Study On Mechanical Properties And Design Method Of Functionally Graded Lining Of Subway Tunnel Deep Buried

With the continuous advancement of urbanization,the development of deep underground space has gradually become a trend.For deep subway tunnels,due to the increase of loads,the lining will have higher requirements for deformation and waterproof properties,which will lead to a dramatic increase in the cost.In order to reduce the lining cost,and at the same time,the deformation and waterproof properties of the lining structure can meet the requirement,the concept of functionally graded material is introduced into the design of the lining structure.In this paper,the elastic-plastic mechanical properties of functionally graded lining are studied by the theoretical analysis and numerical simulation,and the design method is proposed.The main achievements are as follows.（1）The theoretical model of the functionally graded lining under specific elastic modulus function is established,which is suitable for the cylindrical structure of t/R≤0.2 The results show that the influence ofλon internal force and deformation is much greater than that of a and b.In the case ofλ＜1,if a₁=b₂,a₂=b₁,the maximum deformation of functionally graded lining is smaller when a>b.In addition,a and b does not affect the distribution mode of the internal force and deformation.Finally,the difference between theoretical analysis and numerical simulation is about 8%at the maximum deformation.（2）A general calculation model of functionally graded lining considering and not considering the interaction with surrounding soil is established to study the influence of a,b and thickness parametersλ_t on elastic mechanical properties of lining.The results show that the parameters a and b do not affect the internal force distribution mode and deformation mode of the lining,and the power exponent n has little effect on its mechanical properties,which can be fixed to 1.Similar to the conclusion of theoretical study,when a>b,the maximum deformation of functionally graded lining is smaller,and the elastic modulus functionⅡhas greater advantages in reducing the deformation.In addition,the influence of thickness parameter on the mechanical properties of functionally graded lining is much greater than that of elastic modulus parameter,so the design idea of functionally graded lining is obtained.If the concrete with the maximum mark is given,the internal force and deformation of the functional gradient lining are reduced by increasing the thickness,and then the concrete mark of the lining part is reduced by adjusting the elastic modulus parameter,so as to reduce the cost.（3）The elastic-plastic model of homogeneous lining is established,and then the distribution of elastic modulus of functionally graded lining is determined according to the failure characteristics of homogeneous lining,so as to establish the elastic-plastic model of functionally graded lining,and finally the design method of functionally graded lining is obtained.When the elastic modulus functionⅠis selected,the concrete mark of homogeneous lining is arranged in zone IV,and the concrete mark of zone III,II and I decreases successively,and the adjacent concrete mark is selected.When the elastic modulus functionⅡis selected,the concrete mark of homogeneous lining is arranged in zone I,and the concrete mark of zone II decreases by three grades.The economic comparative analysis shows that the functionally graded lining with elastic modulus functionⅠis more economical,but the functionally graded lining with elastic modulus functionⅡis more convenient for construction.Compared with the homogeneous lining,the material cost can be reduced by 5.6%～9.1%.