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  • 1.
    Rönnqvist, Hans
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Assessing internal erosion2007In: International Water Power and Dam Construction, ISSN 0306-400X, Vol. 59, no 11, p. 30-34Article in journal (Refereed)
    Abstract [en]

    The majority embankment dams in Sweden are composed of widely graded glacial moraines in the core, protected by the filters of sand and gravel. However, it is reported that several incidents of sinkholes in Swedish embankment of which attributed to internal erosion in the dam body. Addressing this issue, an investigation is carried to seek to a more discriminatory tool can be derived for assessing potential for surfacing internal erosion in embankment dams with widely graded glacial cores. The Foster & Fell filter testing method for dams makes it possible assessing the filter performance of existing embankment dams with regards to the no, excessive and continuing erosion boundaries in terms of a concentrated leak. The method address the potential for surfacing internal erosion in moraine core embankment dams with levels from high, increased or neutral. With further development of this method, it will provide a qualitative indication of the potential for sinkhole development.

  • 2.
    Rönnqvist, Hans
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Assessing potential for internal erosion in glacial moraine core embankment dams2007In: Dam Engineering, ISSN 0958-9341, Vol. 18, no 2, p. 101-117Article in journal (Refereed)
    Abstract [en]

    Internal erosion, the process of washout of fine-grained material by seepage flow from an embankment dam filling material, can pose a major threat to dam safety. Internal erosion at a far reached stage can surface in the shape of sinkholes, sudden turbid leakages and settlements, indicating that the filling material in the dam is undergoing potentially significant property changes. It was early on found, for instance by Sherard [1979], that embankment dams comprising broadly graded material appear to develop sinkholes more frequent than dams of other material components. And considering that typical Swedish embankment dams are composed of material with broad and wide gradations of glacial origin, in particular the impervious core of broadly graded moraine (till), it should come as no surprise that many embankment dams in Sweden have shown signs of deterioration that can be related to internal erosion. The susceptibility for internal erosion in Swedish embankment dams was perhaps first noticed in a survey carried out by Nilsson et al [1999], where 20 % of the incorporated dams were estimated being affected by internal erosion. To reduce the risks connected to internal erosion it can be necessary to implement dam safety measures preferably at an early stage before the internal erosion progressed to surfacing, but distinguishing which dams that hold a real potential future risk for internal erosion can prove difficult. This paper is based on an evaluation comprising 45 existing Swedish embankment dams and the results show that a more discriminatory predictor, than today’s filter criteria, appears to be needed if embankment dams with widely graded glacial cores with high potential for surfacing internal erosion are to be singled out from dams apparently internal erosion free. The results indicate that not only filter coarseness needs to be addressed when assessing potential for internal erosion in embankment dams with glacial moraine cores, but also the internal stability of the core and filter.

  • 3. Rönnqvist, Hans
    Evaluating Internal Instability and Internal Erosion in a selection of existing Swedish Embankment Dams: Internal Erosion and their Foundations2005In: Internal Erosion of Dams and Their Foundations: Selected and Reviewed Papers from the Workshop on Internal Erosion and Piping of Dams and Their Foundations, Aussois, France, 25-27 April 2005, Taylor & Francis, 2005, , p. 203-207p. 203-207Conference paper (Other academic)
  • 4.
    Rönnqvist, Hans
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Long-term behaviour of internal erosion afflicted dams comprising broadly graded soils2009In: Dam Engineering, ISSN 0958-9341, Vol. 20, no 2, p. 149-197Article in journal (Refereed)
    Abstract [en]

    Internal erosion occurs when fine-grained particles are washed out from a filling material by seepage. Sinkholes and settlements on the dam crest, sudden increased leakage, or muddy seepage may be manifestations of progressed internal erosion. Dams with cores of glacially formed broadly graded soils have been found to be more likely to experience internal erosion than dams composed of other materials. This paper describes and reviews case histories of 30 existing dams constructed from broadly graded soils with performance history of internal erosion. Understanding i) typical signs and observations of internal erosion, ii) the timing of internal erosion incidents, iii) the possible early-warning signs, iv) the possible warning-time, and v) the location of the internal erosion incident on the dam body – may provide tools for early-warning detection of internal erosion prone dams and improve the assessment of internal erosion in existing dams.

