Rock mass structural mechanics is a new theoretical system based on rock mass structural cybernetics and combining mechanics and geology. Rock mass structural mechanics is the basic theory to solve the problem of rock mass engineering construction in civil engineering, mine engineering and national defense engineering construction. With the arrival of the general trend of human marching into the deep underground, there are more and more types and scales of rock mass engineering, and its safety and economic benefits are paid more and more attention, and the demand for rock mass mechanics is becoming more and more urgent. Rock mechanics has been widely concerned at home and abroad, and many monographs, papers and teaching materials have been published, but the engineering community still feels that the existing rock mechanics theory has low ability to solve practical problems. The author points out that there are two reasons:
(1) Rock mechanics research is divorced from geological research, and the abstract rock mechanics model does not conform to the geological reality of rock mass;
(2) The existing rock mechanics theory can't reflect the real law of rock mechanics. The existing rock mechanics theory is transplanted from material mechanics and soil mechanics, which is essentially a continuum mechanics theory and does not conform to the geological reality of rock mechanics.
What is the geological reality of rock mass? After years of research, the author gradually realized that rock mass is a geological body with various discontinuous structures, which is deformed, stressed, broken and bad. Rock mechanics is a science that studies the law, theory and application technology of deformation and failure of rock mass when environmental stress changes. These two words "in" are very important and are the characteristics of rock mechanics. These two characters are strictly controlled by the rock mass structure, that is, the rock mass structure controls the deformation, failure and mechanical properties of the rock mass. 1978 The author puts forward the theory that the mechanical effect of rock mass structure is the mechanical basis of rock mass mechanics, and 1984 puts forward that the cybernetics of rock mass structure is the basic theory of rock mass mechanics. As shown in Figure 3-2, the cybernetics of rock mass structure has two levels: the first level is the control of rock mass structure on deformation, failure and mechanical properties of rock mass, which is the basic theory and core of rock mass structural mechanics. The second level is to apply these three basic theories as guidance to solve practical problems in rock mass engineering. Obviously, the core theory of rock mass mechanics is rock mass structure cybernetics, and the basic methods to solve rock mass mechanics problems are rock mass structure analysis and structural mechanics analysis. The following is the concrete theory of rock mass structural mechanics established by the author on the basis of rock mass structural cybernetics.
Figure 3-2 Block diagram of rock mass structure cybernetics
Figure 3-3 Deformation Diagram of Rock Mass Materials
1. Theory of rock mass deformation law
Many people have studied the deformation constitutive law of rock mass, but most of the research results are divorced from the geological reality of rock mass. When solving rock mass engineering problems, the theory of material mechanics is used to analyze rock mass deformation, and the result is not easy to use. After years of research and practice, the author found that the deformation of rock mass is caused by the deformation of rock mass material and the deformation of rock mass structure, namely:
Principles of geological engineering
As shown in Figure 3-3, the deformation of rock mass material consists of four mechanical components: elastic deformation of structure, viscous deformation of structure, closed deformation of structural plane and dislocation deformation of structural plane. According to this scheme, the author systematically studies the deformation of rock mass materials, and gives 17 kinds of deformation models and constitutive equations (Sun Guangzhong, 1988) according to different geological characteristics of rock mass. At the same time, the deformation law of rock mass structure is also studied, and four deformation constitutive laws of rock mass structure are put forward, namely, sliding deformation law along weak structural plane, extrusion deformation law of weak interlayer, rotation deformation law of block structure and bending deformation law of plate structure. In this way, the author provides the theoretical basis of rock mass structural mechanics for rock mass deformation analysis. However, most of the current rock mass deformation analysis regards the deformation of rock material as the whole deformation of rock mass. Therefore, the theoretical analysis results of rock mass deformation are quite different from the actual observation results. In 1986, the author analyzes the deformation of the side wall of the underground powerhouse of Lubuge Power Station. According to Hooke's law, the deformation of the side wall of underground powerhouse is 0. 19mm, while the actual observation result is 22.5mm, with a difference of 100 times. According to the mechanics theory of plate-cracked rock mass put forward by the author, it is calculated that the deformation of the rock mass on the side wall of the cave chamber reaches 22.7mm and cracks appear in the rock mass. This is very consistent with the actual observation results. This shows that it is unrealistic to analyze rock mass deformation only by Hooke's law, and rock mass structural deformation must be considered in rock mass deformation analysis.
