EXPANSIVE SOILS COMPLICATE TRUCK TERMINAL SITE

Discovery of montmorillonite, an expansive, clay-like soil, complicated the earthwork balance and foundations for a new truck terminal site. Site grading, which was planned to produce 600,000 cu yd of compacted, in-place fill, actually yielded more than 900,000 cu yd. Design and construction was altered to place the fill in its wet, expanded condition and to seal the embankment surface to retain its moisture. An extensive French drain system was installed to keep additional surface water from seeping into the water-bearing fill. The excavated material was spread in 1 ft lifts to which 14 percent water was added. The wet material was compacted to at least 95 percent standard Proctor. As many as 22 lifts were placed and processed. Five percent lime stabilized the upper 6 in. of the top lift, to seal in the added water and to protect the carefully compacted fill from any additional water from the surface. French drains were constructed in 2-ft-wide by 4- to 7-ft-deep trenches across the fills at 150 ft centers. The trenches were lined with filter fabric and then filled with 1 1/8-in. concrete aggregate. More than 700,000 tons of flexible base was placed at a rate of 15,000 tons per day using a laser-guided grader and trimmed to a 1/8-in.-accuracy by a laser-guided trimmer. This 10-month, $13.3-million contract started in late 1987 and was expected to be completed ahead of schedule in mid-1988.