Analysis On Ground Surface Settlement Induced By Undercutting Tunnel In Soils Underlain By Rock

With the development of the urbanization process, the construction technology ofundercut tunnel has been the main technology of tunnel excavation in urban subwaywhere the dense buildings and complex pipelines located. Tunnel excavationinevitably disturbed with the surrounding rock and soil and destroyed the originalstate of equilibrium, so that has a negative impact on adjacent buildings and municipalpipelines. Therefore, in order to ensure the safety of the surrounding environment, it isnecessary to study the ground surface subsidence caused by the tunnel excavation.At present, the research on ground surface settlement induced by undercut tunnelhas focused on the shield tunnel construction of soft soil(in Shanghai) and minedtunnel construction of hard land layer(in Beijing).The research on mined tunnel inSoils Underlain by Rock is seldom. The variation law of ground surface settlementinduced by mined tunnel in Soils Underlain by Rock is based on the results gainedfrom soft soil area and hard land layer. Due to the different construction method andgeological condition, the variation law of ground surface settlement is different. Thisresearch focuses on the variation law of ground surface settlement in the particularsoils underlain by rock area.The paper is based on the Xi-Yong tunnel project with mining method ofQingdao Metro Project1(line3).Combined with field data, the variation law ofground surface settlement in each step of excavation of tunnel with bench method, canbe estimated using the finite element of Plaxis3D Tunnel software. The variation ofground surface settlement with the excavation depth changes can be divided into fourphases, which is small deformation stage, the sedimentation rate increases rapidlyphase, the sedimentation rate increases slowly phase and the sedimentationdeformation stabilization phase. The variation law of surface transverse settlement isthe settlement trough width is shorter than the width of Peck formula regression, and the width is getting smaller with the maximum sedimentation increases.The measured surface settlement agree well with the results by Peck formula,which means that Peck formula is an effective method for predicting surfacesettlement of Qingdao Metro, but it is bigger than the actual results.The paper analyzes the different factors affecting surface settlement whichincludes excavation method，support method and geological conditions。The resultsshowed that the surface settlement of positive step construction method mainly causedby upper step method. The surface settlement caused by no support excavation isgreater than the support excavation does, and the difference increases with theexcavation depth increases. The surface settlement is quite different when theexcavation of tunnel under different geological conditions. it can be controlled underbreeze granite, but it is greater than settlement alarm value under weathered granite.The paper also analyzes the step length and excavation progress which have animpact on surface settlement, and the results show that shorter step length and smallerexcavation progress can reduce surface subsidence to ensure the safety of tunnelcavern.The paper is effective for predicting the variation law of ground surfacesettlement in similar soils underlain by rock.