2. Theory of rock mass failure law
Many people regard this problem as the strength study of rock materials. In fact, it is also divorced from the geological reality of rock mass. According to years of research and practice, the author found that the failure of rock mass is also controlled by rock mass structure. On the basis of summarizing a large number of failure data of rock mass, it is found that there are seven failure mechanisms of rock mass under the control of its structure, as shown in Table 3-2: ① tensile fracture; ② Shear failure; (3) structural rolling; ④ The structure slides along the structural plane; ⑤ Dumping damage; ⑥ Buckling failure; ⑦ Bending failure. The first two are material failure, and the last five are structural failure and structural instability. According to this, seven failure criteria are given, and the one-sided error of evaluating rock mass mechanical failure with single Coulomb-Moore failure criterion is criticized, and the rock mass failure criterion system is established. This argument has been widely verified in practice, and the analysis of the damage of the diversion tunnel of Bikou Power Station clearly illustrates this problem. The rock mass through which the tunnel passes is phyllite with plate-like fracture structure. Coulomb-Moore criterion is adopted in the design process for stability analysis. The results show that the diversion tunnel of 12.9m can be excavated, but it was destroyed during the construction. 1985 The author published the mechanics theory of rock mass with plate-cracked medium, and the original design engineer Ni reanalyzed it with the mechanics theory of rock mass with plate-cracked medium proposed by the author, and found that the cave was unstable. The error of the original analysis results led to the long-term shutdown of the project, which brought great difficulties to the construction.
Table 3-2 Table of Rock Mass Failure Mechanism
3. Theory of laws of rock mechanical properties.
At present, the analysis method of mechanical properties of rock mass is the mechanical test results of rock mass materials plus experience discount, and there is no theory. In the mid-1970s, John, a professor at Ruhr University, proposed that the mechanical properties of rock mass are controlled by the structure of rock mass. Because he didn't grasp the law of mechanical effect of rock mass structure, he didn't solve this problem. After years of research and practice, the author found that the structural effect of mechanical properties of rock mass can be summarized into three laws: ① the law of climbing angle effect; (2) size effect rule; ③ Anisotropic effect rule. When considering the mechanical properties of rock mass, we must also consider the characteristics of engineering structure, so as to get more practical mechanical properties of engineering rock mass. This theory provides a theoretical basis for the analysis of mechanical properties of rock mass.
4. Rock mechanics medium
By studying the laws of rock mass deformation, rock mass destruction and rock mass mechanical properties, the author finds that the basic laws of rock mass mechanics are indeed controlled by rock mass structure. Accordingly, cybernetics of rock mass structure is the basic theory of rock mass mechanics, which not only puts forward the basic argument that cybernetics of rock mass structure is the basic theory of rock mass mechanics, but also establishes the theoretical system of rock mass structural mechanics by using this basic theory. At the same time, some basic research has been done in application. In order to ensure the scientificity of rock mass mechanical analysis and rock mass mechanical model, according to the deformation and failure mechanism and in-situ stress characteristics of rock mass, rock mass is divided into four mechanical media: continuous medium, fractured medium, block fractured medium and plate fractured medium, as shown in Table 3-3. The mechanical analysis methods of various media rock masses are deeply studied, and a complete mechanical system of rock mass structure is established. Guided by the cybernetics of rock mass structure, the principle of rock mass transformation is studied, which makes the theory of rock mass structural mechanics more perfect and more convenient to use.
Table 3-3 Classification of Rock Mass Mechanical Media
5. Mechanics theorem of rock mass structure
Based on the previous research results and the author's research results, under the guidance of 199 1 rock mass structural cybernetics, the author summarizes the core contents of rock mass structural mechanics into the following five items, which are called the basic theorem of rock mass structural mechanics or the basic theorem of rock mass mechanics (Sun Guangzhong, 1993):
Rock mass (1) is a geological body which is deformed and destroyed, consists of certain rock components, has a certain structure and exists in a certain geological environment. Rock mechanics is a science that studies the law, theory and application of rock deformation and failure when environmental stress changes.
(2) Rock mass has its own unique discontinuous structure under the control of structural plane, and the rock mass structure controls the deformation, failure and mechanical properties of rock mass. The controlling effect of rock mass structure on rock mass mechanics is far greater than that of rock materials.
(3) The cybernetics of rock mass structure is the basic theory of rock mass mechanics, the mechanical effect of rock mass structure is the mechanical basis of rock mass mechanics, and the analysis method of rock mass structure and structural mechanics is the basic method of rock mass structural mechanics research.
(4) Rock mass exists in a certain geological environment, and the environmental conditions of rock mass occurrence can change the mechanical effect of rock mass structure and mechanical properties of rock mass.
(5) Under the control of rock mass structure, rock composition and environmental stress conditions, rock mass has a variety of mechanical media and mechanical models, and rock mass mechanics is a mechanical system composed of various media mechanics.