table 5.1 is an Equipment Cost Rate for H Construction Company for May 2004, the prices are sensitive to time and location. Table 5.2 shows the typical crew rate for H Construction Company in May 2004, this rate is also sensitive to time and location.

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27 Table 5.1 Equipment List and Rate for one typical Sewer Crew Typical Sewer Equipment (Private Subdivisions) Purchase Price Hourly Cost Gallons per hour Hourly Fuel Cost Total Hourly Cost Maint. & Repairs Grand Total 330 Excavator 207000 25.88 7.2 10.8 36.68 9.62 46.3 644 Loader 173000 21.63 5 7.5 29.13 4.01 33.14 750 Dozer 155000 19.38 5 7.5 26.88 7.87 34.75 450 Dozer 69000 8.63 2.5 3.75 12.38 4.33 16.71 310 Backhoe 51000 6.38 1.5 2.25 8.63 2.23 10.86 Roller 68000 8.5 2.4 3.6 12.1 2.5 14.6 Pickup Truck 30000 2.31 1 1.5 3.81 3 6.81 Total 990000 120.9 32.8 49.2 170.1 46.18 216.28 Table 5.2 Rate of a Typical Crew for H Company Village Sewer & Storm Crew Responsibilities Quantity Low Rate ($) High Rate ($) Entry Miscellaneous work 3 24.94 28.22 Tail Man Pipe fitting 1 9.41 10.5 Lead Man Position pipe 1 10.5 12.68 Loader Operator Deliver material 1 11.59 14.87 Hoe Operator Bench down, excavate 3 38.05 51.16 Foreman (W&S) Superintend 1 18.41 22.84 Cost per Hour 10 112.9 140.27 The material cost will be material quantity from Figure 5.3 multiplied by the material price from the supplier. The subcontractors’ cost will come from the subcontractors’ bid sheet. The equipment cost will be the cost rate from Table 5.1 which is the hourly rate, multiplied by 10 hours per day and the duration of project in days. The labor cost will be the cost rate from Table 5.2 multiplied by 10 hours per day and the duration of the project in days. The total cost is the sum of the material cost, equipment cost, labor cost, and overhead and benefit. The unit price for each feet of pipe is obtained by dividing the total cost by total length of pipe. The bidding sheet will be prepared in the format presented in Figure 5.4. The next step is to decide the project duration.

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28 Figure 5.4 A Sample Bid Sheet for H Company, March 2004 Estimate Project Duration Several items must be known in order to estimate project duration: The quantity of work for a project. Available resources (how many crews and pieces of equipment are available). The equipment production rate. The crew production rate. The first item is known through estimating. The second item is to make sure what resources are available. The HCC has eight main line crews (water sewage crew) and it usually has five miscellaneous crews (see Figure 5.1). Some crews may already have their work on hand done. Other crews almost have their work on hand done. Management

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29 personnel will know which crew will be available at the required time. Next the equipment and crew production rates will be described. Estimate Equipment Production Rate The equipment production rate is determined by several factors such as, optimum production rate, equipment capacity factor and soil swell (load) factor. For different brands of equipments, the company usually calculates the production rate from the operator’s manual which the manufacturers give to the company. Table 5.3 provides a sample of cycle time for tracked excavators under various conditions. The equipment optimum production rate is calculated as the following: Optimum Hourly Production Rate (CY/HR) = Cycles Per Hour Volumn Per Cycle (Equation 5.1) Most major equipment manufacturers have specification sheets that show cycle times for their equipments. These cycle times are based on tests done under ideal conditions: level land, easy soil, no cross-lines and an experienced operator. Production rate on these specification sheets are often somewhat optimistic. To convert cycle time in seconds to cycle time per hour is dividing cycle time by 3600 (the seconds in an hour). For example, the average cycle time for a 120-150hp tracked excavator during hard digging is 30 seconds, according to Table 5.3. Divide 3600 by 30 seconds to find the cycle time of 120 cycles per hour. To calculate the hourly capacity, the volume of material moved in each cycle must be known. Volume per cycle varies with the equipment capacity and soil swell. Table 5.3 Cycle Times for Tracked Excavator Tracked Excavator, 120-150 hp Engine, 20 feet Maximum Digging Depth Description Time (Seconds) Conditions Fast 18 Trench depth less than 10’ deep, good work room with few obstructions.

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30 Average 22 Trench depth less than 12’ deep, underground utility present, small dump target. Hard digging 30 Trench depth in excess of 12’ deep, overhead obstructions. Tracked Excavator, 250-300 hp Engine, 25-30 feet Maximum Digging Depth Description Time (Seconds) Conditions Fast 20 Trench depth less than 10’ deep, good work room with few obstructions. Average 27 Trench depth less than 12’ deep, underground utility present, small dump target. Hard digging 33 Trench depth in excess of 12’ deep, overhead obstructions. Equipment Capacity Factor: Equipment capacity is shown as heaped capacity on equipment manuals. However fully heaped buckets on each cycle on a job is impossible. It is impossible to get a heaped bucket load when working in saturated sand and gravel. Equipment capacity factors for the equipment such as the backhoe, wheeled loader, and dozer is used to adjust equipment performance estimate. Soil Swell (Load) Factor: Load factor is for compensating for the swell in soil volume. Load factor is calculated by: Load Factor = Bank Volume / (Bank Volume + Swell %) (Equation 5.2) To adjust equipment performance to allow for soil swell, just multiply the hourly production rate by the load factor. Soil condition and degree of compaction affect swell percentage considerably. Finally, the equipment production rate is determined by the following equation: Equipment Production Rate = Equipment Optimum Production Rate Equipment Capacity Factor Soil Swell (Load) Factor (Equation 5.3) Estimate the Production Rate for Each Crew from the Time Sheet The last item before scheduling a project is to calculate the crew production rate from the historical data. The company collects data from the superintendents’ dairy

