SEMINAR ON RCC DAMS Organized by VNCOLD Hanoi, xx September RCC DAMS WORLDWIDE AND IN VIETNAM M. Ho Ta Khanh (VNCOLD)

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1 SEMINAR ON RCC DAMS Organized by VNCOLD Hanoi, xx September 2011 RCC DAMS WORLDWIDE AND IN VIETNAM M. Ho Ta Khanh (VNCOLD)

2 RCC Dams Worldwide

3 Design Criteria and Analysis for Gravity RCC Dams The same as for CVC gravity dams but with different values for the parameters. Mechanical conditions - Strength and Sliding stability - Deformation, settlement : FEM analysis Hydraulic conditions - Permeability - Hydraulic gradient Adopt Vietnamese code if any, but it is possible to use all available codes or guidelines (USA, Canada, GB, France, Germany, Russia, China, Japan, India, etc). No code is better or worse than the others! All these codes are coherent and adopt the same general principles (which are a simplification of the reality). They differ mainly by the presentation and lead to very comparable results! The most important is to adopt homogeneous parameters and criteria (global safety factors and partial safety factors for friction, cohesion and max tensile strength). Don t mix these codes and don t retain, for safety reason, the most unfavourable results! Application with good judgment by experimented engineers is more important than the origine of the code!

4 The conception of a RCC dam must be adapted to the particularities of the RCC technique (Basic principles) Use as much as possible the local materials (aggregates, cementitious materials). Reduce as much as possible the quantities of cementitious materials, in particular the fly ash if it is not available near the site (< 200 km). Adapt the cross-section of the dam to the characteristics of the RCC, and not the opposite! (See examples of the Moroccan and French RCC dams). Each RCC dam must be optimized according to the conditions of the site (flexibility of the design) : avoid to normalize the conception of the dam and the composition of the RCC materials! Facilitate as much as possible the placement of the RCC: Avoid if possible the structures including large openings. Separate, if possible the location of the dam and the the powerhouse (example of Long Tan and Salto Caxias HPP). Select the construction equipment adapted to the rate of placement. If useful, the design can separate the mechanical and the watertight functions.

5 Design and Construction Trends in the U.S RCC Dams by F.Y.Abdo (2010) Perhaps the most notable development in recent RCC gravity dams in U.S.A in the design is: Increasing the dam size in order to reduce the required RCC strength provided an opportunity to use marginal on-site aggregates. Designing the dam to resist full hydrostatic uplift pressure eliminated the need for foundation drains and drainage gallery (for low and medium-sized dam). Eliminating the construction of a stilling basin. The purpose of the next slides is to illustrate these recommendations by some examples of recent RCC dams worldwide.

6 Flexibility of RCC Dam Designs Very different cross-sections according to the quality of the foundation, the aggregates, the type and content of the cementitious materials

7 Longtan Dam (China) 2007

8 Very good aspect of the downstream face with the GEV-RCC method and an intact core 15 m long in the dam. No seepage in the gallery

9 LONGTAN DAM A good example of separation between the dam and the powerhouse. This implementation allows a separation between the CVC and the RCC placements, a continuous regular placement of the RCC and a commissionnig of the 3 first units before the end of construction of the dam (shorter delay than for the powerhouse).

10 SALTO CAXIAS (Brazil)1998 A good example of separation between the dam and the powerhouse and a RCC without fly ash. Same advantage as for the Long Tan Dam concerning the powerhouse implementation.

11 Miel I RCC Dam (Colombia) H = 192 m V = m 3 A good example of a very high dam with cement contents adjusted to the stresses and without fly ash.

12 MIEL I RCC Dam in a seismic area RCC cement contents in the different parts of the dam = 85 to150 kg/m 3. No fly ash.

13 Breña II RCC dam in Spain, H= 119 m, V= 1.6 hm 3 The largest RCC dam in Europe Limestone filler used as cementitious material in the mix. Fixed crest spillway. Stepped spillway on the downstream face. Large crest width to increase the dam volume and lower the max stress.

