Looking to Make an Impact : Firm Drops Steel Weight on Ground in Test of Method to Compact Soil

It was a high-tech test with a lot of low-tech appeal: Take an 18-ton steel ingot, lift it 70 feet off the ground and let it drop.

Griffin Industries was conducting the “dynamic deep compaction” test Monday to see how effectively the process could condense and stabilize a plot of land in Simi Valley, where the developer plans to build 415 homes.

The idea is to prevent liquefaction, which occurs when weak, water-saturated soils turn to jelly during an earthquake.

“When the people move into this development, we don’t want them to worry about that,” said project manager Jake Faller. “We can’t prevent an earthquake or prevent the earth from shaking, but we can eliminate the potential for (liquefaction).”

About a dozen homes were damaged on the east side of the city during the Northridge earthquake due to liquefaction.

Griffin’s 44-acre parcel, which is the site of the annual Simi Valley Days celebration, has a high water table and loosely packed soil that could become unstable during an earthquake.

The company plans to stabilize the soil before building.

Monday’s tests and more tests planned this week will help company officials determine what technique will most effectively pack the soil and prevent liquefaction in the area.

Although the property has always been considered a prime location, it has remained one of the last large undeveloped parcels in the city’s flatlands because of the high water table and problem soils there, Faller said.

Now, however, using newly refined soil-stabilization techniques, the land can be “densified,” Faller said.

The company can use a huge weight to pound the soil in the so-called dynamic deep compaction technique, which was tested Monday.

Or the firm may decide to simply scoop out the loosely packed soil and tightly repack the material. They could also use a large vibrating device that shakes the soil and forces it to resettle into a solid mass, Faller said.

“Essentially, we want to find the best technique for the site,” he said.

On Monday, the company assembled geo-technical engineers and other experts who used remote sound vibration monitors and seismic detectors to plot ground motion. The test should show how successful the soil-compacting process is and how the noise and vibrations would affect neighbors.

The test was conducted by a Santa Paula based contractor, Hayward Baker Inc., which has used its technology in other earthquake-plagued spots, such as Kobe, Japan, Oakland and Northridge.

A light thud could be heard when the 18-ton steel mass plunged into the ground. The finely tuned instruments set up at key locations around the property recorded the impact. Both company officials and consultants monitoring the tests for the city determined that the work would not adversely affect residents around the area.

More tests are planned through the week. The actual work to condense the soils and make the land ready for construction will not begin until at least August, Faller said.