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31 reports. By analyzing these data, crew productivity for laying pipe or installing structures are estimated based on pipe size and pipe depth or structure depth. Figure 5.5 shows an example of one of the superintendents’ daily report sheets for a project. The data recorded on this sheet includes the date, the project location, the work quantities for that day, all the crew member’s names, and the times of arrival and departure, the actual elevation of pipe connection to the structure and some specific activities that are not on the sketch. In order to plot an activity such as lay pipe, the appropriate information needs to be assembled from the daily sheets, such as the information about the length of pipe from structure to structure, the type of pipe, and the average depth of pipe. The data collected from this daily report are: the cubic yard of soil excavated the length of pipe laid the exact labor hours spent for laying pipes The superintendent’s daily report sheet is a data resource to be used for: 1. Payroll for daily laborers and crews 2. Evidence for payment application and change order 3. Producing as-built drawings 4. Project progress tracking and monitoring 5. Historical data record

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32 Figure 5.5 Superintendent’s Daily Report Sheet The company collects data for each type of pipe in order to estimate the productivity of crews.

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33 The productivity of the crews is affected by pipe depth, pipe size, the number of structures (manholes), structure depth, working condition (city or country), and skills of crews. These parameters affect productivity as follows: Depth of pipe and structure (manholes): the deeper the pipe’s location, the more time it takes to excavate the trench, the more time spent on shoring; the lower the productivity of the crew. Table 5.4 shows the production rates for laying 8” PVC sanitary sewer line at different depth. (manholes). Figure 5.6 is drawn based on the data from Table 5.4. The production rate at other depths can be extrapolated by using the curve line in the Figure 5.6. The explanation also applies to the structures. Table 5.5 shows the production rates for installing manholes at different depth. Table 5.4 Production Rate for Laying 8” PVC Sewer Lines for HCC Sewer Pipe Depth Production Rate ( L.F./Day) 0 – 6’ 790.00 6 – 8’ 715.00 8 – 10’ 640.00 10 -12’ 565.00 12 -14’ 490.00 14 -16’ 415.00 16 -18’ 340.00 18 -20’ 265.00 20 -22’ 190.00 Table 5.5 Production Rate of Installing Manholes for H Company Sewer Manhole Depth Production Rate (Hours/Manhole) 0-6' 0.75 6'-8' 1 8'-10' 1 10'-12' 1.25 12'-14' 1.5 14'-16' 1.75 16'-18' 2 18'-20 3 20'-22' 4 22'-24' 5 24'-26' 6

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34 Average Feet/Day y = 3.8711x2 105.69x + 815.1401002003004005006007008009000'-6'6'-8'8'-10'10'-12'12'-14'14'-16'16'-18'18'-20'20'-22'DepthFeet/Day w/o Average Poly. (w/o Average) Figure 5.6 Production Rate of Sanitary Sewer Line Based on Pipe Depth Pipe size: it affects production rate since smaller pipe sizes are easier to install and allow the crews to move faster. Table 5.6 illustrates the production rate for laying storm drainage pipe based on the pipe size and pipe depth. If a pipe is laid at the same depth range, the production rate will decrease with increases in pipe size. Table 5.6 Production Rates of Laying Storm Drainage Pipe Productivity on Pipe Size (feet/day) Depth of Pipe 12”-24” 30” 36” 42” 48” 54” 60” 0’-6’ 596 571 475 449 420 410 400 6’-8’ 525 501 415 374 370 360 355 8’-10’ 483 459 394 350 330 325 320 10’-12’ 453 430 379 330 310 300 280 12’-14’ 430 407 367 275 270 260 250 14’16’ 411 388 357 255 250 240 230 16’-18’ 395 372 330 239 230 220 210 18’-20’ 381 359 320 224 220 200 190 Above 20’ 369 347 300 211 200 180 170

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35 The number of structures: the more manholes that need to be constructed for a project, the more times the work continuity of crews is disrupted; the productivity of crew is slowed down by an increased number of manholes. Working condition: in the city, the crews need to control traffic and pay more attention to existing utility lines, which prevents the crews from moving faster. Table 5.7 shows the average production for projects that H Construction Company undertook. The production rates here do not apparently indicate the differences between city area and rural area since there are other factors that affect production rates, such as pipe size, the number of structures in each project, skills of crews, etc. Table 5.7 Production Rate from Historical Project Projects in rural area Projects in city Depth Range Harvest Meadows (F.T./Day) Hardwood Trails (F.T./Day) Unit88-Villages (F.T./Day) SW67th (F.T./Day) 0'-6' 356 605 842 6'-8' 1106 711 529 8'-10' 561 549 503 640 10'-12' 386 12'-14' 489 258 504 14'-16' 330 193 16'-18' 198 18'-20' 313 20'-22' 162 Skills of crews: obviously the productivity of crews would be higher if the crew members are skilled laborers. The duration of a project is determined by: tiiutilityprojectDD1 (Equation 5.4) Where: projectD : duration of a project; iutilityD : duration of constructing utility line i of a project; i: a specific utility line; t: the total number of utility lines of a project; The duration of a utility line is estimated by:

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36 iserviceimainiholeiutilityDDDD (Equation 5.5) Where: iutilityD : duration of constructing utility line i of a project; iholeD : duration of installing manholes of a project; imainD : duration of constructing main pipe of a utility line i for a project; iserviceD : duration of constructing service pipe of a utility line i for a project; i: a specific utility line; The duration for installing manholes can be calculated by: jiholejiholejiholenrD)()( (Equation 5.6) Where: iholeD : Duration for installing project manholes; iholejr)( : Production rate for installing a manhole at specific depth range j for a specific utility line i (hours/manhole or days/10 manhole); iholejn)( : the number of manholes at specific depth range j of a specific utility line i; i: a specific utility line; j: a specific depth range of manhole; The duration for constructing the main pipe of a specific utility line is determined by: mnimainnmimainnmimainrlD)()(,, (Equation 5.7) Where: imainD : duration for installing the main line of a specific utility line i;

