Abstract:
Nowadays, monitoring seepage, slope stability and deformations is the primary and
most important reason to ascertain the overall safety of earthen dams. This research
study was conducted, with the objective to evaluate static condition seepage, slope
stability, and stress deformation performances of Grindho earthen dam which is found in
eastern Tigray, Northern part of Ethiopia and to come up with possible helpful remedial
measures for the identified safety incidents. The AutoCAD product Geostudio-2007
software was employed to analyse the seepage using SEEP/W, slope stability safety
factors using SLOPE/W and stress deformation using SIGMA/W under different cases of
operations. Results of seepage analysis using SEEP/W was utilized as a parental input for
the analysis of SLOPE/W and SIGMA/W models. Additional actual field data
measurements and observatory investigation also carried out. In this study, Seepage
analysis such as leakage flow rate, pore water distribution and location of phreatic line
are determined using the SEEP/W. From the simulated results the average flow rate of
leakage for the entire length of the dam at full reservoir condition is equal to 0.001163
m3
/s whereas the actually measured quantity of seepage accumulated at downstream toe
of the dam is 0.00647m3/s. The seepage source has been identified using the electrical
conductivity and temperature taken from the reservoir and downstream toe drained water.
Slope stability analysis was performed for the critical slopes using the limit equilibrium
SLOPE/W software based on the Ordinary, Bishop, Janbu, Morgenstern-Price and
Spencer methods safety factors. The stability analysis results indicated that the critical
upstream and downstream slope of the dam are safe within the prescribed USACE and
BDS rang of factors of safety for the possible loading and operation cases. The
result of stress-deformation was analysed using the Finite Element model (SIGMA/W) in
the two cases; during the empty or after end of construction and full reservoir conditions
and the maximum horizontal and vertical displacements are calculated. The resulted
maximum horizontal and vertical settlement for full reservoir conditions is 0.21% and
0.92% of the dam height respectively. According to the (USBR, 2014) standards and
(Hunter and Fell, 2003) recommendation the impervious core material is not safe against
the inside cracking and hydraulic fracturing due to the horizontal displacement and the
dam couldn’t be affected by overtopping problem through the impact of current vertical
settlements. Based on the research findings recommendations and possible remedial
measures that helps to strengthen the safety of the dam are also provided:
