Asphalt Core Rock Fill Dam

Design and performance of the Yele asphalt-corerockfill dam

Weibiao Wang, Kaare Hoeg, and Yingbo Zhang

Abstract: The planning, design, and performance of the Yele asphalt-core rockfill dam in Sichuan Province, China, arepresented. The dam has a maximum height of 124.5 m, is located in a very seismic region with inclement climate, and isfounded on a geologically complex foundation, partly resting on a deep and pervious alluvial overburden and partly onbedrock. With these site conditions only an embankment-type dam was considered feasible, and three different optionswere considered for the design of the impervious barrier: (i) earth core, (ii) concrete facing, and (iii) asphalt core. Thethird option was chosen. The design is based on extensive analyses and laboratory tests, and a special model test was per-formed to study the behavior of the connection between the narrow asphalt core and concrete plinth. An impoundment testwas performed when the dam was 73 m high to test the imperviousness of the constructed core and the connections be-tween (i) the core and plinth and (ii) the plinth and foundation cut-off wall. An extensive field monitoring program wasimplemented. Design predictions are compared with field performance observations of the core and its interaction with theadjacent transition zones.

Key words: embankment dam, asphalt core, laboratory tests, finite element analyses, dam deformations, field monitoring.

Resume : La planification, la conception et la performance du barrage de Yele dans la province de Sichuan en Chine sontpresentees dans cet article. Le barrage en remblai rocheux de Yele, avec noyau bitumineux et une hauteur maximum de124,5 m, est localise dans une region de tres haute sismicite et sous un climat inclement. Le barrage est porte sur une fon-dation geologiquement complexe, en partie sur une couche epaisse et permeable d’alluvions et en partie sur du roc. Sousces conditions, la seule alternative faisable etait un barrage en remblai. Trois options ont ete considerees pour la concep-tion de la barriere impermeable : (i) un noyau en terre, (ii) un revetement de beton et (iii) un noyau bitumineux. Cette der-niere solution a ete retenue. Le dimensionnement est base sur de nombreuses analyses et essais en laboratoire, ainsi quesure une modelisation experimentale particuliere du comportement de l’interface entre le mince noyau central et la plinthede beton. Un essai de mise en eau a ete fait quand le barrage a atteint une hauteur de 73 m afin de tester l’impermeabilitedu noyau bitumineux, et les interfaces noyau–plinthe et plinthe–mur de fondation. Un programme extensif d’observationsa aussi ete adopte. Les predictions faites lors de la conception sont comparees avec le comportement in situ du noyau etde ses interactions avec les zones de transition adjacentes.

Mots-cles : barrage en remblai, noyau bitumineux, essais de laboratoire, elements finis, barrage, observations in situ.

IntroductionThe first embankment dam with a compacted asphalt con-

crete core was built in Germany in 1961–1962, and The In-ternational Journal on Hydropower & Dams (Saxegaard2010) provides a listing of asphalt-core dams that have beenbuilt or are under construction in different countries. The In-ternational Commission on Large Dams (ICOLD) and othershave summarized the experience with the design, construc-tion, and performance of this type of dam (e.g., ICOLD1992; Hoeg 1993; Creegan and Monismith 1996; Schonian1999; Hoeg et al. 2007; Wang 2008).

Most asphalt-core dams have been built in Europe, butChina has also built and is currently building several damsof this type, among them the 170 m high Quxue Dam that

will be the highest so far. Spain, Saudi-Arabia, and Iran re-cently built their first such dams. Canada just completed anasphalt-core dam, the first of its kind in North America (Ali-cescu et al. 2008), and Hydro Quebec has decided to con-struct several more embankment dams of this type in theProvince of Quebec (La Romaine project). Brazil is cur-rently completing its first asphalt-core dam (Foz de Cha-peco), and several dams of this type are being consideredfor a very large hydropower development in the Amazon re-gion.

This paper presents the design and performance of theYele asphalt-core rockfill dam in China, describes the chal-lenging site conditions and the studies performed to ensurethe quality of the asphalt core and its connection with theconcrete plinth, and evaluates the performance of the corebased on field monitoring. Construction started in April2001 and was completed in December 2005.

Yele Dam site conditionsThe Yele hydro project, on the very upper reach of the

Nanya River in the southwest of Sichuan Province, is oneof six projects in a cascade development for electricity gen-eration. The river is 49.5 km long with a hydraulic drop of

Received 11 May 2009. Accepted 22 March 2010. Published onthe NRC Research Press Web site at cgj.nrc.ca on 16 November2010.

W. Wang1 and Y. Zhang. Xi’an University of Technology, 5Jinhua South Road, 710048 Xi’an, China.K. Hoeg. Norwegian Geotechnical Institute (NGI), P.O. Box3930 Ullevaal Stadion, NO-0806, Oslo, Norway.

1Corresponding author (e-mail: [email protected]).

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1714 m and an exploitable hydropower potential estimatedto be 700 MW. The topography of the Yele basin is wellsuited for building a reservoir with a catchment of 323 km2.The annual mean river flow is 14.5 m3/s, which is composedmainly of rainfall, snowmelt, and groundwater. The river ba-sin planning includes a Yele balancing reservoir for year-over-year storage and the following power stations: Yele(installed capacity of 240 MW), Liziping (120 MW), Yao-heba (123 MW), Nanguaqiao (120 MW), Ximagu (42 MW),and Daduhebian (60 MW). Therefore, the Yele reservoirwill play a very important role in the Nanya River cascadedevelopment.

At Yele the winter season is 6 to 7 months long and therainy season is from May to October. Annually there areabout 215 rainy days with a mean rainfall of 1830 mm andair relative humidity of 86%. The annual mean temperatureis 7 8C, ranging from –20 to +28 8C.

Figure 1 shows the geological conditions along the longi-tudinal section of the dam (Yu 2004; Hao and He 2008).The deep overburden from the bottom to the top may beclassified into the following five groups:

(1) Q21I and Q2

2I — gravel with thin silty sand layers.(2) Q3

1II — overconsolidated and stiff cohesive soil contain-ing a significant amount of stones, but with low perme-ability; thickness of 31–46 m.

(3) Q32–1III — gravel with layers of loam; thickness of 46–

154 m.(4) Q3

2–2IV — gravel; thickness of 65–85 m.(5) Q3

2–3V — sandy silt layers with carbonized plant frag-ments; thickness of 90–107 m.

On the left bank, under the 35–60 m overburden, there isfractured and jointed quartz diorite bedrock as shown inFig. 1. The overburden is 55–160 m deep under the bottomof the valley and more than 220 m deep on the right bank.

Dam type selection and designFor the difficult geological foundation conditions with an

irregular and compressible overburden and with the high re-gional seismicity, only an embankment-type dam was con-sidered feasible. Three options were examined for theimpervious barrier in a rockfill dam: (i) earth core (ECRD),(ii) upstream concrete facing (CFRD), and (iii) asphalt core(ACRD). To decide among these options, emphasis wasplaced on costs, sensitivity to severe weather conditions dur-ing construction, earthquake resistance, and compatibilitywith the geological conditions that may cause significantdifferential settlements across the valley.

