Evaluation of Flowable Fly‐Ash Backfill. I: Static Loading

A series of trench backfill tests are performed at Duke Power Company's Marshall Steam Station to evaluate the performance of a flowable fly‐ash backfill versus that of a typical compacted soil backfill. The test site consists of a series of parallel trenches traversing a service road used for hauling fly ash to an on‐site storage area. Instrumented pipe assemblies are installed in trenches that are backfilled using both compacted soil and a previously designed fly‐ash slurry. Pipes of various sizes and materials are instrumented with strain gages to monitor longitudinal and circumferential strains under static and dynamic loading conditions. Instrumented load links are also installed at selected pipe joints to evaluate the relative resistance to joint opening for both types of backfill. Static and dynamic loads are applied by heavy‐vehicle traffic during normal hauling operations. In this paper, is part one of two comparative pipe strain data are presented for static loading conditions. The effects of additional compaction due to normal traffic and subsequent regrading are evaluated for the soil backfill, and strain data are presented for the fly‐ash slurry backfill. The project was designed to demonstrate the feasibility and safety using a flowable fly‐ash backfill in an environment subjected to continual vehicular loading.