Shear Strength Parameters as a Measure of Slope Stability of an Earthfill Dam: A Case Study of Awba Dam University of Ibadan, Nigeria.

Abstract

Failure of earthfill dams can occur as a result of structural instability conditions, seepage conditions and
hydraulic conditions. Earlier studies have proved that Awbaearthfill dam located in University of Ibadan, Nigeria is suffering
from seepage problem and this prompt to focus on itsslope stability. Soil samples taken were from upstream side as this
dictate what would be happening at the downstream side. Nine samples were collected altogether with three samples each at
upstream left side, upstream middle and upstream right side and subjected to consolidated undrainedtriaxial test. The test
gives the shear strength parameters values viz: cohesion, which ranges betweenbetween 3.3 to 3.8Kpa with an average of
3.4Kpa at the upstream left side, 4.1 to 5.0 Kpa averaging 4.4Kpa at upstream middle and 2.2 to 4.3Kpa with average of
3.5Kpa at the upstream right side. Also, angle of internal friction which varied between 200
to 270 with average of 22.700
for
sample upstream left side, 200
and 260 with average of 230
for sample upstream middle and 240
to 260 with average of 24.700
for sample upstream right side. These were used to measure the level of Awbaearthfill dam slope stability. From the results,
it was found that the cohesion values were not adequate whereas angle of internal friction was within the acceptable limit for
both samples collected.This necessitates prompt attention in order to guide against sudden failure of the dam as result
instability of its slope.