Hoeg et al. (2007) provides a general discussion of therelative merits of the three options. In the rainy and coldYele area at high altitude (crest elevation (el.) 2654.5 metresabove sea level (m.asl.)), the water content of the earth corematerial in the local borrow was 10% more than that re-quired for optimum compaction. It would be difficult andtime-consuming to reduce the water content, and core place-ment would have to be stopped during the frequent rainy pe-riods. For the CFRD option, the concrete slabs would beplaced after the upstream slope was completed, and it was

considered difficult to protect the upstream slope from dam-age by sudden heavy rains during the dam construction pe-riod. Furthermore, the impounding could not commenceuntil the dam with a concrete face was completed. This wasa disadvantage at the Yele site, where the reservoir wouldtake a long time to fill as the rate of annual river flow islow. The core for an ACRD may be constructed during peri-ods of rain and cold weather. During heavy rains, the as-phalt mix is stored in hot silos. When the heavy rain stops,the asphalt-core construction can be restarted immediatelyafter cleaning and heating the asphalt surface, without thelong delay associated with the earth core. An infrared heateris mounted in the front of the core paver.

The CFRD requires a longer concrete plinth than theACRD, and if large differential settlements occur, leakagemay develop in the joints between the slabs and in perimeterjoints due to rupture of water stops. At the Yele site, suchsettlements could be caused by the nonuniform geologicalfoundation conditions and severe earthquakes, which maycause large in-plane stresses in the concrete face. On theother hand, the ACRD with a central asphalt concrete core,if properly designed, is considered sufficiently flexible andductile to be able to accommodate differential settlementswithout cracking.

For the site and environmental conditions at Yele, theECRD was estimated to cost approximately 10% more thanthe ACRD, while the CFRD was estimated to cost around10% less than the ACRD. Among the three options, all as-pects considered, the ACRD was selected as the most suit-able (Hao and He 2003).

At the start of the preliminary design of the Yele Dam in1990, there were only a few asphalt-core dams of similarheight: the High Island West and East Dams in Hong Kong(95 and 105 m, respectively), the Finstertal dam in Austria(150 m, but with a core height of only 96 m due to a rockridge under the core), and the Storvatn Dam in Norway(90 m). In 1990 the Storglomvatn Dam (125 m high) in Nor-way was in the final design stage (construction was com-pleted in 1997) long before the start of construction of theYele Dam (Hoeg et al. 2007). However, the Yele Dam wasto be designed and built for a site with much more complexfoundation conditions than any of the previous dams and islocated in a region with much higher seismicity.

Figure 2 shows the maximum area cross section of theYele Dam. The asphalt core in that cross section is 120 mhigh and the total dam height 124.5 m. Figure 3 shows aplan view of the dam with the locations of cross-sectionsA–G shown, and Fig. 4 shows a longitudinal section givingthe locations of the same cross sections. As designed, theYele asphalt-core rockfill dam has a crest length of 411 mwith a 300 m long seepage cut-off wall extension over theright bank. Due to the very high seismicity of the region (Si-chuan Province) with an assumed peak horizontal groundacceleration of 0.45g2 at the Yele site, the dam is designedwith gentle slopes of 1V:2H upstream (where V representsvertical and H represent horizontal) and 1V:2.2Hdownstream, and a wide crest (14 m). In addition, as anearthquake-resistant measure, geo-grids3 were placed hori-

2 See Appendix A.3 See Appendix B.

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zontally to reinforce the top 30 m of the dam (from el.2624.5 m.asl. to the dam crest at el. 2654.5 m.asl.). Withinthe upper 20 m, the vertical height difference between thegeo-grids is 1 m and within the lower 10 m is 2 m. Further-more, to strengthen the lower part of the upstream damslope against large deformations and potential sliding duringan earthquake, 40 m long geo-grids were placed horizontallyfrom the upstream dam face between el. 2594 m.asl. and el.2603 m.asl. The vertical height difference between thesegeo-grids is 1.5 m.

Design and construction of imperviousbarriers in the Yele dam foundation

Figure 5 shows the complex system of impervious barriersinstalled in the foundation to reduce and control the under-

seepage. The foundation barriers may be divided into threemain sections from the left to the right bank: left bank bar-rier section, river bed barrier section, and right bank barriersection. After excavating the top of the overburden at theleft bank, a 20–60 m deep concrete cut-off wall was con-structed through the overburden, down to the sloping dioritebedrock. A grout curtain was injected into the quartz dioritethrough the concrete cut-off wall. A 150 m long and 80 mdeep grout curtain was injected into the quartz diorite fromthe construction gallery (No. 7 shown on the left side ofFig. 5). For the river bed overburden, a 30–60 m deep con-crete cut-off wall was brought 5 m down into the relativelyimpervious soil layer Q3

1II shown in Fig. 1. For the rightbank, the overburden is so deep that the water barriers hadto be built in four stages. The upper first barrier is the 15 mhigh concrete wall extension built in the open excavation;

Fig. 1. Geological cross section of the Yele Dam foundation and abutments. 1, gravel with silty sand layers; 2, stiff, overconsolidated co-hesive soils with stones; 3, gravel with layers of loam; 4, gravel; 5, sandy soil with loam and carbonized plant fragments; 6, quartz dioritebedrock; 7, crevice–lineament. W.L., water level.

Fig. 2. Cross section of the Yele Dam (this is section D as shown in Figs. 3 and 4). All dimensions in metres. 1, asphalt core; 2, transitionzone; 3, rockfill (I); 4, rockfill (II); 5, natural gravel or rockfill (III); 6, toe berm (22 m in thickness and 215 m in length); 7, observationgallery for field instrumentation; 8, concrete cut-off wall. (There is no grout curtain under section D, see Fig. 5.)

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the second barrier is the concrete cut-off wall with a depthof 70 m down to the top of the second level constructiongallery; the third is the 60–84 m deep concrete cut-off wallinstalled from the second level construction gallery, and thefourth is the grout curtain with a maximum depth of 120 minstalled through the concrete cut-off wall. For more detailsabout the very complex system of cut-off walls and groutcurtains, an extremely demanding task, refer to Chen (2003)and Hao and He (2008).

Asphalt-core design investigationsAfter the asphalt-core option was selected in the early de-

sign stage, a special test program was prepared to study thefollowing aspects in more detail (Sun and Wang 1994):

(1) Suitability of aggregates of local quartz diorite and localnatural sands.

(2) Optimum asphalt mix design with the available aggre-gates, filler materials, and bitumen grade.

(3) Triaxial compression stress–strain–strength behaviour ofalternative mix designs.

(4) Testing of tensile, bending, and creep behavior of the as-phalt mix.

(5) Resistance of asphalt concrete to cyclic loading simulat-ing earthquake shaking.

The quartz diorite quarry is located 3 km downstream ofthe dam site nearby an access road, while a dolomite quarryis located in the reservoir area 16 km upstream of the damsite. A special access road would have to be built to use the

Fig. 4. Longitudinal section of the asphalt core for Yele Dam showing locations of cross-sections A–G (see also Fig. 3).

Fig. 3. Plan view of Yele Dam and location of monitoring instruments. 1, displacement bolts; 2, observation gallery; 3, piezometers; 4,access galleries; 5, drainage gallery; 6, grouting gallery; 7, observation huts. Locations of cross-sections A–G are also shown in Fig. 4.



