| Subway foundation pit engineering because of the particularity of its position,compared with the ordinary deep foundation pit engineering has the excavation face a wider and deeper and the characteristics of the environment is more complex,especially in the busy section of cities,in control of its deformation and the impact on the surrounding environment has a very strict requirements,but in recent years due to the improper supporting structure Settings,such as improper excavation method of engineering accidents have occurred.Therefore,based on the Guangzhou metro group co.,LTD.,the scientific research project "Guangzhou metro line 11 Pazhou station deep foundation pit excavation of a large impact on the adjacent metro tunnel safety analysis and protection technology research" as the backing,by adopting the combination of theoretical design and numerical simulation method,studied the subway large deep foundation pit supporting structure in the process of the excavation support and adjacent rock mass stress deformation law,at the same time take into account the palisade structure embedded in the soil depth,thickness of palisade structure,the support layer and inner factors and the relationship between the stability of foundation pit support stiffness,and the supporting structure has been optimized design,make the foundation pit deformation can satisfy the requirements of the current specification of foundation pit.The main conclusions are as follows:(1)Combining the Pazhou station of Guangzhou metro’s actual engineering situation and the theory of large deep foundation pit supporting structure,selecting the reasonable supporting structure measures,using the finite difference software FLAC3D5.0 establishing the model of deep foundation pit excavation and supporting of foundation pit construction process simulation,got the retaining structure horizontal displacement and vertical displacement of foundation pit adjacent rock mass and supporting structure axial force change rule(2)Based on the Pazhou station of Guangzhou metro,the super deep foundation pit excavation and supporting the results of numerical simulation,a known the ground settlement around the trend first increases then decreases,settlement changes from the initial settlement of "triangle" evolved into the "cure" settlement,maximum settlement is 32.538 mm,it is more than the current specification requires 25 mm of foundation pit safety alarm line;The horizontal displacement of the envelope structure is represented by the shape change of"bump" with a small and large center at both ends.The maximum displacement value is 20.526mm,which is close to the 25mm safety alarm line required by the current foundation pit code.The axial force of the support gradually increases with the increase of the excavation depth,and the axial force of the second and third supports is obviously larger,which is basically consistent with the change trend of the horizontal lateral movement of the envelope.(3)On the basis of the simulation results of foundation pit excavation,continue to calculate and analyze the embedded soil depth,the thickness of the retaining structure,the number of internal supporting layers and the internal supporting stiffness of the retaining structure that affect the foundation pit deformation,from which the influence law of each parameter on the foundation pit deformation is obtained,so as to optimize the supporting scheme.The optimized support scheme increases the depth of the enclosure embedded in soil and an inner support,and reduces the thickness of the enclosure to ensure the engineering economy.After adopting the optimization scheme,the maximum ground settlement around the foundation pit was reduced from 32.538mm to 24.769mm,a decrease of 23.88%.The maximum horizontal displacement of the envelope structure was reduced from 20.526mm to 16.593mm,a reduction of 19.16%.After the optimization scheme,the maximum ground settlement around the foundation pit and the maximum horizontal displacement of the envelope structure were both smaller than the 25mm safety alarm line required by the current foundation pit code. |
