1

Prof. Yu. LYAPICHEV (Russia)

Safety problem of the Boguchansk rockfill dam with asphaltic concrete (AC) core

1. Introduction

The safety problem of the 77 m high and 1860 m long Boguchansk rockfill dam with asphaltic concrete (AC) core is considered. This dam is one of the largest in the world rockfill dam with AC core (slides 1-4).

Now after 15 years of delay due to financional problems the dam and 3000 MW hydropower plant are again under construction on the Angara river in Siberia. The hydropower project is being built as part of a joint agreement between aluminium company RusAl and electricity provider Unified Energy Systems (UES) of Russia to create an energy and metals conglomerate, which will also incorporate an aluminium smelter. Approximately US$1.4B will be invested in the project. At present more than 50% of the hydropower plant and spillway dams and only 10% of rockfill dam have been constructed (slide 5). The first stage (1620 MW) of the huge Boguchansk hydropower plant is expected be commissioned in 2010 thus shortening time to improve the old project solutions, adopted 25 years ago and to solve the main safety problems of the dam.

2. Main safety problems and construction technology of the liquid type AC core

The main safety problems of the Boguchansk dam are connected with a liquid (flowable) type (of 11-12% bitumen content) AC core and adjacent coarse transition zones as well as with the seepage control of the AC core foundation.

On the construction site the liquid hot (1500C) AC was poured in steel forms of 1 m height and 6 m length which were removed in 2-3 day after decrease of temperature of poured block down to 450С. Then around the poured block the transition zones of crushed stones (up to 200 mm diameter) and even rockfill were placed in 3 m thick layers, practically, without its compaction (as rollers could easily hurt a weak standing concrete block) followed by placing of the lateral rockfill zones in 6 m thick layers. Then again the subsequent cycle was repeated starting with erection of steel forms and pouring of the next upper block thus heightening of the AC core. During preparation, transportation and pouring of the liquid asphaltic concrete the segregation of its aggregates was not excluded as well as the stratification of mix with formation of layers with excessively high content of bitumen (up to 13-15 %).

It creates the obvious danger of possible squeezing or penetration of bitumen into the large pores (up to 90 mm) of adjacent coarse transition zones under action of high lateral pressure from the body weight of core and water pressure during impounding of reservoir that leads to loss of water tightness of the AC core. The applied technology of asphaltic concrete core construction possesses a number of significant disadvantages: cyclicity, excessively high consumption of bitumen and dependence on negative external temperatures, significant laboriousness and, as consequence, an excessive slowdown of construction time and rise of construction cost. The maximal monthly average placement of the AC core was reached in 1996 (for the period 1988-1997) and amounted only to 450 m3/month. Hence, expected construction time of a dam would reach 16 years, that, obviously, unacceptable.

In these conditions advantages are obvious for applying of modern technology of continuous construction of the compacted AC core in 0,2 m thick layers (with the bitumen content of 6-6,5 %) and transition zones of crushed stones of 0,5-100 mm diameters vibro compacted by the special mechanized complex of firms "Strabag" (Germany) or "Kolo Veidekke" (Norway). In compacted AC core the segregation and stratification of a mix is impossible and the specific consumption of bitumen and

2

volume of a core is almost twice less than in liquid AC core. The continuous effective control of quality of placement of AC core and transition zones, i.e. the dam safety is simultaneously provided.

Unfortunately, during designing of the Boguchansk rockfill dam an available world experience of designing, construction and operation of rockfill dams with compacted AC cores was ignored. Authors of Boguchansk dam project were going on the "special" way, accepted technology of construction of a liquid AC core without its serious scientific and technological validation and without its technical and economic comparison with a traditional compacted AC core.

However, the main thing, not low technological or economic effectiveness but danger of loss of water tightness of liquid AC core, i.e. safety of the dam.

