Abstract
In order to study the mechanical properties of sandstone under the coupling action of chemical erosion and freeze-thaw cycles, the fine-grained yellow sandstone in a mining area in Zigong, China, is collected as the research object. The changes in mechanical properties of yellow sandstone under the coupling action of chemical solution erosion and freeze-thaw cycles are analyzed based on uniaxial compression tests (UCTs) and triaxial compression tests (TCTs). The results show that, with the increase in freeze-thaw cycles, the compressive strength, elastic modulus, and cohesion of the sandstone samples decrease with varying degrees. Under constant freeze-thaw cycles, the most serious mechanical properties of degradation are observed in acidic solution, followed by alkaline solution and neutral solution. Under different confining pressures, the compressive strength and elastic modulus of the sandstone samples decrease exponentially with the increase in freeze-thaw cycles. Under the action of the chemical solution erosion and freeze-thaw cycles, the internal friction angle fluctuates around 30°. For the cohesion degradation, 35.4%, 29.3%, and 27.2% degradation are observed under acidic, alkaline, and neutral solutions. Nuclear magnetic resonance imaging shows that the chemical erosion and freeze-thaw cycles both promote the degradation of rock properties from surface to interior; after 45 freeze-thaw cycles, the mechanical properties drop sharply. To properly design rock tunneling support and long-term protection in the cold region, the impact of both freeze-thaw cycles and chemical erosion should be considered.
Highlights
Sample Preparation. e samples were fine-grained yellow mine sandstone collected from Zigong, China. e mineral compositions of the samples were obtained based on an X-ray diffraction (XRD) analysis and are presented in Table 1. e tests were completed under the guidance of the “Standard for Test Methods of Engineering Rock Mass” (GB/ T 50266-2013) [23]. e samples were processed into cylinders with a diameter of 50 mm and a height of 100 mm (Figure 1). is is in line with the recommendations of the International Society for Rock Mechanics (ISRM)
After 30 freeze-thaw cycles, the samples fail in a wedge-shaped splitting form, which is mainly manifested by wedge-shaped cracks during the failure and crushing process at the terminal face. e combined effect of freeze-thaw cycles and chemical solution erosion leads to particle softening and pore expansion inside the rock sample
Laboratory experiments were carried out on fine-grained yellow sandstone collected in underground mines in Zigong, China. e mechanical parameters and damage properties of yellow sandstone samples under chemical erosion and freeze-thaw cycles are analyzed. e main conclusions are as follows: (1) e compressive strength and elastic modulus of the sandstone samples in three chemical solutions decrease with the increase in freeze-thaw cycles
Summary
After removing the samples with large acoustic wave difference, the remaining ones with consistent mechanical properties were chosen. 3 parallel tests were conducted for each group. E freeze-thaw cycle equipment used in the test is the constant temperature-humidity chamber (Figure 2). A series of UCT and TCT were conducted using the TAW-200 electronic multifunctional material mechanics testing machine. E machine is developed by Qingdao University of Science and Technology and Changchun Chaoyang Testing Machine Factory (Figure 3) and has two loading modes: force and displacement control. The mass and longitudinal wave velocity of the saturated samples were measured, and a series of nuclear magnetic imaging observation tests, UCT and TCT, were performed. According to the self-weight stress σz of the stratum (σz λh, λ is the gravity of the rock formation), the required confining pressures are about 3 MPa and 6 MPa, respectively
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