Experimental Study On The Mechanism Of Instability Of Layered RockMass In Deep Buried Tunnel

Layered rock mass has obvious characteristic of transverse isotropy due to bedding plane, and its failure properties are highly complicated. The anisotropic property of layered rock mass has been concentrated through many decades, and the method of one-by-one analysis is still popular for those thinly layered rock mass with massive different beddings, but it is well known that this method has some problems such as great dependence on engineering practice and low accuracy while high workload. Thus the efficient path for solving the problem is to create a better yield criterion and determine the strength parameter for different rock strata.The dissertation, Sponsored by National Natural Science Foundation of China (Grant No. 50621403;50334060), took Chongqing Gong-he tunnel as an engineering example and studied the failure mechanism of surrounding rock and the correlation with bolt support system by using the methods of theoretical analysis, modeling test, numerical simulation and in situ test, some helpful conclusions were arrived as follows.Firstly, a new failure criterion for transversely isotropic rock mass was proposed with consideration of bedding plane orientation and major principal stress, and the corresponding algorithm, arrived through VC++6.0, can be easily embedded into the software FLAC3D for the geotechnical calculation.And also, three new kinds of model materials with the property of normability, continuous elastic modulus and compressive strength were made for different types of rock mass, in which, sand and barite as main materials, gasoline as diluents, epoxy resin, silicone rubber and rosin as binders, of course, there exist other auxiliary materials.Thirdly, surrounding rock deformation and failure process of layered rock mass in high geo-stress was reappeared through the physical models with different dip angle of rock stratum, and the stress change and failure discipline in the direction of vertical to bedding plane was definitely determined.Fourthly, The stress distribution of surrounding rock in tunnels with no support, common bolts, and long bolts were peered through physical models test, the results show that bolt reinforcement area is a compressive stress field.Additionally, by using strain testing, endoscopic photography and bolt axial stress testing on physical models, the geo-stress redistribution and failure characteristic were studied by comparing two physical models with common systematic bolts and optimized systematic bolts. And the bolt axial stress distribution discipline was also found in different areas, which will be helpful for the revision of bolt design.Last but not least, the initial in situ stress of the mountain massif was inverse analyzed by field test, meanwhile, the influence of anisotropic properties of layered rock mass on the deformation and stability of the tunnel were also evaluated by means of monitoring, measurement and numerical simulation.