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37 imainnmr)(, : production rate for installing the main line of a specific pipe size n at specific pipe depth range m for a specific utility line i (L.F./day). imainnml)(, : length of main pipe of a specific pipe size n at specific pipe depth range m for a specific utility line i; i: a specific utility line; m: a specific pipe depth range; n: a specific pipe size; The duration for installing a service line for a specific utility line is estimated by: kiserviceiseriveiservicemrD)()( (Equation 5.8) Where: iserviceD : duration for installing the service line of a specific utility line i; iservicer)( : production rate of installing service line of a specific utility line i (hours/service line). The depths of installing service lines are always at the similar elevation. Therefore there is only one production rate for a specific service line i. iservicem)( : the number of service lines at of a specific utility line i; i: a specific utility line; If the contract gives the duration and the contract duration is shorter than the duration estimated from the above equations, then the management personnel may add more crews to this project. Whenever the company receives an invitation to bid, the engineer will get a bid package which will include the engineering drawings and specifications. The engineer gives the bid package to the estimators (Estimating department in Figure 5.1). The

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38 estimators then work out a material cost summary while at the same time the scheduling engineer (Scheduling department in Figure 5.1) will estimate the project duration and will produce a rough scheduling. The Project engineer (Manager in Figure 5.1) will estimate the labor and equipment cost according to that project duration and then they will assemble and submit a bid sheet. Project Monitoring and Control After the company is awarded a bid and a contract is signed and the third stage, as shown in Figure 5.2, the project monitoring and control phase will start. The scheduler will distribute a project level schedule using MS-Project to meet the requirements of owner in terms of the completion date of the project. The scheduler will then distribute this schedule to project engineer who will discuss this schedule with superintendent. Because a superintendent is responsible for the site execution and has a lot of experience, they will give some suggestions on that schedule according to his experience, currently available crews and equipments. The project engineer brings back the superintendent’s suggestions and the scheduler will make modifications on that schedule accordingly. After several meetings, the schedule is set and the project is started. The required schedule details will vary at different levels of the schedule. The HCC uses three scheduling levels: the company level, the project level, and the operation level (Figure 5.7). All three level schedules are generated using Bar charts. Bar Chart (Gantt Chart) for the company level schedule: The company level schedule is for the top management. The following information is the top management of the company wants to know:

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39 Figure 5.7 Multiple-Level Schedule System How many projects are on-going? When these projects will be finished? How many projects will start? When these projects will start? Which crew will be available for next project? The company uses the Gantt Chart (Figure 5.8) and a spread sheet (Figure 5.9) to present the information they need. Figure 5.9 is the Crews vs. Projects table and it shows the crew resource allocations along with the current projects. Bar Chart (Gant Chart) for the Project Level Schedule: The project level schedule is not much different than the company level schedule. The same bar chart is used to

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40 monitor the progress for each utility line of a project. At this level, the management personnel are more concerned with finding the answers to the following questions: Figure 5.8 Gantt Chart of Multiple Project Scheduled by MS-Project —— Company Level Is each utility line of a project making progress as planned? If the project is behind schedule, what is the reason for that? Should the project be expedited to catch up with the planned progress? Which project can the additional crews and equipments be pulled from to expedite the progress?

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41 Figure 5.9 Crew Tracking Table Only the first question can be answered using the Bar chart, the others are resolved by using the expertise of the management personnel. Operation Level Scheduling: The foreman, superintendent and project engineer come to work half an hour earlier than other crew members every morning. The H Company holds meetings every morning for foremen and superintendents. In the morning meetings, superintendents with project engineers will assign daily tasks to the crew leader – foremen who will in turn assign the tasks to the crew member. Every morning, after they have been assigned a task for that day, the crew members will go to their assigned site. By the end of that day, usually crew members leave around 5 o’clock. The foreman and superintendent will have another daily meeting after all crews have left. They will discuss with the project engineer the progress of the project for that day; what difficulties

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42 they have encountered; whether it is on schedule or not; what they need for the next day, and then they will submit the daily report sheet of that day. The morning and afternoon meetings are very important for the HCC. They keep the company running smoothly. The problem of this daily report-based system is that by the time the company finds the schedule problem it is too late to fix them. HCC’s Scheduling Problem During the time of author was doing the scheduling for H Company, the following problems were identified: 1. The currently used scheduling method, the Gantt Chart only displays limited information that management personnel needs, especially for the project level planning and scheduling. The company needs a schedule method that can reflect the nature of utility project. 2. Although the company has a three-level scheduling system, the project level and operation level can not figure out the construction interference among utility lines. In the case of two or more pipe lines intersecting somewhere on the site, where the elevation of one utility pipe is lower than the other, if the crews arrive at this kind of location simultaneously, obviously only one crew can continuously work and the other crews have to stop and wait until the first one to finish. This interference slows down the construction progress, interrupts the work continuity of the crews, and therefore lowers the production rate. The following section describes the method of locating interference locations, predicting the possible interruption time, and avoiding these scheduling conflicts.

