MBTA Bus Repair Garage
The Massachusetts Bay Transportation Authority (MBTA) uses the Quincy Bus Garage to repair, maintain, and store many buses that they own and operate. The building includes three garage bays, offices, and locker facilities for the bus operators and repair staff. When an elevated concrete floor slab in one of the bays failed under the weight of a bus wheel, the MBTA retained SGH to investigate.
SGH’s investigation included a visual survey to document the extent and location of damage and deterioration, destructive and non-destructive field testing to collect information about the existing slab construction and materials, oversight of a environmental hazards survey by others to confirm suitability for us to perform an underslab survey, and strength testing of extracted concrete core samples in our in-house laboratory.
SGH observed that the failed, elevated slab exhibited severe corrosion, the slab-on-grade in the repair bay was severely cracked and settling, which affected the operation of the facility, and voids were present below the slab-on-grade of a storage bay. We calculated the capacity of the elevated slab with and without deterioration and evaluated all the floor structures for immediate serviceability and safety issues. In its deteriorated state, we determined that the elevated slab had insufficient capacity to support the applied loads, which resulted in the punch-through failure. We also concluded that the subgrade below the slabs-on-grade settled, which caused voids to form below the slabs and caused the slabs to crack and settle.
SGH developed a repair program that permitted the facility to remain occupied during construction. We developed construction documents for the work that included extensive concrete repairs to the elevated slab, reconstruction of a portion of the slab-on-grade at the repair bay, and void filling with grout below the storage bay slab. The work was successfully completed under an accelerated schedule imposed by funding restrictions.