This document discusses modern structural solutions for large dams, including: 1) New designs for roller-compacted concrete (RCC) dams that improve seismic safety, such as facing symmetrical hardfill (FSH) dams with lean RCC zones and inner rockfill cores. 2) Proposed designs for very tall concrete-faced rockfill (CFR) dams over 100m that decrease cracking risks by including RCC supporting elements under the concrete facing. 3) The Kankunskaya rockfill dam design in Russia that utilizes an asphalt concrete core to improve safety compared to other core types, especially in seismic areas. Case studies and analyses demonstrate the viability of these innovative dam designs.

1. 1
Modern structural and technological solutions for new projects of large
dams in Russia and some CIS countries
Yury Lyapichev, international consultant on dams, Prof., Dr. (Tech. Sc.), Russia
1. New projects of very lean roller compacted concrete (RCC) dams
The modern high (100 m and more) RCC gravity dams with the traditional triangle cross-
section with a vertical upstream facing and a sloping downstream facing (0,8H/1V) on a rigid
(rock) foundation are frequently unsafe solution in the event of an earthquake with a horizon-
tal acceleration of 0.2g and more. Another serious restriction of traditional gravity (TG) RCC
dams is that they are not feasible on a soft (soil) and even on a weak rock foundation (ICOLD
Bulletin 117, 2000). These restrictions of RCC dams can be overcome by changing their TG
profile to the symmetrical triangle cross-section with RCC-1 with very low cementitious con-
tent, without horizontal joints treatment and with a watertight upstream concrete facing. This
new type of lean RCC dam (so called “Facing Symmetrical Hardfill” or FSH dam with both
slopes of about 0,7H/1V) was first introduced by Londe in 1992. Owing to the symmetrical
shape of this dam RCC requires neither high shear nor high compressive strengths and there
is no tensile stress whatsoever in the section at least for an earthquake with a pseudo-static
acceleration of 0.20g (ICOLD Bulletin 117, 2000).
Further optimization of the concept of FSH dam led us to a new type of composed FSH
dam with outer zones of lean RCC-1 and inner wide zone of rockfill, enriched with cement-
flyash mortar (REC) or FSH-REC dam (Fig. 1.1).
Fig. 1.1. 100 m high Facing Symmetrical Hardfill (FSH) dam with outer zone of RCC-3
and inner zone of Rockfill Enriched with Cement (REC or RCC-0)
2x0.3=0.6m
2x0.3=0.6m
Detail A
0.4
CARPI
Detail B
1 RCC-1
REC
REC
REC
Grout
curtain
Gallery CVC
Detail A
1
0.5
1CARPI
membrane
RCC
1
0.4
Detail B
0.5
1
0.4
0.5
1
dam axis
100.00
0.00
RCC
2x0.3=0.6m
2x0.3=0.6m
Detail A
0.4
2x0.3=0.6m
CARPI
membrane
2x0.3=0.6m 1
0.4
RCC-1 1
REC
Detail B
0.5
1
REC
RCC-1
REC
REC
REC
Grout
curtain
Gallery CVC
Detail A
1
0.5
1CARPI
membrane
RCC
1
0.4
Detail B
0.5
1
0.4
0.5
1
dam axis
100.00
0.00
RCC

