Retaining
systems
are required in excavations where the site does not allow for sides to be safely
sloped back. Typically this applies to excavations greater than 8 feet or deeper in soil
or unstable rock.
There are several systems typically used
depending on the conditions. In soil, common systems include H-beam and wood lagging, and
soil nailing. In rock, protection can be as simple as chain link fence to contain loose
rocks or the more positive system or friction rock stabilizers (split sets) and a
shotcrete face.
Top down
construction of walls is the process of completing the retaining or exterior wall from the
top down. The process is usually used in conjunction with soil nailing or rock nailing.
The soil nails serve the function of tying back the excavation and supporting the vertical
loads of the wall. The advantages include significant cost and time savings, the
flexibility to accommodate design modifications during construction, and a "one
wall" system that supports construction and provides a permanent
wall.
Soil
Nailing
is a procedure to
reinforce and strengthen ground adjacent to an excavation by
installing closely spaced steel bars, called "nails", as
construction proceeds from the top down. The process is effective in
cohesive soil, broken rock, shale, or mixed face conditions.
The technique permits flexibility to conform
to a variety of geometric shapes to meet specific site needs.
Spacing, placement angle and nail length can be varied to meet
almost any site-specific conditions such as easement or utility
location problems.
