Study On Mechanical Properties Of Surrounding Rock Of Tunnel Passing Though Huge Filling Cavern

In the 21 st century,China's basic transportation construction is developing rapidly,in the eastern part of China,the high-speed railway network and the highway network are constantly improving,and the traffic construction in the central and western regions is also accelerating.With the development of basic transportation construction,the problems faced by engineers become more and more complex.Traffic construction passes through steep mountains and mountains,constantly facilitating people's travel,but the problem of karst in tunnel construction is very difficult.Crossing the huge filling cavern in the large tunnel of Anliu Railway has brought serious problems such as excessive settlement to the construction.Therefore,this paper synthetically uses theoretical analysis,engineering case analysis and numerical simulation methods to excavate the tunnel through giant filled cavern by different construction methods.Comparing the mechanical properties of the surrounding rock of the cavern with that of the soft surrounding rock in the cavern after reinforcement,furthermore,the mechanical characteristics of surrounding rock in three-step excavation with different circular driving rulers are studied in detail.The research results are as follows:(1)To analyze the engineering conditions of the Dayong tunnel of Anliu Railway.The general engineering situation,stratum lithology,geological structure,ground motion parameters and hydrological conditions of Dawei tunnel are introduced in detail.Exploration of the cavern is carried out to generate a three-dimensional model map showing the relative position of the cavern and the tunnel.And introduces the cavern from the construction point of view,and illustrates the cavern vault falling block on site,which provides a reference and basis for the selection of reinforcement method of cavern section.(2)Difficulties in construction of large tunnels passing through filling caverns are analyzed.The monitoring data show that there is a large settlement at the vault and shoulder of tunnel passing through the cavern section,and the maximum settlement can reach 51 cm;Cavity filling soil is relatively soft,resulting in construction piercing can not be shaped by gravity,which has a greater impact on the later reinforcement and support.In view of the above problems,the corresponding reinforcement methods are put forward to guarantee the normal operation of the project.(3)In this paper,the reinforcement construction process through the cavern section is introduced in detail.By adopting the safe three-step temporary inverted arch excavation method,high-pressure rotary jet grouting pile is used to reinforce surrounding soft rock,and pile-raft structure bored pile is used at the bottom of the tunnel to stabilize the lower part of the tunnel.After the completion of the tunnel construction,light concrete is used to fill the exposed skyscrapers.(4)Although two-step excavation meets the displacement convergence stipulated in the Code for Design of Railway Tunnels,the displacement convergence value of the two-step excavation method is far behind that of the three-step excavation method and the middle wall excavation method.The surrounding rock in practical engineering is complex and unstable.The displacement convergence value of the middle partition method is better than that of the two-step method and the three-step method,but the left half of the excavation needs temporary steel support,and the temporary steel support should be dismantled in the excavation of the right half.The process is uncertain,money-consuming and time-consuming.There are strict requirements for the duration of the tunnel.Therefore,the three-step construction method is chosen as the construction method for crossing the huge filling cavern tunnel.(5)Selected driving footage is 1m,2m and 3m respectively for simulation,and the simulation results are analyzed as follows: Although the three excavation circular footage meet the displacement convergence stipulated in the Code for Design of Railway Tunnels,the displacement convergence value of circular footage of 2 m and 3 m is larger than that of circular footage of 1 m.In practical engineering,the surrounding rock condition is complex,and the deformation of surrounding rock is generally larger than that of numerical simulation software,so it has great danger.Therefore,the circular driving footage of 1 m is recommended as the final driving footage for crossing the huge filling cavern tunnel.