14 Number of dams Rapid Development of Dams in Morocco since 1985 due to RCC advent (low cost and rapid construction) RCC advent Year

15 The Aoulouz RCC dam in Morocco H= 79 m, V= m 3 First large RCC dam in Morocco (designed in 1987) End of construction Flow over the spillway

16 Construction of the RCC Aoulouz dam in 1990 (Note the aspect of the RCC with low cement content and no flyash)

17 AOULOUZ DAM RCC with 100 kg cement/m 3 and clayey fines, no flyash. R 365 =10 MPa

18 Progress in RCC Dams in Morocco since 1987 Various cross-sections of RCC dams No flyash in all the RCC Moroccan dams

19 Low RCC Dams Since 1987, the Moroccan experience proved that RCC technique, in place of masonry or CVC, is an economical solution even for low dam (< 30m).

20 UCS (MPa) UCS (MPa) Examples of unconfined compressive strengths for 3 Moroccan RCC dams with additional fines With100 kg cement/m 3 and additional fines (clayey for Aoulouz, limestone for Sidi Saïd and high quality limestone for Rmel), no flyash Aoulouz Sidi Said Rmel Aoulouz Sidi Said Rmel Days Days

21 Hassan II RCC dam in Morroco (2005):120 m high, 660 m long Granit + limestone filler Dmax: 63mm Cement content : 80 to 100 kg/m 3 R 365 =16 MPa

22 Hassan II RCC dam: Cross-sections and details

23 Cement content = 100 kg/m 3 with filler. Wirgane RCC dam with gated spillway H=70 m (2008) First placement of RCC by the sloped layer method. The advantages of this method were so evident that it was adopted for all the next Moroccan RCC dams, even with medium sizes. Note the 3m high steps on the downstream face corresponding to the height of the10 continuous layers of 0.3m high each.

24 The Taskourt RCC dam in Morocco (2011) Low cement content (100 kg/m 3 ), no flyash and no leakage on the downstream face!

25 Taskourt dam, H= 75 m, L= 416 m Cross sections through spillway and bottom outlet

26 Taskourt dam : placement of the RCC by the sloped layer method

27 Visit of the Taskourt dam (06/06/2011)

28 The Tiouine RCC dam (H= 84m) in Morocco 2011 Cross sections through the spillway and the bottom outlet

29 Production of the inert filler and grading curves of filler and sands The RCC (100 kg cement/m 3, no fly ash, 7% of inert filler) is placed by the sloped layer method

30 Tiouine RCC material Local fine sand and ground inert filler, without fly ash, provide sufficient density, strength and watertightness for the dam, with the minimal cost!

31 Tiouine dam: Placement of the RCC (Note the dry aspect of the RCC very easy to compact)

32 Visit of the Tiouine RCC dam (07/06/2011)

33 Rizzanese dam (France), H= 40.5 m An example of RCC dam on weak foundation, low quality aggregates and low percentage of cement, without fly ash.

34 Rizzanèse dam Spreading the RCC (100 kg of cement/m 3 without F.A) on the bedding mix (mortar)

35 Cementitious content High paste (> 150 kg/m 3 cementitious material) Medium paste (100 < CM < 145) Lean RCC (CM< 99 kg/m 3 ) % 53.4 % 21.7 % 16.9 % 12.7 % 13.3 % Hardfill 0.6 % 2.9 % RCD (Japan) 18.5 % 12.8 % Unknown 3.2 % 0.8 % Comments Increase of «High paste RCC» is due mainly Chinese RCC dams (China has a lot of coal fired thermoplants with low cost of fly ash). Increase of Lean RCC is due mainly to Brazilian RCC dams (The Brazilian RCC dams are far from thermoplants). High increase of the proportion of Hardfill dams (they are not numerous, although very interesting on weathered foundation). Relative decrease of RCD (higher cost, only adopted in Japan). These values reflect the particularities of the site and the conception of the dam but not the proof of the superiority of one technique on the others!

