Retaining Wall Failures Expert Overview

The damages that can result from the failure of a retaining wall range from minor to catastrophic. Retaining walls are structures used to retain soils (i.e., laterally support them) where a change in elevation of the soils on the two sides of the wall is desired. They can be permanent as in the case of site/landscaping walls, or they can be temporary structures as in the case of shoring walls for adjacent excavation/construction. 

Retaining Wall Failures

Retaining walls are considered temporary if they are in place fewer than five years, while permanent retaining walls are typically intended to last between 50 and 100 years. When constructed at the edge of a body of water, retaining walls are referred to as seawalls or bulkheads. Bridge abutments, basement walls, and even in-ground pools are other examples of retaining walls.

Types of Retaining Walls

One way that retaining wall systems can be differentiated is by the system’s lateral load support mechanism. Lateral loads are imparted onto retaining walls from the supported soils, moisture in those soils, and any surcharges upon the soils on the high side (additional loads imparted to those soils). The effect of those lateral loads upon retaining walls is a propensity to slide or over-turn the wall. 

Retaining walls can be constructed out of masonry, poured-in-place concrete, precast concrete, wood, structural steel sections (I-beams, pipes, or tubes), sheet piles, or natural or manufactured stones. 

Intended use, site parameters, economics and even aesthetics play a role in the selection of one type of retaining wall design over another. Permanent retaining wall designs typically consist of:

1. Cantilever walls: Cantilevered walls w/footings and gravity walls. These walls generally use their self-weight and large footprints/foundations, or deep embedments, to resist over-turning and sliding forces.
2. Externally stabilized wall: Walls externally braced with struts, raked beams, or buttresses. These types of retaining walls utilize external structural elements as their lateral load support mechanism. 
3. Internally stabilized walls: Wall panels anchored with multiple layers of geogrids or arrays of soil nails. Internally stabilized retaining walls incorporate “interior” structural grids/anchors extending into the retained soils to engage those soils to provide the requisite lateral support mechanism.

Retaining Wall Failure Scenarios

Retaining wall failures may be local, with minimal impact to the wall’s overall stability, or the failure may be global and defined as a total loss of the wall along with the retained soils. With fewer redundancies in their lateral load support mechanism, global failures of cantilevered-type walls may consist of the entire wall, or large portions thereof, horizontally translating (i.e., sliding failure), failing by overstressing the soils below the footing (i.e., bearing failure), or rotating (i.e., overturning failure). Those failure scenarios are depicted below:

Maintenance of Retaining Walls

Owners of retaining walls are required by local ordinances, building codes, and other applicable standards to properly maintain their retaining walls. Proper maintenance not only helps to assure greater longevity and proper performance of the wall but will also help to identify corrosion or deterioration of the structural elements of the wall system in a timely manner, which should reasonably result in less costly repairs. Federal and state DOT agencies are a valuable resource for proper maintenance planning due to their desire to protect their assets and the public from retaining wall failures.

Retaining Wall Failure Investigations

A forensic investigation of a retaining wall failure by a qualified structural and/or geotechnical engineer will typically consider the following as potential contributing factors:

• Original design of the wall and foundation; was the original design proper?
• Original construction of the wall and foundation; were any errors made during initial construction?
• Changes to the loading of the wall; has there been any increase in the quantity of moisture behind the wall, or has there been additional surcharge loads that were not part of the original design?
• Improper drainage behind the wall; is the wall’s moisture drainage system performing properly?
• Damage to the wall after construction; has there been any vehicular collision or nearby root system that might have affected the foundation system?
• Lack of proper maintenance to the wall and/or the wall’s drainage system; was the wall properly maintained?
• Unanticipated wind or seismic events; was the wall acted upon by a “beyond code” wind or earthquake event?
• Corrosion/deterioration of the structural elements comprising the wall and its foundation; is there any evidence of pre-failure cracked or spalling concrete, corroded reinforcing, etc.?

Material that would be useful in a forensic investigation for a retaining wall failure includes the original plans for the design of the wall and its foundation, a geotechnical report, and all maintenance records. Site inspections of the failed wall and material testing of the structural components is often required. Information gleaned from these sources, along with information acquired during a site inspection and/or material testing must be scrutinized and analyzed in order to identify the cause of the failure or collapse.

There are many factors that can potentially contribute to the structural failure of a retaining wall. The engineers at Robson Forensic approach these investigations not only with experience designing and constructing these features, but also the experience of investigating failures and testifying how and why they occurred.

To discuss your case and how we can assist, submit an inquiry or call 800.813.6736.

Featured Expert

Mark Duckett, P.E., S.I.

Structural Engineer, Special Inspector & Construction Expert

Mark Duckett is an expert in structural engineering, including building design and inspection, professional liability, value engineering, and building defects. He is also an expert in wind… read more.