Hydrotech, nical Constr~J, ction, l/bl. 3~. No. 5. 2000

C O N S T R U C T I O N O R G A N I Z A T I O N A N D P R O C E D U R E S

C O N S T R U C T I O N OF D A M S F O R M E D F R O M R O L L E R - C O M P A C T E D C O N C R E T E . A N A L Y S I S OF S T A T E OF T H E A R T A N D P R O S P E C T S F O R D E V E L O P M E N T

E. A. K o g a n

The search for effective methods of controlling temperature-induced cracking in concrete dams was initiated as early as the 1950s. The situation was fbund diffictflt, since this problem is directly associated with such important indicators as tile completion date of co~struction, its cost, and iabor outl~\ys expended in concreting operations. Over the years, attempts to resolve tile cracking problem by increasingly strengthening measures for temperature regulation have only resulted in further degradation of the above-noted indicators. Attempts to reduce exothermal warming of eoncrete by use of pozzuolanic additives, especially where it has t)een required to provide for impermeability and frost resistance of tile concrete, have also failed to produce the required effec.t. The first successes appeared only after a principal change in the methods employed for concrete placement: dangerous cracks were successfully avoided in constructing tile Alpa-Gera and Chivaira del Miniera (Italy), and Toktogul and Kurpsa Dams (USSR) owing to conversion to the layer-by-la.ver method of concrete placement with tile maximum degree of mechanization in concreting operations. Use of low blocks (with a height of 0.5-0.75 m) and new approaches to sectioning of tile dam (transverse joints have been installed without the use of traditional tbrmwork) have made it possible to utilize a concrete-placement procedure similar to tile procedure used to place earth fills. A more complete solution of the indicated problem was ultimately found on the basis of conversion to lean concrete mL'~es of stiff consistency, which submitted to compaction under vibratory rollers, i.e., just as earth structures are compacted. It is interesting to note that motivation for the search for new methods of concrete placement has gradually converted from a crack-control problem to a plane tbr development of a procedure that will make it possible to reduee significantly tile cost and completion time of the construction of concrete dams and render them competitive with dams formed fl'om local materials. Experience gained in recent years has demonstrated that this situation has created premises fi)r successflfl use of roller-compacted concrete (RCC) in dam construction: significant reduction in concrete-placement times and appreciable simplification of concreting procedures make it possible to lower the construction cost of concrete dams so much that they are becoming more advantageous than rock-fill clams.

The 89-m-high S imadz igawa Dam in Japan, which was completed in i981. was the first large dam formed rein roller-compacted concrete. From tile very outset and until recently, tile Japanese method of constructing roller- compacted dams (RCD method) has, in fact, been the method used for construction of the Alpa-Gera Dam with the difference being that the concrete was compacted not with deep vibrators, but by vibratory roller. The remaining elements of the procedure and design of the dam - the height of the blocks, pauses between placement of tile blocks. seetioning by transverse joints, and requirements for tile treatment of horizontal joints - are sinfilar to construction practice employed for gravity dams by tile layer-by-layer method [1].

Tile construction of dams completely, or to a significant degree from roller-compacted concrete h~.s been a principal innovation in the United States, Australia, and Spain. Six of these dams had been constructed by the close of 1985: Willow Creek, Middle Fork, Winchester, and Galesville Dams in tile United States. the Copperfield Dam in Austr~dia. and the Castile-Blanco Dam in Spain. The accelerated spread of this method of dam construction began in 1936: eight RCC dams were constructed during this year. By the close of 1993, 112 of these dams had been constructed in 18 conntries, an(l at least another 27 dams were under construction [3J.

The dynamics of the (levelopmc.nt of 1R.CC dam construction c~m l)e readily traced by comparing data for mid-1995 and data for the close of 1998. According to N. t2.. H. Dunstan. the nuIuber of I~.CC dams constructed with ~t height of more than 15 m b.v nfid-1995 had reached 130, and a.nottler 31 dams were ill the construction stage. By the ck)se of 1998, 184 RCC dams had 1)eei1 constructed and named, and 25 dams were yet to be constructed [9]. The w)lume of tile constructed (lares was more than 57 nfillion m 3, including the w)lume of roller-('ompacted

Translated from Gidrotekhnieheskoe Stroitel'stvo, No. 5, pp. 30-40. May, 2000.

0018-8220/00/3405-02-13525.00 @2000 I,[luwer Academic/Plenunl Publishers 243

TABLE 1. N u m b e r of Const ruc ted Dams A n d Dams Under Const ruct ion by Close of 1998 [9[

Country

China .lapan Kirgiz Thailand Indonesia Total in Asia. Spain France Greece Rumania Italy Russia Total in Europe United States Canada Total in North America Brazil

