To monitor land deformation in detail, we ran a largescale
field test in which an artificial landslide was induced by the
application of a load to a natural slope. The measured landslide
displacement was reproduced numerically through the use of
finite element model analysis with a two-dimensional elastoviscoplastic
model. The analysis suggested that the strength of the
sliding surface decreased as the landslide mass moved. We
propose a simple method for estimating safety factors. The
method involves back-calculation of shear strength parameters
through reproduction of observed landslide displacements and
calculating the ratio of driving force to resisting force acting on
the sliding surface as modeled by joint elements. This ratio, the
“stability index”, shows the same trend as safety factors calculated
by a two-dimensional limit equilibrium method and a shear
strength reduction method that use back-calculated shear
strength parameters estimated from the limit equilibrium state.
The results indicate that the stability index may be applicable to
the assessment of slope stability.