基于时效变形的脆性围岩最优支护时机研究

现代地下工程支护结构设计的基本指导思想是按照"新奥法"原理,强调通过适时加固围岩,使得围岩成为承载结构的主体。但是对于支护时机的掌握,目前仍然缺乏可靠的理论和公式的指导,只能根据现场监测信息和经验判断来确定。提出脆性围岩的"适时支护",是指在围岩达到弹性极限应变而破坏之前进行支护,即在时效变形作用下,围岩应力处于本构关系弹性段后段,但是还没有进入软化的非稳定段。基于这一思想以及地下工程时效变形特征,提出了最优支护时机的近似计算公式。研究表明:最优支护时机与围岩收敛时间、围岩强度应力比、开挖后应力以及支护围压相关。由于围岩应力处处不同,可以由公式计算得到顶拱、边墙等不同部位的最优支护时机,从而指导支护设计。研究对长期困扰地下工程界的脆性围岩最优支护时机问题提出了一种理论方法。

Optimum support time of brittle underground cavern based on time-dependent deformation

As the basic principle used in modern underground engineering, the New Austrian Tunneling Method focuses on providing timely and optimized safe support to develop the maximum self-supporting capacity of the rock or soil itself for the stability of the underground opening. But up to now, no reliable formula and theoretical guidance for timely support have been established. The support time can only be empirically determined based on the in-situ monitoring measurements. The timely and optimized support which uses adequate self-bearing capability of surrounding rock means that the rock stress is in the final stage of elastic deformation, but before brittle failure occurs when reaching the critical elastic strain limit. Based on this idea and the characteristics of time-dependent deformation of underground engineering, an approximation formula to calculate the optimum support time is proposed. The study shows that the optimum support time is related to the deformation convergence time, ratio of rock strength to geo-stress, stress after excavation and anchorage pressure. The optimum support time for top arch and side walls can be determined according to the stresses of surrounding rock from point to point. This study may provide a theoretical method to determine the optimum support time which is a critical problem of underground engineering for a long time.