Initiation Mechanism of Unsaturated Rock Cracks Driven by Ice–Gas–Heat Flux Coupling During Freezing

In high‐altitude cold regions, ice–water phase change during freezing expands ice and compresses trapped gas in unsaturated rock cracks, whereas temperature gradients induce thermal stress, jointly driving crack initiation. This study derives governing equations for ice–gas mechanics, establishes stress intensity factors induced by heat flux, and formulates an MTS‐based initiation criterion. The effects of freezing temperature, saturation, and heat flux on key crack initiation parameters are analyzed. Within the considered parameter range, freezing pressure, ice–rock interfacial friction, and fissure gas pressure increase as freezing temperature decreases, whereas fissure gas pressure rises sharply under high saturation, making crack initiation mainly tensile. When heat flux intensity exceeds 1000 mW/m 2 , shear effects intensify, and the initiation mode evolves from tensile‐dominated to tensile–shear‐mixed or shear‐dominated. As q increases, the tangential stress changes from cosine‐ to sine‐type distribution, whereas θ 0 decreases in the negative angle range and increases in the positive angle range, with the peak generally shifting rightward.