Atsuo Hirata

Study on the Estimation of the Axial Resistance of Spiral Bar Based on Interaction with Ground

Steel wire, which gives a pre-stress to ground and steel bar such as a rock bolt, are generally used in order to support rock. In this study, we introduce a new type support instead of the former one, like a rock bolt and cable bolt. We call spiral bar the bar that give torsion to the steel plate. It is easy to use the spiral bar like rock bolt, since it has high pullout resistance from ground. If axial force acts on the spiral bar, inner force will arise in borehole because of the spiral shape when grouting or a filling material fixes it. The behavior in the case that the spiral bar receives external axial force was investigated experimentally. And the 3-D numerical analysis was then performed by the finite difference method. A simple equation to estimate axial resistance of arbitrary sized spiral bar with self-enhancement function is proposed. The result of estimation is agreement with one of the experiments and numerical analysis.

Inspection of damaged zone in tunnel walls by a compact vertical seismic prospecting system

This paper presents the contents of the compact vertical seismic prospecting (VSP) system and its application to in-situ measurement. A new method of rock property investigation by using this compact vertical seismic prospecting system is proposed. This investigation system consists of a vibration sensor and a super elastic alloy pipe to press the sensor against the borehole surface, an A/D converter, a computer and a trigger system. The vibration sensor setting on the spring of VSP probe is pressed to the borehole surface and measures the vibration due to a transmitted wave caused by the impact of the hammer on the tunnel wall. The distribution of the P wave velocity in rock can easily be measured along a borehole drilled for rockbolts.

Amplitude Spectra of Blasting Vibration in Tunnel Excavation.

It is important to evaluate the damage of architectures and structures caused by blasting vibration. In this paper, 1) the characteristics of spectra was presented, 2) blasting vibration were observed in underground and on a ground surface, and 3) a simple numerical model was proposed to explain the spectra of the vibration. The used model, which is based on frequency domain using Fourier transform, estimates the blasting vibration spectra in tunnel advance. The spectra of the observed vibration is represented by the product of the blasting source spectra, the wave path effect and the local properties of the ground around sensors. The spectra were characterized by elastic wave velocity, rock density, rupture radius, tensile strength of rock, distance from blasting point to observation site and attenuation coefficient. The proposed method has found with sufficient accuracy to account for the evaluation of the blasting spectra.

A Consideration on the Estimation of Blasting Vibration in Tunnel Excavation.

Estimation of blasting vibration is important for the safety control in blasting work. In the previous report about the blasting vibration in tunnel excavation, the authors proposed a method to predict the amplitude spectrum of blasting vibration.In the present paper, a method to predict the maximum amplitude of blasting vibration is proposed. Analyzing the time series of blasting vibration on the basis of the probability, it is made clear that the maximum amplitude of the waveform in time domain can be evaluated from the amplitude spectrum in frequency domain. Since the amplitude spectrum is theoretically calculated by the previously proposed method, the maximum amplitude of the blasting vibration can be also evaluated theoretically. It is shown that the proposed method gives good estimations for the maximum amplitude as well as the power spectrum of blasting vibration in tunnel excavation.