Abstract

Raise boring machines are used for excavation of shafts and other vertical structures in mining, civil, and construction projects for ventilation, service, transfer of material, and personal access. Experimental studies for determining of penetration index related to rock cutting with raise bore machines are presented. Penetration index is obtained by pushing one bit upon a rock sample under a hydraulic press in the laboratory. Borehole samples obtained from Eti Copper Kure Asikoy underground mine located in Turkey were first tested for defining some of the basic physical and mechanical properties, and then indentation test were carried out due to determine of penetration index. Excavation performance parameters of RBM such as, penetration rate, and thrust force were estimated based on experimental result of indentation tests. Then estimated parameters validated by field results to serve a useful guide for future applications.

1 Introduction

Raise boring machines are used for excavation of shafts and other vertical structures in mining and civil engineering fields. These machines in classical raise method, drill a pilot hole (diameter of hole around 230–350 mm) down to the required depth of the shaft, which can be drilled up to around 2000 m. Once the pilot hole has been drilled to the desired depth, a reamer of up to 7 m diameter is attached to the drill rod. The reamer is then pulled back up to the upper level, creating a round shape. RBM creates a shaft with smooth walls, which usually does not require lining. The hole is more stable than a drilled and blasted method and has better airflow, making it ideal for ventilation shafts. There are several parameters affecting RBM cutting operation. These parameters are categorized in two groups. First group include rock properties parameters (hardness, strength, water content) and second group include machine and equipment parameters (machine position angle, machine power, rotational speed, thrust, torque, cutterhead diameter, length of cutting area, technical personnel).

Few studies have been published in the literature related to predicting the performance of raise boring machines. Morris (1969) developed a semi-empirical method of predicting the boring rate and cutter life. In his method button penetration index with the other factors used to predict the machine performance. Seiler (1972) developed a boreability index by pressing hydraulically a sphero-conical tungsten carbide insert into a flat rock surface. Then by dividing the load to created depth boreability index calculated. Calder (1972) stated the empirical model to predict boring rate from drilling studies. His rotary drilling model relates boring rate to uniaxial compressive strength of the rock, thrust force and hole diameter. Bilgin (1989) and Bilgin et al (2014) stated that, penetration index obtained from indentation tests could be used to estimate the RBM performance. Penetration index (α) is obtained by pushing one bit upon a rock sample under a hydraulic press in the laboratory and it is the slope of load penetration versus load curve or F/d, where F being the applied load and d the penetration. Penetration index is mainly dependent on rock properties and the geometry of the indenter bit. The main aim of this study is to find the penetration index, which obtained from indentation tests. Five borehole samples selected from stud area then by using the stiff MTS machine with a load capacity of 500 kN, the indentation test were conducted in the laboratories. At the end the results validated by a model which suggested by Bilgin et al. (2014) for performance prediction of raise boring machines.

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