2007 Volume 44 Issue 1 Pages 15-24
The changes in pore-pressure, effective mean stress, and deviator stress in the undrained triaxial-compression tests on sands have been numerically analyzed by means of three dimensional Distinct Element Method (DEM) . The value of pore-pressure was assigned to the measurement sphere, the cnetre of which was coincided with the one of each ball element and the diameter of which was twice as much as the ball element. The volumetric changes in those measurement spheres due to the deformation of the cylindrical shaped specimen were calculated and the changes in pore-pressure was obtained by the products of volumetric strain and modulus of compressibility of water. The fluid flow was given based on the Darcy's law. The effective mean stress negatively proportional to the initial void ratio after consolidation was obtained, that is the steady state line was observed, and the loose specimens produced quasi-liquefaction behaviour, in which effective mean stress at steady state was reduced to no more than 25% of the initial confining stress. The medium-dense specimens produced the positive pore-pressure at the beginning of the test and then it reduced its values to remain negative, which successively reproduced the phase transformation that was typical characteristics of the granular materials.
