Study on deterioration of mechanical properties and statistical damage model of freeze-thaw loaded sandstone

In the development of mineral resources and engineering construction in the western region, sandstone is one of the main engineering geological aquifers, and the freezing and thawing environment affects the mechanical and deformation characteristics of sandstone. In order to study the deterioration and damage characteristics of mechanical properties of loaded rocks under the influence of freeze-thaw environment, red fine sandstone in Shaanxi province was taken as the research object, and freeze-thaw cycle tests and uniaxial compression tests were carried out for 0, 5, 10, 20 and 30 times, and the stress-strain curve and mechanical characteristic parameters of the whole uniaxial compression process of frozen-thawed sandstone were obtained. The mechanical characteristic parameters of frozen-thawed rocks were analyzed, and the deterioration model of rock mechanical properties under freeze-thaw environment was established. Based on the influence of freeze-thaw environment on rock damage, considering the characteristics of rock compaction stage in deformation stage, a modified statistical damage constitutive model considering compaction stage is established. The results show that with the increase of freeze-thaw cycles, the proportion of rock compaction stage is increasing, and the peak value should also increase gradually. Brittle failure occurs in the first 30 freeze-thaw cycles, and the brittleness of rock is obviously weakened after 30 freeze-thaw cycles, and the strain softening stage is obvious. The loss rate of mechanical characteristic parameters increased rapidly in the first 10 times of freeze-thaw cycle, and then slowed down obviously. After 30 freeze-thaw cycles, the peak strength loss rate is 47.27% and the elastic modulus loss rate is 60.35%. Among them, the loss rate of mechanical characteristic parameters increases linearly with the number of freeze-thaw cycles, and the mechanical properties of rocks decrease exponentially after freeze-thaw. The peak strength and elastic modulus of rocks under freeze-thaw environment can be accurately predicted by using the pore characteristics of rocks under freeze-thaw environment. The modified statistical damage constitutive model considering the compaction stage has a higher fitting degree with the test curve, and the modified theoretical model can provide reference for the deterioration of mechanical properties and damage prediction of frozen-thawed rocks.