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This project for the Minneapolis/St. Paul International Airport required 100 years longevity.

Click on image to enlarge blueprint.
It’s as if this basement is full of water.

It seems impossible, but it’s true. The below-grade floors are inundated with moisture nearly every time it rains. And with it come the damage, mold, air quality issues and all the costs and headaches associated with cleaning it up.

The problem isn’t the fact that it rains. The problem is that the building isn’t watertight. A small detail? No way. Just ask the owner.

Inspec has a group of architects and engineers who specialize in below-grade waterproofing and drainage systems. Our staff includes a Registered Waterproofing Consultant. Whether working with the building owner directly, or as a consultant to the architect on new projects, we dive in and deliver long-term solutions to your water infiltration problems.

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Case Study

The Green Concourse expansion was a half-million square foot, multi-level structure located at the Minneapolis/St. Paul International Airport. In the spring of 2000, a local architect hired Inspec to design the below-ground waterproofing and subsurface water management systems for all below-ground occupied space, utility tunnels, and foundation walls.

The challenging aspects were:

  • It was predicted that large volumes of ground water would enter the excavation site from below and through the rock face.
  • Waterproofing longevity had to be 100 years.
  • The ground water was contaminated with hydrocarbons and ethylene glycol, both of which will chemically “melt” most waterproofing materials.
  • Given the required longevity, it was critical that the installed system be tested before backfilling; however, conventional flood testing methods were not possible for the below-floor waterproofing or the walls.

Inspec’s design solution was an innovative de-watering system that removed water forced up from below, as well as out of the rock face. This water management system was comprised of a 12" bed of aggregate, filter fabric, and perforated drainage pipes at eight-foot centers. For reasons of longevity, a composite waterproofing system was specified comprised of a thermoplastic membrane and bentonite for its low permeability and inorganic nature, respectively. The unique polyolefin alloy thermoplastic sheet, which had never been installed in the U.S. before, was specified as the primary waterproofing because it is compatible with the damaging hydrocarbons and ethylene glycol contaminates in the ground water. In order to test the wall waterproofing for a watertight seal, a special “pocket” seaming technique was used that permitted the seams to be pressurized to test for leakage.

Obviously, it is premature to say for certain whether this design will remain watertight for 100 years. However, all indications are the owner’s needs have been met by responding to the demands of this particular site with the appropriate systems and materials.

Grand Award – American Council of Engineering Companies

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