Research On Collapse Mechanism Of Tower Rock

Tower rock is the tower-shaped large rock mass with aspect ratio between 1 to 3 and height-diameter ratio more than 3. It is widely distributed in Southwest Mountainous including Chongqing, Sichuan, Guizhou, Yunnan, Hunan, Hubei, et al. Because of its developing environment and structure character, tower rock collapses are typical geological disasters in mountainous region with characteristics of wide distribution, high frequency, suddenness, and wide damage range, which is a serious threat for security of people’s lives and property and construction of cities and towns.Sponsored by the Geological Survey Projects and NSFC, based on the field investigation, the developing geology environment of tower rock were clarified, the formation mechanism and key influence factors were found out. Taking Zengzi tower rock collapse as a case study, the kinematic characteristics of failure were studied by image analytic method, and then the collapse mode was proposed. The key parameters were obtained and the effect of hard rock on rock collapse was analyzed by acoustic emission damage feature test and acoustic emission simulation. The mechanism of damage evolvement and strength deterioration of rock mass on the bottom of tower rock were analyzed with damage mechanics theory, and the stability analysis method for tower rock is presented. Verification and simulation on the failure model and deformation properties of tower rock were carried out by centrifugal model test and finite-difference numerical simulation. The proposal stability analysis method of tower rock has been applied to the control of Jianchuandong unstable rock and suggestion was given pertinently. The main results of the thesis are as follows:(1) The geology environmental, affecting factors and genetic mechanism of tower rock collapses were found out, the dynamics features and internal regularity in the process of the tower rock collapses were studied, the failure model of compressed fracture collapse on the bottom of tower rock was proposed. It is found that the hard rock on the bottom has an important impact on the stability of tower rock, which laid the foundation of mechanics analysis.(2) Damage behavior parameters were got through acoustic emission test and simulation, damage variable were built, damage constitutive model was established, and strength degradation of rock on bottom of tower rock was indicated from the point of damage mechanics.(3) Based on continuum damage mechanics, mechanical model were proposed for tower rock by introducing damage variables, with effective principal stress of compression-shear failure and compression-tension failure as the threshold value, the stability analysis method for tower rock considering damage evolution is presented. With this method, the collapse mechanism of tower rock was explained from mechanical essence. Take Zengzi tower rock collapse as an example, the calculating result is in accordance with the fact.(4) In order to verify the analyzed theory result, test and simulation on the failure mechanism of tower rock under self-weight were carried out by centrifugal model test and finite-difference numerical simulation. The result shows that the strength changes of rock in the bottom damage zone have an important impact on the stability of tower rock, which is consistent with the theoretic analysis.(5) The research has been applied in project of Jianchuandong unstable rock. The stability analysis result of this method is more close to actual situation than traditional method in code. Suggestions of bottom stabilization were proposed, which is not only can save cost, but also can shorten construction period significantly.