Research On Large Cross-section Rectangular Jacking Pipe Under Shallow Underwater Overburden

With the underground space further enlarged,rectangular pipe jacking has been applied in constructing more and more urban underground traffic tunnel through water due to its high construction efficiency and space utilization.The implementation of the large cross-section rectangular jacking pipe under the shallow underwater cover is still to be explored so there is still no enough comprehensive calculation theory and mature experience at home and abroad.In regard to a large-section rectangular pipe jacking project under a shallow overburden in Suzhou,the research was made on the force of rectangular pipe jacking and the mechanism of its impact on the ground surface.Several major points of the research are as follows:1.The stress state of rectangular pipe jacking during jacking was analyzed in this paper.Based on the improved calculation method of surrounding rock pressure and friction resistance,the formula of rectangular pipe jacking force applicable to uniform load of upper part was derived.In addition,the application range of the formula for shallow embedment was discussed.Compared with classical theory,the formula has no empirical value and is of high engineering practicability.2.The general law of rectangular pipe jacking on soil disturbance was analyzed in this paper.Based on Mindlin theory and random medium theory,the influence of rectangular pipe jacking on soil displacement considering multi-factors was deduced.Based on volume filling rate,the soil loss parameters of traditional empirical formula and derived formula in this paper were deduced,which laid a theoretical foundation for specific engineering analysis in the following text.3.Based on the monitoring data of rectangular pipe jacking in sand layer of Suzhou,the changes of jacking force and ground displacement during rectangular pipe jacking were analyzed in detail.In addition to the formulas derived in this paper,various jacking force formulas and empirical formulas of surface settlement were selected for calculation.The results of the formulas were compared with the monitoring values to verify the applicability of the formulas for rectangular pipe jacking in sand layers in Suzhou.Finally,suggestions on parameter selection and formula selection for similar projects were provided in this paper.4.Based on rectangular pipe jacking under shallow overburden of river bottom in Suzhou,the mechanical parameters and soil disturbance during construction are pre-analyzed by using the theoretical formulas mentioned above.A numerical simulation model is established to verify the correctness of the theoretical formula.Then,based on the numerical simulation model,the relationship between ground displacement and grouting pressure,jacking thrust and soil properties of rectangular pipe jacking under shallow underwater overburden is studied.Finally,the differences of surface vertical displacement between river bottom area and bank area are compared to provide support for theoretical research of rectangular pipe jacking under river bottom.