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43 Summary This chapter introduces the HCC’s background, organizational structure, and its project operation model. Three main operation functions are described in detail – estimating, scheduling, and project monitoring and control. The company adopts three levels of scheduling and planning and the scheduling method used is the linked Bar chart. Although the linked Bar chart has some advantages, such as being time-scaled, easy to understand, with marked critical path, etc., it can not meet the information extraction requirements from management personnel, especially at the project level. It does not reflect the true project location with showing the progress. Accordingly, the Bar chart does adequately represent the productivity of crews. Most of all, it also does not represent the interference locations; predict the construction interruption time; and provide the method to avoid the interruptions to keep the work continuity of the crews. The next chapter describes application of a modified line of balance (LOB) method to a sample project, the Unit 97 project.

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CHAPTER 6 CASE STUDY FLORENCE PATH Unit 97 Project The Villages is a huge community development project located in Ocala, Florida. It includes many units, such as Unit 97, Unit 98, and Unit 99, etc. Each Unit is composed of several hundred Housing Lots. Figure 6.1 is an aerial photo of The Villages site. The Villages Unit 97 is a typical project that HCC usually work on. HCC undertakes the construction of the underground utilities of the Unit 97. The utility lines include: Storm Drainage, Sanitary Sewer, Fire/Irrigation Water, and Potable Water. The Roads and Lot Grading are subcontracted out. Figure 6.1 Aerial Photo of The Villages Project 44

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45 The work on each utility line of the Unit 97 project is described as follows (Table 6.1 shows the summary of project information): Storm Drainage: The storm drainage work has 61 different kinds of manhole structures, and 7,113 feet of plastic and metal pipe with diameters ranging from 12 inch to 54 inches. The average depth for laying these pipes is 10.7 feet; the Total earth moving work is 29,753 cubic yard of bank soil. Sanitary Sewer: The work contains constructing 35 manholes and laying 12 single service lines and 97 double service lines. The average length of each single service line is 30 feet long. The average length of each double service line is 25 feet. The pipes of sanitary sewer are 7,663 feet long PVC pipes with diameter of 8 inches. The sanitary sewer line has 18,668 cubic yard bank soil to be removed. The average trench depth is 10 feet. Potable Water: The Potable Water work includes 9,415 feet of main water pipe with diameters from 4 inches to 12 inches, and 3,560 feet of 1 inch diameter service line. It also requires the installation of 16 gate valves, 23 single meter boxes, and 90 double meter boxes. The depth of the main water pipes and service lines must be greater than 3 feet according to the engineering designs. Irrigation/Fire Water: The irrigation/fire water work includes laying 8,895 feet irrigation main pipe with diameters from 4 inches to 8 inches;3,480 feet service lines with diameter of 1 inch. It also requires the installation of 17 gate valves; 9 single meter boxes; and 97 double meter boxes.

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46 Table 6.1 Summary of Project Information Crew Length of Line (feet) Avg. Depth (feet) Range of Pipe Diameter Man-hole Earth Moving Single Service Line Double Service Line Box Meter Gate Valve Storm Drainage 1 7,113 10.7 12”54” 61 29,753CY --Sanitary Sewer 2 7,663 10 8” PVC 35 18,668CY 12 (avg. 30’ long) 97 (avg. 25’ long) -Potable Water 3 9,415 >=3 4”12” --3560 feet long with 1” diameter 23 single, 90 double 16 Irrigation/Fire Water 3 8,895 >=4 4”8” --3,480 with 1” diameter 9 single, 97 double 17 Estimating Construction Duration for the Utility Lines The first attempt to build a schedule consisted of dividing the project into four main lines since the project has four main components: (1) Sanitary Sewer Line; (2) Storm Drainage Line; (3) Potable Water Line; and (4) Irrigation/Fire Water Line. The following section will describe how to estimate the construction duration of the sewer line, the storm drainage line, the potable water line, and the irrigation/fire water line. Estimation of Sewer Line Construction Duration The duration of sewer line construction is affected by the rate of production. It consists of three components: the construction durations for the main sewer line, for the manhole construction, and for the service line. Duration of Main Sewer Line: The Unit 97 project only uses 8” diameter PVC as its sewer pipe. In order to determine the rate of productivity which is affected by the depth of the sewer pipe line, the whole main sewer line is categorized into different depth ranges: 0 – 6’ 6 – 8’

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47 .. 26’-28’ 28’-30’ The depth and length of the main sewer line is itemized based on these categories in Table 6.2. For example, the length of the main sewer line laid within 0’ to 6’ deep range is 3,197 feet, and the length of the main sewer line laid within 8’ to 10’ deep is 284 feet. The total length of main sewer line is 7,663 feet. For the Unit 97 project uses only one pipe size, an 8” diameter PVC pipe. The third column in Table 6.2 lists the productivity of laying pipe on various depth ranges. It shows that the deeper the pipes are laid, the lower the rate of production. The productivity is estimated by the project manager based on the soil condition, pipe size, and depth of pipe laid. The pipe duration column shows the duration of sewer pipe laid on various depth ranges. For example, the duration for laying 3,197 feet of 8” PVC pipe at a depth of 0’ to 6’ is 4.05 days ( 3,197 feet / 790 = 4.05 days). By adding all of the durations listed in the fourth column, the total duration for laying the main sewer line is determined to be14.13 days. Table 6.2 Estimated Duration of Main Sewer Line Depth Length of Pipe Line (feet) Productivity (feet/day) Pipe Duration (days) 0’-6’ 3,197 790 4.05 6’-8’ 1,936 715 2.71 8’-10’ 284 640 0.44 10’-12’ 332 565 0.59 12’-14’ 213 490 0.43 14’-16’ 268 415 0.65 16’-18’ 787 340 2.31 18’-20’ 233 265 0.88 20’-22’ 413 200 2.06 22’-24’ 170 24’-26’ 150 26’-28’ 120 28’-30’ 100 Total 7,663 14.13

