Theoretical Analysis Of Stress Transfer And Its Application In Large Cross Section Tunnel Constructed By Twin Side Heading Method

The development of underground rail transit greatly facilitates travel and improves the quality of life.With the increase of urban population,people have higher and higher requirements for increasing the volume of single passenger transportation of underground transportation,and the span of subway tunnels is becoming larger and larger.The proportion of large section subway tunnel in tunnel engineering is increasing,it can be said that underground rail transit has ushered in a new era of "large section".The large-section tunnel has a larger section and a flat structure.The construction methods are usually carried out by dividing the section into several small caverns and connecting the small caverns into a whole according to the order of excavation and support.This method can ensure the gradual and slow release of the stress of surrounding rock and avoid excessive deformation of surrounding rock caused by excessive stress release at one time.The surrounding rock and support stress vary in each excavation.The total stress of the supporting body increases with the increase of the number of caverns,the total stress of surrounding rock decreases,and the construction of adjacent caverns is carried out.Part of the stress of the surrounding rock is transferred to the surrounding rock of other regions,and part of the stress is increased.Support structure transfer,throughout the construction process is the process of continuous flow of stress.This paper studies the process of stress transfer in each construction section in order to focus on the risk area of excavation support and puts forward an effective method to deal with the stress concentration phenomenon in some areas.The purpose of tunnel support is to limit the deformation of surrounding rock,and the surrounding rock and support become the structures to bear the load from the stratum,which is essentially the same as most structural damage strengthening works.According to this characteristic,this paper first puts forward the transformation ratio formula of stress Zhang Liang invariant and the energy conversion of virtual strain energy of deformation body based on the principle of stress Zhang Liang invariant and virtual work.The theory of stress transfer expressed by shift ratio,which quantifies acomplex stress state by a single stress invariant modulus length,and thus realizes the comparison and calculation of stresses.By calculating the ratio of virtual strain energy before and after reinforcement,the change of virtual strain energy of the original structure is expressed indirectly,so as to show the energy change of the structure before and after the second deformation.This theory can be applied to tunnel engineering and any reinforcement works aimed at improving structural reliability.Secondly,through the large-scale finite element software ANSYS,the construction process of the large-section tunnel with double-side wall with middle wall is carried out in Urumqi second bid section and three-new section large section tunnel.By dynamic simulation,the stress and displacement of the key points of surrounding rock and the variation of supporting axial force bending moment with each construction section are summarized and analyzed.Finally,combined with the data of model calculation,the universal stress transfer theory is applied to the construction of large section tunnel,and the first and second invariants of stress Zhang Liang are calculated for the key points of surrounding rock of each construction section.The influence coefficient of the fictitious strain energy of surrounding rock restrained by support and the ratio of energy transfer of surrounding rock in adjacent two construction sections are studied and analyzed,and the transfer of comprehensive stress of key points of surrounding rock in each construction section is analyzed.The change of fictitious strain energy of surrounding rock under the constraint of lining in a certain range.The tunnel excavation method in this paper is different from that in this paper.Because of the large span and the single tunnel and double lines in the tunnel,the design of the partition wall in the excavation section has dual functions,which can be used as a good supporting structure and divided into functional areas.The common characteristic of the transformation ratio formula of stress Zhang Liang invariant and the energy transfer ratio of virtual strain energy of deformation body in stress transfer theory is that they are independent of the selection of coordinate system.It can truly express the comprehensive stress change and transfer of the key points of surrounding rock,and the change of virtual strain energy of surrounding rock.