RETAINING WALLS (Contractor)

RETAINING WALLS (Contractor)retaining walls are masonry, concrete, timber, steel,
By staff of ACS Distance Educationstone, brick, high-strength polymers, UV-resistant
A retaining wall is any structure that is put into placevinyl and other new materials. Latest trends in
to retain soil moving down a slope. As the soil tendsretaining walls construction has developed in favour
to move with gravity, the retaining wall will have toof segmental walls instead of poured-over concrete,
resist the pressure created by the mass of soil andas they are quicker and more economical to put in
structural water against its upward side. The pressureplace than the latter. A mixture of classical materials
is smaller at the top of the wall, and it increases asand segmented construction is the modular retaining
we approach the wall base. Retaining walls can bewall technology of stone-filled gabions. Other newly
quite small, as those used for landscaping small areas,developed systems consist of timber crib walls and
or be civil engineering works, as those used in roadengineered reinforced soil systems.
building. A special case of retaining wall are dams,MASONRY AND ROCK WALLS The two main
where they have to retain large masses of water,methods of building masonry or stone walls are:
and port, seaside, canals and river civil works, used to1. Dry Walls Dry walls have been built since the Stone
protect land areas from flooding and wave action. InAge in many cultures, and there are remarkable
the latter case they are referred as bulkheads. In allworks done around the world that have lasted
cases, retaining walls have to be able to endure thecenturies. They are built by stacking rocks or blocks
pressure of the soil or water behind it and the waterone on top of another without using concrete or any
at the other side, in ports and dams, for long periodsother `joining' material to stick them together. The
of time. In the case of soil retaining walls, they haveindividual units need to be stacked in a way that they
to be built considering the additional factor of theinterlock as much as possible and with a proper
varying degrees of soil water content during seasonalbatter, a good stability is achieved. The base of this
rainy period or stormy weather.type of wall should be twice as wide as the main
There are several uses for retaining walls: Small andsection of the wall, and when building up soil should
medium size: • As a garden design feature,be propped against the stone for better stability. This
to define garden beds, stairs and multileveled spacesspreads the weight and helps prevent the wall sinking.
• As a physical barrier when required as aThey should have also drainage. Common materials
alternative to hedges • To retain soil andavailable are granite, limestone, marble, sandstone,
make a surface level • To maintain privacyslate and quartzite. For maintenance and repair of
from lower levelled observing points in relation to thehistorical dry walls it is advisable to contact a
garden, as from streets or public spaces below hillspecialist. Large dry walls can be used as retaining
houses.walls in slopes when large stone boulders are used.
Large works: • Road construction •Work is done by specialists companies, and locally
Ports and sea flooding prone areas, seaside roadsquarried stone is used as transport costs of such
and urban spaces. • Canals and riversheavy and large material don't allow for great
• Damsdistances from the quarry. Heavy machinery is used
Here we are going to describe mainly soil retainingin handling the boulders, as they may weight
walls, but we would like to mention one verybetween hundred kilos and several tonnes.
important point in water retaining walls, especially2. Wet Walls The stones or blocks in this wall are
salty or sea water. When building for specialconcreted together. A strip foundation should be laid
conditions as those, special concrete mixes should befirst, with steel reinforcing set in concrete. The
used that: • Dry faster • Resist saltstones/blocks are then laid on top. To further
water chemical and physical erosion. Assistance fromstrengthen the wall, sections of wall are run back into
specialists in the area is essential to ensure the qualitythe embankment at occasional intervals. These walls
of the end results. Any retaining wall design shouldcan be effectively cemented with a mortar mix of 3
consider the following:parts fine sand to 1 part cement.
