Strength and dilatancy of anisotropic cohesionless soils

Abstract

Peak friction angle and critical state friction angle are two key parameters representing the shear strength of cohesionless soils. Peak friction angle of sand is a function of critical state friction angle and dilatancy angle while the angle of dilatancy is a volumetric parameter. Researchers investigating this topic proposed different relationships between peak friction angle, dilatancy angle, and the critical state friction angle. The aim of this study is to investigate and quantify the influences of the critical state friction angle and the angle of dilatancy on the evaluation of the peak friction angle and to identify the variations of these relationships with the state of the cohesionless soil. The term “state of the soil” here defines the stress state and volumetric state of the cohesionless soil and quantified as the mean effective stress and relative density, respectively. For this purpose, a detailed experimental program with more than 80 K0 CD triaxial tests has been conducted on reconstituted sands. Between these tests, several parameters were varied to understand their influences on the peak friction angle and dilatancy. These parameters are relative density, overconsolidation ratio, and effective vertical stress at the end of normal consolidation. Since the tests are Ko tests, the influences of these parameters on the at rest lateral earth pressure coefficient are also examined. Obtained test results have been used for the construction of a new empirical equation that yields the dilatancy angle using mean effective stress (p) and relative density (DR) as input. The major advantage of the proposed equation is that it uses directly measureable and calculable parameters (p and DR). Additionally, it is possible to enhance the quality and versatility of the constitutive models using the proposed equation instead of defining a constant dilatancy angle.Moreover, the the equations proposed by other researchers for calculating the peak friction angle using the constant volume friction angle and dilatancy angle have been enhanced using the data obtained from the current testing program.