Abstract:

Mechanical characteristics and micropore structure of granite under high-temperature (from normal to 1 300 ℃) have been researched with hydraulic servo system MTS 815 and micropore structure analyzer 9310. The results are as follows: ① Mechanical characteristics do not show obvious variations below 800 ℃; strength decreases suddenly above 800 ℃ and bearing capacity is almost lost at 1 200 ℃. ② Rock porosity increases with rising temperatures; the threshold temperature is about 800 ℃; at this temperature its effect is basically uniform with strength decreasing rapidly. ③ The connectivity is good although rock porosity is small. The coexistence of the characteristics of different widths of micro-fissures is displayed in phase pressure-mercury test curves. The accumulated pressure-mercury test curves show a stepwise shape. Ultramicropores gradually convert to micropores and connectivity increases when temperatures are over 800 ℃. ④ Rock fractal dimension of pore distribution decreases with rise of temperature. Thermal damage of rock transforms from irregular crack structure to homogeneous pore structure gradually at high temperature. The weakening of rock heterogeneity is the basic reason for the decrease of fractal dimension of pore distribution.

Key words: granite, temperature load, mechanical characteristics, porosity, fractal dimension