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Ongoing Laboratory Activities | Hydraulics Laboratory Personnel | Research Publications | Office of Bridge Technology: Hydraulics

 

 

J. Sterling Jones Hydraulics Research Laboratory

 

Ongoing Laboratory Activities

 

In Situ Scour Testing Device (ISTD)

In this picture, the first version of the in situ scour testing device is shown. The device was built in a water tank partially filled with soil/sand to simulate the real river condition. The vertical movable device is supported and pushed downwards by two screw jacks. The black flexible hose connection at the left side is the inlet to the device. This flow goes through a labyrinth inside the device designed to eliminate the jet effect from the inlet. In the testing area, the flow creates a reasonably uniform horizontal shear stress on the bed material. The eroded soil is removed by the water flow leaving the device. An inductive distance sensor (LVDT) measures the height of the channel allowing the control system to maintain a constant area between device and soil. The vertical movement during a specific amount of time represents the erosion rate of tested soil.

Concept 1: The in situ scour testing device (U-ISTD) was developed in the lab to demonstrate a concept of producing horizontal shear stress for in situ erosion testing. It features a U-shaped channel that creates steady horizontal flow near the flume bed.

The alternative design of the ISDT consists of a cylindrical body. Two independent rotary parts are mounted inside this body. The outer part is a hollow bronze auger. The inner part, with a yellow impeller at the bottom, rotates at high speed. This rotation causes a water flow similar to the impeller pump. The soil material below the device is entrained by the shear stress. In the middle of the impeller, an inductive distance sensor (LVDT) measures the gap between the device and the soil to allow the control system to maintain a constant distance. As the erosion goes on, the impeller moves along the eroded sediment bed. To prevent the surrounding soil from filling the hole, the bronze auger continues slowly excavating the material outside the erosion chamber.

Concept 2: The in situ scour testing device (I-ISTD) uses a revolving impeller housed in a hollow auger to exert bed shear. The eroded material is removed with flow through internal tubing. The auger excavates the stream bed to allow for sublevel testing.

The C-ISTD in the picture presents an early version for proof of concept. The surrounding glass tube provides visual access during the testing. The erosion head consists of two blue spacers and a clear acrylic body between them. The spacers maintain a small gap between tube and erosion head. During a test, water runs through the gap to the perimeter of the bottom of the head. The only drain in the system is a small hole in the middle of the head. Between the perimeter and the center of the bottom of the erosion head is an erosion chamber shaped to allow a uniform concentric flow. The water running towards the drain produces an evenly distributed shear stress and entrains the sediment. A certain distance is maintained between the bottom of the erosion head and the soil. When erosion occurs, the movement rate of the erosion head represents the erosion rate. This ensures an optimal shape for the erosion chamber.

Concept 3: The C-ISTD, named for its cylindrical-shaped erosion head, produces shear stress by radial flow in the erosion chamber at the bottom of the cylindrical erosion head (between the two blue disks in the photo).

Description: This study develops a scour testing field device (in situ scour testing device) to determine the erodibility of soils around bridge foundations. An effective in situ scour testing device could more accurately define the scour potential for a given set of hydraulic design conditions. Such a field device could provide assistance on a project-by-project basis or in general design methodology.

 

Scour in Cohesive Soils

The photo shows the ex situ scour testing device and its control station. It uses a pump and a moving belt to propel water in a 92-centimeter-long, 12-centimeter-wide, and 2-centimeter-deep channel. In this picture, the moving belt is lifted up to be visible. A direct force gauge accommodates a soil specimen (a diameter of 63.5 mm and a height of 20 mm) on its sensor plate.

The ex situ scour testing device (ESTD) is designed to measure the erodibility of cohesive soils under flow conditions with log-law velocity profiles. It uses a pump and a moving belt to propel water in a 92-centimeter-long, 12-centimeter-wide, and 2-centimeter-deep channel. The velocity profiles are measured using particle image velocimetry (PIV) and simulated by computational fluid dynamics (CFD). In the picture, the moving belt is lifted up to be visible. A direct force gauge accommodates a soil specimen (a diameter of 63.5 mm and a height of 20 mm) on its sensor plate. The gauge can measure instantaneous forces acting on the soil specimen. The specimen can be elevated up and down to keep flush with the channel bottom. The mass loss during a period of erosion can determine the erosion rate under a certain flow condition. The ESTD and the data acquisition are automatically controlled by LabVIEW programs.

The upper photo shows the pugger that mixes and de-airs the soil sample with a short cylindrical sample pushed out on the left. The lower photo shows a close-up of the sample in the erosion channel.

Cohesive soils are prepared by a pugger mixer. Different percentages of clays, silts, and sands can be mixed and vacuumed in a pugger mixer. The mixer then pugs soil specimens with a diameter of 63.5 millimeters. The top part of the picture shows the pugging process. The bottom part of the picture is a snapshot of the erosion recording of a soil specimen.

Description: The study addresses the incipient erosion and erosion rate of cohesive soils. Scour on cohesive soils is a very complex phenomenon that is not completely understood. A special erosion apparatus, the ex situ scour testing device (ESTD) was developed to apply hydraulic loading on cohesive soil samples. The study will develop new design procedures for scour prediction in cohesive soils.

 

New Multifunction Flume System (MFS)

An isometric view of the Multifunction Flume System design is shown without the channel modules. An inlet trumpet is located on the lower-right corner, while a sediment catch and an outlet is shown at the upper-left corner of the image. Between the inlet and the outlet is a versatile platform that can be used for a variety of configurations. It consists of flat panels that provide support and fixture to any conceivable testing apparatus between the inlet and outlet.

Three-dimensional rendering of the assembled new Multifunction Flume System (MFS).

