含水量对季节性冻土区隧道衬砌开裂影响分析

针对我国西北地区一些受季节降雨作用影响明显的季节性冻土隧道,运用传热学和有限元的基本理论,建立ANSYS有限元模型,对不同含水量围岩的温度场、应力场进行模拟研究;探讨含水量对围岩冻结圈范围及冻胀力对衬砌结构体系的影响.计算结果表明:随着含水量的增大围岩的冻结圈变小,冻结深度减小;隧道衬砌内力,随着含水量的增大整体上呈增大趋势; 隧道边墙处拉应力均较大,如当含水量为20 %时,边墙拉应力达到5.6 MPa,这与隧道边墙呈现沿纵向延伸的张拉裂缝相符.依据上述结论,含水量变化对季节性冻土隧道衬砌开裂有较大影响,建议二次衬砌尽量避免采用素混凝土衬砌.

Analysis on Effect of Moisture Content on Tunnel Lining Cracking in Seasonally Frozen Regions

For the tunnels in seasonally frozen soil affected by seasonal rainfall obviously in Northwestern China, FEM model was established with ANSYS by use of the rationale of heat transfer science and finite element method so as to simulate the temperature and stress fields of the surrounding rock with different moisture contents, by which both the effect of moisture content on the freezing-circle range in the surrounding rock, and the effect of frost-heaving force on the lining structure, were discussed. The results show that, as the moisture content increases, the freezing-cricle becomes smaller and the freezing depth decreases; the force inside the tunnel lining presents an increment overall with the moisture content; the tensile stresses on the tunnel side wall are relatively large and, when the moisture content is 20 %, the tensile stress reaches 5.6 MPa, which corresponds to the tensile fractures longitudinally extended on the tunnel side wall. Based on the aforesaid conclusions that moisture content makes a great impact on the lining cracking of tunnel in seasonally frozen regions, it is suggested to try to make the secondary lining to avoid plain concrete structure.