Multiple-arch dam technology enjoyed a certain popularity between the fifties and seventies, but was later discontinued for practical reasons. The multiple-arch dam that is the subject of this paper is especially peculiar since it was built using prefabricated elements and a combination of several pre-stressed steel systems.
This dam consists of 17 buttressed arches with a maximum height of 35 m on a limestone and dolostone foundation. It has a crest length of 531 m and a 15 hm3 reservoir. After 55 years in operation, several apparent degradations have surfaced and a study on the safety of the dam is currently being carried out.
The main concern is the dam’s structural safety, which is apparently linked to the integrity of the post-stressed steel elements and the precast elements in the arches. This paper describes the approach chosen for the remediation study, the visual inspection, and the tests developed on the post-stressed steel and concrete, in order to feed a 3D numerical model of the structure.
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Dams leak! But only some of the leaks require investigation and remediation. When they do, finding the pathway of the leak becomes an expensive and slow process, often characterised by drilling “trial and error” boreholes that further impair the integrity of the structure. A much better alternative is to collect specialised data with highly sensitive instruments along all relevant points, map the data using the latest groundwater geophysics technology or hydrogeophysics technology, create 3D models of the subsurface including the flow path of the leak in question, and finally use software filters and algorithms to predict ongoing effects of the water problem. In this paper three case studies are presented including the Bartley Dam, King George Dam, and the Samanalawewa dam. All of the dams had leaks that concerned the dam owners. The method was applied to determine the location of the seepage paths passing through the dam. Remediation was completed at the Bartley Dam and King George Dam confirming the results from the method. And there are plans for remediation at the Samanalawewa dam. The method saved the clients a significant amount of money because they had a focused remediation. Knowing the dam has been repaired and there are no other leaks provides peace of mind to the dam owners.
An assessment of dam failure consequence for Jandowae Water Supply Dam in South-West Queensland was performed using HEC-LifeSim. The purpose of the assessment was to investigate the applicability of the software to inform decisions on an appropriate regulatory pathway for the dam that reflects the consequences of failure. This paper details the development of the hydrologic and hydraulic models behind the HEC-LifeSim simulations, the assignment of key parameters and their sensitivities, and a comparison of predictions to existing procedures for assessing potential loss of life and populations at risk. The paper reflects upon the level of effort required to develop HEC-LifeSim assessments and the relative benefits gained using this information in the regulatory space.
This paper will explore the differences in pore pressures resulting from saturated and unsaturated seepage (pore pressure) analysis. It will also evaluate some conventional recommendations, such as the inclusion of essential components of the embankment dam and omission of inessential components. In addition, the identification of inessential components will be discussed.
Finally, pore pressures obtained from these analyses will be compared to monitoring data in order to identify the most appropriate seepage (pore pressure) model.
In conclusion, advantages and disadvantages of each method will be discussed and recommendations will be provided in order to gain the most appropriate results.
The results of this paper can be used for designing new embankment dams or safety reviews of existing dams, particularly when there is lack of reliable monitoring data.
Two tailings storage cells were raised by constructing new embankments upstream of the existing
embankment walls. The performance of the new embankments was mainly dictated by the underlying tailings that consisted of a thick layer of very soft to soft fine tailings. The fine tailings in one cell was capped by a layer of sand for more than 30 years hence the tailings had mostly consolidated under the load of the capping. The fine tailings in the other cell was under consolidated because the cell had only been capped for about 18 months before the construction of the new embankment. The capping material was sand extracted from the tailings.
Stratification of the tailings was determined by CPT. Undisturbed samples of fine tailings were obtained by a piston sampler for CIU and oedometer testing to obtain parameters required for advanced soil models SHANSEP and Soft Soil (SS) models. These models were incorporated in full 2-D FE models to analyse the stability and settlement of the new embankments at various locations.
The application of advanced soil models such as SHANSEP and Soft Soil by hand calculation and
conventional slope stability analysis is considered cumbersome and labour intensive. This paper
demonstrates that with the help of FE software (PLAXIS in this case), it is practical to implement such advanced soil models to simulate the behaviours of soft fine tailings with reasonable accuracy. A similar approach could be used to model other fine tailings and soft clays. One should be reminded that the reliability of any analysis method relies on validation of the analysis model and parameters adopted.
Physical modelling of dam structures remains a preferred method for validating and improving dam designs. Flow behaviour in the approach and over the crest of a dam can be accurately studied with traditional methods such as pressure transducers, piezometers and current meters due to the relatively smooth and steady flow conditions. However, characterising flows within a stilling basin is far more difficult due to the complex, aerated and highly turbulent flow conditions. Recent work on detailed measurement of hydraulic jumps using a line-scanning Lidar was adapted for measurement of stilling basin surface profiles in a 1:50 scale model of Somerset Dam, QLD. Lidar was shown to be an effective and efficient tool for providing assessment of the toe jump, boil and flow into the downstream channel.