EL PASO MOISTURE BARRIER STUDY. FINAL REPORT

Moisture barriers were installed in 1985 and monitored on the eastbound and westbound lanes of IH10 near Sierra Blanca in Hudspeth County in District 24, the El Paso District. The site was overlaid by a layer of silty sand interbedded with a sandy clay, beneath which were strata of sand and gravel, brown plastic clay, and bentonitic clay. It was hoped that the moisture barrier would retard or reduce the movements of the expansive subgrade and the resulting pavement roughness. Pavement profiles in each wheelpath were measured with the profilometer and suctions were measured both inside and outside the moisture barriers from 1987 on to the present. Both are analyzed to determine the effectiveness of the moisture barriers when compared with pavement sections without them. The fact that water could enter the clay layers through the sandy and gravelly layers, and that water was readily supplied by the sodded median strip made it difficult for the moisture barrier to function as intended. Nevertheless, it reduced the level of roughness in the inside lanes by as much as twice that of the unprotected sections. The experience has shown the importance of conducting a thorough site investigation prior to installing a moisture barrier and of carrying it to a depth equal to the greatest depth where root fibers are found.