Subgrade Stabilization, Ankeny, IA

Case Study 

Application	Subgrade Stabilization	Job owner	Ankeny Centennial High School
Location	Ankeny, IA	Engineer	Terracon- Des Moines, IA
Product	Mirafi®  RS580i	Contractor	Stahl Construction
		Date of Installation (m/y)	June 2011

THE CHALLENGE

Ankeny Community School District is building a new high school in Ankeny, a northern suburb of Des Moines, Iowa. Stahl Construction Company has been contracted to build the new 50 million dollar high school campus. The new school, Ankeny Centennial High School, is being constructed over an existing soft subgrade. Flat bed tractor trailers with 20 ton payloads delivering wall panels used to construct the building, along with loaded dump trucks, access the jobsite daily.

THE DESIGN

Due to the extremely soft subgrade, an aggregate access road was required for the heavy trucks to gain access to the site. The initial design of the access road included an extruded geogrid placed directly on the subgrade with 6” of aggregate compacted on top of the geogrid. Subgrade pumping occurred due to the heavy truck loading. The geogrid pumped through the aggregate section and severe rutting was experienced. It was determined that separation, filtration and high tensile strength at low strain would be required. The contractor contacted the geotechnical engineer and asked for a new access road design, stating they could not tolerate another failure. Access to the jobsite was critical and could not be interrupted due to rutting.

THE CONSTRUCTION

The geotechnical engineer recommended a new access road design including TenCate Mirafi® RS580i, a high strength woven polypropylene geotextile to be placed on the subgrade. The same 6” aggregate section was compacted on top of the Mirafi® RS580i.

THE PERFORMANCE

Fortunately, the benefits of separation, filtration, hightensile modulus and aggregate confinement achieved by Mirafi® RS580i resulted in remarkably improved performance. Access to the jobsite was no longer delayed as rutting no longer occurred. Construction of the new high school was back on schedule.