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.
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.
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.
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.
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.
Three-dimensional rendering of the assembled new Multifunction Flume System (MFS).
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.
Color-coded gravel for observing failure process in abutment riprap testing.
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.
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.
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.
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.
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.
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Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, VA 22101-2296
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