Assessment of Causes for Partial settlement of Gidabo Dam, Southern Ethiopia
No Thumbnail Available
Date
2017-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa Universty
Abstract
The present study was carried out at Gidabo Dam, which is proposed on Gidabo River in
Oromia Regional State, about 375 km from Addis Ababa, the capital city of Ethiopia. Gidabo
Dam has faced settlement at the conduit outlet foundation during the construction time which
was measured to be about 0.4 m. The main objectives of this study were to assess the possible
causes of partial settlement and to estimate the amount of potential future settlement of the
dam. The general methodology followed for the present study was based on thorough
literature review, field investigations and data collection, analysis and evaluation of various
soil parameters of settlement. For the present study immediate and primary settlement
analysis was carried out. Elastic theory for cohesive soils, Janbu’s approach and one
dimensional settlement analysis were applied to estimate the settlement amount of the upper
part of backfill foundation unit and compressible silty clay layer of the dam foundation. For
the granular soil foundation at the bottom immediate settlement was estimated from in-situ
standard penetration test (SPT) results.
The present study results showed excessive settlement. The estimated settlement is more than
the expected settlement as anticipated in the design of the dam. The differential settlement is
also expected at the contact of the backfill material, at outlet conduit and in between the
intake tower and the outlet conduit. As investigated in the present study, the primary causes
of the settlement are related to unsuitable backfill material comprising alluvium backfill and
clay cutoff, compressible silty clay layer (organic) below the excavation and due to inappropriate
excavation method (dewatering process) followed during the construction stage.
Besides, granular type of soil in the foundation has also contributed for the settlement of the
dam in general, and of conduit section in particular. The study also showed that this
settlement also continue in future. Therefore, it is strongly recommended to adopt appropriate
measures, as suggested through the present study, so that possible safety and stability of the
dam can be ensured during the performance stage.
Key words: Gidabo dam; Settlement analysis; Janbu Settlement analysis; Consolidation
Description
Keywords
Gidabo dam, Settlement analysis, Janbu Settlement analysis, Consolidation