Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ...

114 6. Applications of Terrestrial Laser Scanningvolume, the percentage of road runoff that drains directly into the vegetatedas 36 %, while 64 % of road runoff is dispersed diffusively. As the pollutant load mayproportional to the water distribution, about 36 % of the pollutantvegetated road shoulder immediatelyroad shoulder was calculatedbe considered to beload in the runoff would infiltrate thebelow the road. Thus, infiltration leads to high accumulation ratesand high concentrations of heavy metals and organic substances in the topsoil.This new method for the calculation of small scale catchment areas can be assessed as a success. However,it is recommended to control the results at critical parts of 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 of equilibriumare found. The response of a particular rock mass to these disturbances is greatly influenced byin which rock massesits internalstructure resulting from the occurrence of geological discontinuities with different preferential orientations.This response usually involves rock mass deformations that can be observed by recording the displace¬ments of pointslocated within the rock or on excavation surfaces. Inpractice, the monitoring of suchdisplacements is of great interest as it allows for the understanding of the mechanisms throughwhich rockmasses react to excavation-induced perturbations and for predicting potential stability problems that mayoccur in the future. As aconsequence, in situ characterization of the rock mass structure and displacementmonitoring are two important operations that are routinely carried out during rock engineering projects.Appropriate characterization of the rock mass structure is a time-consuming processas a sufficient numberof features have to be sampled to achieve a reliable description of rock mass fracturing. Moreover, produc¬tion constraints and installation of rock support systems, such as steel meshes or concrete linings, usuallyleave very little time to undertake an extensive survey of geologicalstructures. On the other hand, discon¬tinuity surveying requires safe access to rock surfaces that can only be guaranteed if adequate support isinstalled beforehand. Displacement monitoring is a common practicethat is used to track the evolution ofthe rock mass behaviour. However, this operation is traditionally achieved by measuring the displacementof a limited number of points. Displacement monitoring of points located within the rock mass requires thedrilling of boreholes and the installation of specific equipment. Therefore, the measurement of surface dis¬placements is more frequently performed in practice. In this case, arrays of 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 of points to achieve reliable interpretation ofthe actual rock mass behaviour.The use of 3D laser scanners allows for effective management of the practical constraints encountered inrock engineering since it quickly provides a realistic and permanent representationof excavation surfacesthat requires the installation of a reduced number of physical targets used only for data referencing pur¬poses. This is of great importance in the study of inaccessible and potentially unstable surfaces, which are,thus, mapped at any time from a safe location regardless of the lighting conditions. Because of the highspatial resolution of the data, these tools can also be used for topographical surveysand the documentationof excavation surfaces, which are two additional procedures carried out routinely throughout constructionwork. Finally, the direct collection of digital data results in speeding up processing work through the use ofmodern 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 and analyses.The laser scanner has been used to measure the characteristics of geologicalstructures as well as the surfacedisplacements in an experimental tunnel in the Mont Terri Rock Laboratory, Switzerland.Several exper-