State Puts Freeway Work in High Gear : Safety: Caltrans crews labor day and night to reinforce the Santa Monica and San Diego interchange so it will withstand a major earthquake.

After years of delay, construction crews are now working day and night to reinforce one of the busiest crossroads in the world--the interchange of the Santa Monica and San Diego freeways--to better withstand a major earthquake.

With its antique design and proximity to the deadly Newport-Inglewood Fault, the massive Westside interchange has long ranked as one of the Los Angeles-area freeway links most vulnerable to damage in a strong quake.

But plans to strengthen the columns that support the sweeping overpasses and to shore up the footings beneath the freeway failed to get off Caltrans’ drawing board until recently.

The collapse of a double-deck section of the Nimitz Freeway in last year’s Loma Prieta earthquake sent shock waves rolling through the state’s transportation establishment. Forty-two people were killed when the upper deck of the freeway pancaked onto the roadway below.

Since then, Caltrans’ slow-moving seismic retrofit program has been infused with a new sense of urgency and money.

State lawmakers declared that strengthening the state’s highway system to protect motorists and ensure “the uninterrupted conduct of commerce” is a top priority. And part of a special one-quarter-cent sales tax increase was devoted to retrofitting freeways considered at risk.

The $4.6-million project now under way to reinforce the Santa Monica-San Diego interchange is by far the largest seismic retrofit contract awarded in the Los Angeles-Ventura County area, according to Caltrans District Director Jerry Baxter.

The interchange is a critical link in the area’s transportation system. Caltrans estimates that 543,500 vehicles used the interchange daily in 1989.

“It’s a good place to protect,” Baxter said.

The overpasses and connecting ramps that arc high into the air were designed and built in the mid-1960s, before the 1971 Sylmar quake toppled freeways in the San Fernando Valley.

Experience gained from that quake prompted highway engineers to design new freeway structures to include as much as eight times more structural steel inside the columns, Baxter said.

But the interchange of Interstates 405 and 10 in West Los Angeles was already in place. And its location, a mere two miles west of the Newport-Inglewood Fault, added another element of risk. The fault, which crosses beneath the Santa Monica Freeway in the vicinity of Robertson Boulevard, caused the devastating 6.3-magnitude Long Beach earthquake in 1933 and is believed to be capable of a magnitude 7 temblor.

Under disaster scenarios developed by state officials, a magnitude 7 quake on the Newport-Inglewood Fault in the Los Angeles-Orange County area would be more destructive than an 8.3-magnitude earthquake centered 40 or more miles away on the better-known San Andreas Fault.

After surveying Los Angeles freeway structures, Caltrans assigned its highest rating of seismic risk to three of the connector ramps in the Santa Monica-San Diego freeway interchange. Two other connector ramps received slightly lower risk ratings.

In an early phase of Caltrans’ retrofit program, steel cables were installed to tie bridge decks together to resist collapse.

Then the 1987 Whittier earthquake, which damaged the Interstate 5-605 interchange near Santa Fe Springs, prompted Caltrans to finance university research into ways to strengthen both single- and multiple-column bridges.

“There is new knowledge gained from every earthquake that occurs,” said Scott McKenzie, Caltrans resident engineer on the Santa Monica-San Diego freeway project.

Based on that research, McKenzie said workers from Kasler Corp. of San Bernardino are now wrapping the concrete columns that support four of the interchange’s five connector ramps with a steel blanket three-eighths of an inch thick.

The steel casing “confines the concrete so it doesn’t fail so quickly” from the shaking of a major quake, McKenzie said.

Much of the work takes place during the day, although the heavy volume of traffic in the area requires that some work in the median of the freeway must be done late at night and in the early-morning hours.

McKenzie said the project also includes widening and thickening the footings at the base of the columns that support the freeway. New concrete and steel piles have been driven 50 feet into the ground to support the new footings and prevent movement in a strong quake.

In addition, more steel cables are being installed to reinforce some bridges. The work, which began this fall, is scheduled to be completed in November, 1991.

Under a separate $1.1-million contract, steel blankets are being installed and work on the footings is also being done at the San Diego-Marina freeway interchange three miles to the south.

Baxter said the amount of money being put into the seismic retrofit program significantly increased after the Loma Prieta earthquake rocked the San Francisco Bay Area and Northern California in October, 1989.

The Legislature directed Caltrans to retrofit or replace all deficient single-column bridges and freeway structures by the end of 1992. Multiple-column structures are supposed to be retrofitted by the end of 1994.

However, Baxter said Caltrans will report to the Legislature next month that the cost of retrofitting California’s highway system will be “far . . . above the money set aside” for the program.

The statewide retrofit effort may cost three or four times more than the initial estimate of $300 million. “It’s going to be an enormous program,” Baxter said.

Caltrans engineers are designing the retrofit projects “as fast as we can,” he added. “You’re going to see them all over this area pretty soon.”