The city of Redmond, Washington needed to improve the stormwater holding system within the Overlake Village area. To accomplish this, they contracted GBI to build a massive underground concrete detention vault in the location of an existing Sears parking lot.
GBI removed all surface improvements to begin digging a 75,000 cubic yard hole for the new detention vault. Because of its immense size, we installed a temporary shoring system consisting of drilled H-beam soil nails with a shotcrete facing. Because of ground water, we installed a well point system that dewatered the bottom 20 foot of the hole. GBI also installed an underdrain system, allowing us to begin construction. The concrete vault construction took over six months to complete. After the vault was complete, GBI backfilled the top and constructed a new parking lot to replace the previous one.
The project was completed on time and under budget. The vault is the largest of three stormwater vaults built in the area. It can hold up to 6.5 million gallons of water — about 10 Olympic-sized swimming pools .