Rock bolts are typically used for the ground reinforcement. Except some spot bolts, rock bolts are usually grouted with cement or resin grout. To use the bolts at seepage place or to improve installation speed, various type of friction bolts also have been developed. In this study, Plasma bolt, as an expandable rock bolt type, was developed which can be installed quickly and easily, and show immediate supporting effects by adopting the plasma technique. It is a hollow pipe drawn as round polygon shaped section with concavo-convex like a star shape filled with plasma trigger-parts and materials. Field installation and pull out tests were carried out. To optimize the design parameters of rock bolt, steel material, drawn section shape, cap type and composition of reactants and power factor were selected. The capacity of simultaneous multi installation of rock bolt was estimated according to the electrical condition of a high voltage electric device for generating plasma phenomena. Pull out load of optimized plasma bolt was more than 14 ton, which is sufficient for general tunnel support. Rock bolt installation was expected to be faster than existing bolts by the valuable advantage of simultaneous multi installation with dynamic expansion.

1. Introduction

Plasma bolt is defined in terms of rock bolt that the frictional contact support resulted from the expansion state occurred by dynamic and stable plasma phenomena at inner space of bolt pipe. The bolt pipe is a hollow pipe induced by cold drawn course as round polygon shaped section with concave-convex. Plasma bolt consisted of the bolt pipe and the connection part to be electrically linked to an electric power device of high voltage. This new type of expandable bolt was more realistic and safer about the dynamic expandable type suggested by the precedent study (Jeong et al., 2015). Experimental studies for the above plasma bolt covered the contents of expansion test in concrete block, simultaneous multi reaction test and also in-situ multi installation test. The bolt design was affected by many effect factors about bolt structure and material as steel material, section shape and expansion force of rock bolt and so on. The relative importance between the factors was investigated by robust design for the optimal condition between effect factors of the bolt design.

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