Abstract
In the traditional presplitting blasting, the presplit holes are generally uniformly initiated, which causes local damage to the retained rock mass while forming the damping ditch. In order to determine the optimal delay time of the precise delay initiation hole by hole, the finite element software ANSYS/LS-DYNA is used to build a blasting model of the concrete, which includes concrete, explosive, and air to simulate the crack forming process of the presplitting hole under various initiation modes. Four kinds of initiation modes for blasting, namely, simultaneous initiation with 0 ms, 9 ms, 12 ms, and 15 ms of delay between adjacent holes, are set up to determine the exact delay time of the best presplitting effect. The simulation results show that when the prehole detonates simultaneously, the inner hole crack penetrates the fastest, but the peak stress around the hole is up to 147.9 MPa. When interhole delayed initiation is used, although the time of interhole crack penetration is prolonged, the stress coupling is generated around the precrack and the maximum stress is obviously reduced. The maximum stress generated under the three delayed initiation conditions is only 76.8 MPa. Considering the requirement of damage control of surrounding rock mass and the rapid formation of precrack, 9 ms delay time is determined as the precise delay time of this test.
Highlights
When presplitting blasting is used in the engineering practice, it is important to form satisfying precracks of the presplit holes and minimize the damage on the surrounding rock by blasting
At the time of 14 μs, the stress waves generated by the two blast holes are gradually superimposed together, forming a stress concentration zone between the two blast holes. e explosion stress waves of the two blast holes have a promoting effect on each other; the cracks are produced between the two blast holes. e hole is connected to the centerline; the colour of the stress superimposed area changes to red Density ρo/(g·cm−3) Shear modulus G/Pa Strength parameter 1 A Strength parameter 2 B Strength parameter 3 C Strength parameter 4 N Static yield strength Fc/1011 Pa Tensile strength T/1011 Pa Damage constant 2 D2 Pressure parameter 1 K1
Numerical simulations are carried out on the above four situations with various delay times, namely, the aligned detonation and detonations with 9 ms, 12 ms, and 15 ms delay time. e analysis and discussion of the simulation results are as follows: (1) When both holes are detonated simultaneously, the maximum stress value received by element E is only 147.6 MPa, while the maximum stress is only 56.6 MPa when the detonation is delayed, with the peak stress of each element reduced by 61.65% compared to the simultaneous detonation. e maximum stress value received by the surrounding rock during the delayed detonation is reduced by 61.65% compared with the maximum stress value received when the holes are detonated simultaneously, which effectively reduces the damage on the surrounding rock
Summary
When presplitting blasting is used in the engineering practice, it is important to form satisfying precracks of the presplit holes and minimize the damage on the surrounding rock by blasting. The presplitting blasting mainly adopts the simultaneous initiation method, and the explosion stress waves superimpose onto each other during the joint formation process, which causes great damage to the surrounding rock. Some researchers studied the mechanism and propagation regularity of the precrack cracking through other methods and influencing factors [5,6,7], and the results show that when the presplitting blasting is implemented, the simultaneous blasting exhibits the best cracking effect, but the construction environment is very complex which requires controlled presplitting. Yu et al [8, 9] used numerical simulation software to simulate the blasting
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