Authors
Abstract
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-Raphson 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
behaviour of sand under alternating loading.
The finite element method is used in simulating the behaviour of round
uniform quartz sand under monotonic drained loading with constant mean
stress and cyclic constant volume loading (undrained). 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 behaviour 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 undrained 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-dilatancy line in both compression and extension
regions, beyond which the specimen dilates.
Keywords
)
