Research on creep characteristics and pore structure evolution characteristics of freezing-thawing rocks

Abstract

The rock mass of open pit in cold regions is often affected by freezing-thawing cycles and long-term loads. In order to explore the influence of cold region environment on the stability of rock mass, the red sandstone of a project in northern Shaanxi is taken as the research object, starting with the macroscopic creep characteristics and meso-structure evolution characteristics of freezing-thawing rocks. The evolution of macro-mechanical indexes and meso-parameters during the creep process of freezing-thawing red sandstone is quantitatively analyzed through the loading and unloading creep test of freezing-thawing rock and the NMR detection. The results show that the pore size distribution fluctuates in a small range when the stress level is between 0.3σucs−0.5σucs, and when the stress level increases to 0.5σucs−0.6σucs, the proportion of small holes (T210 ms) increases, and freezing-thawing aggravates the increase of porosity in the creep stage, and the effect of freezing and thawing on porosity growth is more significant at high stress levels. The fractal theory is introduced to characterize the complexity of pore structure. It is found that the large pores have obvious fractal characteristics, while the fractal characteristics of small pores are not obvious. The total pore fractal dimension DT is positively correlated with porosity. The complexity of pore structure only affects the creep mechanical properties of rock when the porosity is large. The freezing-thawing-damage creep model of freezing-thawing effect and creep damage is established. The model curve can well reflect the creep characteristics of the freezing-thawing rock, which is in good agreement with the experimental curve. This study can provide a theoretical basis for rock engineering construction in freezig-thawing environment.

Keywords

• creep test
• freezing-thawing cycle
• nmr
• porosity
• fractal dimension
• creep model