Skip To Main Content
A picture of a steam roller
Drive by the site of the former Lum Elementary School, and you’ll see a site buzzing with activity, as backhoes, bulldozers, and rollers prepare the ground for what will soon be a temporary campus for Wood Middle School students.
Construction vehicles are fascinating for small children, we know, but we think what’s happening beneath the ground will be of equal interest to adults, as it involves an innovative system to fortify the notoriously sandy soils in that area of the island.
As a reminder, AUSD closed Lum Elementary School in 2017 due to the risk of building collapse in an earthquake. That risk was a result of two factors: the highly liquifiable soil and the thin slab foundations on which the Lum buildings had been built. Soil and seismic engineers, as well as the Division of the State Architect (DSA), all deemed that combination of liquifiable soil and weak foundations to be unsafe. By contrast, the foundation for Wood Middle School, which is just across Rittler Field from Lum, has long piers that stretch down into more stable soil.
The site is now being prepared for a campus comprised of temporary classrooms to house first Wood students and staff (while their campus is rebuilt) and then, two years later, Otis students and staff (when their campus is rebuilt). Once the new Otis campus is built, AUSD plans to build a multi-sport athletic facility on the Lum site.
As you can imagine, the foundations and structures of modern temporary classrooms (also called “portables”) are completely different than those of the large classroom buildings built at Lum in 1959. The safety regulations that govern school building are also completely different. In this case, the California Geologic Survey (CGS) has mandated that the sandy soils on the Lum site be remediated with what is called a “geologic raft” in order to negate the risks attendant with earthquakes.
This raft consists of layers of “geo grid” (a very strong netting material), crushed rock, and soil that are repeatedly compacted so as to create a stable foundation that resists liquefaction. (Readers familiar with sheet mulching may be familiar with this “lasagna” layering strategy.) The compaction is done with a “vibratory roller,” which looks much like a steam roller, but adds the element of vibration to the roller weight to push out the air between the rocks and make them fit closely together into very strong, stable layers.
The vibration is strong enough to be felt even on the sidewalks around the site, and several neighbors near Lum have reported feeling it at their homes. We’re aware this can be unsettling – ironically, it feels somewhat like an earthquake . But we’d like to assure all community members that this vibration is normal, and this phase of the work will be done in several weeks. In the meantime, the crew will be using a lighter vibration setting on the rollers when they are working on the east side of the construction site, which is adjacent to houses.
The temporary campus will be completed by the start of school. Over the next several months, we’ll provide periodic updates so that the community can get a behind-the-scenes view of the facility being built from the ground up.
You can learn more about the Wood project and what's happening at the Lum site on our  Wood Middle School Construction and Modernization page.