Manholes are the principal means of access to the sanitary and stormwater collection system.
These structures are typically constructed with a narrow vertical chimney section that extends from the top of the manhole cone to the frame. To bring the frame casting to grade and provide the necessary structural support, courses of bricks, blocks or riser rings are positioned on top of the manhole cone before the frame is set. This is referred to as the “grade adjustment” or “chimney” area of the manhole.
Over time, ground movement, thermal expansion and contraction of the surrounding pavement, freeze-thaw lift, and traffic loading can cause the “grade adjustment” bricks, blocks, and riser rings and their associated adhesive or mortar to deteriorate allowing subsurface water to enter the manhole. Depending on soil conditions and initial backfill methods this water infiltration causes settlement, cave-ins, sink holes and street collapse as the surrounding soils and subgrade materials flow with the water into the manhole.
DrainFlexRib ManholeChimneySeals are installed in new manholes to prevent eventual infiltration and to eliminate the infiltration into existing structures, which occurs during wet weather, between the manhole frame and cone through the “grade adjustment” area.