初支混凝土硬化特性与围岩流变耦合作用机制

喷射混凝土作为初期支护重要组成部分广泛应用于隧道工程。深埋软岩隧道开挖时,喷射混凝土硬化特性及围岩流变效应均于时间有关,使得围岩变形及结构受力错综复杂。基于此,该文建立了考虑喷射混凝土硬化特性与围岩流变效应的耦合解析模型,阐明了流变岩体隧道“支护-围岩”动态演化机制,分析了喷射混凝土设计参数、隧道工程参数及围岩流变特性等对“支护-围岩”动态作用的影响机制,并通过具体实例探讨了不同支护类型的时效支护特性。分析表明：喷射混凝土施作初期刚度较低,在围岩流变特性及开挖空间效应下围岩变形速率大,而喷射混凝土承担荷载较不考虑其硬化特性时要小,对于流变岩体隧道宜采用早强混凝土限制围岩早期变形;围岩流变荷载与喷射混凝土刚度均随时间逐渐增大,不考虑围岩流变效应会低估喷射混凝土对围岩变形控制效果及所承担荷载水平;型钢钢架+喷混支护体系刚度较大有利于限制围岩变形,格栅钢架+喷混支护刚度较小更利于围岩应力释放;隧道支护时机的选择应综合考虑围岩流变效应、支护类型、喷混硬化特性、隧道掘进速率的影响,进一步给出了不同支护类型的支护时机-掘进速度的极限关系曲线。研究成果可为类似隧道工程支护设计、施工提供理论依据。

INTERACTION MECHANISM BETWEEN PRIMARY SUPPORT AND RHEOLOGICAL SURROUNDING ROCK CONSIDERING HARDENING PERFORMANCE OF SHOTCRETE

Shotcrete is widely used in tunnel engineering as an essential part of initial support. When tunnels are excavated in deep-buried soft rock, the deformation of rock mass and the stress on the structure are complicated due to the hardening characteristics of shotcrete and the rheological effect of rock mass. For this purpose, a coupled analytical model considering the hardening characteristics of shotcrete and the rheological effect of surrounding rock is established in this study. The dynamic evolution mechanism between shotcrete support and surrounding rock is investigated. Furthermore, the impacts of shotcrete parameters, tunnel engineering parameters and rheological properties of surrounding rock on the mechanical performance of tunnel structures are analyzed. The time-dependent support characteristics of different support types are discussed for specific problems. The results show that the deformation rate of surrounding rock is large under the rheological characteristics of the surrounding rock and the spacing effect of excavation at the initial stage due to the lower stiffness of shotcrete. However, the stress in shotcrete is small compared with the case negeccting the hardening characteristics. Therefore, early strength concrete should be used to limit the early deformation of surrounding rock for rheological rock tunnels. The rheological load of surrounding rock and the stiffness of shotcrete increase gradually with time. If the rheological effect of surrounding rock is not considered, the control effect of shotcrete on surrounding rock deformation and the stress level could be underestimated. The support system composed of a section steel frame and shotcrete has large stiffness that restricts the surrounding rock's deformation. However, the support system composed of a grid steel frame and shotcrete has less rigidity, which is more suitable for the stress release of the surrounding rock. The influence of surrounding rock rheological effect, support type, shotcrete hardening characteristics and tunnel excavation rate should be comprehensively considered to select a suitable support time. Furthermore, the limit relation curves between support time and excavation speed for different support types are proposed. The research results can provide a theoretical basis for support design and construction of similar tunnel projects.