Upstream construction methodology has been used to raise tailings dams in Western Australia (WA) for more than three decades, and the tailings storage facilities (TSFs) built in this manner have performed satisfactorily so far. The maximum design earthquake (MDE) for most of the existing, upstream-raised TSFs in WA was that corresponding to a 1-in-1,000 year annual exceedance probability (1:1,000 AEP). However, the recommended MDE loading for the High/Extreme Failure Consequence Category in the 2012 ANCOLD Guidelines on Tailings Dams is that of a 1:10,000 AEP. This more stringent seismic design criterion may restrict the use of upstream TSF construction in some areas of WA and Australia in general.
To evaluate the viability of upstream construction for a new or existing TSF, the effects of the earthquake design ground motion (EDGM) on the liquefaction and deformation response of the structure must be understood. The results of such analyses are an essential component in determining whether upstream raising will be feasible, or whether more robust but much more costly centreline or downstream construction methods are required.
A parametric study was completed to investigate the liquefaction and deformation behaviour of a typical, upstream-raised tailings dam under different earthquake design ground motions with different response spectra. The study utilized two-dimensional finite difference code FLAC2D effective stress dynamic analysis, in which the UBCSAND constitutive soil model was incorporated. Twenty-eight earthquake ground motions (matched and unmatched to the target response spectrum) were used in the study and the liquefaction response of the tailings dam model under those ground motions was analysed.
The results of the study demonstrate the importance of appropriate ground motion and response spectrum selection in assessing the seismic performance of an upstream-raised TSF. Liquefaction response was shown to vary with different response spectra, even though the corresponding EDGMs had similar peak ground acceleration (PGA) values. The importance of earthquake frequency content and duration, which in turn are affected by earthquake magnitude, distance and ground motion response, is emphasized. Scaling and matching the earthquake input motion to the uniform hazard response spectrum (UHRS) may result in overly-conservative design. Thus, selection of the most representative EDGM is essential to evaluating expected seismic performance for an upstream-raised TSF, and scaling or matching the earthquake input motions must be done cautiously.
— OR —
Now showing 1-12 of 36 2977:
Tim McMorran and Alan Hull
Accurate assessment of potential fault rupture hazard in dam sites is a critical factor in managing dam safety. Assessment of the location and activity of a surface fault within or near an existing or proposed dam can be technically challenging, expensive and affect design and construction schedules.
Three examples from regions of relatively high, moderate and low tectonic activity are used to illustrate that fault rupture hazard assessment is generally feasible in regions with high rates of tectonic activity, historic earthquake occurrence and the presence of Quaternary and Holocene-age landforms and sediments. In regions with relatively low rates of tectonic activity and landscape development, the fault rupture hazard assessment is more challenging.
The examples illustrate that robust geologic and geomorphic analysis provides critical information on the fault rupture hazard at existing and proposed dams. These analyses assist dam owners to obtain a more complete understanding of the fault rupture hazard at their facility, and support their longer term risk assessments.
Nicole Anderson and Nihal Vitharana
A large number of aging concrete dams in Australia may not meet the requirements of modern dam safety practices. In addition, there is an ever-increasing demand for the supply of water. Continuous concrete buttressing is a method of strengthening existing dams which allows the dam to be raised to augment the storage capacity at an incremental cost.
This paper explores the key design considerations involved in concrete-buttressing existing concrete gravity dams. Critical aspects considered include storage level during construction, interface drainage, interface shear transfer, the relative strength of existing and new concrete and the behaviour during the heating and cooling phases of the heat-of-hydration. The discussions will be of relevance to asset owners and water authorities faced with upgrading existing dams in a time where there is an increasing demand for security of supply of water resources.
M.G. Webby and N.D. Sutherland
Repairs to the floor slab of the outlet transition section of the Pukaki Canal Inlet Structure in November 2009 were likely to have adversely affected the hydraulic jump behaviour in the transition section of the structure and therefore necessitated revision of the safe operating limits for the structure. Three separate series of flow trials were carried out at different lake levels over a period of about a year to carefully observe the behaviour of the hydraulic jump under a variety of gate operating configurations and discharges. New safe limits of operation for the structure were defined for the structure using the flow observations from the flow trials and the framework of analytical models for different types of hydraulic jump. The revised limits of safe operation were successfully implemented in 2013.
Bertrand Rochecouste Collet, Dawid van Wyk and Emmanuel Adanu
The preliminary design of the Kashimbila Multipurpose Dam on the Katsina-Ala River in the Taraba State, Nigeria was initially focussed solely on it functioning as a buffer dam in the case of failure of the natural embankment of Lake Nyos in Cameroon. The failure of Lake Nyos could generate an extreme flood endangering the population in south-eastern Nigeria. As the design process progressed with a more holistic and multipurpose approach, the capacity of the dam was increased to provide irrigation and potable water to the surrounding towns and villages, as well as the generation of hydropower. The dam is a composite structure consisting of a mass concrete gravity uncontrolled spillway, a clay-core rockfill embankment, a 40 MW hydropower station and an outlet works with twin 1.4 m diameter pipes feeding the irrigation pumpstation and water treatment works. This paper covers the design considerations of the Kashimbila Multipurpose Dam and Hydropower Station, with particular emphasis on hydrological challenges and related design solutions.
Kinchant Dam is a zoned earth and rockfill embankment situated on the north branch of Sandy Creek, approximately 30 km southwest of Mackay in central Queensland. Kinchant Dam was constructed in stages. The ‘Initial Development Stage’ which consisted of an embankment length of approximately 3.3 km and full supply level (FSL) of EL 49.21 m AHD was completed in 1977. Further development completed in 1986 (Stage I) increased the FSL to EL 57.21 m AHD with an embankment length of 5.5 km and a maximum embankment height of 22.3 m. The dam has a storage capacity of 62,800 Ml and a 60 m wide emergency spillway with a fixed crest level of EL 58.21 m AHD, one metre higher than the FSL.
A series of investigations have been carried out since its construction as a consequence of both regulatory safety reviews and observed excessive pore pressures within the foundation that have led to wet patches developing at the toe of the dam. In one area at the toe, pore pressures were such that artesian conditions developed. This paper outlines the history of various stages of construction of the dam, the foundation investigations since construction and the safety review and comprehensive risk assessment process that lead to the upgrade design and construction of remedial works. The remedial works include the extension of the downstream filter material adjacent to the clay core and the provision of additional pressure relief wells at the downstream toe of the dam.