不同冷却方式对花岗岩力学损伤特征影响

Mechanical damage characteristics of granite with different cooling methods

通过开展高温作用后的花岗岩在自然冷却与遇水冷却2种条件下的巴西劈裂声发射监测试验,研究了花岗岩不同冷却方式下的物理力学性质、声发射(AE)特征及其内部矿物和微观结构特征变化规律。研究结果表明:在2种冷却方式下花岗岩的抗拉强度、P波波速、弹性模量以及泊松比均随温度的升高而呈现下降的趋势,且遇水冷却时下降幅度更大,其中在500~600℃时由于石英发生相变,使得花岗岩的物理力学性质发生显著变化;花岗岩破坏过程中振铃计数特征、能量演化特征以及声发射b值变化规律与应力曲线的各个阶段基本吻合,遇水冷却时的声发射活动性更强且声发射b值低于自然冷却时的试样,表明遇水冷却时花岗岩主要以大尺度裂纹破坏为主;花岗岩在低温时呈拉伸式破坏,中温时呈现拉伸剪切混合破坏,高温时以拉伸破坏为主,且遇水冷却时试样破坏模式更复杂;高温加热后的花岗岩主要矿物成分未发生明显变化,其中长石和石英含量的变化较为明显;2种冷却方式下花岗岩内部微裂纹(沿晶裂纹、穿晶裂纹、脱离缺陷)的数量、张开度、扩展范围、连通性以及延伸长度均发生明显变化,以高温时遇水冷却的试样损伤程度最为严重,且随着加热温度的不断升高,内部裂纹不断增加,花岗岩的损伤程度也逐渐变大;高温花岗岩快速冷却的损伤机制主要是脱水作用、矿物相变以及热应力的综合作用,本质特征是热应力导致的微裂纹对岩石的弱化作用。

The physical and mechanical properties,acoustic emission characteristics,mineral evolution and microstructure changes of high-temperature granite are studied by the acoustic emission monitoring in Brazil splitting test under two conditions:natural cooling and water cooling.The results show that the tensile strength,P-wave velocity,elastic modulus and Poisson’s ratio of granite under the two cooling methods all decrease with the increase of temperature,and the decrease is greater when the granite is cooled by water,and the physical and mechanical properties of granite change significantly at 500-600℃due to the phase transition of quartz.The AE(acoustic emission)characteristics(AE counts,AE energy evolution and variation of AE b-value)in the failure process of granite are basically consistent with each stage of stress-time curve.The AE activity is stronger when the granite is cooled by water and the b-value of AE is lower than that of the sample under natural cooling,which shows that the granite is mainly damaged by large-scale cracks when it is cooled by water.The granite shows tensile failure at low temperature and high temperature,tensile and shear failure at medium temperature.Moreover,the failure mode of sample is more complex when it is cooled by water.After granite heated at high temperature,the main mineral composition of granite do not change obviously,among which the content of feldspar and quartz change greatly.With the increase of temperature,the number,opening width,extension range,connectivity and extension length of the internal micro-cracks including intergranular crack,transgranular crack,and detachment defect under the two cooling methods all change significantly,and the samples cooled by water at high temperature suffer the most serious damage.The damage degree of granite gradually increases with the increase of internal cracks.The damage mechanism of rapid cooling of high-temperature granite is mainly the combined action of dehydration,mineral phase transition and thermal stress,and the essential characteristic is the weakening effect of micro-cracks caused by thermal stress.