Research On Calculation Method Of Surrounding Rock Pressure For Large Span Tunnel In Shallow Buried Soft Rock Section

With the rapid development of society,the volume of transportation has been increasing.The construction of multi-lane highways is also more and more,along with the construction of large-span tunnel is inevitable.The construction of large-span tunnel with it is inevitable.The surrounding rock mass of the large-span tunnel in shallow buried soft rock section is usually poor,and its self-stability is weak after excavation.The slope gradient of the ground surface is uneven,and most of them have the bias effect.During the design and construction of the tunnel,accurate calculation of surrounding rock pressure has become a problem urgently needs to solve.Based on the project of Longtoushan tunnel in Guangzhou,this paper analyzes the surrounding rock pressure of the large-span tunnel with shallow buried soft rock sections respectively from three aspects: field survey,numerical simulation and theoretical calculation,and mainly obtains the following research results:1.By using FLAC3 D finite difference software,the surrounding rock stress of vertical and horizontal in large-span tunnel with shallow buried soft rock section are simulated and the distribution rule is analyzed respectively based on process design method and state design method,and making the simulation results of the process design method compared and analyzed with the measured results.2.Introduced the calculation principle of surrounding rock pressure theory for shallow tunnels both at home and abroad in detail,discussed the limitations of each calculation method,and indicated the direction for the improvement and correct use of each theoretical method.3.Combined with engineering example,the pressure of surrounding rock of double-hole tunnel with large-span shallow soft rock section is calculated by various commonly used theories of surrounding rock pressure of shallow tunnel,and the surrounding rock pressures calculated based on the state design method are compared and analyzed.Concluded that the clearance and the ground surface slope angle are two key factors that affect the pressure of the surrounding rock of the large-span double-hole tunnel and got a series of other conclusions.4.Deduced the calculation method of surrounding rock pressure of single-slope and variable slope in shallow buried double-hole tunnel based on Xie Jiaxiao theory and limit equilibrium principle of rock and soil from the single-hole tunnel to the double-hole tunnel,and discussed separately the formula of correctness,applicability and innovation.5.Analyzed respectively the influences of the clearance and the ground surface slope angle to the tunnel pressure of surrounding rock based on the calculation method of surrounding rock pressure of single-slope in double-hole tunnel derived from this paper.Concluded that the demarcation criterion of double-hole tunnel in shallow buried soft rock divided by clearance,larger depth of tunnel are more sensitive to clearance when the ground surface slope angle is larger and other conclusions.All in all,any theoretical calculation of surrounding rock pressure will be different from the actual results.The research results obtained in this paper aim to minimize the difference largely and provide reference for the design and construction of the largeg-span tunnel in shallow buried soft rock section.