Constitutive model development

I am looking for an advanced and highly accurate constitutive model that will be used in describing the hydro-mechanical behavior of rocks under triaxial compression. The model must be nonlinear elastic in nature, with a higher level of complexity and accuracy. The model should also be easy to implement, with the end result being designed to provide an accurate simulation of the results it is intended to model. My ideal freelancer will have extensive experience in creating constitutive models, and will be able to work closely with me to create a reliable model that can provide reliable results and enable me to better understand the hydro-mechanical behavior of materials in rock mechanics. In addition, the developed model will further be implemented into DEM simmulation software, particularly FLAC 3D