Measurement device system for the determination of the surface roughness of cracked shotcrete

In shallow tunnelling below groundwater table compressed air is used for preventing water inflow into the tunnel during the excavation work. The air leaks through the unsupported tunnel face and the shrinkage cracks of the shotcrete support and must be compensated by compressors continuously.The air permeability of cracked shotcrete depends from the width of the cracks and the roughness of the crack surfaces. The aim of the research project is to develop a measurement device system for the determination of the roughness of a crack surfase from shotcrete.