Oya tuff, which is categorized as soft rock, has been excavated in Oya area of Utsunomiya City, Tochigi Prefecture, Japan, for building stone and retaining walls for several decades. It is one of the most commonly used rock materials in Japan. As a result, there are many abandoned underground quarries existing in this area. After the 2011 East Japan Great Earthquake, the consideration of the seismic responses of underground quarries has become very important. Almost all of Oya underground quarries have been excavated using room and pillar method except some, which are long wall type. In the study, the quarry under investigation is an active room and pillar type and this paper presents the field measurement techniques used to study the seismic response and micro tremor of the quarry. Through the seismic response analysis, this study tried to clear underground quarries. A numerical model was then developed using a FDM to assess the dynamic stability of the quarry.

1 Introduction

There are over 200 abandoned underground quarries located in Oya town, Utsunomiya city and Tochigi prefecture, Japan. Those underground quarries have been excavated by mining Oya tuff as a building stone for retaining walls and decoration plate for interior walls of houses. In the past there has been sinkholes caused by the underground mines of Oya tuff and in 1989 there was a huge land subsidence which resulted in some property such as houses being damaged (Oyagi and Hungr, 1989). Recently, another collapse occurred in Oya town during the 2011 Great East Japan Earthquake; however, this time, it was collapse of a semi underground mine pillar in Oya town (Aydan, 2015). With occurrence of this events, underground quarries are considered as unstable, therefore, several study was conducted to evaluate the stability (Katayose et. al, 2008, Seiki et. al, 2007 and 2016).

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