A nonlinear stress-strain relationship for soil and rock

While many employ a hyperbolic stress-strain relationship for soils, it is known that such a relationship is accurate over either the small strain range as encountered in earthquake and soil dynamics problems or a relationship with different input parameters that are needed over large strains as is required for finite element analyses of large deformation behavior. The two characterizations do not become one. A proposed power relationship is presented that was developed to characterize the triaxial test stress-strain behavior of cohesionless material from lubricated or “frictionless” cap and base tests (some 144 tests) covering a range in the natural variation in particle size, particle shape and surface roughness, over low to high confining pressure. This relationship covers the range in strain from 10−6 to soil failure. It has been used successfully to date in laterally loaded pile response characterization (the Strain Wedge Model) and shallow foundation load-settlement-bearing capacity response. Most recently, it has been extended to assess the behavior of rock-like material (caliche). The relationship and its comparison with the hyperbolic relationship for large strain and the shear modulus reduction curve for seismic behavior are presented here.