Study On Influence Law Of Shield Construction On Underground Pipeline In Fu-Nan Section Of Nanning Subway

It is of great theoretical significance and engineering value to carry out the study on the stability of the excavation face of shield tunnel construction in the water-rich gravel stratum in Nanning and to induce the deformation law of existing pipelines.Based on the Fu-Nan section tunnel of Nanning Urban Rail Transit Line 2,the thesis carries out research work by combining theoretical analysis,numerical simulation and on-site measurement.The main contents and conclusions include:(1)The main influencing factors and pipeline deformation mechanism of shield tunnel construction pipeline are analyzed,including soil layer parameters,construction parameters and pipeline parameters.The pipeline deformation is the formation loss caused by the shield tunnel construction caused by the pipeline layer.The stress redistribution further causes the corresponding stress of the pipeline to undergo corresponding deformation;according to the distribution of the additional stress on the pipeline,the reason for the corresponding failure mode of the pipeline is given.(2)The numerical solution of vertical displacement of shielded tunnel construction to existing pipelines is obtained by two-stage displacement method,and the sensitivity analysis of relevant parameters is made.The results show that the formation loss rate is the most significant for pipeline settlement.Based on the three-dimensional silo model,the calculation method of the ultimate retaining force of the shield tunnel of the water-rich gravel stratrum is obtained.The rationality of the calculation model is verified by numerical simulation method,and the stability of the excavation surface is obtained.The range of values of the support force is recommended for the reconstruction plan of the shield tunnel with rich water and gravel stratum.(3)FLAC3D numerical calculation is used to study the deformation law of underground pipelines under different buried depths in shield tunnel construction,and the distribution of circumferential and vertical stresses of pipelines after the construction of left and right tunnels is analyzed.The surface settlement curve induced by the left-line shield tunnel construction is Gaussian curve distribution,and the surface settlement curve of the ground settlement curve induced by the right-line tunnel construction is“W”-shaped.When the pipeline and the tunnel are at 90°,the pipeline settlement curve generally obeys the Gaussian curve.The maximum settlement is located directly above the tunnel axis.(4)An on-site monitoring plan for surface settlement and pipeline deformation was developed and a measured study was carried out.The monitoring results show that the measured curves of surface and pipeline settlement are basically consistent with the trend of FLAC3D predicted settlement curve.The research conclusions have reference value for similar projects in Nanning.