Study On Damage Of Frozen Thawed Rock Based On Fractal Theory

Cold region is widely distributed around the world, and the distribution area of cold region in China follows Russia and Canada, only ranking the third in the world. Research on freezing-thawing rock damage characteristics is of great significance to the resources development and geotechnical engineer ing construction in the cold region.This article conducts the analysis on four failure modes of rock particles – peeling, crazing, scaling and fracture through the red sandstone freezing and thawing cycle experiment. The internal microstructure of red sandstone is observed with CT scanning device, and the analys is on the change rule of CT image along with freezing and thawing cycle is made intuit ively. The number of high bright spot around CT image decreases along with the increase in times of freezing-thawing cycle, while brightness gradient of CT image increases along with the increase in times of freezing-thawing cycle. Physical and mechanics parameters of red sandstone are obtained through the mechanical property experiment, concluding that lim it stress decreases gradually, limit ing strain increases gradually, and elastic modulus becomes weak gradually along with the increase in times of freezing-thawing cycle.Based on the fractal theory and according to CT scan image, this paper obtains the fractal dimension features of inner port and density structure of red sandstone in three scopes- overall, total cross-section and core of section. The research finds that the fractal dimension of the overall and total cross-section pore presents the downtrend, showing that the complexity of pore structure form decreases along with the increase in times of freezing-thawing cycle, namely, development of a small amount of pore occupies the dominant posit ion. The fractal dimension of core port presents the uptrend, showing that the complexity of pore structure form increases along with the increase in times of freezing-thawing cycle, namely, production of new pore in the core occupies the dominant position. The fractal dimension of overall density presents the fluctuating changes, showing the overall test piece keeps the certain structure along with the increase in times of freezing-thawing cycle. The fractal dimension of total cross-section presents the downtrend and its value is near 2, showing that total cross-section density tends to uniform distribution along with the increase in times of freezing-thawing cycle. The fractal dimension of core density presents the upward, showing the difference of various points of core density increases along with the increase in times of freezing-thawing cycle. Pore structure change and density distribution change can confirm each other.Through the analysis on red sandstone freezing-thawing cycle and CT scan experiment phenomenon, considering the influence of pore size and pore structure, and based on rock damage theory, this paper obtains the damage expression formula about red sandstone being affected by freezing and thawing cycle, showing that freezing-thawing damage development of red sandstone is affected by the initial pore distribut ion and pore distribution rule determines the main form of the damage curve, and that freezing-thawing damage development of red sandstone is affected by structural changes of red sandstone, and the bigger difference between fractal dimension value DKQ and stable s tructure fractal dimension value DD represents the faster damage development.