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Year:
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2006
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VTRC No.:
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06-R36
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Abstract:
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The purpose of this study was to evaluate the field performance of the first pile-supported highway embankment constructed in Virginia. The project involved construction of an approach to the new bridge over the Mattaponi River, replacing the existing Lord Delaware Bridge at West Point. The scope of work included field instrumentation and data gathering as related to stress transfer and settlement. The objective was to measure actual soil pressures that are exerted at the geotextile fabric bridging pile caps and to measure stresses acting over pile caps. In addition, data analysis was to be carried out to provide information that VDOT engineers could use to optimize future designs of pile-supported embankments. This report contains field monitoring data and analysis. Prestressed concrete piles were driven at 7-ft (2.1 m) spacing and topped with 3 ft by 3 ft (0.9 m by 0.9 m) precast concrete pile caps. Several layers of high-strength geosynthetic fabric were used for base reinforcement. The maximum embankment height was approximately 6 ft (1.8 m). Earth pressure sensors installed onsite confirmed the formation of soil arching in the embankment fill between columns. Numerical analysis pointed to the large impact of the upper foundation soil layer properties on the magnitude of the final embankment settlement and fabric strain. This shows that accurate material characterization is essential for a cost-effective design. Construction of the pile-supported embankment was carried out by a general contractor. No specialized equipment or methods were required. A rapid increase in the subgrade bearing capacity was observed as the construction proceeded. This method appears particularly well suited to time-critical projects.
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