Calcareous clay strata present significant engineering geological challenges, including low freezing temperatures, substantial post-freezing expansion, high susceptibility to disintegration in water, and low strength. These properties readily cause excessive deformation or fracture of freezing pipes during construction, representing a major obstacle in artificial ground freezing (AGF) projects. Establishing an accurate constitutive model for calcareous clay freezing walls is therefore a critical element of their design. A series of triaxial shear tests is performed on calcareous clay retrieved from a mining area in Huainan. Field samples are prepared into standard cylindrical specimens (50 mm diameter, 100 mm height). Specimens are first consolidated within a triaxial pressure chamber and subjected to 24 h freezing curing. Testing is conducted using the W3Z‒200 frozen soil triaxial apparatus at Anhui University of Science and Technology's frozen soil laboratory. Test parameters include a strain rate of 1%/min, temperatures of ‒5, ‒10, and ‒15 ℃, and confining pressures of 0, 1, 3, and 5 MPa. Experimental stress‒strain relationships for the frozen soil are obtained. The Duncan‒Chang hyperbolic model is enhanced by incorporating fractional calculus, resulting in a fractional hyperbolic model specifically for frozen calcareous clay. The parameters of this model are determined, and its performance is compared against the original Duncan‒Chang model. Triaxial shear tests on frozen calcareous clay reveal that, under constant confining pressure, its peak strength increases significantly with decreasing temperature. In contrast, at constant temperature, peak strength increases approximately linearly with increasing confining pressure. The stress‒strain curves exhibit distinct strain-hardening behavior. The fractional hyperbolic model accurately captures this hardening characteristic. This model demonstrates broad applicability, effectively accounting for the simultaneous influence of both temperature and confining pressure. Validation confirms its good-fitting performance, while its relatively few parameters facilitate simple determination. This study utilizes natural soil samples and does not consider variations in water content as an experimental parameter. If moisture content differs significantly in specific engineering applications, the model parameters can be re-determined using the methodology proposed herein. Future research focuses on incorporating moisture content parameters directly into the model for further refinement.
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