Rainfall intensity effects on pavement base layers in Basrah City

Lamia A. Ahmed, Ahmed M. H. Al-Alkadhimi and Wisam A. Najim

Advancement in Science and Technology Research
Published: December 15 2015
Volume 2, Issue 4
Pages 67-76

Abstract

The main objective of this work is to study the effect of rainfall intensity on pavements layers thickness of two types of pavement structure, that is, flexible and rigid pavement. This is done by using Maple 13 software for modeling of this problem and calculation of the rainfall intensity and pavement infiltration. It was found that pavement infiltration increases with increasing rainfall intensity because increase in rainfall intensity caused an increase in the infiltrated water to the base and sub-base layers. Accordingly an increase in pore water pressure resulted which in turn causes an increase in porosity and decrease of base and sub-base degree of compaction. This leads to increase in time-to-drain, decrease in drainage coefficient for base and sub-base, and subsequently increase in their thickness. For flexible pavement, rainfall intensity 256 mm/h gives pavement infiltration, thickness and drainage coefficient of 3.2 m/day, 46 cm, 0.57 respectively, while rainfall intensity 25 mm/h gives pavement infiltration, thickness and drainage coefficient of 0.4 m/day, 18.5 cm and 1.7, respectively. In rigid pavement, rainfall intensity 256 mm/h gives thickness and drainage coefficient of 24.8 cm and 0.9 respectively, while rainfall intensity 25 mm/h gives thickness and drainage coefficient of 21.3 cm and 1.2, respectively. Drainage of accumulated water on pavement is rapidly drained in as short time as possible due to minimize potential moisture damage to a pavement structure. It was found that water in the pavement system can lead to modulus reduction and loss of strength for pavement. Saturation can reduce the dry modulus of both the asphalt layer (30% or more) and the base and sub-base modulus (50% or more). Similarly, modulus reduction of up to 30% can be expected for asphalt-treated bases, and over 50% for saturated fine-grained sub grade soils. It was found that soil types effects of moisture in pavement have been based on conditions of total saturation with loss of pavement strength which affect the state of stress through suction (effective porosity) or pore water pressure, and affect the structure of the soil through destruction of the cementation between soil particles, because of soil types difference in coefficient of permeability. Soil types used in this study include well-graded sand, uniform dense sand and fine-grain soil.

Keywords: Intensity, pavement, rainfall, drainage, sub base, base.

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