Research On Load Sharing Ratio Of Composite Lining In Coastal Tunnel Based On Formation-structure Method

The coastal tunnel is subjected to high water pressure.There are complex ways of force transmission and water conduction among surrounding rock,waterproof layer and composite lining.This paper will study the interface contact forms between different composite lining,as well as the presence or absence of waterproof layer and the different forms of the influence on the internal force characteristics and load sharing of composite lining.In this paper,the internal force characteristics and load sharing ratio of composite lining before and after thawing of frozen ring layer are studied.As the supporting method of mountain tunnel in China and most countries in the world,the composite lining has different views on its design method and concept at present.It is necessary to further explore the load sharing effect of composite lining near the sea.Based on the calculation model of the formation-structure method,this paper studies the internal force characteristics of the supporting structure in different interface contact models between the composite lining,and systematically studies the load sharing law and internal force characteristics of the composite lining in the coastal tunnel.The main contents and conclusions of this paper are as follows:(1)By looking up domestic and foreign literature,combing the current results of researches on load sharing of tunnel composite lining,the structure of composite lining,the calculation theory,and the method of evaluating the safety of the supporting structure have been summarized.What’s more,the analytical method model has been described to solve the force transmission coefficients of the primary support and the secondary lining in the simplified circular lining under the "superimposed beam".The influence of the contact between different forms of lining and the interface contact state of different forms of waterproof layer on the force of the composite lining has also been discussed.(2)Based on the modeling idea of formation-structure method,a three-dimensional solid model of the underground excavation section of Gongbei Tunnel has been established by numerical simulation software ABAQUS,and the equivalent freezing circle formed by tube curtain and frozen soil has been studied before and after thawing.The changing law of load sharing ratio between each layer of the composite lining structure has also been studied.As the results show,the maximum axial force and bending moment of each layer of the composite lining before and after thawing are both located at the foot of the wall,which is the most unfavorable position of the force;the thawing of the freezing ring increases the overall internal force of the composite lining,but does not affect the distribution law of internal force of the composite lining.Before and after thawing,the primary support load sharing proportion is the largest,which is the main bearing structure.Triple lining load sharing ratio less than 10%,only as a safety reserve.(3)The load sharing ratio of the primary support is the largest,and the load sharing ratio of the tertiary lining is the smallest,regardless of whether the waterproof layer is installed between the lining.After thawing,when the waterproof layer is installed,the proportion of the load sharing of the tertiary lining is much larger than that of the non-waterproof layer,reaching30.0%,and only 9.5% when the waterproof layer is not installed.(4)The load ratio of the tertiary lining before and after thawing has increased a lot,from 14.6% to 30.0%,when the lining and the waterproof layer are closely attached.However,when the separation between the waterproof layer and the lining is allowed the increase of the load sharing ratio of the tertiary lining increases from 30.7% to 33.9%,and the increase is not obvious.(5)The shear force between the lining interfaces has a more clear influence on the axial force distribution law of the composite lining,while few effect on the bending moment distribution law.Whether there is a shear force between the lining interface has a greater impact on the internal force of the spandrel,arch toe and wall toe.When there is shear force,the arch shoulder and arch foot of the outer lining are disadvantageous,while the wall foot is advantageous.On the contrary,for inner lining,the arch shoulder and arch foot are favorable,but the wall foot is unfavorable.(6)Whether there is adhesion between the lining interfaces has a significant effect on the distribution law of the axial force and bending moment of the composite lining.When there is no bond between the linings,the axial force and bending moment on the outer lining are generally larger than when there is bond between the linings,and the axial force and bending moment on the inner lining are relatively small.At the same time,the safety factor of the outer lining is smaller,while that of the inner lining is slightly larger.