不同水损伤程度下泥岩断裂力学特性试验研究

Experiment research on the fracturing characteristics of mudstone with different degrees of water damage

为研究不同程度水损伤作用对泥岩断裂力学特性的影响,对水中浸泡不同时间条件下的泥岩半圆盘试件进行三点弯曲试验,同时利用PCI–2型声发射系统对泥岩试件的断裂全过程进行实时监测。结果表明:天然泥岩的断裂力学行为受水–岩作用影响显著,随着浸泡时间的增加,其峰值载荷不断下降,浸泡200 min后,该泥岩纯I型至纯II型断裂韧度分别降低至未损伤条件下的53%,56.5%,61%,64%,64.7%和67.6%,且泥岩的断裂破坏形式由脆性逐渐转变为延性。通过声发射定位确定了不同损伤程度下泥岩半圆盘试件中断裂过程区长度,随着损伤程度加深,断裂过程区长度逐渐减小,声发射事件累计总数不断增加;同时,将试验得到的等效断裂韧度与纯I型断裂韧度的比值与引入T应力后改进的最大周向应力理论比值进行比较,表明在未浸泡及短时间浸泡条件下试验结果符合该理论结果;但随着损伤程度的加深该试验结果拟合曲线逐渐偏离理论曲线,浸泡时间达到200 min时,该偏离情况较为明显。

In order to study the effect of water damage on the characteristics of fracturing of mudstone,three-point bending test was carried out to the semi-circular bend（SCB） mudstone specimens that have been soaked in water for different durations. The real-time monitoring with PCI–2 type acoustic emission system was conducted on the fracturing process of the mudstone specimens. The results show that fracturing behaviors of the mudstone is significantly influenced by water-rock interaction. The peak load of the mudstone specimens decreases with the soaking time increases. After being soaked for 200 minutes,the fracture toughness of mudstone from pure mode I to pure mode II decreased respectively to 53%,56.5%,61%,64%,64.7% and 67.6% of those of the intact specimens,and the failure characteristics of mudstone was changed from brittle to ductile. The length of fracture process zone（FPZ） of the mudstone SCB specimens soaked for different durations was confirmed by the acoustic emission（AE） positioning. As the soaking time increases,the length of FPZ decreases and the accumulative number of acoustic emission events increases. The experimental ratio of Keff/KIC and the theoretical ratio based on the modified maximum tangential stress（MMTS） criterion that takes into account the T-stress matched well when the mudstone SCB specimens are not soaked or only soaked for a short time. However,as the soaking time increases,the experimental results of SCB specimens diverge from the theoretical values gradually. When the soaking time reaches 200 minutes,the deviation becomes very distinct.