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dolomite quarry. Dolomite is alkaline and has very good ad-hesion to bitumen (grade 5, Chinese boiling test, standardDL/T 5362-2006 (People’s Republic of China National De-velopment and Reform Commission 2006)). It is consideredto be very suitable as an aggregate in asphalt concrete.Quartz diorite is slightly acidic and therefore has weaker ad-hesion to bitumen (grade 4). However, as shown by Wang etal. (2010), for hydraulic asphalt concrete with air poros-ity <3%, somewhat poorer aggregate–bitumen adhesion hasno significant effects on the stress–strain–strength behaviourand weathering resistance. Therefore, aggregates from thequartz diorite quarry were considered satisfactory, and thiswas a much more economical solution.

Hydraulic asphalt to be used in a dam core should be vir-tually impervious, flexible, and workable. The aggregatecomposition complies with Fuller’s gradation curve im-proved with a fine grain component smaller than 0.075 mm(filler material) (Hoeg 1993). To ensure very low permeabil-ity (about 10–11 m/s), the air porosity in the dam core shouldbe less than 3% (Hoeg 1993; Wang and Hoeg 2009). Triax-ial compression tests should be carried out under differentconfining stresses to assure that the asphalt concrete exhibitsflexible and ductile (not strain-softening) behaviour requiredto adjust to dam deformations caused by static and dynamicloads and differential foundation settlements. For the YeleDam asphalt core, the bitumen content (type AH-70 in Chi-nese standard DL/T 5411-2009 (People’s Republic of ChinaNational Energy Administration 2009)) is 6.3% by totalweight and the filler content is 12%. About 30% of the fineaggregates (2.36–0.075 mm) consist of natural sands(rounded particles) to improve the workability of the asphaltconcrete.

Many of the details of these experimental studies and testresults are reported by Wang (2008), who investigated thepermeability of asphalt concrete as a function of imposedshear strains. Two-and three-dimensional finite elementanalyses to study stresses, strains, and deformations in dif-ferent embankment zones were also performed.4

An additional test program was undertaken to focus onthe effects of shear displacements causing possible leakageat the joint between the asphalt core and the concrete plinth(Wang and Sun 1997, 1999). Special attention was given tothe mix proportions of the sandy asphalt mastic placed onthe core–plinth interface.

Figure 6 shows the design of the critical asphalt core–plinth connection and the top of the concrete cut-off wall inthe foundation. A model (1:10 scale) was built to test thecore–plinth interface when it was subjected to shear dis-placements in the downstream direction and high water pres-sure (Fig. 7). The asphalt core in the model was 240 mmwide at the bottom, 120 mm wide at the top, and 330 mmin height. The asphalt mastic layer between the core and theconcrete slab was 20 mm thick. The mastic mix consisted ofbitumen type AH-70, limestone filler, and river sand in theproportions 1:2:1, respectively. The core–plinth connectionmodel tests were run at a temperature of 7 8C.

As shown in Fig. 7, the water pressure at the interface be-tween the asphalt concrete core and the concrete plinth waskept at 0.3 MPa (i.e., 30 m of head) during most of the test.The vertical stress at the base of the asphalt core in the YeleDam design was computed by finite element analyses to be1.65 MPa. The vertical stress applied in the model was in-creased gradually up to 1.65 MPa within 30 min. Then theconcrete slab (plinth) was pushed horizontally. The shearstress required to make the slab move relative to the base ofthe core was 0.6 MPa, and the slab displacement rate wasthen kept at 0.1 mm/min. The resulting shear stress on themastic layer was increased from 0.6 to 1.35 MPa during theshearing process. After 200 min of testing, the vertical dis-placement of the core and horizontal displacement at the in-terface were 17.4 and 20.5 mm, respectively. No leakagewas detected even when the water pressure was increasedfrom 0.3 to 1.0 MPa at the end of the test. The slab wasthen pushed at 1 mm/min to reach a shear displacement of22 mm, i.e., 9% of the core thickness. This was the maxi-mum shear displacement the model allowed. No leakage

Fig. 5. Water barriers in the Yele Dam foundation. All dimensions in metres. 1, crest; 2, asphalt core; 3, ground surface; 4, excavation line;5, concrete cut-off wall; 6, grout curtain; 7, construction gallery used for construction of grout curtain and concrete cut-off wall; 8, concretecut-off wall extension built in the open excavation.

4 See Appendix C.

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was detected during the model testing desspite the large im-posed shear strains. The vertical stress, shear stress, verticaldisplacement, and shear displacement versus time for themodel test are shown in Fig. 7. When the model was re-moved from the testing apparatus, some of the mastic wasdiscovered to have extruded, and the mastic layer thicknesshad reduced to 12 mm from the initial 20 mm. However, nocracks or fissures were detected at the core–plinth interface(Chu et al. 2004). The test results showed that the behaviorat the interface was satisfactory even for shear distortionsmuch larger than anticipated in the field.

Dam construction and simultaneousreservoir impounding

The vertical core wall, located 3.7 m upstream of the damcenterline, was designed to be 1.20 m wide at the bottomand decreasing gradually to 0.60 m at the top (el.2653 m.asl.). The base of the core is flared out against theplinth to a width of 2.40 m at the core–plinth interface. Sim-ilarly, the core is flared out against the plinth at the abut-ments to twice the core width at that elevation.

Although before the year 2000 more than 10 asphalt-core

dams had been completed in China, most of them weresmall and the cores had been constructed manually or withsimple and improvised equipment. There was a lack of ex-pertise and available modern equipment to build large as-phalt-core dams. However, at the time, the asphalt core forthe Maopingxi Dam (part of the Three Gorges Project) witha height of 105 m was under construction using a modernasphalt-core paver purchased from the Norwegian contractorKolo Veidekke a.s.

The Yele asphalt-core construction presented a specialchallenge because of the cold and rainy weather and a verytight construction schedule. A Chinese asphalt paver wasbuilt and construction procedures were developed for plac-ing the asphalt core during the night and at air temperaturesdown to –5 8C. The design of the asphalt-core paver wasmade very similar to the Norwegian one used for placingthe Maopingxi Dam asphalt core (Hoeg 1993). Several jobtrials were undertaken before asphalt-core constructionstarted. The asphalt-core paver places simultaneously the as-phalt core and the adjacent supporting transition zones. Thetotal width that could be placed by the new paver was3.8 m; thus, the transition zones on either side of the corewere each 1.3 m wide at the bottom and 1.6 m wide at thetop. The core and adjacent transition zones were built upand compacted in 26 cm thick layers (compacted thickness).During dam construction, the core top elevation was at alltimes above that of the embankment rockfill and did notslow down the rapid construction progress. The Yele as-phalt-core construction was started in November 2003 andwas completed in November 2005. Systematic quality con-trol of the asphalt core was carried out throughout the con-struction period to ensure that the air porosity of the asphaltconcrete in place was less than the specified 3%, whichgives a virtually impervious core (Hoeg 1993). Zones, com-paction specifications, and quality control for the Yele Damare shown in Table 1.

