This work is focused on the development of constitutive models for elastoplastic-fracture behaviour in scenarios characterised by large deformation ranging from laboratory to geolog-ical length scale. Both seepage and geomechanical fields are considered, with the assumption of isothermal field.The standard Drucker-Prager model is enhanced by applying π-plane correction factor, and the use of hardening properties which depends on the evolution of effective plastic strain. Non-associative potential plastic flow function is used to derive the plastic flow vector. To ensure finite energy dissipation during softening, regularisation technique based on fracture energy approach is adopted. The resulting modified Drucker-Prager model is combined with rotating crack model (which relies on Rankine failure criterion) to develop an elastoplastic-fracture framework by considering multi-step stress update procedures. The advantage of multi-step stress update is that the framework allows the use of any elastoplastic model without any major change in the code. Performance of this set of constitutive models is assessed by studying several simulation examples, including bearing capacity of strip footing, crack propagation in a specimen with pre-existing inclined fault, influence of size effect on borehole instability, influence of pore pressure on thrust fault formation, and hydraulic fracture due to fluid injection. Overall, the numerical results show good agreement with available analytical solutions or experimental findings.For basin-scale problem, SR4 model is used due to its capability to capture the evolution of pre-consolidation pressure pc, that is not considered in Drucker-Prager model. In this case, the goal is to simulate basin-scale gravitational deformation in a prograding delta due to fluid overpressure in shale layer with synkinematic sedimentation. With the aid of adaptive remeshing algorithm, the result successfully produces distinct fault patterns across the prograding delta in terms of plastic strain distribution. In particular, three different zones are observed: extensional, transition, and compressional zone. The extensional zone is characterised by basinward-dipping normal faults, whereas the compressional zone is characterised by basinward-verging fore-thrust faults.Overall, the simulation results illustrate the potential that the developed constitutive models under the integrated flow-geomechanical modelling framework could offer to future analysis of more complex geological evolution.
Constitutive Modelling for Sedimentary Evolution at Basin Scale