36 Cement + low-lime FA Cement + highlime FA Cement + ground - granulated slag Combination of pozzolans (no cement) Cement + natural pozzolans Cement + manufactured pozzolans Portland cement alone Unknown 3.2 % % 60.8 % 1.3 % 0.9 % 4.5 % 5.1 % 4.5 % 2.1 % 7.6 % 15.3 % 2.5 % 1.2 % 10.2 % 14.7 % Cementitious materials Comments Decrease of the use of (cement + lowlime FA), which remains however the large majority of cases. Increase of the use of (cement + natural pozzolans), due to the expansion of RCC dams to regions where fly ash (and slag) are not available. Increase of the use of (Portland cement alone), due to the expansion of RCC dams to regions where fly ash (and slag) are not available.

37 Cementitious content of Brazilian Dams

38 Cementitious content of Brazilian Dams

39 RECENT TRENDS IN RCC MATERIALS High or low paste content? All recent RCC materials are in reality «High paste content», it is more exact to replace in this classification : «paste» by «cementitious». The cementitious content The «cementitious materials» include cement and slag but also all the materials that present a «pozzolanic reactivity» (fly ash, natural or artificial pozzolan, some natural fines and rock powder, etc). The use of powdered aggregates More and more used everywhere fly ash or pozzolan are too costly. The use of admixtures in RCC More and more used as they can lengthen the setting time of the RCC (to improve the bonding between the layers) and reduce the water content and consequently the cementitious content.

40 Use of admixtures Without admixture With admixture VB (s) Comments Density VB (kg/m 3 ) Mix efficiency at 180 days (MPa)/(kg/m 3 ) Cementitious content in (kg/m 3 ) Retarding admixtures Cost savings (cement) Construction under high temperature Brazil Morocco To avoid cracks (China) 10 kg/m 3 40 kg/m 3 - Use of a plasticizer retarder admixture (0.8 to 1.12 kg/m 3 ). - There is a reduction of VB time up to 40% for the same water content, or a reduction of circa 10% of water content for the same VB time. - There is an increase of VB density. - There is an increase of the mix efficiency. - For the same consistency and compressive strength, the cementitious content can be reduced (15 to 30% ).

41 Use of powdered aggregate in Elk Creek Dam (USA) The use of fines (in particular limestone powder) is generally very beneficial in the RCC and allows to lower the amount of cementitious materials.

42 RECENT TRENDS IN RCC CONSTRUCTION (1) The use of conveyors: the main advantages are the possible high rate of construction and the non pollution of the RCC layers. This use is now almost generalised for the very large dams. The Sloped Layer Method (SLM): this method is at present more and more applied when the volume of RCC to be placed on each layer is large compared with the capacity of the batching plant. The bedding-mix: used generally in particular cases (cold joints between the RCC layers, medium and low paste RCC, etc). The Grout Enriched RCC (GEV-RCC): more and more used for the upstream and downstream faces of the dam and between the RCC and the CVC structures or between the RCC and the foundation. Give very good results, if correctly applied. To obtain a good result, it is necessary that the grout (cement+water or mortar) is poured at the base and/or in the middle of the new layer (or in a small trench dug in this layer), before its vibration by the needles. This technique is valid even with low cementitious RCC (Chraibi 2010).

43 RECENT TRENDS IN RCC CONSTRUCTION (2) The cooling of RCC: for low and medium high dams (<100 m) : use of low heat cement and fly ash if not too expensive, pre-cooling of the aggregates by air, water spraying of the layers, induced intermediate vertical joints (see photo of the upstream face of Nam Theun 2 dam) to prevent crack extension,for high dams (>100 m) : same precautions, plus an ice cooling plant and an internal cooling of the dam, if necessary. The use of geomembrane: can be an interesting solution when the function of watertightness is separated from the mechanics and the stability functions. For example for the low paste RCC (without fly ash) gravity dams, or for FSHD and CSG dams with very low cement contents. Some designers prefer to adopt a gemembrane protected by precast concrete panels for the upstream face of the dam.

44 Rialp RCC Dam (Spain) Transportation of RCC by conveyor and swinger : quick placement and clean layer surface!

45 Some recent Chinese construction techniques for RCC dams

46 Sommaire Summary Use of Geomembrane Balambano Dam (Indonesia)

47 Sommaire Summary Use of Geomembrane For the Balambano dam the total leakage through the dam is virtually zero (some seepage appeared through the foundation and the abutments) : the geomembrane was thus very efficient for the dam watertightness.