Figure 8 shows the progress of dam construction and im-pounding until October 2007, and the operation until No-vember 2008 is shown in the first figure in the section titled‘‘Field performance observations of the asphalt core’’. TheYele Dam embankment construction started in April 2001and in December 2004 the dam reached el. 2603 m.asl.,which is 51.5 m below the crest of the dam (el.2654.5 m.asl.). In January 2005 a special impounding testwas started. At that time the water level was at el.2552 m.asl. behind the upstream cofferdam, as shown inFig. 8. After one month of impounding, the water level wasraised 35.5 m (to el. 2587 m.asl.). Then the water was low-ered to its original level at el. 2552 m.asl. Observations weremade of the pore-water pressures on the downstream side ofthe core, of the deformations of the core, and of the strains inthe concrete plinth and cut-off wall during the raising andlowering of the reservoir while the embankment height waskept constant at el. 2603 m.asl. The pore-water pressures onthe downstream side of the core wall were measured to beclose to zero during the impounding test, and the deforma-tions of the asphalt core and the strains in the concrete plinthand cut-off wall were very small (see later discussion of per-formance observations). On 9 March 2005 the reservoirwater level was raised again and reached el. 2634 m.asl. on

Fig. 6. Structural connection between the asphalt core and concreteplinth (all dimensions in metres; left side of figure is upstream,right is downstream). 1, asphalt core; 2, transition zone; 3, 1–2 cmthick sandy asphalt mastic; 4, geo-membrane covering foundationto upstream dam toe; 5, silt; 6, filter and drainage layer; 7, concretecut-off wall; 8, reinforced concrete plinth; 9, foundation overbur-den.



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26 October 2005. The embankment reached the crest eleva-tion 2654.5 m.asl. in December 2005.

During operation and power generation the first year, thewater level dropped to el. 2600 m.asl., but rose again to el.2642.5 m.asl. by 12 December 2006 (see Fig. 8). On 23April 2007 the water level had dropped to el. 2609 m.asl.,but on 23 October 2007 it rose again to el. 2648 m.asl.,which is 2 m below full supply water level at el.2650 m.asl. During construction, impounding and operationof the dam was monitored by means of a comprehensive in-strumentation system as described below.

Dam monitoring and performanceobservations

The monitoring system consists of measuring dam body

deformations, seepage through the core, foundation andabutments, water pressures in the abutments and foundation,stresses and strains in the asphalt core, in the concrete plinthand in the cut-off wall, temperatures inside the core, and ac-celerations during any earthquake shaking (Chen 2003;NRBHDC 2007; Chen et al. 2009).

Measured dam surface displacements during and afterconstruction

Figure 3 shows the arrangement of displacement observa-tion bolts on the dam surface. The 99 bolts are installedalong seven longitudinal lines, one on the upstream slope,two on the dam crest, one on the top of core, and three onthe downstream slope. The horizontal distance between boltsis 50 m, corresponding to cross-sections B, C, D, E, and Fshown on Figs. 3 and 4. The geodetic surveys for displace-

Fig. 7. Model test to study behaviour of core–plinth interface when subjected to interface shear displacement and high water pressure.(a) Model of the asphalt core–plinth connection. (b) Measured stresses and displacements versus time for the 1:10 scale model of the asphaltcore–plinth connection. Disp., displacement.

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ment monitoring used six fixed benchmarks in the vicinityof the dam.

Only a few of the dam surface deformation measurementswill be discussed, as in this paper the focus is on the behav-iour of the asphalt core and its interaction with the transitionzones. As an example, the movements of the bolts on the up-stream berm at el. 2620 m. asl., a distance of 79 m from thevertical dam axis, are shown in Table 2. The settlements havebeen measured since 25 July 2005 when the dam rockfill wasat el.2627.8 m.asl. After placement of additional rockfill(26.7 m) to the top of the embankment, and after reservoirraising and lowering during the construction and operation(see Fig. 8), the settlements of the bolts along this berm on10 September 2005 and 9 May 2007 are as shown in Table 2.

Over the almost 2 year observation period, the measure-ments in Table 1 seem very consistent with the largest set-tlement of 82 mm at the maximum section D. On the leftbank, the reduction in effective stresses due to impoundingcaused the berm to heave 9 mm. On the right bank with thedeep overburden, the reduction of the effective stresses dueto impounding caused the berm to heave 25 mm.

Figure 9 shows the settlements of the bolts on the down-stream berms at el. 2594.5 m.asl. and el. 2624.5 m.asl. at theend of September 2007 (20 months after end of construc-

tion). The maximum settlement (combination of constructionand post-construction settlements) is 60 mm between cross-sections D and E. It should be noted that the bolt displace-ments at the lower berm have been measured since 12 No-vember 2005 (when installed) and at the higher berm since15 February 2006.

Post-construction displacement observations at the top ofthe core (3.7 m upstream of the dam centerline), upstreamcrown points, and downstream crown points were started on21 June 2006. Unfortunately, this is 0.5 years after the endof dam construction, so the post-construction displacementsduring the first months are not included. The post-constructiondisplacements recorded on 27 September 2007 are shownin Fig. 10. The maximum post-construction settlement ismeasured to be 45 mm at the upstream crown point incross-section E. However, the settlement may actuallyhave been almost twice that if one were to include thepost-construction settlements during the first 0.5 years afterthe end of construction.

During the post-construction observation period until Oc-tober 2007, the dam had experienced two cycles of waterlevel rising and lowering of around 40 m (Fig. 8). As shownin Fig. 10a, the core crest settlement is 40 mm at section D.The settlement is slightly more at the upstream crown pointand slightly more near the right bank than near the left bank.The downstream crown point shows about 10 mm less set-tlement than the core. The post-construction horizontal dis-placements of the crown points and top of core are shownin Fig. 10b. The downstream crown points show more dis-placement than the upstream crown point and the top of thecore. The maximum is about 27 mm in cross-section D. Thedownstream crown point shows less post-construction settle-ment, but more downstream displacement than the upstreamcrown point, which agrees with the observations from manyother central core rockfill dams (Hoeg et al. 2007). This isdue to the effects of impounding on the behaviour of the up-stream fill.

Up until January 2009, the dam had experienced threecycles of water level rising and lowering, and the dam hadbeen subjected to 10 earthquakes of various magnitudes(Chen et al. 2009; Zhao et al. 2009). The maximum post-construction settlement occurred at the upstream point of thecrest at section D (maximum cross section of the dam), andthe value was about 14 cm in June 2008. For comparison,

Table 1. Zoning, compaction specifications and quality control for Yele Dam (standards SL274-2001 (The Ministry of Water Resources ofthe People’s Republic of China 2002) and DL/T 5411-2009 (People’s Republic of China National Energy Administration 2009)).

Zone (see Fig. 2) MaterialLayerthickness (m)

Compaction byvibratory roller Quality control

Asphalt core Bitumen AH-70, aggregate (0–20 mm) 0.20–0.26 8 passes, 1.5 t Air porosity < 3.0%Transition zone A

1.3–1.6 mGravel (0–80 mm, grain size < 5 mm passing 20%–

40%; grain size < 0.075 mm passing � 10%0.20–0.26 4 passes, 2 t Dry density ‡ 20.6 kN/m3,

porosity � 20%Transition zone B

2.0–4.0 mGravel (0–150 mm, grain size < 5 mm passing

10%–20%; grain size < 0.075 mm passing � 3%0.20–0.26 4 passes, 2 t Porosity � 22%

Shoulder (I) Quarried rock (0–800 mm) 1.0–1.2 8 passes, 20 t Dry density ‡ 21.9 kN/m3,porosity � 24%

Shoulder (II) Quarried rock (0–800 mm) 1.0–1.2 8 passes, 20 t Dry density ‡ 22.5 kN/m3,porosity � 22%

Shoulder (III) Natural gravel or quarried rock (0–800 mm) 1.0–1.2 8 passes, 20 t Dry density ‡ 21.1 kN/m3,porosity � 22% (upstream),24% (downstream)

Toe berm Rock debris (0–1200 mm) 1.0–1.2 8 passes, 20 t Dry density ‡ 19.6 kN/m3

Fig. 8. Progress of dam construction and reservoir impounding.(Note: the reservoir was held back by the upstream cofferdam be-fore the impounding test started at el. 2552 m.asl.)



