Study On Deformation Regularity And Monitoring Indicator Of The Deep Foundation Pit With Pile-Anchor Supporting

In deep foundation pit engineering,the security and stability is the primary concerned content;the deformation of the foundation pit's side wall,which is directly related to the safety of the overall foundation pit,is an important indicator to measure whether the foundation pit in a safety state during the excavation.Therefore,it has become a focus of attention on the research and safety monitoring of the foundation pit deformation.Due to extensive application of the pile-anchor supporting structure in deep foundation pit engineering,especially in Beijing area,it is particularly important to study the deformation regularity and monitoring indicator of this kind of foundation pit's side wall.In this paper,two aspects of the horizontal deformation of the lateral wall of the deep foundation pit with pile-anchor supporting,the horizontal displacement and the inclination angle,are studied.The FLAC3 D software is mainly used to make numerical calculation.Based on a practical project in Beijing area,the three-dimensional finite difference principle was used to calculate and analyze the horizontal deformation regularity of the foundation pit's soil and the supporting pile during each excavation process and analyze the variation of lateral earth pressure behind the side wall in the pile-anchor supporting deep foundation pit.The change of earth pressure shows the foundation pit deformation mechanism.Based on this,according to the principle of differential,the dip angle of the pit side wall is calculated,and the regularity of dip angle change is deduced.Using the scaled test in the laboratory,the deformation and the earth pressure of the pit's side wall under various excavation conditions were inverted,and compared with the numerical calculation results,and the feasibility of using the latter method to make the orthogonal test was demonstrated.The orthogonal test was carried out by changing the embedded depth of supporting piles,the vertical position of the anchor rods,and the upper load of the foundation pits.The result shows that the deformation regularity of the foundation pit's lateral wall with the largest horizontal displacement in its middle area is unchanged.In addition to this,both the dip angle and horizontal displacement has greater sensitivity to the external loads.Relative to the external loads,it is less sensitive to the embedded depth of supporting piles and the vertical position of anchor rods.Thus the applicability of dip angle monitoring indicators and the feasibility of using dip angle to assist monitoring the horizontal deformation of the sidewalls of pits are determined.The dip angle monitoring indicator is confirmed with the value of 0.111°,and the key monitoring position which is located at the lower part of the foundation pit is given.This key position,which accounts for about 87% to 98% of each excavation depth of the foundation pit,is within the range of 0.5 ~ 1.5m above the pit bottom of each excavation.The research content of the horizontal displacement of the side wall foundation pit provides the relevant deformation basis for other similar supporting structure designs.And the study of the obliquity monitoring indicator provides an unconventional method for the foundation pit monitoring,which has the practical significance to guide the engineering.