2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 7
Presentation Time: 9:30 AM


MOHAN, Dennis J., Sewell, NJ 08080, dennis.mohan@wgint.com

This paper describes the use of geology in engineering design illustrated through project case histories. The historic and structural facets of geology are used to understand the depositional environment and orientation of the subsurface. This information is then used in conjunction with a field exploration program to predict site-wide conditions for use in foundation design, settlement analysis, and stability studies. Information is taken from geologic maps and site investigations to identify any significant geologic hazards. Joint plots are prepared for excavations. The attitudes of beds are determined and used in foundation design and slope stability analysis. Methods are applied to both soil and rock sites. Data is plotted on structure contour maps, isopachs and cross-sections for use in determining pile lengths, excavation quantities, groundwater regimes, and in siting structures such as dams and impoundments.

Two case histories will be studied. The first is a power plant in Tennessee located in a suspected impact site. The result is closely spaced near vertical beds of various types of rock including several varieties of limestone. This condition resulted in deep and shallow foundations being needed, eventually requiring an engineer on site to perform the design. Another aspect of this project was the reclamation without removal of ash storage ponds to provide dry ash and gypsum storage.

The second case history involves a power plant in Indiana. The geologic setting is eolian deposits over glaciolacustrine sands, silts, and clays in the cooling lake area, with glacial till and weak compaction shales in the power block. This presented unique foundation and construction concerns and siting issues for the dam and reservoir. The project featured an early use of geotextiles, including as a dam filter.