Davenport Transload Facility

Summary

Kaskaskia Engineering Group, LLC (KEG) performed a geotechnical study for a proposed transload facility in Scott County, Iowa.  While the proposed structures are relatively lightly loaded, there will be significant live loads associated with the freight that will be handled and the equipment used to move the freight around the site.

Project

The field exploration consisted of 29 initial borings and 10 supplemental borings, all advanced to depths of 10- to 50 feet.  The borings and subsequent laboratory tests were used to document the subsurface conditions; the influence of groundwater on construction; identify unsuitable soils; assess the volume change characteristics of the subgrade soils; evaluate bearing capacity for the proposed structures; and provide California Bearing Ratio (CBR) values for the proposed access road, parking lot, and railroad spurs.  A pavement design was subsequently performed for the truck access road and parking lot.

Of primary concern was a layer of organic soil, approximately 5 feet thick, which was encountered in 14 of the borings.  Approximately 2-inches of settlement was calculated from the organic layer.  To limit post-construction settlement of the structures, various options were provided, including removal and replacement of the organic layer, dry soil mixing elements extending through the organic layer, Geopier elements extending through the organic layer,  drilled piers extending through the organic layer, surcharging of the site, soil reinforcement by utilizing geogrids or lime stabilization, and reinforcement of the structures themselves.  Rough cost estimates were provided for the various options.

Surcharging of the site was ultimately decided in consideration of the relative risks and costs associated with the various options.  With surcharging, shallow foundations could be utilized along with slab-on-grade floors.