Hydraulics Research Laboratory

Hydraulics Current Research

• Fish Passage in Large Culverts with Low Flow
• Bridge Pressure Flow in Extreme Clear Water Conditions
• Scour in Cohesive Soils Phase I
• Optimum Bridge Deck Shapes to Minimize Pressure Flow Scour Phase II
• Laboratory Experiments to Determine Wave Forces and Moments on Typical US Highway Bridge Decks
• Pier Scour Countermeasures Using Fluidic Devices

Fish Passage in Large Culverts with Low Flow

The construction of culverts to allow the flow of creeks and streams under roads can often have strong environmental impacts. It is important to ensure that the wildlife is not affected by the culvert, and that fish will pass through the pipe and not be deterred. This study aims to analyze flow patterns through corrugated culverts of various sizes.

The tests are carried out on the Fish Passage Flume. The flume is equipped with several depth sensors as well as a Particle Imagery Velocimetry (PIV) device in order to analyze and characterize flows.

Bridge Pressure Flow Scour in Extreme Clear Water Conditions

The bridge of the future is likely to be one that is inundated from time to time, resulting in pressure flow through the bridge opening. When the bridge deck is submerged, the fluid beneath it is pressurized and the velocity is increased. This elevated velocity results in an increase in the risk of amplified scour, as the fast flowing water has a greater potential to carry the sediment away with it. The aim of this study is to analyze the effects of pressure flow on scour in a variety of situations by means of physical as well as numerical modeling.

The physical experiments are conducted on the tilting flume. Tests are carried out under various flow conditions, time spans, and sediment types. The automated flume carriage is then used to collect data on flow velocities and depth. This data is used to draw velocity profiles and scour profiles.

The numerical analysis is conducted through simulations of the model using fluid dynamics software. The simulation is set up with the same parameters as the physical model in order to make comparison possible. This means that the shape of the bridge deck, the flow characteristics and the sediment type are all identical in both models.

The J. Sterling Jones Hydraulics Research Laboratory is linked to a supercomputer (52 processors) in the Argonne National Laboratory via an Internet2 connection. Data from the experiment is transmitted to the supercomputer to be processed, and the results are returned.

These results (scour profile, velocity profile and other information concerning the flow) are compared with the results of the physical modeling.

Scour in Cohesive Soils

Scour in cohesive soils is a very complex phenomenon that is not completely understood. In order to compensate for this lack of comprehension, there is often a tendency towards wasteful over-designing of bridge foundations. A better insight into the scour of soils such as clay and silt would lead to more efficient bridge design.

Cohesive soils have a much slower rate of scour than non-cohesive soils like sand. The aim of this study is to analyze the rate of erosion in cohesive soils under different flow conditions, and in relation to shear stress and vertical turbulence structures. The Turner-Fairbank Highway Research Center (TFHRC) J. Sterling Jones Research Laboratory is carrying out tests on cohesive soils using its Ex-Situ Scour Test Device (see full description of the device here). In general terms, the scour phenomenon is simulated in this device by propelling a fluid over a soil sample, using a rotating belt. The apparatus also has pressure and shear stress measuring capabilities.

Figure 4. Ex-Situ Scour Test Device simulates the scour phenomenon by propelling a fluid over a soil sample, using a rotating belt. The apparatus also has pressure and shear stress measuring capabilities.

Equation 1. The initial setup for the study involved the use of AK-500 silicone fluid (which has a viscosity 500 times that of water) instead of water in the Ex-Situ Scour Test Device. According to the relationship which links viscosity (µ), velocity (u) and shear stress (t) a high viscosity fluid with a low velocity will develop the same shear stress as a low viscosity fluid with a high velocity. These tests were conducted with a very low belt velocity. Tests were also carried out using AK -50 silicone fluid (with a viscosity 50 times that of water) with a marginally greater velocity. However neither of these setups using silicone fluid displayed degrees of erosion comparable with those of setups using water.

a high viscosity fluid with a low velocity will develop the same shear stress as a low viscosity fluid with a high velocity. These tests were conducted with a very low belt velocity. Tests were also carried out using AK -50 silicone fluid (with a viscosity 50 times that of water) with a marginally greater velocity. However neither of these setups using silicone fluid displayed degrees of erosion comparable with those of setups using water.

Analysis currently being conducted involves the use of water instead of silicone fluid. Due to large slip conditions on the belt, the velocity being generated in the fluid was only 20 to 30 percent of the band velocity at the beginning of testing. In order to correct this, several techniques were tested to increase the roughness of the belt. The current solution achieves up to 90 percent of the band velocity in the fluid, using rubber bars glued to the band.

Figure 6. Analysis currently being conducted involves the use of water instead of silicone fluid.

Due to large slip conditions on the belt, the velocity being generated in the fluid was only 20 to 30 percent of the band velocity at the beginning of testing. In order to correct this, several techniques were tested to increase the roughness of the belt. The current solution achieves up to 90 percent of the band velocity in the fluid, using rubber bars glued to the band. This chart shows an example of the velocity profiles measured during testing using rubber bars glued to the belt. The x-axis shows the velocity of the fluid, the y-axis shows the height above the bed. As the band speed and velocity speed increase, the height above the bed starts to slightly decrease.

Optimum Bridge Deck Shapes to Minimize Pressure Flow Scour Phase II

The bridge of the future is likely to be one that is inundated from time to time where the flow through the bridge opening is under pressure and causes concerns about amplified scour. This study utilizes the Particle Imagery Velocimetry (PIV) capabilities and the shear force sensor that have been developed for the Federal Highway Administration's Turner-Fairbank Highway Research Center J. Sterling Jones Hydraulics Research Laboratory to characterize streamlines and shear stresses on the channel bed for a variety of bridge deck shapes and positions above the bed.

Laboratory Experiments to Determine Wave Forces and Moments on Typical US Highway Bridge Decks

In the past two years, hurricanes have caused devastating failures to a number of US highway bridges along the Gulf Coast. These failures have been attributed to the combination of storm surge and wave loading on the bridge superstructure. There are many bridges throughout the country that are vulnerable to this type of loading. A review of the public domain literature regarding the ability to accurately predict both lateral and uplift forces on bridge spans as a function of wave parameters (height, period, steepness) and the elevation of the span relative to mean water level clearly show the need for carefully planned and executed laboratory experiments.

Several LED's are attached to the model bridge deck which is then placed in the flume. These are used to monitor the motion of the bridge deck.

The objectives of this proposed research are to obtain lateral (horizontal), uplift (vertical) forces and moments on typical US highway bridge structures as a function of:

1. Vertical location relative to the still water level
2. Wave height
3. Wave period
4. Wave steepness and for irregular waves
5. Wave spectra parameters

Refining the theory and conducting laboratory scale experiments will meet these objectives.