Mechanical property deterioration characteristics and a new constitutive model for rocks subjected to freeze-thaw weathering process

The recurrence of freeze-thaw processes induced by day-night and seasonal temperature changes is one of the most important reasons for damage and instability of rock engineering structures in cold regions. The study of the constitutive relationship and the damage degradation of rocks subjected to freeze-thaw weathering process is therefore of critical scientific importance to solving the stability problem of rock excavations in these regions. In this work, the stress-strain relationships of rocks subjected to different number of freeze-thaw weathering cycles were investigated in details. Experimental results show that as the number of freeze-thaw cycles increases, the compaction stage of the stress-strain curve becomes longer with more pronounced nonlinear features, while the uniaxial compressive strength, full compaction stress, tangent deformation modulus and initial deformation modulus all decrease, but the peak strain and full compaction strain all increase. A new piecewise constitutive model based on the characteristics of compaction and post-compaction stages of the stress-strain curve was proposed using a statistical compaction model in combination with the conventional statistical damage mechanics model with the strain equivalence hypothesis. Compared with the reference model, the proposed constitutive model has been demonstrated to be much more effective in describing the stress-strain behaviour of rocks having freeze-thaw damages, particularly when the number of freeze-thaw weathering cycles is significant. For all the experimental cases presented in this work, the coefficients of determination, R2, based on the proposed model are always greater than 0.93, while those of the reference model never exceed 0.85. In addition to, the model parameters have been shown to have clear physical meanings closely related to the characteristics of the measured stress-strain curve. •A simple method was described in this paper to find the full compaction point that separates the two parts on the stress-strain curve.•The effect of freeze-thaw weathering cycles on the pre-peak and post-peak deformation behaviours of the stress-strain curves of rocks was investigated in detail.•A piecewise constitutive model for rocks subjected to the freeze-thaw weathering process was then proposed.