Study on the critical stress threshold of weakly cemented sandstone damage based on the renormalization group method

During the microstructural analysis of weakly cemented sandstone, the granule components and ductile structural parts of the sandstone are typically generalized. Considering the contact between granules in the microstructure of weakly cemented sandstone, three basic units can be determined: regular tetrahedra, regular hexahedra, and regular octahedra. Renormalization group models with granule- and pore-centered weakly cemented sandstone were established, and, according to the renormalization group transformation rule, the critical stress threshold of damage was calculated. The results show that the renormalization model using regular octahedra as the basic units has the highest critical stress threshold. The threshold obtained by iterative calculations of the granule-centered model is smaller than that obtained by the pore-centered model. The granule-centered calculation provides the lower limit (18.12%), and the pore-centered model provides the upper limit (36.36%). Within this range, the weakly cemented sandstone is in a phase-like critical state. That is, the state of granule aggregation transforms from continuous to discrete. In the relative stress range of 18.12%-36.36%, the weakly cemented sandstone exhibits an increased proportion of high-frequency signals (by 83.3%) and a decreased proportion of low-frequency signals (by 23.6%). The renormalization calculation results for weakly cemented sandstone explain the high-low frequency conversion of acoustic emission signals during loading. The research reported in this paper has important significance for elucidating the damage mechanism of weakly cemented sandstone.