循环动荷载作用下脆性岩石疲劳损伤力学特性研究

发布时间：2018-09-01 08:32

【摘要】：近年来,随着国民经济的高速发展,各类基础设施建设和大型岩土工程越来越多,例如,高陡岩质边坡工程、铁路和公路隧道工程、城市地铁工程、大型核电站工程、大型水电站工程、大型地下深埋长隧洞群及矿山深部开采等工程。机械冲击和爆破凭借其高效、经济、快捷的技术特点,广泛应用于工程岩体开挖中,可带来巨大的社会、经济效益。不管用何种方式进行岩体开挖时,其产生的冲击应力波在传播过程中,不可避免会对远离作业点的岩体造成一定程度的损伤和破坏,从而威胁工程岩体的稳定性。因此,为合理指导工程实践,以及根据围岩的疲劳损伤特性充分利用围岩的承载能力,减少不必要的工程浪费,研究岩石在循环动载荷作用下的疲劳损伤力学特性、损伤累积演化规律及破坏模式具有重要的实际意义。岩石是在漫长的地质历史发展过程中,经受各种复杂地质构造作用形成的产物,是由多种矿物晶粒、胶结物等组成的复杂混合体,而且其结构一般都存在大量的地质缺陷。作为一种天然材料,广泛存在于自然界中,是天然的工程材料,对人类的经济活动起着非常重要的作用。岩石在静态或准静态循环荷载作用下的力学特性研究已取得了丰富的研究成果,理论体系较完善。然而,对岩石在动态循环载荷作用下的疲劳损伤力学特性研究明显不足,其理论研究明显落后于工程实际。论文针对脆性岩石在循环荷载作用下疲劳损伤力学特性研究的不足,通过SHPB试验装置对劳伦斯花岗岩进行循环冲击压缩试验,根据试验结果分析应力—应变曲线的变化规律及岩石强度和变形的动态特性；揭示试验条件和试样本身等因素对岩石疲劳力学特性的影响规律；分析岩石的损伤累积演化规律及破坏模式,为指导工程实践提供理论基础。论文的主要研究工作及结论如下： 1.为便于研究岩石试样在循环动荷载下的力学特性,通过改进试验技术,主要通过对岩石试样施加套筒,控制试样应变与轴向变形。 2.岩石试样在单次冲击过程中的应力-应变变化过程,主要分为以下五个阶段：压密阶段、弹性阶段、加速变形阶段、第一卸载阶段、第二卸载阶段；岩石试样在循环动荷载下,弹性模量不断减小,试样抵抗变形的能力不断减弱,力学性能不断损伤,但是在累积损伤的过程中,具有突变性,即冲击前期损伤缓慢,到即将破坏时力学性能剧减；试样在循环动荷载下,其内部裂纹不断萌生、扩展,变形具有突变性,冲击前期以弹性变形为主,无残余变形,冲击后期应变剧增,岩石试样急剧破坏。 3.冲击气压和孔隙率不会影响岩石疲劳力学性能的整体变化规律,但会影响局部阶段的损伤劣化过程,以及影响岩石宏观力学性能与细观结构的损伤程度与速度。冲击气压相对岩石孔隙率,对岩石疲劳力学特性的损伤较大,即岩石疲劳力学特性对冲击气压较敏感。 4.岩石在循环动荷载下,声波速度变化规律与峰值应变变化规律大致对应。波速整体变化趋势不断减小,冲击前期波速缓慢递减,后期快速减小。波速变化规律体现试样细观结构的累积损伤过程,冲击气压和孔隙率不影响波速的整体变化趋势,但会影响局部阶段波速的递减幅度和速度。冲击期间冲击波速不变的可能原因是冲击后的裂纹较小或者冲击后试样裂纹方向与P波的传播方向一致。 5.岩石在循环动荷载作用下的损伤累积过程一般可分为三个阶段：损伤初始阶段、损伤低速发展阶段和损伤加速发展破坏阶段。冲击气压和孔隙率不影响损伤累积演化的整体规律,但会影响局部阶段的疲劳寿命、损伤程度与速度,与岩石宏观应力应变随循环冲击次数的变化规律基本一致。 6.在一定范围的冲击气压下,试样在较小的尺寸范围内,岩石在循环动荷载下的破坏模式为劈裂破坏。其破坏机理为：在冲击载荷作用下,试样在发生轴向压缩变形时,由于泊松效应必然发生横向扩展变形,即横向伸长线应变。由于岩石抵抗伸长变形的能力很弱,当此应变达到一定值时,岩石即发生破坏。
[Abstract]:In recent years, with the rapid development of the national economy, more and more infrastructures and large-scale geotechnical projects have been built, such as high and steep rock slope engineering, railway and highway tunnel engineering, urban subway engineering, large-scale nuclear power station engineering, large-scale hydropower station engineering, large underground deep-buried long tunnel group and deep mining engineering. And blasting with its high efficiency, economy, fast technical characteristics, widely used in engineering rock excavation, can bring enormous social and economic benefits. Therefore, in order to guide the engineering practice reasonably and make full use of the bearing capacity of surrounding rock according to the fatigue damage characteristics of surrounding rock, reduce unnecessary engineering waste, it is important to study the fatigue damage mechanics characteristics of rock under cyclic dynamic loading, the damage accumulation and evolution law and the failure mode. Practical significance.
Rock is the product of various complex geological structures in the long process of geological history. Rock is a complex mixture of many mineral grains and cements, and its structure generally has a large number of geological defects. The research on the mechanical properties of rock under static or quasi-static cyclic loading has made abundant achievements, and the theoretical system is perfect. However, the research on the mechanical properties of rock under dynamic cyclic loading is obviously insufficient, and the theoretical research lags behind the engineering. Actual.
