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To investigate the effects of the oval hole on the strength and the failure mechanisms of rock materials, a series of uniaxial and biaxial compression numerical simulations were carried out using the combined finite-discrete element method (FDEM). Based on the numerical simulation results, the effects of dip angle (β), major–minor ratio (ω) and position of the oval hole on rock strength characteristics crack initiation and development process and final failure modes were analysed in detail. The numerical simulation results indicate that: (1) Under uniaxial compression, the ultimate failure modes of rock containing oval holes can be mainly classified into single inclined plane shear failure, X-shaped tensile-shear composite failure and Y-shaped tensile-shear composite failure. Under biaxial compression, the ultimate failure mode is single-inclined plane shear failure dominated by shear cracks. Whether it is uniaxial compression or biaxial compression, the crack initiation position of the main fracture surface is near the end of the major axis of the oval hole. (2) Under uniaxial compression, the axial stress–strain curve of rock containing the oval hole is smooth before and after the peak, but under biaxial compression, there is obvious fluctuation in the post-peak stage due to crack initiation and propagation. In both uniaxial and biaxial compression, the pre-peak elastic stage of the axial stress–strain curve of the rock containing the oval hole is significantly shortened and the peak stress is significantly reduced compared with the intact rock, which indicates that the bearing capacity of the rock is seriously reduced by the existence of oval hole. (3) When the position and major–minor axis ratio of the oval hole remain unchanged, the uniaxial compressive strength and biaxial compressive strength increase with the increase of the dip angle of the oval hole. When the position and dip angle of the oval hole remain unchanged, the uniaxial compressive strength and biaxial compressive strength decrease with the increase of the major–minor axis ratio of the oval hole. (4) At different dip angles, the brittleness index Bi of rock containing oval holes decreases with the increase of confining pressure, and the brittleness degree shows a gradual weakening trend. At the same time, when the dip angle increases, the decreasing amplitude of brittleness index Bi decreases with the increase of confining pressure. Three types of failure modes of rock with elliptical hole are systematically summarised, and the failure mechanisms of elliptical hole rock are revealed. The influence of different positions, major–minor axis ratio, and dip angle of rock containing oval holes on uniaxial compression and biaxial compression are studied. The relationship between brittleness index and failure mode of rock containing the oval hole is investigated. [ABSTRACT FROM AUTHOR]

To study the toughening effect and the anchoring mechanism of rock bolts, fractured rock specimens with different crack angles and different crack lengths are made of cement mortar. The prefabricated specimens are applied with different anchoring modes for reinforcement, containing no-anchoring, full-length bonded anchoring and pre-stressed anchoring. The uniaxial compression tests of fractured rock specimens under different anchoring modes are carried out, and then the mechanical properties and the failure modes of fractured rock specimens before and after anchoring are analysed. The 'Cavity Damage Effect' is defined and the test results show that the peak strength of the fractured specimens are roughly proportional to the crack inclination angle due to the 'Cavity Damage Effect', the crack is equivalent to a 'cavity damage' inside the prefabricated specimen if the opening of the crack is larger. The crack length can significantly affect the strength and deformation characteristics of no-anchoring specimens, while has little influence on the anchoring specimens. The full-length bonded anchoring and the pre-stressed anchoring can both significantly increase the mechanical parameters (the peak strength, residual strength and elastic modulus) of the specimens, enhance the resistance to deformation of fractured rock mass, and inhibit the expansion and coalescence of cracks. [ABSTRACT FROM AUTHOR]