3. FE analyses of stress-strain state of the Boguchansk rockfill dam with compacted and liquid AC cores with use of different models of materials

To compare the behavior of the liquid and compacted AC core the finite element (FE) analyses of stress-strain state of the dam were performed.

In these analyses the following models of materials were used: for behavior of rockfill - hyperbolic model and the modified elastoplastic Cam-Clay model, taking into account the decrease of shear strength of rockfill with the increase of normal stresses; for behavior of asphaltic concrete - hyperbolic model and two phase visco-elastoplastic model in which the liquid phase (bitumen) is simulated by visco-elastic mode of the Maxwell-Norton type and solid phase (aggregates) - by the Cam-Clay model.

Earlier the FE analyses of two well-known rockfill dams with AC core (58 m high Gross Dunn dam in Germany and 90 m high Storvatn dam in Norway) were performed and compared with their natural observation data to validate the numerical models of NLSTRESS and PLSTRESS programs of the author.

Using the occasion I appreciate greatly the assistance of Honorary ICOLD President Prof. Kaare Hoeg for delivering me some his valuable publications on some well-known rockfill dams with compacted AC cores.

The calculated and observed displacements of Gross Dunn and Storvatn dams by the end of construction and reservoir impounding are in close agreement (slides 7- 8) thus proving the validation of numerical models used in FE analyses of the Boguchansk dam with liquid and compacted AC core.

The main analysis results of the Boguchansk dam are given on slides 9 -12. These analyses showed much more favorable and safe stress-strain state in

compacted AC core comparing with the liquid one, thus proving the necessity to modify the dam design and replace the liquid AC core by the compacted one. The behavior of a liquid AC core is nearly the same as a puddle clay core in embankment dam with nearly 100% bitumen stresses and small stresses in aggregates thus creating the danger of possible penetration of bitumen into large pores of coarse transition zones.

The liquid AC core, unlike the compacted AC core, becomes by the end of construction unstable (mobile) even with well compacted transition zones. Real insufficient compaction (the relative density less than 70%) of transition zones affects greatly on the stress-strain state of liquid AC core which becomes dangerously unstable during construction. The lateral pressure factor in the core reaches 0.9-0.95 and horizontal tensile and vertical compressive deformations in the core are increased in 2-3 times comparing to compacted AC core. Settlements and horizontal displacements in liquid AC core are also increased greatly. The high tensile horizontal deformations occur in the liquid AC core (core greatly extends in both sides) that creates danger of its cracking before the reservoir impounding and squeezing of bitumen and aggregates of AC into large pores of the downstream transition zone. In

3

zones of the increased bitumen content (up to 13-15%) in the liquid AC core the lateral pressure factor comes nearer to 1.0 and there are uncontrolled peaks of extremely high horizontal tensile deformations. No self-curing of cracks by excess bitumen can prevent inevitable loss of water tightness and subsequent intensive seepage through the AC core and erosion of the downstream dam slope. Vertical and horizontal displacements of dam and liquid AC core after reservoir filling strongly depend on deformability (density) of adjacent transition zones. Horizontal deformations of AC core are defined by type of AC: in a liquid AC core these deformations during construction and after reservoir filling are always tensile and very high that leads to its discontinuity or permeability. In a compacted AC core horizontal deformations always compressive that guarantees its water tightness after reservoir filling and under action of seismic forces. By the end of construction of the dam with compacted AC core placed on the 14 m high liquid AC core the latter remains very unstable and tensile (extended in both sides), that creates danger of its discontinuity or permeability, especially, opening of the joint with the overlaying compacted AC core before reservoir filling. Insufficient compaction of transition zones around lower liquid part of AC core results in the deterioration of the stress-strain state of the overlaying compacted AC core.

For revealing advantages of the two-phase AC model the FE analyses of the Boguchansk dam with liquid AC (bitumen of 5.5%) and compacted AC (bitumen of 9%) cores were performed by the author. The received results confirmed the main feature of behavior of this type of dams: the AC core influences only on displacements of central zone of the dam including AC core and adjacent transition zones and, practically, does not influence on displacements of lateral rockfill zones. Stresses in bitumen and aggregates are very different, that allows to understand strong distinction in behavior of liquid and compacted AC cores.

