CRACKING CORE GEOMETRY – NUMERICAL MODELING OF EMBANKMENT CRACKING DUE TO UNIQUE GEOMETRY

摘要

Rueter-Hess dam near Denver, Colorado is being constructed in two phases. The first phase is approximately 135 feet high, while phase two includes raising the dam to approximately 195 feet in height with the raise occurring on the downstream side of the dam. The raise requires a unique shape for the embankment core. Cracking of the core of zoned embankment dams due to differential settlement and subsequent filling of the reservoir is not a new phenomenon. Generally the differential settlement is due to irregular foundation materials, however the unique geometry for the core may also lead to differential settlement, and therefore core cracking. When evaluating alternative core geometries for the dam raise, it was necessary to assess the relative likelihood and extent of cracking for each of the alternatives. This paper presents an analysis method using linear-elastic numerical modeling methods, which models hydraulic fracturing, to provide an assessment of the potential for cracking in the core of the zoned embankment dam. First, the numerical model was used to evaluate stresses resulting from differential settlement of the embankment and foundation materials while considering the actual construction sequence. These stresses were then further modified by subsequent reservoir loading without seepage forces. Steady seepage pore pressures were then applied to the model. The extent to which tension zones propagate provided an indication of the extent of possible core cracking. The propagation of tension zones was significantly influenced by the embankment geometry. This numerical modeling technique was applied to several alternative core geometries. Simple changes between the alternative core shapes resulted in a significant reduction in the extent of core cracking potential. The geometry for the core was then selected based on achieving an acceptable width of uncracked core.