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Editor’s Note: After reading the series of retaining wall articles authored by Michael Simac and Blaise Fitzpatrick in 2007–2008 Geosynthetics, this reader offered the following comments.
Comment
Mike and Blaise,
Great article and on-point.
As an MSE and SRW installer of [more than] 4 million sq-ft, I found your article informative. I wish in this industry there were more stringent standards for companies that install walls over 4 feet. I have expressed this to people in the industry from all levels, and find that I am met with very mixed emotions. It is easy to get certified from a distributor seminar, but to actually have experience in all phases from conception to installation, and dealing with on-site issues properly takes time and effort.
I wish I had a dollar for all the jobs taken by a landscaper with a wheel barrow who thinks he can go above 8–10ft.
The first time I went over 30ft, I did not sleep for a month. Then you go over 40 and beyond and that is when it really gets fun.
I am not an engineer, just a wall builder who loves the process.
John, Pennsylvania
Reply (from the authors)
John,
Thank you for reading the articles, “Three challenges in building SRWs and other reinforced soil structures.” Some project owners and engineering designers have addressed this issue with experienced qualifications in their specifications.
However, you make a very good observation that, on the construction side, there is no formal qualification or certification required for those who construct MSE walls and slopes. There are distributors who offer a “wall construction certification,” with some using the standardized training provided by their trade industry. There are some obvious drawbacks to that approach. County and state jurisdictions have not recognized distributor-based certification programs because they are not standardized, nor mandatory.
You are also correct that MSE walls below 10ft can be built by conscientious installers without problems during or after construction due to conservatism in design and the materials used. This gives contractors building low-height walls a high degree of confidence in their methods. However, as walls increase in height, correct construction procedures and installation details become a much more critical component to short- and long-term performance of MSE wall systems. This is because the forces resisted increase with the square of the height, making a 20ft-high wall, four times more demanding than a 10ft-high wall.
Contractor qualification is also complicated by owners typically purchasing MSE walls with a contractor-supplied design. That approach minimizes the normal checks and balances in a constructed project. Certainly an experienced contractor improves the chances of project success in these circumstances but, unfortunately, does not guarantee it.
When investigating MSE wall failures, one common thread observed by us is a lack of quality control (QC) by contractors and minimal quality assurance (QA) by owners, regardless of contractor experience and qualifications. We have recommended the critical elements of QC and QA be implemented for all MSE wall projects to improve long-term performance. With this approach, the owner is ensured of receiving a quality built project, whether the contractor is learning as he goes or operates efficiently from hard-earned experience.
The good news is that the Geosynthetic Research Institute (GRI), located in Folsom, Pa., is initiating an inspector certification program. (See the website under “Certification of MSE Structures” for description of a one-day course on inspection of MSE structures.)
Keep up the good work,
Blaise Fitzpatrick
Fitzpatrick Engineering Associates
Michael Simac
Earth Improvement Technologies Inc.
Join the discussion
To post your thoughts on these comments, fill out the comment form on the bottom of the article “Three challenges in using SRWs and other reinforced-soil structures: Part 1,” or send your comments to editor Ron Bygness at rwbygness@ifai.com.