2015 – Seismic Analysis of a Concrete Dam with a Complex Configuration: Nonlinear, Time History of Mt Bold Dam

Michael McKay and Francisco Lopez

Mt Bold Dam impounds the largest reservoir in South Australia. The dam wall comprises 19 concrete monoliths, 11 forming a central arch section and 8 forming gravity sections on the left and right abutments. The upstream face of the arch section is vertical, but the top portion overhangs on the reservoir side. The dam was originally constructed in the 1930s, and was raised by 4.3 m in the 1960s. In this upgrade the gravity abutments were raised using mass concrete blocks and the arch non-overflow crest was raised with hollow, reinforced concrete portals. On the spillway section a pier and gate system was installed on top of a hollow ogee section. The maximum height of the dam in its current configuration is 58 m.
GHD has been conducting a staged safety review of Mt Bold Dam since 2011. This included a detailed finite element nonlinear, time-history seismic analysis of the dam-foundation-reservoir system. The analysis was carried out using finite element techniques and included a detailed 3D model of all major components of the dam and different domains of the foundation rock. The nonlinearity of the model was included by explicitly incorporating contact elements at the dam-foundation interface, at the monolith contraction joints, and at some identified unbonded horizontal concrete lift joints within the dam wall. The seismic analysis was conducted for three different accelerograms corresponding to Maximum Design Earthquakes (MDEs) with 1 in 10,000 Annual Exceedance Probability (AEP).
This paper explains the purpose of the study, the adopted methodology and material properties, the results of the modelling phases, and the anticipated seismic behaviour and damage on the main components of the dam resulting from the MDEs. Finally, a conclusion is made in regards to whether or not Mt Bold Dam passes the adopted performance criteria for seismic loading.
Keywords: Arch, gravity, seismic, nonlinear, damage prediction.

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