procedure for installing precast block is similar
to the outline for Pressure Treated Wood walls below. There are no anchors for the
bottom course and stability of this course relies
on burying the first course below the grade at
the bottom of the wall. When a wall is deemed high
enough to require tie backs it is tied back to
the bank of dirt using a flexible nylon mesh
(much like a very thin plastic chainlink fence)
which is laid on top of a course of block and
stretches the length of the wall and back into
the bank of dirt. This requires that the bank of
dirt first be excavated away to the level or
course of block where it is to be installed. Once
the mesh is installed the dirt is replaced and
compacted up to the level of the next layer of
mesh. This tie back mesh should be installed
approximately every 2 to 3 ft. in the height of
the wall. Back filling proceeds along with mesh
installation using the same drainage stone,
filter fabric and styrofoam backing installation
as described in "Pressure
Treated Wood Wall"
construction below. The top of the wall can be
finished off with a cap or "coping".
Planters, Terraced Gardens
precast stackable blocks may be used to
create borders or low walls around
shrub/flower beds to delineate the bed
from surrounding landscaped areas and to
help reduce maintenance. Again they are finished off at the top with
Base preparation varies
with intended purpose and height considerations
but generally clear gravel is used beneath and
behind these walls.
Steps are simply a single course of block with coping on top and interlock
as required behind the cap
to continue the tread.
Using Pressure Treated Wood
Usually the most economical
retaining wall is constructed using pressure
treated wood. Return to Precast Walls
For smaller and terraced
planter applications 4x4 timbers can be used. For
larger walls, which retain higher banks of dirt,
the use of 6x6 timbers is required. A typical
installation procedure might go as follows
(please refer to Retaining Wall Detail diagram below). We start by
excavating a trench along the length of the wall that is wide enough to allow for the width of the
wall and the various back fill components. The
trench is dug deep enough to allow for a minimum
of 8" of drainage stone and to partially
bury the first timber. An optional drain tile can
be installed at this point along the back, bottom
of the trench to aid in drainage in wet
applications. Next we install the 8"
drainage stone base to grade and compact it in
place. Once this is completed we begin installing
the timbers for the first course of the wall.
These are held in place by 4 foot long x 1/2"
diameter steel rods that pass down through holes
drilled in the timber approximately every 8 ft.
along the length of the first course. From here
on additional courses of timber are added and
secured to the previous course with 10"
galvanized spiral (ardox) spikes. Approximately every 3 ft. of
height and 8 ft. of length the wall must be tied
back to an anchor called a dead head using a
steel tie back rod. The dead head may be a
horizontal or vertical timber or a vertical
poured concrete pier buried in the retained
soil some distance behind the the wall. (Note:
There are various modifications to the dead head
and tie back rod systems depending on site
specific application requirements). Once the
finished height of the wall is achieved a backing
of 1" or 11/2" white styrofoam (bead board)
is installed to provide a "shock
absorbing" cushion to guard against frost
pressure against the back of the wall. Filter
fabric is draped against the bank of dirt being
retained to keep soil from contaminating the
drainage zone behind the wall. Finally a minimum
of 8" thick backfill of drainage stone is
placed between the fabric and the styrofoam
backing. All that is left to do is cover the top
of the drainage stone with some filter fabric and
grade topsoil over this and sod affected areas.
Below is a typical Pressure Treated
Wood wall installation cross sectional diagram.