Assessing the coefficient of the earth pressure at rest from shear wave velocity and electrical resistivity measurements

Abstract

Determination of earth pressure coefficient K0 in natural soil deposits is a significantly important issue in geotechnical engineering. This paper evaluates the feasibility of predicting K0 values from measurements of vertical and horizontal shear wave velocities [Vs(VH), Vs(HH), and Vs(HV)], and vertical and horizontal electrical resistivities (SV, SH). A series of seismic piezocone tests (SCPTU), improved crosshole (CH) tests, and soil resistivity tests using a modified laboratory apparatus were carried out at two research sites in Jiangsu Province of China and results were used to develop two existing K0-shear wave velocity correlations for prediction of K0. The seismic and electrical resistivity test results showed that both the shear wave velocity ratios, Vs(HH)/Vs(HV) or Vs(HV)/Vs(VH), and the horizontal to vertical electrical resistivity ratio, SH/SV, may provide a good indicator of the inherent soil anisotropy at these sites. The existing Vs–K0 prediction framework largely requires determining Cs(HV)/Cs(HH) ratio and a simple procedure for evaluating this ratio based on the measured horizontal and vertical electrical resistivities. The K0 values predicted by shear wave velocity at both sites are also compared with values determined by Jaky's formula and Mayne & Kulhwy's formula. In normally consolidated (NC) soils, the K0 values predicted from these methods showed good agreement. However, for over-consolidated (OC) soils at shallow depths, certain variations between different methods are noted. Further investigations of the effects of overconsolidation ratio on K0 predictions will lead to the correction factors for better prediction of K0 for OC soils. This paper has confirmed that reasonable predictions of K0 for natural soil deposits can be made using the proposed methodology.