LOCAL SEDIMENT SCOUR FLUME TESTS FOR HALLANDALE BEACH BOULEVARD (ICWW) BRIDGE PIERS, HALLANDALE (BROWARD COUNTY), FLORIDA FINAL REPORT By
D. M. Sheppard
Reynolds, Smith and Hills, Inc. and
Florida Department of Transportation District 4
LOCAL SEDIMENT SCOUR FLUME TESTS FOR
HALLANDALE BEACH BOULEVARD (ICWW) BRIDGE PIERS, HALLANDALE (BROWARD COUNTY), FLORIDA
SUBMITTED TO: REYNOLDS, SMITH AND HILLS, INC.
FLORIDA DEPARTMENT OF TRANSPORTATION DISTRICT 4
D. M. SHEPPARD
COASTAL AND OCEANOGRAPHIC ENGINEERING DEPARTMENT
UNIVERSITY OF FLORIDA
WPI No. 4110572 State Project No. 86200-1515
UF Account No. 4910 4511 303 12
UPN No. 95030991
LOCAL SEDIMENT SCOUR FLUME TESTS FOR HIALLANDALE BEACH BOULEVARD (ICWW) BRIDGE HERS, HALLANDALE (BRO WARD COUNTY), FLORIDA
The bridge over the Intracoastal Waterway on Hallandale Beach Boulevard in Broward County, Florida is being replaced. Both existing and replacement bridges are Bascule type bridges. The east and west bound roadways are separated and, thus, there will be two similar piers in close proximity to each other on each side of the channel. There is also a small skew and misalignment to the flow. In order to determine the maximum local pier scour that will occur during a design storm event, model studies were conducted in the Hydraulics Flume at the University of Florida. The results of this test are reported here along with recommended design local pier scour depths for 100 and 500 year storm events.
The primary 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 replacement bridge at Hallandale Beach Boulevard over the Intracoastal Waterway during a 1 in 100 year design storm event.
EXPERIMENTAL PLAN AND PROCEDURES FOR THlE TRANSITION TESTS:
The test was 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 3 8.8 ft3/sec (1100 llsec).
The piers were analyzed to determine which combination would be most scour suseptable. It was determined that, in this case, the piers in the greatest water depth would experience the greatest local scour depth. Thus, the test was performed in a water depth of 5.8 in (corresponding to a 100 year water depth of 23.2 ft (7.1 in)).
The following tasks were performed:
A. Models of the proposed piers for the replacement bridge were designed and constructed
(see Figures 1 3).
B. The models were placed in the flume, the sediment in the test area compacted and
leveled, and the instrumentation calibrated (see Figures 4 and 5).
C. A 26 hour duration local scour test was conducted with flows near the critical depth
average velocity (U/Uc = 0.93). U, was computed using Shield's Parameter.
D. The flume was drained and the post experiment measurements were made.
A. The data was reduced and analyzed and corrections made to the results for:
1) the duration of the test (26 hours) not being sufficient to achieve equilibrium, and
2) the depth average velocity during the test (0.80 fi/sec) being slightly less than unity.
Task 3. The final report was written.
The environmental parameters for the test are given in Table 1. The median sediment
grain diameter (D,,) used in the test was 0. 165 mm and the sediment size standard deviation (ay) was 1.29. Table 2 contains the maximum measured and extrapolated scour depths obtained during the test. The extrapolated scour depths are computed by making corrections to the measured values for the test duration not being sufficiently long to reach equilibrium and U/Uc for the test being less than one. Table 3 gives the recommended design local pier scour depths for the proposed piers. Table 3 also gives estimates of local pier scour depths for a 500 year storm.
Drawings of the model piers are given in Figures 1-3. Photographs of the model piers
prior to start of the test are shown in Figures 4 and 5. Figures 6 8 are photographs of the local scour after the 26 hour test. The test was designed to provide a conservative estimate of the maximum local scour that will occur the design storm event. An outline of some of the steps taken to insure that the scour depths are conservative are given in the appendix.
Table 1. Environmental Parameters.
Bridge: Hallandale Beach Boulevard Bridge over the Intracoastal Waterway in Hallandale, Broward County, Florida. Both existing and replacement bridges are Bascule type
bridges. Separate piers for east and west bound lanes with slight skew to the
General: The piers consist of 16 (4 ft diameter) circular piles as shown in Figures 1 and 3.
The bottom of the waterline pile cap is located 12.2 ft above the unscoured bed for
the pier in the deepest water. The piers for the east and west bound lanes are in
close proximity to each other with a slight skew to the flow (9.4') as shown in
Figures 1 and 2. The purpose of these scale model flume tests is to provide design
local scour depths for these structures. The median sediment diameter, D,", and standard deviation, ay, of the sediment used in the flume tests were 0. 165 mm and
1.29 respectively. _____________________Scale: Water Water Depth Average Computed Critical Flow Duration
Depth: Temperature: Velocity (U): Depth Average Skew of Test:
___________ ___________ Velocity (Uc): Angle:
1 : 48 15.8" 31.80 C 0.80 ft/sec 0.86 ft/sec 9.40 26 hr:
Table 2. Measured and Extrapolated Model Scour Results.
Table 3. Predicted Local Scour Depths For Prototype Structures.
Maximum Scour Depth Measured at the End of the 26 Hour Test: 3.77 in 9.58 cm
Maximum Equilibrium Scour Depths: (Corrections made for duration (1.02) and velocity (1.018)) 4.27 in 10.84 cm
Pier: English Metric
No. 2 Near Station 23 + 80
100 year water depth = 22.1 ft (6.74 m) 17.1 ft 5.21 m
No. 2 Near Station 23 + 80
500 year water depth = 28.1 ft (8.57 m) 20.1 ft 6.13 m
No. 3 Near Station 24 + 14
10year water depth =3.4 ft (1.04 m) 7.9 ft 2.41 m
No. 3 Near Station 24 + 14
500 year water depth = 9.4 ft (2.87 m) 16.3 ft 4.97 m
Prototype Soand Bed
Elevotion 15.7' 7
S nd Bedc
Figure 1. Hallandale Bridge Pier Model.
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I I [ I
I f I I
Figure 2. Plan View of Hallandale Bridge Piers for East and West Bound Lanes.
Figure 3. Isometric View of Hallandale Bridge Piers.
Figure 4. View of Model Piers from Upstream Prior to Test.
Figure 5. Close-up View of Model Piers Prior to Test.
Figure 6. Upstream View of Local Scour after 26 Hour Test.
Figure 7. Close-up View of Local Scour After 26 Hour Test.
Figure 8. Close-up View of Local Scour After 26 Hour Test.
Steps were taken in this test to produce a conservative value of design, local pier scour depth. These include the following:
1. The test was 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
3. The 26 hour duration of these tests is sufficiently long to minimize errors in extrapolating the results to equilibrium conditions.
4. Predicted one in one hundred year (storm return interval) water elevation for the site was used to determine the water depth for this test even though peak velocities occur at water
elevations less than the maximum value. In general, equilibrium scour depths increase
with water depth up to a depth equal a structure diameter to water depth ratio of about
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 and certainly not in the interior or near the down stream end.
6. For large, complex, multiple pile structures the variation in the equilibrium scour depth near the structure can be significant. However, until this phenomena is better understood
and predictable, we recommend that the maximum scour depth be used throughout the structure. This, along with the above items, results in a conservative estimate of design
local pier scour depth.