Project · Mercer Island
Stopping a Settling Corner on a Mercer Island Hillside
A daylight-basement house on Mercer Island had a downhill corner that had dropped more than an inch, with cracks running from the basement windows. ECD's engineer traced it to saturated soil from a failed footing drain. The repair used ten helical piers, a new footing drain and tightlined downspouts, completed in three weeks.
What were the symptoms?
The owners noticed a bedroom door that would no longer latch, then diagonal cracks spreading up from two basement window corners. A floor-level survey by our engineer showed the downhill corner of the house about 1.25 inches lower than the uphill side, with the slope concentrated near that corner rather than spread evenly.
What was causing it?
Excavating at the corner showed the original footing drain crushed and filled with silt, and two downspouts discharging onto the ground just above it. Water had been soaking the soil under the footing for years. Because the lot is in a mapped geologic hazard area, the city required a geotechnical engineer's review, which confirmed competent soil several feet below the footing and recommended piers rather than spreading the footing.
How was it repaired?
Ten helical piers were installed along the downhill wall and around the corner, each torqued to a capacity confirmed during installation, then attached to the footing with steel brackets. The corner was lifted partway back toward level, as far as the engineer judged safe without cracking finishes further. A new perforated footing drain was laid in clean gravel, downspouts were tightlined to an approved discharge, and the cracks were sealed by injection.
Scope of work: Mercer Island underpinning
- Engineering evaluation, floor survey and repair design.
- Geotechnical review coordination and Mercer Island permit.
- Ten helical piers with brackets, partial lift.
- Footing drain replacement, downspout tightlines and crack injection.
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