含预制缺陷类岩体模型破断试验与分析

Fracture Test and Analysis of Rock-Mass Model with Prefabricated Defects

为了探究内部缺陷形状由裂隙至圆孔的变化对类岩体脆性材料破断模式与特征的影响,构建了含缺陷的单轴压缩力学模型,并利用水泥砂浆材料制作类岩体试样,系统地研究了缺陷形状由裂隙至圆孔变化过程中含缺陷试件的强度变化特征和裂纹演化扩展机制。结果表明:当荷载方向与缺陷长轴垂直时,缺陷周边应力集中在长短轴端点处且与缺陷无关;缺陷对试样峰值强度影响较为明显,在缺陷形状由裂隙向圆孔变化的过程,峰值强度降低幅度逐渐增大;缺陷变化对试样的裂纹起裂与裂纹扩展的影响不显著;缺陷试样的最终破坏模式可划分为剪切破坏和拉-剪混合破坏,当m值大于0.60时破坏模式为剪切破坏,当m值小于0.33时破坏模式为拉-剪混合破坏。

In the process of formation of natural rock-mass,a large number of cracks,holes and other original defects often occur in interior,the internal defects of rock have a significant impact on the mechanical properties of rock-mass. Therefore,it is important to study the initiation,propagation and fracture of cracks in defective rock materials and rock-mass materials for practical engineering.Hence we explored the influence of the change of internal defects from cracks to holes on the fracture mode and characteristics of rock-mass materials by combining theory with experiment. Firstly the mechanical model of uniaxial compression was constructed and the stress at the hole edge was solved by using the conformal angle mapping method,then the uniaxial compression test was carried out on the defective rock samples made of cement mortar materials.The rock-mass specimens were made by mixing 325#white cement,river sand,and water at a mass ratio of 5∶5∶2,the size of the defective sample after forming is 200 mm×150 mm×50 mm. The defects were created by inserting 3 D printing materials into cement mortar paste and removing them during curing,the long axis 2 a is 40 mm,the short axis 2 b is change values for 1,10,20,30,40 mm,hence the corresponding m[m=(a-b)(/a+b)]values were 0.95,0.60,0.33,0.14 and 0.Uniaxial compression of defect specimens by using the rock mechanics servocontrolled testing system after standard conservation were carried out. The test results show that:(1)Under uniaxial compression,when m is 0 the uniaxial compressive strength of the defective rock-mass is the lowest.The uniaxial compressive strength of the defective specimen increases gradually with the increase of m value,and the peak strength of the defective specimen decreases gradually with the increase of m value.(2)In the process of uniaxial compression fracture of defective rock-mass,the initial tension crack is initiated at the end of the short axis of the defect.With the increase of m value,the initiation position gradually moves to both ends of the long axis,and the crack develops along the direction of the principal stress.Under the action of continuous load,shear cracks are initiated near or far from the long axis of the defect,and the shear crack propagates continuously with the increase of load.In the later stage of crack propagation,spalling phenomenon at the end of the long axis when the m value is large.(3)After uniaxial compression fracture the defective rock-mass will have two fracture modes,namely shear failure and tension-shear mixed failure.When m is greater than 0.60,the failure mode is shear failure,others will happen tension-shear mixed failure.