| The construction of shallow tunnels adjacent to stratum cavities will induce the deformation and damage of the ground,and it is very easy to cause excessive ground deformation and even collapse accidents.This paper adopts the model test,theoretical analysis,and numerical simulation to study a shallow tunnel adjacent to a stratum cavity,which focuses on the mechanism of mechanical interaction between the shallow tunnel and the stratum cavity,the ground deformation and failure characteristics caused by the construction of shallow tunnels adjacent to stratum cavities.The zoning criterion and calculation method for the stratum cavity risk are proposed.And the control measures for the damage of the stratum cavities are provided.The main contents and results of this research are as follows:(1)An analytical model for the construction of a shallow tunnel adjacent to a stratum cavity is established,which overcomes the insufficient consideration of gravity factors and the simple tunnel deformation boundary mode in the existing analytical methods.And the Schwarz alternating principle is adopted to consider the mutual influence between the tunnels and the stratum cavity.The proposed analytical model not only considers the interaction between the stratum cavity and the tunnel but also takes into account the gravity factors of the excavated soil.Based on the deformation conditions and the original surrounding rock stress release conditions on the tunnel boundary,the effect of tunnel excavation is considered either by the source of deformation or the source of force.The analytical model is solved theoretically by both using the complex function method and Schwarz alternating principle,and the iterative calculation is performed through MATLAB programming.The accuracy of the analytical solution is discussed from the perspectives of theoretical characteristics and programming,and verified by the comparison with numerical simulation results.Through theoretical analysis,the mechanics interaction mechanism between the tunnel and the stratum cavity is revealed by the law of ground displacement and stress changes,as well as the deformation and stress of the cavity and the tunnel.And the mechanical reasons for cavity deformation and the intrinsic relationship between stratum cavity deformation and ground deformation are determined.(2)A three-dimensional similar model test system for shield tunnel excavation is developed to reveal the ground deformation and failure mechanism caused by the construction of a shallow tunnel adjacent to a stratum cavity.Based on the self-developed three-dimensional similar model test system,the construction process of a shallow tunnel adjacent to a stratum cavity is simulated,and the influence of the relative position and clear distance between the cavity and the tunnel on the ground deformation is studied.By analyzing the pressure change of the surrounding rock,the stratum failure characteristics and forming process of the soil pressure arch near the tunnel and the cavern are revealed.In addition,a refined three-dimensional numerical model considering the main construction factors is established.The rationality and accuracy of the numerical model are verified by the comparison with the model test results.In addition,an extended study is conducted based on the model test conditions.The influences of the stratum cavity shape,size,relative position and clear distance between the stratum cavity and the tunnel on the ground deformation and the development of the ground plastic zone are obtained.(3)Taking the penetration degree of the ground plastic zone,the maximum principal stress on the cavity boundary and the maximum surface settlement as the distinguishing indicators,a method for the stratum cavity risk zoning is proposed.According to the characteristics of the stress,deformation and stability of the stratum cavity under the influence of adjacent tunnel construction,the risk zoning criterion and calculation method for the stratum cavity are proposed based on the following indicators: the penetration degree of the ground plastic zone,the maximum principal stress on the stratum cavity boundary,and the maximum ground subsidence.And,by using the above-mentioned refined three-dimensional numerical model for the construction of a shield tunnel,a series of numerical simulations are conducted with different factors of the stratum cavity size,the relative position and the clear distance between the tunnel and the stratum cavity.According to the numerical results,the stratum cavity risk zone can be divided into strong-risk area,weak-risk area and risk-free area.Finally,corresponding control measures for the practical engineering are presented for the stratum cavity problem,and the effects of the corresponding control measures are evaluated. |
