Project Type: Evaluation, Forensics
The Vital Structure:
Concrete Utility Tunnel Forensic Evaluation, Cambridge, MA
Issue
Vital Structures, acting as the Prime Consultant, was retained by a prominent Massachusetts University to perform a forensic evaluation of their existing, below grade steam utility tunnel structures. The existing concrete tunnel system is approximately 100 years old and acts as a conduit for utilities and infrastructure throughout the city. Due to the age of the structure, with compromised waterproofing and substandard original construction issues, this concrete tunnel has experienced years of water infiltration and concrete deterioration. This tunnel system is a critical component to the owner’s operation for maintaining their facilities,and as such, must be fully operational at all times.
Diagnosis
With the assistance of a qualified contractor, we performed several destructive test cuts, test pits and removed core samples for petrographic analysis of the existing cast-in-place concrete. Due to the presence of moisture, substandard original construction, influence from adjacent construction throughout its lifespan and high heat/humidity within the tunnel, these sections of steam tunnel were observed to have significant amounts of deterioration. Furthermore, petrographic examination determined that the original cast in place concrete was in generally poor condition, with heavy amounts of carbonation and sodium chloride present within its matrix. In addition to petrographic examination, Vital Structures hired the services of a geotechnical engineer, site civil engineer, acoustics and vibration specialists, and mechanical engineer in an effort to determine the severity of the required repairs and potential impacts to adjacent facilities
Result
Vital Structures provided the owners with an in-depth evaluation report which identified the locations and quantities of defective concrete, results of petrography, summary reports from each of our five (5) sub-consultants and recommended next steps. In general, it was determined that the existing steam tunnels are in poor condition and in need of immediate repair. These repairs will include full-depth replacement of tunnel wall structures, structural strengthening, shallow-depth spall repairs, remedial waterproofing, mechanical utility system upgrades, and much more. The owner is currently in the process of securing capital funding for a large-scale renovation of these sections of tunnel.