State of Art of Compacted Concrete

Face Rockfill DamsB. Materón

(Bayardo Materón & Associates, Brazil)

Bayardo Materón

educated at the Cauca University, Popayán, Colombia (1960) and Purdue

University, Indiana ,USA(1965) where he received his degrees in Civil

Engineering and MSc in Civil Engineering respectively. Since the completion of

the Alto Achicayá CFRD in 1974 he has been involved with many leading

engineering organizations in the field of design and construction of rockfill dams.

He participated in the design and construction of the world highest CFRDs including Alto Anchicaya,

Salvajina, Porce III, Ranchería (Colombia); Foz do Areia , Xingo, Segredo, Ita, Itapebi, Machadinho,

Campos Novos, Barra Grande ( Brazil); Aguamilpa and El Cajon, La Parota and La Yesca

(México);Antamina, Torata ( Perú);Caracoles, Punta Negra (Argentina); Messochora (Greece);

Kannaviou (Cyprus), Bakun (Malaysia); Mohale ( Lesotho), Tiangshenqiao(China), Kárahnjúkar

(Iceland), Berg River and Braamhoek ( South Africa), Siah Bishe ( Iran) and Merowe, Sudan. He is now

a Consultant Engineer working in the field of design and construction of Rockfill Dams and the President

of CFRD Int. Society.

1 Introduction

The development of concrete face rockfill dams is well commented in the technical

literature. Cooke [1]. Initially dumped rockfill was used with problems of leakage and

deformation of the rockfill which caused excessive stresses in the concrete face slab and

rupture of the compression joints.

The transition to compacted rockfill occurred during early 60’s when in Europe was

developed the vibratory compactor roller. Some concrete and asphalt face dams were

built with compacted rockfill and excellent performance.

This article reviews the progress of the high compacted rockfill concrete face dams since

1960 to present, commenting recent observations in dams related with the compression

joints. The article also refers to the design of the joints of high CFRDs and gives

recommendations for future projects of this type.

2 The Development of the Vibratory Compactor Roller

Before the application of the vibratory roller, most of the CFRDs were built by dumping

rockfill in lifts varying between 18 to 60m and sluicing the rockfill by application of water

in a ratio of 3m³ for each 1m³ of rockfill.

The deformation of the rockfill was high causing distresses in the slab with presence of

ruptures and spalling. It is important to mention that CFRDs built with dumped rockfill

presented cracks parallel to the plinth and high spalling in the longest compression joints

when the height of the dam exceeded 75m. Tension stresses close to abutments and

compression stresses buckling the central compression joints were observed.

Therzagui, in 1960, recommended the use of compacted rockfill, in order to reduce

rockfill deformations and sub-sequent damages to the face slab. At the end of 50’s

moderate high rockfills, compacted by vibratory rollers, were built in Europe with

excellent results.

Examples of compacted rockfill were:

Quoich 38m Scotland 3.5t roller

Henne 48m W. Germany 3.0t Tamping plate

Bigge 48m W. Germany 5.0t Tamping plate

Venemo 60m Norway 5.0t Vibratory roller

However, the vibratory compactors were developed in the 60’s when the increase of

compacted concrete face dams was growing up. The vibratory roller compactors opened

the door to increase density of the rockfill and to use different kinds of materials in an

economical and efficient manner.

Nowadays, there are different types of vibratory compactors ranging between 6t to 15t.

The definition of a vibratory roller is always referred to the load acting on the smooth

drum and not to the total weight of the roller. This weight per meter of drum must be

higher than 5t/m, to obtain required densities with vibration ranging between 1400-

1800VPM.

3 Evolution of High CFRDs

Table I, summarizes the evolution of CFRDs since Cethana,110m Australia built in 1971,

to the highest under construction, Shuibuya 233m, China to be completed in 2009. The

table also shows the period of the highest dams.

