Abstract
The rates of chemical reactions are highly dependent on temperature, meaning that the actual geological rock mass is affected by different temperatures. Only when the temperature effect is considered can the mechanism of the influence of temperature on the interaction between water and rock be further understood. It was found that the condition of turbulent flow is more likely to promote the softening of red-bed sandstone than the conditions of laminar flow and static water in an experimental study on the softening effects of different flow patterns on red-bed sandstone. Therefore, based on a multi-functional self-circulating open channel hydraulic test system, this paper designs and completes equal volume saturated tests of red-bed sandstone at low temperature (1 °C), medium temperature (23 °C), and high temperature (45 °C) under the turbulent conditions of three equal temperature gradients. The chemical action of the circulating solution in water flow at different temperatures, the propagation of micro-cracks in rock and the changes in mechanical indexes are discussed. The influence laws and mechanisms of the different temperatures on the softening of red-bed sandstone in turbulent flow are revealed. The results show that low-temperature flow can inhibit the softening of red-bed sandstone in the range of 1–45 °C. With the increase in water flow temperature, the development degrees of micro-structures and the mechanical damage of the corresponding rock become more notable. That is, temperature affects the physical and chemical water-rock interactions and then changes the internal structure of rock, thus affecting the softening and failure processes of red-bed sandstone. The study provides a theoretical basis for the further investigation of the softening laws and mechanisms of other red layered soft rocks by temperature under turbulent conditions.
Highlights
IntroductionAs a kind of special soft rock (that is, the rock whose strength characteristics and engineering forces conform to the parameters described in the literatures [1,2]) which is easy to soften and collapse in the event of water, it is often encountered in major engineering construction efforts, such as the Gezhouba hydraulic engineering project, the Three Gorges Reservoir area, and the South–North Water Transfer Project [3]
As a kind of special soft rock which is easy to soften and collapse in the event of water, it is often encountered in major engineering construction efforts, such as the Gezhouba hydraulic engineering project, the Three Gorges Reservoir area, and the South–North Water Transfer Project [3]
Reference [19] found that mineral dissolution and precipitation and the resulting porosity changes were related to temperature and pressure because the temperature and pressure affect the laws of mass action of the minerals and water-bearing substances involved in the equilibrium reaction
Summary
As a kind of special soft rock (that is, the rock whose strength characteristics and engineering forces conform to the parameters described in the literatures [1,2]) which is easy to soften and collapse in the event of water, it is often encountered in major engineering construction efforts, such as the Gezhouba hydraulic engineering project, the Three Gorges Reservoir area, and the South–North Water Transfer Project [3]. Scholars mainly studied and summarized the influence of temperature on rock mechanics and physical and chemical properties through the direct action of temperature on the rock mass itself [5,6,7,8,9,10,11,12,13,14] Among these studies, the studies of the rock elastic modulus, uniaxial compressive strength, and Poisson’s ratio with the temperature are the most prominent. Reference [18] studied the thermal effects of temperature from 25 ◦C to 500 ◦C on the physical and mechanical properties (mass, density, porosity, longitudinal wave velocity, compressive strength, peak strain, modulus of elasticity) of rock. Reference [20] studied the effect of thermal damage on the physical properties, e.g., bulk density, P-wave velocity, effective porosity of carbonate rocks
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