浅埋隧道局部存水冻胀作用机制与安全性评价

为揭示寒区隧道局部存水冻胀作用机制并提出有效的衬砌结构安全评价方法, 设计了三维地质力学模型试验, 通过设置3种积水范围冻胀试验工况, 观测冻胀过程中裂缝开展和衬砌结构受力等情况; 改进了局部存水冻胀数值计算方法, 建立了基于岩体力学法并耦合冻胀力和围岩荷载的冻胀数值模型, 对比了不同存水位置、不同局部存水厚度和不同存水范围下隧道冻胀力和结构内力的变化规律, 进一步揭示了局部存水冻胀对隧道受力的影响机制, 评判了衬砌结构的安全性。分析结果表明: 局部存水冻胀具有显著的区域性特征, 衬砌冻胀开裂发生在局部存水与非存水交界处, 冻胀力大小取决于交界处冻胀产生的应力集中效应, 衬砌裂缝多为纵、斜向裂缝; 衬砌局部存水冻胀最不利位置由优到劣依次为拱脚、边墙、仰拱、拱腰和拱顶, 衬砌受力随局部存水厚度的增大而增大, 局部存水范围的增大有利于衬砌受力均匀化; 不同部位局部存水冻胀条件下衬砌结构容许压应力比均小于1, 满足抗压检算要求; 拱顶、拱腰和仰拱容许拉应力比均大于1, 不满足抗拉检算要求, 实际工程应针对上述部位采取适当的防冻胀措施予以处治; 揭示的隧道局部存水冻胀作用机制和建立的衬砌结构安全性评价方法为寒区隧道冻害防治提供了一定理论依据。 

Safety evaluation and action mechanism of frost heave with local water storage in shallow tunnel

To reveal the action mechanism of frost heave with local water storage and put forward the effective safety evaluation method of lining structure in cold region tunnels, the three-dimensional geomechanical model test was designed. By setting three different frost heave test conditions with different water accumulation ranges, the crack development and stress of lining structure were observed during the frost heave. The numerical calculation method of frost heave with local water storage was improved. The numerical model of frost heave based on the rock mechanics method and coupled with the frost heaving force and surrounding rock load was established. Under different locations, thicknesses and ranges of water storage, the change laws of tunnel frost heaving force and structural internal force were compared. The influence mechanism of frost heave with local water storage on the stress of tunnel was further revealed, and the safety of lining structure was evaluated. Analysis result shows that the frost heave with local water storage has significant regional characteristics, and the frost heave cracking of lining occurs at the junction between the local water storage and the non water storage, the magnitude of frost heave depends on the stress concentration effect caused by the frost heave at the junction. The lining cracks are mostly longitudinal and oblique. The most disadvantageous positions of local water storage frost heave of lining are the arch foot, side wall, invert arch, waist and vault from the best to the worst. The stress of lining increases with the increase of local water storage thickness. The stress of lining tends to be uniform with the increase of local water storage area. Under the conditions of frost heave with local water storage in different parts, the allowable pressure stress ratios of lining structure are less than 1, meeting the requirements of code. The allowable tensile stress ratios of vault, arch waist and invert are greater than 1, not meeting the requirements of code. In the actual project, the appropriate measures should be taken to prevent the frost heave in the above parts. The revealed action mechanism of frost heave with local water storage and the established safety evaluation method of lining structure can provide a certain theoretical basis for the prevention and control of tunnel frost damage in cold areas.