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Assessment of internal erosion in the glacial till core of a Swedish dam
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.ORCID iD: 0000-0002-5719-3056
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.ORCID iD: 0000-0002-8564-4360
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.ORCID iD: 0000-0001-8739-2219
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.ORCID iD: 0000-0003-1935-1743
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Zoned embankment dams are a common type of dam in Sweden consisting of an impermeable central glacial till core flanked by zones of filter materials and rockfill shoulders. Dams with internal unstable core material allow fine particles to be transported by seepage, which may result in leakage paths and pore-pressure variations. These last two conditions are signs of initiated internal erosion. However, the effectiveness of the filter zone determines if the internal erosion will continue or not. This paper presents the assessment of internal erosion susceptibility of the glacial till core of a hydropower dam located in northern Sweden. The dam has experienced historical damages mainly in the form of sinkhole and leakage related to internal erosion. The study includes the analysis of the particle size distribution of samples obtained from boreholes, as well as a comparison of the geotechnical properties of the core with the Swedish dam safety guidelines available both during the dam construction in 1958 and today. The capability of the filter to stop the erosion process is not investigated.The results show that a well designed and constructed dams can be affected by local layers of internally unstable (suffusive) material susceptible to internal erosion.

The capability of the filter to stop the erosion process is not investigated.The results show that a well-designed and constructed dams can be affected by local layers of internally unstable (suffusive) material susceptible to internal erosion.

Place, publisher, year, edition, pages
2017.
Keywords [en]
internal erosion, glacial till, suffusion, filter, core, dam, embankment dams, Swedish dam, sinkhole, RIDAS, Vattenfall 1958, dam safety, internal instability, erosion, silty sandy gravel, moraine
Keywords [es]
erosion interna, presas, presas de tierra, núcleo, filtro, grava arenosa limosa, internamente inestable
National Category
Geotechnical Engineering Other Civil Engineering
Research subject
Soil Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-65289OAI: oai:DiVA.org:ltu-65289DiVA, id: diva2:1135680
Conference
85th Annual Meeting of International Commission on Large Dams (ICOLD 2017), Prague, Czech Republic, July 3–7, 2017
Available from: 2017-08-23 Created: 2017-08-23 Last updated: 2019-03-19Bibliographically approved
In thesis
1. Suffusion of Glacial Till Dam Cores: An Experimental Investigation
Open this publication in new window or tab >>Suffusion of Glacial Till Dam Cores: An Experimental Investigation
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Suffusion, also called internal instability, is an internal erosion mechanism that occurs in embankment dams when fine-grained particles are washed out of the core soil matrix by seepage. Initiation of internal erosion depends mainly on three major factors: grain size distribution of the soil, stress conditions and hydraulic load; whilst its continuation depends of the filter properties. Broadly graded moraines, as glacial tills, are more susceptible to internal erosion by suffusion than other types of soils used in dams.

Most embankment dams in Sweden consist of a central core of glacial till built more than 50 years ago. At the time of its construction, the available guidelines did not include specific grain size boundaries for the core and the filter related to internal erosion susceptibility. Today, several Swedish embankment dams have experienced incident of internal erosion such as leakages and sinkholes, making internal erosion an important safety issue. This circumstance allows raising the questions: How safe are the Swedish embankment dams and what conditions are needed for internal erosion by suffusion to initiate?

This research aims to contribute to the assessment of dam safety by giving inputs regarding the characterization of internal erosion by suffusion and the relation among the main factors involved on its occurrence (geotechnical characteristics of soil material, degree of compaction and hydraulic load). This in order to increase the knowledge regarding the critical hydraulic gradient needed to develop suffusion in a given till material with a known degree of compaction.

The research includes a laboratory program consistent on suffusion tests, which is an extension of the standard permeability test, and considers post-test examination and diagnosis of the samples. Two main groups of tests were performed: small and large suffusion tests. The small tests serve as a reference of the expected behaviour of soil samples under different boundary and test conditions, which allows optimizing the number of test to be performed in large tests.

Results show that suffusion mechanism can be classified as internal suffusion (or filtration) and external suffusion (loss of soil particles from the soil matrix). The influence of compaction degree on the initiation of suffusion is limited in internally stable soils. However, poorly compacted specimens exposed to high hydraulic gradients could develop both internal and external suffusion if the filter is not capable to retain the eroded particles. The hydraulic conductivity of specimens with internal suffusion tends to decrease with a step wise increase of the hydraulic gradient. Such tendency is the result of the matrix of soil reaching equilibrium with the new seepage stresses. The hydraulic conductivity of specimens with external suffusion tends to increase with the increase of the hydraulic gradient.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019. p. 85
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Geotechnical Engineering
Research subject
Soil Mechanics
Identifiers
urn:nbn:se:ltu:diva-71964 (URN)978-91-7790-280-5 (ISBN)978-91-7790-281-2 (ISBN)
Presentation
2019-03-29, F1031, Luleå University of Technology, Luleå, 13:00 (English)
Opponent
Supervisors
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-03-19Bibliographically approved

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Silva et al. (2017)_ ICOLD 2017(1020 kB)113 downloads
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Silva, IngridLindblom, JennyViklander, PeterLaue, Jan

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