Analysis Of Interaction Between Deep Foundation Pit Excavation And Adjacent Existing Buildings In Sensitive Environment

With the continuous reconstruction of old cities,it is inevitable to excavate the foundation pit around a large number of existing buildings,which makes the foundation pit engineering in a sensitive construction environment.The safety of foundation pit itself and the influence of foundation pit excavation on the stability of adjacent existing buildings should be considered in foundation pit construction.Therefore,the optimization design of foundation pit excavation and support is of great significance.Based on typical engineering cases,combined with numerical simulation,this paper studies the interaction mechanism between deep and large foundation pit excavation and adjacent existing buildings in sensitive environment,and puts forward a number of optimization measures for foundation pit excavation and support.The main research contents are as follows:1)This paper discusses the influence of deep and large foundation pit excavation on the deformation of adjacent existing buildings,and optimizes the design of excavation mode,support mode and internal support type,and puts forward pile-anchor-support retaining structure and opposite-angle support type.The results show that: the pile-anchor-support retaining structure can meet the requirements of economy and safety,realize the optimization of foundation pit support mode,and reduce costs by 20%.Using the oppositeangle support type,the deformation of existing building structure caused by foundation pit excavation can be reduced by 10%.2)This paper discusses the influence of sensitive environment on the stability of deep and large foundation pit excavation.The influencing factors such as the form of building structure,the property of soil layer and groundwater are investigated to provide data support for the promotion of construction scheme.The results show that: the difference of existing building structure has no obvious influence on the deformation of foundation pit,and the deformation trend of foundation pit of brick concrete structure,reinforced concrete frame structure and steel frame structure is basically the same.The deformation of foundation pit is greatly affected by soil properties and groundwater.And the deformation of soft soil foundation pit during dewatering excavation is several times that of hard soil foundation pit without dewatering.3)Based on the on-site monitoring test,the internal force and displacement safety analysis of two special parts of the pile-anchor-support retaining structure are completed.The results show that: the internal force and displacement of the two dangerous parts of the pile-anchor-support retaining structure are controlled within the standard range,and the pile-anchor-support retaining structure can be applied to such sensitive environment,the pile crown beam can restrain the horizontal displacement of the top of the slope protection pile well,attention should be paid to the design and construction of the pile top crown beam.The compression and compaction effect of the upper building on the lower soil can reduce the prestress loss of the anchor cable in the soil,therefore,the safety and stability of the retaining structure are improved to a certain extent.4)Engineering examples and application promotion analysis are carried out,and the rationality of the optimal construction scheme obtained is verified through the comparison of various control indexes.The results show that: the numerical simulation results are in good agreement with the monitoring data,and the construction scheme of pile-anchorsupport retaining structure and sectional layered excavation can effectively ensure the safety and stability of deep foundation pit and adjacent existing buildings in sensitive environment.The existence of internal support can change the deformation state of the building,make the soil between the building and the foundation pit heave under the extrusion of the internal support horizontal support force and soil pressure,and then drive the building to have uplift deformation.