| With the implementation of the western development and the rise of China’s central strategy, large.scale underground engineering under complicated geological conditions is continuous emerging recently, moreover harsh geological environment and weak surrounding rock are encountered in actual projects, and the non.continuous weak structural plane such as joints and cracks usually exists in the rock. All these will bring a big challenge for design and construction of underground engineering. The presence of weak structure plane affects the physical and mechanical properties of the rock mass, and the underground engineering problems are becoming complicated due to the surrounding rock deformation, anisotropic rock strength and low strength characteristics of weak structure plane. So the weak structure plane is still a hot topic in the forefront.Layered rock mass is a sedimentary rock which distributed with a group of dominant weak structural planes, its structural characteristic is the orientation alignment of the bedding surface. This rock mass is widely distributed in the nature, commonly seen in the tunnel, mining, oil and gas development and other underground engineering. As it has layered structure, layered rock mass is a discontinuous, heterogeneous and anisotropic mechanics medium, its deformation and strength characteristics have obviously transverse isotropic property, which has a great difference with the isotropic rock mass. In the underground engineering, the anisotropic of deformation and strength of the rock mass and the low strength characteristic of the weak structural plane make the complex problem of deformation, reinforced supporting and stability of the surrounding rock of tunnel. When making this kind of rock mass engineering construction, the original rock stress equilibrium state is vulnerable to damage, leading to tunnel surrounding rock stress distribution, makes a certain range of rock mass around the plastic deformation occurs, and the plastic deformation area namely ’disturbance’ zone for the study of the topic selection, formation process of the excavation disturbance and its deformation and failure mechanism is very complex. As a result, the comprehensive geological characteristics of layered rock mass and the disturbance of the complexity of the deformation zone, it is necessary for stratified rock mass disturbance zone evolution for intensive research.The article was based on Wuhan Huashan Road tunnel project, closely around the stability problem of the surrounding rock of the layered rock mass in the tunnel engineering to make the meticulous research on the formation and bolting mechanism of the excavation disturbed area of the layered rock mass tunnel. Huashan Road passes through the Baogai mountain, Bomeng peak and Changshan massif of Jiufeng mountain department, along sets the Baogai tunnel and Changshan tunnel, the elevation of Baogai mountain at the top of the tunnel is about 137m,Bomeng peak is about 117m.The maximum embedded depth of the tunnel is 63.5m,the depth of the valley between Baogai mountain and Bomeng peak is about 6.5m.To research the damage mechanism of layered rock mass,the stability of surrounding rock, anchorage mechanism and numerical simulation of tunnel construction process by means of adopting the method of systematic laboratory model test, theoretical modeling, numerical simulation, site monitoring measurement and inversion analysis. Then the results were comprehensively analyzed by comparing to the actual monitoring data of Wuhan Huashan Road tunnel project. The main contents and innovations of this paper are as follow:(1) To study the impact of the weak structure plane, soft and hard interlayer and the changes of dip angle on the properties of layered rock mass strength and the anisotropic deformation, a series of laboratory physical experiments of the layered rock mass and the soft and hard layered rock mass were carried out in this paper, and a series of numerical simulation experiments were taken to search for the failure mechanism and strength characteristics with the dip angle changes by finite element software ABAQUS. Then combining theoretical derivation of layered rock mechanical model, the disruption and strength features and anisotropic strength characteristics of layered rock mass were discussed by exploring the weak structure plane, soft and hard interlayer and the changes of dip angle effects. For layered rock mass, when the dip angle is small (less than 45°), the main failure of rock mass is the rock damaged first, then is the interlayer dislocation failure; when the dip angle increases (45°～75°), the destruction of rock mass is the interlayer shear failure and accompanied by splitting failure; when the dip angle increases to 90°, the destruction of rock mass is interlayer damaging directly, and accompanied by local instability splitting. For the soft and hard layered rock mass, when the dip angle is small (less than 30°), the main destruction of the rock mass is interlayer surface damaged firstly, then is interlayer dislocation failure; when the dip angle belong to 45°～75°, the main destruction of the rock mass is interlayer shear failure, and accompanied by splitting failure of local hard layer rock; when the dip angle increases to 90°, the destruction of rock mass has two forms, one is shear failure of soft and hard interface, the other is the hard layer rock splitting failure of the boundary.