Abstract
The water-softening property of soft rocks is a key problem in geotechnical engineering. A typical red-bed soft rock (the Zigong argillaceous siltstones) with different weathering degree is selected as an example to study the water-softening property and the influence of degree of weathering. A series of mechanical and microstructure tests are carried out to analyze the weathering characteristics and mechanism of the Zigong argillaceous siltstones. The results of mechanical experiments reveal that the water content and the weathering degree of rock specimens both have a weakening effect on the compressive and shear strengths. According to the results of present microstructure tests, the mechanical properties of the Zigong argillaceous siltstones are closely correlated with their physical properties, including internal microstructure and material composition for highly weathered rocks or moderately weathered rocks (in both natural and saturation conditions). Finally, experimental results indicate that the changes of microstructure and internal materials are two main factors that influence rock strength parameters after contacting with water and that these properties reflect the rock weathering degree. In a word, when red-bed soft rocks are encountered in geotechnical engineering, special attention should be paid to presence of water.
Highlights
There are many types of red-bed soft rocks such as red siltstone and red mudstone, which are widely distributed at the Sichuan basin, the Shanganning basin, the Yunnan plateau, and other places in China [1]
Rock strength parameters are very important for engineering design, such as rock slopes and roadways, which often decrease with the increase of moisture content and degree of weathering [2, 11, 15, 16]
The mechanical tests have been successfully conducted on thirty-six argillaceous siltstone rock samples, in which twenty of them were highly weathered, while sixteen of them were moderately weathered, both including natural and saturation conditions
Summary
There are many types of red-bed soft rocks such as red siltstone and red mudstone, which are widely distributed at the Sichuan basin, the Shanganning basin, the Yunnan plateau, and other places in China [1]. Among Southwest China, most red beds belong to soft rocks’ category because its physical and mechanical properties are very poor relatively [1, 2, 4] Such rocks have lower strength (saturated uniaxial compressive strength of rock mass less than 30 MPa), larger porosity, Advances in Materials Science and Engineering. The lithologies of red beds are mainly sandstone, siltstone, silty mudstone, argillaceous siltstone, shale, or claystone When they encounter water, the red beds commonly develop many engineering problems such as erosion, seepage, and softening [2, 3, 5]. A series of mechanical and microstructure tests were carried out to study the water-softening properties of the Zigong argillaceous siltstone under different degree of weathering, some useful conclusions are presented in this paper
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