Study on the Weathering Characteristics of a Solitary Rock in Chishui Based on Pore Structure with Depth

Solitary boulders emerge in the thick-bed red sandstone in the Chishui red bed area due to weathering, which can potentially induce engineering disasters. This paper measures the porosity, pore size, pore throat distribution, T₂ spectrum distribution, chemical oxide content, and rebound value of the red sandstone boulder at different depths, and explores their variation trends, rules, and relationships. The research results show that: (1) the deterioration of red sandstone pores caused by weathering is reflected in the increase of porosity and pore size. The pore size of the red sandstone in the slightly weathered zone is dominated by micro and small pores, accounting for > 75.11%. There are mainly three peaks on the T₂ spectrum curve of red sandstone. With the enhancement of weathering, the T₂ spectrum curve shifts to the right, and the peak area gradually increases as a whole. (2) The element enrichment intensity of red sandstone is in the order of Fe > Ti > Si > Al, and the loss intensity is in the order of Ca > Mg > Na. The growth rate of rock rebound value decreases continuously with the increase of rock depth, and the rebound value eventually tends to be stable. (3) The chemical alteration index CIA can be indicative of the deterioration degree of physical properties (porosity etc.) of red sandstone, and the division of slightly and moderately weathered zones. (4) The rock rebound value shows that the mechanical properties of red sandstone decrease with the increase of weathering degree, which is closely related to the damage of rock pore structure.