• TABLE OF CONTENTS
HIDE
 Cover
 Title Page
 Introduction, objective, experimental...
 Results
 Conclusions
 Tables 1-5
 Figures 1-10






Title: Local pier scour model tests for SR312 over the intracoastal waterway bridge St. Augustine (St. Johns County), Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00089592/00001
 Material Information
Title: Local pier scour model tests for SR312 over the intracoastal waterway bridge St. Augustine (St. Johns County), Florida
Physical Description: Book
Creator: Sheppard, D. Max
Publisher: Coastal and Oceanographic Engineering Department, University of Florida
Publication Date: 1995
 Subjects
Subject: Coastal Engineering
Spatial Coverage: North America -- United States of America -- Florida
 Notes
Funding: This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.
 Record Information
Bibliographic ID: UF00089592
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Cover
        Cover
    Title Page
        Page 1
    Introduction, objective, experimental plan and procedures
        Page 2
    Results
        Page 3
    Conclusions
        Page 4
    Tables 1-5
        Page 5
        Page 6
    Figures 1-10
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
Full Text




UFL/COEL-95/029


LOCAL PIER SCOUR MODEL TESTS FOR SR 312 OVER THE
INTRACOASTAL WATERWAY BRIDGE
ST. AUGUSTINE (ST. JOHNS COUNTY), FLORIDA





FINAL REPORT


By


D. M. Sheppard


July 1995




Submitted to:

Reynolds, Smith and Hills, Inc.
and
Florida Department of Transportation
District 2














FINAL REPORT


LOCAL PIER SCOUR MODEL TESTS
FOR
SR 312 OVER THE INTRACOASTAL WATERWAY BRIDGE
ST. AUGUSTINE (ST. JOHNS COUNTY), FLORIDA.




SUBMITTED TO:

REYNOLDS, SMITH AND HILLS, INC.
AND
FLORIDA DEPARTMENT OF TRANSPORTATION
DISTRICT 2




BY:

D. M. SHEPPARD
COASTAL AND OCEANOGRAPHIC ENGINEERING DEPARTMENT
UNIVERSITY OF FLORIDA


WPI No. 2116967 and 2117109
State Project Nos. 78002-1509 and 78002-1510
Federal Aid Project No. M-9840(3)
RS&H Project No.. 9951431000
UF Account No. 4511305-12
UPN No. 95010490


JULY 1995







LOCAL PIER SCOUR MODEL TESTS
FOR
SR 312 OVER THE INTRACOASTAL WATERWAY BRIDGE
ST. AUGUSTINE (ST. JOHNS COUNTY), FLORIDA.


INTRODUCTION:

A new bridge will be constructed parallel to the existing bridge on SR 312 over the
intracoastal waterway and will carry the west bound traffic. Once constructed, these bridges will
be in close proximity to each other and the potential for hydraulic and scour interaction between
the piers on these bridges exists. Estimating local scour depths for complex multiple pile bridge
piers under storm conditions is difficult. This is particularly true when there is more than one
structure as is the case here. The procedures and equations in HEC-18 are known to be
somewhat conservative to account for the uncertainty in the data on which the equations are
based. The FHWA requires that local scour depths for design conditions be either 1) computed
using the equations and procedures in HEC-18 or 2) determined by performing scale model
flume tests. This report presents the results of local scour flume tests that were performed on
scale models of the most scour susceptible existing and proposed piers for the SR 312 bridge
over the intracoastal waterway. This bridge is located in St. Augustine (St. Johns County),
Florida.

OBJECTIVE:

The objective of this work was to determine the maximum equilibrium local scour depths
(scour depths that will occur at transition from clear water to live bed conditions) that will occur
near the piers during a 1 in 100 year design storm event.

EXPERIMENTAL PLAN AND PROCEDURES:

Physical model tests to determine maximum local sediment scour depths for the most
scour susceptible existing and proposed pier combination on the SR 312 Bridge were conducted.
Geometric scaling was used to size the models water depths, scour depths, etc. The model to
prototype length scale used was 1:24. Drawings of the models are given in Figures 1-4.
Photographs of the model piers prior to the tests are shown in Figures 5, 6 and 8. Local scour
after the 26 hour tests are shown in Figures 7, 9 and 10.

The tests were conducted in the 100 ft long x 8 ft wide x 2.5 ft deep flume in the
Hydraulics laboratory in the Civil Engineering Department at the University of Florida. This
flume has a 100 hp pump and maximum discharge (with the existing weir) of 38.8 ft3/sec (1100
I/sec). This project has benefited from the fact that the flume was already configured for these
types of experiments; and, since other similar tests will be conducted after these tests are
completed there were no pre and post experiment costs. That is, there was no setup and
breakdown costs associated with these tests.







The following tasks were performed:


Task 1.
A. Models of the existing and proposed piers were designed and constructed (see Figures
1 and 2).
B. The models were placed in the flume, the sediment in the test area compacted and
leveled, and the instrumentation calibrated (see Figures 3-5).
C. A 26 hour duration local scour test was conducted with flows simulating a flood
current (i.e., a flow from ocean to bay) (Figure 6).
D. The flume was drained and the post experiment measurements were made.
E. The model's positions were then swapped so that an ebb (bay to ocean) current
situation could be simulated.
F. A 26 hour ebb current test was then conducted.
G. The flume was drained and post experiment measurements made.
H. The data from both tests were reduced and analyzed.

