Small-diameter vertical shafts constructed in the shallow space of steep mountainous areas

Abstract

Japan is a mountainous country comprising several islands, in which mountains occupy 70% of the entire land. Therefore, numerous transmission line towers have been constructed in the shallow space of steep mountainous areas. In such construction, monorails and/or cableways are generally used to transport materials and equipment to the construction site instead of using a construction road, as the former method is more economically viable. However, with this method, drill rigs or vertical shaft sinking machines cannot be transported to the site. Four small-diameter vertical shafts of 2.5 or 3.0 m as the foundation for high-voltage transmission line towers in mountainous areas are traditionally constructed manually in Japan. Over the past two decades, however, dangerous and poor environmental conditions for workers regarding the manual construction of these small-diameter vertical shafts have become a major problem. Meanwhile, owing to the poor environmental conditions of small-diameter vertical shafts to be constructed in the shallow space of steep mountainous areas, a decrease has occurred in the number of young workers entering these projects. Namely, the construction of transmission line towers with using the manually traditional small-diameter vertical shafts is becoming difficult in Japan from abovementioned problems. Hence development of a new technology to solve the problems is necessary for Japan’s economic growth. With this knowledge, the authors have developed a new small-diameter vertical shaft construction system, in which workers do not have to enter the vertical shaft during construction, as machines are used instead. The applicability of the proposed system was confirmed by means of the construction of three actual vertical shafts at two construction sites, as well as in factory and field tests. The applicability and details of the final proposed system are summarized in this paper.