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| Titel |
Subsurface deformation measurements during a fast shallow landslide triggered by rainfall |
| VerfasserIn |
Amin Askarinejad, Sarah M. Springman, Devrim Akca, Ernst Bleiker, Armin Gruen |
| 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 |
250044922
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| Zusammenfassung |
| A forested area in Ruedlingen, northern Switzerland, was selected to investigate the
geotechnical and hydrological response of a steep slope prior to a rainfall induced failure.
Artificial rainfall was applied according to a pre-planned schedule and parameters such as
pore water pressure, volumetric water content, horizontal soil pressure, temperature,
piezometric water level and subsurface deformations were monitored. The latter were
determined from four deformation probes that were developed in the Institute for
Geotechnical Engineering, ETHZ. Strain gauges have been attached at a regular spacing
along a long, slender, flexible plate to enable measurements of bending strain to be made at
different points along it. The strain gauges were connected as “half bridges” to
minimize the temperature effects. A biaxial inclinometer was also installed on the top
of the plate, 20 cm above the soil surface, to measure the tilt above ground level,
providing more boundary conditions to determine the deformed shape of the probe.
The probe is installed vertically inside the soil, while the lowest part is grouted
into the stiffer layer under the topsoil, and is assumed to be stable and without any
rotation. Bending strains and the inclination at the top of the probe are sampled at a
frequency of 100 Hz. These are input into an algorithm to determine a polynomial
relationship of deformations and rotations with depth, so that the initiation of slow
movements and propagation of failure during fast soil mass movements can be
examined.
A 4-camera arrangement was used for the image acquisition to monitor surface
movements using photogrammetric analyses. Approximately 250 white ping-pong balls were
attached to the ground and used as target points. Using a network simulation tool that was
developed in-house, an a priori point positioning accuracy of the ping-pong balls was
estimated to be ± 10.3 mm along the horizontal direction and ± 3.5 mm in the vertical
direction. The cameras operated at a data acquisition rate of circa 8 frames per second (fps).
Image measurements were made using the Least Squares image matching method, which was
implemented in another in-house developed software package (BAAP) to compute 3D
coordinates of the balls.
Two sprinkling experiments were conducted in Ruedlingen, in autumn 2008 and spring
2009, the second of which resulted in mobilising about 130 m3 of debris. In the second
sprinkling experiment, the area of interest was moved ca. 5 metres up the slope. In order to
make the targets more discernable on the image space, the ping-pong balls were replaced with
approximately 80 white tennis balls. A posteriori point positioning accuracy obtained from
bundle adjustment in the first sprinkling experiment was ± 16.5 mm along the horizontal
direction and ± 3.4 mm along the vertical direction. For the second experiment, these
values were ± 11.0 mm and ± 4.3 mm for the horizontal and vertical directions,
respectively.
The results of subsurface deformation during this shallow landslide event are
presented and compared with surface movements determined from photogrammetric
measurements. |
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