Task 2. A preliminary letter report that included the test results and prototype design scour
depths was submitted to Reynolds Smith and Hills and FDOT District 2 on May 31,
1995.

Task 3 This final report was completed and submitted on July 19, 1995.

RESULTS:

The environmental parameters for the two tests are presented in Tables 1 and 2. The
median sediment grain diameter (D50) used in both tests was 0.165 mm and the sediment size
standard deviation (a) was 1.29. The extrapolated scour depths are obtained by making
corrections to the measured scour depth values for duration and U/Uc. That is, the equilibrium
scour depth is predicted based on the scour depths measured at the end of the 26 hour tests and a
second correction is made for U/Uc in the test being slightly less than 1. Table 3 gives the
measured and equilibrium local scour depths for the existing and proposed piers for the design
flood current test. Table 4 gives the same information for the design ebb current test. Table 5
gives the recommended design local scour depths for the prototype piers.

Drawings of the model piers are given in Figures 1-4. Figure 5 is a photograph of the
model piers prior to installation in the flume test area. Figure 6 is a photograph showing the
piers in the test area prior to filling the flume and running the flood current test (i.e. the test with
the proposed bridge pier upstream of the existing bridge pier- view from upstream). Figure 7 is
a photograph of the local scour at the end of the first 26 hour (flood current) test (view from
downstream). Figure 8 is a photograph of the model piers prior to the ebb current test (view
from upstream). Figure 9 is a photograph of the local scour after the 26 hour ebb current test and
Figure 10 is a close-up of the scour near the proposed bridge pier (both viewed from upstream).







CONCLUSIONS:


The test results indicate that there is not a significant effect on the local scour for either
bridge pier as a result of the close proximity of the piers. The upstream pier offers some
"protection" for the downstream pier in that it experiences less scour than it would have had the
other pier not been there (see Tables 3 and 4). Even though the two piers are quite different in
design their design local scour depths are very near the same. This is the result of offsetting
effects such as pile cap size and pier skewness to the flow.

It should be noted that a conservative approach was taken in these model experiments in
that the tests are conducted under conditions believed to produce maximum scour depths. These
include the following:

1. The tests were conducted near transition from clear water to live bed scour conditions
(and the results extrapolated to transition, U/Uc = 1). Flow velocities greater or less than
critical will produce smaller equilibrium scour depths.
2. The sediment grain size distribution used in the test area of the flume is very narrow with
a relatively small standard deviation, a (1.29). Researchers have shown that with all
other conditions being the same, local scour depths increase with increasing uniformity of
grain size.
3. The duration of these tests (26 hours) is sufficiently long to minimize errors in
extrapolating the results to equilibrium conditions.
4. Predicted one in one hundred year (storm return interval) water elevations were used to
determine the water depths for these tests even though peak velocities occur at water
elevations less than the maximum value. (In general, equilibrium scour depths increase
with depth up to a water depth to structure diameter ratio of about three.)
5. The scour producing event is assumed to be of sufficient duration that equilibrium scour
depths are achieved. It is the author's opinion that the duration of most storm events in
Florida is not sufficient to create equilibrium scour depths, even on the leading edge of a
pier structure but certainly not in the interior or near the downstream end of these
complex multiple pile piers.
6. For large, complex, multiple pile structures the variation in the equilibrium scour depth
near the structure can be significant. Once again, until this phenomena is better
understood and predictable, we recommend that the maximum scour depth be used
throughout the structure.

It is not necessary to have large velocities in order to produce local structure-induced
scour near bridge piers. In fact, the maximum scour depths are thought to occur at transition
velocities (transition from clear water to live bed scour conditions) which for most of Florida's
erodable, cohesionless sediments are on the order of 1 to 2 ft/sec. The time required to reach
equilibrium is not known at this time but is thought to be dependent on the size of the structure,
sediment properties, depth average velocity, etc. For many locations the duration of the scour
producing storm event is believed to be the limiting factor for scour depth but until these
processes are better understood, equilibrium scour depths will have to be used for design.







Table 1. Environmental Parameters.
Test A Flood Current (Ocean to Bay). Proposed
Bridge Pier Upstream Of Existing Bridge Pier.


