Dam | EPFL Graph Search

A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability. Hydropower is often used in conjunction with dams to generate electricity. A dam can also be used to collect or store water which can be evenly distributed between locations. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or prevent water flow into specific land regions. The word dam can be traced back to Middle English, and before that, from Middle Dutch, as seen in the names of many old cities, such as Amsterdam and Rotterdam. Ancient dams were built in Mesopotamia and the Middle East for water control. The earliest known dam is the Jawa Dam in Jordan, dating to 3,000 BC. Egyptians also built dams, such as Sa

Mechanics of alkali-silica reaction in concrete across scales

Emil Gallyamov

Alkali-silica reaction occurs in concrete between the alkalis contained in the pore solution and silica in the aggregates. Generation of ASR products gives rise to the internal pressures that cause expansion and cracking. Due to its deleterious effect on concrete, ASR poses a major threat to the safety and operability of the concrete infrastructure worldwide.Recent experimental advances obtained in the scope of the multi-disciplinary Sinergia project entitled ``Alkali-silica reaction in concrete'' of Swiss research institutes shed new light on ASR. Being part of Sinergia, the research conducted in the scope of the present thesis had a goal to fill in the knowledge gap on the ASR mechanics. Therefore, analytical and numerical models facilitated by the novel experimental data have been developed.One of the Sinergia experimental studies showed that the initial ASR products accumulate between the crystal grains of aggregates. We are using this knowledge together with an estimate of the volumetric increase of a typical ASR product to evaluate the crack-growing potential of a single region filled with ASR products. This is done by employing a semi-analytical model of an expanding inclusion of nanometre-size encircled by a disk-shaped crack. The role of the expansion value and the inclusion's size and shape on the resulting crack length is investigated. The analytical findings are confirmed by a finite element model.Another experimental Sinergia study produced a time-series of X-ray tomograms of the ASR-affected concrete, which resolved the evolution of the deformation field, the crack growth and the accumulation of ASR products. This unique set of data is used in the current thesis to study the growth of ASR-crack networks and their role in the macroscopic behaviour of concrete. A novel cohesive elements-based meso-scale model capable of predicting the stable growth of numerous cracks is developed. Several hypotheses on the ASR-loading and cracking mechanismsare proposed and tested by including them in the model. Statistical comparison of the numerical and experimental crack networks provide new insights into ASR-cracking physics.The continuous-damage approach is adopted to improve the efficiency and stability of the meso-scale model. The physics of the model is enriched by accounting for the orthotropic behaviour of damaged elements and the self-contact in cracks. This development allows reproduction of the macroscopic expansion of the concrete samples under substantial uniaxial load, which was not feasible by the earlier isotropic-damage models. Moreover, the role of creep on the ASR in concrete is investigated by combining viscoelasticity with strain-softening.The last subject treated in this thesis is the macroscopic behaviour of ASR-affected structures. A computational multi-scale model of concrete is developed, validated and used to investigate the long-term behaviour of a real ASR-affected dam. The latter was facilitated by the availability of actual field measurements. This approach combines the meso-scale model with the orthotropic damage and the macro-scale model of the dam. The model allows us to relate the macroscopic expansion of concrete to its state at the meso-scale, which comprises the crack network, its openings and orientations, and expansions of individual ASR sites. Coupling of the mechanical model with the transient heat analysis permits to evaluate the role of temperature variations on the ASR expansion.

EPFL2022

Sulfide oxidation and acid mine drainage formation within two active tailings impoundments in the Golden Quadrangle of the Apuseni Mountains, Romania

Linda Frei

Sulfidic mine tailings have to be classified as one of the major source of hazardous materials leading to water contamination. This study highlights the processes leading to sulfide oxidation and acid mine drainage (AMD) formation in the active stage of two tailings impoundments located in the southern part of the Apuseni Mountains, in Romania, a well-known region for its long-term gold-silver and metal mining activity. Sampling was undertaken when both impoundments were still in operation in order to assess their actual stage of oxidation and long-term behavior in terms of the potential for acid mine drainage generation. Both tailings have high potential for AMD formation (2.5 and 3.7 wt.% of pyrite equivalent, respectively) with lesser amount of carbonates (5.6 and 3.6 wt.% of calcite equivalent) as neutralization potential (ABA = -55.6 and -85.1 tCaCO(3)/1000 t) and showed clear signs of sulfide oxidation yet during operation. Sequential extraction results indicate a stronger enrichment and mobility of elements in the oxidized tailings: Fe as Fe(III)oxy-hydroxides and oxides (transformation from sulfide minerals, leaching in oxidation zone), Ca mainly in water soluble and exchangeable form where gypsum and calcite are dissolved and higher mobility of Cu for Ribita and Pb for Mialu. Two processes leading to the formation of mine drainage at this stage could be highlighted (1) a neutral Fe(II) plume forming in the impoundment with ferrihydrite precipitation at its outcrop and (2) acid mine drainage seeping in the unsaturated zone of the active dam, leading to the formation of schwertmannite at its outcrop. (C) 2011 Elsevier B.V. All rights reserved.

2011

Effects of deep pools on salinization in coastal reservoirs

David Andrew Barry, Jing Xu

Coastal reservoir contributes to alleviating the freshwater shortage in stressed areas, and the salinization of reservoir water is one of the most important challenges that coastal reservoir faced. Field-investigation indicates that there are many deep pools located at reservoir bed, and a large amount of high-salinity water was found within a deep pool which was hardly be desalted. Laboratory experiments and numerical simulations with different depth and locations of deep pools were conducted to further discuss the influence of deep pool on the salinization of reservoir and adjacent aquifer. Results showed that deep pool has greatly increased the salinity of reservoir water due to high-salinity water stored in the deep pool, which may act as an extra source of saltwater to the coastal reservoir during the dry season. The increasing depth of the deep pool was found to have negative impacts on the salinity of reservoir water, and as the distance from the deep pools to dam increased, the salinization extent in coastal reservoir decreased. Salinity data from the numerical simulations in coastal reservoirs and adjacent aquifer were matched the experimental data well. Flow field indicates that there is a high exchange capacity zone occurred from the deep pool to the seaward boundary, which gave the reasonable reasons for the existence of high-salinity water within deep pools. Those findings highlight the significant influence of deep pool on the salinization of the coastal reservoir, and explain the increased salinization by the deep pool.

2019

Mechanics of alkali-silica reaction in concrete across scales

Emil Gallyamov

EPFL2022