IMPACT OF CLIMATE ON ROAD FOUNDATION FAILURE AND ITS IMPLICATION FOR ROAD MANAGEMENT IN NIGERIA
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Date
2021-01
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UNIVERSITY OF ILORIN
Abstract
Road foundation consists of subbase and subgrade layers and is a product of earth materials. It responds to the vagaries of weather and climate. Road foundation failure may vary with climate. This variation has been observed in Nigeria. The study examined the impact of climate on road foundation failure in Nigeria and its implication for road management. The objectives of the study were to: (i) examine the pattern of road subbase and subgrade in each morphoclimatic zone; (ii) examine the relationship between climatic variables and road subbase and subgrade in different morphoclimatic zone; (iii) assess the impact of climate on road subbase and subgrade in each morphoclimatic zone; and (iv) compare the geotechnical properties of road subbase and subgrade in the study area with the Federal Ministry of Works and Housing (FMW&H) standard.
Data for the study were obtained from secondary sources. Available climatic data (rainfall, maximum temperature and minimum temperature) for 36years (1980-2016) were obtained from the Nigerian Metrological Agency (NIMET). Geotechnical properties particle size distribution (PSD), natural moisture content (NMC), liquid limit (LL), plastic limit (PL), plasticity index (P), maximum dry density MDD), optimum moisture content (OMC) and California Bearing Ratio (CBR) were obtained from the Pavement Evaluation Unit, FMW&H, Nigerian Building and Road Research Institute (NBRRI) and Federal Road Maintenance Agency (FERMA). Purposive sampling technique was employed in selecting two road networks from each of the four morphoclimatic zones (namely: hot-dry, temperate-dry, hot-humid and warm-humid zones). From these, a total of 697 Kilometers of road and 516 sample points were selected. Principal component analysis, ANOVA, multiple correlations and multiple linear regressions were used to analyze the data.
The findings of the study were that:
i. significant differences (df = 0.05) exist in the spatial pattern of geotechnical properties in the morphoclimatic zones of Nigeria;
ii. many of the climate and geotechnical properties were strongly correlated with values ranging from
r = 0.64 between rainfall and liquid limit in Brinin Yauri-Malando-Wara road to r = - 0.72 between liquid limit and rainfall in Akwanga-Toto-Abuja road;
iii. rainfall, maximum temperature and minimum temperature weakly predicted foundation failure with R2 of 1.40% in the hot humid zone to 35.2 % in the temperate dry zone;
iv. the tested geotechnical road quality parameters for subbase and subgrade materials fell short of the standard of FMW&H in 95% of the sample points; and
v. the geotechnical properties that determine road failure were PSD, NMC, LL, PL, PI, MDD, OMC, and CBR. The percentages of their explanations to road failure vary from 77.7 to 82.8 percents in the subbase category along Port Harcourt-Elele-Umanelu road and Benin-Agbor-Asaba road respectively, while in the subgrade category it ranges from, 71.4 to 82.8 percents in Akwanga-Abuja and Katchia-Kwoi-Nassarawa road respectively.
The study concluded that the influence of climate on road foundation were less severe but vary according to morphoclimatic zones. The study recommended strict compliance with standard specifications and the use of weighbridges to check excess weight on Nigeria roads.
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CLIMATE, ROAD FOUNDATION, ROAD FOUNDATION FAILURE, ROAD MANAGEMENT, NIGERIA