''Horseshoe'' Secant Compression Shoring System For Tunnel Repair-Video

Video Transcription

Video Summary

A sudden ground subsidence event during construction of a drainage tunnel north of Detroit damaged the tunnel liner and boring machine, requiring a fast-track recovery shaft about 100 feet deep with a 50–55-foot opening. Conventional bracing could not provide sufficient clear space, and an obstruction prevented a complete circular shaft. The team designed a secant-pile horseshoe compression ring, transferring loads through heavily reinforced, two-meter king piles supported by a concrete ring beam and rock embedment. Secant piles extended to about 150 feet, with a diaphragm added at excavation level.<br /><br />Construction used large drilling equipment, sectional casing, polymer, and extensive verticality and overlap checks. A GIS system validated pile overlaps, while custom concrete mixes and careful cage installation addressed placement challenges. The team also designed and monitored a heavy-duty working platform over potentially disturbed ground. Instrumentation showed generally uniform deflection consistent with model predictions. The replacement tunnel boring machine ultimately reached the recovery shaft. The presenters emphasized early contractor involvement and collaboration as key to delivering the urgent solution.

Keywords

ground subsidence

drainage tunnel

secant-pile shaft

horseshoe compression ring

tunnel boring machine recovery

early contractor involvement