When the structural value of the old manhole wall is lost, the best option is total replacement without digging. Full-depth excavation for replacement or partial-depth excavation for rigid liner insertion requires pavement replacement, social disruption and by-passing of sewer flows. The best trenchless replacement option with no ill effects is to pour a new concrete manhole fully within the existing manhole.
PERMAFORM® pours a new concrete manhole and permits the internal assembly of steel forms conforming to the interior dimensions rising through the eccentric or concentric cone or flat top then vibrating high strength concrete into the three inch annulus between the forms and the old wall thus building a new manhole within the old. Wherever the old wall is weakest, the new wall is thickest. Both corrosion and chemical protection are available with Cor+Gard® , embedded plastic liners, or ConmicShield® additive in the concrete