水-动力耦合作用下红砂岩力学性质及能量机制研究

Mechanical properties and energy mechanism of red sandstone under hydro-dynamic coupling effect

以干燥试样为对照,对自然、吸水和饱水3类含水试样进行单轴冲击试验,分析水-动力耦合作用下红砂岩试样的动态强度与变形特征以及损伤破坏前后的能量演化机制。试验结果表明:试样的动态抗压强度和峰值应变受含水率和冲击荷载影响较大,而峰值模量主要受含水率影响较为明显,这是由于红砂岩在水弱化作用下颗粒结构疏松膨胀、胶结强度减弱,加之在中高应变率下孔隙水所具有的细观力学效应,致使试样表现出低强度和高应变,而冲击荷载带来的应变率效应则使试样强度增强,塑性变形受到抑制;试样峰值点前吸收的总应变能U多以可释放弹性能Ue存储起来,耗散能Ud占比较小,各部分应变能随着脉冲强度的升高而增加,但随着含水率的变化趋势则不尽相同;不同脉冲强度下的脆性指标修正值BIM(Ud与Ue的比值)显示红砂岩试样的含水率以及冲击荷载的脉冲强度均存在一个阀值,使其塑性变形在水-动力耦合作用下的响应截然不同,而引入的有效冲击能指标K_(eff)显示应变率效应对干燥试样和自然试样的冲击倾向性具有显著影响,对于含水率较高的吸水试样,水弱化作用降低了应变率效应,达到饱水状态时,因为饱和液体对应变率效应的促进作用,饱水试样的应变率效应得到强化。

A series of impact experiments is conducted on natural, soaked and saturated red sandstone samples. The effect of hydro-dynamic coupling on dynamic strength, deformation characteristics and energy mechanism of samples is analyzed by comparing with that of dry samples. Experimental results indicate that dynamic compressive strength and peak strain of samples are mainly affected by the water content and impact load, while the peak modulus is obviously influenced by the water content. The water softening effect leads to loosen expansion of granular structure, which further results in cementation weakening. In addition, the meso-mechanical effect of pore water might lead to low strength and high strain of samples at high strain rate. The strength of samples is strengthened and the plastic deformation is decreased by the effect of strain rate. A large amount of total absorbed energy U prior to the peak stress is transformed to the releasable strain energy Ue, but a small portion of U is transformed to the dissipation energy U^d. The strain energy of each part increases with the increase of the pulse intensity, however the variation with the water content is largely different. A modified brittleness index BIM（ratio of U^d to U^e） shows that both the water content and pulse intensity have a threshold resulting in the response of plastic deformation quite different. The effective impact energy index（K_（eff）） shows that the strain rate effect significantly influence the impact tendency of dry and saturated samples. Water softening effect reduces the effect of strain rate, but the strain rate effect is enhanced when the saturation is reached.