I recently assisted one of our local sales representatives to develop a retaining wall preliminary estimate for a site with very poor silty-clay soils. This time I was fortunate enough to have a soils report for the site prepared by a local geotechnical engineer. As I read the report and looked at the site plan my concern was not for the integrity of the Allan Block retaining wall, but the stability of the overall site. On this particular site, the propose wall would have a steep slope below the wall. Steep slopes below the wall are always a sign of potential global stability issues.
Global Stability
After reviewing all the information, I called the AB local sales representative and told him that I was concerned about the global stability of the site. We ended up proceeding with the preliminary material estimate so that the contractor would have a rough set of numbers to discuss with the homeowner. Prior to sending the information, I was able to talk to the contractor to discuss global stability and recommended that a local geotechnical engineer do a global stability analysis and determine the actual wall design and geogrid lengths.
The contractor went to the homeowner armed with a better understanding of the challenges their job may be hiding, a pending material estimate that he developed, and the AB Commercial Wall Manual open to the page discussing global stability. After sitting with the owners, he was awarded the job because he presented himself as an industry expert selling solutions instead of simply a contractor there to build a wall.
Later that week, the homeowners and contractor met with a local engineer to discuss the job. After a global stability analysis, the engineer provided a detailed construction plan so they could start building the retaining wall. Soon, the owners will be able to enjoy their remodeled backyard with the added confidence that the slope was properly analyzed and stabilized.
Tom
