oa Subsurface Investigation For A Housing Complex In Norton, Virgin-Ia Using Seismic Refraction Methods

Much of the level land which is suitable for building on in the coal<br>fields of Virginia is the result of previous strip or surface mining activities.<br>In this process, the overburden on a hill or mountain is removed until the<br>desired coal seam is reached and mined. The end result of this is a<br>relatively level surface and an abundance of waste-rock. It is a common<br>practice to stockpile the waste material and backfill the area with it at the<br>completion of mining. The objective of this investigation was to determine<br>the depth and extent of the backfile underneath a proposed housing site in<br>Norton, Virginia.<br>In order to determine the depth to bedrock, a seismic refraction<br>survey was conducted. Also, numerous test pits were excavated to rock<br>throughout the site to verify the results of the survey. The results of the<br>seismic survey and the depths to bedrock encountered in the test pits<br>correlated extremely well in areas that had been stripped during mining.<br>Areas near the edge of the site which still contained natural soil were not<br>as well correlated since the stiff natural clay had a similar compressional<br>wave velocity to that of the extremely weathered bedrock. Additionally,<br>the test pits revealed an apparent rock ledge running parallel to the site<br>which the geophysical survey did not clearly show. It was concluded that<br>seismic refraction surveys could be successfully used at similar sites where<br>the depth of fill to bedrock was required.