STABILITY ASSESSMENT OF MAN-MADE SLOPES VS. EXISTING NATURAL SLOPES: A CASE STUDY AT TENNESSEE VALLEY AUTHORITY KINGSTON COAL ASH SPILL

The stability of natural or man-made slopes still remains a topic of significant research, despite notable development in our understanding of its behavior. Due to a coal ash spill at Tennessee Valley Authority Kingston in December of 2008, a case study of the Gupton Farm, also known as the Borrow Area, is an area of interest. As the spilled coal ash was removed, the underlying soil and rock material was transported to the Borrow Area for storage. It was then contoured into various, large man-made slopes. An existing natural slope that covers 8 acres in the Borrow Area is also an area of interest in comparison of erosion characteristics within man-made slopes. The main purpose of this research is to evaluate the future stability of man-made versus existing natural slopes under the influence of weathering processes. TVA had issues with the man-made slopes eroding too quickly and were forced to keep building new slopes. Three man-made slopes and one existing natural slope were selected for the investigation, which satisfy the following criteria: field work accessibility, different ages (2, 5, 7 and 131 years), similar geotechnical and groundwater conditions and land cover (vegetation with 35% coverage). Different analyses were used to approach the main purpose to determine why the selected man-made slopes were eroding faster than the natural slope. The final conclusion is drawn that due to the amount of precipitation that the Borrow Area receives, runoff and erosion is increased on the man-made slopes due to a higher than normal bulk density. The engineering properties of the slope caused problems due to soil compaction being to tight, causing the erosion rate to be drastically higher than the natural slope. Although there were small amounts of vegetation covering the man-made slopes, the amount of erosion caused the plant cover to decrease over time. The main issue and underlying reason why TVA had to keep building new man-made slopes is because man cannot perfectly replicate a natural slope and there will always be higher levels of erosion and runoff occurring.