Abstract
In the process of tunnel construction, gypsum rock is often encountered, and the volume of gypsum rock expands when encountering water, which is easy to cause the occurrence of rock fall, collapse, and other disasters, bringing serious challenges to the safe construction of the tunnel. Therefore, in this paper, four groups of samples under different moisture content are tested by ultrasonography, uniaxial compression, conventional triaxial compression, Brazilian splitting, X‐ray diffraction, and SEM, and then the physical and mechanical properties of gypsum rock are studied, and the conclusion is as follows: the density of the water saturated sample, and the longitudinal wave velocity of the natural sample are the highest. Both the water saturation and dehydration conditions have a weakening effect on the remolded sample of high‐strength gypsum powder. The peak intensity of the sample gradually increases with the increase of confining pressure, and the relationship between the peak intensity and confining pressure of the sample conforms to the Coulomb strength criterion. After high‐temperature dehydration, the sample showed obvious plastic softening characteristics. The cohesion and internal friction angle of the sample are closely related to the water content. The cohesion is the largest in the 45°C dehydrated sample, the internal friction angle is the smallest in the saturated sample, whereas the cohesion is the smallest and internal friction is the largest in the high‐temperature dehydrated sample. The characteristics of failure for the natural and 45°C dehydrated samples are almost the same and most samples show shear or shear‐tensile failure. The shear plane begins at the edge of the end face of the sample and exhibits a typical diagonal shear failure. The high‐temperature dehydrated samples are completely broken under uniaxial and triaxial compression conditions. After high‐strength gypsum powder was used to make the remolded sample, the calcium sulfate disappeared, the water content increased, and the main mineral components of the natural and saturated samples were the same. After dehydration at 45°C, the sample began to release structural water and generate SiO2. After high‐temperature dehydration, the hemihydrate gypsum continued to dehydrate and become soluble anhydrous gypsum.
Highlights
In recent years, with the rapid development of China’s economy and the implementation of the strategy for the development of the western region, the construction of highway and railway tunnels in this region is facing increasing problems
Li et al [20] performed uniaxial compression tests on gypsum rock after different times of wet and dry cycles; the results showed that the water absorption, porosity, uniaxial compressive strength, and elastic modulus were logarithmic functions with the times of dry wet cycles
According to the above analysis, the cohesion and internal friction angle of the sample are closely related to the water content
Summary
With the rapid development of China’s economy and the implementation of the strategy for the development of the western region, the construction of highway and railway tunnels in this region is facing increasing problems. Anhydrite rock, which has typical softening, expansion and corrosion characteristics, is often encountered. Because of the complex deposit conditions, CaSO4 in gypsum rock is deliquescent into CaSO4·H2O, resulting in expansion of its volume, which can increase by 61% [1]. If the understanding of gypsum rock is not clear, serious safety problems, such as roof fall, collapse, and other accidents, may problems. Erefore, it is very important to study the physical and mechanical properties of gypsum rock. Scholars at home and abroad have carried out significant research on the mechanical properties of gypsum rock. Liu et al [2] carried out incremental loading tests of a single sample in natural and water saturated state and analyzed the creep characteristics of gypsum rock under the action of water saturated softening. Chen et al [3] studied
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