Hayward Baker used vibro concrete columns in conjunction with a load transfer platform as a cost-effective alternative to driven piles and drilled shafts for a new four-lane highway bridge across a New Jersey Atlantic creek
New Jersey’s Atlantic County Route 9 traverses several inlets of the Atlantic Ocean before it merges with the Garden State Parkway. At Chestnut Neck, the route was being upgraded to a four-lane highway with central reservation. Where the road crosses Nacote Creek, work entailed demolishing the existing bridge to accommodate the wider replacement.
The approaches for the new bridge consisted of reinforced soil walls, or as it is known in the US, mechanically stabilized earth (MSE), with heights between 3m and 9m.
At the south approach to the bridge, significant amounts of organic soil and peat would result in unacceptable settlement of the MSE walls. Hayward Baker had to find a means of transferring loads to denser soils at depth.
Traditional approaches using driven piles or drilled shafts along the 200m-long wall would have been very expensive, especially if a reinforced concrete mat was utilized.
Hayward Baker’s alternative used vibro concrete columns (VCCs) in conjunction with a load transfer platform installed below the MSE wall. The columns were placed on a 1.5m and 2.3m square grid pattern and, below the highest section of the wall, extended into a dense sand layer at 5m and 10m below the surface.
Hayward Baker then formed a 1m-thick load transfer mat, consisting of three layers of geotextiles, embedded in a well-graded sand fill. This served to transfer the entire MSE wall load to the columns.
As the wall height got lower, Hayward Baker was able to increase the spacing of the VCCs and reduce the length of the columns, saving costs.
Unusually columns were constructed with both expanded base and head sections, as this increased the bearing resistance at the base and the connection between the load column transfer platform at the column heads. |
