10th Asian Regional Conference of IAEG (2015)

Evaluation of Slope Hazards and Landslide-Triggering Factors in Korea

Jeong, Gyo-Cheol (1), Nam, Koung-Hoon(1), Lee, Hak-Yun(1), Choo, Chang-Oh(1) and Yune,Chan-Young (2)(1) Dept. of Earth and Environmental Sciences, Andong National University, Andong, Republic of Korea
E-mail: jeong@anu.ac.kr(2) Dept. of Civil Engineering, Gangneung-Wonju National University, Gangneung, Republic of Korea
Abstract
There are many slope disasters nationwide in Korea during the rainy season hit bysevere rain storm and typhoon from June to September every year. The Korean peninsula
was indirectly affected by typhoons 12th Nakri and 11th Halong taken place in August, 2014.
The rainfall in August was 369 mm, reaching 138% of an average rainfall of August, while
the rainy days were 18.2 that are about 5 days longer than its average. It is acknowledgedthat diverse factors such as topography, geological features, forest types, and forest fire are
combined to induce slope disasters in Korea, even though the rain is one of the main causes.
Therefore, it is hard to predict the causes of slope disasters only based on the rain parameter.
In this study, landslide vulnerability as a function of swelling clay minerals was evaluatedusing ASTER satellite imageries. We examined spectral characteristics changes based on
the field survey, XRD, XRF analysis, and spectroscopic analyses using GER 3700 portable
spectrometer on soil samples obtained from landslide sites, together with ASTER satellite
imageries. According to the results analyzed, most landslide areas are made up of illite-richclay minerals and their spectral properties show differences in the SWIR. The particle sizeand mineral composition were analyzed through the six bands of SWIR on the basis ofspectral characteristics. Illite, one of representative swelling clay minerals, shows
characteristic absorption features: Fe2+ and Fe3+ at 0.9 and 1.0 µm, broad water absorption
features near 1.4 and 1.9 μm, and additional Al-hydroxyl features at 2.2, 2.3 and 2.4 μm,respectively. These absorption properties correspond to the band 5, band 6 and band 7 in theASTER imageries. This study showed the spectral characteristics of the soils and ASTER
imageries by applying SWIRillite model for the multiplication ratio between wavelength
bands, leading to a conclusion that the applicability of ASTER satellite imageries,
combined with analyses of swelling clay minerals, has potential to evaluate and predict thelandslide hazards.
Keywords: landslide, spectral reflectance, clay mineral, ASTER, band math1.

Introduction

expandability and attraction in engineering geology(Al-Rawas, 1999; Fall and Sarr, 2007). Clayminerals have different mineral structures, andphysicochemical properties. Soil expandability
causes main problems encountered in engineeringgeology and is considered intrinsic properties
attributed to the presence of active clay minerals(Al-Mukhtar et al., 2010; Al-Rawas, 1999; Bell,1999; Kim et al., 2005; Seco et al., 2011; Shi et al.,
2002; Snethen, 1975; Sridharan and Gurtug, 2004).
To monitor the presence of clay minerals isconsidered one of the most important factors toidentify
potential
expandablesoils
andcharacterization and quantification of soil areessential in evaluation of soil expandability.

Due to properties of contraction and expansion,clay minerals negatively not only affectconstruction but also produce discontinuities andshear planes on natural slope, leading to slope
unstability that finally causes landslide. The sourceof expandability of clay minerals arises fromchemical attraction of water molecules which areincluded between sheets in the clay structure. Whenclay minerals no longer hold water, clay sheets
become separated, and thus clay structures
gradually begin to be unstable. Such properties arecommon in most soils (Gray and Murphy, 2002)
and serve as main indicators that explain soil1

10th Asian Regional Conference of IAEG (2015)

Remote sensing has been used as one of themost convenient methods to identify spectroscopic
properties in domestic mine areas because it has anadvantage of identification of alteration minerals
and rocks easily and quickly based on spectroscopy,
though it has limitations to characterize mineralclassification (Chi and Lee, 2007; Son et al., 2011;
Lee et al., 2011).
Here, we used spectrophotometer that is
relatively cheap and commonly used in many
research institutes in Korea to measure clay
minerals in soil samples taken from areas wherelandslides took place, and analyzed the applicablepossibility to ASTER satellite images.
2.

spectroscopic properties of ASTER imagery.
3.

Results and Discussion

3.1 Mineralogy and Chemical Analysis of Soil
Based on XRD quantitative analysis of soils
from landslide areas, all areas (18 sites) show
abundant clay content exceeding 50 %, all of which
are composed of kaolinite and illite. YI 07, YI 08,
and YI 13 areas contain illite content higher than
60 %. When kaolinite content is included in the
total clay content, their contents are higher than
70 %. Especially YI 13 sample contains 67 % illite
and includes 77.3 % clay content when consideringkaolinite(Figure 1).

