Abstract
In this study, a model that is closer to the state of fracture presentation in natural rocks has been developed, which is different from the previous. The cross‐flaws can be characterized by the joint persistency (k) and the angle between the primary flaws and axial load (α). The two parameters were varied individually and, by combining them, nine specimens with different nodal parameters were formed. Laboratory specimens and numerical simulations were performed on these specimens to investigate the crack extension process and the variation of crack initiation and coalescence stresses. It is found that a new category of crack coalescence is discovered according to the experimental results besides those reported before, and the angle α affects whether tensile‐shear cracks appear. Also, α has an impact on the location where crack first occurs. The joint persistency k alters rock failure mode and has a substantial effect on crack initiation stress. However, the effect on the aggregation stress is not significant. The crack initiation stress decreases in the case of cross‐flaws in contrast to flat fissures. In addition, the flat‐joint model in PFC2D is used for numerical simulation. It is possible to conduct a study that is difficult to achieve experimentally by using simulations, i.e., only changing one macroparameter without changing others and thus studying the changes in the effect on cracking during fracture. The simulation results are in good agreement with the experimental results. At the same time, the connection mode and the width of the crack coalescence zone of the primary defect, which is difficult to observe in the experiment, are found out from the numerical simulation.
Highlights
Flaws such as faults and joints presenting in rocks are common and are an important parameter for rock engineering designers to consider
The rock mass contains a large number of primary fractures and artificially created fractures, such as preblasting, to form precracks. e presence of precracks deteriorates the mechanical properties of the rock mass and changes the blast stress wave propagation path, which has a significant impact on the blasting effect
Results about Different k. e flat-joint model (FJM) model for k 0.57, 0.67, and 0.80 and the associated screenshots of crack evolution and the final fracture pattern in the experiment are presented in Figure 14. e first cracks are white wing tensile cracks, which are generated after the axial stress reaches 16.04 modulus (GPa) Uniaxial compressive strength (MPa)
Summary
Flaws such as faults and joints presenting in rocks are common and are an important parameter for rock engineering designers to consider. Dynamic ground support in underground mines is used to stop the deformation and damage of the surrounding rock and to reinforce the rock mass by means of support elements. The deformation of the rock mass is often accompanied by the expansion of cracks leading to the effectiveness of the surrounding rock strength and the study of the development of rock cracks becomes very important for the support members to carry out how to effectively stop the deformation of the surrounding rock. It is valuable to investigate the main expansion mode of rock fracture and main fracture types for support design. E presence of precracks deteriorates the mechanical properties of the rock mass and changes the blast stress wave propagation path, which has a significant impact on the blasting effect. Researchers have carried out different studies from experimental, theoretical, and simulation calculations
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