高温后花岗岩力学性质及微孔隙结构特征研究

采用MTS815液压伺服试验系统及9310型微孔结构分析仪对花岗岩在温度作用下(常温～1300℃)的宏观力学性质及微孔隙结构特征进行了较为系统的研究。结果表明:①在800℃之前,岩样力学性质变化规律不明显;超过800℃,岩样强度迅速劣化;达到1200℃,岩样基本失去了承载能力。②岩样孔隙率随温度升高而增大,孔隙率的阀值温度在800℃左右,与岩样在该温度点强度突然降低相一致。③岩样孔隙率较小,但连通性好,在阶段进汞曲线上显示为不同宽度微裂隙并存的特征,累计进汞曲线呈台阶状,温度超过800℃,超微孔逐渐向微孔隙转化,岩样连通性增强。④岩样孔隙分布分形维数随温度的升高反而降低。在高温作用下,岩样中的热损伤由初始非规则的裂隙结构逐渐向均匀化的孔穴结构转化,非均匀性弱化是导致岩样孔隙分布分形维数降低的根本原因。

Research on mechanical characteristics and micropore structure of granite under high-temperature

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.