Fragility Analysis of a Concrete Gravity Dam Embedded in Rock and Its System Response Curve Computed by the Analytical Program GDLAD_Foundation

This research report describes the engineering formulation and corresponding software developed for expressing the computed stability results for an idealized two-dimensional cross-section of a non-overflow concrete gravity dam embedded in rock in terms of a fragility curve for a potential sliding mode of failure. Within the Corps, the term system response curve is being used to describe what is commonly referred to in the technical literature as the fragility curve; used for the hydrologic fragility assessment of concrete gravity dams embedded in rock. This report uses this Corps terminology. Uncertainty in strength, rock joint parameters that impact the flow of water within the rock joints, silt induced earth pressure and (post-tensioned) anchor force(s) are accounted for in a multivariate probabilistic stability analysis resulting in the computation of a system response curve. The PC software package GDLAD_Foundation (Gravity Dam Layout And Design) is used in this R&D effort to perform the computations and construct the system response curve. A sliding stability assessment of a non-overflow gravity dam embedded in rock requires the assignment of uplift water pressure forces acting on the driving, structural and resisting wedges. Incorporated within the GDLAD_Foundation software package is the program Joint_FLOW that is used to assess laminar fluid flow within rock joints, fissure and/or faults contained within the rock foundation. Results from the analysis of steady state laminar seepage within the joints provides for the calculation of uplift water pressures along the joints. Resultant uplift forces are then computed from the distribution of water pressures along these rock joints. The resulting engineering methodology and corresponding software is applicable to a two dimensional model of a non-overflow (concrete) gravity dam founded within rock. GDLAD_Foundation is also capable of performing a deterministic steady state seepage analysis of laminar flow. The original document contains color images.