Performance of Geogrid Load Transfer Platform over Vibro-Concrete Columns

Abstract

A case history involving the use of geogrid transfer platforms over Vibro-Concrete Columns (VCC) to support approach embankments on soft ground is presented The Route 52 Causeway reconstruction project in Ocean City, New Jersey involves the replacement of existing bridges, approximately two miles long, which cross Great Egg Harbor between Somers Point on the New Jersey mainland and Ocean City on the barrier island. Proposed reconstruction involves staged construction of the two-mile long crossing, which will replace the existing four structurally deficient and geometrically obsolete bridges with new bridges and roadway embankments on tidal-marsh islands with a complex depositional history. The project involves the installation of VCC that support approximately 8-m-high (24-ft-high) mechanically stabilized earth walls underlain by a geogrid reinforced-sand platform. The design concept of the embankment supporting system is outlined. A comparison between two methods (British Standard vs. Collin's) for the design of the platform is discussed. The result of a Statnamic Load Testing performed on one VCC is also presented. The performance of the embankment supporting systems is assessed based on monitoring data obtained from various instruments installed during construction including settlement platforms and inclinometers. In addition, a comparison of case histories between geogrids and geotextile load transfer platforms is presented, drawing from a similar experience in a former project. Finally, conclusions are presented regarding the design aspects of the geosynthetic-reinforced load transfer platform and VCC.