Abstract:
Rapid urban development often requires cutting natural slopes, which can cause
deformation and reduce slope stability. The main part of this study focuses on the the
deformation and stability of cut slopes using Liquid Equilibrium Methods and Finite
Element Methods which is achieved by conducting different types of field and laboratory
tests.
The objectives of this research were conceived to study in detail the cut-slopes stability
condition of Morka Gircha Chencha road project. It was realized that detailed slope
stability studies along this road section are very necessary to identify critical slope
geometry and to provide the best preventive measures to minimize the slope instability
problems.
For the present study, a total of 48 analyses were carried out for six cut slopes with four
slope angles; i.e. (1H: 1V), (1.5H: 1V), (2H: 1V), and (2.5H: 1V) before and after water
saturation for each cut slope. The factor of safeties and slope deformation for the selected
slope sections was determined for the different slope geometries and in the presence of
water (saturated condition) using SLOPE/W, and PLAXIS-2D software.
The comparison of the Liquid Equilibrium Methods shows that the Spencer, Bishop, and
Morgenstern-Price Methods yield in most cases identical Factor of Safety (FOS). for
circular slip surfaces. However, the Ordinary and Janbu methods underestimate the Factor
of Safety (FOS). All Liquid Equilibrium Methods, except the Ordinary and Janbu
Methods, estimate higher Factor of Safety than Finite Element analysis in PLAXIS-2D.
Generally, it was observed from both PLAXIS-2D and SLOPE/W models that the
provision of steep cut slope angles, the presence of a high proportion of fine soils, and
migration of moisture from prolonged rainfall duration were the main reasons for the
instability of the cut slopes under this study. Based on the results obtained from both
PLAXIS-2D and SLOPE/W models, it can be concluded that flattening the slope angle
from (1H: 1V) to 2.5H: 1V and above with lowering of the water table would be one of
the techniques to stabilize the slope.
