ABSTRACT:

The authors tried to check the seismic response of some underground quarries for Oya tuff in Oya town, Utsunomiya City, Tochigi Prefecture, Japan through field measurement and numerical analyses. The authors selected some seismic velocity waves from thousands of seismic records to represent site effect around them. The results of FFT analyses showed that natural frequency from field measurement ranges between 5 Hz and 10 Hz. The authors first clarify the frequency characteristics of the quarries with continuous monitoring. Then, the authors consider the influence to seismic wave on 2-D and 3-D numerical models of underground quarries to clarify the fundamental response of underground quarries during shaking. The results show that there is slight discrepancy between the field measurement and the analyses. The authors discuss the reason for such a discrepancy.

1 INTRODUCTION

After the 2011 Great East Japan Earthquake, it is getting important to evaluate seismic stabilities of infrastructures (Aydan et al. 2011). The importance is also the same for underground structures. Oya tuff, which is one of the famous building stone and is classified into pumice volcanic tuff is, have extracted through underground quarrying around Oya town, Utsunomiya City, Tochigi Prefecture, Japan. Until now over 200 nonsupported underground quarries have been excavated since 19th century and almost of them have been abandoned. The numbers of people, who considered those underground quarries as space resources and would like to utilize publicly, are increasing. In this study, the authors tried to check the seismic response of some underground quarries through numerical analysis and field measurement. The authors first carried out field measurement with seismic velocity meters which have densely installed and are in operation since 1989 in this area. The authors selected some seismic velocity waves from thousands records to investigate site effect around the quarries. The authors analysed the frequency characteristics of those quarries using selected records. Then, the authors consider the influence to seismic waves on 2-D and 3-D numerical models of underground quarries to clarify the fundamental response of underground quarries during earthquake shaking. In this study, additional numerical analyses were carried out using some selected strong motions from some strong earthquakes in order to check the response of quarries beneath the underground quarries.

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