Experimental Methods

2.1 Mineral analysis and Spectrophotometer
We analyzed size distribution and mineralogyof soil taken from landslide areas, together with
XRD and XRF analyses. After drying soil samples,
randomly oriented samples for XRD were preparedusing averaged samples with 0.075 mm sieving.
XRD analysis, using Rigaku (made in Japan)
Ultima IV, was performed with CuKα radiation at
60 rpm of the XRD sample holder in order toimprove the reproducibility and to minimize theerror of probe distribution which allows thediffraction intensity with respect to sample
orientation to be homogeneous. XRF analysis,using Rigaku ZSX Primus Ⅱ, was carried out onsamples with irradiation at 20 mm in diameter, Rh
target, 50 kV and 50 mA for 20 minutes. As aspectrometer, GER-3700 spectroradiometer that canmeasure a range of 323∼2,526 nm was used forsoil analysis in the field, with consideration ofsample preparation, methods and conditions toobtain an objective and qualified spectroscopic
reflectance.

3.2 Units
Use SI unit or SI derived units.
3.3 Mathematics
Extreme care should be taken in preparing
mathematical typescripts. All mathematics shouldbe legible, precise and carefully aligned. Thefollowing shows an example of putting an equationin the text:

2.2 ASTER Imagery Data
ASTER, one of the NASA satellite systems,
was launched in 1999 for the purpose of obtaining
multi-spectroscopic satellite data.
ASTER
satellite images provide a total of 15 bands
information including VNIR, SWIR, and TIR: eachhas 15 m, 30 m, 90 m volumetric resolution,respectively (Fujisada, 1995). The scanning area ofASTER imagery covers 60 km × 60 km, commonlyused for investigation of mineral resources on alarge scale. Especially, SWIR(Shot Wave InfraRed) of the 1.6∼2.43 μm region has 6 bands
segmented, so it has the merit to extract mineral
resources and to differentiate absorption bands ofclay minerals.
This study aimed at analyzing landslide using
information band, based on spectroscopic
properties of clay minerals related to theY=A+BX(1)

Where Y and X are the output and input variables,respectively; A and B are constants.
Fig. 1 XRD anslysis of samples YI 07, 08, and13 collected from the landslide sites
The spectroscopic reflectance of illite, one ofclay minerals in soils from the landslide shows
absorption of Fe2+ and Fe3+occurring at 0.9 and 1.0µm wavelength, with strong absorption due to OH
and H2O at 1.4 and 1.9 µm wavelength. In addition,2

10th Asian Regional Conference of IAEG (2015)

there are absorption related to Al-hydroxyl at 2.2,
2.3 and 2.4 µm wavelength(Figure 2).
4.

ASTER imagery has potential for protecting andpreventing landslide. In addition, it is expected that
more reliable database will be established if
intensive
comparison
andcomprehensive
examination are verified using the illite content insoils from areas where no landslide takes place,with application of SWIRIllite model.

Figures, Photographs and Tables

Fig. 3 False color composite image on a
topographic map using band 6, band 7, andSWIRIllite
4.

Conclusions

In this study, we confirm the application of
ASTER imagery, multi-spectroscopic satellite
images taken in April, 2004, to the landslides
around Cheoin-gu, Yongin city, Gyeonggi
Province.
The spectroscopic reflectance of illite, one of clay
minerals in soils from the landslide shows
absorption of Fe2+ and Fe3+occurring at 0.9 and1.0 µm wavelength, with strong absorption due to
OH and H2O at 1.4 and 1.9 µm wavelength. In
addition, there are absorption related toAl-hydroxyl at 2.2, 2.3 and 2.4 µm wavelength. It isevident that different absorption and reflectanceproperties are clearly observed depending on
specific soil compositions.
ASTER spectroradiometic results similarly
correspond to the distribution properties of
expandable minerals which were obtained fromfield investigation and mineral analyses. It is
expected that more reliable database will beestablished if GIS spatial analysis and statisticalanalyses are combined using the clay content insoils from areas where no landslide takes place,with application of ASTER satellite imagery.

Fig. 2 Reflectance spectra of YI 07, 08, and 13
soil sampled from the landslide locations
3.2 ASTER applicability
After applying SWIRIllite model using ASTER
images taken in 17, April, 2004, the images weresynthesized using R/G/B(band 6/band 7/SWIRIllite)(Figure 3). Areas with blue series and bluishgreen series correspond to the areas enriched inillite content. According to comparison of areas
where landslides took place in July, 2011 andASTER images applied to SWIRIllite model, it isapparent that most landslides took place on theillite-rich areas on valley, except for areas withslope angles of below 10°, higher than 40°, wide
contour areas, alluvium areas expressed in yellow,and highlands where blue series is wide and dense.
Therefore we believe that spectral sensing using

Acknowledgements
This research was supported by Basic Science
Research Program through the National Research
Foundation of Korea(NRF) Funded by the Ministry310th Asian Regional Conference of IAEG (2015)

ofEducation,Science(2012R1A1A4A01014940)

andTechnology

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