Study On Stability And Engineering Countermeasures For Shallow Buried Bias Section Of Tunnel Entrance

The North and South Cross-Ridge Tunnel in Kyrgyzstan is a highway tunnel,designed by Russian Design Institute according to Russian standard,built by Chinese according to the construction concept of our country,and supervised by Kyrgyzstan.Systematic analysis and research are carried out on the problems existing in the execution standard in construction,as well as on the construction stability of tunnel opening section and shallow burying bias section.The main work and main results obtained are as follows:(1)In accordance with the Russian code,the North and South Cross-Ridge Tunnel in Kyrgyzstan is classified into categories of rock firmness,which is constructed by the construction side of the Chinese mainland and managed by the national construction side of Kyrgyzstan for the construction supervision.In engineering construction,the determination and approval of construction schemes need to communicate with the conversion problems under different systems and standards,especially the transformation between the classification of surrounding rock based on rock firmness f in Russia and the classification of rock quality in mainland China.According to the principle of equivalent volume joint coefficient,the relation equation between K_V and RQD is derived.Meanwhile,according to the equivalent principle of Uniaxial Compressive Strength,the equation of the relation between BQ and f is compared and analyzed,and the relation equation between BQ and f is obtained.According to the range of mechanical parameters of rock mass suggested in the code of engineering rock mass,the curve of the relationship between parameters and BQ is drawn,and the nonlinear fitting analysis is carried out.The empirical formula of the relationship between the mechanical parameters of rock and f is established and applied to the North and South Cross-Ridge Tunnel of Kyrgyzstan.(2)In view of shallow burying,partial pressure and poor geological conditions,it is necessary to study the characteristics of pipe shed advance support in tunnel entrance section and determine the support parameters of large pipe shed.Simplified beam model based on large pipe shed,considering the supporting effect of loose rock and soil and the deformation and lag effect of initial support,the beam model of pipe shed was improved,and the calculation formulas of deflection and internal force of pipe shed were deduced.It is also applied to the North and South Cross-Ridge Tunnel of Kyrgyzstan.(3)In view of the problem of determining the excavation parameters of tunnel opening section,based on the Xie Jiajie calculation model of surrounding rock pressure of shallow-buried tunnel,the two-dimensional model is extended to three-dimensional model,which ensures the stability of the face and the vault,the formula for calculating the digging length of soft rock tunnel is deduced from the point of view that the surface of the tunnel face is stable and the vault does not collapse.By using this formula,the excavation advance of the north and south of Kyrgyzstan tunnel using step method is analyzed,and the optimum excavation advance is obtained by combining the numerical simulation analysis.(4)The overburden of shallow burying partial pressure section of tunnel entrance is weak,the tunnel support structure is not only subjected to the partial pressure of slope body,but also subjected to the additional thrust caused by the slope stability change due to tunnel construction,which is very disadvantageous to the construction and the structural stress state.The deformation may be too large,the construction is difficult and the support structure is not safe.The surrounding rock pressure of shallow buried eccentric pressure tunnel in potential landslide is analyzed.On the basis of the calculation method of surrounding rock pressure provided by Railway Tunnel Design Code,the stability state of tunnel side through slope is considered.The unbalance thrust method of slope stability analysis is introduced into the calculation of surrounding rock pressure of tunnel,and the calculation method of surrounding rock pressure of shallow buried bias tunnel through side slope based on unbalanced thrust method is put forward.It is also applied to the North and South Cross-Ridge Tunnel of Kyrgyzstan.