Evaluation of intermixing application of geotextiles at subgrade-base interface using accelerated pavement testing

Abstract

This study focuses on identifying and quantifying the potential benefits of a geotextile separator in flexible pavements placed at the interface between a granular base and an underlying soft subgrade with high water content and a granular base. While benefits of using separators in roadway applications have been generally acknowledged, quantification of such benefits has been limited. The evaluation in this study is based on the results from two accelerated pavement tests using a one-third scale Model Mobile Load Simulator (MMLS3) device. Both models have identical configuration except that a non-woven geotextile was placed at the interface between the subgrade and base layer to serve as a separator in one of the pavement models. The subgrade material used in this study involved a soil mixture containing fifty percent kaolin and fifty percent Monterey sand #30. The base material was an angular AASHTO #8 aggregate. Additionally, an instrumentation program was implemented involving sensors to track the earth pressure distribution, the subgrade excess pore pressures generation, the change in moisture content of the subgrade and the horizontal particle displacement of the base layer. During exhumation of the pavement models, base and subgrade samples were collected to quantify the levels of intermixing. The results of the APT were quantified in terms of the traffic benefit ratio (TBR), which was as high as 6.4 for 25.4 mm rutting showing the significant benefit of using a non-woven geotextile as a separator to extend the design life of flexible pavements. The differences in performance observed between the control and the separation pavement models were found to correlate well with the amount of intermixing observed at the interface between subgrade and base layers. A series of soil columns were tested using cyclic loading to extend the intermixing analysis to different subgrade types with different fine content and geotextiles. The study concluded that higher levels of fine contain in the subgrade would lead to higher levels of intermixing. A correlation between the pore size of the geotextiles and the pumping of subgrade into the base was identified suggesting that smaller pore size would mitigate the pumping intermixing mechanism more efficiently.