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48 Manhole Construction Duration: The duration of manhole construction is also affected by the depth of the installation. The deeper the installation, the slower the productivity is. Therefore the rate of production is categorized into various depth ranges as for the main sewer line. The quantities for the manholes are computed based on these depth ranges. Table 6.3 shows the depth categories, manholes, productivity, and duration estimating in each category. For example there are 15 units of manhole being installed within the category 0’ to 6’ deep. The productivity for every 10 units of manholes is 0.75 days. Therefore, the duration for installing 15 units of manhole at 0’-6’ depth is 1.125 days (15 0.75 = 1.125 days). The installation duration for manholes in other depth categories is estimated in a similar way. The total duration for installing the manholes is determined by adding up all of durations for all depth categories and it is 4.375 days. Table 6.3 Predicted Duration of Manhole Construction Depth Manhole (unit) Productivity (days/10 units) Manhole Duration (days) 0’-6’ 15 0.75 1.125 6’-8’ 6 1.00 0.600 8’-10’ 2 1.00 0.200 10’-12’ 3 1.25 0.375 12’-14’ 1 1.50 0.150 14’-16’ 3 1.75 0.525 16’-18’ 2 2.00 0.400 18’-20’ 2 3.00 0.600 20’-22’ 1 4.00 0.400 22’-24’ 5.00 24’-26’ 6.00 26’-28’ 28’-30’ Total 35 4.375 Estimate of Service Line Installation Duration: The service line is a sewer line laid to the each household. It is a line connecting the main sewer line with sewage discharged from each household. There are two types of service lines. They are the single service line and the double service line. The single service line only connects one household to

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49 the main sewer line. The double service line connects two households to the main sewer line. For the Unit 97 project, the average length of the single service line and double service line are 30 feet and 25 feet respectively. There are 12 single service lines and 97 double service lines in Unit 97. The production rates for both types of service line are close, therefore they are supposed to be same -15 unit of service line per day. Therefore the duration for installing the single service line is 0.80 days (12 / 15 = 0.80 days) and the double service line installation duration is 6.47 days (97 / 15 = 6.47 days). The total duration for installing the service lines is 7.27 days (0.80 + 6.47 = 7.27 days). Table 6.4 shows the predicted duration for installing the service lines. Table 6.4 Predicted Duration of Installing Service Line Service Line Units Avg. Length of Each Unit (feet) Productivity ( units/day) Duration (days) Single 12 30 15 0.80 Double 97 25 15 6.47 Total 109 7.27 The total duration for laying the sewer line is computed by using equation 5-5: iserviceimainiholeiutilityDDDD = 14.13 + 4.375 + 7.27 = 25.77 days Here i represents the sanitary sewer line. Estimate of Storm Drainage Line Construction Duration The estimate of the storm drainage line construction duration consists of two components: the duration for the construction of the main storm drainage line, and that for the manhole construction. Estimate of Main Storm Drainage Line Duration: The production rate for laying the main storm drainage line has already been displayed in Table 5.6. It shows various productivity rates based on pipe size and the depth of pipe installation. For example the production rate for the pipe with diameter 30” laid at 6’ to 8’ deep is 501 feet per day.

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50 Table 6.5 shows the length of the storm drainage pipe for the Unit 97 project corresponding to specific pipe size and depth of pipe. The duration for laying the main storm drainage line for a specific depth category is determined by using Equation 5-7:. For example, laying storm drainage pipe in the 6’ to 8’ depth range, involves installing 808 feet of pipe with pipe diameter within 12” to 24” and 536 feet long pipe with pipe diameter of 30” (see Table 6.5). The duration for laying pipe in this depth category is 2.6 days (808.0/525.0 + 536.0 /501.0 = 2.6 days). The total duration for laying the main storm drainage is determined by adding up all of the durations for each depth category. For the Unit 97 project the total duration is 17.8 days. mnimainnmimainnmimainrlD)()(,, = 0.6 + 2.6 + 3.8 + 8.6 + 1.8 + 0.432 = 17.8 days. Table 6.5 Predicted Duration of Laying Main Storm Drainage Line Pipe Length on Various Pipe Size (feet) Depth of Pipe 12”-24” 30” 36” 42” 48” 54” 60” Duration (days) 0’-6’ 372.0 0.0 0.0 0.0 0.0 0.0 0.0 0.600 6’-8’ 808.0 536.0 0.0 0.0 0.0 0.0 0.0 2.600 8’-10’ 718.0 308.0 60.0 83.0 402.0 0.0 0.0 3.800 10’-12’ 778.0 299.0 0.0 514.0 1,429.0 223.0 0.0 8.600 12’-14’ 0.0 0.0 0.0 0.0 475.0 0.0 0.0 1.800 14’16’ 0.0 0.0 0.0 0.0 108.0 0.0 0.0 0.432 16’-18’ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.000 18’-20’ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.000 Above 20’ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.000 Total 2,676.0 1,143.0 60.0 597.0 2,414.0 223.0 0.0 17.800 Estimate of Storm Drainage Manhole Construction Duration: The duration of storm drainage manhole construction is estimated similarly to that for the sewer line manhole installation. It is also affected by the depth of the installation. The rate of production is categorized into various depth ranges. The quantities of manhole are counted for these depth ranges. Table 6.6 lists the quantities of manholes and production

