Lateral Stress Measurements in Direct Simple Shear Device

Monitoring lateral stresses in a soil specimen during monotonic or cyclic shear tests significantly increases the amount of information obtained from these tests. A technique is described for interpreting lateral stress data during consolidation (the initial phase of either type of shear test) and determining the lateral stress level at the start of the shear test. In addition, the coefficient of lateral earth pressure at rest (K₀) is determined.

The Norwegian Geotechnical Institute (NGI) Direct Simple Shear Device was used in this study. Lateral stress measurements were made with calibrated wire-reinforced membranes (acting as strain gages).

Two undisturbed samples of soft marine clay were investigated: a Gulf of Mexico and a Gulf of Alaska sample. The samples were obtained from a depth of about one metre below the sea floor. Large vertical specimen strains were encountered even though the applied consolidation stresses were small (a maximum vertical stress of 0.518 kg/cm²). The technique described includes methods for eliminating possible sources of substantial error at these low stress levels. The values of K₀ as determined from the lateral stress measurements agree well with values determined indirectly.