The influence of high pore-water pressure on the strength of cohesionless soils

Abstract

The influence on the mechanical properties of saturated particulate materials of the component of stress carried by the water filling the pore space is fundamental to both theoretical and experimental studies in soil mechanics. The rôle of pore pressure in controlling compressibility and shear strength is expressed in Terzaghi’s principle of effective stress to a degree of accuracy which is sufficient for most engineering purposes. However, the precise significance of the small but finite area of interparticle contact has remained uncertain in the application of this equation to shearing resistance. In the present paper the possible errors associated with the use of current expressions for intergranular stress and effective stress are examined. These errors are of significant magnitude at high values of pore pressure and low values of the yield stress of the solid forming the particles. A very accurate experimental investigation has been carried out into the sensitivity of shearing resistance to large changes in pore pressure (up to 41.4 MN/m 2 ), using particulate materials ranging in strength from Quartz sand to lead shot. The results indicate that the simple Terzaghi effective stress equation a' - o - u is consistent with all the observations, though for Quartz sand a range of pore pressure changes an order of magnitude higher is desirable for additional confirmatory evidence.