Exploring strength deterioration mechanism of soil-rock mixture based on pore structure characteristics under freeze–thaw cycles

Abstract

The strength deterioration of soil-rock mixtures (SRM) subjected to freeze–thaw (F–T) cycles leads to instability and failure of upper engineering structures in cold regions. However, the mutual feedback response mechanism pertaining to the changes of pore and strength in SRM under F–T cycles are rarely addressed. Nuclear magnetic resonance and triaxial tests were carried out to study the pore structure characteristics and strength response patterns of samples. A correlation model of SRM porosity and strength deterioration was first proposed under F–T cycles, and the model rationality was verified by test data. The results demonstrated that the pore connectivity and porosity increased throughout the F–T process, with the T2 spectral distribution curves exhibiting three peaks. Among these peaks, the main peaks underwent slight changes, while the secondary and micro peaks presented significant changes. Before 3 F–T cycles, the pore distribution evolved to small pores uniformly, followed with the large pores increasing and the micropores disappearing. With increasing of F–T times, the strength and cohesion of SRM experienced a drastic decline, while the internal friction angle demonstrated a slight decrease accompanied by fluctuations. Based on the analysis of test results, a correlation model regarding the porosity and strength deterioration was proposed through the relationship between the micro-structure evolution and the macro–mechanical response during F–T cycles. Furthermore, intrinsic mechanism of SRM strength deterioration under F–T cycles was revealed by considering the pore structure characteristics. The results can provide theoretical insights for the analysis of F–T disaster mechanism and prevention of SRM in cold regions.