Subgrade Stabilization, St. Louis County, MO

Case Study 

Application	Subgrade Stabilization	Job owner	Missouri DOT
Location	St. Louis County, MO	Engineer	Burns & McDonnell
Product	Mirafi®  H2Ri	Contractor	Walsh Construction
Quantity	7,200/sy	Date of Installation (m/y)	October 2013

THE CHALLENGE

A new bridge was being constructed over the Missouri River where saturated soil conditions required the need to remove water from under the pavement section at the bridge approaches. This was a design build project where the Missouri DOT encouraged the design/build teams to explore new and innovative technologies to solve the challenging site conditions. The geotechnical engineer contacted TenCate Geosynthetics to explore the utilization of the TenCate Mirafi® H2Ri* high strength wicking geosynthetic.

THE DESIGN

The objective of using the product was to remove water from underneath the pavement section. The design build team had originally designed a pavement section that included a concrete section over 4” of road base aggregate, 4” layer of drainable aggregate and a prepared subgrade. The inclusion of Mirafi® H2Ri geosynthetic by the design engineer was intended to replace the 4” of drainable base, thus providing equivalent capabilities within the section while reducing overall costs. The high modulus geosynthetic, which provided excellent confinement and separation, allowed for an overall 2” reduction in aggregate base material along with the ability to wick water from under the pavement. The water was able to exit the Mirafi® H2Ri through a combination of day lighting the material onto roadway shoulders or into french drains.

THE CONSTRUCTION

Initial installation of the geosynthetic took place in October 2013 on the north ramp to the west bound approach. TenCate personnel along with their local distributor, ASP Enterprises, arranged for a pre-construction meeting with the general contractor, MODOT field personnel and the sub contractor installing the material. During the meeting and review of the installation procedures the items that were discussed were proper overlaps, cutting and layering of the material and best installation practices.

THE PERFORMANCE

The initial installation of 7,200 square yards of Mirafi® H2Ri began on a Thursday and was completed along with the placement of 6” of compacted aggregate by the following Monday. The day after the geosynthetic was placed, the project site received ¼” rainfall and wicking was evident where the Mirafi® H2Ri was installed. An additional 82,000 sy of material is expected to be installed in the spring of 2014.