The Study Of Surrounding Rock Pressure And Interaction Mechanism Between Surrounding Rock And Supporting Structure In The Weak Rock Tunnels With High Geostress

The supporting structure load is a very important basis for the design and construction of tunnels. The stress redistribution process is very complicated due to the rock mass excavation, and it would be more complicated in bad geological environment. The large extrusional deformation problems were met in many domestic and overseas tunnels, such as Tanern tunnel, Arlberg tunnel in Austria, Enason tunnel in Japan, Jiazhujing tunnel, Wushaoling tunnel, new Guanjiao tunnel and Muzhailing tunnel in China. There are many common characters existed in these tunnels such as weaknesses, higher geostress, large deformation and long duration, etc. If the rules of surrounding rock deformation and stress redistribution are not understood or the supporting structure is unreasonable, excessive deformation and even collapse would be happened in the weak rock tunnels with high geostress because of poor self-stability, large plastic deformation and the obvious rheological properties for the tunnels in weak rock. Therefore, the structural loads and characteristics are especially important for the tunnels in the weak rock tunnels with high geostress.There are still problems existed in underground engineering calculation theory, even though much worch has been done for the weak rock tunnels with high geostress. For example, the existing constitutive relationships can't be applied in all conditions, especially for the weak rock with high geostress. Kastner formula can't calculate the plastic deformation pressures corresponding to the different deformation process. The study of this paper was done based on the problems existed in the current research, the practical engineering problems and the actual demand. Based on the weak rock tunnels with high geostress such as Guanjiao tunnel and Muzhailing tunnel, the surrounding rock pressure and interaction mechanism between surrounding rock and supporting structure in the weak rock tunnels with high geostress were researched and applied through the geostress in-situ measurement, theoretical research and numerical analysis. The main works of this paper can be described as the following items.(1) The surrounding rock pressure is based on the geostress. The geostress rules of qinghai-tibet areas were summarized through the statistical analysis of in-situ measurement results. These rules can be applied to judge the rationality of the in-situ geostress field measurement of qinghai-tibet areas. The geostress in-situ measurement results of Tianchiping tunnel and Liangshui tunnel were judged by the geostress distribution rules of qinghai-tibet areas.(2) If the tectonic geostress is very complex, the only method to get original geostress is the in-situ measurement. In this paper, the geostress data of Tianchiping tunnel and Liangshui tunnel in LanYu railway line were in-situ measured using the hydraulic fracturing method. Based on the in-situ measurement data, the high geostress level and stress distribution rules around tunnel after excavation were analyzed. The macro distributions of Muzhailing tunnel and Tianchiping tunnel were analyzed by the improved BP network.(3) Based on the problems existed in the current research, the tunnel deformation pressure formula were derived adopting the rock mass softening "straight-curve-straight" model and considering the original geostress and tunnel allow displacement (or the actual measurement displacement) as a starting point. In this paper, this formula is called "Kastner extension formula". The correctness and practicability of the formula were validated by a classic example analysis and the successfully applicaion in Muzhailing tunnel.(4) The algorithmic model of the excavation stress release ratio is based on the original geostress and the measured deformantion curve, but it can't be used in the weak rock tunnels with high geostress because of the two existing problems in the excavation. Based on the space effect existing in the excavation of tunnel and forecast methods of improved BP artificial neural network and polynomials, two kinds of methods were put forward for the model to be applied in the weak rock tunnels with high geostress. The two kinds of methods were used in actual tunnels. The rules of structure load and stress release in the weak rock section of GuanJiao tunnel and Muzhailing tunnel were discussed, and their results were also validated by3D numerical analysis.(5) In order to validate the rationality of "Kastner extension formula", the construction process in the weak rock section of Muzhailing tunnel was simulated by3D numerical analysis based on the strain soften model, in which the parameters of surrounding rock changes with strain. The3D numerical results were consistent with the results of "Kastner extension formula". The reliability and applicability of "Kastner extension formula" were proved that it can be used to calculate the deformation pressure of weak rock tunnels with high geostress.Based on the geostress statistical rule of the qinghai-tibet areas, the geostress distribution in the weak rock tunnels with high geostress can be got by the geostress in-situ measurement and continuation analysis. The original geostress is the basis of the study of surrounding rock pressure and interaction mechanism between surrounding rock and supporting structure. Based on the original geostress, the calculation methods and interaction mechanism between surrounding rock and supporting structure in the weak rock tunnels with high geostress were put forward combined with the theory analysis and numerical simulation. In this paper, four main research results were achieved as followings.(1) The geostress rules of qinghai-tibet areas were summarized for the first time. These rules can be applied to judge the rationality of the in-situ geostress field measurement of qinghai-tibet areas. These rules can also be refereced by the reconnaissance, the design and the construction of deep buried underground engineerings in qinghai-tibet areas.(2) According to the large deformation problems of the weak rock with high geostress, the tunnel deformation pressure formula, which can be used in weak rock tunnels with high geostress, were derived adopting the rock mass softening "straight-curve-straight" model.(3) Based on the two existing problems in the excavation, two kinds of methods were put forward for the algorithmic model of the excavation stress release ratio to be applied in the weak rock tunnels with high geostress.(3) To show the characteristic that the weak rock parameters would be changed during the rock deformation process, the strain soften model, in which the parameters of surrounding rock changes with strain, was adopted in the3D numerical analysis. The reliability and applicability of "Kastner extension formula" were proved that it can be used to calculate the deformation pressure for the weak rock tunnels with high geostress.Some new understanding and rules of the surrounding rock pressure and interaction mechanism between surrounding rock and supporting structure in the weak rock tunnels with high geostress were obtained in this paper. These results would become important theory basis for the design and construction of the weak rock tunnels with high geostress. These fruits can also be hoped to play a promotion role for the research of this area.