Study on timing sequence control fracture blasting excavation of deep rock masses with filled joints

Tingting Liu,Junhong Huang,Xinping Li,Guang Zhang,Kaiwen Song,Yi Luo

doi:10.1038/s41598-021-00438-9

Tingting Liu, Junhong Huang + Show 4 more

Open Access

https://doi.org/10.1038/s41598-021-00438-9

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Abstract

During the blasting excavation of deep underground caverns, the effects of the structural surface on crack propagation are usually considered in addition to the clamping effects of high in situ stress. Based on the notched borehole and timing sequence control (TSC) fracture blasting method, this paper studies the effects of different borehole shapes on the degree of damage of the surrounding rock and profile flatness of the rock anchor beams and the effects of different filled joint characteristics on the blasting crack propagation rules. The results show that the damage depth of the surrounding rocks by round hole smooth blasting is approximately twice that by notched hole smooth blasting, by which the profile formed is flatter. The notched primary borehole (PBH) remains a strong guidance for crack propagation in a rock mass with filled joints, while the stress concentration effects of the round target borehole (TBH) cannot fully guide the cracks until they fall within a certain distance between the PBH and TBH. It is favourable for cracks to propagate along the lines between boreholes with larger filled joint strengths and larger angles between boreholes.

Highlights

During the blasting excavation of deep underground caverns, the effects of the structural surface on crack propagation are usually considered in addition to the clamping effects of high in situ stress
A notch hole can supply sufficient space to enable the fragments to swell for rock f ragmentation11–13. Xie[14] numerically simulated the process of notch blasting under high in situ stresses and the Riedel–Hiermaier–Thoma (RHT) model in LS-DYNA, and they proposed a modified notch blasting design method for deep rock masses. Liang[15] discovered that the notch tip would suffer from obvious dynamic stress concentration effects at the blasting load in boreholes. Yang[16] analysed the dynamic propagation behaviours of cracks between boreholes after two notched holes were simultaneously initiated. Jeong[17] considered that notched blasting helps reduced the degree of damage, overexcavation and underexcavation of tunnel surrounding rocks
This paper studies the blasting excavation of a rock mass with filled joints at the rock anchor beam in the deep underground caverns of the Baihetan Hydropower Station based on the timing sequence control (TSC) fracture blasting method for a primary borehole (PBH) notch, to examine the propagation behaviour of cracks in a rock mass with filled joints

Summary

Auxiliary borehole φ 42

Based on the TSC fracture blasting excavation method proposed by Li48, only PBHs are notched in the rock mass model with filled joints; the distance between adjacent boreholes is taken as approximately 19 times the diameter of the boreholes, i.e., 800 mm; the delayed initiation time between PBH and TBH is taken as 1 ms. With an increasing joint angle, the reflection effects of the stress wave on the rock mass between adjacent joints gradually decrease, and the secondary cracks near the TBH are reduced to decrease the degree of damage of the surrounding rocks and help form a flat excavation profile between boreholes.

Conclusions

Discussion