Technology Of Retaining And Protecting For Super-shallow And Large Rectangular Section Urban Underpass

With the vigorous promotion of urban comprehensive corridors and the development of civil air defense projects,large cross section underground passageways will be everywhere.The traditional open-cut construction technology needs to interrupt the roads and relocate pipelines,which can easily cause urban traffic jams,environmental pollution,the residents' lives and so on.It is more and more unfit for the excavation method in the road construction in the large and medium-sized cities in China.Therefore,it is urgent to study the supporting technology of the super shallow buried subsurface excavated large section rectangular underground passageway.Because of the similar projects in the past,the open cut foundation pit support method can be adopted,so few studies results can be found using the methods in this study.At present,the existing technologies have the following problems:1)The domestic and foreign design of the pipe shed pre-support are mainly calculated by the simple beam method,the design theory is mainly based on the engineering analogy,the results obtained by these methods are quite different from the actual situation;2)The internal force change of the steel arch,the changing of the pressure of the surrounding rock and the law of the surface subsidence are not clear;3)It is necessary to study the application of the Peck formula method to predict the surface settlement caused by shallow buried tunnel excavation;4)It is difficult to control the ground settlement induced by tunnel construction,and the corresponding engineering measures should be put forward.In view of the above problems,the main research results of this paper are as follows:(1)Through field test analysis,the laws of the internal force of steel arch,the pressure of the surrounding rock and ground settlement of the ultra-shallow buried underground excavation of large section rectangular underground passage in city are obtained.(2)According to the beam Wenkler model of the elastic foundation,referring to the general elastic fulcrum method of foundation pit support design,the calculation model of the super shallow buried pipe shed steel arch frame is established and its mathematical expression is derived.The design method of the super shallow buried and dark excavation large section rectangular underground passage is put forward in combination with the internal force of the steel arch and the law of the change of the surface settlement.(3)According to the measured data of ground subsidence and the superposition pattern of the Peck formula superposition,considering the depth and width of the mid-hole settlement trough can be calculated by the ratio of the width of the hole and the width of the two side holes by a unified method,we established a fitting function in this study.Through it this study carry out the multi-section fitting analysis,and propose the the new method:the ground deformation induced by ultra-shallow buried excavation of large-section rectangular underground channels can be superimposed by the three superficially-excavated channels separately calculated by the Peck formula.(4)Using numerical simulation method,through the numerical analysis of different strata and different excavation methods,the engineering and technical measures for controlling land subsidence are put forward.