Retaining structures are generally required to laterally restrain soil between areas with different ground levels, sometimes referred to as grade separation. Retaining structures can be vertical or sloped at angles that are too steep for normal soil stability. Typical applications include infrastructure projects like roads and railways but retaining structures are also often used in commercial and residential developments in order to create level terraces on sloping sites.
There are several common types of retaining walls which including gravity walls, piled walls (with and without anchors), cantilever walls, anchored walls, and reinforced soil walls.
Using piles (usually steel or concrete) which extend deep into the ground the bending stiffness of the piles leveraged via the pile embedment retain the soil. These walls can be supplemented by drilled anchors which provide extra lateral restraint and thereby reduce the required embedment length.
Typically constructed from reinforced concrete, either in-situ or pre-cast, these structures take advantage of a widened base to increase bearing resistance which provides additional stability. The base can extend in front or behind the wall face to provide the enhanced
REINFORCED SOIL WALL
Constructed mainly from soil including layers of tensile elements which are typically geosynthetics (geogrids, straps or geotextiles) or steel strips. The tensile elements combine with the soil to create a strengthened composite block material which is internally stable then effectively acts like a gravity retaining structure supporting the soil behind it.
GABION RETAINING STRUCTURES
Gabions provide a simple and cost-effective way to construct a gravity retaining structure and can be stacked to meet increased height requirements. One of the most critical considerations in retaining structure design and construction is the prevention of pore-water pressure accumulation behind the wall. Pore-water pressure is often quoted as the biggest single cause of retaining structure distress and failure. Significantly, gabions are free-draining and therefore are particularly suited to retaining structure construction as they easily permit any groundwater from the retained soil to drain effectively and prevent the build-up of potentially damaging pore-water pressure behind the wall. Gabions are also particularly aesthetically pleasing and can be filled with selected stone to compliment the surrounding architecture and landscaping and can be pocket or terrace planted to add a green aspect to the structure.
GEOCELLULAR EARTH RETENTION STRUCTURE
Geocellular earth retention structures are a variation on reinforced soil structures except that geocells are used to stabilise the soil in layers rather than reinforcement by geogrids. These structures lend themselves to softer finishes where a stepped sloping face can be effectively vegetated to provide a lush green aspect which more readily captures rainfall and thereby sustains the plant life.
GEOGRID REINFORCED SOIL STRUCTURE
As indicated above, reinforced soil structures include geosynthetic (usually geogrid) with high tensile strength laid in horizontal layers within a soil matrix. These structures can be built with a variety of permanent finishes including vertical concrete block facing or green slopes. In combination with Tensar®, TCS offer a range of TensarTech® earth retaining systems with hard and soft/green finishes utilising their uniaxial and biaxial geogrids. Temporary retaining structures are also available like the TR2® system. Please contact us to discuss options.
DRAINAGE BEHIND CONCRETE RETAINING STRUCTURES
As previously mentioned in Gabion retaining walls, inadequate drainage behind the face of retaining structures can lead to a build-up of pressure and this is one of the key causes of structural instability in these systems. Concrete structures are particularly susceptible to this issue, given the relative impermeability of the face, however, this problem can easily be remedied via the application of suitable drainage measures. TCS offers a specific product range that provides effective back-of-face drainage.
TCS Techdrain comprises a rigid polymer cuspated spacer which is combined with a non-woven geotextile filter fabric to create an open, high permeability void that can be affixed to the rear face of concrete retaining structures. The Techdrain geocomposite drain provides a drainage plane which can cover the entire rear face of the structure and is typically 1000 times more permeable than the surrounding soil. Techdrain is also lightweight, easily installed, and can replace significantly larger quantities of drainage gravel, which is not only awkward to place but is likely to be more financially and environmentally expensive.