EVALUATION OF TWO GEOTEXTILE INSTALLATIONS IN EXCESS OF A DECADE OLD

Many erosion-protection installations for roadway embankments were designed and constructed by using geotextiles during the 1960s. Two such installations constructed in 1969 were studied to evaluate the long-term field performance of the facilities and the geotextile material. These projects were the 79th Street Causeway in Miami Beach, Florida, and the Bahia Honda Bridge in Bahia Honda Key, Florida. The 79th Street Causeway was constructed with a woven geotextile as a filter in a rip-rap revetment-type seawall to protect one of the bridge abutments and a segment of the causeway. The geotextile design was used in place of a conventional granular filter design to prevent erosion of the subgrade soils through the rip-rap. The protected section was designed for 3-ft waves and and a 3-ft tidal variation. The Bahia Honda Bridge project was constructed with a woven geotextile as a subgrade-protection filter beneath sand-cement rip-rap-constructed bridge abutments, drains, and seawalls at both ends of the bridge. In this system, a geotextile was used to act as a filter between the rip-rap and underlying soil subgrade to prevent loss of soil due to weathering or wave action through cracks and holes in the rip-rap. The abutments and drains at the Bahia Honda Bridge were exposed to weathering conditions, and the seawall was designed to resist wave action and tidal variations. The performance evaluation of these installations consisted of a review of the design, visual observations, and testing of representative rip-rap, fabric, and underlying soil samples. In the laboratory study, the condition of the excavated fabrics was compared with new fabric characteristics. The study included strength and filtration evaluation of the fabric and gradation analysis of the surrounding soils. Field observations of the performance of the structures, evaluation procedures, and the results of laboratory tests are presented. The effects of construction procedures on long-term performance are also reviewed. (Author)