Tag Archives: Retaining walls

Retaining walls, Lifestyle Landscaping Bundaberg

Build a retaining wall by Lifestyle Landscaping Bundaberg

When constructing a retaining wall there are a number of factors you need to take into account when choosing the right retaining wall for your situation.

1.    what is the likely load to be placed on  the wall from the retained material

2.    Is there a continual seeping of water from the bottom of the wall

3.   what is the catchment area for surface water likely to effect the wall.

4.   How solid is the ground where the wall is to be constructed …. does it need to be excavated and stabilised.

There are many more questions you need to ask for specific situations that require unique solutions, however answering these questions will allow you to choose the most appropriate retaining wall for the situation. There is one simple rule in constructing a retaining wall and if you follow this rule many of your headaches will be avoided.

NEVER allow water to wash over the retaining wall… water must always be drained away to prevent washing over the wall.

If you were to ask what is the single most important factor that effects the long term stability of a retaining what would it be…

Simply  DRAINAGEprovide good drainage and you are well on your way to building a retaining wall that be serve you for years.

Chosing the right type of retaining wall… most often used in and around Bundaberg

1/     CCA treated sleepers/logs

2/    Concrete link block , both vertical stacking and offset blocks

3/   Boulder rock walls.

4/  Concrete block retaining wall with engineered foundations…  often rendered and painted.

CCA treated sleeper or Log walls. _ you must seek independent engineering advise before constructing a wall using this method.. this information is generic in terms.

General specifications are available for constructing walls up to 1m high. With CCA treated timber walls your posts would best be 200 x 75 CCA treated hardwood and as a rule of thumb will be the same depth in the ground as out of the ground with hole diameter of 400mm. Post spacing will vary according the wall height and width of timbers…. often we use 200 x 50  x 3.0m  for rails with posts at 1.5m centres in walls up to 1.0m high. When placing a fence on top of this wall you will need to obtain independent advise as to the necessary modifications to sustain the loads imposed.

When posts are concreted into place leave dry for the day then fix the horizontal timbers with 12mm galvanised  cup head bolts with nuts and washers…must be hot dip galvanised.  All fixing points top and bottom must be fixed with these bolts and all intermediate points fixed with galvanised batton screws to keep the timber in place while under construction.

Ok, so now your posts and rails are in place, you will need to fix geofabric filter cloth to the back of the wall and another layer to be placed from the base of the wall return to the face of the cut , and up the front of the cut . Then allow sufficient cloth to easily return back to the wall.  Filter gravel must be placed 200-300mm wide behind the wall  to the full height of the wall , less say 100mm, then, fold the excess filter cloth over the top of the gravel and back to the wall to prevent later siltation into the drainage layer. This will retain the filter layer in a free flowing condition and prevent excess load being placed on the wall. In some situations a 100mm layer of clay based material is placed on top of the cloth to prevent any possible penetration into the drainage layer as run off. This run off is to be shaped into a spoon drain and directed away from the wall face. Follow these procedures and you will have a long term solution for your retaining wall challenge. Please call the Lifestyle Solutions Centre on 4155 5500 for personal advise for your situation.

Concrete link block , both vertical stacking and offset blocks.

GB masonry Link block terrace wall

GB masonry block wall by Lifestyle Landscaping Bundaberg

Link block walls are becoming very popular with a wide range of colours, styles and finishes. Boral, Hansen, GB Masonary and Bundy Blocks to name a few have a range of blocks that all can be used for situations generally up to 1.2m and beyond with specific advise from the manufacturers. They are simple to lay and while most advise a simple compacted crusher dust or road base base is all that’s required, we recommend pouring a concrete footing (depending on the height of the wall) say 100mm thick  x 400mm wide. This will also avoid the potential for  unstable ground under the wall being an issue. This is often caused by trenches crossing the yard from stormwater, sewer or electrical. Once the base is poured, use a laser level to establish the heights and bed the base course into the moist bed of concrete. Using a 300mm long spirit level ensure the  block is level in both planes. Should you not achieve this the result will cause the wall to till as the error is magnified as you rise further up the wall. In some situations the core of the wall is filled with filter gravel as well as behind the wall. Geofabric filter cloth is to be placed from the base of the wall return to the face of the cut , and up the front of the cut . Then allow sufficient cloth to easily return back to the wall. Filter gravel must be placed 200-300mm wide behind the wall the full height of the wall , less say 100mm, then, fold the excess filter cloth over the top of the gravel and back to the wall to prevent later siltation into the drainage layer. This will retain the filter layer in a free flowing condition and prevent excess load being placed on the wall. In some situations a 100mm layer of clay based material is placed on top of the cloth to prevent any possible penetration into the drainage layer as run off. This run off is to be shaped into a spoon drain and directed away from the wall face. Follow these procedures and you will have a long term solution for your retaining wall challenge. Please call the Lifestyle Solutions Centre on 4155 5500 for personal advise for your situation.

Link block retaining wall by Lifestyle Landscaping Bundaberg

Link block retaining wall by Lifestyle Landscaping Bundaberg

Boulder rock landscaping wall.

Using natural rock boulders allows for a softer effect allowing plants to be placed in the voids between the rocks. Start building the wall by ensuring a spoon drain is shaped around the top of the wall to prevent erosion caused by water washing over the wall. Stagger the placement of rocks to avoid rocks being placed directly on top of the other rock… in effect using smaller rocks in the voids fills these voids and makes for a more solid wall. Walls need to be laid back at a slight angle to avoid the wall toppling over and soil settles. Often topsoil is placed to bed the rocks and as a medium for later planting… SPECIAL TIP.. use a ladder to plant the plants… call us to explain how easy this is to build a rock wall in your back yard…. some link blocks require capping tiles to finish the top of the wall, so watch out for that and others are best laid straight.

Boulder rock wall by Lifestyle Landscaping Bundaberg

Boulder rock wall by Lifestyle Landscaping Bundaberg

Concrete block retaining wall with engineered foundations…  often rendered and painted.

Block wall requires drainage behind the wall

Block wall requires drainage behind the wall

Block retaining walls require specific engineering and is critical to be certain this is followed to avoid later cracks and ultimate failure. Soil tests are required to allow the engineering to be designed to the specific soil type, so this is obviously the most expensive method of construction. Often block walls are chosen to suit the building type and because the wall can be constructed vertically. Sometimes the footings can cause an issue and the toe of the footing can extend 1m or more depending on the wall height. The same procedures must be followed for placement of drainage gravel.

Call the team at the Lifestyle Solutions Centre on 4155 5500 for personal advise for your situation.

bought to you by Lifestyle Landscaping Solutions, 78 Mt Perry Road and written by Peter Moller