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Technicians Work from the Ground Up : Soil Tests Help Builders Stay Step Ahead of Mother Nature

February 24, 1985|TERENCE M. GREEN | Times Staff Writer

There are Southern Californians who have gone to bed in a modish California Ranch house and awakened in a battered split-level.

If they didn't know what soils engineering is before that happened, it's a good bet they do now. And also that they realize the old saying is wrong--what you don't know can hurt you.

There is a lot one cannot know about the ground underfoot as, to pick a spectacular and fairly recent example, the residents of Bluebird Canyon in Laguna Beach found out on Oct. 2, 1978.

And it can hurt you. There were no deaths on that date but 3 1/2 acres of ground slid downhill, a matter of more than 500,000 tons of earth. In the final total, 24 homes were destroyed by the slide or had to be demolished later, streets were torn open or pushed away, gas and water lines were broken; the final damage total was estimated at $15.5 million.

"No geotechnical work was done (when Bluebird Canyon was developed in 1925)," said Michael J. Miller, president of San Diego Soils Engineering Inc. "If there had been, there probably wouldn't have been a Bluebird Canyon."

It wasn't clear whether he meant there wouldn't have been a development or wouldn't have been a disaster but his present concern at Rancho San Clemente, in the hills behind that coastal city, is to see to it that there is a development but no disaster.

As developments go, it's a big one, even for Southern California. Encompassing 1,200 acres, it is master planned for 2,931 dwelling units--single-family detached homes, cluster town houses, condominiums and apartments--with a 10-acre neighborhood commercial center, a neighborhood park and an elementary school.

Also in the master plan are a 299-acre business park, eight acres of additional commercial facilities and a community sports park. The business park will contain offices and facilities for light manufacturing and research and development.

About half the acreage will be left as natural open space, preserving the coastal hills and ridges.

The developer is Irvine-based Western Properties Service Corp., an arm of Western Savings. Site preparation is being performed by McCoy Construction Co. of Woodland Hills and San Diego Soils Engineering of San Diego, a subsidiary of the Irvine-based Irvine Consulting Group Inc., is supervising site preparation and providing geotechnical, soils engineering and other related services.

"It's one of the biggest dirt-moving projects I've ever seen in California," Miller said. "It's the largest single dirt-moving project in Southern California, both in the total square yards and the number moved each day."

When the whole project is completed, probably in three to four years, McCoy will have moved about 40 million cubic yards of earth. The company is moving 130,000 cubic yards a day and when the first phase of site preparation is completed, scheduled for early March, 21 million cubic yards will have been moved.

Huge Machines

The machinery used for that sort of work is elephantine. One of the big track-laying earth-movers was called a "Triple 6" by McCoy's general superintendent, Gerald L. Snyder. Weighing 140,000 pounds, it can carry 45 cubic yards of earth at one time, a total weight, machine and cargo, of nearly 150 tons.

Another gigantic machine is called a D-10 Ripper; a San Diego Soils spokesman said they "move dirt around by the tons but drive like Cadillacs."

(While a visitor found, during a short ride, that the cabs are enclosed and air conditioned, to say they "offer almost all the comforts of freeway driving," according to a spokesman, is an exaggeration.)

The planning for this enormous job was done by four representatives of four specialties: the land planner, the civil engineer, the geotechnical engineer and the developer ("he pays the bills").

Speaking for the third of these specialties, Miller explained that the first thing to be done is to get full information about the site. This is accomplished in three ways: by aerial photography, by "walking the site," officially "field reconnaissance," and by subsurface exploration.

'Old Landslides'

"This site (Rancho San Clemente) is one of the most geotechnically complex ones, because of the number of old landslides--probably more per acre than any other this company has helped develop--and the number of quake faults, all inactive," he said.

What's "inactive?" "No activity in the past 11,000 years."

Making an old landslide safe, so it won't slip again, usually consists of cutting a huge trench across the slide and inserting a sort of wall of heavy material, highly compacted. It could be compared to a retaining wall on a home site, though it could be 50 feet high or even higher and several hundred yards long, or to a dam across a stream.

Compaction is not only necessary for such uses as nailing down old landslides but for roadbeds, building sites, just about everywhere. The basic tool is a huge sheepsfoot roller, as much bigger than the one you use on your lawn as the D-10 Ripper is bigger than your wheelbarrow.

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