Pavement Distress Evaluation along Steep-to-Rolling Highway Sections:

A Case Study of Mau Summit-Timboroa

Abstract

This study evaluates pavement distresses along the 39-km Mau Summit-Timboroa section of Kenya’s A8 highway in steep-to-rolling terrain to enhance infrastructure durability and safety. Objectives include assessing distress types, analysing contributions of traffic loading, speed, material properties, and road gradient to deterioration, and identifying cost-effective pavement designs. Using ASTM D6433 and Kenyan Road Design Manual standards, field surveys, laboratory testing, and layered elastic analysis identified fatigue cracking, rutting, and potholes, yielding a Pavement Condition Index (PCI = 73, Satisfactory). Traffic loading (37.5 million ESALs, 18,581 ESALs/day in 2024), low vehicle speeds (19–23 km/h), weak asphalt concrete (AC, LHS: [τ]₁ = 0.595–0.946 MPa; RHS: [τ]₁ = 0.911–1.561 MPa), dense bituminous macadam (DBM, LHS: [τ]₂ = 0.363–0.665 MPa; RHS: [τ]₂ = 0.511–0.893 MPa), and steep gradients (4.5–9.7%) drive severe left-hand side (LHS) rutting (27.66–38.04 mm) and moderate right-hand side (RHS) rutting (2.17–9.94 mm). High shear stresses (LHS AC: 0.439–0.480 MPa) and temperatures (40°C) exacerbate distress. The stable graded crushed stone (GCS) subbase ([τ]₃ = 0.284–0.55 MPa) contributes minimally. A cost-benefit analysis recommends rigid pavements for high-traffic, steep sections (e.g., Timboroa, 9.7%), polymer-modified asphalt, increased layer thicknesses (AC ≥ 65 mm, DBM ≥ 200 mm), and drainage improvements. Applicable to global highways like Ethiopia’s Rift Valley, these findings optimize maintenance, safety, and durability.