Retaining Walls done the right way
After going to all the trouble of building a retaining wall, the last thing you need is for it to collapse because of mud and water damage at its base. Rock retaining walls are designed to hold the dirt behind them back, but they only work when the dirt drains and dries out. Before the wall's construction, examine the lay of the land to see the way in which the water siphons off it to incorporate the right drainage system into your rock wall.
Defined as an edifice or structure built to prevent soil erosion and keep dirt in place, retaining walls can be built at different heights. It all depends upon the depth of the excavation in front of the wall and the overall landscaping theme. The type of soil behind the wall plays a part in the choice of the building material for the wall and the drains you place in it. Well-built rock retaining walls stay in place by sheer force of the gravity or the weight of the rock. Taller retaining walls may need additional reinforcements to make them stronger.
Design for Water
Begin the design process by watching the land during a heavy thunderstorm. Identify where water collects to incorporate a runoff system for stormy weather. Walls that are 4 feet or taller require special drainage at the base of the wall in addition to any swales -- sloped drainage ditches -- that collect and direct surface runoff atop the dirt behind the wall. Walls built in clay soils or other dirt that does not drain well also need built-in drains at the base of the wall regardless of height.
Keep water away from the site while excavating the area to build the retaining wall. Pay attention to any water seepage in the excavated area, as this indicates you need to add enough drains to keep the area dry. Add a gravel bed beneath the rock wall and directly behind it as high as it is tall, and at least a foot wide or more, against the wall before adding the soil. Toe drains -- typically, 4-inch pipes perforated to accept water seepage from the soil -- must be installed behind the wall at its base in the gravel parallel to the wall to collect water from the gravel and move it away from the wall. A toe drain must vent to daylight at its end, through the wall face or connect to an enclosed drain system.
For long retaining walls, you must vent parallel-to-the-wall toe drains at intervals of 30 to 50 feet. Add tee fittings perpendicular to the toe drain through the wall face to direct water to lower elevations, storm ditches or drains. Cover the opening of all daylight drains with rodent screens to ensure they stay clear. Mark their location to periodically check them to ensure they are not damaged and continue to drain.