Design approach for drainage layer in pavement subsurface drainage system considering unsaturated characteristics

Kalore, Shubham A and Babu, Sivakumar GL and Mallick, Rajib B (2019) Design approach for drainage layer in pavement subsurface drainage system considering unsaturated characteristics. In: TRANSPORTATION GEOTECHNICS, 18 . pp. 57-71.

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Abstract

Providing adequate subsurface drainage feature in a pavement system to remove the infiltrated moisture in a minimum time is an important design consideration, which prevents the premature failure of the pavement system, and hence helps in achieving a significantly lower life-cycle cost. Various surface drainage measures are taken to minimize the ingress of moisture into the pavement gradually lose their efficiency with the aging of the pavement. The use of an appropriate open-graded aggregate course as a drainage layer in the pavement is the best way to minimize the time for which the pavement materials are exposed to saturated conditions. The current drainage guidelines have been developed on the basis of moisture flow under saturated condition. A better understanding and estimation of moisture movement in a drainage layer can only be achieved by using seepage analysis that adopts the principles of saturated as well as unsaturated flow conditions. State-of-art of mathematical tools such as finite difference and FEA methods permits a rigorous solution of Richard's equation for saturated and unsaturated moisture flow in a porous medium, the only major drawback is the need for rigorous modeling and computational tool for the simulations and the design of the drainage layer. This paper focuses on the development of an analytical model for estimating the time to drain considering the unsaturated characteristics of pavement base material and calibration of the developed model based on a mechanistic approach which is relatively inexpensive. The applicability of the approach is explained by using the four-standard aggregate gradations recommended by AASHTO for the drainage layer, as well as a dense graded aggregate layer, and the results are compared with those from the FHWA approach and finite element analysis. The study shows that the developed model performs as good as the finite element analysis, which requires rigorous numerical modeling, predicts drainage times that are significantly different from those obtained from the FHWA analysis, and that it is sensitive to key significant design parameters. Hence, the proposed model is recommended for regular use for the design of the drainage layer and for a parametric study of the complete drainage process.

Item Type:	Journal Article
Publication:	TRANSPORTATION GEOTECHNICS
Publisher:	ELSEVIER SCIENCE BV
Additional Information:	Copyright of this article belongs to ELSEVIER SCIENCE BV
Keywords:	Pavement; Subsurface drainage; Time-to-drain; Unsaturated characteristics
Department/Centre:	Division of Mechanical Sciences > Civil Engineering
Date Deposited:	01 Mar 2019 05:32
Last Modified:	01 Mar 2019 05:32
URI:	http://eprints.iisc.ac.in/id/eprint/61869

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