Slurry induced piping progression of a sand

The motivation and the first objective of this laboratory experimental research is to study whether bentonite slurry, as a permeating fluid in levees during slurry cutoff wall installation, can induce further piping progression. The second objective of this research is to study the piping progression of a sand under different permeating fluids, which are often observed in the field where seepage carrying fine, suspended particles that are eroded from the upstream soil matrix permeates through a downstream piping channel. A simple constant-head hole-erosion test is used to study the piping progression of the sand subjected to three types of permeating fluids: water, slurry with 6% bentonite, water mixed with 1% fines of the same sand that pass the U.S. #200 sieve. A piping hole is preformed in the sand specimen and a constant hydraulic gradient induces concentrated seepage through the hole. Soil erosion rate and seepage with time and the total soil loss are monitored and measured. The diameters of the piping channels at the end of the tests using the three permeating fluids are quantified and compared. Our experimental results found that higher density of a permeating fluid does not induce more erosion. On the contrary, permeating fluids with fines reduce the eroded soil mass by an average of 90% and the average piping hole enlargement by 88%, compared with the results using water alone as a permeating fluid. The size distributions of the soils remaining on the inner wall of the piping channels are similar under the three permeating fluids. The agreement of the three particle size distributions suggests that particle deposition on the wall may not occur and is not a mechanism that accounts for the erosion difference.