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51 rate for each depth category. The installation duration for the manholes in each depth category is computed similarly as that for the sewer line. For example there are 5 units of manhole being installed within the 0’to 6’ depth category. The production rate for every 10 units of manholes is 0.75 days. Therefore, the duration for installing 5 units of manhole on 0’-6’ deep is 0.375 days (5 0.75 = 0.375 days). The total duration for installing manholes is determined by adding up all the duration for all depth categories and it is 6.7 days. Table 6.6 Predicted Duration of Storm Drainage Manhole Installation Depth Manhole (unit) Productivity (days/10 units) Manhole Duration (days) 0’-6’ 5 0.75 0.375 6’-8’ 12 1.00 1.200 8’-10’ 21 1.00 2.100 10’-12’ 20 1.25 2.500 12’-14’ 2 1.50 0.300 14’-16’ 1 1.75 0.175 16’-18’ 2.00 18’-20’ 3.00 20’-22’ 4.00 22’-24’ 5.00 24’-26’ 6.00 26’-28’ 28’-30’ Total 61 6.700 The duration for laying storm drainage line is computed using the following equation: iserviceimainiholeiutilityDDDD = 17.80 + 6.70 + 0 = 24.50 days Here i represents the storm drainage line. Potable Water Line and Irrigation/Fire Water Line The construction of the potable water line and the irrigation/fire water line is not as complicated as the sewer line and storm drainage line. The lines are covered by 4 feet thick dirt. The construction durations for the construction of the potable water line and

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52 the irrigation/fire water line are determined by the production rate of each of these two lines. Table 6.7 lists the predicted cons truction duration for these two lines. Table 6.7 Predicted Duration of Potable Water Line and Irrigation/Fire Water Line Utility Lines Length of Line (feet) Productivity ( feet/day) Duration (days) Potable Water 9,415 920.00 10.23 Irrigation/Fire Water 8,895 930.00 9.56 Table 6.8 lists the information for each line based on its length, crew allocation, rate of production, estimated duration. Th ree crews are assigned to the Unit 97 project. The crew one works on the storm drainage line and crew two works on the sanitary sewer line. Both of crews start their work on the same date (day 0). Crew three works on two lines, the potable water and the irrigation/fire water lines. It works first on the potable water line and then on irri gation/fire water line. Table 6.8 Summary of Unit 97 Utility Lines Utility Lines Crew Duration (days) Length of Line (feet) Rate of Production (feet/day) Start Time Finish Time Storm Drainage 1 24 .40 7,113 291.52 0 25 Sanitary Sewer 2 25.77 7,663 297.36 0 26 Potable Water 3 10.23 9,415 92 0.00 0 11 Irrigation/Fire Water 3 9. 56 8,895 930.00 11 21 Project 0 Max. = 26 Linked Bar Chart and Linear Scheduling for Unit 97 All of the above information is used to develop the Linked Bar Chart schedule and Linear Schedule Method for the Florence Path of Unit 97 project. The Linked Bar Chart is shown in Figure 6.2 and the linear schedul e method diagram is shown in Figure 6.3.

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53 Figure 6.2 Linked Bar Chart Schedule for the Florence Path

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54 The linked bar chart schedule shows repetitive activities (Excavate, Lay pipe, and Back fill) in the storm drainage line and sanitary sewer line. It illustrates how laborious the linked bar chart method is in planning the repetitive projects. Although it is time-scaled chart, the logical links of repetitive activities of each section do not make much sense in the presentation. Neither does it tell the location of the sections, nor does it present the production rate visually and directly. Table 6-8 lists the start time and finish time for each utility line. The estimated project duration is 26 days. Storm drainage and sanitary sewer lines are undertook by two separated crews and they started from day 0. The potable water and the irrigation/fire water lines are constructed by the same crew. The potable water line is installed first. After it is completed, the same crew will start installing the irrigation/fire water line. Line of Balance Method for Unit 97 Project0.002000.004000.006000.008000.0010000.0012000.000510152025Time (day)Length of Line (feet) Storm Drainage Sanitary Sewer Potable Water Irrigation/Fire Water Storm Drainage Irrigation/Fire Sanitary Sewer Potable Water Figure 6.3 Linear Schedule diagram for the Unit 97 Project on Project Level

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55 Although the Linear Schedule Method clearly presents the production rate of each utility line, the start time and finish time, and true progress for the individual schedule date, but it can not illustrate the interference locations, and predict the interference time which may stop the work of crews, delay the project, and incur cost overruns. The following sections focus on application of the Modified Linear Schedule Method to Florence Path which is part of the Unit 97 project. Application of the Modified Linear Schedule Method on Florence Path Florence path is one of streets in the Unit 97 community. The plan and profile of this street is shown in Figure 6.4. The storm drainage and the sanitary sewer lines are laid in the middle of the street, the irrigation line and the water line are laid on the each side of the street. As shown in Figure 6.4, the storm drainage line and sanitary sewer line intersect with each other at several locations. HCC assigns two crews to individually construct the storm drainage and sanitary sewer lines. The problem faced by these two crews is that of how to avoid the construction conflicts at the intersection locations in order to assure the work continuity of each crew. To solve this problem, several issues must be addressed: Exact location of the intersection points Production rate for each utility line Starting time for each utility line The following describe the steps to solve this problem . Identify Intersection Location In order to accurately locate these intersection points, the coordinates, as shown in Table 6.7, of the storm drainage and the sanitary sewer stations on a plane are used.

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56 There are six storm drainage stations and identified as D97-27, D97-26, D97-25, D97-24, D97-23, and D97-22. The distances and displacement on y axis of these stations from referenced station 40+00.00 are listed in Table 6.7. The coordinates of the sanitary sewer line are also similarly listed. The data listed in Table 6.7 is shown in Figure 6.5. The x-axis represents the distance and the y-axis represents the displacement. The x-y relationship equation for each section of the storm drainage and the sanitary sewer lines are located along the line section. Table 6.9 Coordinates of Storm Drainage Stations and Sanitary Sewer Stations (Note: LT (+): left turn, assumed as positive, RT (-) right turn, assumed as negative). STREET Storm Drainage Stations Station # Displacement LT(+), RT(-) Sanitary Sewer Stations Station # Displacement LT(+), RT(-) D97-28 Exist S-3 D97-27 4040.71 11.00 S97-35 4238.1 0.00 D97-26 4037.17 -11.00 S97-34 4454.6 -5.00 D97-25 4292.92 11.00 S97-33 4600.16 5.00 D97-24 4303.45 11.00 S97-32 4748.09 16.00 D97-23 4543.69 11.00 FLORENCE PATH D97-22 4570.38 -11.00 The two intersection points are located for the drainage and sanitary sewer lines as follows: The two intersection locations are (4298.82, -1.42) and (4554.68, 1.88). (Equation 6-1) 878.970231.01.89800893.2xyxy03.3110687.03.37568243.0xyxy (Equation 6-2) and