  • 5.
    Rönnqvist, Hans
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Predicting surfacing internal erosion in moraine core dams2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dams that comprise broadly and widely graded glacial materials, such as moraines, have been found to be susceptible to internal erosion, perhaps more than dams of other soil types. Internal erosion washes out fine-grained particles from the filling material; the erosion occurs within the material itself or at an interface to another dam zone, depending on the mode of initiation. Whether or not internal erosion proceeds depend on the adequacy of the filter material. If internal erosion is allowed, it may manifest itself as sinkholes on the crest, increased leakage and muddy seepage once it surfaces, which here is called surfacing internal erosion (i.e. internal erosion in the excessive erosion or continuation phase). In spite of significant developments since the 1980s in the field of internal erosion assessment, the validity of methods developed by others on broadly graded materials are still less clear because most available criteria are based on tests of narrowly graded granular soils. This thesis specifically addresses dams that are composed of broadly graded glacial soils and investigates typical indicators, signs and behaviors of internal erosion prone dams. Based on a review of 90+ existing moraine core dams, which are located mainly in Scandinavia as well as North America and Australia/New Zealand, this thesis will show that not only the filter’s coarseness needs to be reviewed when assessing the potential for internal erosion to surface (i.e., erosion in the excessive or continuing phase); in addition, the grading stability of the filter and the core material as well as non-homogeneities that are caused by filter segregation need to be studied. Cross-referencing between these aspects improves the assessment of potential for internal erosion in dams of broadly graded soils and furthermore it provides aid-to-judgment.

  • 6.
    Rönnqvist, Hans
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Review of moraine core dams and internal erosion2008In: Dam Engineering, ISSN 0958-9341, Vol. 19, no 2, p. 99-121Article in journal (Refereed)
    Abstract [en]

    Embankment dams comprising broadly graded materials of glacial origin have in the past been identified as being prone to develop sinkholes more frequent than dams composed of materials of other origin. Sinkholes on the crest of a dam are many times an indicator of internal erosion. Internal erosion can initiate and continue to develop for many reasons, but mainly due to root causes coming from core/filter properties and interaction, possibly affected by the dam design and/or construction related reasons. In this paper a review is made on moraine core dams in the literature in relation to performance history of internal erosion. Dam data comprising 90 existing moraine core embankment dams has been compiled and assessed with objective to investigate the occurrence of indicative properties of dams that have developed internal erosion. The data set of dams consists predominately of Swedish dams, but it also includes moraine core dams located in the rest of Scandinavia, in North America, Russia and Australia. The investigation shows that a coarsely graded filter, grading instability of the core and filter, and high susceptibility for filter segregation are properties that are over-represented and possibly indicative for moraine (till) core dams with performance history of internal erosion.

  • 7.
    Rönnqvist, Hans F.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Assessing the surfacing of internal erosion in moraine core dams - II2008In: International Water Power and Dam Construction, ISSN 0306-400X, E-ISSN 1538-6414, Vol. 60, no 4, p. 26-28+30-31Article in journal (Refereed)
    Abstract [en]

    In order to know the potential for internal erosion in embankment dam, a method was proposed for defining structures with a high potential for erosion. The method borrows its idea on an examination of a number of existing embankment dams with moraine cores by investigating the influence of the filter coarseness in terms of filter coarseness and the internal stability of the filter and core material. The new method furthers additional aspects like filter segregation and devoid of sufficient transition layers in order to find indicators of internal erosion prone moraine core dams.

  • 8.
    Rönnqvist, Hans F.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Hydraulic Engineering (moved 20130630).
    Long-term behaviour of dams with internal erosion2009In: International Water Power and Dam Construction, ISSN 0306-400X, Vol. 61, no 7, p. 34-36Article in journal (Refereed)
    Abstract [en]

    The performance history and long-term behavior of the dams mainly comprises of the internal erosion process of graded glacial soil associated with washout of fine grained particles from a dam's filling material by seepage. Internal erosion initiates generally by concentrated leak erosion, backward erosion, and/or suffusion. 30 existing dams comprising broadly graded soils of glacial origin that is, moraines and tills have been reviewed. These are all dams that have differing extents, and have experienced incidents of internal erosion. Incidents are most likely to occur early-on, since almost half of the dams reviewed experienced incidents during first filling or within the first year of service. The most common signs that precede an internal erosion related incident are increase in leakage, muddy leakage and pore-pressure variations in the dam body.

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