TBM Tunnel Repair Using a Secant “Horseshoe” Compression Shoring System

Below I-75 in Detroit, Michigan, the advancing of a tunnel boring machine (TBM) for the construction of a 16-ft (4.9 m) diameter storage and drainage tunnel experienced sudden subsidence. The TBM was damaged to the extent that its shield, cutting head, and extensive interior components needed to be extracted and replaced along with several completed tunnel segments. Subsequently, the tunneling contractor engaged their designers and specialty subcontractors to develop a resolution to ingress the TBM to repair the tunnel liner and critical components on the TBM. The tunneling contractor needed the repair shaft to have a depth of 99 ft (30.2 m), with an unobstructed plan dimension of 50 ft (15.2 m) to accommodate the large components that needed to be removed and replaced, effectively eliminating the use of an internally braced excavation solutions. A unique compression ring was analyzed, although, with the existing tunnel liner obstructing the closure of the compression ring at depth, an innovative solution using a “horseshoe” compression shoring system was developed/analyzed below the tunnel’s crown. Utilizing PLAXIS and SAP2000 models, the 3D soil-structure interaction around the “horseshoe” was used to determine the concentrated stress and deformations generated having an opening in the compression ring. Through very tight installation tolerances, this paper will present the site conditions, innovation geo-structure design, 3D FEM analysis, construction, and challenges associated with this repair shaft.