Dynamic Simulation of the Reinforced Slope Failure at Chi-Nan University During the 1999 Chi-Chi Earthquake - Reinforced Soil Engineering: Advances in Research and Practice - page 463

the analysis. Time history of the acceleration in the east-west direction is taken
as the seismic input since orientation of the slope is approximately in the
direction of north-south.
Properties of the geological deposits used in the finite-element analysis are
listed in Table 1 . Cohesion of the gravel and backfill, however, are greater than
those discussed previously due to the need to maintain the stability of the slope in
the gravity loading, which is imposed on the slope to generate initial stress
condition in the soil mass. The Mohr-Coulomb constitutive model is used for the
geological deposits. The finite-element mesh generated for the reinforced slope
and its surrounding area in shown in Fig. 7 . The number of nodes, elements, and
stress points are 829, 370, and 1110, respectively. Forty layers of reinforcements
are input in the finite-element mesh to simulate the reinforced slope. The seismic
source is located on the lower boundary of the finite-element mesh. The seismic
force lasts for about 90 sec. The groundwater level is not considered in the
analysis. Animation of the slope subjected to seismic forces can be created when
the calculation is completed. A deformed mesh, however, at four different time
steps is illustrated in Fig. 8 . In addition, principal directions of displacement of
the mesh at different time steps are shown in Fig. 9 . The result shows that
deformation of the whole soil mass takes place as of the commencement of the
earthquake. However, the soil mass above the weak plane starts to move at a
greater scale compared to that below the weak plane at approximately the 36th
second in the record shown in Fig. 5 . The soil mass above the weak plane
continues to move downward along the weak plane. In the meantime, the
reinforced slope also deforms significantly.
Questions may be raised regarding whether the slope failure initially results
from the collapse of the reinforced slope itself or if the weak plane is the primary
factor to blame. Fig. 10 shows a vector of the acceleration developing in the slope
at different time steps during the earthquake. The result shows that the
acceleration at the reinforced slope is much greater than that at other areas. Thus,
it hints that the reinforced slope may collapse earlier than other areas in the slope.
However, the dynamic simulation conducted herein may not clearly give
insightful details about this issue. Nevertheless, failure mechanism of the
reinforced slope are summarized and discussed in next section.
6 FAILURE MECHANISM OF THE REINFORCED SLOPE
INDUCED BY THE CHI-CHI EARTHQUAKE
According to the field investigation, the location of the slip surface in the Chi-Chi
earthquake is close to that which took place in 1995 (Genesis Group/Taiwan,
2000). Thus, the reinforced slope may fail through the backfill during the Chi-Chi
earthquake rather than through the existing gravel stratum, which is undisturbed.