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the settlement of the upstream point of the crest for the Stor-glomvatn asphalt-core rockfill dam, also 125 m high, was18 cm after the first 2 years of operation (Hoeg et al. 2007).

Table 3 shows the settlements of the upstream points ofthe crest before and after the Wenchuan earthquake, 12May 2008. When the Wenchuan earthquake struck, the Yelereservoir level was near the minimum operating level el.2600 m.asl. The maximum additional crest settlement duringthe earthquake was about 15 mm at section D. The YeleDam site is located 258 km from the epicenter of the Wen-chuan earthquake (magnitude 8.0) and the intensity (Chinesescale) at the dam site was less than VI (Chen et al. 2009;Zhao et al. 2009). According to the monitored accelerationsfrom nine strong-motion seismographs installed on and inthe Yele Dam, the calculated maximum settlement, horizon-tal displacement (downstream direction), and longitudinaldisplacement (along dam axis) of the dam crest induced bythe Wenchuan earthquake were 19, 25, and 17 mm, respec-tively. The several other earthquakes that have occurredsince the end of construction have had insignificant effectson the dam.

In summary, the dam surface displacements show uniformand consistent deformation patterns even after having expe-rienced the Wenchuan earthquake, and the observed settle-ments are smaller than expected. This must mean that therockfill and gravel are of high quality, the embankment was

very well compacted, and that the alluvial overburden in thefoundation is less compressible than anticipated.

Measured deformations inside the damFive observation huts on the dam crest and five on the

Table 2. Settlement (settlm.) of bolts on the upstream berm at el.2620 m.asl.

Distance (in m) from dam crest on left bank, el.2654.5 m.asl.

100* 120 (B) 170 (C) 220 (D) 270 (E) 320 (F) 343*

DateWater level(m.asl.)

Embankmentlevel (m.asl.)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

25 Jul 2005 2584.5 2627.8 0 0 0 0 0 0 010 Sep 2005 2619.3 2637.8 –4 1 23 35 25 6 –149 May 2007 2610.1 2654.5 –9 16 52 82 61 33 –25

Note: B, C, D, E, and F refer to section locations shown on Figs. 3 and 4.*Points located over the left and right banks just inside the embankment.

Fig. 9. Settlement of bolts on the downstream slope. (Observationperiods: el. 2594.5 m.asl., 12 November 2005 – 30 September2007; el. 2624.5 m.asl., 15 February 2006 – 29 September 2007.)

Fig. 10. Post-construction settlement and horizontal displacement ofcrown and top of core. (a) Post-construction settlement at the top ofthe core and the upstream and downstream points on the crown.(b) Post-construction horizontal displacement in the downstreamdirection at the top of the core and the upstream and downstreampoints on the crown. (Measurements started 0.5 years after the endof dam construction.)

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berms on the downstream slope were constructed (seeFig. 3). They are used for collecting all the measurementsof displacements inside the dam. The vertical displacementsinside the dam are obtained by water level settlement gagesand the horizontal displacements by extensometer measure-ments relative to the movements of the bolts on the observa-tion huts. The reinforced concrete observation gallery insidethe downstream dam body is located 8 m downstream fromthe dam axis. The base slab is at el. 2560 m.asl., 30 m abovethe dam plinth, which ensures that it is well above the lineof saturation (see Figs. 2 and 3). The gallery is used to col-lect measurements of pore pressures in the dam foundation.The instrumentation leads that collect strain measurementsin the plinth and cut-off wall are routed through a prefabri-cated vertical concrete pipe, which is located in the down-stream shell near the right abutment. The instrumentationleads that collect measurements taken in the core and transi-tion zone are routed vertically through the transition zone.During dam construction, the instrumentation leads weretemporarily protected by vertical steel pipes.

Three vertical pipes with a total of 29 electromagneticrings were installed inside the downstream transition zonebehind the core, to measure local vertical and horizontal dis-placements. The rings were arranged with an individualheight difference of 10 m.

Special gages were installed at the upstream and down-stream interfaces between the core and transition zones tomeasure differential settlements between the core and transi-tion zones at different elevations. The gages were modifiedjoint meters used in concrete structures with one end anch-ored in the core while the other was fixed in the transitionzone. The gages were only installed over the lower part ofthe core in each cross section (over the lower 25 m incross-section D and over the lower 15 m in sections B andF). Vertical strain meters were also installed on the upstreamand downstream faces of the core over these same lowerparts to measure strains in the asphalt concrete. Total pres-sure cells were installed at the bottom of the asphalt coreon top of the plinth near cross-sections A and D. Further-more, shear displacements were measured by gages installedat the interface between the core and concrete plinth to de-termine the shear distortions at the interface.

The structural connection between the asphalt core and re-inforced concrete plinth is shown in Fig. 6. Strain meterswere mounted on the reinforcing steel in the plinth to meas-ure steel stresses, and there were four lines of optic fibresensors to monitor potential cracking in the concrete plinth.

Observed settlements in the downstream transition zone inAugust 2007 (i.e., 19 months after the end of construction)

are shown in Fig. 11. The maximum settlements, includingthe foundation settlements, at sections B, D, and F were560, 1060, and 550 mm, respectively. The vertical strain inthe transition zone varied significantly over the height, butthe average compressive strains were 0.9%, 1.3%, and 0.8%in the three sections, respectively. The maximum horizontaldisplacements in the downstream transition zone in thedownstream direction (normal to the dam axis) at sectionsB, D, and F were 30, 207, and 33 mm, respectively. In thelongitudinal direction (along the dam axis), the maximumdisplacements towards the right bank in these three sectionswere 94, –240, and –144 mm, respectively.

The measurements of strains in the plinth (as of January2009) indicate low values and no cracking has occurred.Strain meters are also installed in the cut-off wall at fourtransverse sections, and the observed results indicate verysatisfactory performance (Wu et al. 2009; Zhao et al. 2009;Zheng and Wang 2009).

Field performance observations of theasphalt core

The measured settlement differences between the lowerpart of the asphalt core and the adjacent transition zones,and the maximum measured compressive strains in the up-stream and downstream faces of the core, are shown in Ta-ble 4. The observation date is 18 October 2007, when thereservoir level was at el. 2647.5 m.asl. Since then and up toNovember 2008, the settlement differences between the coreand transition zone and the compressive strains in the corehave shown almost no change (Wang and Zheng 2009).

Table 3. Settlements of the upstream points of the crest before and after the Wenchuan earthquake, 12 May 2008.

Distance (in m) from dam crest on left bank el.2654.5 m.asl.

67* 120 (B) 170 (C) 220 (D) 270 (E) 320 (F) 365*

DateWater level(m.asl.)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

Settlm.(mm)

25 Apr 2008 2602.0 31.5 88.3 116.1 128.8 128.2 102.9 56.619 May 2008 2603.7 32.6 94.1 123.5 143.4 136.0 114.6 58.2

*Points located over the left and right banks outside the embankment.

Fig. 11. Settlement inside the transition zone behind the core atthree cross sections. Observation date 3 August 2007.



