GEOTECHNICAL ASSESSMENT OF THE NEMBE - BRASS ROAD, BAYELSA STATE, NIGERIA

Abstract

The Nembe - Brass Road is both significant and important for the development of Nigeria. Although the road has been in successive development plans, it had never been implemented for over 50years. This paper provides a geotechnical assessment of the subsoil along the proposed alignment, contributing data and evaluating the conditions and challenges likely to be encountered. The road which spans 48km, is underlain by very soft and weak clay with moisture content between 50-200%, largely unconsolidated with undrained strength (2-14kPu), liquidity indices that suggest semi-solid soil state and plasticity indicative of diverse origins. Bearing pressures are very low in large segments of the road (in over 70% of the length) with settlement up to 5m some areas. Ground improvement involving placement of fill or direct excavation/replacement considered in are unviable in segments with clay thickness greater that 7.5m and settlement larger than 2.5m because of serious adverse ecological and socio-economic effects. This meant that a combination of ground improvement and piling can be implemented to minimise cost. Piling option is largely preferred in the 20-30km chainnage, characterised by thick clay sequences and river crossings, in spite of its high cost, due to long-term stability and minimal adverse eco-hydrological effects.