Abstract
As a typical representative of red beds, the softening and disintegration of red sandstone when it encounters water is an important cause of initiated engineering disasters. However, research on the softening of this kind of rock has mainly focused on the still water–rock interaction. There is still a lack of quantitative analysis and a mechanistic explanation for the basic experimental study of dynamic water–rock interactions. Therefore, based on the independently developed multifunctional open channel hydraulic test equipment, the still water was used as the reference by designing the saturation test of red sandstone under two typical flow patterns—laminar flow and turbulent flow—and combined with a three-dimensional numerical simulation; specifically, the chemical, physical and mechanical effects of different flow patterns on the softening of red sandstone are discussed, and the mechanism of the influence of different flow patterns on the softening of red sandstone was further revealed. The results show that under different flow patterns, as the flow of water increased, the alkalinity of the circulating solution became stronger, the speed of stabilization of the ion concentration became faster, the development of the microscopic structure of the corresponding rock became higher and the decrease in mechanical strength became greater. The flow state affects the processes of rock softening and breaking by acting on the rock from the three aspects of chemistry, physics and mechanics. The study makes up for the deficiency of the quantitative analysis index of rock softening under dynamic water conditions and further improves the influence mechanism of different flow patterns on soft rock softening in red beds under dynamic water conditions. This research also provides a specific method for the protection of estuarine and coastal bank slopes with rich red-bed soft rock dissection under different flow patterns.
Highlights
As a kind of special soft rock, red sandstone is often encountered in major engineering construction efforts, such as the Gezhouba hydraulic engineering project, the three Gorges Reservoir area and the South-to-North Water Transfer project
Zhou et al [4] conducted an experimental study on the saturated water of red-bed soft rock under still water conditions, and it was pointed out that the main reason for the decrease of physical and mechanical properties of rock mass caused by water softening of soft rock was that the water–rock interaction changed the structure of soft rock, which was the result of the combined action of physics, chemistry and mechanics
The effect law and mechanism of different flow patterns on the softening of red sandstone under dynamic water conditions can be further illustrated by the stress and deformation of the water–rock interface caused by different flow patterns
Summary
As a kind of special soft rock, red sandstone is often encountered in major engineering construction efforts, such as the Gezhouba hydraulic engineering project, the three Gorges Reservoir area and the South-to-North Water Transfer project. Scholars have mainly focused attention on the softening mechanism of this kind of rock mass under hydrostatic conditions [1,2,3,4,5,6,7,8,9]; for example, Hadizadeh et al [1] considered that the size and morphology of pores in sandstone, the composition of the cemented matter and the boundary condition of particles were the main factors affecting the water–rock interaction. We have already formed a more perfect theory on the softening mechanism of red-bed soft rock under static water conditions, real-life disasters such as bank slope collapse and slides still exist. The explanation of the softening mechanism of red-bed soft rock under still water conditions does not meet the protection demand of actual hydraulic engineering and the red-bed bank slope
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