| Characteristics of the construction condition of the considered deep foundation pit for Hefei Metro Line 1 are typical of complexicity,for it is surrounded by many important buildings of various types and the distance between the deep foundation pit and the Nanfei River is extremely short.Therefore,it is very possible that coupling or superposition of disadvantageous factors can be induced by excavation of the considered deep foundation pit.This phenomenon will result in unstable deformation of the excavated ground and even collapse of the buildings adjacent to the considered deep foundation pit.In this context,the objective of this study is to acertain the coupling effects of the construction conditions for the considered foundation pit within Hefei Metro Line 1 on internal force and deformation characteristics of pit support structure and response of the surrounding buildings.The research work and the conclusions drawn from this study are as presented below.(1)Detailed analysis of Hefei Metro’s survey data and sufficient field research are implemented.The results indicate that engineering properties of the soil closely related to construction of Hefei Metro Line 1 exhibit special characteristics: the upper part of the ground is soft while hard soil is located in the lower part,and weak expansion of the soil can occur when mixing with water.(2)The effects of excavation of the considered foundation pit on the horizontal deformation characteristics of underground diaphragm wall are detailedly analyzed by using FLAC3 D,a commonly used numerical simulation software.It can be concluded from the numerical simulation results that with an increase in the cover depth the horizontal deformation of the underground diaphragm wall increases,leading to the underground diaphragm wall moving inside of the foundation pit.This moving inside creates a curved shape of the underground diaphragm wall.Due to the influence of uneven compression caused by the buildings adjacent to the foundation pit,the zero-slope point on the curved underground diaphragm wall is located below the elevation of the bottom of the foundation pit.And this point is moving deeper with the advance of excavation of the foundation pit.(3)On the basis of the numerical simulation results,variations of the bending moment and axial force in the piles are detailedly studied for different construction conditions.It can be indicated from the results that horizontal displacement or deflection of the pile subjected to horizontal loading is generated.This horizontal displacement or deflection is coordinating with that of the underground diaphragm wall and the floor,inducing horizontal resistance in the pile.The horizontal displacement of the pile decreases with an increase in the embedded depth of the pile due to the fact that the resistances of the underground diaphragm wall and the floor are great enough.When the embedded depth of the pile reaches a critical value,the effect of the load on the pile can be neglected,meanwhile,the pile can be regarded as a footing beam in which one of its ends is embedded in the soil.(4)By conducting in-situ monitoring of the surrounding environment during excavation of the foundation pit,the effects of excavation of the deep foundation pit on the response of the buildings adjacent to the deep foundation pit are investigated.It is found that the settlements at the monitoring points increase with an increase in the excavation depth of the foundation pit.Besides,the settlement at a monitoring point that is nearer the foundation pit is greater than the far monitoring point.Therefore,it is suggested that construction monitoring be strengthened and temporary support be installed in order to reduce the risk brought by the coupling effect of the construction condition.Based on field research,in-situ monitoring and numerical simulation using FLAC3 D,the internal force and deformation characteristics of the piles in the pit support structure for Hefei Metro Line 1 have been detailedly investigated in this paper,which brings about some beneficial conclusions.These conclusions can provide some references for the design and hazard analysis of important foundation pit engineerings in Hefei and even Jianghuai region. |
