New Method for Determining the Coefficient of Earth Pressure at Rest, K0

ABSTRACT: Vertical and lateral earth pressures must be considered in the design of underground structures, including tunnels, retaining walls, and deep excavations. Vertical pressure can be determined by in situ measurement, or calculated if the depth and material characteristics of the overburden are known. Lateral earth pressure is more challenging to measure accurately in situ. Underestimating lateral earth pressures may result in unanticipated soil movements and wall collapse, therefore knowledge of the lateral earth pressure, is vital for sound infrastructure design and long-term integrity. Lateral pressures are typically estimated using the coefficient K0, defined by Terzaghi as the coefficient of earth pressure at rest. The accepted theoretical approaches to determine K0 are based on the Rankine and Coulomb theories; however, both make assumptions and may not provide accurate K0 values. There are several laboratory tests for K0 determination, most of them requiring complicated and sometime cumbersome equipment. A new method for determining K0 was developed in the GHD Geotechnical Laboratory. A series of drained K0 tests were performed on saturated soil using modified triaxial equipment. This paper presents the experimental equipment and procedures, and discusses the laboratory K0 measurements obtained.