Constitutive modeling and finite element analysis of ground subsidence due to mining

An improved numerical procedure based on the nonlinear finite element method is developed to predict ground subsidence caused by underground mining. The following features are emphasized: (i) an appropriate constitutive model to accurately describe the nonlinear behavior of the rock and the unconsolidated (soil) materials in the overlying strata; and (ii) an accurate simulation of excavation sequences consistent with the actual underground mining. An elasto-plastic single surface constitutive model is developed to characterize the stress-strain behavior of rocks and soils. An optimization procedure is developed to evaluate the material constants associated with the proposed model. Stress-strain and volumetric responses for a number of tests are predicted and compared with experimental data and good agreement is observed. The constitutive model is implemented into a two-dimensional nonlinear finite element computer code with plane strain idealization. An accurate algorithm is adopted to simulate the process of underground mining. The computer code is used to analyze the collapse which occurred in the Blue Goose Lease #1 Mine in northeastern Oklahoma. A parametric study is conducted to investigate the effect of selected factors on the shape and extent of the subsidence profile as well as the distribution of stresses in the unmined regions. Analyses of the numerical results indicate that the nonlinear finite element technique can be employed to meaningfully predict and characterize the ground subsidence potential due to underground mining provided that the mine geometry and the material properties are described accurately.