Bridge: SR 312 over the Intracoastal Waterway Bridge (St. Johns County), Florida.
General: The ship impact piers on the channel were considered to be the most scour
susceptible. The existing and proposed bridges are in close proximity to each other
and there was concern about an overlapping of the scour holes. This proved to not
be a problem. The objective of these scale model flume tests is to provide design
local scour depths for the proposed bridge piers. The median sediment diameter,
D5s, and standard deviation, a, of the sediment used in the flume tests were 0.165
mm and 1.29 respectively. The velocities were chosen so as to produce U/U0
values slightly less than 1. The existing bridge piers are skewed 290 to the flow.
The proposed piers are inline with the flow. Test A simulates the conditions created
by the propagation of storm surge from the ocean to the bay-river system.
Scale: Water Average Depth Average Computed Critical Flow Duration
Depth: Water Velocity (U): Depth Average Skew of Test:
Temperature: Velocity (Uc): Angle:
1 : 24 19.3 in 29.80 C 0.92 ft/sec 0.99 ft/sec 0 /290 26 hr




Table 2. Environmental Parameters.
Test B Ebb Current (Bay to Ocean). Proposed
Bridge Pier Downstream Of Existing Bridge Pier.

Bridge: SR 312 over the Intracoastal Waterway Bridge (St. Johns County), Florida.
General: The ship impact piers on the channel were considered to be the most scour
susceptible. The existing and proposed bridges are in close proximity to each other
and there was concern about an overlapping of the scour holes. This proved to not
be a problem. The objective of these scale model flume tests is to provide design
local scour depths for the proposed bridge piers. The median sediment diameter,
D5s, and standard deviation, o, of the sediment used in the flume tests were 0.165
mm and 1.29 respectively. The velocities were chosen so as to produce U/U,
values slightly less than 1. The existing bridge piers are skewed 290 to the flow.
The proposed piers are inline with the flow. Test B simulates the conditions created
by the return of the storm surge from the bay-river system to the ocean.
Scale: Water Average Depth Average Computed Critical Flow Duration
Depth: Water Velocity (U): Depth Average Skew of Test:
Temperature: Velocity (Uc): Angle:
1 : 24 19.3 in 29.20 C 0.92 ft/sec 0.99 ft/sec 290/00 26 hr







Table 3. Measured and Extrapolated Model Scour Results
Test A Flood Current (Ocean to Bay). Proposed
Bridge Pier Upstream Of Existing Bridge Pier.


Maximum Measured Scour Depths at:
Measured:
Proposed Pier (deepest scour depth) 4.52 in
Existing Pier (deepest scour depth) 4.19 in
Maximum Equilibrium Scour Depths at:
(Corrections made for duration and U/U, Extrapolated:
1.11 for duration and 1.02 for U/UI)
Proposed Pier 5.12 in
Existing Pier 4.75 in


Table 4. Measured and Extrapolated Model Scour Results
Test B Flood Current (Ocean to Bay). Proposed
Bridge Pier Downstream Of Existing Bridge Pier.

Maximum Measured Scour Depths at:
Measured:
Proposed Pier (deepest scour depth) 3.99 in
Existing Pier (deepest scour depth) 4.50 in
Maximum Equilibrium Scour Depths at:
(Corrections made for duration and U/Uc Extrapolated:
1.11 for duration and 1.02 for U/UA)
Proposed Pier 4.52 in
Existing Pier 5.10 in


Table 5. Predicted Local Scour Depths For Prototype Structures.

Maximum Equilibrium Local Scour
Depths for Prototype Piers and Existing Proposed
Dolphin Systems: Pier Pier:
Test A Flood Current (Ocean to Bay) 9.5 ft 10.24 ft
Test B Ebb Current (Bay to Ocean) 10.2 ft 9.04 ft
Maximum Local Scour Depth 10.2 ft 10.24 ft












-- 18.25" --
8 2.00" 1.12" 1.12

\ 2.38" -0 00000 0 -3

8.25" 3.50" +- 3 @ 2.00"


0.60." -- 12.25" -2.25"
0.60"



EL 1.75" l---- 12.50" --- 1.75"
RUN
R LEVEL
5.50"






15.75"
19.30"


SAND
BED

2.50"



0.60"
13.50" 14.00"






FLUME BOTTOM








Figure 1. Drawing of model of existing SR 312 Bridge pier used in local scour test.


























































Figure 2. Isometric view of model of existing SR 312 Bridge pier used in local
scour test.
8





























12.50" -


1.00"


MODEL
7.88" -TEST RUN
WATER LEVEL
T7


:IIIII::Iu I


00"


- 1.00"


-- SAND BED


19.30"


13.50"





FLUME BOTTOM


Figure 3. Drawing of model of proposed SR 312 Bridge pier used in local scour test.


9


12.75"








13.50"


T *I"* I^


7-171 TI rl TI rr





r 0


l IIIiii 1 M I


4N/ ^" /\/ ,v


7.88"


5.50"
2.

3.75"


j7



























































Figure 4. Isometric view of model of proposed SR 312 Bridge pier used in local
scour test.
10





























Figure 5. Photograph of model piers prior to installation in flume test area.


Figure 6. Photograph of model piers prior to flood current scour test (viewed from
upstream).































Figure 7. Photograph of local scour near bridge piers after 26 hour duration flood
current scour test (viewed from downstream).


Figure 8 Photograph of piers prior to ebb current scour test (viewed from upstream).





























- $1-


F1


Figure 9 Photograph of local scour after 26 hour ebb current test (viewed from
upstream).




















c ........









Figure 10. Photograph of scour near Proposed bridge pier after 26 hour ebb current
test (viewed from upstream).




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs