Abstract:
A water tunnel advancing below I-75 in Detroit, Michigan experienced a sudden, uncontrolled inundation with flowing soil. The Tunnel Boring Machine (TBM) was damaged to the extent that its shield, cutting head and extensive interior components needed to be extracted and replaced. The tunnel was 17 FT in diameter with crown over 79 FT deep at the time.
The tunneling contractor immediately engaged their designers and specialty subcontractors in order to develop a scheme to access and repair the machine. They required a shaft 99 FT deep to reach the machine, with unobstructed plan dimension of 50 FT to accomodate the large components that needed to be removed and replaced. This precluded the application of an internally braced excavation and instead earth support solutions focussed on use of a compression ring. However, since the disabled TBM obstructed completion of the compression ring below its invert, an innovative solution was needed for the project.
A conventional compression ring was constructed using 5 FT diameter drilled shafts down to the top of the stranded TBM. In areas outside the machine footprint, the secant shafts were extended to over 150 FT depth, creating a horseshoe of support with toe 50 FT below the planned excavation invert. Larger diameter "King Pile" shafts were drilled either side of the TBM tail, overlapped into each end of the secant "horseshoe". The king pile shafts, together with a heavily reinforced ring beam above the crown, acted as a door frame to transfer hoop loads from the incomplete secant arc into reaction supports above and below the TBM. These oversize king pile shafts were extended and socketed into rock over 70 FT below tunnel invert.
Very tight installation tolerances were necessary to maintain secant shaft alignment to depths exceeding 150 FT. The project operational, geotechnical and quality data was managed and visualized using a custom GIS interface. This paper will present the design approach employed and review the construction and quality program selected to recover this machine, as presented by the designers (AECOM) and specailty contractor (Malcolm Drilling).