SYMPOSIA PAPER Published: 01 January 1998

Flowable Fill Promotes Trench Safety and Supports Drainage Pipe Buried 60 ft (18.3 M) Under New Runway


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.

Author Information

Hegarty, JR
Prein & Newhof, Grand Rapids, MI
Eaton, SJ
Rust Environment & Infrastructure, Des Moines, IA
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Developed by Committee: D18
Pages: 255–264
DOI: 10.1520/STP13078S
ISBN-EB: 978-0-8031-5383-7
ISBN-13: 978-0-8031-2477-6