Numerical Tests On Mechanism Of Zonal Disintegration In Deep Tunnels

With the fast development of national economic construction and national defense construction, the development of underground space is becoming deeper step by step. Under the influence of the high ground stress, the engineering response of deep rock mass shows some new characteristic scientific phenomena, such as the phenomena of zonal disintegration.The most distinguished difference between deep and shallow engineering is so called high geostress. The failure mode of the deep rock mass depends on the property of rock mass and the geostress state. The surrounding rock in shallow tunnel is classified into loose zone, plastic zone and elastic zone while the surrounding rock around deep tunnel is classified into fractured zone and non-fractured zone which occur alternatively and called zonal disintegration. The mechanism of the phenomenon is not clear yet.This research is supported by the National Natural Science Fund of China (No.50809012, 40638040), the National Key Basic Research Science Foundation(No.2007CB209400) and the National Natural Science Fund International Research Project (No.50820125405). Based on the understanding of heterogeneity of rock mass, a series of numerical tests of zonal disintegration in rockmass around deep tunnels are carried out on the RFPA3D-parallel system which can reflect the progress failure of rock mass vividly. There are a number of factors affecting on the zonal disintegration phenomenon, the research focus on several crucial affecting factors, such as loading state, rock mass conditions and shape of tunnels. The results of numerical tests on mechanism and evolution laws of zonal fracture are put forward. The following conclusions could be derived from the test results presented in this paper.(1) The zonal disintegration is the result of circular tensile within surrounding rock mass under the loading of principal stress in the tunnel direction;(2) The whole process of zonal disintegration phenomenon has been observed that from the crack initiation, extended and through, the results has great theoretical and practical significance on mechanism and evolution laws of zonal disintegration;(3) The evolvement of the cracks is discontinuous, maybe evolve into an integrated circle fracture; or create a spiral fracture. The evolvement process of fracture is a random process.