(2) The mechanical properties of layered rock mass are anisotropic obviously because of the existence of directional structural plane. The layered rock mass are regarded as a composite medium composed by bedrock and directional structural plane. Then the anisotropic model based on Drucker.Prager criterion was proposed by considering mechanical characteristics of bedrock and directional structural plane separately. The proposed model not only overcomes the problem of layer structural plane characteristics that conventional model of layer rock mass cannot reflect, but also overcomes the problem of failure characteristics of bedrock that cannot be considered independently before. On this basis, the method to solve the model was proposed, and the calculation program was developed based on the secondary development platform of ABAQUS, and comparing with classical theory to verify the effectiveness and practicality of the proposed model. Then the proposed model was applied to the rock foundation engineering and underground engineering, the calculation results can reflect anisotropy of layered rock mass, and are basically consistent with actual engineering. The proposed model can reflect the anisotropic deformation and strength of layered rock mass objectively.(3) With the development of monitoring measuring and computer technology, it provides a new way to obtain surrounding rock mechanical parameters and initial stress field of layered rock tunnel. The conventional inversion methods applied to underground parameters inversion are searching inefficiently and having large computation, to solve this problem, the simple method. simulated annealing algorithm for coupled had been raised in this paper for providing feedback problems of site monitoring data during tunnel construction. The error function was established by the measured and calculated values of the measuring point, and the penalty function to optimize the object function was conducted and finite element commercial software as a separate module was embedded into the improved optimization algorithm, and optimization inversion analysis program compiled. The effectiveness of the method was verified by using typical example, and the method with less iteration can be obtained the results that met the accuracy requirements, so it is a feasible method can be applied to complex initial rock stress field inversion, the seepage field and displacement back analysis in practical engineering.The excavation of the layered rock mass tunnel and numerical simulation of the supporting engineering is a very complex mechanical problem in the construction process. The low strength and mechanical anisotropic characteristic of the structural plane complicates the stability of surrounding rock. Simplified numerical treatment method of surrounding rock anchorage for rock bolt element embedding technology was suggested according to the construction measures and the corresponding geologic information of the tunnel excavation. Finite numerical simulation model considering the construction process was established, the evolution process of the tunnel excavation, supporting and balance of the layered rock mass was numerically simulated, the evolution and anchorage mechanism of the excavation disturbed area of surrounding rock in different construction quality and methods was explored, then the influence of the structural plane property,construction conditions and the stress release to the disturbance of surrounding rock was investigated, and the physical essence of deformation damage of the layered tunnel surrounding rock was revealed. The result of the research shows that the property and disturbance of the structural plane have more influence on the stability of surrounding rock, and the more the group of the level, the bigger the plastic zone of surrounding rock is, while the plastic zone corresponding to the bedrock is gradually reduced, that is the failure of rock mass is mainly controlled by the level group. The established model can effectively describe the open and close effect of the weak surface and the anisotropic of rock mass strength, does not need to divide the finite element mesh along the level, and simplifies the finite element modeling and calculation.(5) Based on Huashan Road tunnel project in Wuhan to conduct the site monitoring of tunnel surrounding rock and supporting structure.And establishing finite numerical simulation model, proposing reasonable surrounding rock parameters through inversion analysis of finite element optimization, and simulation results were in good agreement with field observations when compared with measured data values. Then to analyze the disturbed zone, deformation and the force rule of bolt systematically by simulating the process of excavation and support of the three.dimensional elastoplastic finite model, and numerically simulating the next excavation to predict the reasonable of tunnel surrounding rock deformation, stress, plastic zone distribution and support analysis during excavation construction, and to predict the stability of the tunnel surrounding rock and provide the protection for the safety of construction projects. |
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