Improved Methods for Filtration, Drainage and Structural Evaluations With and Without Geocomposites for Subsurface Drainage of Pavements

Abstract

Pavements are continuously exposed to the environment leading to ingress of water from multiple sources that structurally weakens the pavement materials. The conventional solution for drainage requires granular material of a minimum thickness of 250 mm, reflecting a massive demand for suitable quality aggregates. The potential alternative to reduce the demand is incorporating a drainage geocomposite in pavements. In this thesis, improved methods for filtration, drainage, and structural evaluations with and without geocomposites are developed. The unbounded granular materials are required to be internally stable to perform self-filtration. This study investigates the practical utility of Cu and Cc in evaluating the internal stability of soils. A theoretical approach for predicting critical hydraulic gradients is developed based on the notion of differential void states of fine fraction of internally unstable soils. Granular and geotextile filters are provided in the subsurface drainage systems to limit soil erosion and allow unimpeded water seepage. In this thesis, improved design criteria are developed for the filter requirements of soil retention, hydraulic conductivity, and clogging. Further, a new approach based on the demand-capacity model is developed for the hydraulic design of granular and granular-cum-geocomposite drainage layers in pavements. Lastly, the influence of the granular filter characteristics and geocomposite on the modulus of the subgrade-subbase interface is investigated based on the Resilient Modulus tests of composite samples. Improvements to current codal provisions and specifications for subsurface drainage of pavements are suggested and illustrated.