Shield Structure Under Consideration Ofjoint Effect And Differential Settlement Study Of Tunnel Force Characteristics

With the operation and use of shield tunnels in China’s metro cities,various problems have arisen,and scholars and experts have progressively researched the relevant aspects of shield tunnels.At present,a great deal of research has been carried out on various aspects of shield tunnel mechanics and structural properties,and considerable results have been achieved.In the transverse dimension,the key point of research is the influence of the annular joint on the force deformation of the lining ring;in the longitudinal dimension,the key point of research is the longitudinal force response and deformation of the tube sheet induced by the differential settlement of the tunnel.In this paper,through model tests and numerical simulations,the deformation and force characteristics of the tube sheet in shield tunnels under the influence of different joints and differential settlement effects are analysed and discussed respectively.The main research contents and results are as follows:(1)A "spring + bolt" pipe joint design method was proposed to simulate the prototype pipe bolt joint,and the equivalent analysis of tensile and flexural stiffness was carried out to calculate the equivalent conditions of the joint and the prototype bolt joint,and then the feasibility of the model pipe joint was verified through comparative tests and actual measurement data.The results show that this model joint is operable and suitable for relevant model test studies,and can be used as the basis for later model test studies.(2)Based on the designed joint model,stacking model tests were carried out on the homogeneous circular tunnel,slotted tube sheet and designed joint tube sheet respectively.The results show that: the joint stiffness reduction and discontinuity have certain effects on the convergence deformation,section bending moment maximum and distribution of the tube sheet,and have less effect on the axial force;the existence of the annular joint of the tube sheet causes the bending moment distribution to be readjusted,and the more dense the joint arrangement is,the more severe the adjustment is,which leads to This leads to a decrease in bending moment in some areas of the tube sheet and at the annular joints,but the maximum bending moment value of the tube sheet is increased instead.(3)A refined numerical model of the shield tube sheet that can take into account the stiffness reduction,discontinuity and preload of the annular joint is developed and compared with the homogeneous circular ring and slotted tube sheet,and the numerical feasibility is verified by combining the previous model tests.The study shows that: the stiffness reduction causes the zero point,extreme value and envelope of the bending moment to shift upwards;the discontinuity increases the maximum bending moment by nearly 10%,and a small amount of joint opening occurs;increasing the preload force can effectively reduce the transverse deformation of the tube sheet,but too much will also aggravate the tube sheet breakage,so the balance between the transverse deformation of the tube sheet and the local stress concentration damage should be grasped when applying the preload force.(4)The shield tunnel structure model tests were carried out on the premise of considering the longitudinal joints,with the following conditions:(1)the unevenness of the underlaying soft and hard ground,and the local stacking load,etc.The test results show that:(1)the unevenness of the underlaying soft and hard ground causes the tunnel settlement peak to increase abruptly by nearly 91%,with the peak settlement occurring on the soft side of the soil layer mutation,and also causes the peak lining convergence to increase by nearly 42%,occurring in the hard soil area;(2)the local The impact of the stacking on the moment distribution of the tube sheet is small,but the impact on the extreme value is large,especially at the top and bottom of the arch where the moment increases significantly;(3)the tunnel in the soft soil area of the structure of the internal force is obviously variable,so that the tunnel lining moment distribution abruptly changed,especially at the bottom of the arch where the bending moment suddenly increased by 110%,making the tube sheet more likely to produce crack damage.The structural reinforcement should therefore be strengthened in areas of soft soil to resist adverse forces.(5)The structural response of the shield tunnel to longitudinal internal forces,structural misalignment and joint opening under uneven and localised mounding loads was further analysed by means of numerical simulations,and the feasibility of the numerical model was verified in conjunction with the previous test results.The study shows that:(i)the longitudinal bending moment increases rapidly in the vicinity of the foundation junction due to the soft and hard unevenness of the underlying strata,and slows down away from the junction;it causes the axial force curve to resemble M along the longitudinal direction,peaking at the left and right sides of the strata junction and decreasing at the centre of the junction;(ii)the longitudinal misalignment is concentrated on the soft side of the soil junction,and its misalignment value is5-6 times higher than that of the hard side,while the stress concentration is more intense near the top and bottom of the vault.(iii)Increasing the preload of the ring joints on the soft soil side can effectively reduce the sum of differential settlement,but with the increase of preload its effect is weakening,the preload is 300-350 k N when the rebound,the curve rebound because:preload increases to a certain extent,the adjacent two pipe piece stiffness is obviously increased,resulting in the stiffness difference with the other side increased,but the total settlement increased slightly.