Influence of Static and Cyclic Loading on Mechanical and Hydraulic Properties of Soils with Different Textures and Matric Potentials

Abstract

Mechanical, hydraulic, chemical or biological processes on various scales and intensities can alone or as coupled processes cause soil deformation. To quantify the effect of mechanical and hydraulic stresses on changes in soil functions, vertical displacement and pore water pressure were measured on repacked soils with three different textures (sand, silt loam and clay loam) at two matric potential values (−60 and −300 hPa). Two types of loading (static and cyclic loading) and three compaction levels (50, 100, and 200 kPa) were analyzed. In the case of static loading, the time‐dependent vertical displacement curves for all treatments under all compaction levels are similar in shape but different in scale. However, different situations of time‐dependent changes in pore water pressure were found due to different internal soil strength. An exponential change in pore water pressure as a function of vertical displacement was observed for treatments at −300 hPa matric potential during static loading regardless of vertical holes. In the case of cyclic loading, vertical displacement increased during loading but an elastic rebound was observed during unloading. Pore water pressure changed differently for different treatments. During cyclic loading, there was a linear relationship between the change in pore water pressure and vertical displacement for all treatments. The alternation of soil strength due to compaction is reflected by the effective stress. In our experiment, we found that, as the stress application increased, the effective stress decreased for wetter soils (−60 hPa), and increased for drier soils (−300 hPa). Hence, future soil deformation models need to include changes in pore water pressure as an important stress variable for unsaturated soils. Meanwhile, we found that the soil perforation technique may alleviate the negative effect of soil compaction by improving soils physical conditions.