The full state of stress in monotonic simple shear tests on sand

Abstract

The simple shear test has been an important tool in practical geotechnical engineering and the study of soil behaviour. The attractiveness of the simple shear test is founded in its relative ease of specimen preparation, similarity to at-rest conditions during consolidation and rotation of principal stresses during shear. Despite this test's attractive qualities, there are significant deficiencies in the interpretation of standard test results: horizontal normal stresses are not known and excess pore pressures are often interpreted from assumptions about constant-volume tests without saturation. To address this problem, a set of monotonic tests were performed on a sand, during which horizontal normal stresses were measured in the central portion of specimens. Based on the measurements, the full state of stress was defined, stress paths were drawn and directions of the principal stresses were determined. Outcomes showed that the conventional approach of estimating excess pore pressures as the change in vertical pressure to maintain constant volume in response to shear is problematic, and friction angles interpreted from conventionally measured shear and vertical stresses may be grossly underestimated in some cases.