2. 2
The outer zones of this dam with slopes of about 0.5-0.7 (depending on site conditions) and
width of about (3+0,1H) m (where H – water head in meters) can be made with very low ce-
ment contents (<70 kg/m3
). By placing the Carpi watertight membrane on the upstream dam
slope (instead of more labor-consuming and expensive reinforced concrete facing), the uplift
in RCC joints or cracks is eliminated, thus, with no consequence either on water tightness or
safety of the dam. The Carpi membrane is placed after completion of the dam to overcome
any difficulties with thermal cracking in RCC zones.
REC (rockfill of 5-300 mm diameter, enriched with cement-flyash mortar) in the central
zone of the dam can be placed in 60 cm thick layers while RCC layers in the outer zones in
30 cm layers. Than 10-15 cm thick cement-flyash mortar is spread over a rockfill layer and
penetrates into the coarse pores of rockfill. The penetration can be facilitated by 2 passages of
Dynapic sheep roller and subsequent compaction can be achieved by 2-3 passages of Bomaq
vibrating roller used also for compaction of RCC outer zones of the dam.
Owing to higher rockfill layers (60 cm) than traditional 30 cm of RCC and using Carpi
membrane on the upstream slope instead of reinforced concrete facing the speed of construc-
tion of FSH-REC dam will be higher than homogeneous FSH dam. Naturally, construction of
the FSH-REC or FSH dam should be tested on the site. But the structural (seismic) aspects of
a new design of FSH-REC or FSH dam should be performed in advance because at the
present the required seismic (dynamic) analyses of these dams are not available.
According to our stability analysis of the 100 m high FSH-REC dams during its construc-
tion the minimum cohesion of RCC of outer zones and REC should be not less than 0,5 MPa
to obtain the required cohesion during simultaneous placing of outer zones of RCC and cen-
tral zone of REC. This RCC cohesion value of 0,5 MPa corresponds to the minimum cohe-
sion of RCC-1 joints without treatment. For RCC and REC materials the minimum inner fric-
tion angle of 450
is assumed, which corresponds to the preliminary design of RCC dams.
Table 1.1 and 1.2 show the comparison, in terms of factors of safety against sliding at the
foundation, of a 100 m high traditional RCC dam with vertical upstream and sloping down-
stream facings (Sd=0.7; 0.8 and 0.9) and an FSH-REC dam of the same height and both
slopes (Su=Sd=0.4; 0.5 and 0.7).
Table 1.1
Foundation type
Factors of dam stability against horizontal sliding
(static case/seismic case) for downstream slope (H/V)
0,7 0,8 0,9
Rock 1,91/1,47 2,14/1,60 2,37/1,73
Alluvium 1,33/1,02 1,50/1,12 1,66/1,21
Moraine 1,24/0,95 1,39/1,04 1,54/1,13

3. 3
Table 1.2
Foundation type
Factors of dam stability against horizontal sliding
(static case/seismic case) for both slopes (H/V)
0,4 0,5 0,7
Rock 2,59/1,91 3,15/2,21 4,27/2,74
Alluvium 1,99/1,33 2,20/1,55 2,98/1,92
Moraine 1,65/1,22 2,01/1,41 2,73/1,75
Three types of foundations were considered: rock foundation (with the angle of inner fric-
tion =450
), alluvial ( =350
) and moraine ( =300
and cohesion C=0,1MPa) foundations.
Two operation cases were considered: static case with a maximum reservoir level and
seismic (pseudo static) case with a ground acceleration of 0.2g. In seismic case the shear
wedge method was used for the calculation of accelerations distribution in both dam because
this method corresponds to the actual shear movements of RCC dams during earthquakes.
For both dams the uplift was taken at 40% of the force developed by a straight percolation
line from full reservoir head upstream to no head at the dam.
According to Russian design norms for gravity dams (1987) the minimum allowable factors
of safety against sliding on the contact dam-rock foundation for static and seismic cases are,
correspondingly, 1.32 and 1.18. It means that RCC or PG (gravity dam of conventional con-
crete) dams aren’t feasible on soft foundation (alluvium, moraine, etc.).
According to the new Russian anti-seismic design norms for dams (2003) the seismic (dy-
namic) analysis are to be performed for high dams (100 m and higher) located in moderate or
high seismic regions.
The dynamic analysis of the 100 m high FSH-REC dam with slopes of 0.5V/1H was per-
formed by the method used now in the Geodynamic Center of Hydroproject Institute.
The synthetic horizontal and vertical accelerations with peak values of 0,8g were norma-
lized as the Maximum Design Earthquake (MDE) with the peak ground horizontal and vertic-
al accelerations of 0.2 and 0.14g, correspondingly and as the Maximum Credible Earthquake
(MCE) with the peak ground horizontal and vertical accelerations of 0.4 and 0.28g.
The same shear strength values of RCC-1 and REC joints were adopted in the dynamic
analysis as in the previous linear spectral analysis.
The results of dynamical analysis of the 100 m high FSH-REC dam with slopes of 0.5V/1H
for action of MDE are presented on Figs. 1.2.
Thus, it is clear that the FSH-REC dam is safe for the MDE case, and that there is no de-
velopment of tensile stresses or opening of RCC-1 joints.

