住宅近接地で発破併用の機械掘削工法により硬岩地山を掘削: 国道18号坂城更埴バイパス稲荷山トンネル

摘要

The Inariyama Tunnel, which is a part of the National Route18 Sakaki-Koshoku Bypass, is located in Chikuma City, Nagano Prefecture. The excavation length is 162m to bore mainly rhyolite. Many residents and soexist near the tunnel, so measures against noise and vibration were challenges of the construction. In the beginning of excavation, the tunnel was bored using a 300kW road header, but hard rhyolite that exceeded 130N/mm~2 was found deep in the tunnel, made it difficult to drill through. Auxiliary blasting was used as a measure. By creating free faces on heading with auxiliary-blasting using an explosive amount that met the noise regulation set by the construction, and using potential cracks as a trigger to loosen the ground, it enabled the mechanical excavation to use.%一般国道18号坂城更埴バイパスは埴科郡坂城町から千曲市に至る道路である.このバイパスは， 現国道18号の渋滞緩和，交通事故対策と併せ千曲川左岸地域の活性化を図ることを目的として建設事業が進められている.（仮称)稲荷山トンネルはこのうち千曲市より長野市へつながるバイパス延伸区間（延長2.6km)に位置する（図-1).