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Landscape Whitby University Werks
Landscape Whitby University Werks
Landscape Whitby University Werks
Landscape Whitby University Werks
Landscape Whitby University Werks
Landscape Whitby University Werks
Landscape Whitby University Werks
Landscape Whitby University Werks

Landscape Whitby University Werks
 
Landscape Whitby University Werks

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Construction Technique

Using Precast Concrete

The 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 and Steps

Smaller 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 coping.

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.


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