Experimental Investigation on the Evolution Mechanism of Resistivity in Limestone Under Triaxial Loading-Induced Damage

Electrical resistivity is a sensitive indicator of rock damage, yet the quantitative link between pore-structure change and resistivity response under varied hydro-thermo-mechanical conditions remains poorly constrained. In this study, triaxial compression tests were conducted on saturated limestone at confining pressures of 5–20 MPa, pore pressures of 0–9 MPa and temperatures of 20–80 °C, with synchronous measurement of electrical resistivity and pore volume; in situ X-ray computed tomography (X-CT) was performed on miniature specimens at six characteristic loading stages to resolve the accompanying mesoscale pore-structure evolution. Resistivity tracked pore volume closely, rising to at most 1.16 times its initial value as pre-existing microcracks closed, then falling once crack propagation restored fluid connectivity, with the turning point occurring at approximately 50% of the peak deviatoric stress. A resistivity change rate per unit pore volume (ρ′) is introduced to separate the two contributions: its stage-averaged magnitude during unstable crack propagation is about 8.5 times that during linear compression, showing that crack opening alters resistivity far more efficiently than closure of an equivalent pore volume. Consistently, the cementation exponent decreased monotonically throughout loading while the electrical tortuosity reversed from increasing to decreasing at crack initiation, indicating that deformation reorganizes the topology of the conductive network rather than merely its volume. X-CT reconstruction shows pore orientation migrating progressively toward the loading axis, with 93% of the pore volume concentrated within the 18–27° interval after failure, matching the macroscopic shear angle. Crack connectivity, rather than pore fluid content, therefore governs resistivity in damaged limestone, providing a quantitative basis for resistivity-based early warning of rock mass instability in underground engineering.