Simulation Of Propagation Of Tensile-Induced Earth Fissures Due To Groundwater Extraction

Earth fissures have already become a kind of significant urban geo-hazards. Due to the difficulties in observing soil fissuring and the complexity of soil deformation, current researches on earth fissures are still largely limited to qualitative field surveys and hazard evaluation to some existing fissures. With the development of failure mechanics, it naturally occurs for people to use failure mechanics to simulate earth fissures, and some achievements have been reached. Based on the previous studies, this paper did not use the method and strength theory of traditional continuum mechanics and the assumption of brittle failure of soil, but applied theories and methods of failure mechanics to the simulation of soil cracking, Based on a conventional finite element method program, Crack Band Model, which is developed from Smeared Crack Model, is built to simulate the whole process of soil cracking, with the Crack Opening Displacement (COD) and energy release rate used as the fracture criterion to describe the dynamic propagation of fissures. Then the model has been preliminarily validated by comparing the simulation results to the data acquired from an existing experiment. Finally, tensile-induced earth fissures triggered by groundwater extraction under three kinds of geological conditions have been simulated and analyzed. For each geological condition, the mechanism and the distribution of tensile earth fissuring and the influence of the occurred fissures on further soil deformation are explained.It is shown that the CBM is a feasible approach for simulating model I crack initiation and propagation in soil, which has been examined by the data from laboratory tests and the field observations of initiation and propagation of tensile-induced earth fissures. Most simulated fissures are initiated at the ground surface and propagate downwards, with significant horizontal and relatively small vertical displacement gradient, which means a great fissure aperture and a rather small vertical offset. However, a greater vertical offset is observed on a fissure formed at a pre-fault. Although the influence of shear strain on earth fissures is currently ignored, it can also be inferred that with the depth of fissure growing greater, the tensile-induce fissure may play a similar role as a pre-fault in the soil layer, which may lead to a change of failure model from pure tension to tension-shear.