Development of technology for the construction of low-cost road embankments

  • Gift Obuzor

    Student thesis: Doctoral Thesis


    It is envisaged that flood plains will be put into more active usage to meet the increasing demands for road infrastructural development as well as relieve the pressure exerted on arable lands owing to infrastructural development activities. This is consequent upon the general shortfall in the availability of soils possessing the right engineering properties to carry infrastructures such as roads which consume large tracks of land. Expanding the global infrastructural base is inevitable due to the ever increasing human population and the need to meet their social, economic, political and transportation needs. However, owing to the prevailing environmental awareness campaigns fronted by different environmental agencies, there is the need to regulate and monitor the interaction of the processes involved in the provision of these needs with the limited resources as well as the environmental aftermath associated with such operations. The stabilization of flood plain soils for road embankment construction is envisaged to reduce the demand on the material resources required to build classical high embankments in flood prone areas as well as offer implied mitigating dimensions in the restoration of environmental integrity. This impliedly will reduce the use of traditionally unsustainable methods of soil stabilization such as, the excavation and importation of new materials, to a more robust system that will offer environmental friendliness amidst value engineering for better strength and durability results.

    The experimental processes involved the simulation of flooding scenarios in the laboratory, to monitor the strength and durability aspects of low-bearing-capacity soils (such as Lower Oxford Clay) stabilized with blended mixes of the traditional stabilizer of lime and the novel materials of lime and Ground Granulated Blastfumace Slag (GOBS) by-product combined. Preliminary investigations were carried out on the Lower Oxford Clay soil to establish the moisture and compaction requirements of the material. Different mix compositions were formulated by incrementally replacing the amount of lime in the system with GOBS. This was based on the premise that high stabilizer contents could offer better stabilization to flood susceptible geo-materials upon flooding. A high stabilizer level of 16% was therefore investigated. Regimes of different blending ratios were established as follows: 16%Lime-0%GGBS, 12%Lime-4%GGBS, 8%Lime-8%GGBS, 4%Lime-12%GGBS and 0%Lime-16%GGBS and tested at moisture contents of 23%, 28%, 33% and 38%. The two extremes 16%Lime-0%GGBS and 0%Lime-16GGBS were used as controls.

    A system of elimination based on strength criteria was employed, where only the 8%Lime- 8%GGBS and 4%Lime-12%GGBS mixtures were deemed fit to be investigated further to determine their resistance to challenging environmental factors of flooding. The test samples were cylindrical, measuring 50 mm in diameter and 100 mm long, and these were compacted using a static compaction apparatus to achieve Maximum Dry Density (MDD). Depending on the testing regime to be applied to a given specimen, a curing pattern was defined and samples were wrapped in cling film to minimise moisture losses. At the end of each curing period of 7, 14, 28, 56 and 90 days, one of the experimental procedures which ranged from Unconfined Compressive Strength, Water Absorption, Volume Stability, Permeability, Soaked Strength and Durability Index Assessment or Compressibility Assessment was carried out on the moist cured samples. Following these assessments, the 4%Lime-12%GGBS mix composition was appraised to have overall improved characteristics with the added benefit of reduced cost of material utilisation.

    Based on the available data, regression analyses were carried out and equations established for predicting the strength values of stabilized materials. Using these equations further extrapolations were made and the observable trends were those of the dependence of compressive strength on the age of moist curing and the compaction moisture contents at which samples were produced at given blended mixture.

    Cost-benefit-risk analysis was also carried out with a further cost annualisation of the capital and operational cost of a selected system. It is reassuring to learn that at replacement level of lime with GOBS of 4%Lime-12%GGBS it was possible to establish multi-binder mixtures that could be effectively used for sustainable construction in flood prone areas with enormous savings accruing from the possible higher strength and enhanced durability indices achievable over traditional unsustainable options of continued over-reliance on lime and Portland cement.
    Date of AwardAug 2011
    Original languageEnglish
    SupervisorRoderick Robinson (Supervisor)


    • Roads
    • Embankments
    • Design and construction
    • Road drainage

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