4. 4
The results of dynamical analysis of the same FSH-REC dam for action of MCE with the
ground peak horizontal and vertical accelerations of 0.4 and 0.28g are presented on Fig. 1.3.
Fig. 1.2 Fig. 1.3
The cracking pattern (Fig. 1.3) in the dam body for the MCE case is deteriorated compar-
ing to the MDE (Fig. 1.2): in the lower part of the dam the cracks (joints opening) propagated
from the upstream slope towards the dam axis. However, owing to the upstream impervious
Carpi membrane, the uplift propagation through RCC and RSC joints is impossible and seis-
mic safety of the dam is provided.
The cracking or joints opening in the RCC outer zones during the MCE can be excluded or,
at least, decreased by joints treatment in these zones (bedding mix) that can increase twice or
more RCC joint cohesion. In this case another solution is remained: to decrease the steepness
of both slopes from 0.5 to 0.6 thus excluding any treatment of the RCC joints.
Thus, the 100 m high FSH-REC dam with both slopes of 0.5H/1V has, at least, the double
seismic (dynamic) safety against action of the MCE.
Conclusion
It is shown that new type of FSH-REC dam with the outer zones of lean RCC and inner
wide zone of rockfill enriched with cement mortar (FSH-REC dam) of height up to 100 m on
rock or soil foundation is a very attractive alternative comparing to traditional RCC or PG
dams. The seismic (dynamic) analysis of the 100 m high FSH-REC dam with both slopes of
0.5H/1V has shown the excellent behavior of its symmetrical cross-section for action of very
strong earthquake with peak ground horizontal and vertical accelerations, correspondingly, of
0,40 and 0.28g. Owing to Carpi impervious membrane placed on the upstream slope there are
no uplift pressure in the lean RCC joints of the dam for action of very strong earthquakes.
It’s recommended these dams for consideration in new projects in seismic regions of Russia.

5. 5
Some examples of new FSH dams from very lean RCC
- Cindere FSH dam (h=107 m) constructed on soft rock foundation in very seismic region
(Turkey, constructed in 2005), Figs. 1.4 and 1.5, photos 1-3.
Fig. 1.4
Fig. 1.5
Fotos 1-3. Various phases of construction of
Cindere FSH dam

6. 6
- Yumagazinskaya FSH-REC dam (h=65 m) on soil foundation in seismic region (Russia,
design alternative), Figs.1.6, 1.7 and 1.8.
54
3
2
RCCRCC
REC
CVC
CVCCVC
1
ФПУ = 270,0 м
0,7
1
РПУ = 260,0 м
НПУ = 268,5 м
4,12
215,7 м
89,05
111,31
10,31
209,0 м
6,6
1
0,7
14,36
261,3 м
274,0 м
209,0 м
Fig. 1.6 Fig. 1.7
Fig. 1.8
- Ituanga FSH dam (h=180 m) on rock foundation in very seismic region (Колумбия,
to be constructed in the nearest future), Fig. 1.9.
Fig. 1.9

7. 7
2. New structures of concrete facing rockfill (CFR) dams
Many more than 100-150 m high CFR dams have serious problems with intense cracking of
concrete facings and large opening of perimeter joints that’s results in dangerous seepage and
subsequent high-cost repair. The effective method to prevent these problems was proposed
for 275 m and 190 m high CFR dams in very seismic regions in Russia and Colombia
- Kambaratynskaya-1 CFR dam (h=275 m) on rock foundation in very seismic region
(Kyrgyzstan, design alternative), Figs. 2.1-2.2.
Fig. 2.1
Fig. 2.2

8. 8
- Sogamoso CFR dam (h=190 m) on rock foundation in very seismic region (Colombia, un-
der construction), Figs. 2.3 and 2.4.
The 2-D stress-strain state analyses of Kambaratynskaya-1 and Sogamoso CFR dams were
performed using ADINA program with elasto-plastic model of rockfill with Mohr-Column
criterion. The great influence of consequence of dam construction and reservoir filling on the
stress-strain state of dams was received.
The new effective method of decrease (40-55%) of deflection of concrete facing by inclu-
sion of roller compacted concrete (RCC) supporting elements or zone (instead of transition
zone) under the middle or whole part of concrete facing was proposed for these dams.
The project of Kambaratynskaya-1 CFR dam with integrated RCC zone under concrete
facing is much more technically and economically effective comparing with the blast-type
rockfill dam proposed in Soviet time.
The proposed inclusion of RCC supporting element under the middle part of the concrete
facing of Sogamoso CFR dam was assumed in the design.
Fig. 2.3
Fig. 2.4