Const- ructed

31) 32 1 l

64 21 6 3 2

33 1 29 2

31 14 2

Under con- struction

10 I

15

Total

40 36 1 1 1

79 2l 6 3 2 1 1

34 29 2

31 16

Country Const,- Under con- rutted struction

Mexico 5 5 HoJld uras '2 '2 Columbia '2 '2 Argentina l 1 Chile l l Dominican Republic 1 1 French Guiana l 1 Venezuela 1 1 Total in Central and 25 5 30 South America South African Republic 13 1 14 Morocco 8 1 9 Angola t l Algiers 1 1 Eritria 1 I 1 Total in Africa "2"2 4 26 Australia 9 !) Total 184 25 209

concrete, which was equal to 35 million m 3. The to t a l number of dams during tile three years had increased from 161 to 209. These d a t a represent only dams more t han i5 m high, which had been cons t ruc ted , or were under construction. W i t h o u t these constr ict ions, the to ta l list of RCC dams is somewhat greater . According to our d a t a bank. which includes cons t ruc ted dams, dams under cons t ruc t ion , dams under design, and dams scheduled fbr design. the complete count a m o u n t e d to 212 dams l)y mid-1995. This count includes not only dams const ructed of roller- compacted concrete, bu t also dams in which ro l l e r -compac ted concrete was used either tbr s t reng then ing (fbr example, the arch dam of the G i b r a l t a r Dam in the Uni ted S ta tes ) . or only for individual small eIements (fbr example, the I taipu Dam in Brazil) .

R,CC dams tha t have been constructed, or a re under cons t ruc t ion are dis t r ibuted th roughou t the entire, world under a b road range of c l imat ic condit ions in bo th deve loped and developing countries. These dams were uniformly dis t r ibuted by cont inent in 1995: approx imate ly four in Nor th Amer ica , fbur in Asia, fbur in Europe. and four in other regions. The geography of the dams had changed by the close of 1998: 38% of the dams were fonnd in Asia. 16% in Europe, 15% in Nor th Amer ica , 14% in Cent ra l and Sou th America , and 12% in Africa. T h e dams constructed or un(ler const ruct ion encompass 28 countries of all the wor ld ' s cont inents (Table 1).

Since the two lead ing countries in the cons t ruc t ion of RCC dams (China attd J apan ) are located in Asia, it is precisely this region t h a t occupies the leading pos i t ion with respect to number of dams const ructed and dams scheduled for const ruct ion . I t is possible to isolate the fbur leading countr ies China, J apan , United States, and Spain - which conta in app rox ima te ly 60% of the t o t a l number of dams where ro l le r -compacted concrete has been used.

RCC dams have been const ructed in var ious cl imatic zones, including zones with high and low air tem- peratures and under ex t r eme ly humid condit ions. For example , the 120-meter Ven K h a r u n D a m with a volume of 1,690,000 m 3 was cons t ruc ted in Algiers at an air t e m p e r a t u r e above 43°C. The Upper St i l lwater Dam with a height of 91 m and vohime of 1.125,000 m a and the 40-meter Rober t son Lake Dani with a volunie of 28.000 ni a were constructed, respectively, in the United Sta tes and Ca na da , a t ambien t winter-air t empera tu re s to mimes 35°C. In the l l 3 -m-h igh Pangue D a m in Chile with an R C C volume of 660,000 m a, conc rde was p laced over a period of 13 months with a to ta l p r ec ip i t a t i on of 4.436 mm ( inchld ing three months when 3.130 mm of ra in fell) [9].

A new type of lean-concrete dams - dams formed from a stiff fill ("hardfil l") - have recent ly appeared [2]. In fact. cement - s t reng thened rock-fill dams s i tuated, for example , in regions with a high seismic load, or on r e l a t i v e h weak fomnlat ion beds, m a y be classed anlong these dams. The first large "hardfill dam" was conli)leted ill 1993 (the Maraph ia D a m in Greece) . A somewhat smal le r clam uti l izing the same construction ideas was built on a weak fimndation bed in 1989 [3].

I t can be conchtded tha t the new method of cons t ruc t ing dams of rolk,r-(-on~pacted concrete has just i f ied itself by now. Cer ta in t rends , which have been p roven in pract ice, are, unconditiomdly, s table , and al though large differences will r emain in cer ta in detai ls and approaches cor responding to the broad spec t ru in of conditions un(ler

244

120

ll0

1 O0

90

~, 80 E r~

70

60

-~ 50

4O

30

20

10

/

J / / 1

/ 3

Year completed

Fig. 1. Tota l lllllnl~cr ¢~t'~l;,lub cons t ruc ted annual ly with various tyt)es of roller- compacted coucr~,|~ , I,,,t~l~- prior to 1994): 1) high paste content; 2) med ium paste content : 3) .I,l)an 11('[)): 4) low pas te content: 5) "hardfill" t ype of dam.

which the dams are const ructed , r ~ t , v it ix a,~w possible to formula te basic results of experience gained wi th the cons t ruc t ion of RCC dams.

Cla,s.si:ficatio'n artd Dcsig'n Primi/d,, ,,] RCC Darns. The development of dynanf ic approaches to design pr inciples and methods of RCC dam c,m.-t rm, i~m. which have been approved in various countr ies attd under different condi t ions , was completed within 1)lincilml I~,mu~laries app rox ima te ly by 1992; this enables us to d ivide dams into the following types, which have nmintaitw~l ;, ~lal~Ie d i s t r ibu t ion with respect to pe rcen tage in recent years [9]:

dams t~brmed from lean roll~,r-c~ m, t J~,~l~., 1('~ m('I'ete in which the content of the b inder (cement plus pozzuolana) is less than 100 k g / m a - - 12%;

dams built in accordance with the' R( 'C method , ms is done in Japan, ms a rule, have a b inder con ten t of 120-130 k g / m 3 - 18%;

dams fbrmed from ro l l e r -compmwd c~mcrete with an ~werage binder content of 100-150 k g / m 3 - 22%; and, dams formed from roller-compa(t~'~l c~mcrete wi th a high binder content (more t h a n 150 k g / m a - 46%. Dams with a high binder cont('nt arc designed with impermeab le lavers tha t cohere well one to the other .

