Abstract:
Recently, landslide has occurred in Werie – Maykinatal road section of the Mekelle - Abi
Adi - Adwa road project in Tigray Regional State, northern Ethiopia. This study aimed at
investigating the geotechnical characteristics of type soil/rock, evaluating the stability
condition of the slopes, and provision of recommendations on remedial measures in
order to address the landslide problems. The approached/ methods used include: field
work, laboratory tests and slope stability analysis. The field investigation involved
description of soils/rock, inventory and detailed characterizations of the landslide
affected sites (slope angle, dimensions of failed slopes, and any signs of instabilities) as
well as sampling of soils for laboratory analysis. For the present study, based on the field
manifestation of instability two most critical slope sections were identified for detailed
slope stability analysis. ASTM (American Society Test Material standard) method was
used to determine the properties of the soils in the laboratory. Tests carried out include:
grain size, Atterberg limit, natural moisture content, shear strength and specific gravity.
A total of six samples representing from two most critical slope sections in Werie –
Maykinatal road were studied, with a view of determining their sliding potential. The
results of geotechnical analysis revealed that the soils contain 1.62-1.97 % clay and silt,
43.56-65.37 % sand and 31.28-54.16 % gravel. Based on the unified soil classification
system, the soil samples were classified as well-graded gravel and Poorly-graded gravel
with clay and sand with group symbols of GW and GP-GC respectively. Results of the
direct shear tests revealed that the cohesion and angle of internal friction varies between
25.3-73.65 kPa and 17.16-27.93 degrees respectively. The stability of the slopes were
analyzed using Geo studio Slope/W software and result show that the factor of safety
(FOS) values from site1 and site2 are 1.203 and1.372 respectively. This show the slopes
are marginally stable and are being affected by slope instability. A modified slope angle
(gentle slope) is recommended with a FOS value of 1.683 and 1.793 forsite1 and site2
respectively. The factor of safety (FOS) for modified slope angle was higher when
compared to the FOS values from natural slope due to the effect of steep slope on the
natural slope. In order to mitigate the problems provision of gabion retaining walls
integrated with drainages are recommended. Moreover, surface water drainages (road
surface and side ditches) are suggested. Benching of the upslope can also minimize the
slope instability of the road sections.
