The stockpiles were designed to meet or exceed the required factor of safety of 1.3 for static undrained, 1.1 for slickensided and 1.0 for seismic conditions. The stockpile stability was checked for each year of the construction. The maximum calculated settlement is about 7 feet (2.2 m). Construction The construction was comprised of earthworks to prepare a graded foundation ground surface, placement of a geogrid, with crushed granular material, followed by the installation of the wick drains. The drainage blanket provided a drainage path for water released from the wick drains at the ground surface. It also provided a stable platform for the operation of the wick drain installation equipment. Monitoring instruments were installed to monitor the performance of wick drains during the stockpile operation. Earthworks construction The first step of wick drain construction was the stripping of organics and surficial debris to expose the competent subgrade. Subgrade preparation included cut and fill grading and compaction of the subgrade to develop a uniformly graded ground surface (Figure 2). The earthworks were designed to provide a ground surface that was suitably graded for wick drain installation while at the same time reducing the required amounts of cut and fill. A layer of either geosynthetic geogrid and geotextile composite or reinforced woven geotextile material was placed over the prepared ground, mainly to increase the foundation strength to support the wick drain installation rigs (Figure 3). For this project, due to the high cost of the drainage blanket material, the use of geosynthetic reinforcement was more cost efficient than simply increasing the thickness of the crushed granular drainage blanket. FIGURE 2 Executing the cut and fill grading plan FIGURE 3 Geotextile-geogrid installed over approved subgrade GeosyntheticsMagazine.com 21http://www.GeosyntheticsMagazine.com