A b inde r content of 150 k g / m 3 was (let<'rmim.,I as the level a t which impermeabi l i ty of the in-si tu ro l l e r -compac ted concre te (also including the horizontal joints) is equivalent to the impermeabi l i ty of convent iona l concrete in g rav i ty d a m s (a permeabilit.y of tim order of 1()-i~) m/see) . F igure 1 shows a plot of the increase in the total number of the different types of dams comple ted by the (.los~, of each year (prior to 1994). One can see t ha t since 19~9, the number of d a m s completed each year had averaged approx imate ly 16, of which 10 had been cons t ruc t ed with a high b inder content , and six were of the o ther types [:31 .

Approximate ly two- th i rds of all RCC dams COllstructed in recent years possess concre te with a high b inder content . All I/CC dams in Spain an(l ( ' ssent ialh the ma.iority of dams in China conta in concre te with a high b inder eontent . All dams in J a p a n use the RCD m d h o d developed by the Japanese Min is t ry of Cons t ruc t ion and reflect charac te r i s t i c Japanese fbatures. Us(~ of a lm)ad spec t rum of accet)taI)le types of dams is charac ter i s t ic of the Uni ted Sta tes . After 1986 (dams const ructed u I) to that t ime can be considered f i rs t -generat ion (lanls), 21 danlb have been cons t ruc ted in the United States : of these dams. two were fbrmed fl'om lean concrete (9.5%), seven with a m e d i u m cement content (35.5~)), and 12 with a high binder content (57%). The same p ropo r t i ons are repea ted fbr dams cons t rue ted throughout the ent i re worl(t (oxcluding the dams in Japan) .

Use of ro l ler -compacted concrete throughout the ent ire volume of the body of the dam, or min imiza t ion of the volume of conventional concrete has been an indis i )utable t rend of recent years. Th is t r end is combined wi th use of an elevated binder content while retaining a stiff' consis tency of the concrete mix.

2 4 5

TABLE 2. Parameters of Most Outstanding Dams Constructed of R.oller-Compacted Concrete

Record dam indicator

Highest dam Greatest volume Greatest length of dam along (:rest.

Dam

Urayama .k [iyagase Kapanda

Country

Japan

Japan Angola

Height, m

[56

155 110

Length, m

372

400 1203

"~'ohlltle~

thousands O|' 1II 3 .

12.9.I (~860)

t5;~7 (2001) 757 (li5-~)

Volume of reser- voir. millions

Of IIl 3

58 19

4795

C o m m e n t : * - the vohnne of roller-compacted concrete: the total vohnne of the dam is given in the parentheses.

Of tile four countries in which the greatest nmnber of RCC dams have been constructed, three have therefore selected their own special approach, which is the most acceptable for their conditions, and one (United States) uses a broad range of the construction methods employed throughout the entire world.

Advantages of RCC Darns. As compared with other construction methods, economy and rate of construction are the two basic ~ulvantages of dams formed from roller-compacted concrete. Practice has demonstrated that a dam formed [:rom roller-compacted concrete is usually 25-40% cheaper than a gravity dam formed from conventional concrete, 5-15% less expensive than an arch dam tbrmed from conventional concrete, and 0-25% less expensive than a rock-fill dam. Thus, the installation of an RCC dam on a good foundation bed is ahnost always the least expensive niethod of construction.

The rapid rate at which roller-compacted concrete is placed provides many advantages: it pernfits the con- struction of a comparatively high dam in a single dry season, and therefore reduces the need to discharge water during operations, or to construct a dam in a single summer in a severe climate, where construction is limited with respect to time. A cost reduction for both the client, and also the contractor, and a rapid return of capital expenditures for the project are, however, the principal advantages.

Figure 2 shows the duration of concrete placement in a dam. There are several examples of dams of sufficient height, which were built in a very short time, for example, the Stage Coach Dam (United States) with a height of 46 m and 34,000-m 3 volume of roller-compacted concrete, which was constructed in not nmch more than :37 days [3]. The average placenmnt rate, however, is approximately 6 m of height per month. Thus, ~ 100-meter dam is usuallv constructed in 16 months, and within the range between 11 months for high placement rates and 20 months for lower rates. As compared with the average rate of construction of other types of dams, dams built in accordance with the RCD method take approximately twice as long to constrtlct. It is possible that this is dictated by the more complex method of construction.

Certain information on the most outstanding R.CC dams is presented in Table 2. Design.s of RCC Dams. The dimensions of the dams varied little on average fbr the first 10 years, right up

to 1994. The average height of dams constructed anmlally fluctuated from 40 to 50 m with the dam containing an

average vohlme ranging from 100,000 to 200,000 m :3. Beginning in 1995. however, an increase is observed in the dimensions of dalns fbrmed from roller-compacted concrete (Fig. 3). During the next three years, and also for dams under construction, the dimensions averaged throughout the years were as follows; a height of 60-80 m, and a vohnne of 270,000-450,000 m a [9].

