ABSTRACT
The interaction between the arches, either of wood or steel, and the ground is very low due to the difficulty in ensuring the contact between the arches and the ground, caused by the overbreak. In regular tunnel constructions, arches made with HEB-180 profiles or heavier are used. The lattice girders are joined together by screwed plates; in a similar way as HEB profile arches. Rock bolts are bars made of steel or polyester resin with glass fibers, with a diameter of around 25 mm that are placed inside bores drilled in the ground and fixed in it by chemical action or by friction. Rock bolts anchored with cement were already used in the 1960s but the installation procedure was purely manual, the performance rates were low and the anchor quality was difficult to control. The load capacity of a rock bolt is transmitted to the ground by means of a bearing plate, which is screwed to the bolt.
