Abstrak
Landslide Risk Analysis Subject to Geological Uncertainty a viewpoint from a simplified model
Oleh :
Joni Fitra - S941808010 - Sekolah Pascasarjana
Landslide is the primary driver of the denudational process and sediment source
dominantly onsite. Landslides are one of the most disastrous effects in Taiwan;
groundwater or flood erosion is highly attributed to the landslide. The slope dip angle and
water-induced slope cause increased driving force and decreased resisting force, causing
a slope landslide. This condition generally affects slope stability to the understanding
effect of dip angle attributed to the landslide. In this study, we attempt to consider the
uncertainty of the dip angle in slope stability analysis. The dip angles employed in this
study were based on Highway no. 3 sliding events in Taiwan. Four different measurement
sources, i.e., Central Geological Survey (C.G.S., Taiwan), Compass measurement before
the sliding event, Surface measurement after the event, and LiDAR-derived data, were
employed in this study.
Four methods were employed to analyze attributed dip angle to the landslide, i.e.,
Limit Equilibrium, monte Carlo simulation, Point estimate method (P.E.M), and 3DEC
software simulation. In this research, the Monte Carlo simulation was used to quantify
the effect of the geological uncertainty. Various dip angles (with mean and standard
deviation) were employed to generate 100000 dip angle samples.
The limit equilibrium was used to quantify the safety factor of each measurement dip
angle in the condition of no cohesion, no anchor, and no water pressure effect. The point
estimate method was used to predict the probability of displacement length, displacement
width, and debris volume. The point estimates method also predicts the risk of
displacement length to the building in two scenarios applied. 3DEC software was used to
simulate the simplified model 100m by 100m by 100m were cut off by dip angle of each
measurement and various joint spacing.
Limit equilibrium results show that the LiDAR measurement source provides the
highest safety factor of the slope due to the lowest dip angle. Monte Carlo simulation
results show LiDAR Measurement Source provides the lowest failure probability of
16.9%, and Central Geological Survey (C.G.S., Taiwan) Measurement provides the
highest failure probability of 78%. 3DEC simulation shows the effect of damping factor,
dip angle, and joint spacing on the displacement length, displacement width, debris
volume, and mechanical time of debris to stabilize. The point estimate method (PEM)
shows that the LiDAR measurement source provides the lowest probability of 17% of the
debris reaching the building at a distance of 50 meters and probability 0% of the building
at a distance of 200 meters for all measurement methods.
Finally, the risk might be unacceptable for the building at a distance of 50 meters from
the slope toe because probability has not reached 0% and expense much money. The risk
might be acceptable for the building's minimum distance of 150meters. Further, the
measured dip angles were converted to the projected dip angle based on the plane's strike.
Therefore, based on the engineering design concept, if the design is performed using the
C.G.S. data, the engineering design must be very conservative compared to the design
using the LiDAR data