Strength Degradation of Sandstone Under Coupled Loading and Freeze-Thaw Cycles: Experimental Study and Discrete Element Numerical Simulation.

Previous studies have mainly examined sandstone freeze-thaw degradation under unloaded conditions, whereas the continuous influence of sustained stress on compressive and tensile properties remains unclear. To address this issue, water-saturated specimens were subjected to axial loads of 0-2 MPa and 0-10 freeze-thaw cycles, followed by uniaxial compression and Brazilian splitting tests. A two-variable exponential strength model and a load-freeze-thaw coupled discrete element model were established. Both strengths decreased with increasing freeze-thaw cycles. Under no load, after 10 cycles, the uniaxial compressive strength and tensile strength decreased by 27.85% and 36.67%, respectively, indicating higher freeze-thaw sensitivity of the tensile property. Loading mitigated strength loss: after 10 cycles, the two strengths of the 2 MPa group were 9.59% and 10.53% higher than those of the no-load group. The retention effect on compressive strength first increased and then decreased, whereas that on tensile strength increased with cycle number. The discrete element results showed that frost-heave cracks evolved from local initiation to connection and clustering, with tensile cracks dominating. Loading reduced tensile bond breakage and slowed crack accumulation and subsequent coalescence, linking the observed strength retention to the inhibition of mesoscopic tensile damage.