Deformation Behavior Of Adjacent Retaining Walls In Group Excavation

The different construction sequence of each pit and the interaction between the pits in group excavation will result in complex stress condition of both soil and retaining structures.As a result,the limitation of the existing design method is increasing.Therefore,it is necessary to study the interaction mechanism between adjacent excavations and propose design methods for retaining structures subjected to confined soil which can provide usefull guidance for practical engineering.In this paper,active earth pressure and lateral wall deflections in deep excavation group is studied theoretically and numerically.The effect of soil width on transition of lateral earth pressure is investigeted.A new beam-spring approach for earth pressure and wall deflection in adjacent excavation is proposed which couples the wall displacement and active earth pressure.Moreover,an improved numerical method is presented which considers the effect of small strain stiffness on performance of deep excavations.Finally,a comprehensive method is integrated and applied to design and analyze two group excavation case histories at West Shanghai Railway Station and Post-Expo,respectively.The main contributions of this thesis are described as follows:(1)The mechanism of soil width on active earth pressure is investigated and an analytical method is proposed for active earth pressure acting on retaining wall subjected to confined backfill.Discrete-based numerical simulations with confined backfill are conducted to study the lateral earth pressure acting on rigid retaining walls.The effects of backfill width on translation of total lateral earth pressure,the active earth pressure distribution and the total lateral active earth pressure are analyzed.Then the slice element method is adopted to set up the governing equation and it is solved by integration method to yield the formula of total lateral active earth pressure.The difference method is used to solve the formula and finally the inclination of sliding plane and lateral earth pressure acting on retaining wall subjected to confined backfill is obtained.Finally,the proposed method is validated by both the discrete-based numerical simulations and model test data reported in published literature.(2)An analytical model for non-limit active earth pressure with confined backfill is proposed and embedded in the beam-spring approach.First,the mobilization models of friction angles are proposed based on discrete-based numerical results.Then the mobilized friction angles are used in sliding plane model and slice element method to deduce the analytical model for non-limit lateral earth pressure with confined backfill.The analytical model embedded in beam-spring approach by replacing the lateral earth pressure outside the excavation.The static equilibrium governing equation is set up which considers the relationship between lateral earth pressure and wall displacement.An improved beam-spring approach is proposed by an iteration solving approach.Both the analytical model for non-limit active earth pressure and the improved beam-spring approach are verified by discrete element-based numerical simulations and previous published data in literature.(3)A numerical method which considers the effect of small strain stiffness is presented for estimating excavation-induced wall deflection and ground settlement.The proposed numerical method with Mohr-Coulomb(MC)constitutive model considers the effect of small stain stiffness of soil and is validated by a well documented case history.Results show that the proposed method is effective for modeling the excavation-induced wall and ground movements.The proposed numerical method is applied to study performance of excavation adjacent to substructure and two adjacent excavations using idealized models with Shanghai soft clay.Moreover,several numerical simulations with different distances between two excavations are conducted and the effect of soil width on active earth pressure and lateral wall deflection is investigated.(4)A comprehensive method is proposed for design and analysis of group excavation by integrating the proposed active earth pressure formula,the improved beam-spring approach and numerical method.The design and analysis procedure is presented and key parameters in each step are suggested.Five steps are included in applications.First step is preliminary design.Then the critical interaction distance is determined based on soil parameters and excavation depth.After that,the internal force including envelopes of bending moment and shear force of retaining structures is calculated using the improved beam-spring approach.The forth step is to study the interaction between the pits in excavation group.Finally,a comprehensive monitoring program is conducted to ensure the safety of the construction.The proposed comprehensive method is used to design and analyze two group excavation case histories,i.e.Post-Expo group excavation and West Shanghai Railway Station group excavation.Results reveal the practicality of the proposed method.Moreover,it is further verified by the field data.