Abstract

Full-scale linear cutting test is one the most preferred and reliable methods for performance prediction of mechanical miners. Raise Boring Machines (RBMs) are one of these mechanical miners which are commonly used for drilling / excavation of shafts for different purposes in mining and tunneling projects. This study aims at investigating experimentally double spiral (scroll) cutting pattern in raise boring machine. Full-scale linear cutting tests are performed by using button (kerf) cutting tool. The tests are performed at line spacing of 25 mm and varying depths of cut per revolution by using two hard rocks (diabase and granodiorite) that were obtained from the Yusufeli Dam and HEPP project site. The average and maximum normal, rolling and side forces; specific energy; yield; and coarseness index are measured in each cut. The study indicates that optimum ratio of line spacing to depth of cut per revolution are obtained as 8.3 and 4.2 for diabase and granodiorite samples, respectively.

Introduction

Shafts have an important role as access, transportation, and ventilation in mining, tunneling, and underground construction. In recent years, the raise boring method is widely used for shaft excavation in different projects. Raise boring provides a safe means of excavating a circular hole between two levels of a mine without the use of explosives. A raise boring machine (RBM) is set on a platform on the upper level to drill a small hole (around 230-350 mm) compared to reaming diameter, known as the pilot hole, up to the cavity below. Once the drill has been completed, the pilot bit is removed and is replaced by a reamerhead, of the desired diameter of the shaft, which is rotated and raised back toward the upper level. The drill cuttings from the reamerhead fall to the bottom of the hole and the reaming process creates a cylindrical hole with smooth walls. Safety, cost reduction, and faster advance rate are the important advantages of this method. However, this method possibly encounters serious troubles in fractured or weathered rock masses, such as the collapse of shaft walls, stoppage of excavation, and breakage of tools. These troubles lead to an extension of construction period and an escalation of budget. Therefore, it is essential to understand the rock mass conditions around a shaft before or during excavation [1].

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