How Do You Drill Under a River of Traffic?

On a typical Wednesday in February 2009, over 120,000 vehicles flow east and west past Veteran Av on Wilshire Bl. If only one person sits in each car-not impossible in Southern California-the number of people traveling on that stretch of Wilshire would exceed the populations of Inglewood or Santa Clara or Costa Mesa.

Closing Wilshire west of the I-405 to construct a sewer, even if those closures occurred during off-peak hours, might petrify even the calmest Los Angeles driver.

Fortunately, jack and bore came to the rescue. Although jack and bore may sound like an unsuccessful folk-rock duo, they are actually a small-diameter tunneling technique that enables a 24-inch-diameter sewer line to be driven under Wilshire Bl, without damming the river that is Wilshire traffic.

Using a 30-inch-diameter auger, which resembles an enormous blue drill bit, workers drill from the Veterans Administration property north of Wilshire Bl to Veterans Administration property south of Wilshire Bl. The "jack" in jack and bore comes from the technique that jacks or drives metal casing through the soil as the auger bores a tunnel.

Two hundred feet of 24-inch-diameter sewer pipe will be installed from north to south, while the same length of 18-inch-wide sewer pipe will be installed beside the first.

Boring a level path for these sewers is critical because sewer lines rely on gravity to continue flowing. For that reason, a specialized probe travels that route first, ensuring that the auger drills a level tunnel.

Because sewer lines are placed deeper underground than other utilities, the boring had to occur below existing utilities that parallel or bisect Wilshire Bl. Workers stand approximately 20 feet below the surface to drive the auger and tunnel casing through the soil under Wilshire Bl.

Workers stand in two excavated boxes with reinforced walls. Once the sewers are completed, these boxes-then closed at the top-will be accessed through manhole covers.

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A worker guides a 24-foot-long auger as a crane lifts it from a work area north of Wilshire Bl. Another auger at the lower left waits to be removed. Chain rigging is used due to the sharp edges and irregular shape of the auger. These photos were taken January 11, 2011.

 

Workers use a diesel engine mounted on a short track to extract another auger from the new tunnel under Wilshire Bl.

 

The specialized probe that ensures the sewer tunnel will have the correct slope waits to be removed from the excavated work area south of Wilshire Bl.

 

These patient 24-inch-wide sewer pipes wait to be slide into the tunnel underneath Veterans Administration property north of Wilshire Bl.

 

The matching end of the 24-inch-wide sewer pipes shown above.

Ned Racine