Load Test of a Large Bored Pile for the Golden Ears Bridge

Using Osterberg cells (O-cells), a load test was conducted on a large bored test pile constructed in 2006 for the Golden Ears Bridge project, east of Vancouver, British Columbia. Unique aspects of the test included depth and diameter of shaft, subsurface conditions, excavation technique, weight and length of rebar cage sections, cleanout of excavation, and positioning of the two O-cells. Using a special spherical grab, a 2.5-m-diameter shaft was excavated to 74.5 m depth using polymer slurry drilling mud. Presence of the O-cells assemblies hampered final cleanout of the excavation, and shaft integrity below the lower O-cell was affected by the presence of chunks of stiff clay, probably scraped from shaft sidewall during installation of the reinforcing cage. Despite this, testing of the shaft mobilized a combined toe and side shear resistance of over 62 MN and demonstrated that, for a top loading of 50 MN, the test pile would displace only 30 mm. From this, it was also concluded that noticeable creep of the shaft would not begin until top loading exceeded 30.5 MN. The test results allowed reducing the length of the main bridge piles and improved confidence in the foundation design.