热破裂花岗岩渗透率变化的临界温度

利用600℃20 MN伺服控制高温高压岩体三轴试验机测量了"鲁灰"花岗岩(200 mm×400 mm)在三轴应力作用下升温过程中渗透率的变化。发现热破裂花岗岩的渗透率随温度变化存在一个临界温度Tc,即300℃。低于该临界温度时,渗透率较小,其量级为10-19m2,并且增幅较小;高于该温度后,渗透率出现了突变,且增幅较大,300~400℃,其数值增加一个量级,为10-18m2;在400℃时,渗透率的数量级增大至10-17m2。同时采用MPV-SP显微光度计定量地研究了"鲁灰"花岗岩试样20~400℃热破裂过程中裂纹数量的变化。长度大于5μm(即l5μm)和长度大于10μm(即l10μm)的微裂纹数量出现两个峰值,并且l5μm的微裂纹数量变化的峰值温度均小于l10μm的微裂纹数量变化的峰值温度;300℃后l10μm的微裂纹数量增加较快,其增加速率约1个/10℃。300℃后微裂纹的快速增加是导致热破裂花岗岩渗透率突然增加的主要原因。

Critical temperature of permeability change in thermally cracked granite

The permeability of Luhui granite with 200 mm in diameter by 400 mm long was measured at triaxial stresses and elevated temperature by “600 ℃ 20 MN servo-controlled triaxial rock mechanics testing machine”.It is found that 300 ℃ is the critical temperature (Tc) of permeability change with temperature in thermally cracked granite.The magnitude of permeability is 10-19 m2 with a low increase below Tc and the permeability whose magnitude is 10-18 m2 increases drastically with high amplitude at 300-400 ℃ while the magnitude is 10-17m2 at 400 ℃.Simultaneously，the change of micro-crack quantity in thermally cracked Luhui granite at temperature up to 400 ℃ was quantificationally investigated by MPV-SP micro-photometer.Two peaks of micro-crack quantity that the length is more than 5 μm and 10 μm respectively exist at temperature up to 400 ℃.The temperature scope of micro-crack quantity peak in l>5 μm are less than that in l>10 μm.The quantity of micro crack whose length is more than 10 μm increases sharply at the rate of one per ten degree at temperature above 300 ℃.The drastic increase of micro crack above 300 ℃ is the main reason that permeability increases sharply at temperature above 300 ℃ in thermally cracked granite.