AN INTEGRATED STRATEGY FOR SEEPAGE CONTROL FROM BULL RUN DAM # 2 SPILLWAY APPROACH CANAL

摘要

The steady rise in groundwater levels in the central area north of the Bull Run Dam # 2 spillway, and the November 1995 landslide of the slope below indicated that the stability of the area was degrading with time. If left untreated, seepage through the heterogeneous landslide debris could continue to erode and pipe the fine-grained soils, leading to larger erosion channels. To minimize the potential for future landslides in this area, and to identify subsurface conditions and high permeability zones, a comprehensive field exploration program was conducted to evaluate the slide debris north of the approach canal. The main objective of the exploration program was to couple this new information with the historical piezometric readings in order to identify and isolate zones of seepage and to refine preliminary conceptual mitigation options. As a result of the detailed field program, earlier conceptual mitigation options are now being refined to target high seepage areas. A clearer definition of the seepage areas has minimized uncertainties associated with the mitigation measures, resulting in a more cost-effective solution. The recommended option will be part of an integrated approach in long-term seepage control and will be designed with the flexibility for expansion if additional seepage reduction is desired.