Retaining Walls

Retaining wall landscapeWhen designing the landscape for our home garden, we are sometimes faced with the problem of how to manage and exploit sloping yards. Leveling the ground in order to make it functional and inviting can prove rather onerous, both in labor and in money.

Slopes offer us a chance to create different ground levels connected with beautiful stairways or other landscaping features, thus lending our garden its own special character.

These levels may serve a dual purpose, functioning both as retaining walls, containing the soil and preventing erosion, and as exterior architecture features, helping us separate the garden into themed areas and create distinct focal points. We can also build raised beds for perennials and flowers alike.

The materials and building techniques are varied. The most common materials used in building a retaining wall are:

  • stone: preferred for its rustic feel, although it may prove rather expensive. Fitting the stones requires accuracy, while making mortar joints look natural is a job for experienced builders.
  • brick: it somehow gives a formal and dignified impression; prices tend also to be elevated. It needs a certain skill to achieve that regular, elegant look

Retaining wall_brick

  • timber: this material is relatively cheap and way more manageable than stone and brick, but it can’t be raised very high, unless an engineer helps you with designing it and locating crucial structural elements (e.g. deadmen). Another disadvantage is that timber walls are much more short-lived than other types of retaining walls.
  • concrete: it is strong and, generally, holds well without failing if the preparatory work (design, backfilling, drainage) is done correctly. However, if a concrete wall gets damaged, patching may not be feasible, and removing it will definitely cost you. Its greatest disadvantage, though, is its visual aspect: few things are less attractive than a plain concrete wall; one way of mitigating the effect is to embed decorative designs.
  • interlocking concrete blocks: similarly to interlocking concrete pavers, these blocks are mortar-free and easy to assemble. The industry has made great progress during the last decades: their appearance is quite natural, and you can easily find a wide variety of sizes, shapes and colors to fit your special landscaping project. Walls erected with ICBs can be raised up to 20 feet, depending on the type of blocks used.

Important warning

A retaining wall is not a simple fence wall: its construction is more complicated, as there are several factors involved in its design – especially (but not restricted to) if it’s going to be more than three feet high.

Have a structural engineer design your wall: the criteria he will use and the calculations he will make are a science taught in universities for good reason. A careful professional study of the locale, an analysis of the various factors (soil, weather, materials, regulations, desires, etc) will provide all the necessary insight into the actions to be taken.

Retaining walls must be well-designed and well-built according to the rules of the craft, or they risk failing. Failure of the wall will most certainly cost you a bundle, and this is the best scenario. Damages to property or lives are also a probability.

Risks, Considerations, and Coconut Oil?

In the U.S. we have hard water, especially in the Southwestern part of the United States. There’s a solution called 100SS cleaner which is a liquid concentrate with coconut oil that helps maintain polished concrete’s sheen.

Also to consider is the soil contained by a retaining wall exerts very strong horizontal pressure. If the wall is not well-constructed, it may:

  • Crack
  • Bulge
  • Sag
  • Seep
  • Lean
  • Collapse

In fact, a retaining wall does not have to collapse to fail; not performing as expected is enough of a definition for failure. Tearing the wall and rebuilding it may be the only solution in a substantial number of cases.

Some times, the ground itself tends to slide. This risk becomes more serious in the following cases:

  • After hard and repeated rains
  • In seismic zones
  • With clay soils (they swell)
  • With very high walls

Being aware of the type of soil surrounding the wall, in order to make correct static calculations, is extremely important.

See: Retaining Wall – Types, Planning, Stability, Failures & Recommendations

Retaining wall, stone & stairs

Causes of Retaining Wall Failure

As it turns out, there are numerous causes for inadequate designing and/or construction of a retaining wall. The presence of even one of the causes listed below is enough to turn a handsome landscaping feature into a death trap (the list is not exhaustive):

  • Inexisting or ineffective drainage: the most common reason for retaining wall failure, as it makes soil pressure exerted on the wall build up;
  • Lack of soil analysis / skipping calculations: hazardous design, poor estimate of the wall’s and foundation’s required dimensions;
  • Lack of rigid foundations;
  • Poor load bearing capacity of the ground;
  • Poor compaction: the ground needs to be compacted several times (at the point of excavation, after the gravel base has been added, each time backfill is added);
  • Insufficient anchoring;
  • Use of inappropriate materials;
  • Defective verticality of the wall
  • Inexisting or insufficient reinforcement (steel reinforcements for concrete walls, geogrid for modular block and stone retaining walls)

Other Considerations

  • Check your local building codes: approved design may be needed to get a building permit for walls above a certain height.
  • Call the local utility companies before you dig to have them mark the location of the utility lines: buried lines may not only be dangerous, but they may also prevent you to build the wall where you want.
  • It is also a good idea to verify the lot lines and inform the neighbors that they will be construction going on.

As with everything, careful planning is the key to a successful landscaping retaining wall construction. Before making any final decisions, before ordering materials, before getting set to work, consult with your local engineer or construction company and ask for a meticulous study of the terrain and environment, in order to avoid ulterior trouble, inflated costs, or an occasional lawsuit.

Image sources: Stone steps to the beach, Brick steps & pavement, Fieldstone stairs

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