大变形灾害是红层软岩地区隧道安全建设的“卡脖子”难题，其主要诱因之一是红层软岩显著的流变性。软岩的流变特性与应力路径相关，但已有研究却较少考虑隧道开挖卸荷应力路径的影响，时常导致支护措施的选择不当而引发灾害或增加造价。本项目以深埋滇中红层软岩为研究对象，通过辨识隧道开挖诱发的典型卸荷应力路径，设计并开展四种不同应力路径下的分级加载蠕变试验和应力松弛试验，揭示深埋红层软岩的蠕变特性和应力松弛特性；基于试验结果，论证流变触发阈值和长期强度，探讨流变的发生机制，总结应力路径对蠕变特性、应力松弛特性和流变破坏机制的影响规律；基于非稳定性屈服面理论，采用软化机制模拟加速流变过程，提出考虑应力路径影响的长期强度准则和粘塑性势函数，形成红层软岩的弹粘塑性模型并数值验证，给出模型参数的取值方法。研究成果将为红层软岩隧道的大变形灾害控制提供关键技术支撑，并有利于丰富我国软岩工程力学的基础理论。

Large deformation is the main engineering problem that affects the safety construction of tunnels in the red-bed soft rock area, and its one main accounted reason is the significant rheological behavior of red-bed soft rock. The rheological characteristics of soft rock is related to the stress path, but the existing researches pay less attention to the effect of different unloading stress paths induced by tunneling, resulting in unsuitable supporting measures and causing disasters or increasing the cost. Therefore, this project aims to investigate the rheological behavior of red-bed soft rock under different stress paths and build a new elastic viscoplastic constitutive model. The deep buried red-bed soft rock in central Yunnan province is chosen as the research object. A series of numerical analysis of tunneling in the red-bed soft rock will be first carried out to reveal the typical unloading stress paths induced by excavation, and the corresponding test program in the laboratory would be designed. Then the three-axial creep test and stress relaxation test under four different loading/unloading programs will be performed to obtain the creep characteristics and stress relaxation characteristics of deep buried red-bed soft rock. Based on the experimental data, the rheological trigger threshold and long-term strength will be discussed; the rheological failure model will be investigated; and the effect of stress paths on the creep, the stress relaxation and the rheological failure mode will be summarized. The softening mechanism will be adopted to simulate the accelerated creep behavior, and a new long-term strength criterion and a new viscoplastic potential function will be proposed to consider the stress path effect. An elastic viscoplastic constitutive model will be finally formulated based on the nonstationary flow surface theory and validated using the test data. The method to derive the model parameters will be also given. The outcomes of this project can technically support the tunnel construction in the red-bed soft rock area and enrich the fundamental theory of soft rock mechanics in China.