| Utility tunnel has outstanding advantages in solving urban municipal pipeline laying,maintenance and operation,and has played an important role in improving urban resilience,and has become one of the urban lifeline projects in the 21st century.Xi’an urban geological conditions are special,so far the development of 14 ground fissures,basically all over the whole urban area.The unique urban geological environment has put forward new problems and challenges for the construction of utility tunnel.As a long linear underground structure,the utility tunnel will inevitably cross the ground fissures obliquely.How to deal with the impact of the ground fissure development environment on the structure of the utility tunnel is a scientific research topic that needs to be solved urgently.In view of this,this article takes the utility tunnel project of Kechuang Road in Xi’an as the scientific research background.Using physical model testing,numerical simulation and theoretical analysis as the means,a systematic study was carried out on the deformation and destruction mode,scope of damage and design of structures for disaster prevention of the double-cabin utility tunnel structure obliquely crossing the active ground fissure.The work and conclusions are as follows:(1)A physical model test with a geometric scale of 1:15 was carried out to study the deformation failure mode and failure range of the utility tunnel structure 45°obliquely crossing the ground fissure.The test results show that:With increased hanging wall settlement,a void zone appears at the bottom of the hanging wall structure,and the overlying earth pressure on the void section structure will no longer pass through the cross-sectional shear center,resulting in a concentrated torque in the void section structure.The structure undergoes torsion deformation and even torsion failure,within the range of 2.9D～5.1D(D=0.277m is the height of the centerline of the section)in the foot wall.Then bending,shear deformation and destruction occurred,and the destruction range was within the range of 0.9D to 2.9D in the foot wall.(2)Aiming at the torsional deformation and failure of the utility tunnel,based on the theory of confined torsion of closed thin-walled bars,the analytical solution of torsional deformation of the utility tunnel under the action of concentrated and uniform torques is established;while solving for the concentrated torques,the distribution pattern and characteristics of the contact earth pressure at the top of the utility tunnel in the ground fissure environment are studied,and the calculation method of vertical earth pressure on the utility tunnel structure in the ground fissure section is proposed.The maximum value of shear stress in the cross-section of theutility tunnel structure obtained from the theoretical analysis is 0.39N/cm~2 and the maximum value of positive stress is 13.26N/cm~2,which are in good agreement with the shear stress and positive stress in the cross-section of the utility tunnel structure obtained from the physical model test.(3)Numerical simulation of the structure of the utility tunnel obliquely through the active ground fissure was carried out.The results of the numerical simulation of the deformation damage mechanism show that:at the beginning of the settlement of the hanging wall,the bottom of the structure starts to produce a void zone,the foot wall structure is under overall compression,the hanging wall structure is under overall tension,and the hanging wall undergoes torsional deformation relative to the foot wall;the structure is in a complex bending,shear and torsional stress state,and both horizontal and vertical shear stresses reach their maximum values at the ground fissure.Numerical simulation results of torsional deformation damage show that the twisting angle and shear stress of the utility tunnel structure reach their maximum values at the ground fissure under the action of concentrated torque-uniform torque.The numerical simulation results are in general agreement with the physical model test results and the theoretical analysis results,which verifies the reasonableness of the deformation damage model and the theoretical analysis method.(4)Through the physical model test,numerical simulation and theoretical analysis,it can be seen that the deformation and damage mode of the utility tunnel obliquely through the active ground fissure section is:first torsional deformation damage occurs,then bending and shear deformation damage occurs;the deformation and damage range is from 12.35D in the hanging to 8.64D in the foot wall(D=4.05m is the height of the centerline of the section),and the foot wall structure deformation degree is higher than the hanging wall structure.(5)Based on the current"Code for Design of Concrete Structures","Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts"and the theoretical analysis of this article,the torsion,shear and bending design methods of the utility tunnel obliquely crossing active ground fissures are proposed,and the disaster prevention measures for the utility tunnel structure across the ground fissure section are given,and special deformation joints should be set in sections for the utility tunnel structure across the ground fissure section.The influence of the seaming pattern and the length of the segmented joints on the structural forces of the utility tunnel is discussed through numerical simulations,which show that the use of the seaming pattern with opposite joints can effectively reduce the adverse effects of the activities of ground fissur on the structure of the utility tunnel,and the segmented length of 10m is appropriate. |
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