Analysis On The Building Behaviour Induced By The Excavation And The Protection Of Building With Shallow Foundation In Soft Clay

Excavation will cause a series of complex problems including deformation of retaining structure,soil displacement and settlements of adjacent buildings.Nowadays,the development of underground space is an inevitable trend in central areas of cities.The areas and depths of excavations have been increasing,which have a significant influence on the surrounding buildings.In order to ensure the safety of existing facilities,the requirements of deformation are becoming stricter and stricter.So there are lots of practical meanings to predict the deformation and damage degree of buildings around excavations and to study the protection measures.The characteristics of deformation nearby facilities was analyzed using field data in Hangzhou and theoretical analysis.The key findings are summarized as below:(1)A simplified theoretical method is proposed to predict the additional settlements and axial forces of excavation-adjacent existing building floating piles in soft clay.The soil displacement is simplified as a line or broken line along the depth direction depending on the distance from the excavation.Between 0 and 1.0He,the soil displacement is simplified as a line.And between 1.0He and 1.0He,the soil displacement is simplified as a broken line A hyperbolic model is applied to calculate the skin friction and tip resistance induced by the vertical soil displacement.The parameters of the hyperbolic model are corrected to fit data from in-service piles.Based on the load-transfer curve method,the additional settlements and axial forces are determined.The measured data of 26 piles from two excavation cases in Hangzhou,China,show good agreement with the calculated values and the error between these two values is lower than 30%.Because of the upper structure,the theoretical settlements for piles near the excavation are larger than those obtained from the measured values;for distant piles,this relationship is reversed.(2)An estimation method for building damage level considering the spatial effects of soil deformation around the excavation is proposed.And this chapter investigates the building damage induced by excavation conducted for a three-storey basement in Hangzhou,China depending on the settlement,horizontal displacement and cracks.Surface settlements around the excavations(the depths of excavations are between 15m to 18 m)were analysed to obtain a surface profile along the excavation.The results show that the profile can be simplified to a parabolic model.A damage criterion based on the average state of strain in the distorted portion of the structure was derived considering the spatial effects of soil deformation.Different damage criteria including tensile stress,cracks,distortion(?),and horizontal strain(?x)were used to evaluate the damage level of the building.The result obtained from the damage criterion presented in this paper agrees well with the actual building damage level.(3)This chapter presents an investigation on building settlement induced by excavation in Hangzhou,China.The field observation yielded that pile foundations can obviously decrease the excavation-induced settlement.A theoretical design method of underpinning piles was derived to determine the distribution and length of piles.A hyperbolic model was applied to calculate the skin friction induced by the vertical soil displacement.The parameters of the hyperbolic model are corrected to fit data from underpinning piles.Rigid plastic model was selected to calculate the inner friction resistance of soil plug.Based on the load-transfer method,the new additional settlements can be obtain.If the settlement does not meet the requirement,it is reasonable to adjust by increasing the pile length.