For bitumen content of 5.5 % in compacted AC core (slide 12, A) stresses in bitumen and aggregates are of same order, but in a different state: bitumen with its low shear strength quickly reaches the state of plastic yielding or flow in the isotropic stress state. In aggregates, on the contrary, the difference between vertical and horizontal stresses is significant and the ratio σx/σy=0.,55 does not change, practically, in height of AC core. For bitumen content of 9 % (slide 12, B) bitumen takes up larger part of pressure that is caused by its low compressibility. Total principal stresses in compacted and liquid AC cores are of the same order and vertical stresses are much smaller, than in the adjacent transition zones, but horizontal stresses are similar. In practically incompressible bitumen horizontal stresses are very close to vertical stresses.

In both AC cores by the end of construction vertical (compressive) deformations are close (2.6% in compacted AC core and 2.3 % in liquid one). Horizontal deformations, on the contrary, are various due to different volumetric compressibility of two AC. In all liquid AC core these deformations are tensile (in average 1 %), i.e. the AC core extends due to its high horizontal thrust on the transition zones. In all compacted AC core, on the contrary, horizontal deformations are close to zero that corresponds to a condition of stability.

During reservoir filling the AC core is subjected mainly to hydrostatic pressure, horizontal and shear stresses caused by deformations of central part of dam are strongly increased. Stress distribution in compacted AC core after reservoir filling is similar to stress distribution by the end of construction (slide 12, A). Stresses in bitumen increase on 50 % and remain isotropic while in aggregates the main rise of horizontal stresses occurs in the base of the compacted AC core.

On the other hand, in the liquid AC core almost all hydrostatic pressure is taken up by bitumen that leads to isotropic total stresses in it (slide 12, B). However shear

4

stresses in the base of AC core increase enough to cause shear resistance of aggregates in which deviator of stresses grows very quickly. It can be explained by the dilatation of aggregates which cannot develop due to bitumen, but at the same time it causes decrease of mean stress in bitumen and, thus increase of same stress in aggregates. The stress state in the dam foundation reflects these differences, especially in the AC core, where, depending on the bitumen contents, the stress state is deviatoric or isotropic. As to deformations the similar tendency is observed in both AC cores. After reservoir filling the vertical deformations in both cores nearly have not changed, but horizontal ones have greatly changed. Horizontal compression of compacted AC core is increased in its foundation up to 1.8 % and in the liquid AC core the horizontal tension of 1 % is kept in the upper 2/3 of its height and gradually changed into small compression (0.8 %) without taking into account the possible bitumen squeezing into adjacent transition zones.

Stresses in the liquid AC core by the end of reservoir filling are always above the hydrostatic pressure represented by curve W (slide 12, B). Results of the analysis strongly depend on the bulk modulus of bitumen and how it changes depending on degree of the bitumen saturation. In general, results of this analysis correspond to above mentioned results of similar analyses with use of hyperbolic and modified Cam-Clay models of the AC core and rockfill materials.

4. Simulating of grouting effect of transition zones around the liquid AC core

Tight grouting of coarse transition zones results in considerable improvement of the stress-strain state of liquid part of AC core and at the same time in partial deterioration of the same state of the lower part of the compacted AC core. The grouted transition zones behave as a rigid block preventing lateral extension of liquid part of AC core but at the same time induce the increase of vertical stresses or overhanging of upper part of transition zones (slide 11). There is no experience of rockfill grouting in the world except grouting of gravels and pebbles in very permeable foundations of some embankment dams that shows the increase of the deformation modulus of grouted gravels in 2-2,5 times, that it is not enough for rockfill of transition zones (minimum in 5-10 times).

