Ethiopia's Bowa Dayole Dam Faces Geological Challenges

In Ethiopia, where food and water are often scarce due to weather and droughts, the Bowa Dayole masonry gravity dam is set to irrigate nearby farmlands. However, the dam's foundation is made up of complex geological formations, including highly fractured and weathered aphanitic basaltic rock, and weak unwelded to welded tuff rock. To tackle these issues, an engineering geological evaluation was conducted. Geologists mapped the site, surveyed discontinuities, drilled cores, tested permeability, and analyzed samples in the lab. They found various lithological units like colluvial and alluvial deposits, aphanitic basaltic rock, and tuff units with different levels of fracturing and weathering. The strength of these rocks, as measured by the Point Load Index Test, ranged from very low to high, at 0. 16 MPa to 146. 88 MPa.

The quality of the rock mass, analyzed using the Rock Quality Designation method, was found to be poor to excellent. Hydraulic conductivity tests showed that excessive leakage isn't expected at the dam site. The allowable bearing capacity of the aphanitic basaltic rock ranged from 0. 54 MPa to 6. 77 MPa at the abutment and 0. 1 MPa to 18. 86 MPa at the foundation. For the tuff rock at the dam's foundation, the allowable load-bearing capacity was much lower, at 0. 037 MPa to 0. 11 MPa. Despite the poor bearing capacity of the tuff rock, uniform settlement can be managed by ensuring even load distribution with the help of the aphanitic basaltic rock and proper foundation construction.

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