Table C1.3.

Comparison of alignment alternatives for a section of new road, Ethiopia

Comparison parameterAlignment option
Option 1Option 2
Cost (US$ million)3.09.1
Length (km)5.45.9
Length ≥9% gradient, but <12% (km)1.270.77
Length at 12% (km)0.411.15
‘Substandard’ horizontal curve radii20 m @ 227+378
20 m @ 227+408
26 m @ 225+750
26 m @ 225+791
Others are ≥29 m
25 m @ 226+261
28 m @ 225+775
25 m @ 225+824
Length of potential slope instability above alignment – cut slope hazard (km)2.351.35 (assumes 50% of box cut alignment across upper terrace encounters slipped/failed taluvium, and that the outline design for box cut side slopes are stable)
Length of potential slope instability below/through alignment – formation hazard (km)0.250.15 (assumes that the only section susceptible to failed/failing ground below the road is in the vicinity of the bend beneath the box cut exit)
Soil cut to fill (×103 m3)57.2199
Rock cut to spoil (×103 m3)108545
Boulders excavation class A to spoil (×103 m3)Assumed small414
Boulders excavation class C to spoil (×103 m3)660
Soft cut to spoil (×103 m3)47490.5
RC retaining wall concrete (×103 m3)0.680
RC retaining wall rebar (tonnes)53.460
Masonry retaining wall (×103 m3)0.420
Foundations for retaining wallsLow–mod bearing capacitiesAccording to the outline design, no walls required
Drainage considerationsNormalNormal plus drainage of 1.4 km of box cut and erosion control structures over fill slope at box cut exit on cliff
Uncertainty of ground conditionsLow–modMod–high