Strongly advancing placement of lateral rockfill prisms (with difference of 6 m and more between top elevations of rockfill and AC core) can lead to a rebound (rising) of the top part of AC core and transition zones or to possible softening of its materials, that is inadmissible. This problem demands special investigations after reception of the necessary geotechnical data of grouted transition zones before the construction of the major part of the 1-st stage dam.

5. Static and seismic stability of the dam

In the old dam project the seismic aspects were not considered as the dam site was located in the low seismic region according to the old (1981) seismic map of the former USSR. At present according to the new (2003) seismic map of the maximum possible earthquakes in Russia the seismic intensity of the dam site is 8 grades and the peak ground acceleration is 0,2g.

In analyses of static and seismic stability of dam slopes by program UST (modified Terzaghi and Bishop methods) the decrease of the inner friction angle φ of rockfill with the increase of normal pressure was taken in account that allows to design an optimum and economic dam structure using anti-seismic layer of large stones (rip-rap) placed on both slopes and zonification of rockfill according its quality (external zones of solid rockfill and inner zones of weathered rockfill).

Taking into account the important factor of the variable shear strength of rockfill in the dam zones the minimum safety coefficients of seismic stability of both slopes for

5

flat sliding surfaces were increased on 10-15% comparing to ignoring this factor. On the contrary, for deep siding surfaces the average safety coefficients of seismic stability of both slopes were decreased on the same 10-15% comparing to ignoring this factor. Thus the favorable smoothing of safety coefficients of seismic stability of both slopes was received (slide 13)

6. Principal remarks on dam design solutions

a) There is no control of a state of the lower (14 m high) part of the liquid AC core below el. 144.0 due to unusual support of the core on a separate concrete plate instead of the special arch roof of the control and grouting gallery as adopted in many large rockfill dams with compacted AC cores (slide 6).

b) Instead of gravelly moraine (slide 6) on the downstream side of the liquid AC it was necessary to arrange short (15 m high) AC core or trench cut-off wall (slightly above maximum downstream water level) to eliminate the downstream water pressure that could permit to control the lower part of AC core. The similar solution is often accepted in some large rockfill dams with high downstream water levels.

c) As the grouting curtain is designed under the bottom of gallery instead of supporting plate of AC core, the reservoir pressure will be applied to the bottom of core plate, that in the absence of water stops in the joint between gallery block and core plate can lead to a dangerous leakage and seepage through the joint (slide 6).

d) The adjunction of liquid AC core to practically vertical (V/H=20/1) wall of the adjacent section of spillway concrete dam is designed without control of the contact between AC core and concrete wall through a control shaft in this wall or other possible solutions. This uncontrolled contact is also as well as in case of the joint between separate gallery block and core support plate is a place of possible uncontrolled leakage and seepage in the liquid AC core of the dam.

7. Principal recommendations

a) To provide safety of the Boguchansk rockfill dam its design should be changed and its construction should be continued based on the technology of a compacted asphaltic concrete (AC) core.

b) To prevent lateral extension and discontinuity of the lower liquid part of compacted AC core and bitumen and aggregates squeezing from the 14 m high part of liquid AC core, the transition zones around liquid part of AC core should to be grouted tightly so that the deformation modulus of the grouted zones can be increased not less than in 10 times.

c) Tight grouting of transition zones should provide the tight contact between lower liquid part AC core and these zones to prevent contact opening and lateral core extension. It’s important to prevent the lateral spreading of grouts in transition zones to provide the tight contact.

d) The final technology of grouting should be based on the test grouting of transition zones and results of its control.

e) Due to very severe climate of dam site (-50oC in winter) and very short construction season (not more than 6 months) the maximum possible bitumen content (7-7.5 %) with low viscosity of B180 is preferable for compacted AC core of the dam. This bitumen content also increases the self-healing of possible cracks in the core and allows lower heating temperatures during AC placement and compaction.

