Search

The coefficient of earth pressure at rest (K0) for normally consolidated clays increases nonlinearly with increasing consolidation pressure toward a steady value under high pressure rather ...

In order to investigate the mechanism underlying the reported nonlinear at-rest coefficient of earth pressure,K0of clays at high pressure, a particle-scale model which can be used to calculate vertical and horizontal repulsion between clay particles has been proposed. This model has two initial states which represent the clays at low pressure and high pressure, and the particles in this model can undergo rotation and vertical translation. The computation shows that the majority of particles in a clay sample at high pressure state would experience rotation during one-dimensional compression. In addition, rotation of particles which tends to form a parallel structure causes an increase of the horizontal interparticle force, while vertical translation leads to a decrease in it. Finally, the link between interparticle force, microstructure, and macroscopicK0is analyzed and it can be used to interpret well the nonlinear changes inK0with both vertical consolidation stress and height-diameter ratio.

This For mastering the effect of particle size to strength and deformation characteristics of sand under high pressure, DRS-1 high pressure direct shear test system is used in shear test for 3 groups of sand under pressure of 12 to 15 MPa. Through analysis of the test results, it is obtained that standard sand under high pressure shows strain hardening and volume contraction characteristics. The relationship curves of stress-strain and volume contraction-shear strain appear as hyperbola, they can be simulated by Duncan-Chang hyperbolic model. Sand with small particle size has better group, greater density and higher strength, but the shear contraction is not obvious. Sand with poor group has particle crushing under high pressure, which makes the soil particles rearrange and then the average porosity decreases at the same time large pores disappear, so finally it shows a more significant shear contraction characteristic.

At-rest earth pressure codfficient,K0,is very important in geotechnical engineering design and finite element analysis. At present, it’s treated as a constant usually for given soil in FEM analysis. However recent test results indicate that K0of both clay and sand varies with pressure increasing nonlinearly. It’s shown that Duncan-Chang model, a kind of hypoelastic model widely used, can reproduce K0varying with pressure. The calculating procedure of K0derived from Duncan-Chang’s E-B model is proposed, and then influence of model parameters on calculated K0is explored. Studies show that cohesionless soil’s calculated K0decreases with pressure increasing, while cohesive soil’s calculated K0increases with pressure increasing. Three of the seven model parameters, m, Kband Rf, have a positive correlation with calculated K0, and there is a negative correlation between the residual parameters and calculated K0.The influence of seven model parameters on the calculated K0decreases gradually in the following order: m ,n, Rf, φ, c, K, Kb.