Steve O’Brien, Christopher Dann, Gavan Hunter, Mike Schwermer
One of the principal geotechnical issues identified for the Hinze Dam Stage 3 project was the potential for internal erosion and piping within the extremely complex geology at the right abutment. A plastic concrete cut-off wall was selected as the best solution to reduce the risk of piping to acceptable levels and careful planning of this work was required to manage a range of key project risks that included complex technical challenges, potential risks to dam safety, the environment, the surrounding community as well as delivering the works on a tight construction schedule to an agreed budget value. Construction of the 220m long and up to 53m deep cut-off wall, the largest wall of this type constructed to date within Australia, was undertaken by Bauer Foundations Australia and completed in January 2009. A major key to the success of the project was the planning and risk reduction measures that were undertaken during both the design and construction phases, a summary of which is presented in this paper.
Keywords: Cutoff Wall, Plastic Concrete, Hinze Dam.
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Many earthen dams and embankments throughout the world are in need of remediation to address seepage or other issues and ensure structural integrity. Borehole drilling plays a vital role in facilitating implementation of remedial designs, both in the initial information gathering stage and the actual construction of a chosen remedy.
Within the past six to eight years Sonic drilling has become recognized within the geotechnical community as a viable method to meet overall project objectives and address site specific issues for a variety of projects. Key aspects of Sonics include: the ability to efficiently penetrate difficult subsurface conditions, provide a continuous core sample of unmatched quality, and minimize or eliminate risk to the structure from the drilling process. This paper focuses on the application of Sonic in support of a remedial effort at Wolf Creek Dam, including information on the background and overall objectives of the project, a brief explanation of the Sonic method, the scope of services required at the site, and the specific reasons for utilizing Sonic in this case.
Keywords: sonic drilling, grout curtain, Wolf Creek Dam, dam remediation
Tariq I.H. Rahiman, Amanda Barrett, Greg Dryden, Mike Marley, Cecile Coll
In this study we present the engineering geology of complex Late Carboniferous to Early Permian silicic volcanic rocks underlying the Connors River dam site located on the Connors River, at Adopted Middle Thread Distance (AMTD) 97.7 km. The initial investigation of the site by SMEC in 1976 characterised the bedrock as simple laterally continuous layers of rhyolite and pyroclastic rocks. Engaged by SunWater Limited since October 2007, Golder Associates have utilised a range of modern investigative techniques to reveal a more intricate bedrock geological model.
Geological mapping, targeted vertical and angle geotechnical drilling and trenching reveal that the dam site foundation consists of complexly laid felsic crystalline volcanic flow deposits, volcaniclastic (pyroclastic) deposits, and mafic intrusives. Petrographical tests depict a broad range of rock types that includes rhyolite, rhyodacite, dacite, basalt, volcanic breccia, lapilli tuff and tuff. Surface structural mapping and downhole acoustic televiewer profiling reveal that defects of varying orientations have developed in the rocks mainly as a result of tectonism. The rock defects are predominantly open joints and faults, and minor bedding, flow bands, decomposed seams and veins. The permeability of the bedrock, which appears to be primarily controlled by rock defects, was assessed using the results of Lugeon tests.
Rock stratigraphy, mineralogy and texture combined with high resolution seismic tomographic imaging were used to delineate three main engineering rock units. Unit 1, the oldest, occurs on the right abutment and consists mainly of slightly weathered to fresh, high to very high strength dacites and rhyodacites. Unit 2 occupies the central area of the dam foundation and overlies Unit 1. It comprises weakly bedded, slightly weathered to fresh, high to very high strength volcaniclastic rocks. Unit 3, consisting of variably weathered, high to very high strength flow banded and autobrecciated rhyolite, is the youngest unit and it overlies and partially intrudes Unit 2. All three rock units are intruded by slightly weathered to fresh and very high strength basalt, either as dykes or sills. The rock mass properties of the rock units were evaluated based on rock strength tests and the geological strength index (GSI).
