Shotcrete Layer Research Articles

Bolt-anchored steel-fibre-reinforced shotcrete linings

One way to obtain an advanced rock reinforcement is to use reinforced shotcrete which interacts statically with rock bolts. This investigation was carried out in order to obtain a better knowledge of the effects of steel fibres in shotcrete and also of how to design the bolt anchor which is important for the static interaction between the shotcrete and the rock bolt. 22 large scale tests on bolt anchored reinforced shotcrete layers were performed. 19 of the layers were reinforced with Bekaert steel fibres, two were reinforced with cold tensioned reinforcement mesh and one with an annealed mesh. The parameters varied were the amount of fibres, the fibre length and the design of the bolt anchor in the shotcrete. For each large scale test adhesion tests on the rock-shotcrete interface were performed as well as strength tests on sawn out shotcrete cubes and beams both with and without fibres. The concrete mass was tested using cast cubes. Four large scale tests on extremely thin fibre reinforced linings without bolt anchorage were performed. Two specimens contained steel fibres and two glass fibres. Small scale shear tests on cracked steel fibre reinforced specimens were performed. Six tests were successful and these are reported. (Author/TRRL)

7. Analysis and monitoring of the Miyana railway tunnel constructed using the New Austrian tunnelling method

This paper presents a case study of the New Austrian Tunnelling Model (NATM) for the construction of a double-track railway tunnel through semi-hard dolerite rocks. The Japanese National Railways have studied and employed the NATM for their various tunnel projects since around 1976, and this tunnel, the Miyana Tunnel, can be considered as a forerunner for the NATM application in Japan. The agreement or lack of agreement between the calculated and the measured values are compared for convergences, ground displacements, axial forces in rock bolts and stresses in shotcrete layers. Some characteristics of tunnelling in semi-hard rocks by the NATM are carefully studied, and the appropriate design systems are introduced for the establishment of safe and economical construction methods. The measured values are generally on the safe side when compared with the calculated values, and it is suggested that the preliminary design of a tunnel in semi-hard rock could be reasonably conceived and carried out by linear elastic numerical analysis using the finite element method.

Swedish approach to rock support : Kramers, M Int Water Power Dam Constr, V30, N9, Sept 1978, P31–35

Swedish experience shows that a proper understanding of the process of tunnel support using a thin layer of shotcrete, coupled with modern methods of application should lead to a wider application of the system. The author evaluates the design approach to shotcrete support based on measurements, rock classification and experience. The important advantages of shotcreting, either as a temporary or permanent support are given. These include economy, adaptability, no need for shuttering or complicated equipment. Recent developments in Swedish remote-controlled shotcreting equipment are described. The operation of the robot system is outlined; its major advantage is in its capacity to tackle and pass a cave-in quickly and efficiently. A reliable combined transporting and batching system, the trixer, has been developed. The use of liquid accelerators and proportioning pumps are described. Research into the use of steel-fibre reinforcements is outlined. (TRRL)