<p><p><h2>Preferred Design Procedure</h2>Empirical evaluation, mechanistic approach, and an accelerated testing procedure are three preferred design procedures for the geosynthetic separation in pavement systems. The empirical evaluation of the geotextile separator includes evaluating subgrade conditions, gradation of the base and subgrade soils, geotextile survivability and opening requirements, filtration requirements, and constructability requirements. This method is described in the FHWA Geosynthetic Design and Construction Guidelines Holtz et al. (2008). The remaining two design procedures are based on a limited number of successful case histories.</p><p>The mechanistic approach includes determining the rut depth measurements to predict the service life of the pavement with a separator. The resilient modulus properties using the non-destructive geophysical methods such as Falling Weight Deflectometer (FWD) tests are obtained by back-analysis. The back-calculated elastic moduli are used to characterize the existing structure and foundation soils needed for design.</p><p>The accelerated testing procedure uses an accelerated load in the experiment. The accelerated load is applied as expected as or higher than that in the field to evaluate the performance of the separation layer which correlates to the long-term field performance.</p><p>The Federal Highway Administration (FHWA) has a design document for this technology. The document is summarized below:</p><p><table class='tablepress' id='tablepress-301'><thead><th><center>Publication Title</th><th><center>Publication
Year
</th><th><center>Publication Number</th><th><center>Available for Download</th></thead><tbody><tr><td >Geosynthetic Design and Construction Guidelines</td><td ><center>2008</td><td ><center>FHWA NHI-07-092 </td><td ><center>No</td></tr></tbody></table></p><p> </p></p>
<p><p><h2> References</h2>AASHTO. (2006). <em>Standard Specifications for Geotextiles - M 288.</em> Standard Specifications for Transportation Materials and Methods of Sampling and Testing, 26<sup>th</sup> Edition, American Association of State Transportation and Highway Officials, Washington, D.C.</p><p>Al-Qadi, I.L. and Appea, A.K. (2003). “Eight-year of field performance of a secondary road incorporating geosynthetics at the subgrade-base interface.” <em>Transportation Research Record </em>No. 1849, 212-220.</p><p>Giroud, J.P. (1981). “Designing with geotextiles.” <em>Journal of Materials and Structures</em>, Vol. 14, No.82, 257-272.</p><p>Guram, D., Marienfield, M., and Hayes, C. (1994). “Evaluation of nonwoven geotextile versus line-treated subgrade in Atoka Country, Oklahoma.” <em>Transportation Research Record</em> No. 1439, Washington, D.C. 7-12.</p><p>Holtz, R.D., Christopher, B.R., and Berg, R.R. (2008). <em>Geosynthetic Design and Construction Guidelines</em>, FHWA Publication No. FHWA HI -07-092, Federal Highway Administration, Washington, DC, 592 p.</p><p>Signore, J.M. and Dempsey, B.J. (2002). “Accelerated testing procedures for evaluating separation layer performance in open graded base courses.” <em>Transportation Research Record</em> No. 1808, 134-143.</p></p>