LANDSCAPING
GARDEN MAINTENAINCE
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Articles of Interest
Materials and Characteristics of Retaining Walls
Types of retaining walls used in landscaping
1 Brick
2 Concrete Block
3 Rock - Veneer (Pitch)
4 Dry stone
5 Boulder
6 Crib - concrete
7 Crib - wooden
8 Timber Log - CCA, Bush log
9 Timber Sleeper - CCA, Old Railway
10 Link Wall Systems - Terrace Block, Diamond crib, Inca, Windsor
11 Formed concrete
12 Gabions
13 Concrete sleeper
14 Mixed materials
BRICK
single brick isn't very strong
double brick with reinforcing in centre is stronger.
looks very pleasing
readily available
many different patterns and colours
drainage required behind
CONCRETE BLOCK
looks neat and appealing
readily available
strong when reinforced and core filled with concrete
multipurpose
can be rendered over and coloured or painted
fast construction
can be faced with tiles/ stone glued to surface for appearance
drainage required behind
ROCK – Pitch
very strong
aesthetically pleasing
can be laid wet or dry stacked
can be mortared together
high skill level required
can be costly
time consuming
variety of materials and patterns
drainage required behind
BOULDER – Dry pack rock
large rocks
set in dry using their weight as strength
sloped backwards
reinforced with geo-textile
may need large machinery
well drained soil needed behind
drainage required behind
concrete footing sometimes required
fast construction
CRIB – concrete
inter locking layers stacked on top of one another, sloped backwards
set out in headers and stretchers
strong
easy to construct
relatively cheap
CRIB – timber
same principle as concrete
can use CCA logs and timber sleepers and posts
TIMBER LOG – CCA/Tan E
pleasing appearance
reasonable strength - may need reinforcing
can also be done in pallisade
good weather resistance
expensive compared to timber sleeper
uprights with concrete footings
fast construction
can be bolted together
TIMBER SLEEPER
similar to CCA Log only square appearance
similar properties
relatively cheap in comparison to log
may need reinforcing with tie backs
uprights with concrete footings
fast construction
LINK WALL SYSTEMS
inter-locking
engineer approved
easy to construct
reasonable strength
relatively cheap
readily available
many colours
FORMED CONCRETE
strong and comparatively cheap
simply boxed up and filled with concrete
can be reinforced
can be rendered, plastered or bagged
can be veneered with stone or tiles
drainage required behind
GABIONS
wire baskets filled with stone
stacked together
need machinery to lift and move
strength in their own weight
MIXED MATERIALS
creative design
combination of different materials
add variety to retaining wall appearance
construction methods vary depending on material used
aesthetically pleasing
ANGLES OF REPOSE
The angle of repose of a soil in landscaping is the gradient of the slope at which the soil settles naturally. A firm soil will have a steeper angle of repose than a loose soil.
Angles of repose will be affected by the water content of the soil - the wetter the soil, generally the lower the angle of repose. Embankments formed at gradients steeper than the angle of repose will need to be immediately stabilised at that angle, otherwise natural forces will reduce the angle.
While each soil type is stable at the angle of repose, an unstabilised slope will be subject to erosion by wind, water or physical use.
Probable angle of repose (natural)
very wet clay 15°
wet clay 18°
wet sand 25°
sandy gravel 26° - 27°
dry earth/dry clay 30°
damp sand 33° - 34°
dry sand 35° - 36° shingle 40°
well drained clay/moist earth 45°
clean gravel in natural deposit 50°
SURCHARGE ANGLE
Surcharge angle in landscaping is the angle between the slope of soil behind the wall and the horizontal.