Soil response at low stress in laminar box tilt table testing

The capability of direct in-soil measurement of shear stress and shear strain has been applied to 1 g tilt table laminar box tests. The aim of the study is to evaluate the stiffness response of the material tested under low to ultra-low vertical stresses. The tests were performed with specimens of fine uniform sand within a laminar box of dimensions 300 mm × 400 mm × 300 mm. Tests were performed at three different density ranges, under static, dry conditions. Measurement of shear stress and normal stress were made on the bottom boundary of the specimen; shear stress and shear strains were measured within the specimen as tilting of the laminar box was applied. This arrangement allows the soil specimen to respond naturally, with the sensors reacting to the response of the soil. A combination of two test configurations were applied: one to consider stress equilibrium; and a second to capture material properties. Measurements from the stress equilibrium testing configuration illustrate agreement and consistency with assumptions of infinite slope theory. Measurements from tests performed in the material property configuration capture the shear stress–shear strain response as a function of depth. The results clearly illustrate the stiffness response of the material at very small confining pressures.