Abstract
Weak lateritic subgrades are more often than not encountered during road construction in Ghana. This makes it necessary to find economically efficient ways to improve the engineering properties of these marginal lateritic soils. The objective of this study is to investigate the effects of coconut fiber (30 mm, 60 mm and 90 mm fiber lengths) and palm fiber on some geotechnical characteristics of a weak lateritic subgrade. The lateritic soil was collected from the KNUST campus and blended with various percentages of the fibers varying between 0.1 and 1.0% by weight of dry soil. The mixed materials were then subjected to various laboratory tests including compaction, unconfined compression test and 4-day-soaked California bearing ratio test. From the results, it was observed that increasing the fiber content decreased the maximum dry density and increased the optimum moisture content. The inclusion of the fiber increased the soaked CBR from 7 to a maximum of 18, 22, and 25 at 30 mm, 60 mm and 90 mm fiber lengths, respectively. The unconfined compressive strength also increased from 140 to a maximum of 353 kPa, 398 kPa and 447 kPa, respectively, for 30 mm, 60 mm and 90 mm fiber lengths. Similarly, palm fiber inclusion recorded maximum soaked CBR value of 14% and UCS value of 352 kPa. These peak values were obtained at optimum fiber contents of 0.2%.
Highlights
Low volume roads play a major role in the socioeconomic development of rural communities
The surface morphology of the fibers obtained from the analysis of the Scanning Electron Microscopy (SEM) images at different fiber conditioning ( ‘as received,’ 14-day soaked, 30-day soaked and 60-day soaked) is shown in Figs. 4 and 5 for coconut and palm fiber, respectively
The 4-day-soaked California bearing ratio (CBR) and unconfined compression test (UCS) of the lateritic soil reinforced with and without coconut and palm fibers were compared to the Ghana Department of Feeder Roads specifications for low volume road
Summary
Low volume roads play a major role in the socioeconomic development of rural communities. The bulk majority are unsurfaced and referred to as ‘gravel roads.’ These gravel roads consist of subgrade with up to about 150 mm subbase layer thickness. Lateritic soils are the most abundant naturally occurring materials used for the construction of both the subgrade and subbase layers Most of these lateritic soils usually have high fines content [15], making them unsuitable for road construction. When such materials are encountered along a road alignment during construction and are not well treated, they develop into ‘soft spot’ section leading to premature failure of the road before their designed life. The other way is to use Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
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