f) The seismic stability of both dam slopes for 1-st (53m high) and 2-nd (77m) stages of dam construction can be provided only with the intensive vibrating compaction of rockfill and placement of 10 m thick anti-seismic rip-rap layer on both slopes.

g) Strongly advanced placement of lateral rockfill zones can lead to a rebound of the top part of AC core and transition zones or to softening their materials, that is inadmissible

6

(Presentation of Slides)

Slide 1: General schemed lay-out of the Boruchansk HPP (3000 MW)

Slide 2: HPP and spillway dams view (August 2003)

Slide 3: Downstream view of HPP and spillway dams (March 2003)

7

Slide 4: General lay-out of the Boguchansk rockfill dam (height of 77 m, length of

1860 m) with liquid asphaltic concrete (AC) core

ПК 17+30

ПК 17+30

141.000

142.000

30

29

28

27

26

2524

23222120

19

17

16

15

14

13

136.

75

136.75136

0.10

0.10

1:1

.4 1:1

.4

1:1

.4

1:1

.4

202.000

187.000

172.000

135 135

.5

136

Крепление откоса

каменной наброской.

1:1

.41:1

.4

1:1

.41:1

.4

202.000

187.000

172.000

151.000

136.5

136.5

212.000

212.00012

диаграммы.

Разбивочная ось асфальтобетонной

3433

214.03130

135.5

135

136.

5

135

.5

136.5

136

136

ПК 13+48

Выход на поверхность "слабых"

глинистых песчанников.

Контур развития элювия-песчаники,разрушенные

до глинистого,реже песчано-глинистого состояния.

Портал.

<1:4.21

<1:4.2

1

<1:3.7

Ось верховой перемычки.

Портал.

133.5 1:3

1:3

137.5137

136. 5

136

135.5

134.5

135

135

135.5

133.5

140150

160

170

180

190

200

210

205

215

220

217.5

215

217.5

220

Конец-плотины.

205

210

187.000

200

190

195180

170

160

150

140

137

.513

7

136.5

13

61

35

.51

35134

.5

134

133.5

133

133

133.5

134

13

4.5

135

135.5

135.

5

13

6

136

135

135

148.000

Ось низовой перемычки.

0.0080.008

0.06

152.000

0.06

1:1

.4

1:1.41:3

0.06

Дрена №2

Дрена №1

Контрбанкет

верхнего

бьефа.

Контрбанкет

нижнего

бьефа.

0.06

0.06

151.000

Пригрузка верх-

него откоса.

Крепление откоса каменной

набраской толщиной 2.5 м.

Противоползневые и противо-

фильтрационные меропртятия.

Цементационная

штольня.

к п

ри

чал

у.

на промбазу.

145.0

00

152.000

162.000178.000

179.500

194.500

212.000

202.000

212.000

165.000

161.000

141.000145.000

141.000

151.000

141.000

149.000147.000

144.000

79.60

ПК 13+48

ПК 11+74.10

ПК 11+74.10

136

1:3

136

135

.5

135

135.

5

135

.5

Номера секции

бетонной плотины.

Ось временного судо-

ходного шлюза.

Глухая часть

секции 30 - 34.

Напорная грань

плотины.

Крепление откоса каменной

набраской с проливкой. бетоном

1:3

1:3

1:1

.4

1:1

.4

1:1

.6

1:1

.6

Ось верховой перемычки.

Границы пачки "слабых" пород Q1 и к2

Ослабленный контакт между

осадочными породами и долеритами.Проран

Генплан Богучанской грунтовой плотины на реке Ангара.

