The initiation, expansion, and penetration of microscopic cracks in rock is the macroscopic manifestation of creep. This paper investigates mechanical creep characteristics and fracture evolution processes in rock masses with different fracture angles, lengths, and rock bridge dip angles. Single fractures, dual parallel fractures, and fracture groups are considered. The approach comprises discrete element simulation based on continuum mechanics, utilizing the continuous and discontinuous software, GDEM. Single-fracture rock masses are characterized by a progressive fracture development mode dominated by tensile shear failure. The rate of creep and fracture magnitude both increase according to fracture length. With increasing fracture inclination angle, creep rate and fracture magnitude increase and decrease. The creep rate and degree of rupture are highest for fractures inclined at 30°. The dual-fracture rock mass exhibits both tensile crack failure and compressional shear failure. Creep rates are highest, and rupture effects are most apparent at rock bridge inclination angles of 90°. If the rock bridge is too long or too short, the stable creep stage is prolonged, but the creep acceleration stage intensifies due to interaction between fracture-bounded rock masses. The failure mode, in this case, involves collective failure by tension fractures and compressional shear. Creep rate and fracture magnitude increase with the number of fractures, which accelerates rock mass deformation to a certain extent. However, when the number of fractures reaches a certain threshold, a relatively stable structure may become established, slowing down the creep rate, especially during the creep acceleration stage. This study can provide a theoretical basis and reference for investigating the creep rupture law of rock mass engineering and the prevention and control of fractured rock mass geological disasters.
To study the influence of weak interlayers on the creep failure characteristics of rock masses, based on the continuous-discontinuous method (CDEM), the uniaxial compression creep experiments of rock masses containing weak layers were numerically simulated; and the weakened rock masses under different conditions were analyzed in detail. We focused on the final failure mode and creep curve of the rock mass with a weak interlayer (θ = 30°, d = 20 mm, c = 1) as examples by selecting the crack distribution state of the model during compression at different time steps. We analyzed the propagation and convergence mode of cracks in a rock mass with weak layers. The research results show that the existence of weak interlayers affects the integrity of the rock mass and the creep failure mode. With the increase in the inclination of the weak interlayer, the failure mode of the rock mass changes from shear failure through the weak layer to slip along the weak layer. For shear failure, the total strain and steady-state creep rate of the rock mass first decrease and then increase, showing a U-shaped distribution; as the thickness of the weak interlayer increases, the rock mass always follows the shear in the weak layer. Creep failure occurs on the fracture surface, and the total strain and steady-state creep rate of the rock mass are positively correlated with the thickness. If the thickness continues to increase, there is no significant difference in the creep characteristics of the rock mass; the volume occupied by the soft rock in the body increases, the overall rigidity of the rock mass decreases, and the plastic deformation increases. The form of creep failure of the rock mass changes from sliding shear failure along the weak layer to sliding shear failure through the weak interlayer. The total strain and steady-state creep rate of the rock mass increase with the increase in the number of weak layers; the greater the distance between the weak layers, the smaller the total strain and steady-state creep rate of the rock mass. The slower the crack growth rate, the less likely the rock mass to undergo creep damage.
To investigate the influence of the weak layer dip angle on the creep rupture of the composite rock mass, this paper conducts a graded loading creep experiment on the composite rock mass with different dip angles using the acoustic emission method to examine the fracture evolution process. With increasing load grade, the cumulative total ring count of the rock mass shows a “U”-shaped trend, and the acoustic emission spatial positioning results show that acoustic emission events in the rock mass fracture process are primarily concentrated in the vicinity of the weak layer, while events in other areas are few and dispersed. For rock masses with weak layer dip angles of 0° and 15°, cracks occur in both soft and hard rocks, where shear cracks are dominant in soft rocks, tensile cracks are dominant in hard rocks, and finally, the rock mass mainly exhibits tensile splitting failure. For rock masses with weak layer dip angles of 30° and 45°, most of the cracks exist in the interior of the soft rock, which is dominated by shear cracks. With increasing graded loads, the shear cracks continue to develop along the direction of the weak layer, the upper rock mass keeps slipping and dislocating, and the final failure mode is mainly shear-slip failure. The damage evolution varies with the inclination angle of the weak layer, which can be divided into three stages: initial damage accumulation, damage acceleration, and damage destruction. This demonstrates the ability to predict, prevent, and control the occurrence of creep disasters in rock masses with weak layers.
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