Thesis Open Access

stability and performance assessment of a slope: a case of Bonga-Felegeselam road project

Aklilu shitu

Thesis supervisor(s)

Eleyas Assefa ( PhD )

This thesis presents the investigation, analysis, design and proposed remedial measures for
two cut slope related instability locations stationed at Station 16+900 to Station 16+980 of
the left hand side (LHS) and Station 35+200 to Station 35+300 both left hand side and right
hand side (LHS) and (RHS) of LOT I: Bonga – Felegeselam Asphalt Road Project located
in Southern part of Ethiopia.
In this thesis work, first slide characterization of the cut slope instability areas which
includes the cut slope location, dimensional variables and engineering classification of the
soil through detailed site investigation and testing was carried out. The residual shear
strength parameters were determined from a Triaxial consolidated undrained (CU) test for
each cut slope instability location using undisturbed samples obtained from four test pits
which are two from station 16+980 that is at 3.5m depth and at 7m depth and for the other
station that is station 35+270 the first sample is taken at 3.5m depth and the next layer at
8.5m depth. Analysis of the slope after the characterization of the cut slide was carried out
by the conventional 2D limit equilibrium stability analysis and finite element analysis using
both deterministic and probabilistic concepts and the analysis reveals the drained condition
with full saturation scenario is the governing for both station and the values obtained are
for the first station that is 16+980 factor of safety is 0.916 with a probability of failure of
66.9% that is obtained using limit equilibrium method and 0.762 using finite element
method. And for the other station the factor of safety obtained are 0.657. Finally, using the
results of the investigation and analysis, combination of control and restraint remedial
measures were proposed and designed at the respective cut slide locations so that the
construction of road at these locations were finalized.
Generally, it was observed that the provision of steep cut slope angles and migration of
moisture from prolonged rainfall duration were the main reasons for the instability of the
cut slopes under this study.

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