143.000

Slide 5: Typical sections of the Boguchansk rockfill dam of the 2006 ready state

and the 1st and 2nd stages of construction

8

Slide 6: Foundation part of the Boguchansk liquid AC core

1 - liquid AC core; 2 - grouting gallery; 3 - transition zones of coarse crushed stones (up to 200 mm); 4 - drainage control pipe; 5 - gravelly moraine; 6 - blanket of sandy clay; 7 - gravel; 8 - transition zone of rock muck; 9 - rockfill

9

Slide 7: Comparision of observed and calculated displacements and deformations in compacted AC core of Gross Dunn dam (Germany)

Vertical normal stresses (t/m

2) in the dam by the end of construction

20

40

30

60

50

70

0-10 -5 dx,5 10 (cm)dy-15-20-25-30

1

2

3

y(m)

Horizontal (dx) and vertical (dy) displacements in the core height by the construction end:

1, 2 - calculated displacements (dx) and (dy) (cm); 3 - observed displacements (dy) (cm)

10

20

30

40

50

60

0-0.5-1 , eps-y (%)eps-x10.5 1.5 2

1

2

3

растяжение сжатие

Horizontal (eps-x) and vertical (eps-y) deformations (%) in the core height after reservoir filling:

1, 2 - calculated deformations (eps-y) and (eps-x); 3 - observed deformations (eps-x)

20

40

30

60

50

0-10 -5 dx,5 10 (cm)dy-15-20-25-30

1

2

3

-35

Horizontal (dx) and vertical (dy) displacements in the core height after reservoir filling:

1, 2 - calculated displacements (dx) and (dy) (cm); 3 - observed displacements (dy) (cm)

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00 200.00 220.00

0.00

20.00

40.00

10

Slide 8: Comparision of observed and calculated displacements and deformations in compacted AC core of Strorvatn dam (Germany)

3- dx, 4- dy: после наполнения ВБ 1- dx, 2- dy: после строительства (см) по высоте диафрагмы плотины (Сторватн).

Рис. 4-13. Горизонтальные (dx) и вертикальные (dy) перемещения

2

41

3

10

50

-60 -50 -40 -30 -20 -10

10

30

20

40

60

80

70

90

y(м)

20 (cm)0 dydx,

Horizontal (dx) and vertical (dy) calculated displacements (cm) in the core height:

1, 2 - (dx) and (dy) by the construction end; 3, 4 - (dx) and (dy) after reservoir filling

(%) по высоте диафрагмы плотины (Сторватн).

1- (eps-x), 2- (eps-y}: после строительства

3- (eps-x), 4- (eps-y): после наполнения ВБ

Рис. 4-14. Горизонтальные (eps-x) и вертикальные (eps-y) деформации

1

eps-x, eps-y (%)

32

4

10

20

30

40

60

50

70

90 y(м)

80

-1 -0.5 0 0.5 1 1.5 2

растяжение сжатие

Horizontal (eps-x) and vertical (eps-y) calculated deformations (%) in the core height:

1, 2 - (eps-x) and (eps-y) by the construction end; 3, 4 - (eps-x) and (eps-y) after reservoir filling

0.00 50.00 100.00 150.00 200.00 250.000.00

50.00

Рис. 4-18. Изолинии горизонтальных перемещений (т/кв. м) (случай -(С+ВБ))

90.00--

65.00--

Horizontal calculated displacements (m) in the dam after reservoir filling

Observed displacements (scale in m) of the dam by October 1986

11

Slide 9: Calculated displacements and deformations in liquid type AC core of the Boguchansk rockfill dam (Russia)

Horizontal (dx) and vertical (dy) displacements (cm) in the core height:

1, 2 - (dx), (dy) for well compacted transition zones by the end of construction; 3, 4 - (dx), (dy) for badly

compacted transition zones by the end of construction; 5, 6 - (dx), (dy) for badly compacted transition

zones after reservoir filling

Horizontal (eps-x) and vertical (eps-y) deformations (%) in the core height:

1, 2 - (eps-x), (eps-y) for well compacted transition zones by the end of construction; 3, 4 - (eps-

x), (eps-y) for badly compacted transition zones by the end of construction; 5, 6 - (eps-x), (eps-

y) for badly compacted transition zones after reservoir filling

12

Slide 10: Calculated displacements and deformations in compacted type AC core of the Boguchansk rockfill dam (Russia)

