Top down
construction combines soil
nailing and the construction of the retaining wall or
exterior wall. The concrete wall is constructed in
lifts as the excavation progresses and becomes the
retaining system for the excavation. Up to 22 inch
thick walls and multiple layers of reinforcement have
been constructed using this technique.
The top down construction offers many advantages over
traditional systems. Significant cost savings have
been realized by constructing the retaining system and
the final wall in a single pass. Wall finish can be a low
cost "gun" finish or wood float finish, like
the inside of a swimming pool. The wood float
finish is better than a normal formed wall.
If the lift lines are objectionable, a thin coat of
shotcrete can be applied over the entire surface or the
wall painted.
Construction
schedules can be compressed by eliminating the time to
construct the retaining wall. The finished wall is
completed while excavation is taking place. On some
projects the exterior walls above grade were started
before the below grade walls were completed.
A checker board pattern of drainage fabric eliminates
leakage through the wall. The system drains out
the bottom through vent pipes or a collection system is
constructed along the bottom to carry water out and away.
