Deformation and pore water pressure change during static and cyclic loading with subsequent shearing on soils with different textures and matric potentials

Abstract

Soil deformation on arable lands due to heavy machine traffic always results in compaction and stress dependent shearing. The deteriorated effects of compaction on soil pore functions have been often reported, but less is known about the shearing-induced deformation. To better understand the combined effect of compaction and shearing on soil deformation and pore water pressure uw, measurements were performed on repacked soils with three textures (silt loam, sandy loam, and sand) and two matric potentials (-60 hPa and -300 hPa). Soils were sheared after two types of loading (static loading and cyclic loading) with three compaction levels (50, 100, and 200 kPa). Compaction was the main stress accounting for the loss of soil void ratio e and volume, on the contrary, shearing slightly increased void ratio and volume due to particle rotation in the shear zone. At -60 hPa, soil water ratio stepwisely decreased with compaction and subsequent shearing process. The soil volume change induced by compaction and shearing resulted in an obvious increase in uw. The higher the stress levels and initial matric potential, the more prominent changes in soil deformation and uw. Compared with static loading, further decrease of soil volume and increase of uw were observed under cyclic loading. Soils pre-compacted by cyclic loading always showed high and relatively constant uw values during shearing. The results demonstrated that compaction increased uw by decreasing e and increasing the degree of water saturation while shearing enhanced these effects by means of rearranging particles and blocking the water-filled pores. Therefore, after shearing, soil pore functions were further deteriorated compared with the initial state before compaction.