Abstract
The objective of this study is to develop a new vibration-free excavation method based on vermiculite expansion for rock cracking and to evaluate the performance of the heating system via elastic wave monitoring. Natural vermiculites expand rapidly in volume when heated above 800 °C. MgO powder is used to evenly transmit the surface temperature of a heater rod, which can attain high temperatures rapidly, to the vermiculites. The insertion direction of the heater rod greatly affects the expansion pressure. Three cuboid rock specimens are prepared and equipped with the heating system at different hole-to-face distances. Crack propagation is monitored by a pair of disk-shaped piezoelectric transducers. For short hole-to-face distances, the wave velocity and maximum amplitude rapidly decrease after certain time. For the greatest hole-to-face distance, the shear wave velocity remains constant during the test, while the maximum amplitude decreases after a certain time. The time taken for the velocity and amplitude of the shear waves to decrease reasonably corresponded to that taken for detectable crack propagation to occur on the surface of the rock specimen. The proposed method and materials may be useful from the viewpoints of rapid expansion, economy, and crack control.
Highlights
Various excavation methods are employed for constructing tunnels and underground spaces; drilling and blasting is one of the common excavation methods
This paper describes the development of a modified heating system based on vermiculite expansion for rock fracture and the monitoring of the performance of the heating system by using elastic waves
A new vibration-free excavation method based on vermiculite expansion for rock fracture was proposed in this study
Summary
Various excavation methods are employed for constructing tunnels and underground spaces; drilling and blasting is one of the common excavation methods. The propagation of the stress waves, which are induced during the blasting process, to the ground surface may cause vibration and noise. To minimize such vibration, controlled blasting methods such as line-drilling and pre-splitting are used at the tunnel perimeter [1]. The blast-induced stress wave can still propagate through the connected area between empty drilling holes. Various excavation methods were developed to reduce the blast-induced vibration. Jeng et al [2]
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