Spatial Variability of shotcrete thickness

An important task during the construction process is to validate the dimensions and properties of a given structure. The dimensions like for instance the thickness of a construction element should be measured after finishing building it. The aim is to compare the measured value with the design value to avoid that elements do not correspond to the input requirements. Moreover, the measurements are helpful to analyse the statistical distribution of the investigated geometrical property by computing e.g. a histogram, which visualises the dispersion and enable the calculation of the probability of failure for a specific structure or element.In this work, a shotcrete layer has been analysed in order to provide information about the homogeneity of the shotcrete thickness in a pre-determined tunnel section. The calculation method is based on two laser scans, before and after applying the shotcrete. Due to the construction process, the shotcrete layer will not be totally equal, which might be a safety problem. Especially, when the shotcrete layer is thinner than required and hence, the actual variation of the shotcrete must be considered and verified.To determine the statistical distribution, correlograms and histograms have been computed for a wall area in a tunnel in Southern Sweden. The correlogram shows the distance where the values have a correlation to each other and usually this distance is called scale of fluctuation. For the wall section, this scale of fluctuation has been calculated for the length (0.8m) as well as the height (0.8m). Compared to the original sample distance, e.g. distance of the rock bolts, the variance for the calculation of the probability of failure might be reduced.