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The data show that there are large variations in the meas-ured differential settlements, but the asphalt core has settledmore than the transition zone in all measurements. The maxi-mum recorded settlement difference in November 2008 wasabout 60 mm. Figure 12 shows the differential settlementcurves with time at el. 2558 m. asl. in section D. The curvesshow that the settlement differences took place during thedam construction period, and there is virtually no measured in-crease in differential settlements after the end of construction.

Figure 13 shows vertical core strain versus time. Thecurves show that around 90% of the asphalt strains tookplace during the dam construction and impounding period,and there is minimal measured increase in the core strainsduring the subsequent 3 year operation period. The compres-sive vertical strains on the upstream and downstream sidesof the asphalt core in the lower 25 m of the core wall incross-section D were measured to be 2.5%–3%, while theaverage compressive strain in the downstream transitionzone over the corresponding height was 1.7%. As shown inthe figure, the 12 May 2008 Wenchuan earthquake had in-significant effects on the strains in the core.

The temperature of the core is observed with 14 tempera-ture sensors at sections B, D, and F. During the first monthafter asphalt concrete placement, the temperature droppedfrom around 160 8C to less than 20 8C and gradually reducedwith time. The temperature at the bottom of section D was13.7 8C in December 2004, 12.4 8C in December 2005,9.5 8C in December 2007, and 9.4 8C in November 2008. InJuly 2009, the temperatures at different points in the corewere in the range 7.2–12.5 8C (Wang and Zheng 2009).

Evaluation of asphalt core performance

Interaction between asphalt core and adjacent transitionzones

The vertical compression stresses measured by the totalpressure cells at the bottom of the core are 0.65 MPa nearcross-section A and 2.1 MPa near section D (see Fig. 4).These values have stayed almost constant from the end ofdam construction (December 2005) to the latest observationin November 2008, showing only very small variationscaused by fluctuations in the reservoir level (Wang and

Zheng 2009). The measured stresses are 90% (section A)and 70% (section D) of the stresses computed by multiply-ing the local height of the core with the unit weight of thematerial above. The stress computed by the finite elementanalyses for cross-section D was 1.65 MPa, which is consid-erably less than the measured stress of 2.1 MPa. This meansthat the arching effect between the core and the stiffer tran-sition zones is smaller than that modeled by the finite ele-ment analyses. This is probably due to the inadequatemodeling of the viscoelastic–plastic behavior (with tempera-ture and time) of the asphalt core during construction. Themeasured arching effect corresponds to a small average ver-tical, upward shear stress of around 4 kPa on both sides ofthe core. The constitutive modeling of asphalt concrete be-havior for use in numerical analyses must be improved togive more reliable analyses in better agreement with fieldobservations.

Interesting comparisons may be made between the fieldmeasurements from the Yele Dam and the Maopingxi Dam.The Maopingxi asphalt-core dam is 105 m high with a crestlength of 1840 m. The dam was built from 1997 to 2003 andwas extensively instrumented (Xu et al. 2009). The meas-ured results, 5 years after end of construction, indicate thatthe maximum settlement difference between the core andthe transition zones was 48 mm, and that occurred 14 mabove the core base. The vertical strains on the upstreamand downstream side of the asphalt core are all compressivewith a maximum value of 4%. The compression stress meas-ured at the core bottom against the concrete plinth is1.5 MPa for the maximum dam section, which is 60% ofthe stress computed by simply multiplying the local heightof the core with the unit weight of the material above. Sheardisplacements at the core–plinth interface normal to theplinth in the downstream direction were measured to be lessthan 2 mm (Zou et al. 2008). When considering the differ-ences in dam geometry, zoning, and material properties be-tween the Yele Dam and Maopingxi Dam, one mayconclude that the measured behaviour of the two asphaltcores seem very consistent with each other.

It is a difficult task to take measurements of differentialsettlements between the hot core and the adjacent transitionzones and to measure strains in the core itself, but it has also

Table 4. Measured settlement differences between the asphalt core and the upstream and downstreamtransition zones and measured compressive strains in the core.

Settlement difference between thecore and transition zone (mm)* Compressive strain in the core (%)

SectionElevation(m.asl.) Upstream Downstream Upstream face Downstream face

B 2594 59 38 — —2604.4 7 59 2.9 1.22609.5 29 20 — —

D 2534.4 — — — 3.12548 20 20 2.5 3.12558 48 55 — 2.7

F 2585 50 40 — —2595 39 30 — —2600 39 34 2.6 2.9

*Positive value means that the core has settled more than the transition zone.

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been attempted for some earlier dams. Measurements atStorvatn Dam, Norway (Adikari et al. 1988), showedsmaller differential settlements (10–30 mm) than in theYele and Maopingxi dams, and in the case of Dhunn Dam,Germany, there was virtually no measured differential settle-ment (Strobl and Schmid 1993).

For earth-core dams there is concern about the arching ef-fect in the core between the adjacent filter zones and a possi-bly significant reduction in effective stresses in the core,which then may crack due to hydraulic fracturing. This is ofmuch less concern in a core of ductile asphalt concrete, whichalso has some tensile strength, and the International Commis-sion on Large Dams (ICOLD 1992) states that hydraulic frac-turing cannot occur in an asphalt concrete core. In the YeleDam core, the total stresses towards the bottom of the coreare higher than the corresponding water pressures, so the ef-fective stresses are positive. However, in other situationsthere may be a concern about hydraulic fracturing. Therefore,the authors are currently carrying out laboratory experiments

at Xi’an University of Technology to study whether condi-tions may arise that potentially could lead to the phenomenonof hydraulic fracturing in an asphalt concrete core.

Back-analysis of strains in the core based on measureddam and foundation settlements

For a dam resting on a compressible foundation wherelarge differential settlements may occur, whether transversecracks or fissures may develop through the asphalt-corewall needs to be considered. Differential settlements weredefinitely a concern for the Yele Dam at the design stage.However, the field measurements show that the foundationsettlements are relatively small, and the settlement profileacross the valley is rather gradual and almost symmetricalabout the centerline of the valley. A simplified back-analysisof the shear strains in the core was performed using the ob-served foundation settlements 2 years after construction.

The finite element analysis of strains in the asphalt core isbased on the following simplifications and assumptions:

Fig. 13. Strains at upstream (up) and downstream (down) faces of the core versus time at different heights above the plinth at section D.Latest observation date 1 November 2008.

Fig. 12. Settlement differences between asphalt core and transition zones versus time at el. 2558 m.asl. at section D. Latest observation date1 November 2008.



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(1) Two-dimensional (2-D) plane strain analyses have beenundertaken using the software SIGMA/W in GeoStudio2004.

(2) The settlements along the plinth, as shown in Fig. 14,have been increased in proportion to the dam height (asthe dam was constructed in 13 layers).

(3) The unit weight of the asphalt core (25 kN/m3) has beenreduced to an equivalent unit weight of 18.4 kN/m3. Thisis done to simulate the effect of skin friction (arching)between the core and transition zone on either side ofthe core. The magnitude of the reduction was determinedby using the total stress measured at the base of the corein section D.

Having observed the settlements at sections B, D, and Fin the downstream transition zone and the settlement differ-ences between the asphalt core and transition zone (Fig. 12and Table 4), one may estimate the settlements of the as-phalt core at these three sections. The comparisons betweenthe calculated (by the 2-D finite element analyses) and ob-served settlements in the core at sections B, D, and F areshown in Fig. 15. In the analysis, the equivalent Young’smodulus for the core was taken equal to 45 MPa and Pois-son’s ratio equal to 0.4 based on the laboratory test resultspresented by Wang (2008) for the asphalt concrete used inthe core of the Yele Dam.

