尖端相交裂隙砂岩强度与破裂演化特征试验研究

Strength and fracture behaviors of sandstone samples containing intersect fissures under uniaxial compression

岩石中裂隙的分布形态对岩石力学特性的影响极为显著。通过对含尖端相交裂隙砂岩试样进行单轴压缩试验,研究了2条相交裂隙分布方向角β和夹角α对砂岩强度、变形及破裂演化特征的影响。试验结果表明:随着β角的增大,试样峰值强度逐渐增大,平均模量先增大后减小。当β角为0°时,试样表现为双裂隙外尖端贯通破坏,当β角在30°~45°之间时,试样表现为单裂隙外尖端开裂破坏;当β角在60°~90°之间时,试样表现为双裂隙外尖端独立开裂破坏。随着β角的增大,裂隙内尖端的裂纹发育程度逐渐减弱。随着α角的增大,试样峰值强度逐渐减小,平均模量表现出先减小后增大再减小的趋势,当α角在30°~60°之间时,试样表现为单裂隙外尖端开裂破坏;当α角在90°~150°之间时,试样表现为双裂隙外尖端开裂破坏。随着α角的增大,裂隙内尖端裂纹发育程度逐渐减弱直至无裂纹产生。利用声发射仪记录了试样加载过程中的声发射特征,结果表明AE事件数主要集中在峰值和峰前非线性段,宏观裂纹的起裂、扩展和贯通都会产生明显的AE事件。

Mechanical behaviors of rocks are significantly influenced by the distribution patterns of fissures. By conduc- ting uniaxial compression tests on sandstone samples containing two prefabricated fractures which interact with each other at the tip,the effects of distribution direction angle （β） and the included angle of intersecting fractures （α） on strength, deformation and fracture evolution properties of sandstone samples were respectively studied. The results show that the peak intensity of samples increases gradually with the increase of angle α, while the average modulus increases first and then turns to decrease. Coalescence failure between the outer tips of pre-existing fractures occurs to rock sam- ples with α of 0°, and when fl varies between 30° and 45°, the failure form is characterized by one crack formed at the outer tip of one prefabricated fracture. In the range offl from 60° to 90° ,the cracks generated at the outer tips are in- dependent when ultimate failure occurs to rock samples. With the increase of angle α, the crack growth degree at the inner tip of fractures decreases gradually. With the increase of the included angle a, the peak intensity of samples de-creases gradually, and the average modulus decreases first, then increases and decreases once again. When α is be- tween 30° and 60°, one crack initiates at the outer tip of one prefabricated fracture, while in the range 90°- 150°, two cracks are formed at the outer tips of two fractures respectively. With the increase of the included angle α, the crack growth degree at the inner tip of fractures decreases gradually until no crack initiation. Acoustic emission （AE） char- acteristics were recorded during the loading process by using the acoustic emission equipment, and the results show that AE events mainly occur at peak intensity and nonlinear stage before peak intensity. Pronounced AE occurs when- ever the macroscopic crack generates and propagates.