The traditional triangular profile of the gr~vity dam is considered the most appropriate profile for use of roller-compacted concrete to the maxinmnl extent right u t) to 1()0~ with respect to vohnne, i.e., built completely of RCC. Figures 4, 5. and 6 show the actual profiles of dams in certain comltries, from which a difference is seen in the approaches taken in these cotlntries. Solutions closest to the classical triangular profile are characteristic of dams built in Spain (Fig. 6) [7]. Broadening of the lower section of the dam by inclining the thrust face in the lower third of its height is employed in Japanese Dams (Fig. 5). Sitnilar solutions are also characteristic of gravity dams formed from conventional concrete, in Japan: this is associated with elevated seismicity and the quality of the foundation beds. In Chinese RCC dams (Fig. 4) [5], originality of adopted structm'al sohttions is probably associated with the need to pass high flow rates of water through spillways. Nonstandard design sohltions fi)r RCC dams have been used in Morocco and Australia. It should be i)ointed out that the diversity of structural solutions employed, especially in sonic methods of fbrming the external faces, vertical transverse joints, and other elements of the dam, is increasing as the technology of roller-compared concrete develops. Several principally new structural solutions will be discussed below in greater detail.

Ternperat'a'rc-Sh'~97.kage Joi'nts. By the end of 1987, almost 70% of the dams constructed did not have

246

150-

E 100- g

50-

I t I I I I 6 12 18 24 30 36

Duration of concrete placement in months

Fig. 2. Construct ion ra te of RCC dams as function of thei r height (status prior to 1994).

I 4 0 ~

1983 85 87

~ 500

400

200

~ 0 89 91 93 95 97 Under

construction

Fig. 3. Change in average d imensions of RCC dams con- s t ruc ted annually [9].

t r ansverse .joints. This percentage then dropped to 35% in 1988-1989, and in 1990-1993, only 12% of the R C C dams did not have joints in some form. Thus, there is a significant range of solutions used in this respect: from d a m s built wi thou t joints to dams in which .joints are instal led from ti le ups t r eam to tile downs t r eam faces. In J apanese datns. sec t ioning by tempera ture-shr inkage joints in FICC dams is employed essentially in the same manner as in dams formed from conventional concrete, with the difference being tha t joints are created in ro l le r<:ompacted concre te by forming a notch with a v i b r a t o r y blade and embedding a p las t ic or metal plate. In recent years , blind jo in ts -notches . or notches-crack ini t iators have come into increasingly b roader use, including in arch dams .

"'Hardfill'" Darns. The above-mentioned "'hardfill" dams should be classed among the newest t rends. In 1992, Londe and Lino [2] p roposed a new design of 1RCC dams with a symmetr ic t ransverse profile and an an t i - f i l t ra t ion shield on the ups t ream slope. Use of a lean ro l le r -compacted concrete called "hardfil l" ensured low-cost cons t ruc t ion . The symmet r i c cross-sectional profile instills high re l iabi l i ty as compared with a convent ional gravity dam. re(luc(,s s t resses in the body of the dam. and make.s it possible to cons t ruc t the dam on a weak tbun(tat ion bed, or in highly seismic regions. A profile of t r iangular configuration with slopes of 1:0.7 oil. the u p s t r e a m and downs t ream sides is sugges ted as the most re l iable solution. In this case, the resu l tan t of the hydros ta t ic load and dead weight is loca ted at the center of the suppor t section, creating condi t ions for the most uniform stress d i s t r i bu t ion along the contac t with the fbundation bed.

The authors of this proposal t reat the new ma te r i a l "hardii l l" -- as someth ing similar to soil cement or roller-c, ompacted concrete with modification of r igid technical requirements, which are usual ly the same as the

247

7467

7401 ~,oo ~"7 ~ ~cc"~

Shaibenshui Xin'anjiang

v~47

7220

7114 l ,o .3 I

Jiangya

7449

V 12(

RCC " ' , ~ ' '7565 !V 335

/ 55 63 ;

$hanxi Zhuning s2

Silin

91

v

i " ~ auangzhou Dzheibesn;u

% 0 791 -- V I I.___.~

R200 ,

i 7 68 ~ ~ ~ ~ ~ ~ 86 -i .~ 32 ~ ~. 33 J. 82 Mianhuatan Daochaoshan Menteichen Shaimenten

Wenquanpu

71158

64~..,,,

-

I

z583 ~": 71'

Khaibin

~583 71077

b)

1~ RI50

t ~ 28.24 Puding

238

40 2" Beilian'ya Shaipai

Fig. 4. Dams of China: a) gravi ty : b) arch.

character is t ics for t rad i tkmal concrete . Modification of the concrete requ i rements makes it poss ib le to use a m a t e r i a l tha t is bes t sui ted for low stress: this. in turn, suppor ts a symmet r i c d a m profile [2]. The first d a m of this t ype Maraph ia - was constructed in Greece in 1992-1993. I t has a height of 26 m, a length of 265 m, and a concre te volume of 33,000 m 3. The u p s t r e a m and downstream slopes are 1:0.5. Tile rolled layers are 0.3 m thick, and the consmnpt ion of binders is a ~btlows: 55 k g / m 3 of c, ement and 15 k g / m 3 of pozzuolana. The Ano M e r a Dam in Greece with a height of 32 m, which was const ructed in 1994, is s imilar [3].

248

Normal support ~ 290,0

Miyagase I : x\ \ .< H=155m ~==~~'~a"

2 '\'>

/ ; _ _g . . . . . . .

,~ 120,3 je 30J,

V 578,0 r"" '1

V 476,5

, " " \ "4

~7 247,0

'7 229,0 ~ ) o o Asakhi-Ogawa ~

tt =84 m

67,2

Vig. 5. Dams of .Japan.

