I am currently involved in a project in the oil sands that involves geogrids. Recalling days long ago, I wrote the following today to recount my experience.
The site is the Operating Industries Inc. (OII) landfill in Los Angeles. The 130 acres of the old landfill rise some 300 feet above grade over refuse in a deep quarry that received waste and hazardous materials dating back to the mid 1950s.
Beneath the landfill is an active fault that could one day produce a large earthquake. The north side of the landfill rises steeply at an inclination of 1.4 horizontal to 1.0 vertical. At the base of the slope is the 60 Freeway, always busy with six lanes of traffic in and out of downtown Los Angeles. At the base of the south slope are homes.
We were there to design and build the closure or remediation works. It took years and hundreds of millions of dollars. Everything we did had to be approved by the Environmental Protection Agency (EPA), the Californian authorities, and Caltrans which is the agency that designs, builds, and operates the California highway system. They have great geotechnical engineers who know seismic slope stability.
We wrote about the project and the work we did. In brief we stripped off the random soils that did not control infiltration and replaced them with a new soil cover. Some call it a store and release cover, some call it an evapotranspirative cover. Being humble, we called it a mono-cover—one soil only.
On the north slope, where the slope is so steep, we built a long and high geogrid reinforced retaining wall to enable us to reduce the slope inclination a little. The rest of the north slope cover includes a layer of geogrids every five feet. The geogrids are tied into the refuse to make the whole system act together in the event of the big earthquake. I still recall the lonely nights as I did hand calculations to establish that in the big one, the geogrids and soil would move no more than one foot—which had been agreed on as the stability design criterion.
Today you can drive the 60 between the 710 and the 605 and see the landfill. It looms large and proud. A testament to the processes of design, review, approval, and never-ending debate we endured to convince all to do what was done. There was a formal calculation for every detail. There was a design report on every topic. There were drawings and specifications filling rooms. We did formal QC and formal QA. The EPA, their consultants, and other involved agencies reviewed everything and questioned everything. It was fun and it worked. Go take a look or cast your eyes upwards as you drive the 60.
