Research On Deformation Response Characteristics Of Shield Tunnel Under Adjacent Soil Disturbance

This study focuses on the deformation response characteristics of shield tunneling lining under adjacent disturbances.Firstly,an elaborate numerical model of one ring incorporating reinforcing rebar,bolts,groove and tongue,interface friction and concrete segments was established.The response characteristics of shield tunnel,which including deformation mode,bending moment and axial force,cracks,stress of tensile rebar,stress of bolts and compressive strain of concrete;and its internal relation under overlying loading and overlying unloading conditions were analyzed systematically.The plastic hinge theory was introduced to reveal the failure mechanism of shield tunnel,and the control indexes during construction under different working conditions were presented.The similarities and differences of structural response characteristics and failure process under different working conditions were proved.Second,an elaborate numerical model of three rings incorporating reinforcing rebar,bolts,groove and tongue,interface friction and concrete segments was established to analyze shearing force between rings,maximum dislocation,stress of bolt and compressive strain of concrete adjacent to bolt hole under shear load.Further,the variation of shear stiffness and its cause have been analyzed.Compared with the theoretical calculation,the distribution of modification coefficient of longitudinal shear stiffness can be obtained.And then,the reasonable value range and the optimal value of modification coefficient of longitudinal shear stiffness was given based on the mathematical statistics method.Finally,based on Timoshenko Beam Simplified Model,reasonable modification coefficient of longitudinal shear stiffness has been adopted,an analytical model for soil-tunnel interaction analysis of overlying long-distance excavation was established,and the influence mechanism of long distance foundation pit excavation on the uplift deformation and groundwater leakage of the tunnel was also discussed.Main research results are as follows:(1)The deformation response characteristics and failure process of tunnel lining under the overlying loading has been revealed.The results show that convergent deformation under overlying loading condition is always in the "horizontal oval" mode,and the vertical convergent deformation increases as the load increases.The bending moment and axial force also increase with the increase of load,and the direction of which does not change.Therefore,the stress state and distribution of bolts,rebar and concrete do not change.For overlying loading condition,the cracks mainly appear in the loading stage,and the cracks only penetrats along the longitudinal direction,but not along the thickness direction.The convergent deformation of the structure under overlying loading condition can be divided into linearly increase stage,quasi-linearly increase stage,nonlinearly increase stage and failure stage.The structural stiffness continues to decrease with the increase of load,but the cause of the stiffness loss in each stage are different.the cause of structural stiffness loss of linearly increase stage,quasi-linearly increase stage,nonlinearly increase stage and failure stage are concretes are in plastic tensile state,intensive cracks and the stress-strain relationship of concrete coming into decline phase,the plastic hinge formation,concrete crushing,respectively.(2)The deformation response characteristics and failure process of tunnel lining under the overlying unloading has been revealed.The results show that convergent deformation in loading stage of overlying unloading condition is in the "horizontal oval" mode,and gradually changes to "vertical oval" mode as the load decreases.Under the overlying unloading condition,the bending moment and axial force increase with the increase of load in the loading stage,and then decrease first and then increase with the decrease of load in the unloading stage,and the direction of bending moment changes,which leads to the change of the stress state and distribution of bolts,reinforcing rebar and concrete.Therefore,cracks appear in the loading and unloading stages of the overlying unloading condition,the new cracks and the old are connected along the thickness direction.Therefore,compared with the overlying loading condition,the overlying unloading condition is apt to cause groundwater leakage.The convergent deformation of the structure under the overlying unloading condition can also be divided into linearly increase stage,quasi-linearly increase stage,nonlinearly increase stage and failure stage.In the linearly increase stage,quasi-linearly increase stage,and failure stage,the change law and its reason of structural stiffness are identical to the overlying loading condition.However,in the nonlinearly increase stage,due to the change of the state of bending moment,the concrete stiffness recovers,therefore the structural stiffness significantly increases,followed by the continuous decrease due to the occurrence of intensive cracks and the formation of plastic hinge,which is very different from the overlying loading condition.(3)The failure mechanism has been proposed,that is,the amount of plastic hinge exceeds the degree of statical indeterminacy is the root cause of structural failure.For one segmental ring,the formation of 4 or more plastic hinge is the fundamental cause of structural damage.On this basis,it is clear that the convergent deformation of the structure under the overlying loading condition should be less than 59.50 mm and the unloading ratio under the overlying unloading condition should be less than 0.68.Compared with the plastic hinge forming process,it is found that the load duration of the structure failure under the overlying unloading condition is much smaller than that under the overlying loading condition,so the failure process under the unloading condition is closer to "brittle failure",which should be paid more attention in engineering practice.(4)The reasonable range of modification coefficient of the longitudinal shear stiffness and optimal value has been given.An elaborate numerical model of three rings incorporating reinforcing rebar,bolts,groove and tongue,interface friction and concrete segments was established to analyze variation of shear stiffness under shear load.Compared with the theoretical calculation,the distribution range of the modification coefficient of longitudinal shear stiffness is obtained as [0.2,1.1].The reasonable value range obtained based on the mathematical statistics method is [0.4,0.8],and the optimal mean distribution is [0.64,0.68].(5)An analytical model for soil-tunnel interaction analysis of overlying excavation was established.The soil-tunnel interaction was simplified as the Timoshenko beam resting on Winkler foundation,based on superposition principle,the proposed model was adopted to anaylse a case history.The result show that the proposed analytical model is reasonable.The groundwater leakage generally occurred between the location with the maximum opening of joint and the location with the maximum shearing dislocation.The lesson from this was that not only the total deformation but also the joints deformation caused by differential settlement should be concerned in practice.According to the statistical analysis,the shear deformation generally accounts for about 21.41%.Despite of this,the induced shearing dislocation is significant compared with opening caused by bending deformation,which can be more important for waterproof in joints.The analytic model should not neglect the shearing deformaiton of the tunnel.