【作者】 张庆；

【导师】 杨小林； 贠小有；

【作者基本信息】 河南理工大学 ， 工程力学， 2007， 硕士

【摘要】 目前,关于岩石强度和破坏机理等方面的研究文献可谓是浩如烟海,但是有关岩石双轴压缩力学特性的文献却廖若晨星。在过去很有限的岩石双轴受力研究中,所采用的双向加载装置基本上都是基于已有的单轴压缩试验机改造而成,双向刚度相差悬殊,在一定程度上影响了实验结果的说服力;已进行的研究不够系统、无法形成体系;现有的岩石破坏准则大多忽略了中间主应力的影响。针对以往双轴试验装置存在的不足,河南理工大学和加拿大McGill大学合作设计建造了大吨位双向等刚度加载系统。利用该装置可以对50mm,75mm,100mm,125mm和150mm的岩石、砼等立方体试件开展单向和双向压缩试验。本项研究应用该装置对75mm和100mm石灰岩立方体试件进行了双向加载试验及双向快速加载试验。此外还按照国际岩石力学学会标准对同批岩石试件的单轴和三轴力学特性进行了测试。通过对实验结果的分析,发现在双向加载条件下,石灰岩的破坏强度相对单轴强度有所提高;中间主应力对岩石的破坏强度有着显著的影响。而且随着中间主应力增大,石灰岩试件强度存在一个增大再降低的过程:当中间主应力达到单轴强度的70～80%时,其双轴抗压强度最大;超过该值时,强度反而降低,但仍然高于单轴强度。同时,由于侧向约束的存在,岩石的破坏方式也有了显著的变化:岩石双轴受压破坏是拉剪破坏,即先从自由面受拉成层剥落,试件受压面不断被削弱,最终发生剪切破坏,具有延性破坏的特点;破坏具有较明显征兆,可以为生产实践中岩石发生双轴受压破坏提供预测。通过对100mm石灰岩立方体试件以5MPa/s的速率双向快速加载试验,测得其强度反而较1MPa/s加载速率强度下降约10%左右。尺寸效应作用不明显,影响效果小于5%。但试件形状对岩石强度影响很大,75×75×75mm立方体试件单轴抗压强度比Φ50×125mm的圆柱体试件单轴强度提高了67%。更多还原

【Abstract】 Nowadays, there are too much research literatures on the strength and failure mechanism of rock, but few of them put sight on the geomechanical behaviour of biaxially loaded rock. Among the previous limited research of biaxial compression, the ready-made uinaxial loading apparatus were usually employed to setup biaxial loading apparatus by adding a perpendicular loading frame. Anisotropic stiffness of two loading frames always exists, so the research results are not comprehensive; the research are not systemic and most current failure criteria ignore the affection of intermediate principal stress.In order to solve the above problems and try to explore geomechanical behaviour of rock material, a new Isotropic Biaxially Loading System (IBLS) which has higher loading capacity than previous apparatus, has been designed and established by Henan Polytechnic University of China and McGill University of Canada. IBLS can be used to investigate bigger rock or concrete samples by both uniaxial and biaxial loading conditions than previous investigations.By IBLS, the investigation of both 75mm and 100mm cubic limestone specimens was implemented. In order to generalize the results of the test, uniaxial and triaxial compression tests on the cylinder specimen were conducted according to the related standards of ISRM.Based on the test results, it is found that the biaxial strength of limestone is more than its uniaxial strength, and the intermediate principal stress can obviously affect the strength of rock. With the increase of intermediate principal stress, the biaxial strength ascends at first and then descends; when the value of intermediate principal stress gets 70~80% of uniaxial strength, the biaxial reaches its peak value, after that the biaxial biaxial declines but the biaxial result is still larger than uniaxial strength.Also because of the existing of lateral confine the failure mode of rock changes: biaxial failure of limestone is tension-shear failure. The rock first spalling is from free surface for the reason of tension and with the specimen is undermined gradually at last the specimen collapses for the reason of shear. Meantime the failure is accompanied with obvious premonition and is helpful in actual engineering by predicting the appearance of biaxial failure of rock. After the rapid loading test of 100mm cubic specimen at the velocity of 5MPa/s, the biaxial strength drops about 10% compared with the biaxial strength at the velocity of 1MPa/s. Scale affects the biaxial no more than 5%. On the contrary, the shape of specimen affects the biaxial remarkably, for example, the uniaxial strength of 75mm cubic specimen is 1.67 times of that ofΦ50×125mm cylinder.更多还原