Aiming at the insufficiency of fatigue damage mechanics research on brittle rock under cyclic loading, the cyclic impact compression test of Lawrence granite is carried out by means of SHPB test equipment. According to the test results, the variation law of stress-strain curve and the dynamic characteristics of rock strength and deformation are analyzed. The influence of some factors on the fatigue mechanical properties of rock is analyzed, and the cumulative damage evolution law and failure mode of rock are analyzed.
The main research work and conclusions are as follows:
1. In order to study the mechanical properties of rock specimens under cyclic dynamic loads, the strain and axial deformation of rock specimens are controlled by applying sleeves to the rock specimens through improving the test techniques.
2. The stress-strain change process of rock specimen during single impact is divided into the following five stages: compaction stage, elastic stage, accelerated deformation stage, first unloading stage and second unloading stage; under cyclic dynamic load, the elastic modulus of rock specimen decreases continuously, the ability of resisting deformation of specimen decreases continuously, and the mechanical properties are not. Fracture damage, but in the process of cumulative damage, has catastrophe, that is, the damage in the early stage of impact is slow, and the mechanical properties of the specimen will be reduced sharply when it is about to be destroyed; under cyclic dynamic load, the internal cracks of the specimen are continuously germinated, propagated, and the deformation has catastrophe, the elastic deformation is dominant in the early stage of impact, without residual deformation, the strain increases sharply in the late stage of Rapid destruction.
3. The impact pressure and porosity will not affect the overall variation of the fatigue mechanical properties of rocks, but will affect the damage deterioration process in the local stage and the damage degree and velocity of the macro-mechanical properties and micro-structure of rocks. Mechanical properties are sensitive to impact pressure.
4. Under cyclic dynamic loading, the variation law of acoustic wave velocity corresponds to the variation law of peak strain roughly. The overall variation trend of acoustic wave velocity decreases continuously, and the wave velocity decreases slowly at the early stage of impact, and decreases rapidly at the later stage. The trend, however, will affect the amplitude and velocity of the wave velocity in the local stage.
5. The damage accumulation process of rock under cyclic dynamic loading can be generally divided into three stages: the initial stage of damage, the stage of low-speed damage development and the stage of accelerated damage development and failure. The macroscopic stress-strain of rock is basically the same as that of cyclic impact.
6. In a certain range of impact pressure, the failure mode of rock under cyclic dynamic load is splitting failure in a smaller size range. The failure mechanism is that when the specimen is subjected to axial compression deformation under impact load, the transverse propagation deformation, i.e. the transverse elongation line strain, will inevitably occur due to Poisson effect. The ability to resist elongation deformation is very weak. When the strain reaches a certain value, the rock will be destroyed.
【学位授予单位】：中国地质大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU45

【参考文献】