1. Shape and Substance of the wall. The wall mustWet walls can be built with different materials: stone,
follow the shape of the embankment it is retaining,stone or masonry blocks and bricks. When using
as close as possible, to avoid carting large quantitiesstone, there are three main types depending on the
of soil either in or out of the work site. Thetype of stone used: • Rubble is when uncut
substance which the wall is built from is largelystone is used, • Ashlar uses cut stone, and
determined by what materials are available. Dry walls• Veneer consists on a layer of stones that
(without cementing) need a solid base/foundation. Aare cemented to the face of a previously
mortared wall needs a concrete strip foundation andconstructed wall.
weep holes for drainage. The design should alsoCONCRETE Concrete blocks are quite a versatile
consider that with different seasonal temperatures,material for building walls with as they can come in
there will be lateral expansion of the wall; thereforemany colours and different sizes. Some blocks should
expansion joints should be incorporated. If the wall isbe built on a concrete foundation but needs no
longer than 10 m then it may be necessary tobuttressing. If extra strength is desired it can be
provide expansion joints as it may be liable toreinforced with rods running from the foundation up
subsidence and contraction or expansion and crack. Athrough the hollow concrete blocks and concreted in
gap of 1/2 inch, in a staggered fashion, should beplace. Capping is best done with a pre cast slab.
sufficient to allow movement and not spoil theThere are in the market nowadays solid concrete
appearance of the wall.blocks than have interlocking lips which provide strong
2. Positioning of the wall to minimise soil movement.bonds between blocks without the use of mortar or
All walls should slope back into the embankment. Thiscement foundations, as a type of modern dry wall.
slope is called "the batter". A minimum batter shouldThey are useful for retaining walls below 100 cm.
be approx. 1 cm for every 6 cm in height. Ideally, theWith these materials building retaining walls is simpler,
ground at both the top and bottom of a wall shouldquicker and costs are lower. They come in many
be fairly flat, to minimise erosion. The batter iscolours and in smooth or rough quarried-stone looks,
essential for wall stability in all retaining walls above 1and the shapes that can be created range from
m height.straight classical lines to gentle innovative curves.
3. Drainage both above and below the wall. ThisNonetheless, care should be taken preparing the
factor is obviously more critical in clay soils. A spoonsurface where the wall will be installed, to avoid
drain may be built at both the top and bottom of thefuture problems with ground level movements, and
wall. Subsurface drains and rubble back filling towith drainage. Similar blocks in bigger sizes, more
facilitate drainage has also to be used in thesedepth and weight (up to 55 Kgs each) can be used,
positions. If surface drainage is allowed to run overin conjunction with geosynthetic reinforcement, to
the top of the wall, it can cause bad erosion behindbuild walls of any height and small batters.
and at the base of the wall, very quickly.OTHER MATERIALS
There are different types of retaining walls. GravityInnovative products for retaining walls have appeared
walls rely on the weight and size of the materials torecently in the market that can offer economic
retain the soil, and they may have batters tosolutions when large retaining walls are needed, and
increase stability. These are the most common onesthey are offered in a range of appearances, from soil
nowadays in landscaping works. They are built withlike looks to veneer type facing. Facings can be done
'classic' materials like stone or masonry, or with newwith shotcrete, pressure treated wood, or sheet
materials such as high strength polymers. Gravitymetal panels. One of the options is with material
walls must be at least 50 to 60 % as thick as themade of recycled car tyres. This option is good for
walls' height, or thicker if there are surcharges on thelarge areas as well as for smaller ones, although they
wall. Cantilever walls rely on the weight of the soil onneed to be installed by professional companies. Walls
top of a large wall footage to compensate for thecan be built with many shapes and wall heights,
soil pressure against the vertical wall. They may haveallowing for design flexibility. If you are also keen to
additionally buttresses spaced to reinforce the wall.favour environmental solutions, this can be one of
This technique is not as used now as it was before.them. The product is relatively new, but it has been
Sheet pilling is a technique offered to build waterfrontused already in a variety of projects, such as ponds
retaining walls with materials like vinyl, polymer coatedand animals enclosure, soil retaining walls for canals
timber and steel fasteners. Materials used for buildingand road drainage.