48 Sommaire Overtopping protection of Summary embankment dam by RCC : Brownwood Country Club Dam (USA) Initially 6 m high earth dam First earth dam in USA to receive RCC overtopping protection (1984) Initial Flood = 74 m 3 /s Revised Flood (PMF)= 330 m 3 /s Overtopped 6 times since its construction with no damage Volume of RCC = m 3 placed in 2 days 1/3 of the cost for increasing spillway capacity by traditional method

49 Two Vietnamese RCC Dams Dinh Binh Dam Son LA HPP

50 Dinh Binh Dam Cementitious content of RCC (per m 3 ) Cat RCC 150 RCC 200 Cement (kg) Fly Ash (kg) Sand (kg) A.0.5x2 (kg) A.2x4 (kg) A.4x6 (kg) Water (l) TM-20 (l) P-96 (l)

51 Materials CONCRETE MIX Units Cement Flyash Total kg/m 3 VND kg/m 3 VND VND 1x2, OK6-8M150, coarse aggregate M150, coarse aggregate 2x4, OK6-8 M150, coarse aggregate 4x6, OK6-8 m m m RCC MIX RCC MIX, M200 m RCC MIX, M150 m The RCC material costs (2007) are almost the same than the conventional concrete material costs due to : the high percentage of cementitious materials, the similar treatment of aggregates.

52 Comments about the Dinh Binh RCC The RCC cost of Dinh Binh dam (as other RCC dams in Vietnam) is high compared with CVC. Why and how to lower it? Not optimal design: the design must optimize the cross-section of the dam, and avoid as much as possible openings in the RCC. It is unecessary to design several costly watertight barriers in the dam body. The most important is to select an adapted RCC material, to optimize consequently the design and to have a good control during the RCC placement. High fly ash cost: use fly ash only if there is a thermal powerplant near the site. Too high content of cementitious materials : avoid to normalize a minimum RCC strength (for example RCC150 or RCC200), as for the CVC! Adjust this minimum value according to the results of each optimization (materials/analysis) of the design. The strengths of the RCC are too large compared to the required strengths. The watertightness of the dam and its durability can be obtained by other cheaper alternatives. The cost of the cementitious material must be lower than 30% of the total cost of the RCC material, it is here almost equal to 50%! Low rate of construction: improve the organization of the works, adopt as much as possible a continuous placement. Poor construction equipment: for dams with large volume (> 1 to 2 millions of m 3 ), select the RCC transportation by conveyor belt. Is the RCC always the most economical alternative? The advantages of the RCC technique are not conclusive for low and medium dams, with large openings, built for flood control.

53 Son La Dam Mix Proportions per m 3 : Cement PCB 40 = 60 kg/ m 3, Pulverized Fly Ash = 160 kg/ m 3 Comment: The required high tensile strength to resist to the design earthquake loadings is linked to the shape of the cross section of the dam.

54 Son La : The penstocks and the powerhouse In this part of the dam, the RCC is used only in the bottom and, not easiliy, in the upper part, downstream the intake. The placement of the RCC cannot be continuous on the dam. The commissioning of the power house cannot be done before the end of construction of the dam.

55 Son La RCC sequence and rate of placement The placement of the RCC is very discontinuous with peak near m 3 /day (costly construction equipment) and many weeks without placement. 11-Jan Jan-08 8-Feb Feb-08 7-Mar Mar-08 4-Apr Apr-08 2-May May May Jun Jun Jul Jul-08 8-Aug Aug-08 5-Sep Sep-08 3-Oct Oct Oct Nov Nov Dec Dec-08 9-Jan Jan-09 6-Feb Feb-09 6-Mar Mar-09 3-Apr Apr-09 1-May May May Jun Jun Jul Jul-09 7-Aug Aug-09 4-Sep Sep-09 2-Oct Oct Oct Nov Nov Dec Dec-09 7-Jan Jan-10 4-Feb Feb-10 4-Mar Mar-10 1-Apr Apr Apr-10 in Hundreds Volume, m Son La Hydropower Project Daily RCC Production from 11 January April 10 Total Volume of RCC Produced Accumulated Volume Maximum Daily Production to Date m Accu. Volume, m 3 Date

56 Sinking of the truck in the RCC Too much paste and water in the RCC. Sufficient water content is required for good bond between the layers but too much water (bleeding and laitance) is detrimental. Avoid as much as possible the use of trucks on the RCC layers. Use as possible conveyor belt and swinger.

