The effect of reservoir drawdown and long-term consolidation on the deformation of old embankment dams

An existing 15 . 5 m high main dam embankment at Abberton Reservoir in Essex was completed in August 1938, since when its performance has been satisfactory. However, the upstream embankment shoulder of the original dam suffered a deep-seated failure through its foundation towards the end of construction in July 1937, 9 days before a similar and well-known failure occurred at Chingford Reservoir in close proximity to Abberton. Whereas the failure at Chingford became an important case in the history of soil mechanics through the involvement of Karl Terzaghi and marked one of the first applications of modern soil mechanics principles, the failure at Abberton has remained largely unknown, until recently when raising of the existing dam started to be considered. This paper describes advanced finite-element analyses which were carried out to investigate the failure of the original dam at Abberton and the stability of the existing main dam. The parameters used in the constitutive models were derived on the basis of the available site investigations and laboratory testing and on experience in the back-analysis of other failures in London Clay. The analyses demonstrated that the upstream shoulder of the original embankment failed through the mechanism of progressive failure, which involved the top of the stiff plastic London Clay rather than the overlying alluvium in the foundation. The relatively rapid rate of embankment filling, achieved by using modern earthmoving equipment, contributed significantly to the original dam failure. The analyses also demonstrated satisfactory behaviour of the existing dam during reconstruction, the first impounding and in the long term, with its response being similar to that observed. Thus the constitutive models used and parameters derived were successfully calibrated against the observed behaviour of both the original and existing main dams at Abberton, and could be used in predicting the behaviour of the dam during and after its proposed raising.

“…The apparent difference can be explained by creep and reservoir operation settlements (see e.g. Tedd et al, 1997;Vaughan et al, 2004), which the current analysis does not account for.…”

Section: Existing Dammentioning

confidence: 69%

Finite-element analysis of the failure and reconstruction of the main dam embankment at Abberton Reservoir, Essex, UK

Kovacevic¹,

Hight²,

Potts³

et al. 2013

“…45, and a large difference in behaviour is apparent ; settlement at Walshaw Dean Lower is much greater and influenced by reservoir drawdown to a much larger extent than as predicted by the simple models. Figure 46 shows settlement as a function of depth of drawdown for the puddle clay core embankment dams in the BRE-Yorkshire Water monitoring programme (Tedd et al, 1997b). Further data published by Tedd et al (2002) confirmed the general pattern of drawdown behaviour.…”

Section: Crest Settlementmentioning

confidence: 73%

“…Monitoring of crest settlement has an important role in assessing the long-term performance and safety of embankment dams, and in collaboration with Yorkshire Water BRE carried out a programme of field studies to investigate the effects of operational cycles of reservoir drawdown and refilling on embankment deformations (Tedd et al, 1990(Tedd et al, , 1994(Tedd et al, , 1997a(Tedd et al, , 1997b. Complementary analytical work was carried out at Imperial College (Kovacevic et al, 1997).…”

Section: Crest Settlementmentioning

confidence: 99%

“…47. Effect of minor and major unloading-reloading cycles in oedometer test on mudstone fill from Ogden dam (after Tedd et al, 1997b) with a major drawdown is illustrated by the oedometer test results. At a typical location within the upstream shoulder close to the embankment centreline, A represents the vertical stress at the end of construction of the embankment.…”

Section: Crest Settlementmentioning

confidence: 99%

See 1 more Smart Citation

The engineering behaviour of fill materials: the use, misuse and disuse of case histories

Charles

2008

A number of developments in our modern world, including increasing urbanisation, major land reclamation schemes and the disposal of vast quantities of solid waste generated by mining and industrial activities, should ensure that, for the foreseeable future, fills will be of increasing significance in geotechnical engineering. An engineered fill, which has been heavily compacted in thin layers under closely controlled conditions, should be a relatively uniform material and have behaviour that is easily predicted on the basis of average properties. In contrast, poorly compacted fill dumped with little control in deep lifts is likely to be in a loose state and exhibit great diversity in its geotechnical properties: the behaviour of such heterogeneous fill will bear little relation to average properties, and will be controlled largely by zones of fill in a metastable state with unpredictable behaviour. Case histories that include field measurements-that is, quantitative data-are of particular value in gaining an understanding of the performance of fill materials. Case histories of fill behaviour are examined in four areas of practical interest to the geotechnical engineer: (a) the geotechnical behaviour of opencast mining backfills; (b) the performance of rockfill dams; (c) the effectiveness of ground treatment; and (d) the condition assessment of embankment dams. In each of these areas the lecture focuses on the results of long-term field monitoring at a number of sites, from which some general conclusions are drawn. Discernment is required in the study of case histories, but despite shortcomings, they provide a much needed counterweight to excessive theorisation.

“…Tedd et al (1997) monitored the effect of reservoir drawdown and long-term consolidation on the deformation of a number of old dams. Where there was a central clay core, significant crest settlement was measured on reservoir drawdown, but this was not the case where there was an Skempton & Vaughan, 1993) CONTRIBUTIONS TO GÉ OTECHNIQUE 1948-2008: SLOPE STABILITY AND EMBANKMENT DAMS upstream watertight element.…”

Section: Embankment Damsmentioning

confidence: 99%

Contributions to Géotechnique 1948–2008: Slope stability and embankment dams

Charles¹,

Bromhead²

2008

The paper reviews the main contributions to geotechnical engineering in the allied fields of slope stability and embankment dams over the past sixty years of Géotechni-que. Skempton's Rankine Lecture is probably the most important single contribution to the science of slope stability engineering, through the initial enunciation of the linked ideas of slip surfaces and residual strength. Embankment dam engineering papers do not have such a single identifiable seminal publication, but the contribution of Rankine Lecturers to the science of embankment dams is equally evident.