Strength deterioration and damage mechanism of grout-reinforced fractured sandstone under the coupled effects of acidic erosion and freeze-thaw cycles

Abstract

To investigate the effects of acidic erosion coupled with freeze-thaw (f-t) cycles on the strength and stability of grout-reinforced red sandstone, specimens with full-penetrating and half-penetrating fractures at different inclination angles (IAs, 0–90°) were fabricated. These specimens were then reinforced with a new high-strength fast anchoring agent (HSFAA) material and subjected to coupled treatments of acidic erosion (hydrochloric acid (HCI) solution at pH = 2) and f-t cycles (0–40 cycles). Subsequently, the grout-reinforced specimens (GRSs) were tested for mass, P-wave velocity, uniaxial compressive strength (UCS) to investigate the mechanism of strength deterioration induced by the coupled effects of acidic erosion and f-t cycles, whilst scanning electron microscopy (SEM) and industrial computed tomography (CT) tests were performed to explore their microstructure damages. The findings indicated that as the number of coupled treatment cycles increased, the mass, P-wave velocity, UCS, elastic modulus (E) and deformation modulus (D) of GRSs with full-penetrating and half-penetrating fractures experienced significant decreases, with the fastest decline occurring within the first 20 cycles. GRSs with full-penetrating fractures exhibited more severe performance deterioration compared with those with half-penetrating fractures. The coupled effects of acidic erosion and f-t cycles resulted in the gradual development of intergranular and transgranular cracks on the red sandstone surface, and the generation of a complex crack network on the HSFAA surface. After 40 coupling treatment cycles, the 3D crack volume of GRSs with full-penetrating and half-penetrating fractures increased by 30.31 % and 49.52 %, respectively, compared with untreated GRSs. The primary mechanisms responsible for the strength reduction and damage of GRSs included the chemical dissolution of gelling products in the HSFAA, the frost heaving stresses induced by f-t cycles, and the gradual detachment at the interface between HSFAA and sandstone.