Study On The Failure Of Joint Brittle Rock Masses With 3D Flaw In Numerical Simulations Of Geotechnical Engineering And Experimental Methods

There are abundant primary and secondary flaws in rock mass. They start the evolvement of initiation, propagation and coalescence under the influence of forces, such as engineering excavation, water flow, wind's credibility and so on, which takes a great effect on rock strength and fracture pattern, meanwhile, the reciprocity of flaws produces many channels, which make pathway of underground water and affect rock's seepage property, engineering materials, for example rock bolts, are likely to be eroded, all these cause bad effect on the stability of rock mass. Consequently, the failure mechanism of multi-fissured rock mass is always focused by the researchers of geology field. The engineering problems often are simplified to two-dimensional (3D) models in most of the previous studies, but fractures are 3D actually, as a result, it leads a great loss of much 3D fracture information in the simple 2D model. Researchers start to focus on the fracture mechanism and failure mechanism of 3D fractured rock mass, also theoretically significant to rock mass's design, construction and stability.Owing to the fact that there is seldom a flaw abided by some discipline in real rock test coupons, so, analogy materials are applies in the research on failure mechanism of brittle multi-fissured rock mass. In order to simulate the properties of multi-fissured rock mass, the analogy material must satisfy the brittle rock mass's main distinctions, furthermore, some principled flaws should be lain in a enough big rock test coupon. In the thesis, a pretty brittle analogy material is developed, whose ratio of compressive and tensile strength is 5 at normal temperature, and up to about 7 or 8 at a certain low temperature. Its brittleness is increased by one time than previous analogy materials. This analogy material is limpid enough to observe the inside 3D flaw's evolvement of propagation; it can simulate the rock mass very well. Moulds that contain prefabricated 3D flaw of arbitrary angles, number and space are developed in succession, providing convince for the made of 2D or 3D-fractured test coupons. A high resolution vision is set before the pressing machine to record the fracture process of inside 3D flaws, and it's more effective.From uniaxial compression, the analogy material's evolvement of initiation, propagation and coalescence is analyzed. According to the stress-strain curve and phenomena, the process can be divided into four stages, initial compaction, elastic deformation, secondary flaws'evolvement of initiation, propagation, accelerated crack propagation, failure. From the results, it indicates that 3D crack propagation is much more complexes than the 2D crack propagation, such as, petal crack, wrapping wing crack fin crack and so on, a entire specimen has larger compressive strength and smaller deformation. The failure form mainly focuses on cleavage cracking.The full growth process of 3D flaw is simulated with volume element method with FISH programs in FLAC3D software. The uniaxial compression and multi-axial compression simulate conditions of different angles, distances, and transfixion specimens within crack, also time and corresponding stress to its evolvement of initiation and coalescence. The simulation results show that 3D crack propagation is much more complexes than the 2D crack propagation, such as the wring action of the crack plane, and the 3D coalescence pattern of cracks. The failure form mainly focuses on cleavage cracking.Corresponding stress to crack initiation, time, damaged unit size and strength is non-monotone against angle and spacing, Corresponding stress to crack coalescence, time, damaged unit size and strength is monotone against angle and spacing, and multi-axial compressive performs a similar principle. The simulation results provide a new method to further study of 3D flaw fracture.