高地应力定义及其定性定量判据

Concept of high geostress and its qualitative and quantitative Definitions

地应力大小是地下工程设计的基本参数,直接影响工程岩体的力学行为。与高地应力相关的工程问题自20世纪80年代开始受到关注,但迄今未见高地应力的明确定义。国内曾先后提出多种地应力分级方案,但分级结果与工程岩体的实际行为存在一定差距,部分预测为高地应力的工程未出现高地应力现象(如官地地下厂房),而预测为低地应力的工程(如二滩地下厂房)却出现严重的岩爆等高地应力现象。针对此问题,在国内常用地应力分级方案基础上,讨论了影响地应力分级的主要因素,将高地应力划分为初始高地应力与诱发高地应力两类。诱发高地应力是洞室群效应产生的高二次应力与爆破开挖动力扰动单独或联合作用的结果;给出了高地应力的明确定义,即量值足以导致结构体或岩块破坏的地应力,并在前人研究成果的基础上提出了定性判据;重新定义强度应力比为岩石干燥单轴抗压强度与实测最大主应力之比,建议了新的地应力分级方案(定量判据)。25个工程实例证明,建议方案的吻合率远高于国内常用地应力分级方案。建议方案的级差大致与CD Martin等1999年的建议方案相当。

The magnitude of initial geostress is one of the key parameters for designing underground structures and can directly influence the mechanical behavior of engineered rock masses. Although attention has been paid to the engineering problems related to high geostresses since 1980 s, no clear definition is ever made thus far. In China, several rating schemes have been proposed for defining initial geostresses, but the rockmass behaviors inferred from such schemes differ more or less from the real ones. For example, no obvious high geostress characteristics were ever witnessed in some predicted high-geostress engineering sites（e.g. Guandi underground powerhouse）, whereas heavy rockbursts could happen in the sites supposed to have low geostress（say, Ertan underground powerhouse site）. To resolve this issue, the rating schemes for initial geostress commonly practiced in China is briefly introduced first; then the major factors affecting the geostress rating are discussed; finally high geostress is classified into two categories, i.e. the initial high geostress and the induced high geostress. The induced high geostress is a combined result of the high secondary stress concentration due to cavern groups and the dynamic disturbance due to blasting excavations. The criterion defining high geostress is clearly specified, which is the threshold of geostress that can induce failure of the embedded structure or the rockmass, and a qualitative criterion is also summarized based on the previous research results. The ratio of strength to stress is redefined as the uniaxial compressive strength of dry intact rock to the measured maximum principal stress, and a new initial geostress rating scheme（quantitative criterion） is suggested. The suggested scheme is validated using the monitoring data of 25 engineering cases, showing that the accuracy of the suggested scheme is much better than the commonly used rating schemes in China. The suggested scheme is similar to that proposed by CD Martin et al. in 1999.