Research On Deformation Rule Of Rock Mass In Front Of Excavating Face In Weak Rock Tunnels With High Geostress

The application of deep space will be the inevitable trend of tunnel and underground engineering in the future. Researchers and designers take more and more attention to the deformation of rock mass in front of excavating face of tunnel in the case of the application of the theory named “The ADECO-RS method”. At present, few research work has been done on the deformation rule analysis of rock mass in front of the excavating face in weak rock tunnels with high geostress, due to the buried depth, complex geological conditions and deformation monitoring difficulties of rock mass in front of the excavating face. The study in this paper focused on the deformation rule analysis of the rock mass in front of the excavating face in weak rock tunnels with high geostress by model test. Furthermore, a reasonable excavating and supporting method are studied by three-dimensional numerical simulation based on the test result which shows the evident rule of deformation. The main work of the thesis and conclusions obtained are as follows:(1) The laboratory test is performed by applying the orthogonal test method. The different mixture of the raw materials, that is, loess, gypsum, quartz sand, cement and water, are considered to do the test. The weak rock similar material is obtained based on the test. The physical and mechanical parameters of similar material better conforms similar conditions which the simulation of practical engineering should obeyed.(2) The model test chamber is designed which can provide loads in three directions. The high geostress is simulated by the three-dimensional test with the similar material inside the chamber. Further more, the tunnel excavation is simulated and stresses as well as deformations of the similar geological material are monitored. By the analysis of the test data, the deformation rule of the rock mass in front of excavating face and the surrounding rock of tunnel was concluded.(3) It can be seen from the rock mass deformation rule in weak rock tunnel with high geostress, based on the model tests, that approximately two-third of the advanced deformation happened among the range, which is called the core rock mass, between excavating face and the section with the distance of 0.5 times of the tunnel diameter in front of the tunnel excavating face. The extruding deformation of core rock mass is the main part of the advanced deformation in weak rock tunnel with high geostress. Therefore, to reasonably control the advanced deformation of the tunnel, the core rock mass part must be pre-reinforced.(4) In order to study the response of the characteristic of rock mass deformation, rock stress distribution and lining stress. Three kinds of excavating and supporting method are used in the three-dimensional numerical simulation of the tunnel construction by FLAC3 D, while the core rock mass segment lieing in 0.5 times the tunnel diameter in front of excavating face was reinforced.(5) During the construction of the weak rock tunnel with high geostress, the reasonable and sufficient deformation happened in the core rock mass should be allowed. The preconvergence deformation of surrounding rock could be adequately developed. Only if the core rock mass of tunnel had fully extruding deformation, then the stress of surrounding rock should be re-distributed by the way of releasing and transferring. In such a process, not only the loadbearing arch was formed, but also the stress distribution of surrounding rock turned more reasonable. When the extruding deformation was strictly limited, the geostress would concentrated to the surrounding rock of tunnel, which can lead to a wide range of surrounding rock around the tunnel seriously crushed, then the surrounding rock was instable, and the deformation was too large, so the stability of the tunnel is difficult to control.