In-situ test on force characteristics of miniature pile-anchor-support combination support system for deep foundation pits in miscellaneous soil strata
In order to investigate the stress characteristics of the deep foundation pit pile-anchor-support combined support system in plain fill soil layers,in-situ tests on micro piles,anchor cables,and supports were conducted,relying on a deep foundation pit project in Qingdao City.The evolution laws of bending moment of double-row micro steel pipe piles and axial force of pre-stressed anchor cables under different excavation conditions were analyzed.The stress characteristics of front and rear row piles and the stress distribution of pre-stressed anchor cables in this support system were revealed.The influences of adjacent buildings,exposure time of foundation pit,and removal of steel supports on the internal forces of the support system were discussed.The results show that:1)During the excavation process of the foundation pit,the front row piles play a dominant role in bearing the load.As the excavation reaches the base,the maximum positive and negative bending moment values of the pile body increase,and the extreme points continuously move downward.The bending moments of the pile body above the excavation surface are distributed in a positive"S"shape.2)Increasing excavation depth significantly increases the bending moment of the pile body within 1.0 m above and below the excavation surface,and the inflection points of the front row piles are located 0.5 m below the steel support and at the excavation surface position,respectively.3)During the excavation process,the axial force of the anchor cables decreases along the burial depth,and the axial force after 1.5 m from the front end of the anchor segment remains basically unchanged or shows minor fluctuations.4)The stress in the anchor segment is highly concentrated within the first 4.0 m from the front end of the anchor segment,which accounts for about 44% of the length of the anchor segment.The anchor segment end does not generate axial force,and this length can be optimized.5)The influence of adjacent buildings on the stress of micro steel pipe piles is small.With the increase of exposure time of the foundation pit,the bending moment of the pile body shows a slight increasing trend.After the removal of steel supports,the variation of bending moment of the front row piles is concentrated within 0.38H-0.96H(H is the excavation depth of the foundation pit).6)The pile-anchor-support combined support system can effectively limit the deformation of the foundation pit,and selecting reasonable support pre-stress is the key to the design of this type of foundation pit.
plain fill soil layersdeep foundation pitmicro steel pipe pilesanchor cablessteel supportsin-situ test
万方数据
维普
