Extended transformed stress space for geomaterials and its application

Because the three-dimensional strength of soil, rock, and concrete is influenced nonlinearly by the hydrostatic pressure and Lode's angle, the failure surface is irregular in stress space, especially in the large stress range. Based on Lade's criterion, exponential failure function in coordinate p-q, and the concept of original transformed stress space, an extended transformed stress space and its corresponding transformed stress tensors are proposed in this paper. Compared with original transformed stress space, the extended one would be suitable to the large stress range. Processing test results in extended transformed stress space, the unified stress-strain relationship for a certain geomaterial can be easily obtained from the test results. The validity of extended transformed stress space is confirmed by test results of soil, rock, and concrete. Based on extended transformed stress space and the Modified Cam-Clay Model, a new constitutive model is also proposed in this paper, which can be used to predict three-dimensional stress-strain relationship for soils in the large stress range. The capacity of this model is demonstrated using triaxial test results of Toyoura sand with different stress paths in the large stress range.