5 Reasons why Retaining Walls can Fail

5 Reasons why Retaining Walls can Fail

‘Failure’ of a retaining wall does not specifically mean collapse of the full structure, rather signs of impending instability and the imposed likelihood of a future collapse are present. While total collapses are extremely rare, the results are often overturned walls, slides, and topples that…

‘Failure’ of a retaining wall does not specifically mean collapse of the full structure, rather signs of impending instability and the imposed likelihood of a future collapse are present. While total collapses are extremely rare, the results are often overturned walls, slides, and topples that are precipitated by a large movement of the soil that can influence such an extreme result. Despite the remedy for such extreme faults being a complete rebuild, Kelownan’s often face more minor deficiencies in their commercial and residential retaining walls.

 In most Okanagan’s cases the retaining wall will reveal tell tall signs of faults with enough notice to contact an engineering professional to assess the remedy options available. The most common sign of compromised structural integrity is tilted angles of the wall which are out of plumb that are more than 1/16 inch for each foot in height. Eg: If you have a 8 foot retaining wall the plumb deviation should not deviate in excess of 
½ inch.

At Phoenix Ridge Quarry we have curated five common reasons why your retaining walls might have held you back but have began to fail.

1. Reinforcing within Improper Locations

If the wall exhibits excessive deflection or cracking then the size, depth, and spacing of the reinforcement used within the wall should be evaluated by an engineering professional. The engineering professional can assess if reinforcing was implemented within improper locations by using a Pachometer as well as obtaining stem material. Once the placement has been evaluated you can often work backwards by reinforcing the wall in weak areas to accommodate the current load, thus avoiding a retaining wall progressive failure.

2. Saturated Backfill Regions

Retaining walls are typically (and properly) designed to mitigate backfill moisture by utilizing a well drained granular backfill process. If drainage is impeded by surface moisture penetration, the pooled water behind the wall would suggest weakening of the structural elements, increased pressure placed upon the now weakened wall, and improper grading techniques that led the water there. The primary purpose of a properly developed granular backfill is to grade precipitation away from the wall in an opposing direction. At Phoenix Ridge Quarry we recommend using crushed aggregate within your backfill as it cannot compact like soil and assures adequate drainage.

3. Weep-less Weep Holes

If you are noticing a lack of water escaping from your weep holes there is a high chance its pathway has become clogged with debris. At Phoenix Ridge Quarry we strongly recommend utilizing crushed aggregate as a material at the opening of the weep hole to direct filtration to the pathway and limit the amount of debris that enters the piping. This practice will encourage debris to be left within the aggregate (which prompts seasonal cleaning similar to your roofs gutters) but is a preventative step to avoid more complicated measures to unclog the weep hole. We recommend testing the weep holes in the beginning of the Spring season to see that water is properly filtered and directed through the desire pathway.

4. Engineering Design and Detailing Errors

Relatively rare to see when an experienced engineer is selected, design errors can come in differing forms and are often the result of insufficient or changing information. Potentially when the wall was designed the height was calculated but due to recent construction the height required has increased. This problem is not as simple as adding an additional foot of material. Instead, re-evaluation of the reinforcement and the potential load pressure should be assessed to determine if the design can handle the change without compromise.

5. Foundation Problems

When initially constructing a retaining wall a geotechnical report should be performed to determine the guidelines for design, specifically the allowable load pressure verses soil bearing potential and friction factors. The site’s qualities will determine any restrictions or allowances within the retaining wall design in an attempt to avoid any of the listed reasons of failure for retaining walls. Following these guidelines should ensure a solid foundation for the retaining wall, but often this report is overlooked by designers. It is highly recommended that a geotechnical report be performed on the retaining wall for longevity, safety, and efficiency of the design.

Possible solutions for why retaining walls fail can be provided by assessment from an engineering professional and may include extending the footing, replacement of backfill, reinforcement of the front of the wall, or landscaping in the form of reducing the retained height to alleviate pressure. Special provisions can be made to improve success of your retaining wall including a pitch learn towards the soil its retaining, tie backs installed in the posterior of the wall, properly installed weep holes, as well as footings (a bed of compacted gravel) used when the soil is susceptible to Kelowna winters, specifically ground freezing temperatures.

At Phoenix Ridge Quarry we provide exceptional materials that can help in the initial design or repair process of your retaining wall. Visit our product page for the wide array of granite available for your retaining wall design or repair.

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