Settlement of a 15-Meter Deep Fill Below a Building

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by Percy M. Wimberly, III, (M.ASCE), GAI Consultants, Inc, Monroeville, United States,
Samuel G. Mazzella, (M.ASCE), GAI Consultants, Inc, Monroeville, United States,
F. Barry Newman, (M.ASCE), GAI Consultants, Inc, Monroeville, United States,

Document Type: Proceeding Paper

Part of: Vertical and Horizontal Deformations of Foundations and Embankments

Abstract: The site for a building in western Pennsylvania was undermined, with the mine base about 15 m below planned final grade. Rock above the mine was highly fractured and of poor quality, indicating a risk of mine subsidence. An area slightly larger than the building was overexcavated to the mine base and backfilled with soil and sedimentary rocks from nearby borrow sources. Six months after fill completion, distress occurred at a building corner and settlement was noted in a nearby catch basin. Over about four months, the building corner settled about 2.5 cm. Little future settlement was predicted, but settlement continued. About two months later, GAI Consultants, Inc., was retained to investigate and assess the cause(s) of the settlements. The investigation showed very soft to hard, fine-grained fill with rock fragments and some rocky layers. Ground-water levels were near the fill base. It was concluded the settlement was due to inadequate fill compaction. The owner elected to monitor settlements and repair the structure, as required. Surveyors have monitored settlements since November 1985. Up to 21+ and 14+ cm of settlement have been measured at 12 exterior and 21 interior building points, respectively. Up to 30+ cm of settlement occurred from the estimated as-constructed elevations. This paper discusses the construction process, subsurface investigation, and observed settlements, along with settlement effects on the structure and methods to avoid the problem in the future.

Subject Headings: Structural settlement | Soil settlement | Mines and mining | Fills | Structural analysis | Rock fills | Soil analysis | Compacted soils | Pennsylvania | North America | United States

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