Research On Load Sharing Ratio Of High Water Pressure Composite Lining Based On Load-structure Method

There are many design concepts for supporting structure in composite lining design,and engineering practice design relies more on engineering analogy.The determination of the load sharing ratio of primary support and secondary lining support structure still lacks a reliable calculation method.In some projects,the support structure design assumes that the secondary lining bears all the loads,ignoring the use of initial support,which is obviously inconsistent with the facts.Therefore,this article is very necessary to study the load sharing ratio of composite lining structures under high water pressure.Based on the engineering background of Gongbei Tunnel,this paper establishes a composite lining calculation model that regards each supporting structure as a joint bearing structure based on the numerical calculation software ABAQUS,and systematically analyzes the internal force and safety factors of the large-section composite lining under external water pressure.The load sharing ratio of the composite lining is studied.The results achieved so far are as follows:(1)The numerical and theoretical solutions of the original cross-section finite element model and the equivalent circular composite beam theoretical model verify the reliability of the ABAQUS in analyzing the internal force of the composite lining(IFCL).(2)Analyze the mechanical properties of the composite lining under the two load conditions of surrounding rock pressure and surrounding rock + external water pressure,and before and after thawing.The research results show that under the pressure of surrounding rock + external water and after thawing,the increase of internal force of initial support is greater than that of secondary lining.The reduction of the safety factor on each section of the initial support is more obvious than that of the secondary lining.The secondary lining’s safety factor decreases by an average of 5%,after thawing which is negligible.The internal force analysis shows that when the load on the composite lining increases,the increased load is more borne by the initial support.(3)The internal force and safety factor of each supporting structure change with the change of the friction coefficient.When the load is the same as the supporting structure parameters,the total internal force in the single-layer lining is greater than the total IFCL.The comprehensive safety factor analysis shows that the composite lining structure is better than the single-layer lining structure in the shallow-buried large-section tunnel in the water-rich area.(4)In the model considering the waterproof layer,the internal force of initial support is obviously higher than that of secondary lining.When the load borne by the secondary lining is reduced,but the safety factor may not be improved.The load sharing ratio calculated by the model is obviously lower than that of the secondary lining which belong to the model that only consider the use of the waterproof layer and the theory of composite beams.The use of models that only consider the use of the waterproof layer or the theory of composite beams to determine the load sharing ratio of the secondary lining may result in the design that the secondary lining bears too much load,resulting in excessive structural safety.(5)The thickness of the waterproof layer has almost no effect on IFCL.The change of its elastic modulus can change the internal force distribution of the composite lining to a certain extent.When the elastic modulus of the waterproof layer increases,the safety factor of the composite lining increases too.