Hydro vision 2011 russia. lyapichev presentation (7 p)

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 horizontal 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 content, 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)

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 cement 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.

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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 construction 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 construction 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 central zone of REC. This RCC cohesion value of 0,5 MPa corresponds to the minimum cohesion of RCC-1 joints without treatment. For RCC and REC materials the minimum inner friction 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 downstream 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 0,9Rock 1,91/1,47 2,14/1,60 2,37/1,73

Alluvium 1,33/1,02 1,50/1,12 1,66/1,21Moraine 1,24/0,95 1,39/1,04 1,54/1,13

Table 1.2

Foundation typeFactors 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 4,27/2,74Alluvium 1,99/1,33 2,20/1,55 2,98/1,92Moraine 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 friction =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 concrete) dams aren’t feasible on soft foundation (alluvium, moraine, etc.).

According to the new Russian anti-seismic design norms for dams (2003) the seismic (dynamic) 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 performed by the method used now in the Geodynamic Center of Hydroproject Institute.

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The synthetic horizontal and vertical accelerations with peak values of 0,8g were normalized as the Maximum Design Earthquake (MDE) with the peak ground horizontal and vertical 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 development of tensile stresses or opening of RCC-1 joints.

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 comparing 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 seismic 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.

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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

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- Yumagazinskaya FSH-REC dam (h=65 m) on soil foundation in seismic region (Russia,

design alternative), Figs.1.6, 1.7 and 1.8.

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

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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

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- Sogamoso CFR dam (h=190 m) on rock foundation in very seismic region (Colombia, under

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 inclusion

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

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