The U.S. Army Corps of Engineers (USACE) has a robust Dam Safety Program (DSP) that utilizes risk- informed decision-making to prioritize its portfolio of dams in need of further study and modifications. USACE also utilizes a two-tiered governance structure in which one body makes portfolio recommendations around risk management while the other body oversees the execution of the agency’s routine DSP and makes policy recommendations. The routine program consists of the activities required for interim risk reduction measures, inspections, instrumentation, monitoring, assessments, operations and maintenance, emergency action planning, training, and other dam safety activities. An internal program management tool exists to monitor and track all these activities and generate metrics around execution of the routine DSP, however, it does not include metrics around other aspects of the DSP like governance, asset management, public safety and security, flow controls, or audits/reviews. USACE hopes to identify gaps in its DSP that can be used to correct shortcomings, continuously improve, and to increase the resilience of its DSP, which will enable each project to deliver benefits to the Nation. The Centre for Energy Advancement through Technological Innovation (CEATI), through its Dam Safety Interest Group (DSIG), collaboratively developed a spreadsheet tool known as the Dam Safety Maturity Matrix (DSMM). The DSMM is a facilitated exercise used to help evaluate how well-developed a program is across 12 elements considered to be typical and important of most dam safety programs. Each of the elements is then deaggregated into sub-elements, each of which can be evaluated by the team. The maturity ranges across 5 levels from Needing Improvement to Leading Edge. After all sub-elements are evaluated, an aggregate maturity level is computed that gives an estimation of the overall maturity level of the program. USACE will present the results of its pilot project using the DSMM and share lessons learned regarding its implementation. The short-term goal is to identify program strengths and areas for improvement, while the long-term goal of USACE using the DSMM is to participate in bench- marking across multiple agencies and international dam owners regarding their dam safety programs, for which has never been done to the knowledge of this author.
Identification of people impacted by a hypothetical dam-break flood is required to understand the potential hazard a dam poses to downstream communities. The New Zealand Dam Safety Guidelines and the Australian Consequence Categories for Dams define these people collectively as the “Population at Risk” (PAR) and recommend that evaluation of PAR should include both permanent and temporary populations. However, there is limited guidance on specific methods to determine these populations. This paper provides an outline of an evidence-based, repeatable method to determine the PAR (both permanent and temporary) within a dam-break flood inundation zone. The method is intended to provide guidance for people tasked with estimating PAR in accordance with the New Zealand Dam Safety Guidelines. The methodology provides a current practice framework for users to apply and estimate the PAR in a clear and defendable manner.
The Keepit Dam Safety Upgrade Project is being implemented to bring the 54m high concrete gravity dam in line with current guidelines for flood and earthquake loading. Stage 2A of the project involves the installation of two vertical 91 strand post-tensioned anchors on each monolith of the spillway section.
During coring of the anchor head blocks for the vertical anchors, deep cracks were observed across some monoliths, dipping diagonally in an upstream direction. In two of the monoliths the cracks were found to be continuous enough to possibly daylight at the upstream face and form freestanding blocks. If the freestanding blocks postulate is correct, the block stability could be currently relying on the friction of the cracked surface and on the engagement with shear keys of adjacent monoliths, which are provided in the vertical contraction joints.
This paper will explain the complex 3-D nonlinear Finite Element Analysis (FEA) conducted to replicate the conditions of the cracked spillway monoliths during the post-tensioned anchor installation. The nonlinearity captured the expected opening, closing and sliding of the crack, as well as its potential pressurisation, and the residual shear strength retention due to asperities of the crack surface. For the shear keys of the vertical contraction joints, the nonlinearity captured the force-deformation relationship of the plain concrete, up to a brittle failure condition if the shear strength threshold was reached.
The 3-D nonlinear FEA was also used to design the optimum number of Macalloy post-tensioned bars required to stitch the freestanding block to the monolith, so that the vertical anchors can be safely installed. In addition, the remedial design accounted for future extreme design flood and extreme earthquake loading conditions, the latter modelled with a time-history analysis.
Many dams have low level outlets, most of them put in place as diversion structures during construction. However, once dam construction is complete and reservoir filling begins, the reality is that low level outlets are used very infrequently, and sometimes not at all.
This paper will discuss the merits of decommissioning low level outlets vs maintaining them as operational dam safety critical equipment. In this context the paper will examine the criticality of low level outlets in relation to the type of dam, the Potential Impact Category of the dam, the ratio between outlet capacity and mean reservoir inflows, possible resource consent issues and required maintenance and testing regimes.
Trustpower’s dam portfolio consists of a variety of dam types with multiple different types of low level outlets. Case studies from the portfolio will be used as arguments for maintaining or decommissioning the low level outlets in order to develop evaluation criteria for low level outlets and provide a basis for how to treat them from a wider dam safety perspective.
As part of the development of some dams and hydroelectric power schemes, deep infrastructure is often required which requires and understanding of the in situ stresses of the rock mass. Recent works completed in southern Australia and Europe have led to improved methodologies for conducting effective, reliable, and repeatable measurements of in situ strain and/or deformation, as well as the subsequent estimation of in situ stress.
In situ stress testing is generally an item that is specified as part of a geotechnical investigation, however it is not commonly well understood in terms of reliability, repeatability, or, in fact, what the result actually means and its implications to project design. Commonly, a handful of tests are completed, with variable results, which often generates more confusion than answers.
This paper provides a discussion of recent in situ stress testing completed for two deep Australian projects. It summarises the aim of the investigations, test selection process, laboratory testing, data review and model development. This is to illustrate how complex the estimation of in situ stress can be and some of the pitfalls that may be avoided whilst acquiring and assessing the data. It also examines several different testing methods available in the Australian and International industry and some of the analysis techniques available to dam and tunnel projects. Finally, the paper provides an update on topical developments provided at recent workshops in Europe.
Many numerical simulations have tried to model the failure-induced displacements of earth structures due to liquefaction. In this paper, the challenges in modelling such as the large displacement and non-immediate failure of earth structures due to liquefaction are discussed. An advanced bounding surface plasticity model is used to simulate the dynamic behaviour of saturated porous media. A series of benchmark welldocumented seismic events are analysed, and the results are compared to the reported laboratory and field observations. These analyses consist of one centrifuge test on liquefiable sand (Model #12 of the VELACS project) and one earthfill dam (Lower San Fernando Dam in California) subjected to seismic loading that leads to liquefaction. The capability of the model to capture the flow failure due to liquefaction is demonstrated and results are compared with other attempts in the literature to capture similar responses.