预制平行双节理类岩石材料板动态破坏试验研究

Dynamic Failure of Simulated Rock Mass Plate Containing Two Parallel Cracks

大型土木工程选址通常会遇到较复杂的地质结构.在工程建设或运营期间,往往受到地震、爆破等动态荷载作用,动载下其基础坐落的岩体内蕴含的节理裂隙会被激活发展,严重威胁着大型岩体工程的安全,因此,研究含节理岩体在动荷载作用下裂纹的起裂及扩展机理十分必要.试验基于断裂力学理论,取含平行双节理的类岩体材料作为研究对象,以节理角度作为变量,制作水泥砂浆试块,利用分离式霍普金森杆(SHPB)加载系统和数字图像相关(DIC)技术,动态捕捉节理的起始扩展及动态传播过程,分析其破坏形态、位移场和应力场,结果表明:①随着节理角度从 0°至 90°逐渐变化,样品强度呈现出先增大再减小,最后再增大的变化规律;②不同角度双裂纹试样均呈现X型主裂纹分布破坏,试样中心部位出现应变集中,岩桥连通破坏.岩桥破坏类型主要有两种,一种为两条节理尖端斜对角线相连的Z型破坏,另一种为口字形破坏.此外,高加载率会改变Z型岩桥破坏的连通位置;③同等加载条件下,0°节理试样裂纹尖端应力较小;15°~45°节理试样裂纹尖端应力略高,呈现出随加载率先增大后减小的形态;60°节理试样组受压明显导致节理面摩擦增大,使得Ⅱ型应力强度因子 KⅡ持续增大;75°~90°试样组应力场由于相对加载方向垂直度较高,导致 KⅡ相对较小,变化幅度也较小,破坏形态基本对称,不同裂纹尖端的 KⅡ差值也较小.试验结果反映了节理岩体在动态荷载下的扩展机理,为工程建设及地质灾害防治等领域提供了一定的理论支撑.

Major civil infrastructure sites are usually located in high-altitude gorge areas with complex geological structures.When subjected to dynamic loads such as earthquakes and blasting,the development of rock mass fractures is particularly intense,which seriously threatens the safety of rock mass projects.Therefore,it is necessary to study the crack initiation and propagation mechanism of rock mass under impact loads.Herein,based on theory of fracture mechanics,the experiment is designed to study the fracturing behavior of cement mortar specimens with parallel double joint angle as a variable using the split Hopkinson pressure bar(SHPB)system together with an ultrahigh- speed camera and digital image correlation(DIC)technology.The initiation and expansion of the joint cracks are captured,the failure mode is monitored,and the displacement and strain fields are analyzed.The results show that ①As the joint angle changes gradually from 0° to 90°,the strength of the specimens exhibits an increasedecrease- increase trend.②All the specimens with parallel double cracks present an X-type failure pattern with strain concentration occurred at the specimen center.The rock bridge connects through the fracture phenomenon. There are two main types of rock bridge failures,one is the Z type damage connected by two flaw tips diagonally,and the other is the “mouth” shape damage. In addition,the high loading rate will change the connected position of the Z type rock bridge failure.③The stress is low at the joint tip for 0° specimens;for specimens with 15°-45° joint angles, the stress at the joint tip is slightly high,showing an increase-decrease-increase trend with similar loading rate;in the 60° joint angle group,the surfaces friction of flaws is obviously increased,which increases the type Ⅱ intensity factor KⅡ;and for 75°-90° joint angle group,KⅡ is relatively lower owing to the loading direction,with a small magnitude of KⅡ difference and symmetrical damage morphology,the KⅡ difference at different crack tips is also small.The study reveals the failure pattern and failure mechanism of jointed rock mass under dynamic load, which provides certain theoretical support as a reference for engineering construction and geological disaster prevention and control.