Sanitary sewer right of ways straddling lot lines can be particularly troublesome if a problem occurs with a line and trenchless repairs aren’t possible. This was the case on an 8″ gravity line in Arlington, Virginia. Extensive structural damage to the line caused repeated backups and raised stability concerns for multiple retaining walls which had been constructed over the line.
The walls ranged from four to eight feet tall, and were a mix of concrete and natural stone.
Timber-shored, hand-excavated work was done on the high side of the wall to expose and replace the affected lines. Because of stability concerns with the walls, the geotechnical engineer specified material no heavier than 25lbs/cuft.
The only access was pumping material from the street, down a decorative flagstone pathway between two homes, and into the excavated pits.
CJGeo proposed 25lb/cuft wet cast density permeable cellular concrete for the backfill material. Because there is no aggregate, it can easily be pumped through small diameter lines at low pressure, which addressed the accessibility concerns.
Because the material is permeable (modified ASTM D-2434 2.0cm/sec), it is freely draining and reduces hydrostatic loads on adjacent structures.
CJGeo mobilized twice for the phased project, and backfilled each of the pits in a single lift.