114 6. Applications <strong>of</strong> <strong>Terrestrial</strong> <strong>Laser</strong> Scanningvolume, the percentage <strong>of</strong> road run<strong>of</strong>f that drains directly into the vegetatedas 36 %, while 64 % <strong>of</strong> road run<strong>of</strong>f is dispersed diffusively. As the pollutant load mayproportional to the water distribution, about 36 % <strong>of</strong> the pollutantvegetated road shoulder immediatelyroad shoulder was calculatedbe considered to beload in the run<strong>of</strong>f would infiltrate thebelow the road. Thus, infiltration leads to high accumulation rates<strong>and</strong> high concentrations <strong>of</strong> heavy metals <strong>and</strong> organic substances in the topsoil.This new method for the calculation <strong>of</strong> small scale catchment areas can be assessed as a success. However,it is recommended to control the results at critical parts <strong>of</strong> the surface drain, e.g.inlet with small scale tracerexperiments, which only requirea few minutes.6.2 Static Application: Rock Engineering Applications6.2.1 IntroductionEngineering works in rocks induce disturbances in the original state <strong>of</strong> equilibriumare found. The response <strong>of</strong> a particular rock mass to these disturbances is greatly influenced byin which rock massesits internalstructure resulting from the occurrence <strong>of</strong> geological discontinuities with different preferential orientations.This response usually involves rock mass deformations that can be observed by recording the displace¬ments <strong>of</strong> pointslocated within the rock or on excavation surfaces. Inpractice, the monitoring <strong>of</strong> suchdisplacements is <strong>of</strong> great interest as it allows for the underst<strong>and</strong>ing <strong>of</strong> the mechanisms throughwhich rockmasses react to excavation-induced perturbations <strong>and</strong> for predicting potential stability problems that mayoccur in the future. As aconsequence, in situ characterization <strong>of</strong> the rock mass structure <strong>and</strong> displacementmonitoring are two important operations that are routinely carried out during rock engineering projects.Appropriate characterization <strong>of</strong> the rock mass structure is a time-consuming processas a sufficient number<strong>of</strong> features have to be sampled to achieve a reliable description <strong>of</strong> rock mass fracturing. Moreover, produc¬tion constraints <strong>and</strong> installation <strong>of</strong> rock support systems, such as steel meshes or concrete linings, usuallyleave very little time to undertake an extensive survey <strong>of</strong> geologicalstructures. On the other h<strong>and</strong>, discon¬tinuity surveying requires safe access to rock surfaces that can only be guaranteed if adequate support isinstalled beforeh<strong>and</strong>. Displacement monitoring is a common practicethat is used to track the evolution <strong>of</strong>the rock mass behaviour. However, this operation is traditionally achieved by measuring the displacement<strong>of</strong> a limited number <strong>of</strong> points. Displacement monitoring <strong>of</strong> points located within the rock mass requires thedrilling <strong>of</strong> boreholes <strong>and</strong> the installation <strong>of</strong> specific equipment. Therefore, the measurement <strong>of</strong> surface dis¬placements is more frequently performed in practice. In this case, arrays <strong>of</strong> object pointsfirmly anchored within the first centimeters behind the rock surface at different locations alonghave to be installedthe surface.In both cases, it is necessary to monitor a sufficient number <strong>of</strong> points to achieve reliable interpretation <strong>of</strong>the actual rock mass behaviour.The use <strong>of</strong> 3D laser scanners allows for effective management <strong>of</strong> the practical constraints encountered inrock engineering since it quickly provides a realistic <strong>and</strong> permanent representation<strong>of</strong> excavation surfacesthat requires the installation <strong>of</strong> a reduced number <strong>of</strong> physical targets used only for data referencing pur¬poses. This is <strong>of</strong> great importance in the study <strong>of</strong> inaccessible <strong>and</strong> potentially unstable surfaces, which are,thus, mapped at any time from a safe location regardless <strong>of</strong> the lighting conditions. Because <strong>of</strong> the highspatial resolution <strong>of</strong> the data, these tools can also be used for topographical surveys<strong>and</strong> the documentation<strong>of</strong> excavation surfaces, which are two additional procedures carried out routinely throughout constructionwork. Finally, the direct collection <strong>of</strong> digital data results in speeding up processing work through the use <strong>of</strong>modern computer resources. Therefore, terrestrial laser scanning has a high potentialsince it can be usedas an efficient tool to record data required for various routine rock engineering applications <strong>and</strong> analyses.The laser scanner has been used to measure the characteristics <strong>of</strong> geologicalstructures as well as the surfacedisplacements in an experimental tunnel in the Mont Terri Rock Laboratory, Switzerl<strong>and</strong>.Several exper-
6.2 Static Application: Rock Engineering Applications 115Figure 6.7: <strong>Laser</strong> scanner inside the excavated niche including object points signalized by spheresîments are currently undertaken in this laboratory to underst<strong>and</strong> the behaviour <strong>of</strong> a rock formation, l eOpalmus clay, that has been identified as a potential host for a radioactive nuclear waste repositoryTheexcavation is a 5 m long <strong>and</strong> 3 8m diameter circular tunnel, cf Figure 6 7, which was extended in sevensteps with pauses for several investigations including total station surveying <strong>and</strong> laser scanning Figure6 8 shows different views <strong>of</strong> the point cloud that resulted from the surveying <strong>of</strong> the tunnel at the end <strong>of</strong> itsexcavation The mam objective <strong>of</strong> the work was to assess the potential <strong>of</strong> laser scanning in quantifying accu¬rately geometrical characteristics <strong>of</strong> geological structures <strong>and</strong> in deriving time lapse surface displacementmaps <strong>of</strong> object points as well as <strong>of</strong> rock surfaces with a high spatial resolutionFigure 6.8: Point cloud representing the final geometry <strong>of</strong> the tunnel exteriorthe rock mass (left) <strong>and</strong> interior view <strong>of</strong> the tunnel (right)view <strong>of</strong> the tunnel, as seen from inside6.2.2 MethodA majorconcern when measuring displacement data is the installation <strong>of</strong> an appropriate<strong>and</strong> stable refer¬encesystem This reference frame is defined by reference points, which are fixed in regions that are notinfluenced by the excavation <strong>of</strong> the tunnel during the observation period Based on previous displacementmeasurements made at the Mont Tern laboratory, l e convergence measurements, the zones that were not
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