9. 9
3. Kankunskaya rockfill dam with the compound asphalt concrete core (ACC)
Kankunskaya hydropower plant (1200 MW) is to be constructed in Southern Yakutia in
2013-2025 as the first principal hydroproject of the South-Yakut hydropower complex.
According to the contract between FNK Engineering and St-Petersburg branch of Hydro-
project Institute in the design documents of Kankunskaya hydropower plant FNK Engineer-
ing has developed 4 alternatives of rockfill dam with ACC.
By 2010 in the world about 120 ACC rockfill dams were constructed and successfully op-
erated, including about 30 dams over 100 m height mainly in China (Quxuе 170 m, Houziyan
198 m (project), Yele, 125 m, Guanmaozhou, 109 m, Maopingxi, 104 m, etc.), Norway (Stor-
glomvatn, 128 m, Storvatn, 100 m), Iran (110 m), in North of Canada (Romaine, 109 m), etc.
3.1. Basic advantages of ACC rockfill dams
1. 50-years successful operation of many dozens of high ACC rockfill dams without their ac-
cidents or leakages shows their higher safety in comparison with high rockfill dams with clay
cores and concrete facings, especially in difficult climatic, geological and seismic conditions.
2. The asphalt concrete cores (ACC) are widely applied because of their important advan-
tages in comparison with clay cores, concrete facings, geomembranes, etc.:
water tightness, allowing to apply thin core; stability to erosion and ageing; high resistance to
seismic loads; significant tensile and shear deformations without cracking even at negative
temperatures; several grades of bitumen and admixtures may be used to improve the mechan-
ical properties of the asphalt concrete to satisfy strict design requirements for a severe cli-
mate; viscoelastic, plastic and fluid properties providing ACC flexibility for large deforma-
tions at high static and seismic loads; the unique self-sealing and self-healing ability of as-
phalt concrete may eliminate the need for remedial measures due to possible fissures and
cracks caused by earthquakes and differential settlements in ACC rockfill dams.
3. ACC exhibits viscoelastic-plastic, ductile behavior and have therefore the ability to re-
lieve any stress concentrations and self-heal any tendencies to fissure or crack formation; they
can also tolerate foundation settlements and embankment deformations due to static and
earthquake loading better than clay cores and concrete facings, and therefore one can accept
the use of lower quality rockfill. ACC is protected from impact loads and damage by reser-
voir debris, deterioration due to weathering, ice loadings, etc.
4. ACC easily adapts to displacements of the adjacent transition zones. Application of ACC
contrary to clay cores practically does not depend on extreme weather (strong rains, a cold
below a minus 50
С), that allows in Siberia (including Yakutia) to extend a construction sea-
son nearly for 2 months and to receive ecological effect because of absence of clay quarries.

10. 10
The basic requirements to 232 m high Kankunskaya rockfill dam due to its high responsi-
bility, severe climate, difficult geological conditions and high seismicity are the followings:
dam safety; dam technological adaptability and economic efficiency of dam construction.
For considered project of the Kankunskaya rockfill dam it’s necessary to develop the scien-
tifically proved effective structural and technological solutions providing for the dam its reli-
able operational behavior and high technical and economic parameters for heavy natural cli-
matic conditions of construction.
3.2. Alternatives of Kankunskaya ACC rockfill dam
Taking into account results of the analysis of up-to-date experience of application ACC
rockfill dams four alternatives of Kankunskaya ACC rockfill dam have been considered:
Alternative 1.1 with the compacted asphalt concrete core (Fig. 3.1);
Alternative 1.2 with the liquid asphalt concrete core (Fig.3.1).
Fig. 3.1. Alternatives 1.1 or 1.2 of Kankunskaya rockfill dam with compacted or liquid ACC.
In alternative 1.1 hot (plus (160-170°С) asphalt concrete is placed and compacted together
with up- and downstream transition zones of 0,2 m thick and 1,5 wide filters. Placing and
compacting of ACC at negative temperatures can results in a low quality of this core.
In alternative 1.2 with the liquid (flowable) ACC the technology of construction of Bogu-
chansk ACC rockfill dam is used, which has some disadvantages among which the main one
is danger of squeezing of bitumen in adjacent transition zones.
In alternatives 1.1 and 1.2 under conditions of chocking-up (arching) of both cores on the
adjacent transition zones and decrease of vertical normal stresses in both cores at action of
forces of friction on external sides of core during reservoir filling which can be result in ten-
sile deformations and cracking in the base of core that’s inadmissible.

