Effect of suffusion on mechanical characteristics of sand

The mechanical characteristics of earth dams and levees, such as settlement, permeability, and strength, can be affected by internal erosion in the forms of piping and suffusion. This paper reports a preliminary experimental study on the changing mechanical characteristics (permeability, consolidation) with the progression of suffusion of a sandy soil. The internal erosion tests are conducted using a triaxial apparatus. The pedestal of the triaxial cell is modified to allow seepage and eroded soil particles to exit the specimen into an effluent tank. The seepage is induced in the specimen by controlled constant hydraulic gradient. The eroded soils are collected in the effluent tank so that the erosion rate and extent can be measured. Variations of the specimen's permeability and volume during the erosion are recorded. With approximately 5.5% fines in the sand, the test suggests that suffusion can occur and cause soil settlement. Suffusion of finer particles may also clog the downstream soil layer and results in permeability reduction. Suffusion and volume reduction gradually diminish relatively quickly to an un-measurable level after 4hr of seepage through the soil under a hydraulic gradient of approximately 20.