Behavior of Rigid and Flexible Culvert Pipes Under Deep Fill

About the report:

Along a section of Interstate 77 in Carroll County, in the mountainous region of southwestern Virginia, it was necessary to construct a fill approximately 258 ft (78 m) deep. The flow of a mountain stream had to be carried through this massive embankment and, because of the nature of the terrain, it was decided to use a temporary steel culvert and a permanent concrete culvert. The unusual features of this project provided a unique opportunity for a detailed experimental field study of the response of rigid and flexible culverts under deep fill. A 60-in (1.52-m) nominal diameter corrugated steel pipe approximately 1,875 ft (572 m) long was instrumented and installed under a fill approximately 256 ft (78 m) deep as a part of the construction of Interstate 77. The steel culvert, which served as the temporary carrier of the mountain stream under the roadway, was instrumented to provide for determinations of the longitudinal and circumferential strains and cross section deformations at different heights of fill. The permanent reinforced concrete culvert had a nominal inside diameter of 96 in (2.44 m), a length of 795 ft (242 m), and was designed for a cover of 163 ft (50 m). The instrumentation associated with the concrete culvert consisted of two transverse rings of deflection gages to permit a determination of the deformed shape of the cross section. In addition, a series of settlement plates was placed in the embankment above and adjacent to the concrete culvert. Although only limited strain data from the steel pipe were available for analysis, the variation of strain versus fill depth was determined for selected locations. Strain data indicated the existence of high stresses and localized yielding which might be expected for the corrugated geometry used. Deflection gage data were obtained up to a fill of 256 ft (78 m) for the steel pipe and up to 125 ft (38.1 m) for the concrete pipe. These data appeared to be extremely reliable. Using these data, deformed cross sections of the culverts were plotted for the various fill levels. Knowledge of the deformed cross section also permitted the determination of the circumferential bending moments. Plots were made of crown deflection versus fill depth and the maximum crown deflection measured was determined to be in excess of 6 in (0.15 m) for the steel pipe but only 0.10 in (0.25 cm) for the concrete culvert. Crown deflection was also found of the placement of a total fill of 256 ft (78 m), well in excess of the design fill, the steel culvert appears to remain structurally sound. Research personnel who took deformation readings inside the steel culvert after the fill had been completed reported no plate tearing nor serious bolt tipping. However, the pipe has undergone severe local plastic deformations in the region of the crown. The concrete pipe, on the other hand, exhibited rather serious cracking and spalling at longitudinal locations along the spring line. Settlement curves, plotted from the recorded settlement data, provided detailed information concerning the amount and rate of settlement in the vicinity of the concrete culvert. Settlements of almost 5 ft (1.52 m) were observed as well as two separate periods of rapid settlement. As of October 1976, both culverts were still intact and useful, although efforts were under way to improve the condition of the concrete culvert before abandoning the temporary steel pipe.

Authors