Rock creep modeling based on discontinuous deformation analysis

Creep is one of the major problems of deep underground mining that must be studied theoretically, experimentally, and numerically over a long period. Experiments and field tests are methods which can directly and more accurately describe the engineering practices as compared with others. However, these approaches are also time-consuming because creep problem of rock engineering, such as the roadway/tunnel squeezing phenomenon, usually lasts from several months to a few years. A numerical method can be employed to overcome this time-consuming problem. The discontinuous deformation analysis (DDA) method was originated in 1984 and received considerable attention from geo-engineers and researchers. The current paper discusses the creep calculation methods using the continuous and the discontinuous methods, and proposes a creep analysis method based on DDA. The method proposed in this paper can directly change the stiffness matrix while inheriting the advantages of the original DDA. Applying this method does not require any changes in the contact part of DDA. Thus, this method does not have any effect on the open–close iteration and convergence and can solve the creep problem, while maintaining the advantages of the original DDA. We theorized that creep problems are static problems, and based on this, the work using DDA in this study was divided into two parts: (1) addition of a new loop for the original DDA to “discredited” the total creep time into several time elements, thereby changing the material properties in each time element; and (2) division of each of the time elements by the time steps, similar to the original DDA. In this manner, one creep problem can be solved via assembling of static problems. Afterwards, the method mentioned above is employed to modeling a tunnel case. The evolution of the displacement filed and stress field during creep are analyzed and discussed.