An elasto-plastic model for saturated loosely compacted completely decomposed granite

Abstract

A constitutive model for saturated loosely compacted completely decomposed granite (CDG) under triaxial compression is developed. Using a total of 70 triaxial compression tests as the calibration basis, we established a relationship between the normal compression line (NCL) of the soil and its dry density, and a relationship between the position of the critical state line (CSL) of the soil and its maximum dry density obtained from the standard Proctor test. The state boundary surface proposed by Yu (International Journal for Numerical and Analytical Methods in Geomechanics, 22, 621–653, 1998) was adopted in the current formulation. An empirical relation correlating the amount of fines present with the shape of the yield surface was developed to quantify the effect of particle size distribution (PSD) on the mechanical behaviour of the soil. By introducing a stress-path-dependent correction factor, we showed that the original Cam clay flow rule was generally successful in describing the dilatancy of loose CDG. The model requires only nine basic parameters and was further verified against 18 triaxial compression test results obtained from an independent study. Satisfactory agreement between the simulation and test results was achieved.

Keywords:

• constitutive modelling
• stress–strain relations
• completely decomposed granite
• elasto-plastic
• critical state
• soil plasticity