Hierarchical element integration technique in discrete element simulation of rock failure

Abstract

Discrete element method has a congenital advantage over the continuous numerical methods for simulating the damage and fracture of geo-materials, as its calculation principles align with the discontinuous nature of these materials. Due to the unclear relationship between element scale and element strength (size effect), the element parameters, especially for the field-scale model, are quite hard to be reasonably determined, causing computational efficiency and accuracy cannot be balanced. To address this issue, the hierarchical scaling size effect model was developed to characterize the relationship between the strength and size of rock material. Based on which, an element integration technique was proposed that achieves a match between element strength and size. Discrete element simulations of laboratory tests demonstrated that, compared to the grain-based model (GBM), the calculation accuracy is maintained while the number of elements can be reduced by 2 to 3 orders of magnitude, indicating more than 100-fold improvement in calculation efficiency. This element integration technique was also employed in the simulation of field-scale hydraulic fracturing to demonstrate its feasibility in capturing the failure evolution in rock mass from a few centimeters to tens meters. Additionally, the mechanism of fault slip induced by hydraulic fracturing was roughly discussed.