| The utility tunnel has become an important infrastructure in urban modernization construction,because of its characteristics of modern,scientific and intensive.It is necessary to set up multiple working shaft along the utility tunnel to provide the necessary space for the tunnel excavation and pipeline layout and maintenance.The working shaft is small plane size and large excavation depth,which has obvious spatial effect of structural performance.As well as,in coastal and riverside soft soil areas,the utility tunnel construction should pay attention to the influences of excavation deformation of working shaft on structural performance.Taking working shaft project of Gaishan-Dongtai 220 k V transmission line tunnel as background,the structural performance of working shaft in soft soil area is analyzed.The research follows the principle of exploring the law of plane model of deep and large foundation pit first and then conducting spatial effect analysis of working shaft foundation pit.Based on the principle,the behavior of working shaft foundation pit and structural performance of working shaft considering excavation deformation are analyzed.The main research contents and achievements are as follows:(1)A verified numerical method of foundation pit plane model considering the small strain characteristics of soil is used to systematically analyze the influence of foundation pit design parameters and geological conditions on foundation pit deformation.It is found that the most critical factors affecting the deformation of foundation pit are excavation depth,excavation width,thickness of soft soil layer and compression modulus of soft soil layer.Considering the influence of various key factors on the deformation of foundation pit,the prediction function of excavation deformation under plane strain state is proposed.Verified by several measured data,the proposed plane strain state deformation function of foundation pit can well predict the deformation of deep and large-scale foundation pit in soft soil area.(2)The parameter analysis of the spatial deformation characteristics is conducted by the 3D numerical method and the quantification of the spatial deformation characteristics are described by the spatial effect index PSR.Combined with the plane strain state deformation function of foundation pit,the spatial deformation prediction function of foundation pit is proposed.By comparing with the numerical calculation results,it is proved that the spatial deformation function of the foundation pit can predict the spatial deformation of the working shaft foundation pit.(3)Based on the numerical calculation results,the pattern,range and value of the horizontal and vertical deformation of deep soil behind retaining wall are analyzed.Combined with the analytical formula obtained by the virtual image method,a method for estimating the deep soil deformation behind retaining wall by the lateral deformation of the retaining structure is established,which can provide evidence to evaluate the impact of excavation on the surrounding environment.(4)According to the deformation characteristics of multi-struts support and the spatial effect of working shaft foundation pit,the space earth pressure calculation method of support in non-limiting state is established.Verified by the measured data,this method can both be used to calculate the earth pressure of multi-struts support and the earth pressure of working shaft support.(5)Based on the traditional incremental design method of support structure,a modified design method considering excavation deformation and spatial effect is established.In addition,a method of stability against basal heave considering the width and spatial effect of foundation pit is established to provide a suggested depth for the foundation pit support structure of the working shaft.The modified incremental method is introduced and verified by a case,which can be a reference for the design of working shaft support structure.(6)Using the 3D numerical method,the deformation and internal force of the main structure of the working shaft during construction and use phase are analyzed.The internal force and deformation of the composite wall and each floor are calculated by using the frame model incremental method.Comparing the calculation results of the frame model with the results of the3 D numerical model,it is verified that the proposed frame model incremental method is reasonable and accurate for the design of the working shaft structure.This method can provide a reference for the design of the working well structure. |
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