Numerical analysis of the effects of vesicle distribution characteristics on the engineering properties of volcanic rocks

Vesicles can be of different sizes and shapes and can be randomly distributed within vesicular volcanic rocks. This study investigates the variation of engineering properties of vesicular rocks due to the changes in vesicle distribution characteristics for different cases of bulk porosity and vesicle diameter using a systematic numerical simulation program using the finite element method-based rock failure process analysis (RFPA) software. Models with uniform-size vesicles and combinations of different proportions of different-sized vesicles were considered to resemble natural vesicular rocks more closely, and ten different random vesicle distributions were tested for each case. Increasing bulk porosity decreased the uniaxial compressive strength (UCS) and elastic modulus of the specimens, and the specimens with the lowest bulk porosity showed the greatest range of UCS values in the case of uniform-size vesicles. The effect of vesicle diameter on UCS showed an unsystematic response which was understood to be a result of different vesicle distribution patterns, some of which facilitated a shear failure. Specimens with multiple-size vesicles in different proportions revealed that the variation of UCS due to vesicle distribution characteristics is minimum when the bulk porosity is equally shared by different size vesicles. In addition, when the proportion of smaller-sized vesicles is higher, UCS showed an increase compared to that of the equal proportion of different size vesicles case at low porosities, but a decrease at higher porosities. Variation of elastic modulus showed minor, unsystematic fluctuations as a function of vesicle diameter and different proportions of different-sized vesicles, and the range for different vesicle distribution patterns was narrow in general. Overall, the findings of this study recommend cautious use of the engineering properties determined through a limited number of laboratory tests on vesicular rocks.

加、卸载条件下花岗岩损伤演化分析（英文）

在不同围压下进行三轴试验,研究花岗岩在加载和卸载过程中的损伤演化特征。通过分析试样的轴向应力、轴向应变变化表明,在轴向应变较低时,试样卸荷破坏失效与加载条件下的不同。围压越高这种不同越明显。本文提出了一种新的描述脆性岩石割线模量随轴向应力变化的方程。试件的破坏机制表现出2种不同的模式:在纯加载荷下,试样没有明显的剪切断裂,而卸载试样则表现出多个相交的断裂。此外,分析了在加载和卸载条件下,试样在变形过程中的耗散和弹性能的演化规律。此外,根据损伤过程中的能量耗散和割线模量演化来评价2种损伤指数的变化,并观察到2种损伤的演化过程都能很好地区分损伤演化的关键阶段。