Arch. Dams. E x p a n s i o n of t h,, rang, ' , ~t" Ilsr of rol ler-compacted concrete to arch dams can be called ti le second innovat ion of recent years. Al though tw,~ , r ( .h -grav i ty dams (Knelpor t and Uolvdans) with a height of 50 and 70 m, respectively, had been previousIy c(mst rm-tc,(1 in tile South African }Republic, and a p rog ram for the cons t ruc t ion of o ther pure ly arch dams h a d been a,hrrti×~,d, the first arch dam - the Puding Darn with a height of 75 m was cons t ruc ted in China in 1993. In vi(,w of t lw impor tance of this problem, let us cite deta i led da t a concerning this d a m [4].

The Pud ing D a m is loca ted in a rchl t ively narrow Callyorl ( L / H = 2) of nonsymmetr ic section in a region wi th a sub t rop ica l c l imate in the monsoon zone. The average air t empera tu re is 14.7°C, and the average water temI)era ture is 16.5°C. T h e average ('Oml)Ut(,d t empera tu re of the concrete iIl tile dam dur ing its service life has been 16.4°C. The hydropro jec t is being used tot wa te r power, irrigation, water supply, and recreat ion. The volmne of tile reservoir is 421 million m a. T h e dam. which has a crest length of 196 m, has a t apered arch with a s ingle-centered configm'ation: tile thickness is 28.3 m ahmg t im foundat ion bed. and 6.3 m at the crest (except for tile centra l spillway por t ioa ) . The blind sect ions of the d;./iii have a s lope of h0.35 on the downst ream face. The spillw~\y por t ion of the d a m has a prac t ica l profile in the Ul)lmr elevat ions, and a. vertical downst reanl Nee jus t below it. The u p s t r e a m face of the dam is vertical, wi th the exceI~tion of the zone ad.ja('(mt to the foundat ion bed, where it has a sl ight adverse gra(lient. Despi te its near ly 200-nleter length, there are no tempera ture-shr inkage joints in the dam. and only three jo in ts -notches were ins ta l led on the ups t ream side.

In the Puding Dam, rol ler-( 'omimcted concre te was used in a predominant par t of its volume: 103,000 m :~ of the to ta l volmne of 137,000 m a. Conventional concre te was used on the lower sm'face in an app rox ima te ly two-meter zone. on the spillway, and in the bulwarks of the fbur spans in the center of the dam.

Two composi t ions of ro l le r -compacted concrete were used: alI_ NS-2 composi t ion on the side of the thrust face. and an NS-3 compos i t ion in the remain ing zone. The compositioms of the concrete sand their basic indicators are presented in Table :3. A Class 525 cement wi th art MgO cotrtent of 2.3%, which has a weak tendency to expand. was employed: this should presumal) ly c o m p e n s a t e fi)r tit(, concrete 's shrinkage. The fly ash cor responded to the

249

Santa Eugenia 6,5

• 209.0

RCC2

CC i 75

RCC I ~

• 130,0

Val

620,0 • ~;%. ~29, l__.._.~5

- - l 0.8 !. ~--]i

~ i Ventilation pipe ~ . ~ / . Bottom discharge

Conventional ~,~,~--~\~N~-~.~X / / concrete ~ ~.~N~'~,~,~'Nv-~N-~-'~.~X " / I 55

~ Gate chamber J

~ > ' - " ' ~ x x ? " ' ~ \ " v > " t x " i ' d J . . . . g [ . . . . . 1. ¢~7 ' . . . . . . . . . & l . . . . t . . . . m" i ,

~-' Conventional concrete

0 , 7 5

1 334 25v2, [q • T ~-" 331•0 y t

lO,

0,0 l l -

Serra Brava

6,5 o,751l 336.67

~1 "~1 N~ ~ 3 q 0"3k) 0 '045

" N , . 00s

Senza 8 Detail 1

1335,8 • " . Detail 1 . . . . . "~"

O,a,na o . . . .

0,4,

~%"~,'~NN%XNx~.~ Conventional ~ - - - - ~ ~ ~ ~ . ~ concrete

: ( ' / : "X . ' . . " '

1 2 9 4 ~

CC

Rialp

w436,0

10~.~ '~%'~" / -%~ '~ • 359,8

339,0 "['L~'] 1~" Drainage Grout curtain1"7 =P I

Fig. 6. Dams of Spain.

Class II standard. Crushed limestone having a low coefficient of linear expansion (5.5 - 10-($/deg C) was used as coarse aggregate; this aggregate was considered suitable for the prevention of thernml cracking.