Horizontal (dx) and vertical (dy) displacements (cm) in the core height:

1, 2 - (dx), (dy) by the end of construction; 3, 4 - (dx), (dy) after reservoir filling

Horizontal (eps-x) and vertical (eps-y) deformations (%) in the core height:

1, 2 - (eps-x), (eps-y) by the end of construction; 3, 4 - (eps-x), (eps-y) after reservoir filling

13

Slide 11: Calculated deformations in compacted type AC core constructed above liquid AC core of the Boguchansk rockfill dam

Horizontal (eps-x) and vertical (eps-y) deformations (%) in the core height

by the end of construction without grouting of transition zones

Horizontal (eps-x) and vertical (eps-y) deformations (%) in the core height

by the end of construction with grouting of transition zones

14

Slide 12: Calculated stresses and deformations in bitumen and aggregates of liquid and compacted type AC core of the Boguchansk dam

A Bh/H h/H

11

0.5 0.5

1 11 1

2 2

2 2

sigm-y sigm-y sigm-xsigm-x

0 5 10м 1мра

AB

0 0 -25-25-5 -5-5 -5-10

Рис. 5-7. Горизонтальные x и вертикальные y напряжения (т/кв.м)по высоте диафрагмы после строительства плотины (1-

напряжения в битуме, 2 - напряжения в заполнителе)

(А) –укатанной АФБ (Б=6%), (В) – литой АФБ (Б=10%)

Рис. 5-8. Полные главные напряжения sigm-1 и sigm-3 (масштаб в МПа)в центре

плотины cтроительства. (А) –укатанной АФБ (Б=6%), (В) – литой АФБ (Б=10%)

Horizontal (sigm-x) and vertical (sigm-y) stresses (МPa) in height of compacted (A) and

liquid (B) AC cores of the dam by the end of construction: 1 – stresses in bitumen; 2 - stresses in aggregates

h/H

0.50.5

1 1

03 eps

eps-xeps-yeps-y eps-x

eps2 1 -1

сжатие растяжениесжатие растяжение

A B

3 2 1 0 -1

h/H

Vertical (eps-y) and horizontal (eps-x) deformations (%) in height of compacted (A) and liquid (B) AC core by the end of construction (extreme right lines) and reservoir filling (extreme left lines)

Vertical (sigm-y) and horizontal (sigm-x) stresses (t/m2) in height of compacted (A) and

liquid (B) AC core after reservoir filling: 1 - stresses in bitumen; 2 – stresses in aggregates; q – deviator of stresses; W – hydrostatic pressure

15

Slide 13: Results of static and seismic stability analyses of slopes of the Boguchansk dam with the constant shear strength of rockfill

φ = 400

16

Slide 14: Results of static and seismic stability analyses of slopes of the Boguchansk dam with the variable shear strength of rockfill

τ =1.1σ0.87

17

Slide 15: Proposed typical sections of the 1-st stage construction of the

Boguchansk rockfill dam with compacted AC core

1 – AC core compacted in 20 cm thick layers; 2 – 1.5 m wide transition zone of

crushed rock muck d=0,5-100 mm compacted in 20 cm thick layers; 3 – 2 m wide

transition zone of crushed stone d=5-300 mm compacted in 40 cm thick layers;

4a – dolerite rockfill d=5-600 mm compacted in 100 cm thick layers; 4b – dolerite

rockfill d=5-1000 mm compacted in 200 cm thick layers; 4c – available dolerite

rockfill compacted within zone 4a; 5 – rip-rap protection with dolerite stones

(average diameter 600 mm); 6 – transition zone of dolerite rockfill; 7 –

compacted gravelly moraine; 8 – blanket of compacted sandy clay; 9 – gravelly

sand filter; 10 – additional dumped rockfill