Modelling the behaviour of sand under strain-controlled loading by the finite element method

Abstract EN

Strain-controlled tests are conventional in soil mechanics laboratories.

It is intended in this paper to simulate both triaxial and simple shear tests theoretically by using the finite element method.

The solution of the nonlinear equations is obtained by several iterations.

The Newton-Rap son with tangent stiffness method in which the stiffness matrices are tangents is adopted.

The model used in this paper is the ALTERNAT model which forms the major component of a double hardening model for the mechanical behavior of sand under alternating loading.

The finite element method is used in simulating the behavior of round uniform quartz sand under monotonic drained loading with constant mean stress and cyclic constant volume loading (untrained).

The monotonic test was conducted with constant mean stress, where the specimen was compressed in one direction and extended in other directions while the mean stress (the average of the principal stresses) is kept constant and equal to 137 kPa.

It is noticed that the peak stress is occurring at very small strain (0.122).

The stress-strain behavior may be attributed to the particle roundness and grain size uniformity.

In the cyclic tests, the specimen is sheared by cycling the shear strain while the volume was kept constant.

By doing this, an untrained strain-controlled cyclic test similar to that typically done in many laboratories is numerically simulated.

It was found that the mean stress during shearing is higher than the initial consolidation pressure.

This implies that only negative pore pressures occur in the first two cycles.

A careful study shows that there exists an effective stress ratio line or zero-militancy line in both compression and extension regions, beyond which the specimen dilates.