Sunao Kunimatsu

Effects of soil profile and characteristic of exciting force on propagation of ground vibrations

Ground-borne vibrations caused by vibration sources such as road traffic and construction exhibit complicated properties during propagation from the vibration source to the inside of a building. In the present paper, a numerical analysis technique for the system of vibration source and propagation path of ground vibration is developed in order to systematically determine the propagation properties of the vibration as part of developing a predictive technique for exposure evaluations by vibrations in three directions at receiving points of vibration in the human body. First, the exciting forces in three directions for input into the numerical computation are inversely-estimated by using the measured acceleration records of the measurement points, which are near the vibration source. The thin-layered element method is used for numerical computation of the ground vibration. Then, the calculation results for the ground vibration obtained by using the estimated exciting force are compared with the measured results, and the influence of the stratified structure of the ground on the exciting force and the propagation properties of the ground vibration are studied. From these results, in a prediction of the ground vibration in three directions, it is emphasized that it is necessary to consider the influence of horizontal exciting force, although attention has been paid to only the vertical exciting force for simulating ground vibration.

Blast Densification Method: Sound Propagation and Estimation of Psychological and Physical Effects

Experimental results on the propagation of blasting sounds from underground explosions for preventing liquefaction of ground are described. Psychological and physical effects of blasting sounds are estimated by comparison with previous studies on the effects and evaluation of continuous low-frequency sounds. The blasting sounds generated by underground explosions were impulsive low-frequency sounds, which predominantly involved frequencies of several Hz. Frequencies above 100 Hz tended to attenuate to a greater degree during propagation from the blasting area. Sound pressure levels at frequencies above 20 Hz exceeded the hearing threshold level as well as the threshold for rattling of building fittings for low-frequency sounds even at a point about 400 m distant from the blasting area. To predict the attenuation of the blasting sounds and estimate the appropriate distance for reducing the possibility of complaint, results of numerical calculations by the parabolic equation method together with meteorological data are shown.

Recent research activities for the assessment of vibration in living environment with respect to human perception in Japan

The number of complaints against vibration has been increasing gradually in recent years in Japan. This fact may imply problems of the Vibration Regulation Law that was implemented almost 30 years ago so as to regulate vibrations caused by factories and construction works and to mitigate vibration problems caused by road traffic. A group of experts has been investigating an assessment method that may be able to assess recent vibration problems reasonably since 2004. This paper presents a part of group activity that aims at improving the understanding of human vibration perception and applying it in vibration assessment in living environment. Results obtained from experiments involving human subjects to determine perception thresholds of whole‐body vibration are summarised.

A Prediction Method of Blast Vibration Based on Multi-Reflection Method for SH Wave to Allow for Geological Structure.

In order to predict blast vibration more precisely, we attempted to use the following equation described by circular frequency, that is used in the earthquake engineering field.O(ω) =G(χ)·H(ω)·S(ω)where, O(ω) is spectra of the wave motion of ground surface, G(ω) is the geometrical attenuation related energy spread during wave propagation, H(ω) is the transfer function and S(ω) is the source function.We developed a computer program for a multi-reflection method based on Haskell (1960) to get H(ω) in above equation. For S(ω), we used the equation derived by Sharpe (1942). Finally, we had reasonable results for wave motion of a point of ground surface by calculating inverse FFT of O(ω) obtained by convolution of H(ω) and S(ω) about two layers model and four layers model.

Sound energy distribution at an intersection of underground tunnels: Full scale experiments

Experiments on sound propagation in small‐scale tunnels with a branch have been carried out from the viewpoint of safe and rapid information transmission underground. The influences of intersection angles and acoustical properties of inner walls of the tunnels on sound propagation were examined in previous studies [J. Acoust. Soc. Am. 100, 2567 (1996)]. In the present work, sound propagation in a full‐scale underground tunnel with a branch is considered. The experimental tunnels are supported by iron frames and concrete lagging, and the cross sections are arch shaped with an area of 4.2 m2. Experimental results indicate influences of the intersection on propagation attenuation at a frequency of around 200 Hz. Whole tendencies of sound attenuation are also affected by relative arrangements of sound source and receivers, and sound attenuates more at the receivers, which are out of sight from the source than for those in sight. For the purpose of the sound‐field estimations, the characteristics of sound prop...

Sound energy distribution at an intersection of an underground tunnel: Additional small‐scale experiments

In studies on some interactions between sound propagation characteristics and environmental factors underground, small‐scale experiments on the sound energy distribution at an intersection of tunnels have been carried out in an anechoic room. The small‐scale tunnels were made by acrylic plates, and the original surfaces of inner walls were assumed to have an acoustically hard condition, while surfaces of the walls covered by flannel were acoustically soft. Impulsive sound was generated electrically as a sound source was applied, and propagated sounds were measured by an omnidirectional microphone. The experiments were carried out under several kinds of conditions for angles at the intersection and positions of the sound source. Influences of intersection on the sound energy distribution were indicated by comparisons between the measuring points before and behind the intersection with different angles. In addition, the influences of the acoustical characteristics of the inner walls and positions of the sou...

Blast sound propagation over hilly land

A blast sound propagates over a long range, because of its large sound power of sources and low‐frequency components. Blasting operations are often conducted at a hilly side and as a result, sometimes the sound of the blast influences the life environment beyond the hilly undulations. At both hilly sites with heights of up to several tens of meters and flat lands, excess attenuation of blast sound was measured at points of several hundred meters away. Frequency spectrums of excess attenuation beyond the hilly side show that (1) up to around 100 Hz, excess attenuation increases in proportion with frequency, and for more than 100 Hz, it shows mostly constant values of around 40 dB; (2) shapes of frequency spectrum of the excess attenuation show similar pattern with the ones of flat land; and (3) shielding effects of hills mainly appear at the frequency range around 100–250 Hz. From these results, the authors discuss the possibility of sound propagation modeling by extending usual models for flat land.