Excess pore pressure accumulation in sands: A shear strain threshold concept for optimization of a laboratory testing programme

In particular during storm events, an accumulation of excess pore pressures may occur in the soil around cyclically loaded offshore foundations which can negatively affect the structural integrity of the foundation. As input for analytical or numerical calculation methods, high-quality laboratory test results are needed. Numerous tests are usually necessary to describe the soil behaviour over the full range of stress and strain boundary conditions. Therefore, an optimization of the test programme in terms of the number of required tests is highly desirable. In the paper, results of an extensive test programme, comprising Resonant Column (RC) and displacement-controlled cyclic Direct Simple Shear (DSS) tests on three sands are presented. Based on the findings, a shear strain threshold concept is developed in which different general soil behaviour of sands under cyclic loading is distinguished by shear strain ranges. The thresholds can be determined by RC tests and multistage cyclic DSS tests. As a main result, the soil response over the full range of possible boundary conditions can be quantified with a combination of only a few RC, multistage DSS and DSS tests. Finally, equations to parametrize the experimental results are discussed.