Research On Deformation Law Of Underground Structure Of Super High-Rise Building Adjacent To Metro Station Under Top-down Excavation

With the development of urban construction, new challenge to design andconstruction of retaining structure of foundation pit is presented because of theincreasing excavation scale. As a new construction method, the supporting system oftop-down method which consists of plates, beams and columns of main structure saveda large number of money, which gradually was used in deep foundation pit engineering.Being a complex construction method, if its design or construction was improper, graveeconomic losses and human casualties would be caused, therefore it is necessary toresearch top-down construction method. Based on deep foundation pit engineeringconstructed by top-down method for the New Traffic Building of Hefei, the influence ofstress and deformation exerted by excavation upon retaining structure, soil and adjacentsubway station was investigated.The main research contents and conclusions are as follows:（1）The influence of top-down construction method on surface settlement anddeformation of supporting structure was studied.Three-dimensional finite elementmodel to simulate foundation pit excavation of New Traffic Building of Hefei wereestablished by MIDAS/GTS in order to research the influence of top-down constructionmethod on surface settlement and deformation of supporting structure. The resultsindicated that top-down construction method could decrease the deformation offoundation supporting structure and ground surface settlement, which all remainedunder control，and pointed out that dual-purpose diaphragm wall played an importantrole in the top-down construction engineering.（2）The influence of the strength of cement soil piles on the deformation ofdiaphragm wall was studied. By analyzing different strengths of cement mixed piles, itshowed that improving strength of the cement mixed piles could decrease thedeformation of new diaphragm wall beside cement mixed piles and increase thedeformation of diaphragm wall shared with metro station. Therefore, when choosing thestrength of cement mixing pile, the deformation of new diaphragm wall and wall sharedwith metro station should be taken into consideration.（3）The influence of stress and deformation of the top-down construction on theexisting metro station was studied. The scheme of top-down construction was selectedaccording to the above analysis and influence of top-down construction on the existing metro station was studied at great length. The results showed that the change in thesettlement and internal force of the metro station was large in the areas near foundationpit, especially the central wall in the station，but the change in the areas far away fromfoundation pit was small. The deformation of plate near wall increased and themaximum differential settlement arose between two pillars near the wall afterexcavation. Therefore, more attention should be paid to monitoring the area of the largerforce and deformation during construction.（4）Relevant suggestions were put forward. It was concluded that the impact on thesurrounding environment was decreased effectively and the Metro station was protectedeffectively by selecting the process reasonably under top-down construction in complexenvironment. Correlative factor of top-down construction were summarized andrelevant measures and suggestions were proposed, which provide a reference for thesimilar construction engineering.