冻融后石英砂岩三轴蠕变特性试验研究

Experimental study of creep properties of quartz sandstone after freezing-thawing cycles

为探讨高寒地区高陡岩质边坡的时效劣化机制,对经历不同冻融循环次数后的石英砂岩进行常规三轴和三轴蠕变试验,分析了冻融作用对岩石在短期受荷和长期受荷下的力学特征。试验结果表明,冻融作用对短期受荷下砂岩力学性能影响较小,常规力学参数及声发射现象随着冻融循环次数增加变幅较小;在长期受荷作用下冻融对砂岩时效力学特征影响显著,表现为各蠕变力学参数均随冻融循环次数增加而明显变化,是由于冻融导致裂隙壁疲劳受损,其后壁上颗粒在长期荷载作用下能够充分调整变形,冻融造成的微损伤会引起较强的蠕变性。提出考虑冻融蠕变损伤差异的长期折减系数,表征冻融后岩石抵抗长期荷载的能力。冻融后岩样在短期荷载及长期荷载作用下的破坏模式均为剪切破坏,但在长期荷载作用下的岩石破碎方式随着冻融循环次数增加逐渐由单一的斜剪切面向"X"状共轭剪切面演化,岩石更加破裂。研究结果对于高寒山区重大工程的全寿命周期评价具有重要意义。

The degradation mechanism and time-dependent failure mechanism in high steep rock slope are investigated in the cold region. Experiments of triaxial compression and triaxial creep are carried out on the quartz sandstone samples experienced different freezing-thawing cycles. The difference of mechanic property and failure model under the action of short-term stress and long-term stress are focused on. Experimental results show that the freezing-thawing action made little effect on mechanical properties of sandstone under short-term stress. The conventional mechanical parameters and acoustic emission (AE) phenomenon just decreased slightly with the increase of freezing-thawing cycles. However, the freezing-thawing action made great effect on mechanical properties of sandstone under long-term stress. With the increase of the freezing-thawing cycles, the creep mechanical parameters changed with increasing freezing-thawing cycles obviously. This is because that the freezing-thawing result in the fatigue damage of the crack wall and the particle in the crack wall can deform sufficiently, causing the obvious creep properties. The long-term reduction factor, which can predict current situation accurately, is proposed for symbolizing the ability of resisting to long-term load of sandstone. In addition, the failure patterns of rock under the action of short-term and long-term stress after different freezing-thawing cycles both are shear failure. But the broken way of rock under the action of long-term stress developed gradually from single oblique cutting surface to X-shape conjugate shear surface with increasing freezing-thawing cycles and the broken degree is more serious. The result is of great significance for the whole life cycle assessment of major projects in highland and cold region.