| As engineering rock mass,jointed rock mass is widely exposed in tunnel,mining engineering,water conservancy and hydropower,slope.Under the influence of natural attributes such as discontinuity,grouping and randomness,jointed rock mass shows complex deformation and failure characteristics,which significantly affects and restricts the mechanical behavior and stability of engineering rock mass.The weakening of jointed rock mechanical properties is the key factor that leads to the significant increase of instability risk in jointed rock engineering.Therefore,the study of failure mechanism of jointed rock mass has always been a hot topic in rock engineering.In the previous researches,most of the scholars regard the failure of jointed rock mass as a two-dimensional plane problem.However,in essence,jointed rock mass has three-dimensional characteristics.If it is simplified into a two-dimensional problem to study,there will be a certain gap between it and the real rock mass failure.Therefore,it is of profound significance to the design and construction of rock mass engineering to study the failure mechanism of built-in three-dimensional discontinuous jointed rock mass.Many scholars prefabricated joints with certain geometric distribution rules in traditional rock-like materials(cement,mortar,gypsum,etc.)to study the expansion and evolution process of internal joints of samples.However,because the expansion of internal joints of traditional rock-like materials is not visible,the expansion process cannot be observed.In view of the above problems,this paper uses epoxy resin,curing agent and accelerant to produce rock-like samples with high brittleness and transparency,adopts mica sheet as prefabricated joints,and uses high-speed camera to observe the crack propagation and penetration law at the tip of the internal joint unit under uniaxial compression.Specific work and main achievements are as follows:(1)Epoxy resin,accelerator and hardener were selected as raw materials for preparation of rock-like samples.Based on the orthogonal test,the curing ratio,promotion ratio and freezing time were taken as influencing factors of rock-like samples,and the variation rules of uniaxial compressive strength,tensile strength,brittleness index and deformation index of rock-like samples under various factors were obtained,as well as the typical failure mode of the samples.The influence mechanism of various factors on the mechanical properties and failure modes of the samples was summarized and analyzed.On this basis,the optimal ratio of transparent rock-like materials with typical brittle failure characteristics was determined.(2)Based on the ratio of transparent rock-like materials with typical brittle failure characteristics,transparent rock-like samples with single three-dimensional joints were prepared.Uniaxial compression tests were carried out on single three-dimensional joint specimens with different inclinations(0°,15°,30°,45°,60°,75° and 90°),and real-time monitoring was carried out by high-speed photography.The characteristics of stress-strain curve,the initiation mode of crack at the tip of single three-dimensional joint and the final failure mode of the sample were analyzed.The results show that the strength of the specimens with single three-dimensional joints decreases first and then increases with the increase of joint dip Angle,and the strength of the specimens reaches the minimum when the joint dip Angle is 45°.The cracks at both ends of the joint appear in the order of feather crack,wrapped airfoil crack,petal crack and butterfly crack,among which butterfly crack has not appeared in many scholars’ previous studies.(3)Uniaxial compression test was carried out on transparent rock-like samples with built-in three-dimensional joints,and real-time monitoring by high-speed photography was carried out.The stress-strain curve characteristics,initiation mode of crack at the tip of three-dimensional joints,through path between three-dimensional joint units and final failure mode of the samples were analyzed.The change of joint dip Angle and joint spacing has a significant effect on the strength and failure mode of the sample,which is shown as follows: with the increase of joint dip Angle,the strength of the sample increases first and then decreases,and reaches the minimum at 45 °.With the increase of joint spacing,the sample strength also increases.When the joint dip Angle is 0°,the sample shows blasting failure;when the joint dip Angle is 15°,30°,45°,60°,75° and 90°,the sample mainly shows brittle fracture failure.(4)Uniaxial compression test was carried out on transparent rock-like samples containing three kinds of circular cavities with different aperture sizes,and real-time monitoring with high-speed photography was carried out.The test results show that the strength of the sample decreases gradually with the increase of the aperture size.The circular cavity samples show progressive failure characteristics,that is,the crack initiation first occurs at the edge of the cavity,when the crack initiation stress is not reached,there will be small cracks,when the crack initiation stress is reached,there will be large cracks.Then,under continuous loading,the crack eventually propagates along the central axis of the cavity,resulting in through tensile crack until the specimen is damaged. |
