Experimental study on the evolution of frozen wall and temperature field in artificially freezing fractured rock mass

Dominant flow channels may develop along fractures embedded in rock strata. Freezing pipe operations in artificial ground freezing (AGF) engineering are frequently disrupted by such channels. This disruption delays frozen wall development and poses a risk to shaft lining construction because of structural weakening. However, experimental investigations into the freezing process in fractured rock masses remain scarce. In this study, the evolution of the frozen wall and temperature field was explored via visualization physical model tests. The test results revealed that the fracture and rock mass development rates increased under the following three conditions: reduced fracture aperture (d), decreased fracture flow velocity (v), and sand filling. Specifically, increases of 5% (as d decreases from 3 to 0.5 mm), 25% (as v decreases from 600 to 40 m/d), and 15% (sand-filled) were obtained. The asymmetry of the temperature field and the frozen wall development rate were significantly influenced by changes in the heat transfer mechanism during phase transition. Following the transition to ice, conductive heat transfer emerged as the predominant mechanism. Concurrently, the fractured rock mass was thermally influenced by the collective action of all the freezing pipes.