Construction Technology Study On Earth Pressure Balanced Shield Tunneling Through Buildings With Large Slope In Sand Layer

At present,with the continuous scaled-expansion of cities and increasing growth of urban population,urban traffic problems are becoming more and more prominent due to limited availability of urban land space.In order to effectively alleviate the ground traffic pressure,subway constructions are becoming an inevitable trend.Due to clustered urban buildings,tunnels will inevitably underneath pass through the buildings when shield constructing method being employed in the construction of subways,which will affect the buildings.How to predict and control the settlement of the ground and structural buildings caused by the excavation of shield tunneling is a major challenge for construction of shields.In order to ensure the safety of subway construction,ground and structural buildings,domestic and overseas scholars have undertaken a lot of researches and analysis,and have reached some major achievements.Based on the shield tunnel project of the first inter-city subway line constructed in Guangzhou,the paper briefly introduces the shield construction principle and construction process.Through theoretical research and on-site monitoring,related analysis is conducted to study settlement developing regularity of ground surface and structural buildings caused by shield tunnel construction,and the corresponding construction technical measures are proposed as possible reference for the shield construction passing underneath of structural building in the steep slope sand layer.The main contents are as follows:(1)Using finite element software to simulate the shield tunneling machine underneath passing through the buildings in the sand layer,calculating the settlement of the building,which is conducive to make pre-control measures for possible settlement due to shield tunneling construction,providing numerical simulation reference for similar stratum construction.(2)When the tunneling shield underneath passing the building in a steep slope sand layer,it is easy to cause damage to the building.Through series of countermeasures of controlling settlement,including continuous shield tunneling process,pressure control of soil silo,pre-setting of the excavation speed,dregs improvement,excavation amount limitation,Prevention of falling groundwater,adjustment of attitude parameter of shield,timelysynchronization of grouting and tunnel tail sealing,the above problems can be effectively solved.(3)When the tunneling shield underneath passing the buildings in the sand layer,the development range of lateral and vertical settlement caused by the excavation of the shield tunnel is obtained.The maximum settlement occurs after the shield tail passes the house,and when the shield enters the buildings.When the approaching distance between shield and the building is the length of 2 times of the tunnel diameter,the longitudinal settlement of the stratum begins to increase significantly.During the shield is passing,the settlement increases significantly.After the shied passed the building and rear distance more than 2times of tunnel diameter,the settlement gradually decreases and tends to be stable.(4)Incorporation of the shield construction process of Nanli section of Guangzhou-foshan subways,the main construction parameters and monitoring data of the shield tunneling in the sand layer are summarized,which provides construction parameters reference for other potential similar shield tunneling projects underneath passing through buildings in steep slope sand layer.