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UndergroundDevelopment of a Centrifugal Sprayed System for Shotcrete Application

Hiroshi Yamachi, Masataka Uozumi, Yuji Nagano,Youichi Nakano, and Shunsuke Sakurai

A new Japanese Ministry of Health document provides regulations and guidelines for the allowable dust concentration in tunnel works. The recommended maximum concen-tration should be less than 3.0 mg/m3 (2.3 mg/y3) at 50 m (164 ft) from the tunnel face. To observe this guideline, it