Abstract
In this study, the relationship between the pore structure and macroscopic mechanical characteristics of coarse-grained soils from mine dumps is explored under various freeze–thaw cycles. A series of experiments were conducted on the mine dump materials using a standard cube sample of 7 cm × 7 cm × 7 cm, a moisture content of 7.5%, and a density of 2.34 g/cm3. The pore structure test and uniaxial compressive strength test were carried out on the coarse-grained soil samples under different freeze–thaw cycles by using a nuclear magnetic resonance (NMR) instrument and a universal servo material testing machine. The study explores the change law of the strength and pore structure of coarse-grained soil, and establishes the correlation model between the pore structure and mechanical characteristics. The results showed that: (1) With the increase in the number of freeze–thaw cycles, the porosity of the coarse-grained soil gradually increased, and the bonding ability between the internal soil particles weakened, resulting in a decrease in strength. (2) With the increase in freeze–thaw cycles, the proportion of pore volume of the main peak and secondary peak 2 of T-2 spectrum curve increases gradually, and the internal pore structure of coarse-grained soil gradually develops towards medium and large pores. (3) There is an exponential function between the variation of pore volume proportion of each peak of coarse-grained soil and the relative strength value, and there is a good fitting coefficient between the two, indicating that the change of pore structure can well reflect the evolution law of strength.
Highlights
(3) There is an exponential function between the variation of pore volume proportion of each peak of coarse-grained soil and the relative strength value, and there is a good fitting coefficient between the two, indicating that the change of pore structure can well reflect the evolution law of strength
The dump is mainly composed of waste rock and soil particles stripped during mining, and its mechanical properties are closely related to the stability of the dump, which is the basis for the study of the stability and disaster mechanism of the dump [6–9]; understanding the mechanical properties of the soil in the dump under the action of freeze–thaw cycles will be helpful to store the dump materials scientifically, optimize the dump process, and analyze the stability of the dump slope, as well as the disaster risk prediction to ensure the safety of life and property of the surrounding people [10–14]
It was believed that the effect of freeze–thaw cycles on shear strength was the main one, which was reflected in the cohesion; the difference in the gravel content will make the shear index of the coarse-grained soil different
Summary
With the gradual increase in the mining scale of mineral resources, the number of mine dumps is increasing, and the mechanical properties of the soil in dumps are being given more and more attention [1–3]. S [40] used the Brunauer–Emmett–Teller (BET) and SEM to analyze the microstructural changes and interfacial interactions of fiber–clay particles, and found that the total pore volume and average pore size of the clay samples increased 30 and 42%, respectively, under freeze–thaw cycles; the change of pore structure is manifested as the change of mechanical properties on the macroscopic level, which can be used to reflect the change law of strength to a certain extent [41]; Xu, L [42] pointed out that there was a negative correlation among the porosity, pore orientation and mechanical parameters of expansive soil samples, and the change of the microstructure of expansive soil would directly affect the mechanical properties; Li [43] established the relationship between the ratio change rate of each peak and the mechanical characteristics based on the spectral area ratio of each peak in the NMR.
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