Developing a Comprehensive Road Design Model for Mitigating Pothole Formation in Newly Constructed Flexible Pavements: A Case Study of Machakos-Kangundo Road, Kenya

Abstract

Premature pothole formation in flexible pavements remains a major challenge in road infrastructure management, leading to increased maintenance costs, reduced pavement service life, and compromised road safety. Although existing mechanistic-empirical pavement design approaches consider traffic loading and structural response, they often treat environmental conditions, material characteristics, and construction quality independently, limiting their ability to predict localized pothole development in tropical environments. This study developed an integrated model for enhancing road design against pothole formation using the Machakos-Kangundo Road in Kenya as a case study. A mixed-methods case study design was adopted, combining field investigations, laboratory testing, traffic surveys, pavement condition assessment, and spatial analysis. The 38 km road corridor was divided into 20 m chainages to determine pothole frequency and distribution. Laboratory tests included Atterberg limits, California Bearing Ratio (CBR), compaction characteristics, and asphalt core density, while traffic loading was evaluated using Equivalent Standard Axle Loads (ESALs). Environmental data comprising rainfall and temperature records were integrated with construction quality and pavement performance indicators to evaluate their influence on pothole development. The results showed that potholes were concentrated between chainages 18 + 000 and 24 + 000 km, corresponding to sections characterized by poor drainage, weak clayey subgrades, inadequate compaction, and high heavy-vehicle loading. Soaked CBR values ranged from 5.2% to 13.8%, while high plasticity indices and low compaction levels were strongly associated with increased pavement distress. Traffic projections classified the corridor as Traffic Class T3 with cumulative loading between 4.65 and 5.73 million ESALs over a 15-year design period. Based on these findings, an integrated pothole susceptibility model incorporating traffic loading, environmental conditions, material properties, pavement performance indicators, and construction quality was developed. The model provides a practical framework for improving pavement design, optimizing maintenance strategies, and reducing premature pothole formation in tropical environments.