Retaining walls come in various varieties, depending on the purpose they are meant to serve. From addressing aesthetic purposes to safeguarding busy roadways, these architectural structures have evolved to suit a wide range of soil types, weight and height parameters, supporting structures, accessibility of the site, the slope of the ground above and at the bottom of the proposed wall and so on.
These blocks, however, are known to have suffered failures, to disastrous effects, in the absence of proper planning, lack of reinforcing the material and simply due to the ongoing erosion of the backfill. It is thus necessary to customise these barriers, keeping in mind the unique demands in each setting.
– Gravity walls: the most common kind of barrier
The earliest known form of retaining wall, these depend on two factors to counter the lateral pressure exerted by the backfill: a) their own weight; by virtue of their massive size and b) their setback/batter (in layman’s terminology, it refers to the slope of the wall); by leaning in the direction of the retained soil.
In its crudest form, one can build these structures using boulders or rock rubbles. While that may be pleasing to the eye in a typical Australian garden, specialised blocks made of large pre-cast concrete or timber are usually employed in larger and taller structures, and increasingly in the more fashionably designed gardens. Modern gravity walls also employ concrete crib walls, gabions (sheets of steel wire cages), though they are mostly used on roadsides.
Rather than letting the structure alone to withhold the soil, the latter can also be conditioned to add to the strength of the retaining wall. This is achieved by way of using Mechanically Stabilised Earth (MSE). This process includes the artificially strengthening the soil by using layered horizontal mats (called ‘geosynthetics’) so that the soil and the wall together hold back the soil from breaking through.
– Cantilevered walls: the choice for residential purposes
The basic structure for this kind of barrier is in the form of an inverted ‘T’ (consisting of a horizontal footing and a vertical stem), which is designed to transfer the horizontal pressure of the backfill to the ground below, by converting it onto vertical pressures. This kind of retaining wall finds application as integral basement walls and often spots buttresses on the front or counterfeit to their back as a means to increase stability.
These walls typically employ less material than gravity walls and are a common feature in many Australian homes. A common cantilevered wall is built of reinforced concrete, timber sleeper walls, steel/timber sheet piles or concrete–filled block-work.
– More sophisticated situations demand greater variety of retaining walls
Barring these above-mentioned more commonly used structures, special requirements such as soft or unstable soil conditions and excessively heavy weight of the load necessitate the use of more complex forms of barriers like sheet piled walls and anchored walls. Sheet piles usually act as temporary supports to enable more permanent construction to undergo, while anchored walls are predominantly found along mountainous roadways.
Building a retaining wall for small-scale domestic purposes can be dealt with by yourself (assuming you possess restricted know-how of the concerned skill). In such projects, aesthetics is also an oft-considered factor. The bigger projects involving large-scale constructions, however, are dependent on meticulous calculations, soil-testing and engineering and design abilities. Builders thus are often required to choose from a number of options, ranging from the kind of building material to the type of design best suited to withhold the designated pressure. Failure to make the right choices can, after all, culminate into disastrous consequences.