Analysis And Comparative Study On The Construction Methods Of Reverse Operation And Parallel Operation Of Shaft Underground Stereo Parking Garage

In the context of the rapid economic development of our country,the siphoning effect of big cities has strengthened,the urban population is rising strongly,and the problems of urban road congestion and"difficult parking"have been further aggravated.The research and development and construction of underground parking garage technology is very necessary and feasible to solve the problem of"difficult parking"in urban areas.It can effectively improve the existing underground garages that require a large area of underground space and high cost.Based on the engineering characteristics of the underground three-dimensional parking garage of the shaft type,this paper analyzes and studies the force characteristics of the garage foundation pit supporting structure and the main structure by comparing the normal method and the reverse method.（1）Firstly,it explains the structure,working principle and working process of the shaft type underground parking garage,and introduces the detailed steps of using the reverse construction method to construct the shaft type underground parking garage.Compared with the traditional garage,its space utilization rate is higher.It is tall and suitable for construction in urban centers,old communities and other areas.At the same time,the cylindrical support structure has uniform force,safe structure and can effectively exert the good compressive performance of concrete.（2）According to the characteristics of the sand-rock composite stratum in Nanchang area,the supporting form of row piles+ring beam internal support is determined.The row piles adopt the form of occluding cast-in-place piles,which has good water stopping effect and is economical and safe.Using the"plane vertical elastic foundation beam method"combined with the equivalent elastic stiffness coefficient of the ring beam,the three-dimensional problem of the circular foundation pit support structure was simplified into a two-dimensional problem,and the Lizheng deep foundation pit support design software was used to carry out it Overall calculation analysis and stability check.（3）Using the finite difference software FLAC^3Dto carry out three-dimensional numerical simulation of the whole process of excavation of the shaft type underground parking garage,it is concluded that the maximum horizontal displacement of the supporting pile occurs at 0.6 times the depth of the foundation pit,and the supporting pile bears Two-way bending moment;the pit bottom uplift is the largest near the center of the foundation pit;the maximum settlement of the surrounding soil occurs at a distance of 15m from the edge of the foundation pit,and the settlement gradually decreases and approaches zero after 32m from the foundation pit.（4）Using finite element analysis software to conduct a numerical simulation analysis of a wellbore underground three-dimensional parking garage constructed by the top-down construction method,and compared with the calculation results of the conventional normal construction method,it is concluded that the maximum horizontal displacement of the supporting pile is reduced by 40.9%when the top-down construction method is used.,The maximum negative bending moment is reduced by 16.22%,the maximum positive bending moment is reduced by 19.25%,and the pit bottom uplift is only 33%of the normal method,and the ground settlement is only 45.6%of the normal method.The calculation and analysis of the main structure show that the shear force,circumferential axial force and negative bending moment at the connection between the garage floor and the column are larger than other parts of the floor,and the positive bending moment and vertical deformation are greater in the middle of the floor.