Keywords: engineering geology, dam foundation, volcanic rocks, Connors River, dam site
Alice Lecocq, David Brett, Mike Rankin
Tailings Dams class amongst the world’s largest man made structures. They are interactive structures that evolve over time, with tailings discharge, water management, embankment raising and finally closure and abandonment. Understanding of the design, the impact of operations and regular, committed surveillance is essential to ensure the safety and performance of a tailings dam. Dam Safety Management Plans should be developed to optimise these parameters. These plans should include Operation, Maintenance and Surveillance (OMS) manuals, emergency response plans and monitoring databases. They should be managed by the mine management and implemented by the operations personnel.
The tailings dam operators are the key to a successful dam safety management program. It is imperative that the tailings dam management and operators appreciate the risks inherent with the facility, their role and their responsibilities. They also need to have an appropriate understanding of the tailings dam design features, failure modes and safety triggers. With training it is expected that personnel will be better able to recognise and act on safety issues arising.
The paper presents case histories of tailings dam failures due to poor operation and management and outlines the operational requirements and risks inherent with tailings dams. The paper discusses the training approach and criteria to be adopted, and describes a training course developed by the authors for mine management and operators. The paper examines the feedback collected from the courses held at several mines. A model to successfully implement a surveillance program with the involvement and leadership of the operators is proposed.
Keywords: TSF failures, surveillance program, OMS manuals, training of personnel.
Chi Fai Wan, Tom Haid, Jim McClain, Kelly Rodgers
The dams market in California is alive again with phenomenal growth driven by an increasing need for storage to hedge against ongoing water scarcity due to climate change and a growing demand for reliable water supplies driven by population and economic needs. To meet the region’s water supply needs the San Diego County Water Authority has launched the Emergency Storage Project (ESP), an extensive program to create a system of reservoirs, interconnected pipelines and pumping stations to provide more flexibility for water deliveries to the San Diego region, especially in the event of an emergency, such as a devastating earthquake. The Water Authority has planned for water needs in an extended drought by creating the Carryover Storage Project (CSP), which provides additional storage to capture water in wet periods for use in dry periods.
Up to 90 percent of the region’s water supply is imported by pipelines travelling hundreds of kilometres across earthquake fault lines from Northern California and the Colorado River. The major component of the fourth and final phase of the ESP is the San Vicente Dam Raise. The project includes raising the existing dam by 35 m to increase the reservoir and provide an additional 187 million m3 of water storage for the region. This will be the largest dam raise in the United States and the largest roller compacted concrete dam raise in the world. The Water Authority has contracted with Parsons/Black & Veatch Joint Venture to provide construction management services for this vital project. The dam raise is another one of the marquee water supply dams and reservoir projects that the Joint Venture members have been involved in Southern California, after successful completion of the Diamond Valley Lake for the Metropolitan Water District of Southern California and the Olivenhain Dam for Water Authority.
This paper presents a brief description of the San Vicente Dam Raise, the underlying water shortage and the emergency backup needs, and the need for carryover storage. The dam raise design has been previously presented in numerous papers and publications. Therefore, following an overview and general project description, this paper focuses on the critical role that effective construction management plays in implementation of a dam construction project of this size and complexity. Key construction management activities that are discussed in the paper include engineering design constructability reviews, independent cost estimation and scheduling, on-site laboratory management and quality control, and contractor oversight. The construction manager will be involved in this project through final design and construction over a five-year period.
Keywords: Water Scarcity, San Diego County Water Authority, Emergency Storage Project, San Vicente Dam Raise, Roller-Compacted-Concrete (RCC), Construction Management, Climate Change.
Robert Kingsland, Glen Burton
The management and closure of tailings dams can present mines with a trailing liability potentially extending well beyond the life of the mine. The dilemma faced by mine operators is that a tailings storage facility (TSF) is usually required to be in service up until the last product is mined and processed, but the stored tailings may be too weak to support the capping of those facilities for some years after the last tailings deposition. This paper presents the authors’ experience in the geotechnical characterisation of tailings and failure mode analysis required for tailings dams cover design, with particular reference to coal mines in the Hunter Valley. Techniques for field and laboratory determination of strength and consolidation parameters are presented. Failure modes for capping cover and displacement cover alternatives are discussed. Alternative cover techniques including strategies for improving and/or accelerating tailings strength gain are also discussed. Finally, areas needing further study are noted.
Keywords: tailings storage facilities, tailings dams, closure, capping, cover design.