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SUMMARY OF GEOLOGIC SETTING
Understanding the geological history of the area surrounding the proposed new stadium is important at this stage of the project as it informs us as to what we expect to find during the subsurface exploration program. Further, the elements described below need to be considered to ensure the efficient and successful design and construction of the new stadium. This section begins with a discussion about the formation of the rock found beneath the site, provides a brief narrative of the relevant tectonic history that stressed and strained the rock, and describes the surface processes that placed soil over top of the rock.
Bedrock Geology
The ground beneath the proposed stadium has a mantle of glacial till soil resting on top of Devonian-age sedimentary rock. The rock types vary with depth and lateral extent, but shale is the most predominant rock type. The shale is made of thin beds, commonly less than an inch thick, that are stacked together into units ranging up to 15 feet thick. Occasional layers of harder limestone are encountered between shale beds, typically occurring in single beds ranging from 4 to 18 inches thick.
The shale in the area is derived from clay or silt that were subjected to pressure from being buried beneath subsequent sediments. The burial pressure converted the clay or silt into shale. This process leaves the shale in a “fissile” state, meaning that the shale can be broken along existing planes with relative ease. The limestones in the area were cemented by calcium carbonate and they are harder to break compared to the shale. Both the shale and limestone are horizontally bedded. During a site visit, we were able to observe an exposure of the shale rock in a mechanical room on the western side of the stadium. The photograph above shows the thin-bedded nature of the shale rock below the weathered zone.
Tectonic History
Western New York is several hundred miles inland from the passive continental margin of the east coast of North America. The tectonic forces that built the Appalachian Mountains also uplifted the rock of Western New York into an elevated plateau but left the horizontally bedded sedimentary rock relatively unreformed compared to the folded-rock belt regions to the southeast in Pennsylvania. Past tectonic forces caused the beds to tilt slightly downward toward the south at an average of 30 feet per mile. The same tectonic forces broke the rock into systematic patterns of joints. The joint patterns correlate to the direction of the tectonic forces, which at the proposed stadium site caused one prominent joint set approximately east-west and another prominent set approximately north-south. Intersecting joints effectively reduce the effort required to excavate the rock.