Types of retaining walls
While there are many different methods to constructing retaining walls, the following are the most common.
Gravity walls
These older-style retaining walls are typically fabricated from stone or, in some cases, other heavier materials, principally relying on their substantial weight to resist pressures of the adjacent soil. Normally, contractors should build the wall so it is at least 50 per cent as thick as the height of the wall. Modern gravity walls include concrete crib walls, gabions, boulders, and large, precast concrete blocks. Gabions are usually a type of soil strengthening that uses wire-mesh cages into which cut stone is placed that work to reduce internal movement and erosive forces.
Cantilever walls
Cantilevered walls are made from a relatively thin system of steel-reinforced, cast-in-place concrete or mortared masonry, fixed at one end, usually by way of a cantilever foundation. The wall operates like a beam, in that it converts horizontal pressures from behind the wall into vertical pressures onto the ground. Occasionally, these types of walls are buttressed on the front to improve their stability against heavy loads.
Anchored walls
These walls are pinned—both top and bottom—typically with cables, which are anchored in the rock or soil behind it. Anchors are driven into the material and then expanded at the end of the cable, either by mechanical means or by injecting pressurized concrete into the hole. The concrete expands to form a bulb in the soil. The wall may be embedded at the base and tied to a slab at the top.
Reinforced soil or nailed walls
These systems make use of reinforcing grids to contain and stabilize the slope. The traction-resistant reinforcement elements change the nature of the soil mass and reduce the earth pressure acting on the wall. In mechanically stabilized earth walls, the soil is artificially reinforced with layered horizontal mats or, in some cases, geosynthetic material. These systems, which use tie-backs, geogrids, or anchor systems, require a considerable amount of space to install correctly. With the development of more durable and quickly constructed systems, such as SRWs, traditional building materials, and systems like masonry, timber, and reinforced concrete began to lose their appeal.
Make the grade
The use of retaining walls in general has increased dramatically in recent years as both highway upgrades and the continuing development of commercial and residential properties have demanded improvements in change-in-grade construction techniques.
Urban construction in cities and towns involves considerable challenges as a result of narrow construction envelopes surrounding transportation corridors and property right-of-ways. On a more immediate and practical level, trees and power lines may limit access to the site.
Rapid urbanization and the need to soften vertical landscapes have accelerated the acceptance of SRWs which typically require less space and provide an attractive and esthetically pleasing façade. Gravity SRWs also provide design flexibility, improved performance, and reduced cost. These systems have also been successfully used as an erosion-resistant embankment and slope retention for lakes, rivers, and other hydrological applications.
SRWs have also been used to enable grading of development sites to boundary limits, thus maximizing the usable area. In addition, they have enabled widening and improvement of transportation corridors and storm water channels within existing rights-of-way.
