青藏高原片麻岩宏微观冻融损伤特性试验研究

Experimental Study on Macro and Micro Freeze-thaw Damage Characteristics of Gneiss in Qinghai-Tibet Plateau

为研究青藏高原等高寒山区岩体在冻融循环作用下的损伤特性,对西藏林芝地区分布广泛的片麻岩开展了不同循环次数下的冻融试验:通过扫描电镜与核磁共振试验,分析了岩样微观孔隙结构的扩展发育特征;采用单轴压缩试验结合声发射技术,获得了岩样宏观力学特性的劣化规律。结果表明:片麻岩微观结构的冻融损伤主要表现为颗粒剥落与微裂纹扩展两种模式,且同一位置处的损伤程度随冻融循环次数的增加先增强后减弱;片麻岩的孔隙度随冻融循环次数的增加而增大,但不同孔径孔隙的变化规律表现出一定的差异性;冻融损伤片麻岩在单轴压缩试验中的声发射活动均可以分为平静期、增长期与陡增期三个阶段,各阶段的声发射信号密度随冻融循环次数的增加而变大,但累计振铃计数和累计能量随着冻融循环次数的增加呈现先增加后减小的趋势;片麻岩试件表面颗粒大面积脱落的阶段与其抗压强度明显降低的阶段相对应。

To study the damage characteristics of rock mass in alpine mountainous areas such as the Qinghai-Tibet Plateau under freeze-thaw cycles,freeze-thaw tests under different cycles were carried out on gneiss widely distributed in Nyingchi,Tibet.The expansion and development characteristics of microscopic pore structure of rock samples were analyzed by scanning electron microscopy and nuclear magnetic resonance.The degradation law of macroscopic mechanical properties of rock samples was obtained by uniaxial compression test combined with acoustic emission technology.The results show that the freeze-thaw damage of gneiss microstructure is mainly manifested in two modes:particle spalling and micro-crack propagation,and the damage degree at the same position increases first and then decreases with the increase of freeze-thaw cycles.The porosity of gneiss increases with the increase of freeze-thaw cycles,but the variation of pores with different pore sizes shows some differences.The acoustic emission activity of freeze-thaw damaged gneiss in uniaxial compression test can be divided into three stages:quiet period,growth period and steep increase period.The acoustic emission signal density of each stage increases with the increase of freeze-thaw cycles,but the cumulative ringing count and cumulative energy increase first and then decrease with the increase of freeze-thaw cycles.The stage of large area shedding of particles on the surface of gneiss specimen corresponds to the stage of obvious decrease of compressive strength.