TECHNICAL | HYDRO POWER CAVERNS
Largest design flows for PSP caverns (m3 Sardar Sarovar, India
Tai’an, China Bailanhe, China
Shin Takase, Japan Torrejon, Spain
Symbols in the list of caverns should read as Pillar
Cover Factor Net H
Total C Unit C F,K,P h,v
Lhead Ltail
Pillar width to parallel cavern (m) Overburden height (m)
Horizontal in situ stress ratio Net water pressure height (m) Total installed capacity (MW) Specific installed capacity (MW) Francis, Kaplan, Pelton turbine Horizontal, vertical axis Headrace tunnel length (m) Tailrace tunnel length (m)
Key to excavation shape B
C H
M T
Bullet
(Semi-) circular Horseshoe Mushroom Trapezoidal
Conventional plant with separate transformer hall Q flow
(m3
/sec) 50
250 450 650 850
1,050
Length (m)
62 79 97
115 132 150
(m3
/sec) 50
Length (m)
150 250 350
105 119 132 145
Area (m2
)
460 540 620 700 775 855
Area (m2
)
760 845 930
1,020
Volume (m3
)
24,000 46,000 68,000 89,000 111,000 133,000
Pumped storage cavern with separate transformer hall Q flow
Volume (m3
)
70,000 91,000 111,000 132,000
/sec)
1,260 1,040 740 670 650
Key to host rock group 1
2 3 4 5 6 7
8 9
NB:
Key to rock class 1
2 3 4
Limestones
Other calcareous rocks Fine grained clastic rocks Coarse grained clastic rocks Volcanic rocks, e.g. basalt Plutonic rocks, e.g. granite Epimorphic rocks, e.g. phyllite Mesomorphic rocks, e.g. quartzite Katamorphic rocks, e.g. gneiss Combinations are possible, e.g. 6,9
Very good (RMR >80, Q >50) Good (RMR >60, Q >5) Fair (RMR >40, Q >0.7) Poor (RMR <40, Q <0.7)
Conventional plant without separate transformer hall Q flow
(m3
/sec) 50
250 450 650 850
1,050
Length (m)
91
103 114 125 136 148
(m3
/sec) 50
Length (m)
95
150 250 350
105 115 125
Area (m2
)
615 680 750 815 880 950
Area (m2
)
755 795 835 875
Volume (m3
)
40,000 60,000 81,000 101,000 122,000 142,000
Pumped storage cavern without separate transformer hall Q flow
Volume (m3
)
68,000 80,000 91,000
102,000
It may be concluded from the figures presented in
this edition that an intact rock pillar height of 50m is a suitable asymptotic value regardless of cavern height and unfavourable rock quality, particularly within distinctly bedded and inclined rock layers.
5. GEOTECHNICAL RISKS Geotechnical risks during cavern construction are comparable with those associated with tunnel construction, but with significantly higher impact with regard to delays and costs due to the almost impossible task of support reinforcement at higher excavation levels. In previous case histories, ‘adverse site conditions’ are seen as part of a realized risk within all possible construction risks.
18 | September 2023
Even in ‘best case’ scenarios, studies show that
the number of risks increase by 40-50% during construction. As a summary of general or project- specific investigations, the percentage observations of considerable, serious, and severe geotechnical risk impacts may be 55-65%, 15-20%, and 20-25%, respectively. An ideal distribution for four impact grades, including
disastrous risks, would be 54%, 27%, 13%, and 6% for a first attempt. A 67% serious risk and 33% severe risk occurred due
to late realisation under time pressure. Likely risk is 25%, occasional risk is 55%, and unlikely risk is 20%. A list of adverse site conditions at approximately 50 hydro caverns was first compiled and published by Hoek
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