Failure assessment of dysfunctional flexible pavement drainage facility using fuzzy analytical hierarchical process

Drainage system is an important facility in the road which aids the road pavement to withstand and absorb storm water and environmental stresses. When it is inadequate, the roadway suffers premature failure due to increase in moisture content of the pavement materials. For technical emphasis of the hazardous effects of dysfunctional drainage facilities on road, a case study of a failed highway, connecting Anambra state and Imo state Nigeria, was investigated. Site observation, samples collections and experimental methods were carried out in this study with the aim of investigating the drainage challenges which resulted to the failure. Soil classification and determination of the general subgrade soil properties were carried out through experimental methods. The soil was classified as A-6 by AASHTO with 32% liquid limit, 17% plastic limit, 15% plasticity index, 18% of OMC, 1.97 g/m(3) of MDD, SG of 2.6 and 20% CBR-value which indicated high swelling potentials unsuitable for road construction. The asphalt concrete properties results showed averaged stability, BCT, flow, voids in total mix and voids filled results of 4.5%, 3200 N, 1.88 mm, 12% and 55% respectively, which failed to meet the FMW specifications. The road drainage facility which was observed as the primary cause of the deterioration was systematically assessed using FAHP and AHP multi-criteria technique in decision making to ascertain the cause of inefficient pavement drainage facility leading to rapid road failure. Through experimental results obtained and relevant literatures, ranking values were properly assigned to generate the PwCM used for determination of the criteria weights. The computed priority vector showed a result of 4.52% for slope stability problems, 57.28% for inadequate drainage/culvert capacity, 11.68% for drainage discontinuity and 26.52% for material related problems. The generated results were validated using student's t test statistical analysis at 95% confidence level to obtain P(T<=t) two-tail, Pearson correlation and t Critical value of 0.99992, 0.99983 and 3.182, respectively, which indicates that no significant difference exist between the two results. Topography study, rainfall intensity evaluation and re-designing of the highway drainage system were recommended with reconstruction of the failed road using standard materials.