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57 Figure 6.4 Florence Path Plan and Profile

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58 Storm Drainage Line Sanitary Sewer Line Figure 6.5 Storm Drainage Line and Sanitary Sewer Line in X-Y Coordinate System Linear Scheduling on Florence Path Table 6.10 shows the information about each section of storm drainage line on the Florence Path: the length between two stations, average depth of section, pipe size of that section, and production rate and construction duration. Table 6.11 shows the information about the sanitary sewer line. Table 6.10 Production Rate and Duration for Each Section of Storm Drainage Line Start Station End Station L.F. between Two Stations (L.F) Average Depth (L.F) Pipe Size (Diameter) Production Rate (LF/Day) Cumulative Duration (days) D97-27 D97-26 23 5.14 18” 596 0.04 D97-27 D97-25 254 6.54 30” 501 0.55 D97-25 D97-24 25 5.92 18” 596 0.59 D97-25 D97-23 253 7.23 24” 525 1.07 D97-23 D97-22 35 7.68 18” 525 1.14 Total 1.14

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59 Table 6.11 Production Rate and Duration for Each Section of Sanitary Sewer Line Start Station End Station L.F. between Two Stations (L.F) Average Depth (L.F) Pipe Size (Diameter) Production Rate (LF/Day) Cumulative Duration (days) S97-35 S97-34 216 20.23 8” 640 0.34 S97-34 S97-33 146 9.71 8” 565 0.60 S97-33 S97-32 149 10.60 8” 790 0.78 Total 0.78 Adjusted Linear Scheduling for Florence Path Based on the information presented on Table 6.10 and 6.11, a Linear Scheduling diagram is shown in Figure 6.6. The lines show the planned schedule for the storm drainage and sanitary sewer line and are not straight lines which indicate that each section of the lines has different production rate. Both utility lines start from day 0. The storm drainage line will be finished on day 1.74 and the sanitary sewer line will be completed on day 0.78. Figure 6.6 Linear Scheduling and Adjusted Linear Scheduling for Storm Drainage Line and Sanitary Sewer Line

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60 However, the two utility lines meet at locations (4298.82, -1.42) and (4554.68, 1.88). Figure 6.6 shows the interference locations. As planned, the storm drainage crew will arrive at the first and second interference locations at days 0.5899 and 1.1367 respectively and the sanitary sewer crew will arrive at the first and second interference locations at days 0.0949 and 0.5171 respectively. As required, the sanitary sewer line must be constructed ahead of the storm drainage line at the interference locations since its elevation is lower than the storm drainage line. In addition, the time buffer between them has to be at least 1 day. Under this constraint, the drainage line has to be displaced along time axis (y-axis) for 1 day. The upper line shows the adjusted planned schedule for the storm drainage line. It starts at day 1 right after the beginning of sanitary sewer line construction. The storm drainage crew will arrive at the location (4298.82, -1.42) and (4554.68, 1.88) on days 1.0994 and 1.6367 respectively. At the same time the planned schedule of sanitary sewer line remains the same position. Therefore the time buffers at the first and second interference locations are respectively 1.0051 day and 1.1196 days. This adjusted schedule satisfies the construction requirements, avoids the work space interference, and maintains the work continuity of the work crews. Summary This chapter introduces the Unit 97 project and analyzes the application of linked bar chart scheduling, linear scheduling method, and modified linear scheduling method to the Unit 97. The linked bar chart illustrates how laborious the linked bar chart method is in planning the repetitive projects. Although it is time-scaled chart, the logical links of repetitive activities of each section do not make much sense in the presentation. Neither

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61 does it tell the location of the sections, nor does it present the production rate visually and directly. Although the traditional Linear Scheduling method clearly presents the production rate of each utility line, the start time and finish time, and true location of individual schedule date, but it can not illustrate the interference locations, and predict the interference time which may stop the work of crews, delay the project, and incur cost overruns. Then the modified Linear Scheduling method is applied to Florence Path of Unit 97. This method identifies the interference locations and adjusts the schedule to meet construction constraints to avoid the construction interference and keep the crew work continuity. Table6.12 shows the result through the comparison of three schedule tools over the real project – Florence Path. The next chapter concludes this study and discusses recommendations for future research on scheduling underground utility projects. Table 6.12 Comparison of Schedule Tools Over the Project – Florence Path Linked Bar Chart Linear Schedule Method Modified Linear Schedule Method Time-based chart Space-based chart Time buffer Space buffer Identification of project progress Sort of without identifying the exact location Production rate Flow of labor Different production rates indicate the flow of labor Different production rates indicate the flow of labor Space Conflicts

