HWA GeoSciences developed an innovative testing program that allowed the city of Everett to create an upscale project in the moisture sensitive, clay-ridden glacial till near the Snohomish River.

Photo courtesy of HWA GeoSciences HWA GeoSciences developed a way to treat glacial till soils near the Snohomish River in Everett to accommodate an upscale project.

The developer recommended that the “all-weather working surface” consist of a two-foot-thick layer of imported and compacted gravel borrow across the site. This option would have cost the city an estimated $4.1 million. HWA recommended a lower-cost option instead: cement-treating the soil on site.

The HWA program evaluated the material properties of glacial till soils at low cement-application rates. By balancing cement content, native soil composition, curing times and compaction effort, the firm was able to yield a material with the desired all-weather and excavation characteristics at a low cost while recycling on-site soils.

HWA’s field and laboratory testing provided insight into the material properties of glacial till soils treated at various low-cement application rates and compacted at differing time intervals. The presentation of this data convinced the developer that cement-treating the on-site soil was beneficial to all parties.

The willingness of HWA to use a nonstandard approach ultimately saved the city of Everett more than $3.4 million.