57 Comparison Long Tan/Son La RCC Dams Long Tan Son La Volume of the dam : 6.6 hm 3 First concrete placement : November 2003 Volume of the dam : 4.6 hm 3 First concrete placement : April 2007 End of concrete placement : November 2007 End of concrete placement : August 2010 Duration of dam construction : 48 months ( m 3 /month) Duration of construction : 40 months ( m 3 /month) Commission of the 3 first units : May 2007 Commission of the first unit : December 2010 Delay between the concrete dam placement and commission of the 3 first units : 3.5 years Delay between the concrete dam dam placement and commission of the first unit : 3 years

58 The Son La Design 1. The fly ash contents a high percentage of L.o.I and it is far from the site. It has to be transported by trucks on roads frequently cut by landslides during the rainy season. It is expensive and depends on an unique Vietnamese provider (Pha Lai powerplant). 2. The most economical alternative is to reduce as much as possible the quantity of fly ash. Is it possible and how to do? By giving a batter of 0.15 to 0.20 to the upstream face, instead of vertical, it will be possible to reduce the maximal tensile strength (at maybe 0.3 to 0.5 MPa). With this last value of the tensile strength, the max required compressive strength of the RCC can be reduced to 15 MPa. This value of RCC compressive strength (at 365 days) can probably be obtained with only 130 kg of cement* per m 3 (and some 7% milled fines) without fly ash, or with 100 kg/ m 3 of cement and 50 kg/ m 3 of flyash (total=150 kg/ m 3 compared with 220 kg/ m 3 used). * This relative high percentage is due to a rather low grade cement (PCB 30 or 40), with then a relative high cost for the transportation. The volume of the dam will be a little higher but, as the unit cost of the RCC is lower, the total cost of the dam will certainly decrease. - To improve the watertightness, the upstream face of the dam could be enriched in cement and fly ash by the GEV-RCC method or by CVC. A light reinforcement mesh can be put, if necessary. - Even with 130 kg of cement per m 3, the cooling of the RCC will not pose more problems than the present situation, provided the vertical joints are correctly implemented.

59 Conclusion about some Vietnamese RCC dams An optimal RCC dam should not be a traditional gravity dam in which the conventional concrete is simply replaced by RCC. The studies of the RCC materials should be carried out before the design and the analysis of the structure (and not the opposite as in many Vietnamese projects!), as they depend on the most available and economical materials which can be obtained on the site. The most economical solution is not always the minimum dam volume with a large amount of fly ash whenever this material is not available near the site. The conception of a RCC dam must be flexible and must be optimized among all the possible RCC alternatives (different cross section, RCC composition, RCC zoning, separation of mechanical and watertight functions, etc). Don t adopt the same cross section and the same RCC for all the sites!

60 A particular type of RCC dam: The Face Symmetrical Hardfill Dam (FSHD) and Cofferdam A new shape : fit with incompetent or low resistance foundation A cheap material : hardfill low cost aggregates natural alluviums mug from excavation soft rock low cement content Untreated natural alluviums Rio Grande dam in Peru

61 100 m 100 m AVANTAGES OF SYMMETRICAL PROFILE - low and uniform vertical stress repartition - little change in the vertical stress with reservoir filling, - no tension at the dam heel, - uniform and reduced shear stress at the base with the seismic load - small influence of uplift forces improved stability conditions in case of earthquake and large overtopping 1 C A 2 1 D 1 Ful 1 2B 2C Empty u d (MPa) (MPa) A 0.7 = 0.36 = 24 kn / m 3 = = 23 kn / m PG C r itical r esultant For ear thquake 0.2 g FSHD C=2.40 Critical resultant For earthquake0.2g E m pt y 1 A = 1.39 B = 1.41 D B C = 1.15 Full D = u d Uplift U plift