The computer-generated image shows the velocity distribution in the trumpet and immediate downstream of the trumpet. The velocity is color coded. It shows that the velocity distribution downstream of the trumpet is reasonably uniform and free of adverse pressure conditions.

Computational fluid dynamics simulation on the inlet performance of the MFS.

Description: The new Multifunction Flume System (MFS) is designed to support a variety of hydraulic and sediment transport modeling. Its capability of high bed shear simulation and sediment recirculation is unique to the United States. The new flume can accommodate a large range of tilting, channel width, channel/pipe geometry, and clear-water/live-bed capability. Computational fluid dynamics simulation is used to assist the design and the performance evaluation of the main components, such as the inlet trumpet. It shows whether the selected shape and dimensions offer the desirable velocity distribution at the specified flow rate. Proposed modular channel sections can be rescaled to different cross sections and also be replaced by other hydraulic structures needed for potential projects, such as pipes. Construction is expected to start in late 2013.

 

Smart Scour Countermeasure

This picture illustrates rock riprap apron performance as a scour countermeasure under flood-flow conditions. The riprap mattress is placed around a vertical-wall bridge abutment model. The failure zone of the riprap is marked by red painted rocks to enhance the monitoring approach during the test using a high-speed camera.

Color-coded gravel for observing failure process in abutment riprap testing.

This picture shows a sequence of four images showing rock riprap shear failure at the upstream front face of a vertical-wall abutment under flood-flow conditions. During the test, the sequence of images was recorded underwater with a frame rate of 125 frames per second using a high-speed camera.

Failure process of abutment riprap captured by high-speed camera.

Description: Physical and computational fluid dynamics (CFD) modeling using a vertical-wall abutment and a rectangular pier are being performed to study different rock riprap apron layouts based on design guidelines from Hydraulic Engineering Circular (HEC) 23 and field installations. The tests are being conducted separately on both fixed and erodible beds using different riprap sizes around a vertical-wall abutment and around a rectangular pier. A high-speed camera (62 to 500 frames per second) is used to capture initial failure of the rock within the failure zones. The laboratory results will provide more comprehensive data on the performance of riprap in its capability to withstand the turbulence and hydraulic stress generated in the vicinity of a bridge pier or bridge abutment under flood-flow conditions.

 

Hydraulic Performance of Shallow Foundations for Support of Bridge Abutments

The picture shows a sequence of the construction of the physical scaled model of a GRS vertical-wall bridge abutment seating on a reinforced soil foundation (RSF). The excavation for the RSF construction is shallow. The construction of the GRS-Abutment starts on top of the RSF. An additional picture shows the pullout tests performed using a scaled model of a GRS mini-pier to calibrate the connection strength between the blocks and the reinforced soil mass.

Physical modeling and validation of GRS vertical-wall bridge abutment seating on a reinforced soil foundation (RSF). The picture on the left shows the pullout tests performed using a scaled model of a GRS mini-pier to calibrate the connection strength between the blocks and the reinforced soil mass.

This image illustrates a physical scaled model of a GRS vertical-wall bridge abutment during a test in the tilting flume. The superstructure sits on top on the abutment, inducing vertical loading according to the similarity theory. The performance of the abutment is tested against flow velocities similar to flood-flow conditions in the field.

Hydraulic performance testing of GRS vertical-wall abutment.

Description: One of the hazards of placing a structure in a river or channel is the potential for scour around the foundations. Scour around a shallow foundation, or undermining, can cause excessive deformation or structure collapse. The objective of this research project is to study the performance of shallow foundations using a scaled model of a Geosynthetic Reinforced Soil (GRS) vertical-wall bridge abutment. The GRS-abutment is seated on a shallow reinforced soil foundation (RSF) composed of granular fill material compacted and encapsulated in geotextile. The settlement and external stability (deformation) of the GRS-abutment is monitored with a laser distance sensor mounted on a scanning robotic carriage.

Bridge Pier Scour Research

The picture shows a scaled model (1:60) of pier 22 of the Feather River Bridge on Route 20 in Sutter County, California. The complex pier model is composed of a mix of piles (90 existing H-piles surrounded by 10 new retrofit piles). A physical scour study of the scaled pier model is being conducted in the Tilting Flume at Turner-Fairbank Highway Research Center’s J. Sterling Jones Hydraulics Laboratory.

A scale model (1:60) being constructed at TFHRC J. Sterling Jones Hydraulics Research Laboratory for physical modeling of the Feather River Bridge on Route 20 in Sutter County, California.

The picture shows a) Computational fluid dynamics simulation results of the bed shear stress induced by a defined approach flow around a group of H-piles with a skew angle of 45°. b) The H-piles composition of the scaled model pier 22. The pile cap is meshed in order to map the bathymetry between the H-piles at equilibrium scour.

Computational fluid dynamics (CFD) simulation used to validate the scale model design for experiment study of the Feather River Bridge: a) CFD results showing bed shear produced by the model pile geometry. b) Meshed pile cap that provides access to scoured bed mapping.

Description: Due to the high flow that occurred in March 2011, a massive scour hole developed around pier 22 of the Feather River Bridge (Br. No. 18-0009) on Route 20 in Sutter County, California. This scour has left the structure vulnerable to failure during the next high-flow event and instigated an emergency structural retrofit of the pier. Scour research on a 1:60 scaled model of pier 22 is being conducted to estimate the potential maximum equilibrium scour depth of the new retrofitted design in clear-water conditions. Flow conditions to be tested are a Q100 flood event and the March 2011 flood. The physical modeling is being conducted in the Tilting Flume at the Turner-Fairbank Highway Research Center (TFHRC) J. Sterling Jones Hydraulics Research Laboratory, along with a computational model (computational fluid dynamics) to study bed shear stress fluctuations for scour at various depths.