The observed and calculated settlements at these threesections match reasonably well below el. 2625 m.asl., butnot towards the top of the core. As geo-grids were placedhorizontally over the top 30 m of the dam, they confine thehorizontal displacements of the top part of the dam body,which then undergoes smaller settlements. This is not mod-eled in the back-analysis and is one reason why the calcu-lated settlements over the top 30 m are much bigger thanthe observed settlements.

The back-calculated shear stresses and shear strains in thecore are shown in Fig. 16. The results from the back-analysisconfirm that the most critical location for the asphalt core is160 m from the left bank, where the bottom of the cut-offwall leaves the rock base and goes over to the more com-pressible overburden. The computed stresses and strains atthis location are shown in Table 5. The shear stresses are al-most symmetrical around the deepest section of the dam dueto the rather symmetrical foundation settlement pattern thatwas measured and used in the analysis (Fig. 14). The settle-ments are only slightly larger on the right bank than on theleft bank, where the depth to bedrock is much smaller.

Stress–strain–strength tests were performed on 100 mmdiameter samples drilled out of the asphalt core during con-struction. The results from strain-controlled compression tri-axial tests, keeping the lateral confining stress constantduring each test, are shown in Fig. 17. The tests were run at7 8C. The stress–strain curves show a very ductile asphaltconcrete behavior with insignificant strain-softening evenfor tests with very low confining stress (Wang 2008). Thisis characteristic of the behavior of hydraulic asphalt concretewith a bitumen content between 6.5% and 7.5% (by totalweight), 12%–15% filler content, an aggregate grain-sizecurve that satisfies the Fuller distribution of particle sizes,and maximum aggregate size between 16 and 20 mm. Thebehavior is that of a ductile, viscoelastic–plastic material

with self-healing (self-sealing) properties should any fissuresor cracks occur due to excessive shear distortions.

Eberlaste Dam, Austria, was one of the first asphalt-coreembankment dams ever built (1962–1964). It rests on adeep and compressible alluvial foundation, and large differ-ential settlements have taken place under the dam, causingsignificant shear distortions in the asphalt core (Hoeg1995). However, even in that case, no leakage due to crack-ing in the core has occurred. As the designers of the Eber-laste Dam had anticipated large differential settlements,they specified the use of an especially soft grade of bitumenin the asphalt concrete to be able to accommodate largeshear distortions without cracking (Rienossl 1973). This isone of the advantages of an asphalt-core embankment dam:the geomechanical properties of the asphalt concrete may toa certain extent be tailored to the specific design conditions,making it well suited for use in a dam water barrier.

Based on the finite element analysis results presented inTable 5 and the test results for the Yele asphalt-core speci-mens, one may conclude that the computed stress and strainstates inside the core are safely within a stress–strain rangewhere there is no danger of cracking due to high shearstresses or significant shear dilation that could increase the

Fig. 14. Measured settlements along the plinth at end of construc-tion and impounding. (These settlements are used as input in thefinite element back-analysis.)

Fig. 15. Comparisons between the measured and calculated settle-ments in the core at sections B, D, and F.

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permeability of the core. The measured field behaviour ofthe core–plinth interface in the Yele Dam is also very reas-suring.

Asphalt core as impervious barrier

Thirteen pizeometers were installed in the downstreamtransition zone adjacent to the core at sections B, C, D, andE, and 15 piezometers were installed upstream and down-stream near the joint between the asphalt core and concreteplinth at these same sections. Fifteen piezometers were in-stalled in the foundation under sections B, C, and D, and 20piezometers were installed from the observation gallerydown to 2 m below the dam base.

About 200 m downstream of the dam toe, a measuringweir was installed to measure the seepage rate coming fromthe river bed section, left side of the dam, and left abutment.Most, if not all, of the seepage through the right side of thedam and through the right abutment is assumed to be col-lected and measured by the 12 weirs installed on the right

Fig. 16. Computed maximum shear stresses and strains in the core. (a) Maximum shear stress contours (kPa) in the asphalt core from theback-analysis. (b) Maximum shear strain contours in the asphalt core from the back-analysis.

Table 5. Stress and strain state in the most critical location of the asphalt core at section C.

State Vertical Longitudinal Hor.–vert. shear Max.Max.shear

Major principalstress

Minor principalstress

Ratio of major tominor principal stress

Stress (MPa) 1.73 1.08 –0.19 N/A 0.38 1.78 1.08 1.65Strain (%) 1.9 –0.15 1.18 2.04 2.34 N/A N/A N/A

Note: Hor.–vert., horizontal–vertical; N/A, not applicable.

Fig. 17. Triaxial compression test results from 100 mm diametersamples drilled out of the Yele Dam core during construction.Results presented for different levels of confining stress.



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bank in the drainage gallery, construction gallery, accessgalleries, and a drainage ditch (see Fig. 3).

During the impounding test, very little seepage was re-corded and the pore pressures measured on the downstreamside of the asphalt core above the plinth were zero or negli-gible up to a reservoir level of about el. 2630 m.asl. Whenthe reservoir level exceeded el. 2633 m.asl., there was a sig-nificant increase in seepage through the right bank. Whenthe reservoir was at el. 2648 m.asl. (i.e., only 2 m belowfull supply level), the pressure at plinth level on the up-stream side of the core was 118 m while the pressure headin the river bed at the downstream side of the core was stillonly 7 m under section D. However, the pore-water pressurein the foundation under section F on the right bank was ob-served to be high, increasing with the reservoir level. Thesignificant seepage beneath the cut-off wall at this sectionwas of concern, and in early 2006 a deep drainage well wasinstalled in the foundation through the observation gallery.In December 2007, when the reservoir was at el.2650 m.asl. (i.e., full supply level), the maximum total seep-age was 358 L/s, which is still smaller than the maximumseepage value of 500 L/s anticipated during design (Wanget al. 2009). From May to September 2008, additional grout-ing was carried out, and new drainage wells were drilled inthe drainage gallery in the right bank. When the reservoirwas at full supply level again in November 2008, the totalseepage was reduced to 277 L/s.

Based on the measured pore pressures in the downstreamdam body, at the plinth level downstream, and on the resultsfrom the impounding test, one may conclude that insignifi-cant seepage is coming through the asphalt core and thecore–plinth interface.

Concluding remarksFor the complex foundation and inclement climatic condi-

tions at the Yele Dam site, which is in a highly seismic re-gion, a rockfill dam with a central core of asphalt concretewas selected rather than a dam with an earth core or con-crete facing. The design of the dam has been presented inthis paper with an emphasis on the design and constructionof the asphalt concrete core.

The properties of asphalt concrete may to a certain extentbe tailored to specific design and site requirements, and fieldexperience and research show that asphalt concrete is a ‘‘for-giving’’ material very well suited for use in the imperviouscore of an embankment dam.

An extensive field monitoring program was implementedfor Yele Dam, and the recorded results have been comparedwith those of other high rockfill dams with an asphalt core.Special attention has been given to the interaction betweenthe core and adjacent transition zones.

