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.
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The Waimea Community Dam will be the largest multipurpose concrete face rockfill dam (CFRD) to be constructed in New Zealand. This 53 m high CFRD will impound a reservoir of 13 Mm3 and is essential to securing the future water needs of the community and environment of the Waimea Plains and wider Tasman/Nelson region.
The design of this unique large dam in the New Zealand context was a long-term collaboration of local dam design expertise and international experience that took the ‘historic precedent based design approach’ for CFRD’s and supplemented this with modern embankment design techniques for the highly seismic environment at the dam site. Design of this High Potential Impact Category dam presented a range of technical challenges for the designers and wider project team, which required new and innovative design solutions and approaches.
The dam features a number of unique arrangements in the New Zealand context including:
The project had its origins in the early 2000’s. Detailed design commenced in 2010, and was externally peer reviewed. The detailed design stage was undertaken in an Early Contractor Involvement (ECI) process which was completed in February 2019.
This paper covers the important seismic design aspects for this large dam, including understanding and designing for the potential range of displacements and embankment deformations to inform the crest parapet wall and diversion culvert designs, and understand how differing rockfill properties might affect the dam performance. Quantifying the range of potential dam performance enabled a more resilient dam design.
If a risk-based approach is used to assess the spillway adequacy for large dams, then an estimate of the annual exceedance probability (AEP) of extreme rainfalls is required up to and beyond the Probable Maximum Precipitation (PMP). This paper describes how two site-specific approaches described by Nathan et al. (2015; 2016) were used to estimate the AEP of extreme rainfalls for seven catchments, ranging from 1300 km2 to 114,000 km2, in the northern-coastal region of Australia. The results are then compared with the regionally-based Laurenson and Kuczera (1999) relationship for estimating the AEP of the PMP, which is recommended by the Australian Rainfall and Runoff 2019 guide to flood estimation (Nathan and Weinmann, 2019). This shows that the site-specific assessments have produced a rarer estimate of the AEP of the PMP compared with Laurenson and Kuczera (1999), particularly for the catchments >10,000 km2. For some of these locations, this has allowed the dam owners to plan risk-based upgrades with more confidence.
The purpose of this paper is to document a limited review of the existing concrete chute spillways in the United States Army Corps of Engineers (USACE) portfolio of dams. This internal review was undertaken in response to the partial spillway failure of the Oroville Dam concrete chute spillway in February 2017, the partial spillway failure of the Guajataca Dam concrete chute spillway as a result of Hurricane Maria in September 2017, and to address the request by the United States Congress for USACE, United States Bureau of Reclamation (USBR), and the Federal Energy and Regulatory Commission (FERC) to review their respective portfolios for similar spillway vulnerabilities as Oroville Dam. The intent was to screen for existing concrete chute spillways within the USACE portfolio that may be susceptible to damage/failure during operation.
Earthquake design of a dam and associated appurtenant structures is a key aspect of dam design in the modern era. This paper outlines the design process undertaken to address potential earthquake loading for the 32m high outlet tower to be constructed as part of the new Eurobodalla Southern Storage project on the NSW South Coast. The driver for the project is to provide increased water supply security to communities on the South Coast, an area that is currently serviced by a single reservoir and is subject to frequent water restrictions. Construction is planned to commence for the project in early 2021.
This paper presents the design methodology undertaken to meet the requirements for earthquake design and presents a novel defensive design solution to improve the reliability of the outlet works for post-earthquake operation. The Authors contend that utilising this approach in design of future outlet towers will provide a greater level of confidence in the ability to undertake intervening measures following a severe earthquake. Moreover, the technology has the potential to serve as a relatively inexpensive interim upgrade measure for existing outlet towers expected to sustain an unacceptable degree of damage under earthquake loading.
K.A. Crawford-Flett, J.J.Eldridge, E.T. Bowman, C. Gordon
This paper provides an interpretation of factors governing the manifestation of internal erosion in a New Zealand canal that was constructed during the 1970s. Liner and subgrade soils were sampled during de- watering of Tekapo Canal in 2013, following the surveillance of erosion events over the preceding decades. This paper focuses on the interpretation of erosion susceptibility of liner and subgrade soil gradations sampled at four locations. Of the four locations, Sites 2, 3, and 4 were associated with internal erosion defects. A single location (Site 1) was selected to provide benchmark “intact” (un-eroded) samples.
Interpretation of susceptibility of the widely-graded soils to internal erosion mechanisms was achieved through the application of established empirical techniques for internal stability, filter compatibility, and segregation. Analysis of gradations, which are believed representative of some – but likely not all – canal soils, showed that Sites associated with erosion defects had liner-subgrade interfaces that permitted “some erosion” (NE < D15F < EE), while the Site showing no sign of erosion possessed an interface that met modern filter retention criteria for No Erosion. Based on gradation analysis, internal instability is considered a possibility for subgrade materials in particular. It is possible that subgrade materials that fail No Erosion criteria for liner retention may not represent as-built material and may instead have lost finer fractions in situ due to seepage-induced instability, leaving a coarser-than-placed and filter-incompatible subgrade.
This case study demonstrates the use of gradation-based empirical methods as initial screening tools to assess the susceptibility of soils to internal instability, filter compatibility, and segregation. The relationship between the internal stability of a filter and the filter’s particle retention performance (compatibility) is emphasised. As well as gradation susceptibility, the assessment of other factors such as segregation and hydraulic loads must be considered in order to better-understand susceptibility to erosion mechanisms.