Workshop of the ISSMGE TC 32, September 2010, Budapest Dikes failures and limit states of the HYD in EC 7 Ivan Vaníček Czech Technical University in Prague Faculty of Civil Engineering Geotechnical Department 1

2 Workshop of the ISSMGE TC 302, September 2010, Budapest

3 Workshop of the ISSMGE TC 32, September 2010, Budapest

4 Workshop of the ISSMGE TC 32, September 2010, Budapest

5 Workshop of the ISSMGE TC 32, September 2010, Budapest

6 Workshop of the ISSMGE TC 32, September 2010, Budapest

Workshop of the ISSMGE TC 302, September 2010, Budapest Earth structures in Water Engineering Large dams Small dams Anti flood protection systems (Dikes) Canals (e.g. Panama canal) Reservoirs (e.g. of pumped storage hydro plans) all now fully under EC 7 both 2 positions Soil and rock as construction material Interaction with subsoil (ground) 7

Workshop of the ISSMGE TC 32, September 2010, Budapest 3 Geotechnical Categories 1.GC 2. GC 3.GC Negligible risk No exceptional risk Very high risk Limit states Ultimate limit states Serviceability limit state GEOE d ≤ C d STR E d -design value of the effect of actions EQU C d limiting design value of the effect of an action UPL design values for limiting movements and deformations HYD 8

Workshop of the ISSMGE TC 302, September 2010, Budapest Large Dams Total failureDefects (accidents) 1-1,5% ÷5% Main problems Higher flow through dam body by preferential paths = tension cracks = differential settlement = internal erosion Smaller problems Overflowing Slope stability 9

Workshop of the ISSMGE TC 32, September 2010, Budapest Specificity of 2002 year floods Character of high-flood-water wave Red – Vltava river – České Budějovice Blue – Malše river – Roudné Orlík dam – normal state Character of high flood- water wave for dam Orlík Red – inflow to the reservoir (3900 m 3 /s) ≥ Q 1000 Blue – outflow Green – water level Orlík dam – flood in

Workshop of the ISSMGE TC 32, September 2010, Budapest Floods Blatná

Workshop of the ISSMGE TC 32, September 2010, Budapest Floods

Workshop of the ISSMGE TC 302, September 2010, Budapest Historical earth dams 13 in Middle Ages around 1500 – 1700 A.D. - about of small dams, now about homogeneous from local material – granite elluvium for bigger ones the outlets were reconstructed - old wooden ones were substituted by concrete ones for 100 year flood Main problem – for 2002 floods Q max much higher than Q 100 Result of which – overflowing Domino effect!

Workshop of the ISSMGE TC 32, September 2010, Budapest Floods Pond Metelský – two dam failures

Workshop of the ISSMGE TC 32, September 2010, Budapest Floods Pond Veský – downstream slope erosion

Workshop of the ISSMGE TC 32, September 2010, Budapest Floods 2002 Road E 49 Pond Zámecký downstream slope erosion 16

Workshop of the ISSMGE TC 302, September 2010, Budapest Floods Pond Podhajč – dam failure

Workshop of the ISSMGE TC 302, September 2010, Budapest Floods Pond Dolejší – two dam failures

Workshop of the ISSMGE TC 302, September 2010, Budapest Basic limit states causing failures a)Internal erosion Metly Podhajský b) Surface erosion Zámecký Dolejší 19

Workshop of the ISSMGE TC 302, September 2010, Budapest Hydraulic failure HYD The provisions of the Section apply to four modes of ground failure induced by pore-water pressure or pore-water seepage, which shall be checked, as relevant: failure by uplift (buoyancy) failure by heave failure by internal erosion failure by piping 20

Workshop of the ISSMGE TC 302, September 2010, Budapest Example of conditions that may cause piping 1 free water table 2 piezometric level in the permeable subsoil 3 low permeability soil 4 permeable subsoil 5 possible well; starting point for pipe 6 possible pipe 21

Workshop of the ISSMGE TC 32, September 2010, Budapest Suitable structural measures are: application of berms on the land side of a retaining embankment, thus displacing the possible starting point of piping farther away from the structure and decreasing the hydraulic gradient at this point; application of impermeable screens below the base of the hydraulic structure by which the ground-water flow is either blocked or the seepage path is increased, thereby decreasing the hydraulic gradient to a safe value. 22

Workshop of the ISSMGE TC 302, September 2010, Budapest Internal erosion Failure by internal erosion is produced by the transport of soil particles within a soil stratum, at the interface of soil strata, or at the interface between the soil and the structure. This may finally result in regressive erosion, leading to collapse of the soil structure. 23

Workshop of the ISSMGE TC 302, September 2010, Budapest The measures most commonly adopted to reduce erosion or to avoid hydraulic failure are: lengthening the seepage path by screens or shoulders; modifications of the project in order to resist the pressures or gradients; seepage control; protective filters; avoidance of dispersive clays without adequate filters; slope revetments; inverted filters; relief wells; reduction of hydraulic gradient 24

Workshop of the ISSMGE TC 302, September 2010, Budapest Summary Limit states which are playing most important role for earth structures in water engineering are: Internal erosion (including piping) Surface erosion EC 7: Internal erosion is specified only in very broad way – also the way by which this limit state should be verified - can we use the adoption of prescriptive measures or experimental models? Surface erosion is not specified at all (although was mentioned in early versions) 25

Workshop of the ISSMGE TC 302, September 2010, Budapest Internal erosion Questions? What is critical gradient? How this gradient can be predicted – especially for unsaturated conditions ? Which filtration criteria can be recommended for non-cohesive and cohesive soils? Must we select filtration criteria for soils with cracks? How recommended filtration criteria have to be verified? What to take as representative size of grain (or opening for geotextiles filters) for protected soil and for filter? How to evaluate a potential danger of filter size separation during filling? How important is the role of the soils susceptibility to the erosion? Have special conditions to be specified for dispersive soils? Have we to leave all these questions on National Annexes to EC 7 or have we to try to find more common and acceptable solution in Europe? 26

Workshop of the ISSMGE TC 302, September 2010, Budapest Surface erosion In the Czech Republic we are using the experimental models and prescriptive measures: Where it is possible to select the place where overflowing can start (causing minimum problems) - there the crest of dam (dike) is decreased (e.g. 0.3 m) and reinforced. 27 The example for the reconstruction of old earth dam, where additional spillway reinforced by concrete was applied

Workshop of the ISSMGE TC 302, September 2010, Budapest Application of anti erosion geo mattresses with vegetation (grass) 28

Workshop of the ISSMGE TC 302, September 2010, Budapest Dikes reinforced with fibre-brick-concrete 29

Workshop of the ISSMGE TC 302, September 2010, Budapest Acknowledgement: The work presented in this paper was carried out with funding from the MSM CR grant number Sustainable construction. 30 Thank you for your attention