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Retaining Wall Mistakes

Building a retaining wall is a great way to fully use uneven land in your yard, while also creating a beautifully engineered wall that accents your outdoor style. However, homeowners often run into problems after building their retaining wall. An poorly designed retaining wall can collapse if not constructed properly. Perhaps the retaining wall failed simply because the builder underestimated the requirements for a retaining wall of that size, or was not aware how to avoid common mistakes when building retaining walls.

The immediate physical causes of failure are water damage, ground pressure, stress, inherent structural weakness, structural  instability and material failures.  There are many complex reasons for damage or complete structural failure of retaining walls, but  a combination of contributing factors and mistakes may include:

-Inadequate assessment of site conditions
-Underestimating the forces of nature
-Inadequate design 
-Confusing the aesthetic requirements of a wall with structural necessity

Avoid these common errors when constructing any retaining wall:

Inadequate assessment of site conditions

An insufficient structure can result from failure to assess the site properly and accurately  identify conditions. Provide a reasonable assessment of requirements by looking at older, long-established walls in the area. What materials are they built of, and how? A common mistake is to base a wall design only upon appearance or cost. Consider obtaining professional advice if the wall must be over 6′ in height.

Underestimating the forces of nature

It is important to consider retaining wall drainage in the process of building your wall. It can be vital in ensuring that the wall remains upright, and that too much wet earth doesn't cause it to buckle or even collapse. Poor drainage is often the cause of retaining walls failing, and then it is often too late to put right. Avoiding some mistakes like this can help you to keep your wall strong for years to come. When you are installing the landscaped earth, which the retaining wall is designed to hold up, you should fit in some PVC pipes. These will allow water to drain out of the earth, and prevent your soil from getting waterlogged and excessively heavy. When you are constructing the wall, add a layer of loose rocks and stones between the earth and the wall. This will help provide drainage, particularly during heavy rains. You should add sawdust or other absorbent particles to the stones to help them soak up the soil. Adding drains to the foundation of your retaining wall drainage is vital. Perforated drains allow the water to flow out of the wall, preventing it from collapsing under the weight of too much water. Where excessive surface water causes surface erosion further up slope, plan a system to remove the water systematically.  Collect the water at it’s source, if possible.  Consider building a French drain to prevent excessive surface water from washing down the hill, over or through the retaining wall.

Inadequate design

Failure to alternate structural joints is a very common mistake. It may be tempting and easier to avoid cutting blocks, logs, or timbers and install  the joints  “straight up”instead of staggering the joints.  Although it is convenient to build in that fashion with less cutting,  doing so is a dangerous practice.  Joints of several courses lined up vertically from the top of a wall to the bottom, introduce  substantial weakness  into an otherwise stable, strong design.

To avoid that problem, carefully stagger all  joints in each subsequent course during construction regardless of style or type of materials used in construction. The mason’s rule is applicable:   place  one over two, and two over one. Staggering the joints substantially increases the potential  strength of any assembly.  The sole exception to this rule is where timbers are long enough to extend the whole length of the construction, but even in that situation, if the wall is high, deadmen timbers must be installed for strength, which may involve cutting the timbers and resulting in joints, or alternatively, installing anchor cables

Confusing the aesthetic requirements of a wall with structural necessity

Selecting the Correct Materials for Conditions:

Selecting permeable clay brick for wall construction where soils are constantly wet or  freeze-thaw cycles predominate will virtually guarantees destruction and early failure . Mudstone, soft sandstones, and some other natural rocks are not durable, and many will crumble within a few years  under wet conditions. Harder, less porous rock will last for centuries. It is self-evident that building a high stone wall with poor mortar and rounded or poor quality stones on a poor foundation is a pending disaster for the simple fact of gravity. Choose rock, stone, and block materials carefully and make that selection based upon the characteristics of the wall you wish to build. Familiarize yourself with the  durability of the materials you are considering. Choose materials proven reliable by use in similar conditions.

Incorrect Selection of Timbers:

Using untreated timber or the wrong species of wood as a cost-saving measure is false economy. Wood in contact with damp earth rots very quickly because of natural organisms and the dissolution  of chemical components of the wood. Retaining walls built of untreated timbers or logs are short-lived and will show signs of decay quickly. Depending upon conditions, some may even fail completely within two or three years. Using cedar, redwood, or other rot-resistant timbers will delay deterioration for a substantial length of time but chemically or creosoted timbers will survive many years under damp and less than ideal  soil conditions.

Bottom line, if a retaining wall is not designed properly and correctly built to meet all reasonable conditions expected, it will be subject to damage. Failure of the wall is inevitable.