| Due to the rapid development of the urban city,the underground stucture is becoming larger,deeper,and more difficult.It is a common phenomenon that the new tunnels are adjacent to existing structure.Based on this situation,a complex project of constructing a new tunnel in the limited space formed by existing underground structures has appeared.The soil movement near the tunnel can be restrained by the existing structure.In return,the existing structure will also be affected by tunnel excavation.Nowadays,there is a lack of research on such kind of engineering problems.Therefore,the study about the influence between the surrounding environment and the construction of new tunnels in limited spaces is of great significance,which can help to ensure the safety of existing structures and the construction of new tunnels.On the base of the combined construction project of Shanghai metro line 14 and the upper existing structure,this study aims to further analyze the influence on the surrounding environment induced by shield tunnelling under enveloped situation.To study the soil disturbance and the performance of existing underground structure,model test,numerical simulation and theoretical analysis were carried out.The research contents and main conclusions in this dissertation are as follows:Firstly,based on the principle of similarity,a model test about shield tunnelling enclosed by upper structure and the bilateral diaphragm wall was carried out to study the general laws of soil movement and deformation of the existing underground structure.The results showed that due to the strong integrity of the existing underground structure,as the rate of soil loss increased,the settlement of the existing underground structure gradually increased and an overall settlement of the existing underground structure would occur.The surface settlement trough also develops gradually.The structure-soil separation zone would appear in the limited space during the excavation of the tunnels,and this area would gradually develop with the increase of soil loss.The structure-soil separation zone was located above the tunnel.Secondly,a refined three-dimensional numerical model was established to obtain the accurate results of soil displacement and the deformation response or interal force distribution of the existing underground structure.The numerical models which contained/excluded the existing underground were also established and the results under these two situations were compared to explore the obstructive effect of the extsting underground structure.The results showed that when a tunnel was constructed in a limited space,the surface settlement region and the maximum surface settlement would be reduced by 65% and 60%,respectively,than that obtained from the condition of no underground existing structure.This phenomenon claimed that the limited area formed by the existing underground structure and the diaphragm wall had a significant blocking effect on the soil movement.The displacement of the soil in the limited space and the ground surface reflected a three-dimensional settlement distribution pattern within the 2.5H(H represented the depth of the shield machine)behind the excavation surface.There was no ground surface uplift during the excavation,which was different from the result obtained from the condition that the construction of tunnel in semiinfinite space.With the progress of the tunnel construction,the bending moment of the top slab of the existing underground structure gradually decreases while the bending moment of the bottom slab keeps increasing.This is because the top slab was mainly "dragged" by the midlle wall.The results obtained from the numerical simulation were also compared with the model test results and field measured data to verify the rationality of the numerical model and the accuracy of the calculation results.Thirdly,the CIU test was employed to study the stress-strain relationship of Shanghai medium and shallow buried soft clay.Based on the CIU test result,a method for determing the degree of soil disturbance for Shanghai soft clay was proposed.The results reflected that the failure shear strain of the Shanghai No.(3)and No.(4)soft clay was around 5.48%.By combining the judge criterion and the numerical simulation,the soil disturbance zone and the distribution law of soil disturbance caused by construction of tunnelins in limited space were obtanined.The resulted showed that the soil disturbance zone was a “butterfly” shape.The distance between the upper boundary of the soil disturbance and the tunnel was 0.44R(R represented the radius of the tunnel),which is 34.3% less than the distance in semi-infinite space.The distance between the lower boundary of the disturbance zone and the bottom of the tunnel was 0.43 R,which is 31.7% less than that in the semi-infinite space.The distance between the boundary of the disturbance zone and the waist of the tunnel was 1.1R,which is 14.1% less than that in the semi-infinite space.When the edge of the soil disturbance zone did not reach the existing underground structure,the soil disturbance zone and the distribution law of soil disturbance degree remained the same.Based on the distribution law of soil disturbance zone,the definition of three-sided-eneveloped finite space was proposed.At last,through analysis of the interaction mechanism between shield tunneling machine and soft soil,the modified iterative calculation of the three-dimensional soil displacement in the limited space was proposed.In addition,the “existing underground structure-soil” coupling deformation calculation method was also proposed.This method can calculate the deformation of the existing underground structure and the displacement of the soil in the limited space.Through this method,the threedimensional deformation distribution of the existing underground structure and the soil along the direction of shield tunneling can also be obtained.The validity of the proposed analytical method was verified by numerical simulation results. |
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