Research On The Application Of Micro-pile Support In The Pit Structure Adjacent To The Anti-pressure Platform Pit Of The Subway

With the continuous acceleration of the construction speed of large and medium-sized cities in China,the increasingly tight supply of urban land,and the rapid rise in construction land costs,ultra-high and ultra-deep projects have gradually taken the mainstream in urban construction in China.Such projects generally use structures such as frame-core tube and tube-in-tube,which often lead to a lower structural bottom elevation in the core tube area than in the podium area,This resulted in a "pit in pit" structure with an excavation depth of generally over 5m;When the height difference between the inner and outer pits is greater than 5m,the design scheme often needs to be demonstrated again based on the hydrological and geological conditions after the completion of earthwork excavation,in order to minimize the construction difficulty of the support structure at the height difference position,improve the overall construction quality,and effectively shorten the construction period while ensuring the safety of the foundation pit.For the pit-in-pit support structure,the scope of application may also vary according to its own characteristics.From domestic and international reports,there are several or even dozens of cases of safety accidents of different degrees in foundation pit projects every year,such as the collapse of the pit or the damage to the buildings around the pit,which will not only prolong the construction period and increase the construction cost,but also cause serious casualties,the consequences of which are incalculable.In this way,a qualified and reasonable pit-in-pit support structure is a necessary condition for pit excavation.Based on the foundation pit engineering of Qinchengda Paradise Phase I Project in Zone C,this paper proposes a micro pile support structure with a reverse pressure soil platform structure adjacent to the subway passage foundation pit to solve the problems such as insufficient slope distance at "soil platform","pit in pit",and other parts,and the traditional support form of shotcrete anchor cannot meet the safety requirements.That is,using micro piles(with I-beam embedded in the rotary shotcrete pile)for vertical support,numerical simulation research is conducted through FLAC3 D,Verify that the support structure is feasible.During the construction process,the subway channel foundation pit and pipeline adjacent to the pit in the pit were monitored.The results showed that the monitoring data of each monitoring item were within the control range and were normal.The channel foundation pit,subway,and pipeline were not affected by the pit in the pit excavation construction.The support scheme is reasonable and feasible,and avoids the impact on the foundation pit adjacent to the subway passage to the maximum extent.It has certain reference value for similar projects in the future.Figure [45] Table [20] Reference [81]...