Building Retaining Walls

Tips on Constructing a Retaining Wall

By Mark J. Donovan

Retaining walls are used to hold back soil and to tier land in elevation. Retaining walls are commonly used in backyards and garden areas to create level areas for backyard use and plantings. Prior to building a retaining wall careful planning is necessary. The yard needs to be properly assessed for contour, drainage and soil conditions so that the retaining wall not only looks aesthetically attractive but also functions as an integral part of the landscape. Also, a retaining wall holds back a great deal of pressure.

As a result it is important that the retaining wall be structurally sound to support the immense pressure. More times than I can remember I have driven by homes where the retaining wall was either crumbling or leaning over.

Retaining walls are often constructed today out of preformed, interlocking concrete blocks. In New England, they are also frequently constructed out of large stones or boulders due to the natural abundance of Granite.

In some situations it may be necessary to have multiple retaining walls in a yard to terrace it off in a number of flat regions. In other situations, where there are very steep grades for example, it may be necessary to construct segmental retaining walls. Segmental retaining walls consist of a facing system, usually consisting of modular concrete blocks, and a lateral tieback system that is buried in the backfilled soil area behind the retaining wall.

The modular concrete blocks and the lateral tiebacks interlock with each other to create a very solid and stable retaining wall. Segmental retaining walls enable the construction of higher and steeper walls.

With any retaining wall construction project, work starts with digging a trench and installing a compacted gravel base. The deeper you can install the trench the less likelihood of the retaining wall heaving due to winter frost. Ideally the trench should be dug to a depth below the frost line for your local area. The compacted gravel base also serves as an excellent level medium so that the retaining wall is level from side to side.

After the construction of the retaining wall trench and compacted gravel base is complete, courses of interlocking concrete retaining wall blocks or large stones can be positioned into place. It is important that each new course of concrete blocks is staggered from the row just below it so that the retaining wall is rigid from side to side and from top to bottom.

Also, a level should be periodically used to ensure the retaining wall remains level side to side as each additional course of concrete retaining wall blocks are installed.

Before backfilling behind the retaining wall, landscaping fabric should be installed up against the back of the wall to prevent soil from weeping through to the front of the retaining wall. Also, additional crushed stone and 4 inch PVC drainage piping should be installed behind the retaining wall.

Building a retaining wall.

The PVC piping should be installed to drain water away from the retaining wall to the lowest point in the yard. After installing the landscaping fabric and drainage piping, the retaining wall can then be backfilled, the local area graded with topsoil, and the localized area grass seeded.

One final note: Building retaining walls is extremely heavy and laborious work. Consequently it’s a wise idea to consider renting a small Bobcat tractor to dig the trench and aid in hauling the concrete retaining wall blocks or stones.

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