Table I Progress in Height of Some CFRDs

DAM HEIGHT M COUNTRYFACE SLAB

AREA M²

YEAR OF

COMPLETION

REMARKS

HIGHEST PERIOD

Cethana 110m Australia 30.000 1971 1971-1974

Alto Anchicaya 140m Colombia 22.000 1974 1974-1980

Mohale 145m Lesotho 87.000 2002 Highest in Africa

Salvajina 148m Colombia 57.500 1983 Highest in gravels

Xingó 150m Brazil 13.500 1994

Messochora 150m Greece 51.000 1995 Highest in Europe

Porce III 155m Colombia 57.000 2010 U.C.

Foz do Areia 160m Brazil 139.000 1980 1980-1993

Tankeng 161m China 68.000 2006

Tiang Shen qiao 178m China 180.000 1999 Highest in Asia

Hongjiadu 182m China 76.000 2007 U.C.

Barra Grande 185m Brazil 108.000 2006

Mazar 185m Ecuador 45.000 2008 U.C.

Sanbanxi 186m China 94.000 2008 U.C.

Aguamilpa 187m Mexico 137.000 1993 1993-2006

El Cajón 189m Mexico 99.000 2006 Complete

Kárahnjúkar 196m Iceland 93.000 2007 U.C.

Campos Novos 202m Brazil 106.000 2006 2006 Highest

Bakun 205m Malaysia 127.000 2007 U.C.

La Yesca 210m Mexico 129.000 2010 U.C.

Shuibuya 233m China 120.000 2009 U.C

U.C. = under construction

Cethana and Alto Anchicaya were dams well compacted without distresses in the face

slab due to the high rockfill modulus of compressibility ranging between 145MPa and

135MPa respectively.

It has been observed that some cracks sub parallel to the plinth are occurring in

compacted dams due to geometry of the abutments. These cracks are similar to those

observed in dumped rock fills with low moduli.

The effect of grading of the rockfill is very significative in the modulus of the

compressibility of the compacted rock. It has been observed that rockfill from basalt, with

uniform grading, results in high void ratio with rockfill moduli ranging between 30 to

60MPa. ( Itá, Machadinho, Foz do Areia, Mohale, Segredo, Barra Grande, Campos

Novos)

Well graded rockfills result in low void ratio and high moduli of compressibility, ranging

between

140MPa and 400MPa (Cethana, Alto Anchicaya, Aguamilpa, Salvajina).

Gravels fills are in general well graded and gives high modulus of compressibility and low

deformations in the face slab.

Fig. 1 Cethana Dam, Australia. Highest in 1971-1974 Fig. 2 Campos Novos Dam, Brazil. Highest in

2006.

It is extremely important to evaluate the compressibility of the rockfill before determining

the thickness of layers, the number of passes of the vibratory roller and the addition of

water to the fill.

Recently, during the construction of El Cajón,189m, Mexico, Mendez [2] was observed

that a generous application of water (>250 l/m³) and layers of 0.80 -1.00m thick

produced moduli higher dam 140MPa, when the fill was compacted with 6 passes of a

12t vibratory roller.

4 The Use of Extruded Curb

The transition material, 2B, located under the face slab, Fig. 3, was modified by James

Sherard using a processed material with a maximum size of 0.08-0.10m, 35-55% of sand

and fines passing the sieve N. 200 between 2-10%, Materón [3]

This material compacted horizontally by a vibratory roller requires additional compaction

in the up-slope direction of the upstream slope of the dam and protection against erosion.

Many dams were affected by erosion caused by heavy rains or eventual overtopping of

the diversion cofferdams. Consequently, a permanent protection of the upstream face of

the dam was provided by asphaltic emulsions or shotcrete. These operations were costly

and time consuming.

The use of the extruded curb was developed during the construction of the Itá dam,

120m, Brazil and the method simplified the execution of the CFRDs with many

advantages.

