Study On Effect Of Underground Pipelines Due To Metro Station Foundation Pit Excavation

Fuminglu Station foundation pit engineering of Ningbo Metro Line 1 is taken as study background in this dissertation, because there exist four underground pipelines nearby this foundation pit and all lies in the scope of 3.5~7.8 m. Therefore, how to ensure the safety of the underground lines in foundation pit construction is a key to this engineering. Such methods as field test, theoretical analysis and numerical calculation are combined to deeply study the influence of foundation pit excavation on underground pipeline, and the following conclusions are obtained:(1) Firstly, basing on field test, the displacement of pipeline and diaphragm wall, the working force of internal struts and settlement of surrounding road are monitored, and especially the horizontal and vertical displacement of the pipeline during the foundation pit excavation is discussed. From analysis of the field test data, it can be concluded that: The settlement of the underground pipelines is closely related to the distance from its location to the foundation pit, the buried depth and so on of the pipelines; The settlement of underground pipelines is greatly influenced by the scheme of excavation and support types; Take the coal gas pipeline as example, its vertical displacement can be expressed as cubic polynomial.(2) Secondly, the elastic foundation beam theory is adopted to discuss the deformation and mechanical mechanism of underground pipeline. The calculation method of pipeline displacement based on elastic foundation beam theory from field test displacement curve is firstly put forward. Taking the coal gas pipeline as example in this dissertation, its vertical displacement curve equation is obtained from elastic foundation beam theory and Matlab software.(3) Finally, numerical method is adopted to analyze the influence of foundation pit excavation on underground pipeline, in which underground pipeline is regarded as shell element, and contact between diaphragm wall and soil. From the calculation and analysis, the following results are obtained:①Because the construction of diaphragm wall and reinforcement of soil in foundation pit scope, the underground pipelines produce about 10cm and 30~50cm initial horizontal and vertical displacement respectively. Then, with excavation and support of foundation pit going on, the displacement of every pipeline all decrease. In the end of excavation, the final horizontal displacement of every pipeline is 3～7cm, and the final vertical one is 7～20cm; Adding internal struts can effectively reduce the displacement.②Through analyzing the internal force change law of different pipelines during excavation of foundation pit, the internal force of power pipeline is larger. Meanwhile, with the increase of excavation depth, only the force of gas pipeline varies greatly in early period, then goes stable. Also, the force of every pipeline can be evidently improved with internal struts support during excavation.③Though the three-dimensional numerical calculation, from the aspect of the vertical displacement, it is found that the pipeline sinks during initial excavation. And along the length direction of the pipeline, the sink nearest to the foundation pit is largest, while towards two ends, the sink gradually decreases. As excavation depth increases, the pipeline is gradually being lifted, which looks like a parabola. However, the horizontal displacement is shown as departure from the direction of foundation pit;④Adding internal struts can effectively reduce the displacement of underground pipelines, to the project in this paper, the displacement with and without internal struts are -0.57mm and -0.78mm respectively, when the depth of excavation is 10m, and the maximum horizontal displacement of the pipeline is reduced about 27%.⑤The elastic modulus of diaphragm wall has great impact on the displacement of underground pipelines.