常用围岩分类方法对某深埋隧洞的适用性分析

The applicability of the common surrounding rock mass classification methods in a deep buried tunnel

某深埋隧洞局部地应力高达42 MPa,局部外水压力高达10 MPa,具有高地应力、高外水压力的特点。一般认为,最大主应力大于20 MPa属于高地应力,外水压力远大于1 MPa为高外水压力。采用Q系统、RMR分类、水电规范HC分类、国标BQ分类等4种常用围岩分类方法对该隧洞进行了围岩分类。分类结果表明,高地应力条件下,Q系统的适用性较好,RMR分类、HC分类、BQ分类适用性均差。4种分类方法在高外水压力条件下的适用性均差。出现上述现象的主要原因有:Q系统通过最大切向应力与岩石抗压强度的比值σθ/σc的大小,反映高地应力对围岩类别的影响。故其在高地应力条件下的适用性较好;RMR分类没有考虑高地应力对围岩类别的影响。其分类结果在高地应力区特别是岩爆段偏高;HC分类在高地应力区简单地采用降级的方法。其分类结果误差较大;BQ分类对岩石强度过于敏感。其分类结果在高地应力区过于保守。这4种方法均未考虑高外水压力对围岩类别的影响。论文提出了一种“归一化方法”,可以对不同分类方法分类结果进行相互比较。

A deep buried tunnel in China has the characteristics of high field stress and high external water pressure. It has reached 42 MPa field stress and 10 MPa external water pressure in some areas. In general, if the major principal stress is greater than 20 MPa, the field stress is called high field stress. And the high external water pressure is pointed to the external water pressure which is much greater than 1 MPa. The four common surrounding rock mass classification methods, Q-system, RMR method, HC method, and BQ method are used in the surrounding rock mass classification. The classification results show that the Q-system has a good applicability and the other three methods have a bad applicability in the conditions of high field stress. The four common methods have a bad applicability in the conditions of high external water pressure. The main reason for the above results is as following. The Q-system considers the high field stress by introducing σθ/σc,σθ is the maximum tangential stress （estimated from elastic theory）, and σc the uniaxial compression strength （MPa）. So the Q-system have a good applicability in the condition of the high field stress. However, the RMR method doesn＇ t consider the high field stress. It＇ s classification results are higher than the actual values in the high field stress areas, especially in the rock burst areas. The HC method simply decreases the grade of surrounding rock mass quality of the high field stress areas. It＇s classification results often have big errors. The BQ method is too sensitive to the rock strength, it＇s classification results are often conservative in the high field stress areas. The four methods didn＇t consider the high external water pressure. In addition, a new method which is called normalization method and used to analyse the compatibility of classification results coming from different classification methods is proposed.