FLOWABLE FILL PROMOTES TRENCH SAFETY AND SUPPORTS DRAINAGE PIPE BURIED 60 FT (18.3 M) UNDER NEW RUNWAY

摘要

In 1995, Kent County International Airport began building a new crosswind runway. The new runway traversed a 66-ft (20.1 -m) deep ravine and a stream. Designers chose to enclose the stream in a 60-in (1500-mm) inside diameter reinforced concrete pipe before building the runway embankment. To minimize earth loads on the rigid concrete pipe, a narrow 10-ft (3-m) trench was specified. Safety authorities demanded a wider trench, however, in spite of vertical clay trench walls. Because a wider trench would place unacceptable earth loads on the pipe, designers proposed a modified narrow trench and backfilling the pipe with flowable fill. Flowable fill was placed to the springline; then granular soil was compacted to 12 in (30 cm) above the crown of the pipe before a clay embankment was placed over it to the final grade. The culvert pipe has been inspected three times since installation and is performing well.