Study On Critical Parameter In Cover Karst Collapse By Model Experiment And Numerical Simulation

Engineering practice shows that due to the complexity of geological conditions in Nanning-Guangzhou railway at karst roadbed, especially, influence groundwater migration ability of the karst fissure width, length and other principal character, which have a effect at field experiment result. And because of the varieties of restriction in field experiment, it is difficult to make a thorough investigation of characteristic in hidden karst tunnel and the corresponding collapse status. It is harder to determine and carry out the typical standard test series conditions. So, through to the investigation and research at scene, structural rock mass model with karst fractured, establishing typical karst roadbed test model, carrying out the model test simulation, explore the feasible way to solve the karst roadbed grouting permeable rate standard in Nanning-Guangzhou railway. This thesis is based on the karst subgrade in Nanning-Guangzhou railway, the method of critical collapse width of karst subgrade is studied by model experiment and numerical simulation, which will provide the theory basis for the engineering practice.Firstly, critical collapse width of karst subgrade is studied by model experiment in this thesis. The model test set erosion model and rainfall model respectively, and conduct a test in crack width of different models, thus the change rule of width of the collapse can be analysised. The test results show that the karst collapse critical crack width really exist for cover type karst. The size of crack crack width and the characteristics of sunken pit are closely related to cover soil density, the size of particle, groundwater level, upheaval degree and so on. On the basis of model experiment, numerical simulation is used as a comparison, which can analysis the process of karst collapse better, and confirmable the karst collapse critical crack width directly perceived through the senses. There are some different fractures setted up in numerical simulation. The results show that the soil settlement mutate when the crack width become2mm, which fit in with the result of model experiment. According to the comprehensive analysis of fissure change and soil mass excavation case, it is thought that the karst collapse critical crack width for2-3mm.By numerical simulation the limit height of critical soil cave is calculated in this thesis, and have a contrast with the consequence calculated by theoretical formula.Which offer a new way to resolve the limit height of critical soil cave in different cases.