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CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS Conclusions Construction companies are forced to be more efficient and achieve competitive operational advantage due to an increasingly competitive environment. The benefits of effective planning, scheduling and control of construction projects are obvious. Although the popular scheduling methods, such as Gantt chart and its variation (linked Gantt chart) and Critical Path Method (CPM), are really beneficial to the construction industry, these methods are still criticized while applied to scheduling linear construction projects. The linear scheduling concept was introduced to solve the scheduling problems in linear construction projects. The linear scheduling method and its variations are beneficial to linear construction in its representation of productivity and project progress corresponding to true location. However, most of linear scheduling method studies focus on activities of a linear project. The current linear scheduling method and its variations have not been used to study the scheduling problems for multiple utility lines which happen often in the utility construction company. These utility lines intersect with each other at certain locations as per the design. Each line at the intersection location has its own elevation. Crews are assigned to work on each line. These crews may arrive at the intersection location simultaneously which causes work space conflicts. The current linear scheduling method and its variations do not indicate the interference locations, predict the interference time, or help avoid work space conflicts in order to keep the crew work continuously. This study proposes using the modified linear scheduling method to: 62

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63 indicate the interference locations for projects with two or more utility lines estimate the interference time of these utility lines adjust the original construction schedule This method is used to manage an actual project that the author worked on. The project is one of the typical projects that the HCC undertakes. The project has four utility lines: storm drainage, sanitary sewer, portable water line, and irrigation/fire. In the case of Florence Path the storm drainage and sanitary sewer lines intersect with each other. The modified linear scheduling method is applied to accurately identify the intersection points, to estimate the construction interference time, to adjust the schedule to avoid the construction interruption, to keep the continuity of crew work, and to avoid the construction delays and cost overruns. Recommendations for Future Research Although this study develops the modified linear scheduling method to solve the interference problems in scheduling multiple utility line projects, it only explores two utility line problems. If more lines are involved, more construction constraints will be imposed on the scheduling process, and the method will become more complicated. However, this challenge is worth exploring since it may improve the linear construction scheduling. Secondly, although the main lines of utility line projects are linear and construction of them involves the repetitive activities, the schedule of spurs of main lines such as service lines has not taken into account in this study. However it becomes research issue since it also consumes resources and breaks the work continuity if not appropriately scheduled.

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64 Thirdly, the production rates used in the scheduling process are from historical data and are based on field experience; they are the best resource for estimating the production rate for the future projects. Although the modified linear scheduling method could accurately identify the interference locations and estimate the interference time, actual construction productivity may vary from the as planned ones used in the as-planned schedule and the actual interference times may be different from the ones used in the as-planned schedule. The application of stochastic methods or sensitivity analysis to determine the production rates may overcome this limitation. Fourthly, the whole process involved in the modified linear scheduling method is not difficult to understand and implement, but it involves extracting data from engineering drawings, converting them to linear equations, solving for the intersection points, identifying the interference time, and adjusting the schedule. The processes are time consuming in data input and involve large amounts of computation in finding solutions for sets of linear equations if the project is big. The automatic integration of CAD with computerized linear equation solutions and the modified linear scheduling graph will also need further research efforts.

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LIST OF REFERENCES Ammar, M. A. and Mohieldin, Y. A. (2002). Resource Constrained Project Scheduling Using Simulation. Construction Management and Economics, 20, pp. 323-330 Arditi, D. and Albulak, M. Z. (1986). Line-Of-Balance Scheduling in Pavement Construction. Journal of Construction Engineering, 112(3), pp. 411-424 Arditi, D., Sikangwan, P., and Tokdemir, O. B. (2002), Scheduling System for High Rise Building Construction. Construction Management and Economics, 20, pp. 353-364 Chrzanowski, E.N. and Johnston, D.W. (1986). Application of Linear Construction. Journal of Construction Engineering, ASCE, 112(4), 476-491 Flood, I. (2005). BCN4720 Construction Planning and Control. University of Florida, Gainesville, Florida Harris, R.B. (1996). Scheduling Projects with Repeating Activities. UMCEE Report No. 92-96, Civil and Environmental Engineering Department, University of Michigan, Ann Arbor, MI. Harris, R.B. and Ioannou, P.G. (1998). Scheduling Projects with Repeating Activities. Journal of Management in Engineering, ASCE, 124(4), 269-276. Lumsden, P. (1968). The Line of Balance Method. Pergamon Press, London Lutz, J.D. and Hijazi, A.(1993). Planning Repetitive Construction: Current Practice. Construction Management and Economics, 11, 99-110 Mattila, K.G. and Abraham, D.M. (1998). Resource Leveling of Linear Schedules Using Integer Linear Programming. Journal of Construction Engineering and Management, ASCE, 124(3), 232-244 Mubarak, S. (2003). Construction Project Scheduling and Control. Prentice Hall, Upper Saddle River, New Jersey. 13-14 Rahbar, F.F. and Rowings, J.E. (1992). Repetitive Activity Scheduling Process. Trans. Am. Assn. of Cost Engrs., 2, 0.5.1-0.5.8. Reda, R.M. (1990). RPM: Repetitive Project Modeling. Journal of Construction Engineering and Management, ASCE, 116(2), 316-330 65

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66 Russell, A. D. and Wong, W.C.M. (1993). New Generation of Planning Structures, Journal of Construction Engineering and Management ASCE, Vol. 119, No. 2, pp. 196-214 Selinger, S. (1980). Construction Planning for Linear Projects. Journal of the Construction Division, ASCE, 106(CO2), 195-205 Stradal, O. and Cacha, J. (1982). Time Space Scheduling Method. Journal of the Construction Division, ASCE, 108(CO3), 445-457 Suhail, S.A. and Neale, R.H. (1994). CPM/LOB: New Methodology to Integrate CPM and Line of Balance. Journal of Construction Engineering and Management, ASCE, 120(3), 667-684

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BIOGRAPHICAL SKETCH Bin Cheng earned his bachelor’s degree in electrical machinery engineering in China. He began studying English after he came to America. He attended the M.E.Rinker, Sr. School of Building Construction at the University of Florida to obtain his Master of Science, which he was awarded in December 2005. The future holds bright things for Bin. He has already started using his knowledge and skills in design and construction management, learned from the University of Florida, to lead a successful career. 67