Research On Model Test And Deformation Characteristics Of Carbonaceous Phyllite Tunnels With Squeezing Geostress

The problem of large deformation with squeezing weak surrounding rock is very common in tunnel constructions. In addition,the disasters which are directly caused by the deformation problem occur frequently, such as exceeding clearance limit, primary support craze, surrounding rock collapse and so on. Therefore the controlling technologies of large deformation are always the crux in the construction of squeezing weak surrounding rock tunnel. Indeed, the comprehensive understanding of the deformation law of surrounding rock is the basis of finding reasonable controlling methods.The deformation and stress characteristics of the surrounding rock with squeezing geostress are systematically studied in this thesis. Basing on the relevant study at home and abroad, the deformation laws of surrounding rock during the tunnel construction by bench cut method are summarized. Moreover, LiangShui tunnel project, whose main geological feature is carbonaceous phyllite widely distributed, is taken as background. Combining the means of physical model test and numerical simulation, the main research work and results are as follows:(1) Depending on orthogonal design, a kind of carbonaceous phyllite similar material is developed. Loess, quartz sand, cement, gypsum and pure water are used as raw materials, and bulk density, cohesive strength, friction angle and deformation modulus of the surrounding rock are taken as the target parameters. The new similar material is an ideal similar material for simulating the characteristic of the physical mechanical parameters of carbonaceous phyllite.(2) A whole set of equipment is accomplished. The equipment includes test bench,loading system and measurement system, and it can be used for studying the change characteristics of deformation and stress of the surrounding rock with squeezing high geostress weak tunnel. What’s more, its main advantages are flexible load, stable stress, high accuracy and good economy.(3) Two kinds of equivalent support structure are designed by combining the present research results and engineering experience. One is stiffness-equivalent support with thin iron sheet for supporting material, which is to simulate the surrounding rock deformation with the stiffness-equivalent strong supporting. The other one is deformation-equivalent support with wire mesh for supporting material, which is to simulate the surrounding rock deformation with the stiffness-equivalent weak supporting during the whole construction process.(4) In order to study the temporal and spatial effects of surrounding rock deformation during tunnel construction, the total deformation is divided into three parts. Under the condition of squeezing high geostress, the percent of afterwards deformation is the least,whereas the sum of advanced deformation and initial deformation makes up more than two-third of the total deformation.(5) By comparing the surrounding rock deformation under different support strength, the influence of support strength to surrounding rock deformation is analyzed. The weak surrounding rock should be allowed to appropriately deform under the condition of squeezing high geostress. Besides, it can avoid the load effect of surrounding rock in the vault, and improve the work coordination of supporting structure and surrounding rock.(6) The stress redistribution is studied under different support strength, and the results show that intensive stress concentration in the vault is induced by excessive support strength under the condition of squeezing high geostress.(7) The rules of surrounding rock deformation, which are drawn from physical model test, are verified and richen by using the FLAC3 D software. Combining the test conditions and results of the physical model test, the three-dimension numerical analysis of the tunnel excavation process is conducted. Furthermore, the surrounding rock deformation and stress changes of any position are obtained.(8) Finally, all the work and the main conclusions of the thesis are summarized. Also,some further research suggestions in the aspect of similar material, supporting means and excavation method are also put forward.