Drilling began Tuesday morning in Alhambra for the California State Department of Transportation’s State Route 710 Tunnel Technical Study Geotechnical Exploration Program. The drilling will continue now through May in Alhambra, Los Angeles, South Pasadena and Pasadena.
This only months after voters passed Measure R, the half-cent sales tax measure, which is expected to fund about $780,000 of the about $3 billion tunnel.
According to Douglas Failing, director of Caltrans’ district No. 7, additional private funding also is available for the project.
At about 2 p.m., workers had been at the Alhambra site five hours and sunk their equipment about 60 feet down into the earth. That’s just more than a quarter of the distance needed for each of the planned about 33 holes, to be drilled during the study of earth and sub-soil conditions beneath various sites within Caltrans’ designated zones.
The drilling is expected to give Caltrans an idea of where not to put a planned 710 Freeway-connector tunnel.
“This is not to predict a route,” said Douglas Failing, director of Caltrans’ district No. 7, during a press conference Tuesday afternoon at the Alhambra drilling site.
“We’re looking more for where not to drill than where to drill,” Failing said, adding that the types of soil aren’t so important as the consistency of the soil.
“You want a certain amount of rock. You want consistency. When you go into various types, such as rock, sand, rock, that’s not good,” he said.
Depending on analysis of soil conditions and seismic reflection (electronic imaging) tests 200 to 300 feet underground, officials expect to be able to predict the feasibility of putting a “route neutral” 4.5 - to 5-mile long tunnel under streets and homes between the 10 freeway, where the 710 freeway currently ends, and the 210 freeway.
If built, the tunnel will be “the longest tunnel of this size in North America,” Failing said, adding that there currently are longer tunnels in Norway and other European countries.
Caltrans’ study also will include a series of shear-wave seismic testings, using geophones, designed to show how vibrations affect the ground at that depth.
The tests are not to simulate the anticipated vibrations of vehicles within the tunnel, Failing said, adding that mapping earthquake fault lines will be part of the study.
However, constructing underground in an area known for earthquake activity is not uncommon, Failing said, listing other areas with underground tunnels, such as the San Francisco Bay area, Spain and Russia.
Although most of the drilling sites are for the planned tunnel, some additional sites will be drilled by crews near the south ending of the Glendale (2) Freeway, for separate research, Failing said.