PASSABILITY CRITERIA FOR UNPAVED ROADS The experience of an operational road engineer guided by research findings PRE
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OUTLINE OF PRESENTATION . Assumed degree of engineering of unpaved roads.Classification of materials as earth or gravelHDM III Design criteria for earth roadsEffects of high wheel loads and high tyre pressuresCriteria to ensure wet weather, passabilityU.S Corps of Engineers criteria for the thi
PASSABILITY CRITERIA FOR UNPAVED ROADS The experience of an ...

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1. PASSABILITY CRITERIA FOR UNPAVED ROADS (The experience of an operational road engineer guided by research findings) PRESENTATION BY MARTIN HMENSA DEPARTMENT OF FEEDER ROADS, GHANA

2. OUTLINE OF PRESENTATION Assumed degree of engineering of unpaved roads. Classification of materials as earth or gravel HDM III Design criteria for earth roads Effects of high wheel loads and high tyre pressures Criteria to ensure wet weather, passability U.S Corps of Engineers criteria for the thickness of gravel surface material Economic analysis of alternative interventions to ensure passability Recommendations

3. ASSUMED DEGREE OF ENGINEERING Road formed with adequate camber and side drains Bridges and culverts provided Low-lying sections raised in waterlogged areas Road is unpaved (no bituminous seal)

4. CLASSIFICATION OF MATERIALS AS EARTH or GRAVEL Earth: = 30% of material passes the 75?m sieve. CBR = 10% (?) Gravel: <30% of material passes the 75?m sieve. CBR >10% (?) CBR > 35% (Ghanaian specification) Materials with 10% < CBR< 35% - Underestimated strength.

5. HDM III DESIGN CRITERIA FOR EARTH ROADS Model developed by Greenstein and Livneh (1981) with data from Thailand and Ecuador C2 = 0.0138 (N 0.175 )(P 0.580 )(Q0.490 ) where C2 = soaked CBR of roadbed soil, in percent N = the number of passages to failure P = equivalent single wheel load, KN Q = tyre inflation pressure, KPa Failure criterion : 75mm rut depth.


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