The concrete mix was placed in layers each a0-a5 cm thick prior to compaction, leveled by bulldozer, and compacted with two "Bomag" vibratory rollers. The regime employed fbr vibratory-rotter compaction called for two

2 5 0

T A B L E 3. Typica l Composi t ions of Ro l l e r -Compac ted Concre te in Pud ing Arch D a m (China)

( 'haracteristic NS-2 coli'l- NS-3 com- position position

('ompressive strength atler 90 days, MPa Tensile strength, MPa Shear strength, MPa Permeability, re~see Content:

cement, kg//ltI 3 fly ash, kg/m a water, kg/m a sand, kg/m a crushed stone < 20 mm. kg/m :~ crushed stone < ,10 ram. kg/m:" crushed stone < 80 ram, kg/m "~ additives, %

Stiffness of concrete mix. sec Vv~ter-binder ratio Content of sand in aggregate mixture

20 ~> t . 5

2 10-s

8.5 103 94

836

830 554 0.85

1 0 ± 5 0.5

0.38

t5 1.5 2

1 0 - ~s

5-1 99 84 768 454 604 -i54 0.85

I 0 + 5 0.55 0.34

passes wi thout vibrat ion at the outse t and te rminat iou , and six in t e rmed ia t e passes wi th vibraeion (2 + 6 + 2). Two manua l v ib ra to ry compactors With a (2 + 24-30 + 2) compact ion regime resul t ing in a layer thickness of 25-30 cm after conq)act ion were used on the concrete mix placed near formwork. A 15-20 toni under lying cement / f ly-ash g rou t was placed to inlprove cohesion between the layers of ro l le r -compacted concrete . The concrete was placed in ti le d i rec t ion froin the downstream to tile ups t rean l face within the limits of the s t r ip where the fbrmwork had been instal led. A nletal l ic cantilever form 4 m high was used.

According to technical specifications, the t empera tu re of the concrete mix be ing placed should not exceed 15°C. During monitoring in ti le course of construct ion, the t e n lpe r a tu r e of the concrete did not exceed 16.4°C at the t ime of its placement. A max inmm concrete t empera tu re of 30.8°C was recorded. No unexpected cracks were observed.

During construction, the spring flood of 1992 was passed th rough the uncomple ted dam in conformity wi th design. In that period, the flow of water was uninter rupted: this lowered the p robab i l i t y of t empera tu re - induced cracking markedly. Careful inspect ion r e v e a l e d t h r e e j o in t / no t c h - in i t i a t e d cracks tha t had developed as the concre te g radua l ly cooled and during i m p o u n d m e n t of tile reservoir. On the o the r hand, however, no cracks were de t ec t ed in other a reas where they could have appea red [4]. Despite the fact t i ta t the joints-cracks were not grouted, they did not p l ay a negative role. and ti le Pud ing D a m is functioning normal ly as a regular arch s t ruc tu re [9].

The positive experience gained wi th cons t ruc tkm of the Pud ing arch dam has opened prospects for use of roller-compactexl concrete in o ther arch dams, including those wi th a height to 100 meters . In China. for example , p lacement of rol ler-compacted concrete in ti le 132-meter Shapai arch d a m with a ro l le r -compacted-concre te volume of 3!)3.()(10 m a was begun in 1998.

F()vr~m~io'r~, qf Dam Fa, ces. For the m a j o r i t y of dams where ro l le r -compac ted concre te is employed, the ex te rna l faces are tbrmed by placing convent ional v ib ra t ed concrete near t i le formwork. ( ) t i ler methods used to form the ups t r eam and downstreanl faces and spi l lways ill tRCC dams are also known at tile same tiine. The p ropo r t i on of those (lares where 100% of the s t ructm'e consists of ro l le r -compacted concrete, the p lacement of which includes tile tornrot( , behind the fi)rmwork on ti le ups t r eam and downs t ream faces, has increased in recent years. This is especia l ly m)ticcalHe in Spanish dams. where the use of a high binder content makes it possible to ob t a in good results.

S tepped thces bo th on tile lower buhvark and spillways are r a the r popular and have been used ill 37~X~ of the d(~uustrcam faces and 35(~, of t i le st)ilhvays. For tile downs t ream faces, s teps otti~r and number of adwmtages , since they ar~' easier to form than all inclined face: it is easier to build spi lhvays with s teps in the upl)cr section, when it is ad< h,~l tater as a separa te s t ruc ture ; s teps create a character is t ic featm'e tha t is p leas ing to the eye, and offer easy accessihi l i ty for perk)die inspect ions of t i le dam. A major advautage, which deals with energy dissipat ion at re la t ive low lh~w rates over the surface area, is offered hy such a spillway. W h e n the discharged flow is less than 25 m3/sec per ru lming meter, use of s teps makes it possible to const ruct a toe bas in of smaller dimensions, attd in this manner , to genera te a significant saving of resources [3].

251

TABLE 4. Cohesion (MPa) along .Joints in Roller-Compac- ted Concrete (9{}-Day Concrete) [81

Cement content, kg/m :~ 70 i00 t25 Joint "'maturity." 125°(7 - h 0.55 0.95 1. i Same, 325°C -h 0. l 0.85 1.15 Same, 600°C , h 0.35 0,70 1.0 Same with set retarder. 1.05 1.75 2.3 ~ 0 0 ° C - h

Same with underlying layer. 1.3 2.i 2.7 1200 ° C - h

One of the latest innovations is a grout-enriched vibrated rol ler-compacted concrete (GEVR [9]), which was first used in the construction of the J iangya Darn in China (128 m high, volume of 1,060,000 m3). In actuality, it has been proposed to introduce a cement grout to an RCC type of concrete mix for G E V R concrete prior to and after its placement so that it is rendered suitable for use of internal (deep) vibrators. Thus, modified roller-compacted concrete is beeonfing an effective material ~br placeme~lt in the vicinity of formwork in the ups t ream and downstream faces, or near tile abutments of the dams toward the flanks. In the lat ter case, the grout is distributed on the abutment, and the roller-compacted concrete is then placed. On the whole, the concrete mix is worked by deep vibrator along the abutment. The principal advantage of G E V R concrete is tha t there is no need to t ransport a concrete mix of plastic consistency, which may become segregated, and only the grout need be delivered. The latter can be t ransported in a mixer, or transferred by pump. Use of G E V R concrete is a promising sohttion, since it is possible to s impli~ the procedure used to place the roller-compacted concrete.

