Abstract
Abstract. When ground conditions are weak, particularly in free formed tunnel linings or retaining walls, sprayed concrete can be applied on the exposed surfaces immediately after excavation for shotcreting rock outcrops. In these situations, shotcrete is normally applied conjointly with rock bolts and mesh, thereby supporting the loose material that causes many of the small ground falls. On the other hand, contractors want to determine the thickness and volume of sprayed concrete for both technical and economic reasons: to guarantee their structural strength but also, to not deliver excess material that they will not be paid for. In this paper, we first introduce a terrestrial LiDAR-based method for the automatic detection of rock bolts, as typically used in anchored retaining walls. These ground support elements are segmented based on their geometry and they will serve as control points for the co-registration of two successive scans, before and after shotcreting. Then we compare both point clouds to estimate the sprayed concrete thickness and the expending volume on the wall. This novel methodology is demonstrated on repeated scan data from a retaining wall in the city of Vigo (Spain), resulting in a rock bolts detection rate of 91%, that permits to obtain a detailed information of the thickness and calculate a total volume of 3597 litres of concrete. These results have verified the effectiveness of the developed approach by increasing productivity and improving previous empirical proposals for real time thickness estimation.
Highlights
Engineers working in the Architecture, Engineering and Construction (AEC) field quite often need to design and build structures that are situated in densely populated urban areas
We propose an automatic, non-destructive, LiDAR-based method to accurately estimate the thickness and volume of sprayed concrete on anchored walls from data points acquired by a three-dimensional Terrestrial Laser Scanning (TLS)
These matched point clouds are afterwards inspected for outlier detection and removal
Summary
Engineers working in the Architecture, Engineering and Construction (AEC) field quite often need to design and build structures that are situated in densely populated urban areas This involves a high risk, because if an accident happens, the damage can be large. In excavations of intermediate and great depth, safety will be probably compromised if fractures, discontinuities, disintegration, weathering or loosening exist In those situations, rock bolts are used for stabilizing rock excavations and prevent rockfalls (Cai et al, 2015; Srivastava and Singh, 2015). Rock bolts are used for stabilizing rock excavations and prevent rockfalls (Cai et al, 2015; Srivastava and Singh, 2015) They improve properties of the jointed rocks, frequently combined with wire mesh and sprayed concrete. Very few empirical approaches have been proposed to compute the shotcrete layer thickness, and they tend to use parametric or statistical models to study the distribution of sprayed concrete on the wall (Rodríguez et al, 2009)
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