Understanding the Four Retaining Wall Types
In the Pacific Northwest, you often see retaining walls along the sides of roads and highways, used to help prevent rocks, dirt and other debris from spilling into traffic. A retaining wall is simply a structure designed to hold back soil when there is a change in the ground’s elevation. When such a wall is in place, you can create an area that is level on a sloped surface. The ancient Romans, for example, built retaining walls so they could construct roads through uneven terrain.
Retaining walls can also be used in private yards and gardens to help prevent soil erosion, create usable beds out of steep terrain and even add decorative accents or functional seating to a yard. Through trial and error, humans have created four basic retaining wall types, each of which serves a specific purpose.
Gravity Retaining Wall
A gravity retaining wall is short (3-4 feet tall) and uses its own weight to hold back rocks and soil. Such walls are generally made of stone, brick, cinder blocks or concrete and depend on the weight and friction of the interlocking wall materials to be greater than the force of the earth they retain.
Gravity retaining walls are thicker at the bottom than the top, similar to a concrete median on a divided highway, and are battered backwards. A battered wall slants back toward the soil it’s holding, creating a sloped look at the front. The base of a gravity wall should be half to three-quarters of the wall’s height. For example, if a wall measures 4 feet in height, the base should be 2-3 feet wide.
Piling Retaining Wall
Piling retaining walls, or sheet pile retaining walls, are used in areas where the soil is soft and there isn’t a lot of room to create a wide barrier. A piling retaining wall consists of wood planks, steel or vinyl that has been driven into the ground and fixed by soil on either side. When you see this type of barrier above ground, you are generally seeing only one-third of the materials, because the remaining two-thirds are below the ground.
Tall piling retaining walls use a tieback anchor to help the barrier stay in place. Individuals place such anchors behind the face of a wall and the soil’s potential failure plain. A cable then connects the anchor to the retaining wall. They key to a piling retaining wall is to make sure the piles can withstand the bending forces created by the dirt on either side of the barrier.
Cantilever Retaining Wall
Cantilever retaining walls, made of mortared masonry or concrete, contain steel reinforcements within them. When a wall is not surrounded by dirt, it often has the shape of an upside down letter T or a backwards letter L. Just as the name suggests, the wall cantilevers the weight of the earth to its attached footing. The horizontal pressure behind the wall then gets transferred to the vertical pressure below the ground. Therefore, it’s vital to place the footing below the frost level in the earth.
A cantilever retaining wall may have a uniform thickness or a front-buttressed wall and/or a counterfort along the back. A counterfort is a right-angled wing wall, which looks like a right triangle that is placed at the main trend of the wall. Compared to gravity retaining walls, cantilever walls require fewer construction materials. This type of wall, however, requires special engineering to make sure it can withstand the weight of the dirt.
Anchored Retaining Wall
An anchored retaining wall is like any of the previously mentioned walls, but it is stronger because of the addition of extra cables or stays that are anchored into the earth or soil behind the barrier. The cable and anchor act like a large nail that helps secure the retaining wall to the soil or rocks behind it. The anchors expand within the soil or rocks with the help of pressurized concrete that expands into a bulb shape, or by mechanical means. Anchored retaining walls are ideal for loads that are heavy, tall or in areas where space is limited.
Regardless of the type of retaining wall you need for your home, consult with a contractor before you begin your project. Spending a little money up front can help prevent enormous unnecessary expenses in the future.