Study On Deformation Controlling During Construction Process Of Subway Deep Foundation Pit

Along with increasingly nervous of unban constructional land.Most of deep foundation pit are constructed at the compact district of unban,there are many exiting buildings and underground utility around foundation pit.It must have negative effects for stress and deformation of exiting building and structures around foundation pit.The stress state and deformation of deep foundation pit have close relationship with construction procedure in the foundation pit project,which is called the time—space effect.Based on a practical project in Tianjin,this thesis systematically discussed the basic principle of the time—space effect,earthwork excavation principle.The time-space effect principle was introduced into the foundation pit design.The main work and conclusions are as follows:Both at home and abroad to collect and arrangement of top down and cover to dig and time-space effect principle related articles material,summarizes its development history.From the top down time and space effect cover dig theory study and the application in the engineering in three aspects,through analysis and summarizing,sort out scientific and reasonable research approach.Using professional geotechnical engineering calculation software PLAXIS to simulate the foundation pit excavation process,compare and analsyz the working conditions of exchange support instead of full scaffolding.Accuratly simulate the process of the steady decline in underground water level and the hardening law of soft soil stress with strain,through the simulation analysis and research the following conclusion are conclued: precipitation process leads to deformation of the foundation pit supporting structure and surrounding soil and the deformation lead by precipitation process is fair with the working condition of unloading;Compared with conventional convert support changing,the scheme of full scaffolding as supporting structure take the obvious advantages of the simple construction and short time,although foundation pit of the scheme of full scaffolding is slightly larger than supporting scheme,the deformationmeets the specification requirements,so as the project the full hall scaffolding instead of support exchange is feasible and right plan.Combined with a cover to dig inverse do deep foundation pit engineering of typical design section,the simulation of construction process,points four construction steps calculation,get the corresponding retaining structure lateral deformation and the ground surface settlement results.Compared with the observed data,it is shown that the numerical simulation results illustrated a true deformation of the retaining structure and surface settlement law of development.With the increase of the deep foundation pit digging,the deformation of subsoil increased gradually and with the floor construction the rebounds of pit bottom showed a trend of decrease.The lateral displacement of retaining structure increase with the increase of dig deep,maximum deformation value appeared at the bottom of the pit in every excavation step.The surface settlement increased with excavation depth.In order to study the construction process time effect on the factors influencing the stability of the foundation pit,the numerical method were adopted to simulate the procedure of pit excavation.The results show that the different construction schedule to the pit rebound and ground surface settlement influence significantly.The same construction condition,construction with the extension of time,the deformation of foundation pit present growth trend.In order to study the space effect on the factors influencing the stability of the foundation pit,a section of the third step of construction as an example,respectively simulated three partitioned excavation way,that is,from left to right in turn from the middle to the excavation on both sides of the excavation from two sides to intermediate excavation.The analyzing results show that before the middle of the foundation pit excavation site and then again to both sides respectively to control the deformation of the foundation pit excavation best effect.