| At present,the applications of shield tunnel are continuously expanding as the construction conditions are gradually ranging from shallow environment to the deep rocks.However,the applications in deep ground conditions are still uncommon.It is still controversial about the loading characteristics of the segment structures and the interaction between surrounding rock and support structures under deep conditions.Especially for shield tunnels with large cover depth in soft rock,how to consider the characteristics of tunnel excavation and support under the influence of surrounding rock creep,and how to effectively control the surrounding rock pressure are of great significance and engineering value.Based on the Donghuan Tunnel of Guangzhou-Foshan Loop Line,the load-bearing characteristics of segmeantal lining structure is studied according to the analyses of creep properties of surrounding rock and the creep parameter inversion by means of data investigation,theoretical analysis and numerical simulation.Then the surrounding rock pressure control strategy and the interaction between surrounding rock and support structure under deep soft rocks is systematically investigated.The main contents and results are as follows:?1?Based on the results of uniaxial compression creep test in rock interior,a constitutive model is selected to describe the rock creep characteristics.The creep parameters identification program is developed using FLAC3D and MATLAB softwares according to the particle swarm intelligent algorithm?PSIA?,then the creep parameters of rock mass are obtained by inversion analyses.?2?A finite difference element model is established to describe the whole process of shield tunnel construction.The long-term action of the shield tunnel structure with large cover depth in soft rock is studied considering the rock creep effect.The influence of cover depth and section size?diameter?on deformation,internal force and contact pressure of segment structure is analyzed with the deep soft rock condition.?3?The main factors which affect the surrounding rock pressure are defined for the dynamic construction of shield tunnels and the"two-stage analysis method"is applied to the whole construction process of shield tunnel.With separately considering the two stages of a shield tunnel construction,the control strategy of surrounding rock pressure is analyzed by means of convergence-constraint method for shield tunnels in soft rock with large cover depth.?4?The numerical analysis models are established for the first and second stages of shield tunnel construction respectivelybased on the two-stage analysis method.Then the relationship between the overbreak gap,the length of shield and the lag distance of filling layer behind the segments and the displacement and stress release of surrounding rock are analyzed and the effects of surrounding rock stress release ratio,filling layer thickness and filling layer elastic modulus on the interaction between surrounding rock and supporting structure are presented for soft rock shield tunnel with large cover depth.In addition,the control effect of special composite supporting structures comprising segmental lining and bolts on surrounding rock pressure is discussed with further analyses. |
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