Study On Deformation And Support Optimization Of Urban Tunnel Adjacent To Deep Foundation Pit

In recent years,with the increasing shortage of urban land,the building height is increasing,and the foundation pit is getting deeper and deeper.At the same time,the urban pipe gallery integrates all kinds of pipelines,such as power,communication,water supply and drainage,showing great advantages and rapid development.The construction of foundation pit adjacent to the urban pipe gallery starts to appear continuously.At present,there are few researches on foundation pit support and deformation of adjacent urban pipe gallery building.In this paper,based on the foundation pit engineering of the first phase construction project of a square in zhongtie,chengdu,and the particularity of adjacent comprehensive pipe gallery on the west and south sides of the project,the supporting scheme of the building foundation pit is studied,and the single row pile is determined to support the foundation pit.There are four types of single-row pile support,including 8 a-type piles,34 b-type piles,73 c-type piles and 35 d-type piles,totaling 150.According to the foundation pit support scheme,the foundation pit engineering monitoring scheme is designed,and 55 observation points are arranged to monitor the whole construction process of the foundation pit support pile roof horizontal displacement,surrounding ground settlement,deep horizontal displacement of pile body and pipe gallery settlement.The results show that:(1)the construction of foundation pit construction process,the horizontal displacement of the pile head increases,the maximum value is located at west point,13.63 mm,and the utility tunnel excavation construction stage,the horizontal displacement of the point are reduced,the south middle and west point relative peak decreased 16.65% and 12.03% respectively,and then increased in the pipe gallery structure construction stage,but the overall is still less than its peak at the end of the building foundation pit construction phase of the horizontal displacement.(2)the ground settlement of the building foundation pit near the pipe gallery increases rapidly in the construction stage of the building foundation pit.After the completion of the excavation,the east midpoint is the maximum settlement point,reaching 2.76 mm,and then grows slowly and becomes stable.(3)the settlement value of pipe gallery foundation pit is mainly divided into three stages,among which the building foundation pit excavation stage grows slowly while the pipe gallery foundation pit excavation stage increases rapidly,and gradually stabilizes in the pipe gallery structure construction stage.Its maximum displacement is located at the observation point of the pipe gallery on the south side,with a maximum value of 2.85 mm.Finally,based on the finite element method and the modified moorcoulomb constitutive relation,the numerical simulation of the construction process of the foundation pit is carried out,and the accuracy of the simulation is verified by comparing with the monitoring data.By applying the verified numerical simulation method,this paper analyzes the influence of the construction changes of building foundation pit,pipe gallery foundation pit and pipe gallery structure on the horizontal displacement of foundation pit supporting pile roof,and optimizes the supporting structure of row pile of building foundation pit,and the results show that:(1)the utility tunnel excavation,the structure of the utility tunnel construction first,cause the supporting pile top horizontal displacement is smaller than building foundation pit construction first,largest and horizontal displacement obviously uneven around building foundation pit,and the utility tunnel and construction of foundation pit spacing is small even more significant,southwest first peak displacement relative to the construction of foundation pit construction on both sides,reduce 3.3 mm and 5.47 mm respectively,south of the decrease of the gallery and the foundation pit of the amplitude is bigger because spacing smaller,for supporting pile top horizontal displacement,pipe rack foundation first,and then construction pipe rack structure,the excavation construction of foundation pit for the optimal construction sequence.(2)optimizing the pile diameter and distance of the supporting pile near the pipe gallery can ensure the stability of the foundation pit and reduce the engineering cost.Among them,the pile diameter on the west and south sides is 1.4m and 1.3m respectively,and the pile distance on both sides is 2.8m,which is an optimal arrangement.