About a month ago, crews built an 80-foot concrete piling in the ground near Highway 145 and the Fresno River in Madera County.
On Wednesday, another set of workers set out to batter it to its breaking point with a series of explosives-powered blows -- all part of testing intended to aid engineers as they design bridge pillars for California's high-speed train system.
This was the third in a series of tests over the past couple of weeks to examine the strength of the pillar design and soil conditions near the Fresno River, where an elevated bridge more than 1,000 feet long is planned to span the river and nearby Highway 145 and Raymond Road.
The first blast of the day shook the ground at the test site shortly after 11:30 a.m., after several hours of preparation. Crews from Florida-based Advanced Foundation Testing packed about seven pounds of nitrogen cellulose into a 150,000-pound steel cylinder, wired up explosive charges, and pushed the ignition button. The explosion -- think car engine on steroids -- propelled a piston into the side of the concrete piling.
The piling didn't budge, but the blow shoved the heavy steel blast container backward several yards in a classic display of Newton's Third Law -- for every action there is an equal and opposite reaction.
At least two increasingly powerful blasts were planned for the afternoon, ultimately building up to a 23-pound load of explosives behind the piston blow. The goal, said Applied Foundation Testing owner Don Robertson, was to identify the depth below ground at which the lateral force would ultimately cause the piling, loaded with sensors, to fail. The test is intended to mimic forces that a concrete bridge foundation and the surrounding soil might experience during an earthquake.
AFT is a subcontractor for Tutor Perini/Zachry/Parsons, the group hired last year by the California High-Speed Rail Authority to design and build the first 29-mile section of the state's high-speed train line from the northeast edge of Madera to the southern edge of Fresno. The bridge over the Fresno River is one of three elevated sections included in the contract. The other two are over the San Joaquin River and Herndon Avenue near Highway 99 and the Fresno-Madera county line, and over Highway 99 at the south end of Fresno.
Construction of the rail line is expected to begin this summer, most likely in downtown Fresno, according to the rail authority. Demolition of buildings to make way for the line began this month in central Fresno.