Environmental Impacts Due To Shield Tunneling In Karst Region Covered With Sandy Strata

Based on shield tunnel project of Maanshan Park Station to Liantang Village Station of Guangzhou Metro Line 9,the construction technology and its environmental effects in strong karst area with upper-soft and lower-hard ground were discussed comprehensively in this study.During the shield tunneling,not only the quality of the tunnel construction should be ensured,but also the influence on surrounding soil and nearby buildings of shield tunneling must be considered.Establish realistic finite element model of the project,and then through comparing the simulation of two-lane tunnel with measured data to get the actual ground loss produced by shield tunneling.And then the environmental effects and the internal forces of shield lining get a comprehensive analysis.Relying on the karst geological characteristics of shield tunnel project,approach to karst is proposed.Using a series of control measures on construction process to ensure the success of project through the upper-soft and lower-hard stratum,the project is efficiently finished with high-quality.Effective theoretical reference and technology reference are provided for future construction of shield tunnel in similar complex karst region with upper-soft and lower-hard stratum.The main contents and research results are as follows:(1)Karst treatment during shield tunneling in karst region: Through the karst treatment process of this project,treatment standards,treatment measures,treatment effect testing methods and the relevant measures for shield machine tunneling through the karst region.Cave grouting construction process' s effectivenessat in the interface of karst region for shield tunneling project is proved and it is with great reference to similar projects.(2)Forming control technology of shield tunnel construction in the soft and lower hard stratum: the construction of the shield tunneling mode,rationalization tunneling parameters,driving attitude control were studied,summed up a series control measures of shield tunnel construction in the soft and lower hard stratum.Combined with existing theories of information and comprehensive analysis of site construction practice,the construction parameters of shield tunnel construction in soft and lower hard stratum in the karst area were optimized.(3)Environmental effects of shield tunnel construction in soft and lower hard stratum in the karst area: arrangement of the monitoring program for site monitoring was introduced,and monitoring data were analyzed to study the mechanism of the phenomenon.Land subsidence in tunnel axis position and settlement of nearby houses were collected and analyzed.What's more,the applicability of control measures of shield tunnel construction in the soft and lower hard stratum in the karst area were verified,successfully controlling the environmental effects of shield tunneling construction.(4)Finite element numerical simulation of shield tunnel construction: a three-dimensional finite element model for shield tunnel construction of Ma Anshan Station to Lian Tang Village station of Guangzhou Metro line nine was established.Based on the measured data,ground loss generated by shield tunnel construction was obtained,and the internal forces in the tunnel and the displacement of surrounding soil were analyzed.Via comparison of site monitoring data and calculation results,environmental effects of shield tunnel construction in soft and lower hard stratum in the karst area were discussed.