A column supported embankment design method was selected for the approach embankment design.  In this design, 18″ diameter concrete columns will be spaced 8 feet center-to-center for the first 106 feet (starting at the bridge abutment).  After the first 106 feet, the spacing of the concrete columns increases to 10 feet center-to-center until the end of the approach.  The load transfer platform used in this design will be 3.25 ft thick.  The load transfer platform is used to distribute the load of the embankment to the columns below.  Additionally, Tensar Biaxial Geogrid BX1500 was selected as a reinforcement layer between the load transfer platform and the top of the concrete columns.  This reinforcement is necessary to prevent the columns from punching through the fill of the embankment.  Each approach embankment will require 105 18″ concrete columns and 7632 sq. feet of geogrid reinforcement.

With an embankment height of 10 feet, the bridge abutment dimensions were determined as indicated on the drawing provided. Because the abutment is supported by piles, the bearing capacity was not determined for the soil directly beneath the abutment. The wall was checked for sliding and overturning. For sliding, the resistance force was calculated to be approximately 5,000 lb/ft with a driving force of 3,500 lb/ft. The abutment was resistant to sliding along the base. For overturning, the resistance moment was calculated to be 31,000 lb*ft/ft and the overturning moment was 13,500 lb*ft/ft. The abutment was safe from overturning.