Solution for Existing Foundations built on Weathered Rock-Lateral Restraint with Drilled Micropiles-Video

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An engineering team rehabilitated the 82-year-old Henry Hudson Bridge in Manhattan, replacing severely deteriorated concrete while keeping traffic moving. During excavation beneath the bridge, workers unexpectedly found several feet of highly weathered rock under existing foundations—far weaker and easier to excavate than anticipated. They stopped work and backfilled the area while the team investigated the ground conditions.<br /><br />Rather than underpin foundations that would later be replaced, engineers designed a rigid, internally braced support-of-excavation system to restrain the weathered rock and protect the bridge piers. They assessed potential settlement and its effects on the bridge, then installed monitoring. Recorded settlement was about a quarter inch, safely below the level that could damage the structure. Construction resumed, demolition proceeded, and the bridge remained safe. The unforeseen condition led to extra work and a paid claim.

Keywords

Henry Hudson Bridge

bridge rehabilitation

weathered rock excavation

support-of-excavation system

foundation settlement monitoring

construction claim