62 Some examples of FSHD and FSH cofferdams: - Cidere and Oyuk FSHD in Turkey - Koudiat Acerdoune FSHD in Algeria - Saf Saf FSHD and FSH cofferdam in Algeria

63 CINDERE DAM (Turkey) 2002 Sommaire Summary H = 107 m L = m V = m 3 (RCC = m 3, CVC = m 3 ) Q (Peak Flood) = m 3 /s Foundation : Micaschist E s = 2.75 to 3.70 GPa R cs = 3.3 to 15.3 MPa Seismicity OBE = 0.20g MCE = 0.40g RCC cementitious materials : 50 kg/ m 3 P.C + 20 kg/ m 3 F.A R c = 6 MPa (180 days) Covered geomembrane upstream

64 OYUK Dam (Turkey) 2007 H = 100 m L = 212 m Q (Peak Flood 1/10 000) = 530 m 3 /s Foundation : Gneiss and micaschist Seismicity : OBE = 0.24g MCE = 0.40g Cementitious materials : 50 kg/m 3 P.C kg/m 3 F.A R c = 6 MPa (90 days)

65 Koudiat Acerdoune (Algeria), H = 121 m, Crest Length = 493 m A high RCC dam located in a seismic area with low grade aggregates and with very bad foundation (schist and marl) with important rock slides during the construction. This dam was designed and constructed by French consultants and contractors.

66 Koudiat Acerdoun : Composition and characteristics of RCC Initial design Final design Quantity of RCC m m 3 Cement content 77 kg/m kg/m 3 Fly Ash content 87 kg/m 3 0 Limestone filler content kg/m 3 Required compressive strength 19 MPa at 90 days 11 MPa at 90 days Max temperature 25 C 25 C Choice of a FSHD cross-section to adapt the design to the very low quality of the foundation and of the aggregates, with a reduction of Rc. Replacement of the costly fly ash by a limestone filler ground in situ.

67 Diversion works for the Saf Saf FSHD (Algeria) Low protection against flood during the construction The Q 10-year flood = 890 m 3 /s, but the capacity of the diversion canal is only 150 m 3 /s (annual flood). - In October 2008, a peak discharge flood of 500 m 3 /s overloaded the canal capacity and the dam was overtopped with a 1.5 m overflow depth, the base of the dam (3 m) was under construction. - No damage resulted from this flood (no erosion of the crest, the U/S and D/S faces of the dam). The works could start again after a 2 weeks cleaning period.

68 Failure of the Cua Dat CFRD (Vietnam) during the construction To minimize the cost of the diversion structures, it was admitted to divert the flow during the wet season of 2007 by only one tunnel (D=9 m) in place of 2 tunnels (D= 11 m) of the initial design, with a possible overtopping of the main dam 25 m higher than the river bed. Unfortunately an extreme flood (8000 m 3 /s), much higher than expected (5300 m 3 /s), destroyed the gabion protection, the cofferdam and a part of the dam during the construction (but without serious damage downstream).

69 Observation about FSHD for dam and cofferdam 1. A FSHD is particularly interesting for the sites with weak foundation, high floods (often difficult to estimate precisely) and in seismic area. A FSHD can be overflowed without serious damage during the construction permitting significant savings in diversion works. FSHD may be consequently an interesting alternative to CFRD for the sites with high floods and highly weathered rocks in foundation. For this reason several FSHD are presently under construction in Morocco in place of the traditional CFRD alternatives (Mr. Chraibi). 2. FSHD (or CSG) cofferdams - as demonstrated by their very good resistance to large overflows - seem to be the best solution in case of overtopped structures, even they may be a little more expensive than an embankment. 3. The failure of the Cua Dat CFRD must not lead to rule out the method of diversion with overtopped structures - which allows generally important cost and delay savings - but to adopt an adequate mode of protection of the downstream slope of the embankment and, if necessary, of its toe and abutments. It is probable that, if the downstream slope of this dam were protected by a downstream FSHD in place of the gabions, the main dam and the RCC would have resisted to the flood or be only superficially damaged.

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