Study On Reasonable Distance And Constrution Reinforcement Technology For Small-distance Tunnels In Cities

With the continuous development of urbanization,cities often face problems such as traffic congestion and inconvenient travel.Developing urban underground traffic is the future direction of urban development.In recent years,more and more tunnel projects have been built in densely populated cities.Due to the limitation of terrain,two-line road tunnels often have to choose a small-distance tunnel structure.Due to the large excavation section of the small-distance tunnel,it is easy to cause the surrounding rock to be unstable,resulting in the collapse of the structure.At the same time,the tunneling of the small-distance tunnel is likely to cause large settlement on the ground,causing road cracking and damage,and the surrounding buildings are inclined or even collapsed..Therefore,in order to ensure the safety of construction and operation of small-distance tunnels in cities,the guidance of urban small-distance tunnel construction is provided.Based on the elastoplastic finite element theory,the excavation model of small-distance tunnels is established.The systematic research and analysis of the reasonable distance of excavation,the reinforcement method of the middle rock wall,the reinforcement effect of the middle rock wall and the protection of the adjacent piles by the isolation piles have obtained the following main research results:(1)Based on the tunnel excavation mechanics,the stress,displacement,plastic zone distribution and ground settlement of the surrounding rock after excavation of small-distance tunnels under different distance are analyzed.The critical point of the above indicators with the change of the distance is analyzed.From the perspective of subtraction,the critical point of safety coefficient and equivalent plastic strain with the change of the distance is analyzed.Based on the angle of elastic strain energy density of tunnel excavation,the elastic strain energy density of small-distance tunnel excavation is analyzed.The critical point of the change in the distance.Based on the above three angles,the reasonable distance value of urban small-distance tunnel is proposed.(2)The area affected by horizontal displacement,vertical displacement and stress concentration of the middle rock wall is analyzed.The middle rock wall is divided into regions,and combined with the characteristics of different reinforcement methods,a newsafe,reasonable and economical reinforcement method is proposed.Based on the three-dimensional numerical model of the reinforcement method,the practicability of the reinforcement method is verified.(3)A three-dimensional numerical model for the excavation of the adjacent buildings in the small-distance tunnel was established.The protection effect of the double-row isolation piles is analyzed.The mechanism of the isolation piles to protect the buildings is revealed,and the length parameters of the isolation piles are optimized.