Treatment of Surface of Horizontal Joints Between Layers and Their Quality. Surface treatment of the joints between layers of roller-compacted concrete remains a unique problem in which no t rend can be traced in the construct ion of RCC dams. The degree of t reatment fluctuates from its tota l absence to use of freshly t r immed ("green-cut") joints and/or their coating by an under t ,mg layer of grout (as in RCD structures) . The linfiting "matur i ty" of the joints, or the time to the s tar t of their t reatment, with the elapse of which the surftce is cleaned, and/or the underlying layer should be placed, are specially indicated for certain dams. The limiting "matur i ty" fluctuates from 200 to 700°C • h or front 6 to 24 h at a temperature of the order of 30°C [3]. "With other conditions equal, it is obvious that a more easily placed concrete will ensure a be t te r interlayer bond than a concrete tha t is more difl=icult to plac, e.

It has been demonstrated that certain surface-treatment measures m a y actually reduce the negative effect of joints. According to Schrader [8], joint "matu r i ty" and use of an underlying layer or a concrete composition with the addition of a set retarder exerts a marked influence on the cohesion along the joints (Table 4).

According to these data, the addit ion of a set retarder and use of an underlying layer increases cohesion by a factor of two-three, but here, the coefficient of friction is virtually unchanged and remains equal to unity on average. It is also possible to make note of the positive role played by an increase in cement consumption. Schrader [8] indicates tha t in addition to these factors, o ther circumstances also exert an influence on the qual i ty of the horizontal join~,s in roller-compacted concrete: aggregate segregation on the surface of the joint, precipitat ion in the form of rainfall, the wetness, density, and roughness of the surface, the means by which the concrete mix is delivered, etc. A point system of evahlating joint quality, according to which five conventional evaluations are set forth for joint quali ty as a function of a joint-quality index equal to the sum of the points defined for eight groups of effective factors, has been proposed in this connection. Moreover, correction factors for the design strength of the concrete, which take into account the different effect of joint quali ty on the conipressive attd tensile strengths, cohesion, and coefficient of friction, are introduced as a function of the joint-quali ty index. These correct ion factors are different for two varieties of roller-compacted concrete (Table 5).

According to our experiments on cores removed fronl the body of the Kapanda Dam, a pronomiced increase ill tlle shear strength of the joints is observed with ;-tit underlying layer: an increase of from 0.33 to 1.(}6 an(l fl'om 1.0 to 1.23 MPa in the cohesion att(l coeffMent of friction, respectively [6]. There are also da ta indicating that neither cleaning of the sm'face, nor underlying layers inlprove the iulpernleability of the concrete placenient [3].

Placeability of Concrete ll~i:c. An increase in the placeability of the coticrete mix, which is usually determined by tile VeBe inethod or in accordance wiU1 the VC method of testing, equivalent to the Japanese standard, represents a general t rend for roller-compacted concretes. In the niid-1980s, placeability corresponding to a shuni~ time of fi 'om approximately 30 to 35 see was the general t rend for roller-compacted concretes. More modern roller-compacted concretes now have a placeability corresponding to a slutllp time of approximate ly 15 see [131.

252

T A B L E 5. Cor rec t ion Factors for Des ign Strength of Year-old R o l l e r - C o m p a c t e d Concrete as Func t ion of . lo in t -Qual i ty Index [8]

Evaluation of joint quality

Type of roller-eompacted concrete

Very poor LJQI < - 6

Joint-quality Lean with no underlying layer Lean with underlying layer or with index (LJQ[) retarder and no lmderlying layer

('ompression, coet- ('ohesio,l. tension ( 'ompression. coe]- ('ohesion. tension ficient o[ [riction ficient of tYiction

Excellent 3 1.03 1.1 1.03 I. [ L.JQI > l 2 1.02 1.07 1.02 1.07

1 1.01 1.04 1.01 [.04 Good 0 1.0 1.0 1.0 1.0

- 1 0.99 0.95 0.99 0.97 Satisfactory - 2 0.98 0.9 0.98 0.92

- 3 0.96 0.84 0.97 0.87 -,4 0.94 0.76 0.95 0.8

Poor - 5 0.91 0.67 0.93 0.75 - 6 0.88 0.56 0.9 0.7 - 8 0.8 0.32 0.83 0.57

-- [0 0.7 0. l 0.75 0.-12

La~ler Thickness. Disregarding RCD dams , which have thicker layers of f rom 500 to 1000 mm. tile op t ima l layer th ickness is 300 m m in the majori ty of o the r dams ~brnLed from ro l l e r - compac ted concrete ( approx ima te ly 70%). In t i le remaining dams , tile layer thickness fluctuates between 250 (the m a j o r i t y of dams in tile Sou~h Afr ican Republ ic ) and 400 ram. All dams completed in 1993 had a layer thickness of 300 ram, with the exception of the 1-{CD (l&nls.

