Experimental study on subsurface erosion of peats

Subsurface erosion threatens the stability of levees and earth dams. A less understood aspect of subsurface erosion is the erosion potential of peat. In the Sacramento-San Joaquin Delta in California, some levees were built on peat deposits. This paper reports the preliminary laboratory study of subsurface erosion of peat. Two types of peats are tested. Hole erosion tests are conducted using a triaxial apparatus. The triaxial cell is modified to allow the eroded peat particles to exit the cell into a pressurized sedimentation tank. The peat specimens are saturated and consolidated under four different effective stresses. Then hydraulic gradient is incrementally applied to the specimen to find the critical hydraulic gradient. Based on the preliminary research, it is concluded that (1) when peat is consolidated under embankment load, even with small effective stress of 34 kN/m², internal erosion is less likely to occur, (2) due to the high compressibility of peat, consolidation under increased embankment loads tends to close (or heal) initially formed piping channels.