By Scott Ellenbecker
California’s State Route 1, often called Highway 1, is one of the most scenic routes in the world for its rugged beauty. However, the Big Sur coastline it follows is geologically active and unstable. Broken and weak rocks are covered with eroded soils highly prone to landslides. As a result of groundwater, surface water infiltration, erosion and storms, this area – and particularly Pitkins Curve – has been in constant need of repair since 1937.
Caltrans determined that the safest, most cost-effective way to prevent damage to the roadway and injury to motorists would be to bridge Pitkins Curve and build a rock shed at Rainrocks, a neighbouring area of roadway instability. Golden State Bridge Inc., based in Martinez, California, has been on the $29.4 million job since December 2009.
Placing the pilings with Symmetrix
Since Pitkins Curve runs along a steep cliff, bridge construction must proceed from a temporary trestle bridge. Atlas Copco’s Symmetrix System has played a key role in placing its pilings.
With a 120-foot standard swinging lead on the ground, Golden State loads the casing and the Symmetrix system. A Grove HL150C crane then picks up the 120-foot lead to position the pipe pile (casing) and begins drilling. The Symmetrix system advances the casing simultaneously as it drills the hole for the pile.
According to Doug Podraza, sales specialist with Atlas Copco Construction Mining Technique, Symmetrix is the best choice for the varying ground conditions.
“There are portions of rock, portions of soft material. There are also angles and steep slopes. Symmetrix makes it easy to advance the casing and will allow Golden State to use the same pilot bit in order to do both the temporary and permanent casings on the job. They will only have to switch the casing shoe and ring bit.”
Golden State has been getting productivity rates of about one foot a minute during production drilling with Symmetrix. They can drill a 50- to 60-foot hole in less than an hour. As a result, they are installing about four piles a day.
David Riccitiello, president of Golden State Bridge, said “We usually use pile hammers, but we didn’t feel comfortable driving in this material because it varies between hard and soft. We are running large equipment on the access road and the trestle line we’re building, so we wanted the piles keyed in some fairly hard stuff. We could also recover a lot of the bottoms that we were going to use and not spend as much money as other systems to advance the casing.”
The permanent bridge
Both sides of the temporary bridge will go out five spans, leaving an open space in the middle, allowing for construction of two permanent piers. To do this, they will construct a coffer dam on the bedrock. Next, they will drill and sink four piling shafts into the bedrock. Then they will place rebar and pour the concrete to form the piling. There are four 60-inch-diameter pilings reaching a depth of 68 feet nine inches for each nine-foot by 12-foot pier.
Golden State will post-tension the footing to the pile. A series of rods will extend from inside the rebar cage for the pilings up through the top of the footing. After the footing is poured, a hydraulic jack will tension the rods to a specified amount of pressure, essentially cinching the footing and the piles together.
The temporary trestle bridge will also serve as the false work to support the superstructure of the permanent bridge. From each abutment to 35 feet past the new piers, the bridge will be cast-in-place. The remaining 240-foot centre span of the bridge will be cantilevered. When the two ends are about 12 feet from the centre, a closure pour will connect them.
Weather, access, and even a landslide have created some challenges, but overall Golden State is pleased with the progress of the job. Riccitiello is quick to credit his team and the support from Atlas Copco.
“Generally when you buy something you don’t see anybody, but Atlas Copco taught us how to use the equipment and stayed with us on the job. When we had problems they took action quickly, sometimes overnight with a six-hour drive to Sacramento in order to have equipment fixed and back on the job by morning. We ultimately feel this will be a successful job, and a big part of it will be the DTH hammer for sure. We’re very happy with Atlas Copco.”