Modeling of rock multiple fractures system with a new contact algorithm and a novel approach for complex topology construction

Abstract

Multiple fractures intersection induced by crack propagation and coalescence is extremely significant for revealing the fracturing essence and establishing mechanical models of natural rock with complex fracture network. A complex discrete interface dynamically adding algorithm (CDIDA) and a potential function-based fracture contact calculation method (PBFCC) are proposed for multiple fractures propagation with complex topology in rocks. Through combining fracture representation with dynamic cyclic “nodal splitting” and nodal assignment with local topological structure identification, CDIDA is proposed to dynamically construct the complex fracture network for the discrete interface approach. CDIDA is able to efficiently establish reasonable local interface topology as the premise of accurately calculating the interaction of multiple fracture systems. Noting that the line attributable to any fracture interfaces can be defined as a set of discrete points, PBFCC transforms the complex contact calculation into the equilibrium problem of these points connecting with hypothetical bonds. The constitutive relation of these bonds is based on a modified potential function, and it is changeable and movable according to the current fracture interface configuration. PBFCC avoids the computing problems such as setting prior contact pairs and contact detecting at each iteration, and is suitable for complex interface contact scenarios with large grid deformations. Moreover, PBFCC ensures that the complex interacting mechanical field calculation of the multiple fracture system is reduced to individual discrete point level, leading to the advantages of high efficiency and wide applicability. Based on the numerical implementation in Cellular Automata Software for engineering Rockmass fracturing process (CASRock), single edge fracture, collinear tensile fracture system, multiple fracture system and complex multiple fracture system simulations are provided to validate the efficiency and accuracy of the proposed methods.