Based on the field measurements, back-analyses, tests onthe properties of the asphalt concrete and the joint betweenthe core and plinth, one may conclude that the asphalt coreof the Yele Dam performs very well. There are no indica-tions of any leakage through the core or at the joint betweenthe asphalt core and concrete plinth above the foundationcut-off wall.

However, as anticipated at this geologically very difficultsite, there is some leakage under the dam in spite of the ex-

tensive use of deep cut-off walls and curtain grouting. Inlate 2008 the leakage amounted to about 280 L/s. Continu-ous surveillance is taking place to study and control the de-velopment of this underseepage.

AcknowledgementsThe first and the third authors would like to thank Profes-

sors Sun Zhentian and Wu Liyan and the late ProfessorsDing Purong and Yang Quanmin at Xi’an University ofTechnology, Xi’an, People’s Republic of China, for their co-operation during several research programs on the Yele as-phalt core since 1991. The authors thank the Nanya RiverBasin Hydro-Electric Development Cooperation, the damowner, for permission to present the performance observa-tions of the Yele Dam.

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haviour of Storvatn Dam, Norway. A case of prediction versusperformance. In Proceedings of the 5th Australia-New ZealandConference on Geomechanics, Sydney, Australia, 22–26 August1988. Institution of Engineers, Barton, Australia. pp. 86–92.

Alicescu, V., Tournier, J.P.S., and Vannobel, P. 2008. Design andconstruction of Nemiscau-1 Dam, the first asphalt core rockfilldam in North-America. (Proceedings of the Canadian Dam As-sociation 2008 Annual Conference. Winnipeg, Man., 27 Septem-ber – 2 October 2008.) Canadian Dam Association Bulletin,21(1): 6–12.

Chen, X.G. 2003. Monitoring design for the asphalt core rockfilldam of Yele hydropower station. Sichuan Water Power, Decem-ber 2003. [In Chinese.]

Chen, J.C., Wang, X.B., He, Y.L., and Xiong, K. 2009. Analysis ofthe data from earthquake monitoring of Yele Dam. In Proceed-ings of the 1st International Symposium on Rockfill Dams,Chengdu, China, 18–20 October 2009. China Water PowerPress, Beijing. pp. 851–858.

Chu, W., Yu, L.S., and Wu, L.Y. 2004. Joint structure model testof asphalt concrete core of embankment dams. Journal of North-west Hydroelectric Power, 20(1): 23–26. [In Chinese.]

Creegan, P.J., and Monismith, C.L. 1996. Asphalt concrete barriersfor embankment dams. American Society of Civil Engineers(ASCE) Press, New York.

Hao, Y.L., and He, S.B. 2003. Layout of Yele hydropower station.Sichuan Water Power, December 2003. [In Chinese.]

Hao, Y.L., and He, S.B. 2008. Design of Yele asphalt concrete corerockfill dam. Dam construction in China – state of the art. Chi-nese National Committee on Large Dams, Beijing. pp. 226–233.

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Hoeg, K., Valstad, T., Kjaernsli, B., and Ruud, A.M. 2007. Asphaltcore embankment dams: recent case studies and research. Inter-national Journal on Hydropower and Dams, 13(5): 112–119.

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Appendix AThe Yele Dam is located in the northern part of the seis-

mically active fault zone of the Anning River region, andthe reservoir is about 2 km west of the Anning River down-stream active faults. The basic seismic intensity of the damsite is VIII (Chinese scale) and the design intensity is IXwith a peak horizontal ground acceleration of 0.45g.

The Yele Dam seismic analyses were carried out by tak-ing the peak horizontal rock ground acceleration of 0.45g inthe river direction and 0.3g in vertical acceleration. The cou-pling coefficient of earthquake horizontal and vertical accel-erations of 0.5 was used. The earthquake was assumed tolast 40 s in a time-domain analysis. The predicted maximumearthquake-induced settlement, horizontal displacement(downstream direction), and longitudinal displacement(along the dam axis) of the dam crest were 62, 188, and52 mm, respectively. Based on the results of the analyses,the dam design as presented in this paper is considered tobe very earthquake resistant.

Appendix BIn the original design, the earthquake resistance was in-

creased by using reinforced concrete beams in the top partof the dam. As this was found to be impractical from a con-struction point of view, it was decided to use geo-grid rein-forcement instead. That was the first time geo-grids were tobe used to increase earthquake resistance in an embankmentdam in China. The type and physical parameters of the geo-grids used are: maximum tensile strength ‡ 250 MPa; max-imum longitudinal tensile load ‡ 150 kN/m; maximumtransverse tensile load ‡ 80 kN/m; maximum tensile strain ‡8%; tensile load ‡ 60 kN/m at a tensile strain of 3%. Thetensile strength at joints was specified to be ‡ 50 kN/m.When using geo-grids in such designs, the material of thegeo-grids should be made of polypropylene or high-densitypolythene and an oxygen-resistance agent should be addedto prevent the geo-grid from ageing.



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Appendix C

ReferenceDuncan, J.M., and Chang, C.-Y. 1970. Nonlinear analysis of stress

and strains in soils. Journal of the Soil Mechanics and Founda-tions Division, ASCE, 96(5): 1629–1653.

Table C1. Dam fill material parameters used in Duncan–Chang model (Duncan and Chang 1970) in finite element analysis.

Material(see Figs. 1 and 2) Rf K n G F D Kur K0 DK

C’(kPa)

Density(g/cm3)

Q21I 0.65 1950 0.76 0.38 –0.023 4.5 3800 40 0 70 2.42

Q22I 0.65 1800 0.72 0.35 –0.023 3.8 3600 40 0 70 2.42

Q31II 0.68 900 0.74 0.38 –0.026 4.3 2200 37 0 80 2.45

Q32–1III 0.70 1100 0.78 0.38 –0.04 5.6 2200 38 0 80 2.24

Q32–2III 0.59 1300 0.76 0.39 –0.035 5.9 2600 39 0 60 2.35

Q32–3IV 0.65 900 0.73 0.38 0.02 5.7 2200 37 0 60 2.20

Asphalt core 0.76 850 0.33 0.38 0.05 15 1200 27 0 200 2.43Transition zone (dry) 0.67 1200 0.52 0.32 0.06 5 2400 43 5 0 2.2Transition zone (wet) 0.67 1080 0.52 0.32 0.06 5 2100 41 5 0 2.2Upstream rockfill (dry) 0.72 1000 0.5 0.33 0.06 6 1800 48 5 0 2.2Upstream rockfill (wet) 0.72 900 0.5 0.33 0.06 6 1600 46 5 0 2.2Downstream rockfill (II) 0.65 1200 0.45 0.31 0.03 3 2000 50 5 0 2.25Downstream rockfill (I) 0.72 1000 0.5 0.33 0.06 6 1800 48 5 0 2.2Toe berm 0.65 800 0.45 0.31 0.05 3 1800 48 5 0 2.3Downstream rockfill (III) 0.75 800 0.4 0.28 0.05 3 1600 36 3 0 2.2

Note: Rf, ratio between the asymptote to the hyperbolic curve and the maximum shear strength; K, modulus number describing the material stiffness; n,a value describing the rate of change of the material stiffness as a function of the confining stress; G, F, and D, test parameters related to material volumechange; Kur, modulus number used during unloading and reloading; K0, material friction angle in degrees; DK, increase of material friction angle indegrees; C’, cohesion intercept.

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Asphalt Core Rock Fill Dam