Modern dams in different countries have adopted this technology, which consists of

building a curb of lean concrete over the transition material before the construction of the

next layer. Fig. 4

Advantages of this method have been commented by others. (Resende - Materón) [4]

Which is being applied in the highest concrete face dams anywhere.

Fig. 3 Typical zoning of the CFRD

5 Recent Observations in the Compression Joints

Cracking and over stresses in the compression joints are occurring in high CFRDs in a

similar way observed in dumped rockfills with very low modulus of compressibility.

The first distress in the compression joints was reported for the Tiangshengqiao I, 178m,

China, on July, 2003. A second incident occurred in the same construction joint, which

was previously repaired, on May 2004. The Joint was repaired again by placing a 50 mm

compressible filler. No more damages have been reported.

The second distress incident was presented in Barra Grande, 185m, Brazil, when the

reservoir reached 85% of the maximum head. This event occurred in September 2005.

In October 2005, a similar observation was presented in the longest compression joint of

Campos Novos, 202m, in Brazil extending the damage to the bottom of the dam, and

with some inclined disruptures. In February 2006, some similar disrupters were observed

in Mohale, 145m, Lesotho, Africa.

The excessive compression breaks the concrete affecting the waterstops and increasing

leakage.

It appears that in high dams, specially located in narrow valleys, the deformation of the

face slab induce high compressive stresses in the central compression joints, when the

rockfill modulus of compressibility is relatively low. Fig. 5

6 Design Criteria for High CFRDs

The design criteria discussed in this item refers to the compaction of the rockfill and the

criteria for selecting the dimensions of the face slab and joints. Criteria to determine

slopes and stability analysis are not discussed in this article since they are widely

discussed in International Proceedings. [5];[6];[7];[8];[9]

Fig. 4 Typical construction of extruded curb Fig. 5 Excessive stress in the compression joint,

affecting the reinforcement, concrete and

waterstops

6.1 RockfillGenerally, compacted rockfill is designed with the international nomenclature indicated in

Fig.1

Zone 2 B: “Cushion Material” may be compacted in layers of 0.30; 0.40 and 0.50m

depending of the vibratory, compactor roller and the size of the dam. The usual number is

4-6 passes of the 10t vibratory roller, with a static load of 5t/m over the smooth drum.

Zone 3 A: It is built with the same thickness of zone 2B and compacted as described for

zones 2B, Zones 3B, 3C and T use the recommendations indicated in the Table 2.

Table 2 Required Compaction for high CFRDs

Zone

Layer

Thickness

m

Vibratory

Compactors

N.

PassesWater CU Observations

3B1.0m

0.6-0.8 m

10T

12T

4-6

6

200l/m²

>200

15

15

Heavier Vibratory rollers are adequate.

Weight 5t/m drum

3C1.20

0.80

10T

12T

4-6

6

200l/m³

>200l/m³

15

15

Heavier Vibratory rollers are adequate.

Weight 5t/m drum

T1.0

0.80

10T

12T

4-6

6

200l/m³

200l/m³

15

15Located in the middle of the dam.

In narrow valleys where A/H² 4 the compaction has to be intensified to obtain high

modulus of compressibility, where:

A = Face slab area in m² H = Height of the dam in meters

6.2 Concrete Face slabThickness and reinforcement

Thickness of the slab should be as follows:

a) Well graded rockfill H <120m

Use formula: T= 0.30+0,002H m

as applied in Australian Dams. T = Thickness in meters; H = Height in

meters.

