Using Cone Penetrometry Profile to Study Soil Deformation under Plate Sinkage Test

Abstract

Plate sinkage test (PST) is an in situ method for measuring soil compaction and behavior under agricultural vehicles. One of the disadvantages of this method is that the measured properties (e.g. pre-compaction stress and modulus of stiffness) could not be easily related to a specific soil layer. The objective of this study was to investigate the possibility of using cone penetrometry as a quick and simple method for determining soil deformation and stress distribution under PST. The study was conducted on a silty clay loam soil (Typic Haplargids, USDA; Calcaric Cambisols, FAO) in central Iran. Cone index (CI) was measured along a transect with horizontal distances of 4 cm on the soil near where PST was conducted and along the centerline of plate after running PST. The iso-strength (CI) contours on vertical plane showed the effects of soil layering (anisotropy), soil strength changes with depth and water content on soil behavior under PST. The measured properties by PST might be related to the soil zone where the significant change in soil strength after compaction is occurred. At high water contents, the stress-affected zone and soil lateral deformation was extended beyond the plate due to lubrication effect of water on soil flow. At low water contents, soil compaction was mainly occurred vertically and the high soil strength (CI) zone happened immediately beneath the plate. When the strength of subsoil was high, the soil under the plate was mainly deformed laterally. The results showed that the soil bearing capacity and the extent of soil vertical and lateral deformations completely depend on relative soil layers' strengths and water contents. This implies that the pre-compaction stress determined by PST represents the in situ bearing capacity of the stress-affected soil zone. Cone penetromerty profile as a quick and simple method could be recommended for determination of soil deformation pattern under the plate sinkage test.