Select'ior~, of Basic Para'm, eter'.s of Roller- Co're, patted Concrete. Based on analys is of tile s ta te of the a r t and t rends in d a m cons t ruc t ion using ro l l e r<ompac t ed concrete, the following p a r a m e t e r s and approaches, which are r e c o m m e n d e d as an op t ima l a l ternate scheme in cer ta in publicat ions [3], can be t e rmed most widespread:

the pr ior i ty is to del iver quality and cons t ruc t io~ rate, and to a lesser degree, to reduce cost; a b inder content r ang ing from 150 to 225 kg/m'~: a m a j o r par t of the b inder (from 50 to 75%) is low-alkali fty ash (or o the r pozzuolam~): the concrete nfix be ing rolled should have a placeabil i ty corresponding to a s lump t ime of the order of 15-25

sec on the VeBe ins t rmnent ; the faces are formed by placing convent ional v ibra ted concrete beh ind forms, a l though recently, roller-

c o m p a c t e d concrete has been placed all the more frequently direct ly behind forms wi thout cover concrete: if the specific flow r a t e on the spillway is less than 25 m3/sec /m, the sp i l lway face can be s tepped: it is bes t to instMi th rough transverse tempera ture-shr inkage joints spaced 20 to 45 m on centers: the layer thickness af ter compaction is, as a rule, 30 cm: and, the me thod of t r ea t i ng the surface be tween layers of concrete is selected as a function of the required qua l i ty

of concre te placement; it m a y fluctuate fi'om a t o t a l absence of t rea tment to the p lacement of an underlying layer. Concl'usions Analys is of ahnost 20 years of exper ience with the use of ro l l e r -compac ted concrete in dam cons t ruc t ion

enables us to conclude tha t in designing a concre te dam fbrmed fl'om ro l l e r -compac ted concrete, it is always possible to ca lcu la te for the select ion of optimal sohl t ions, at least f'ron~ a number of so lu t ions tha t have been proven fbr o ther dams . Exposed t r ends and the most widespread conditions for use of ro l l e r - compac ted concrete, including the p rocedura l e lements of its p lacement , require the i r own a([justment and a d a p t a t i o n in each design in confornl i ty wi th tile specific c i rcmnstances of the project. Desp i te the predominance of these t rends , they should be retbrred to as cr i t ical , s ince dams formed from rol ler-compacted concrete are tmique an(l should r e spond to sI)ecific condit ions, mid the se lec t ion of different so lu t ions should co r respond to technical requirements of the design. The most preva len t condi t ions under which roller-comi)actcd concre te is used in danls should not therefore be considered universal; lnoreover , ninny other a l t e r n a t e schemes of s t r uc tu r a l and i)rocedural sohtt ions are also approved in actual prac t ice .

Ti le modern prac t ice of constructing d a m s front rol ler-compacted concre te has accunmla ted a whole arsenal of proven sohlt ions, which open broad possibili t ies and prospects tbr the design and cons t ruc t ion of reliable s t ruc tures . At t i le s ame time, it is not exc luded that in a specific case, some controversial m o m e n t s inay arise where the p lace lnent of concre te ill test blo('lcs p r io r to the s tar t of concre t ing for the dam will be r equ i red for its solution.

253

R E F E R E N C E S

1.

3.

4.

5.

6.

7.

8.

9.

L. A. Toll~chev, V. S. Shangin, K. K. Kuz'min, A. T. Oskolkov, V. B. Sudakov, E. A. Kogan et M., "In- structions l~br use of layer-by-layer (Toktogul) method of placing concrete in hydraulic consmwtion," in: /nstit'~,tional Constr~,ction Re.q'~Lla.tion 06-7~ [in RussianJ, Min4nergo SSSR, Moscow (1974).

P. Londe and M. Lino. "The phased symmetrical hardfill dam: a ~mw com:ept fbr R.CC.'" Wa~cr Po'mer a~.d Dam Con.str'uc~.ion (February. 1992).

M. R. H. Dunstan. "'The state-of the-art of R.CC dams." I'nter'na, tiorzal Jo'ur'nal on Hj/drvpo'wer" a'n,d Dams, 1. No. 2 (March, 1994).

B. "Wang, D. V~2ms, and Y. He. "Construction of the Pnding RCC arch dam," 2ntc~tatiorza, l ./ourw, al on Erffdropower and Dams, 1, No. 2 (March, 1994).

C. Shem "New tech~lical progress of RCC dam construction in China." in: Proceedings of the I'nterw, ational S!/mposi'urn on RCC Dams. Vol. 3, 2-4 October 1995, Santander, Spain.

E. A. Kogan and V. E. Fedossov, "Roller-compacted concrete and strength of horizontal construction joints." in: Proceedings of the [nter~ational Symposium on RCC Dams, Vol. 1, 2-4 October 1995, Santander. Spain.

M. A. Franco and J. Y. Cordova, "The Spanish approach to RCC dam engineering," [nter~ational .lowrnal on H?jdropower and Darrzs (May. 1995).

E. K. Schrader, "Deveiopment, c~trrm~t practices, controversies, and options(' in: Re.scr'voirs in Rivc.r Basir~ Developrner#.: Prvceedirzgs of the ICOLD S:qmposi'urn (Oslo. 6 July 1995), Vol. 2. A. A. Balkema, Rot terdam (1996).

M. R. H. Dunstan, "lRecent devetoi)ments in R CC dams(' I'nter~,ationag Jo'~rnal on I-I:~jdropower" and Darn,s, 6, No. 1 (1999).

254