11. 11
Alternative 2 with the compound ACC formed by up- and downstream facings from pre-
cast concrete plates with the waterproof geomembrane on their external sides with subsequent
filling of cavity between plates with the liquid asphalt concrete (рис.3.2).
Fig. 3.2. Alternative 2 of Kankunskaya rockfill dam with the compound ACC and facings
from precast concrete plates
Alternative 3 with the compound ACC formed by up- and downstream facings from steel
sheets with the waterproof geomembrane on their external sides with subsequent filling of
cavity between sheets with the liquid asphalt concrete (Fig. 3.3). The compound ACC is ac-
cepted vertical with its 0,5 m thickness on the core crest and 2,2 m on the base.
Fig. 3.3. Alternative 3 of Kankunskaya rockfill dam with the compound ACC and facings
from steel sheets
The compound ACC with its flexibility, practically the same as the liquid ACC (alternative
1) during rockfill construction and reservoir filling follows displacements of the adjacent
transition zones and prevents squeezing of bitumen in these zones.
Except for functions of waterproofing and forms for liquid asphalt concrete, facings from
precast concrete plates or steel sheets, covered by geomembrane, carry out function of sliding
joints: great decrease of friction factor between the compound ACC and transition zones. It

12. 12
allows to lower chocking-up (arching) of the compound ACC on these zones which can lead
to forming of vertical tensile deformations and horizontal cracks in the base of core.
3.3. Basic assumptions of analysis of stress-strain state of ACC rockfill dam
1. Safety of Kankunskaya rockfill dam with all 4 alternatives of ACC is appreciably de-
fined by the stress-strain state of core. The estimation of durability of ACC is carried out on
the base of the received state of core, thus as criterion of strength of ACC according to which
the strength of ACC is provided in case of absence of tensile deformations in core.
2. Characteristics of rock foundation, physical-mechanical and thermal-physical characte-
ristics of soils of rockfill dam and asphalt core, the schedule of dam construction and reser-
voir fillings are accepted according to the project data presented by St. Petersburg Hydropro-
ject Institute and the same data from similar ACC rockfill dams throughout the world.
3.4. Results of analysis of seepage regime in the ACC rockfill dam and its foundation
The analysis was made by solution of stationary seepage problems in a characteristic strip of
seepage flow in the dam foundation coincident with dam cross-section in the river channel.
Fig. 3.4. Results of seepage analysis in the foundation of the ACC rockfill dam
1. The required depth of grout curtain in the river channel of ACC rockfill dam and its
bank slopes, including section of right bank abutment in zone of seepage in river banks.
2. Unloading of the basic part (80 %) of the seepage flow through the dam foundation will
happen in the downstream part of dam on the length equals 0,3Н behind the concrete gallery.
3.5. Results of analyses of thermal regime in the ACC rockfill dam and its foundation

