机制砂混凝土隧道衬砌结构裂损机理研究

Crack mechanism of machine-made sand concrete tunnel lining

为明确铁路隧道机制砂混凝土衬砌结构边墙环向开裂原因,开展了模筑混凝土短柱承载特性试验,利用基于损伤力学的有限元方法,结合模筑混凝土收缩形变试验,分析了机制砂混凝土的收缩变形特征和偏心短柱的承载特性。借助DIANA10.4程序进一步建立机制砂混凝土隧道衬砌结构的三维数值仿真模型,综合考虑围岩荷载、机制砂混凝土收缩效应以及隧道衬砌结构整体受力状态,探讨了机制砂混凝土隧道衬砌结构裂损机理。研究结果表明:随着混凝土强度等级的提高,机制砂混凝土构件与河砂混凝土构件承载能力与抗裂能力均逐步增强,但延性呈逐渐下降趋势;在模筑混凝土短柱承载特性试验中,混凝土强度等级较低构件(C20、C25、C30)破坏特征呈延性,混凝土强度等级较高构件(C35、C40)破坏特征呈脆性;混凝土强度等级相同的情况下,机制砂混凝土构件抗裂与承载能力较河砂混凝土构件虽有所提高,但由收缩效应产生的收缩应力较大,易导致结构裂损;收缩效应是导致机制砂混凝土隧道衬砌结构边墙处出现环向裂缝的主要原因;在保证结构安全的条件下,应适当减小混凝土强度等级、加强养护,降低机制砂混凝土收缩率,以减少衬砌结构裂损现象的出现。研究结果为解决机制砂混凝土隧道衬砌环向开裂问题提供了参考。

To clarify the causes of circumferential cracking in the side walls of the mechanism sand concrete lining structure of railroad tunnels,a load bearing characteristics test of short columns of molded concrete was conducted.Using the finite element method based on damage mechanics and combined with the shrinkage deformation test of molded concrete,the shrinkage deformation characteristics of the machine-made sand concrete and the load-bearing characteristics of the eccentric short column were analyzed.With the help of DIANA10.4 program,the three-dimensional numerical simulation model of the mechanism sand concrete tunnel lining structure was established.The cracking mechanism of the mechanism sand concrete tunnel lining structure was discussed by considering the surrounding rock load,the shrinkage effect of mechanism sand concrete and the overall stress state of the tunnel lining structure.The results show that with the increase of concrete strength grade,the load-bearing capacity and crack resistance of machine-made sand concrete members and river sand concrete members are gradually enhanced,but the ductility shows a gradual decrease trend.In the test of bearing characteristics of molded concrete short columns,the damage characteristics of concrete members with lower strength grades(C20,C25,C30)are ductile,and the damage characteristics of concrete members with higher strength grades(C35,C40)are brittle.In the case of the same concrete strength grade,the cracking resistance and load-bearing capacity of the mechanism sand concrete members are improved compared with the river sand concrete members,but the shrinkage stress generated by the shrinkage effect is larger,which can easily lead to structural cracking.The shrinkage effect is the main cause of circumferential cracks at the side walls of the mechanism sand concrete tunnel lining structure.Under the condition of ensuring the structural safety,the concrete strength level should be appropriately reduced,maintenance should be strengthened,and the shrinkage rate of the machine-made sand concrete should be reduced to reduce the appearance of the cracking phenomenon of the lining structure.The results of the study can provide a reference for solving the problem of circumferential cracking of mechanism sand concrete tunnel lining.