Project Type: Evaluation, and Design
The Vital Structure: 

Replacement of Electrical Manhole Roof Slab, Cambridge, MA 

Issue

 

Vital Structures was contacted to evaluate leaking and deterioration of a 13,800 volt electrical manhole situated under a public street, planter and sidewalk in Cambridge MA.

Diagnosis

 

Vital Structures performed an evaluation including confined space entry to the vault, concrete sounding, and exploratory test cuts of deteriorated concrete around the manhole opening. The roof slab was noted to be severely delaminated and spalling due to long term moisture infiltration from the sidewalk and planter above. The vault walls had miscellaneous cracking, leaking penetrations and corroded anchors, however the walls and floor slab were noted to be in good overall condition.

 

 

Solution

Vital Structures prepared design documents and performed construction administration for the structural and waterproofing repairs, including a new concrete roof slab and concrete repairs at the manhole interior. The repair solution included the following:

  • Concrete repairs, removal of abandoned/corroded embedments, and epoxy crack injection were performed from inside of the manhole.
  • The manhole roof slab was removed and replaced. Vital Structures designed the roof slab for AASHTO HS-25 axle loading and replicated the existing slab thickness to preserve grading and elevations of the sidewalk and street above.
  • Asphalt-modified urethane waterproofing was applied to the roof slab and topped with a drainage mat and protection layer before reconstructing the sidewalk and planter.
  • A new riser, water-stops, cast-iron cover assembly and transitional waterproofing were provided to prevent water infiltration around the cover.

Evaluate. Guide. Revitalize.

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