Abstract
Open-pit slopes contain numerous nonpenetrating, intermittent joints which maintain stability under blasting operations. The tip dynamic response coefficient (DRC) of parallel cracks in a typical rock mass under combined dynamic and static loading conditions was calculated in this study based on the superposition principle. The dynamic response law of the intermittent joint in the slope under blasting was determined accordingly. The influence of many factors (the disturbance amplitude of dynamic load, the lateral confining pressure, the length of rock bridge, the length between cracks, the staggered distance between cracks, and the crack inclination angle) on the dynamic response was theoretically analyzed as well. The ABAQUS numerical assessments were conducted on simulation models with parallel cracks under combined dynamic and static loading conditions. The results show that a larger dynamic load amplitude and smaller crack inclination angle/confining pressure result in greater Type II dynamic strengthening effect on the crack tip. When the length of the rock bridge between cracks (s) is smaller than the half length of the crack (a), the dynamic strengthening effect at the crack tip weakens gradually with increase ins; whens/a≥1, the strengthening effect is almost unchanged. With the increase in the staggered distance between cracks (h), the dynamic strengthening effect of the crack tip weakens at first and then strengthens; the strengthening effect is weakest whenh/a=0.4; the crack propagation under combined dynamic and static loading is the most sensitive to the lateral confining pressure (σ3) and is the least sensitive to the inclination angle of the cracks (α). Theoretical results are validated by comparison with numerical simulation results. Such information regarding the dynamic response law of the parallel cracks in rock masses under dynamic and static loading conditions is conducive to further research on the mesofailure mechanism of open-pit mine jointed rock slopes under blasting operations.
Highlights
The fracture failure characteristics of the deep rock mass in an open-pit mine slope are different from those of the shallow rock mass under blasting conditions
For the State B2 with vertical stress, the cracks are closed under compression, and there is only stress intensity factor (SIF) of Type II (KBΙΙ2 ) at the crack tips, which can be calculated according to Formula
The above analysis indicates that a smaller inclination angle of the nonpenetrating joint in the slope makes the crack tip more significantly affected by the dynamic load, in which case cracks are generally more likely to occur
Summary
The fracture failure characteristics of the deep rock mass in an open-pit mine slope are different from those of the shallow rock mass under blasting conditions. The SIF of the crack tip in the rock mass stress State A (KA) under the combined action of dynamic and static loads (Figure 2) can be considered equivalent to the sum of the static SIF (KB) and the dynamic SIF (KC). For the State B2 with vertical stress, the cracks are closed under compression, and there is only SIFs of Type II (KBΙΙ2 ) at the crack tips, which can be calculated according to Formula (3). According to the superposition sketch shown, the SIFs at the crack tips under biaxial compression can be expressed as follows: K. Substituting Formulas (5) and (10) into Formula (1) yields the following expression of the SIFs at the crack tips under combined dynamic and static loading conditions:. SIFs at the crack tips under dynamic and static loading conditions, respectively
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