Overlying strata movement characteristics and water conducting fracture zone height prediction for deep coal mining in arid Western China

The deep mining of coal seams in the central Ordos Basin, a critical arid region of western China, is governed by the unique mechanical behavior of ultra-thick, weakly cemented sandstones of the Cretaceous Zhidan Group, which challenge classical overburden control theories. To elucidate the deformation mechanisms of this special overburden and assess its implications for groundwater protection, this study integrates physical similarity simulation, laboratory rock-mechanical testing, microstructural analysis, and distinct-element numerical modeling (UDEC). A 1:500 similarity model simulated the stratigraphic sequence and mining progression. Results reveal that during single-panel extraction, the main roof initiates deformation at a 150 m face advance, with subsidence reaching 5.55 m at a 300 m mining width. Under multi-panel continuous mining, the high-position weakly cemented sandstones exhibit large-scale coordinated bending and plastic flow, forming a distinctive “subsidence–rotation” deformation pattern that propagates upward. Triaxial tests confirm the rock’s low strength and high confining-pressure sensitivity, with peak strength ranging from 27.8 to 71.1 MPa, cohesion of 6.7 MPa, and an internal friction angle of 38.7°. Failure modes transition from tensile splitting at low confinement to shear and plastic flow at higher pressures. Microstructural analyses (SEM/EDS) identify well-rounded quartz grains, extensive intergranular pores, and weak calcite–feldspar cements, explaining the observed high deformability and low bearing capacity. UDEC simulations of multi-panel mining captured progressive horizontal separation, stress redistribution, and composite tensile–shear failure. The water-conducting fracture zone (WCFZ) is shown to develop upward to the base of the Jurassic Anding Formation, with a maximum height of 186 m when the width-to-depth ratio exceeds 1.5. These findings characterize the deformation features of weakly cemented overburden and establish a mechanical basis for predicting the WCFZ, providing critical insights for overburden management and groundwater resource protection in deep coal mining under arid conditions.