On the “elastic” stiffness in a high-cycle accumulation model for sand: a comparison of drained and undrained cyclic triaxial tests

Abstract

High-cycle accumulation (HCA) models may be used for the prediction of settlements or stress relaxation in soils due to a large number of cycles (N > 103) with a relatively small-strain amplitude (εampl < 10−3). This paper presents a discussion of the elastic stiffness, [Formula: see text], used in the basic constitutive equation of an HCA model, [Formula: see text], where [Formula: see text] is the trend of effective stress, [Formula: see text] is the trend of strain, [Formula: see text] is the rate of strain accumulation, and [Formula: see text] is the plastic strain rate. [Formula: see text] interrelates the “trends” of stress and strain evolution. For the experimental assessment of the bulk modulus, [Formula: see text], the rate of pore-water pressure accumulation, [Formula: see text], in undrained cyclic triaxial tests and the rate of volumetric strain accumulation, [Formula: see text], in drained cyclic tests have been compared. The pressure-dependent bulk modulus, K, was quantified from 15 pairs of drained and undrained tests with different consolidation pressures and stress amplitudes. It is demonstrated that both the curves [Formula: see text] in the drained tests and u(N) in the undrained tests are well predicted by the authors’ HCA model if the elastic stiffness is determined using the method described in the present paper. A simplified determination of K from the unloading and reloading curve in an oedometric compression test is discussed.