A Vibration-Isolating Blast Technique with Shock-Reflection Device for Dam Foundation Excavation in Complicated Geological Conditions

Haoran Hu,Peng Yan,Ming Chen,Wenbo Lu,Qidong Gao

doi:10.1155/2018/8029513

Abstract

Under complicated geological conditions, the vibration in the dam foundation caused by blasting can lead to further deterioration of the foundation rock mass and adversely affect the safety of foundation. In order to effectively control the vibration in dam foundation rock mass, a new bench blasting technique with shock-reflection device is proposed. It introduces a shock-reflection device consisting of high wave impedance block and cushion material, which is placed at the bottom of vertical borehole. This shock-reflection device can effectively reflect the explosion shock wave from vertical direction to horizontal direction after detonation, which can make blasting energy concentrated on the rock mass above dam foundation, so the vibration in the foundation can be controlled. Field blasting experiment was carried out to contrast the blasting induced vibration in foundation rock by bench blasting with shock-reflection device and conventional bench blasting. The results indicate that the vibration in the foundation rock can be reduced by 30%~57%. In addition, the vibration at the bottom of the borehole is also demonstrated by numerical simulation, with results similar to the field experiments. The production experiment results show that the new blasting technique can replace the conventional excavation method of dam foundation in complicated geological conditions, and the new blasting technique has been successfully applied to the Baihetan dam foundation excavation.

Highlights

The energy released by the explosives during the blasting process is not completely used by the rock mass fragment, a large part of which will induce vibration of the retained rock mass [1, 2] and inevitably influence its internal structure
Where PPVwith is the PPV of the borehole with the device; PPVwithout is the PPV of the borehole without the device; ηppV shows the blasting vibration amplitude reduction after adopting the bench blasting with shock-reflection device
Through theoretical analysis and blasting vibration numerical simulation based on ANSYS/LS-DYNA, combined with field experiments, the following results are achieved: (1) The shock-reflection device is a combination of spherical block made up of high sonic impedance concrete or cast iron and flexible cushion made up of coarse sand

Summary

Introduction

The energy released by the explosives during the blasting process is not completely used by the rock mass fragment, a large part of which will induce vibration of the retained rock mass [1, 2] and inevitably influence its internal structure. In the excavation process of dam foundation or slope, much attention needs to be paid to the vibration control [4]. Serving as its typical feature during blasting excavation, multiple stress wave reflections occur under the action of dynamic load due to existence of rock joints within the columnar jointed basalt, which may result in dynamic tension failure and lead to the fracture of the joint surface. If blast-induced cracks occur, developing and converging with each other, the columnar jointed basalt will lose its bearing capacity [5, 6].

Results

Discussion

Conclusion