The mechanical properties of rocks in three-dimensional states of stress with various rates of deformation

Abstract

1. The graph of the strength of a rock vs the deformation rate (with the latter varying over 12 orders of magnitude), when plotted in semilogarithmic coordinates, has at least one horizontal part where the strength is independent of the rate of deformation and of the time, and also a part with a small slope (against the log\(\dot \varepsilon _1\) axis) and a part with a large slope (against the log\(\dot \varepsilon _1\) axis) where the strength depends most markedly on the deformation rate. These relations cannot be represented analytically by a single equation (2), such as that following from the kinetic theory of strength. In this case the kinetic theory of strength requires modification. 2. The authors derive an equation of the limiting state (strength), taking account of the deformation rate and the form of the state of stress. This equation gives the strength characteristics for various deformation rates and also the long-term strength characteristics on the basis of a minimum number of necessary experiments. 3. The authors experimentally establish and investigate an effect of anomalous increase in the plasticity and loosening of rocks with increase in\(\dot \varepsilon _1 = 10^{ - 2} - 10^2 \sec ^{ - 1}\). These deformation rates occur in shock bumps, rock bursts, and other dynamic phenomena in coal mining, in blasting and earthquakes, and also during drilling and breaking of rocks by cutting and percussive tools, etc. 4. In the range\(\dot \varepsilon _1 = 10^{ - 3} - 10^{ - 5} \sec ^{ - 1}\) there is a minimum in the plasticity and loosening of rocks. This range of rates is characteristic of mechanical tests on rock specimens in normal laboratory presses. This rate occurs in rocks near extraction operations. 5. At low deformation rates (from 10\t-5 to 10\t-10 sec\t-1), the plasticity and dilatation of the rocks again increase. In this rate range, creep processes occur. These rates occur in pillars and in rocks surrounding development and main workings, etc. 6. The authors have found and investigated the strength and deformation indices and the effects are of fundamental importance. In many cases they can exert a decisive influence on the energy balance of deformation and fracture and on the stability and mechanical state of the rocks. The effects influence the stress distribution, for example, in the abutment pressure zone, the behavior of rock during blasting, the occurrence of shock bumps, rock bursts, tectonic processes, earthquakes, etc.