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| Titel |
Rockfall hazard assessment by using terrestrial laser scanning. A case study in Funchal (Madeira) |
| VerfasserIn |
Hieu Trung Nguyen, Tomás Fernández-Steeger, Rodriguez Domingos, Thomas Wiatr, Rafig Azzam |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043198
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| Zusammenfassung |
| Rockfall hazard assessment in a high-relief volcanic environment is a difficult task,
facing the challenge of missing standard rating systems and procedures. Likewise
mountainous areas, further handicaps are a restricted accessibility to the rock faces
and the high efforts in terms of time and labour force to identify and rate these
problems. To develop a procedure for rockfall hazard assessment, the island of Maderia
is a good research area to investigate rockfalls in a volcanic environment under
sub-tropic humid climate conditions. As the entire island is characterised by high
mountain ridges and steep deep valleys in lavaflows and tuff layers, the occurrence of
rockfalls is a frequent and a serious problem. These hazards are the most frequent
causing severe damage to infrastructure and fatalities. In this research, slopes in
Funchal city have been mapped and investigated regarding their rock fall hazard
potential. The analysed slopes are build-up of lava flows with column structures and
intercalated breccias, pyroclatics or tuff layers. Many of the columns already lack
basal support and show a wide joint spacing, threatening houses and streets in the
city. TLS data acquisitions in May and December 2008 provide information for
detailed structural analysis, detection of unstable areas within a slope and rockfall
simulations. High resolution scans have been recorded on uncovered rock surfaces with
detectable joints while in areas with dense vegetation a lower resolution has been
chosen. Although it makes sense to scan an entire area with the best acquirable
resolution, the resulting enormous data require powerful computing environments and
will slow down data processing. To speed up the data processing, a conventional
local digital elevation model (DEM) built up the geometric basic model. Its main
disadvantage is that it is not possible to project overhanging parts or notches within the
steep slopes which have an important influence on the accuracy of any rockfall
simulations. By implantation of the high resolution scans of the TLS into the local
DEM, an improvement close to a solely high-resolution digital elevation model
(HRDEM) can be achieved. The rockfall hazard assessment starts by comparison of
time-shifted datasets and with additional automatic jointing analysis. Based on
this data 3-D displacements and associated kinematical failure mechanism can be
identified. Using on this information, it becomes possible to determine specific
parameters for numerical rockfall simulations like average block sizes, shape or potential
sources. Including additional data like surface roughness the results of numerical
rockfall simulations allow to classify different areas of hazard based on run-out
distances, frequency of impacts and related kinetic energy. The analysis shows that
rockfall favourable occurs in areas where notches and undercuts, due to the lesser
erosionresistence of pyroclatics or tuff layers, appear. In case of a rockfall the typical
blocks have a cylindrical shape, a volume of 1 m3 and are able to hit the entire
area. The results can help to provide useful information for civil protection and
engineering countermeasures. Repeated TLS scans on the same area will continue
the observation and the progress of instability and mass movement occurrence. |
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