Study On Mechanical Characteristics Of Micro Steel Tubular Pile Supporting Structure Of Foundation Pit Based On Distributed Fiber Sensing Technology

With the proposal of China ’s " new infrastructure " plan,the urban rail transit system will be increasingly improved,and the subway construction process will be accelerated.In the face of complex construction conditions,the stability of foundation pit support structure will become an important issue.In this thesis,the micro steel pipe pile supporting structure of the foundation pit of Houpantao Village Station of Xuzhou Metro Line 3 is taken as the research object.The distributed optical fiber sensing technology is used to determine the flexural modulus of the cement slurry steel pipe pile through laboratory tests and field measurements.The deformation characteristics of the micro steel pipe pile and the rock and soil behind it during the excavation of the foundation pit are studied.The strain,deflection and bending moment distribution of the micro steel pipe pile are analyzed,and the stability of the foundation pit supporting structure is evaluated.The conclusions of the thesis are as follows :(1)According to the stress characteristics of the supporting structure of the foundation pit,the deflection-strain calculation formula of the micro steel pipe pile is derived based on the measured strain of the distributed sensing fiber.Based on the mechanical model of simply supported beam,the elastic-plastic ultimate bending moment of cement slurry steel pipe pile composite is theoretically analyzed and verified.(2)Based on the data of optical fiber strain,deflection and bending moment,the flexural performance of cement slurry steel pipe pile is studied.The influence of filling material on the flexural bearing capacity of steel pipe pile is analyzed.The flexural strength of steel pipe pile is linear with the strength of filling material.The elastic modulus of steel pipe piles with different filling materials is obtained.Based on the bending moment data of steel pipe piles,the catastrophic state of steel pipe piles is determined.(3)According to the interaction characteristics between the foundation pit supporting structure and the rock and soil behind the pile,the mechanical model of steel pipe pile deformation is constructed.The stress evolution mechanism of steel pipe pile under different excavation depths and the deformation evolution characteristics of steel pipe pile in soil-rock structural plane are discussed.(4)The soil pressure,deflection,bending moment,shear force distribution of micro steel pipe pile and the safety factor of foundation pit supporting structure are calculated by using Lizheng deep foundation pit software.Based on the software simulation results and the calculated deflection of the sensing fiber,the basis is evaluated.