Gas inclusions and their expansion power as foundation of rock “locked in” stress hypothesis

Abstract

About 35 years ago, Professor TAN Tjong-Kie proposed the hypothesis of rock “locked in” stresses and considered the “locked in” stresses were the failure cause of rock engineering projects. In recent years, Professor WANG Sijing and Professor QIAN Qihu have made some qualitative discussions on the hypothesis. However, this hypothesis has received very little attention and quantitative investigation. In this paper, the author puts forward and attempts to show that the tiny gas (or liquid) inclusions in contact rocks are a specific, concrete and measurable inclusion type of variable and considerable “locked in” stresses and kinetic energy. The pressure and volumetric expansion energy of a gas inclusion are a type of “locked in” (or sealed) stresses and internal deformation energy of actual existence and active power. The author gives the governing equations to calculate the pressure and volumetric expansion energy of gas inclusions, which is shown with calculation examples. The pressure of the gas inclusions is equivalent to the average value of the in-situ stresses in deep rocks. The gas inclusions, sealed in micro-defects or voids of deep rocks, are the common tensile or expanding volumetric force sources for the occurrences of many failures in the surrounding rocks of excavated or engineered caverns or tunnels in deep rock ground. Because of differences in the physical and mechanical properties of the surrounding rocks, the compressed and dense gas inclusions can cause the following three results and/or phenomena. They are (a) stable walls, (b) brittle fractures and (c) large deformation of the surrounding rocks. Hard and brittle intact rocks can have brittle fractures in the forms of rock burst, mine earthquake, rock split, and zonal disintegration. Soft and ductile intact rocks can have the deformation failure in the forms large deformation, creep and pressure bump accordingly. In addition, the gas inclusions with high pressure can be the source of abnormally high in-situ stresses in some special deep rock grounds.