Effect of Wetting on Constant Volume Shear Behavior of Compacted Silty Soil

Natural slopes and embankments typically have negative pore water pressure. They are generally unsaturated, which increases the shear strength and, as a result, the stability of the slopes. The infiltration of rainwater into the ground during a rainy event causes a decrease in the matric suction, ultimately reducing the soil shear strength and leading to slope failures. Therefore, when analyzing the stability of such slopes, it is critical to assess the strength and deformation characteristics of unsaturated soil. A double-cell triaxial test apparatus was utilized in this study to examine the shear strength and deformation behavior of compacted silty soil due to water infiltration. Laboratory element tests were conducted on samples prepared with an 80% degree of compaction and an optimum water content of 20%. The soil samples were isotropically consolidated under a confining pressure of 500 kPa before being sheared with constant volume under constant water content conditions. Pore water pressure was increased just before the shear process to reduce matric suction and initiate water infiltration. From the test results, it was found that the degree of saturation increased by an average of 42.5%, 66%, and 75.5%, while the maximum shear strength decreased approximately by 16%, 18.5%, and 20.5% when the suction was reduced from 20 to 10 kPa, 5 kPa, and 0 kPa, respectively.