冻融温变速率对岩石受载特性的影响规律

以贺兰山岩画、云冈石窟等中常见的硅质胶结砂岩为研究对象，对不同温变速率冻融后岩样进行称重、超声波测试和单轴压缩试验，探究了冻融后岩石物理力学性质随冻融温变速率的变化规律；根据冻融后岩石受载过程中的声发射和微震特征，揭示了温变速率对冻融后岩石内部不同尺度裂纹扩展的影响规律及其内在机制。研究表明：（1）随着温变速率增加，岩样冻融后的微裂纹增多，颗粒间联结强度减弱，峰值强度、弹性模量降低，破坏应变及损伤参量D_e、D_v增大；（2）冻融岩石受载过程中，微裂纹具有“初始压密―扩展孕育―急速扩展”的演化特征，宏观裂纹演化过程可分为“匀速扩展－急速扩展”两个阶段，其中宏观裂纹的急速扩展阶段还呈现出“孕育－扩展－再孕育－再扩展”的波浪式发展特点；温变速率越大，冻融后岩石受载过程中的微裂纹、宏观裂纹扩展越快，且更易于进入急速扩展阶段；当温变速率增大到一定数值后，微裂纹、宏观裂纹从加载开始即以较高速率扩展，直至岩样破坏；（3）微裂纹孕育阶段和加载全过程的声发射振铃相对增长速率，以及宏观裂纹匀速扩展阶段的相对时长、微震振铃相对增长速率均与损伤参量D_e、D_v具有较好的拟合关系，能够反映冻融循环对岩石的初始损伤作用；（4）冻胀力随温变速率增加而增大，导致不同温变速率冻融后岩样的初始损伤不同，这是引起冻融后岩石受载过程中裂纹扩展、声震特性出现显著差异的内在原因。

Influence of freeze-thaw temperature change rate on mechanics feature of rock during loading process

Thesiliceous and colloidal sandstone is common in Helan Mountains Rock Paintingand Yungang Grottoes. The weighing test, ultrasonic test and uniaxial compression test were conducted on the rock subjected tofreeze-thaw cycles at different temperature change rates to investigate theinfluences of temperature change rate on the physical and mechanicalproperties. The evolution and internal mechanism of crack propagation in rockafter freeze-thaw cycles at different temperature change rates were revealedbased on the features of acoustic emission and microseism during uniaxialcompression loading process. As the temperature change rate increases, themicro-cracks increase and the joint force between particles decreasesgradually, resulting in the lower peak strength and elastic modulus. Thus, thefailure strain and damage parameters D_e、and D_v increase with the increase of temperaturechange rate. During the loading processof rock, the micro-crack propagation progress shows an ‘initial compaction–propagationincubation–rapid propagation’ evolution feature, while the macro-crackpropagation progress can be divided into two stages as ‘uniform propagation–rapidpropagation’. And the rapid growth stage of the macro-crack also shows thewave-like development characteristic of ‘incubation–propagation–incubation–propagation’.The micro-crack and macro-crack propagation rate during the loading processincreases with the temperature change rate. It is easier for micro-crack andmacro-crack to enter each rapid propagation stage at a larger temperaturechange rate. When the temperature change rate increases to a certain value, themicro-crack and macro-crack propagate at a high rate from the beginning ofloading progress to the failure of rock sample. The damage parameters D_e and D_v have a good fittingrelationship with the relative growth rate of acoustic emission ring down countduring the propagation incubation stage and the whole loading process formicro-crack, and the relative length and relative growth rate of microseismring down count in the uniform propagation stage for macro-crack. Thesevariables can be used to reflect the initial damage of rock induced byfreeze-thaw cycles. The frost heaving force increases with the increase oftemperature change rate, resulting in the different initial damage offrozen-thawed rock at different temperature change rates. It is the internalmechanism leading to the significant difference in crack propagation, acousticemission feature and micro-seismic feature of frozen-thawed rocks duringuniaxial compression loading process.