Settlement Measurements of 50-ft High Embankments at the Chesapeake & Delaware Canal Bridge

This is a case history of instrumented settlement measurements on 49 to 56' (15-17 m) high bridge approach embankments of Delaware State Route 1 crossing of the Chesapeake & Delaware Canal. Details of instrumentation and its installation are stressed. The project's instrumentation measured settlement by three independent methods: (1) liquid-filled tubes connecting reservoirs outside the fills to pressure sensors buried beneath, (2) horizontal inclinometer casing extending across the fill, and (3) settlement plates at the base of the fill with survey rods extending to the surface. The settlement measurements had the dual purposes of indicating when settlement rates had slowed enough to begin construction of pile-groups for bridge abutments that terminate within the embankment fill, and to provide comparisons between settlement results, ease of use, and costs and labor required to get data from the three systems. The results from the three measurements agreed closely. The south side where soil was sandy and settled approximately 4 in (10 cm) whereas the north side with clayier more compressible soil settled approx. 8 in. (20 cm). Measured settlements were significantly less than calculated settlements.