13. 13
Fig. 3.5 (at the left). Isolines of temperatures in the dam and its foundation for time of end of dam
construction and reservoir filling up to Normal Operation Level (НПУ)
Fig. 3.6 (on the right). Isolines of temperatures in the dam and its foundation for time of temperature
field stabilization in the dam (after 30 years of operation)
Analyses of thermal regime in alternatives of the ACC rockfill dam were performed by
program Abaques (USA).
In the end of construction the zone of negative temperatures covers almost all dam cross-
section including the upstream part of the dam. In the dam foundation there is a small zone of
positive temperatures that is connected with influence of these temperatures of the rock base.
Near to the bottom of asphalt concrete core there are positive temperatures. For time, corres-
ponding to the temperature field stabilization of the dam (after 30 years of operation), almost
in all upstream part of the dam there is a zone of positive temperatures. Near the foundation
of downstream part of the dam there is a narrow zone of positive temperatures.
3.6. Basic results of analyses of stress-strain state of alternatives of ACC rockfill dam
1. By the end of construction of liquid and compacted alternatives of ACC rockfill dam
there is a great unloading of vertical stresses or non-uniform chocking-up (arching) of cores
on transition zones: smaller - in upstream part of the dam and greater - in downstream part, as
result of the influence of frozen rockfill in downstream part of the dam.
2. In alternatives 1.1 and 1.2 the tensile stresses can arise in the base of both cores that can
lead to cracking of core base and losses of its water tightness.
3. Analyses of ACC rockfill dam with compound core have shown, that the increase of de-
formation modulus of rockfill in downstream part of the dam from 60 up to 160 МПа (influ-
ence of frozen rockfill) results in much more favorable stress-strain state of compound core -
in 1,2 times decrease of core settlement and 2,6 times decrease of its deflections.
4. Results of coupled analyses of thermal regime and stress-strain state of ACC rockfill
dam taking into account the sequence of dam construction and reservoir filling in alternatives
2 and 3 ACC rockfill dam with compound core have shown the following:
- installation around of liquid concrete core in all its height of sliding concrete or steel fac-
ings with an external geomembrane considerably improves the stress-strain state of the liquid
core and increases its cracking resistance and water tightness;
- in ACC rockfill dam with compound liquid concrete core there are three waterproof con-
tours (two external facings around liquid asphalt concrete core), that in difficult operating
conditions at low temperatures and high water pressures greatly increase the dam safety.

14. 14
Рис.3.7. Horizontal (above), vertical (in the middle) and shear (in the bottom) stresses after reservoir
filling in rockfill dam with compound liquid concrete core, filled in a cavity between concrete plates
Fig. 3.8. Horizontal (above) and vertical (in the bottom) displacements stresses after reservoir filling
in rockfill dam with compound liquid asphalt concrete core, filled in a cavity between concrete plates
Fig. 3.9. Distribution of vertical stresses σy (on the right) and deformations εy (at the left) on upstream
face of compound liquid concrete core: dark blue color - after reservoir filling; red - later 30 years

15. 15
3.7. Results of analyses of static strength of rockfill dam with compound core
Computed values of safety factor of strength and stability of the dam are followings:
- by the end of dam construction and reservoir filling: k=1,71;
- after 30 years of dam operation (after reservoir filling): k=1,65.
Results of analyses of seismic resistance of ACC dam by spectral and dynamic theories
1. Normative value of safety factor of Kankunskaya ACC rockfill dam under action of
maximum possible earthquake (MPE) is determined equal to 1,06. Strength and stability of
the ACC rockfill dam is provided in all design cases with normative safety factors.
2. In analyses of stability of dam slopes by method of the circular sliding surfaces values of
safety factor are more than normative values which for the basic combination of loadings
(static case) is equal to 1,25 and for special combination of loadings (seismic case) -1,063.
3. Analyses of seismic resistance of the ACC rockfill dam by the linear spectral and wave
(dynamic) theories have shown, that seismic resistance of the dam with compound liquid as-
phalt concrete core, located between concrete facings, is quite provided.
3.8. Technical and economic comparison of alternatives of the ACC rockfill dam with
compound asphalt concrete core
Comparison of alternatives 2 and 3 of the ACC rockfill dam with compound core have
shown, that they are characterized by:
- high reliability and safety in difficult conditions of dam operation;
- high technological adaptability with an opportunity of full mechanization of works with
their high quality and maximal lengthening the period of works in the winter;
- close cost indexes with small (1,46 billion rbl.) excess of cost of alternative 3 above alterna-
tive 2 that makes 4 % from total cost of the ACC rockfill dam.
In the following design stage it is recommended to develop in details alternatives 2 and 3
for a choice of the most effective alternative of the ACC rockfill dam with compound core.