If the rockfill modulus is lower than 100MPa use

T= 0.30+ 0,003H m

Use rebars 0.5% in both directions close to abutments and 0.4% in both directions in the

compression area.

b) Well graded rockfill H >120m

Use formula: T= 0.30+0.002H up to 120m

H>120m use T=0.0045H

Similar use of reinforcement as in a) above

c) Uniform grading rockfill H <120m

Use formula: T=0.30+0,003Hm

Use rebars 0.5% in both directions close to abutments and 0.4% in the compression

area.

d) Uniform grading rockfill H >120m

Use formula: T= 0.30+0,003H up to 120m and

T=0,0045H for H>120m

However, if rockfill modulus is lower than 100MPa increase the thickness of the central

slabs to :

T=0.40m+0.003H up to 120m

For H 120 use T=0,0063Hm

6.3 Joints1. Perimetric Joint

Use conventional perimetric joints. Fig. 6 shows the perimetric joint adopted in El Cajón,

189m, México

Fig. 6 Perimetric joint used in El Cajón, México. (F. Mendez)

2. Tension Joints

Use conventional tension joint with copper water stop and mastic on the upper portion of

the slab.

3. Compression Joints

Use compression joints as follows:

(1) Keep the theoretical thickness over the mortar pad.

(2) Place the mortar pad inside the extruded curb.

(3) Reduce the vertical web of the copper water stop to 2cm

(4) Use a filler in the joint. Wood filler or asphaltic filler to mitigate high compressive

stresses.

(5) Reduce the upper V notch to maximum 2cm, or not use V notch

(6) Install anti-spalling rebars. Fig.7

Fig. 7 Compression Joints as used in Kárahnjúkar,Iceland (H. Perez,MWH)

7 Conclusions

(1) The compacted CFRDs are being applied more frequently in increasing high

structures due to progress in the compaction equipment and new construction techniques

such as the extruded curb. Credit is also given to innovative design of the components of

the dam.

(2) Although the concrete face rockfill structure is safe, the design of the compression

joints and central slabs require modifications, as recommended in this article, to cope

with the high compression stress observed recently in high dams.

(3) High concrete face dams should be better compacted as a whole, to increase the

rockfill modulus of compressibility and minimize deformations of the face slab. Thinner

layer thickness, addition of water and more intense compaction will help to obtain denser

rockfills.

References

[1] Cooke J. Barry; the Concrete face rockfill dam; Especial publication edited by J.

Barry Cooke Consulting Engineer San Rafael, California, USA 1984.

[2] Mendez Fidencio; Rapid Construction of the El Cajón CFRD; Hydropower & Dams

Issue One, 2005.

[3] Resende Fernando; Materón Bayardo; Itá Method-New Construction Technology for

the transition Zone of CFRDs; CFRD 2000 Proceedings International Symposium on

Concrete Faced Rockfill Dams; September 2000; Beijing, China.

[4] Materón Bayardo; Transition Materials in the Highest CFRDs; Hydropower & Dams,

Volume Five, Issue Six, 1998.

[5] Proceedings, Concrete Face Rockfill Dams, Design Construction, and Performance,

ASCE, Detroit, October 1985.

[6] Proceedings, International Symposium on High Earth- Rockfill Dams - Especially

CFRD, Beijing, October 1993.

[7] Proceedings, Second Symposium on Concrete Face Rockfill Dams, Brazilian

Committee on Dams, Florianopolis, Brazil, October, 1999.

[8] CFRD 2000, Proceedings International Symposium on Concrete Faced Rockfill

Dams, Beijing, and September 2000.

[9] Cooke J. Barry Volume, Concrete Face Rockfill Dams, Beijing September, 2000.

CFRD Int. Society holds its Presidential business meeting

The meeting was held from 19:00~21:00 May 21, 2007 in the Three Gorges Xiba Hotel

China .

Mr. Bayardo Materon Chaired the meeting. Decisions were made as follows:

1. The Journal of CFRD Int. Society is to be published quarterly from this Sept. 2007 in

China, which is in charge of by Mr. Chen Qian.

2. Every member of CFRD Int. Society ought to pay 40 USD as membership fee each

year for publication of the Journal.

Attendees were:

Mr. Alberto Scuero , Italy ,  Vice President of CFRD Int. Society

Mr. Cao Keming, China, Vice President of CFRD Int. Society

Mr. Chen Qian, China, General Secretary of CFRD Int. Society