Drainage and Separation, Northern, IL

Case Study 

Application	Drainage and Separation	Job owner	Amcol
Location	Northern Illinois	Engineer	Construction Design Group
Product	Mirafi® HP570	Contractor	K & L

THE CHALLENGE

An office building is located in a “natural" office park located in northern Illinois. The parking lot for the office building supports delivery truck traffic. Drainage from the lot had to be treated in bio-swales. Soft soils presented part of the problem. The lot was planned on a slope, where each sub-area had approximately one foot of fall from the adjacent areas.

THE DESIGN

A strong, woven geotextile was required that would allow for both drainage and filtration. The parking lot base was compacted open graded stone. Mirafi® HP570 was placed with 6” drainage tiles and backfilled with an open-graded crushed stone. The tiles were terminated into the bio swale to intercept water before dropping to the lower “terrace.”

THE CONSTRUCTION

The parking lot was installed in early Spring in 2008. Landscaping is on-going (finished project photos taken 11/10/2008). A base course layer of 3/4"-1" open graded stone was placed over Mirafi® HP570. Mirafi® HP570 was overlapped 18" to maintain separation beneath the stone during construction.

THE PERFORMANCE

The parking lot has been completed and put into use. Traffic loading has included commuter vehicles, as well as construction traffic working on the commercial buildings on site. Long term, the lot will be open to commuter traffic and delivery vehicles. Drainage has been achieved, as well as maintaining LEED requirements for the parking lot. The engineer selected Mirafi® HP570 for several reasons. Using a high strength geotextile was necessary to reduce differential settlement in areas where pockets of soft soils were encountered and to carry the heavier construction loads. The drainage characteristics of Mirafi® HP570 allowed for the free movement of water from the base course out to the drainage swales. Finally, the separation provided by the geotextile will allow the open graded aggregate to remain free of contamination of the softer sub-soils and continue to drain, as designed. Though the parking lot has only recently been put into use, all indications are that it should function as designed for many years to come.