Development of the water-conducting fracture zone in longwall top-coal caving mining with super-large mining height and weak cemented overburden

This study investigates the height evolution of the water-conducting fracture zone (WCFZ) under super-high mining conditions in the 1101 longwall face of Zhundong No. 2 Mine. Based on 28 measured datasets, a multivariate nonlinear regression model is proposed, outperforming traditional empirical formulas in accuracy. Numerical simulations reveal four developmental stages of the WCFZ: initial acceleration (0–180 m), deceleration (180–270 m), renewed acceleration (270–420 m), and stabilization (≥ 420 m). Morphologically, the WCFZ transforms from arch-shaped to trapezoidal and ultimately to a flattened arch. Three-dimensional simulations show synchronized evolution between the plastic zone and the WCFZ. Field validation is achieved through microseismic monitoring and borehole leakage data. A critical mining height of 16 m is identified, beyond which WCFZ growth shifts from linear (11.38 m/unit) to nonlinear (19.45 m/unit), causing destabilization of the beam-arch structure and promoting vertical fractures. Fracture patterns vary by lithology: weakly consolidated strata form mesh-like networks, while cemented layers exhibit stepwise, slip-induced fractures. This study offers an accurate prediction model and insights into WCFZ mechanics for improved mining safety and groundwater protection.