Canadian Dam Association Bulletin - Summer 2017 - 17

into North dipping and South dipping.
These shears, for the most part, dip
into the right bank.
Shearing beneath the river is not as
prevalent as on the right bank. The
most prominent and continuous shear
observed in the river area is a shear
that dips towards the left bank (northerly) at 9 to 15° and has offsets ranging
up to 0.8 m.

3. SELECTION OF THE TYPE OF
DAM AND CONFIGURATION
OF THE PROJECT
3.1 Main Dam
During the initial stages of the
configuration design, several studies were undertaken to investigate
various options for the main dam.
Due to the very weak sedimentary
bedrock and the low modulus of the
bedrock at Site C, concrete gravity
type dams were ranked the lowest
viable option for the main dam. There
is no precedent for a concrete gravity
dam of the height required at Site C
constructed on similar weak bedrock.
The selected main dam type was an
earthfill dam with an impervious
core. The selection was influenced
by the local availability of till and
gravel to construct the main dam and
the ability of an earthfill dam to handle the predicted movements in the
abutments over time.
During the studies for the selection
of the main dam, several analyses were
undertaken to investigate the stability
of the concrete gravity dam options.
These studies revealed that stability of
concrete gravity dam structures in the
river channel could only be achieved
by engaging passive resistance of the
foundation bedrock downstream of
the structure. The weight of the concrete gravity dam itself was insufficient to provide the required shear
resistance on the continuous bedding
plane in the bedrock beneath the dam
due to the low shear strength of these
bedding planes. Hence, the principal
resistance mechanism was the passive resistance of a theoretical wedge
downstream of the concrete gravity
structure.
Canadian Dam Association * Summer 2017

4. ARRANGEMENT OF THE
HEADWORKS STRUCTURES
4.1 Optimization of
the Project Layout
There is a plateau on the right bank
of the Peace River at the dam site that
is at, or slightly above, the maximum
normal reservoir level for the Site C
project. The plateau is overlain by
approximately 10 m of overburden.
The suitability of this plateau for
placing the headworks of the powerhouse and spillway was one of the
reasons why this particular site on
the Peace River was selected for the
third hydroelectric generating station
in the river system.
The headworks structures comprise the intakes for the powerhouse
and the spillway structures that
support the spillway gates. These
are concrete gravity structures. The
hydrostatic horizontal thrust on
the headworks structures is carried
down to the foundation bedrock
beneath the structures and transferred into the foundation by shear
and compression along the concrete/
rock interface. The stability of the
concrete gravity structures along
the concrete/rock interface was a
key consideration in addition to the

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678727_Mavel.indd 1

stability of the foundation bedrock
beneath the headworks structures.
At Site C, it was found that the
stability of the bedrock beneath the
headworks governed the layout of
the headworks. The presence of weak
bedding planes in the rock beneath
the headworks, particularly BP-25,
which only as a coefficient of friction of 9° and no cohesion strength,
governed the sliding stability. BP-25
daylights in the valley wall so the
shear resistance at the bedding plane
can only be mobilized by the shear
friction on the bedding plane; no contribution from passive rock pressure.
The presence of relaxation joints in
the bedrock, which would be on the
"upstream" side of the headworks
structures, also had negative implications on the stability.
The stability analysis assumed full
headwater pressure in the relaxation
joints down to the intersection of
these joints with BP-25. Since the bedding plane is considered undrained,
an uplift pressure along BP-25 was
accounted for, varying from full headwater pressure at the intersection with
the relaxation joint to tailwater where
the bedding plane daylights in the valley wall.

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17

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Table of Contents for the Digital Edition of Canadian Dam Association Bulletin - Summer 2017

Board of Directors
President's Message
Roller Compacted Concrete Buttress at the Site C Clean Energy Project
Hurricane Igor's Impact on Newfoundland Power's Small Hydro
CDA Conference Heads to Kelowna!
CDA Directors & Officers - Call for Nominations
2017 CDA Awards - Call for Nominations
CDA Developing New Ways to Distribute Guidelines
Notice of Annual General Meeting
Time to Renew Your Membership
Buyers' Guide and Trade List
Canadian Dam Association Bulletin - Summer 2017 - intro
Canadian Dam Association Bulletin - Summer 2017 - 1
Canadian Dam Association Bulletin - Summer 2017 - 2
Canadian Dam Association Bulletin - Summer 2017 - 3
Canadian Dam Association Bulletin - Summer 2017 - 4
Canadian Dam Association Bulletin - Summer 2017 - 5
Canadian Dam Association Bulletin - Summer 2017 - 6
Canadian Dam Association Bulletin - Summer 2017 - Board of Directors
Canadian Dam Association Bulletin - Summer 2017 - 8
Canadian Dam Association Bulletin - Summer 2017 - President's Message
Canadian Dam Association Bulletin - Summer 2017 - 10
Canadian Dam Association Bulletin - Summer 2017 - 11
Canadian Dam Association Bulletin - Summer 2017 - Roller Compacted Concrete Buttress at the Site C Clean Energy Project
Canadian Dam Association Bulletin - Summer 2017 - 13
Canadian Dam Association Bulletin - Summer 2017 - 14
Canadian Dam Association Bulletin - Summer 2017 - 15
Canadian Dam Association Bulletin - Summer 2017 - 16
Canadian Dam Association Bulletin - Summer 2017 - 17
Canadian Dam Association Bulletin - Summer 2017 - 18
Canadian Dam Association Bulletin - Summer 2017 - 19
Canadian Dam Association Bulletin - Summer 2017 - 20
Canadian Dam Association Bulletin - Summer 2017 - 21
Canadian Dam Association Bulletin - Summer 2017 - 22
Canadian Dam Association Bulletin - Summer 2017 - 23
Canadian Dam Association Bulletin - Summer 2017 - Hurricane Igor's Impact on Newfoundland Power's Small Hydro
Canadian Dam Association Bulletin - Summer 2017 - 25
Canadian Dam Association Bulletin - Summer 2017 - 26
Canadian Dam Association Bulletin - Summer 2017 - 27
Canadian Dam Association Bulletin - Summer 2017 - 28
Canadian Dam Association Bulletin - Summer 2017 - 29
Canadian Dam Association Bulletin - Summer 2017 - 30
Canadian Dam Association Bulletin - Summer 2017 - 31
Canadian Dam Association Bulletin - Summer 2017 - 32
Canadian Dam Association Bulletin - Summer 2017 - 33
Canadian Dam Association Bulletin - Summer 2017 - 34
Canadian Dam Association Bulletin - Summer 2017 - 35
Canadian Dam Association Bulletin - Summer 2017 - CDA Conference Heads to Kelowna!
Canadian Dam Association Bulletin - Summer 2017 - 37
Canadian Dam Association Bulletin - Summer 2017 - 38
Canadian Dam Association Bulletin - Summer 2017 - 39
Canadian Dam Association Bulletin - Summer 2017 - 40
Canadian Dam Association Bulletin - Summer 2017 - 41
Canadian Dam Association Bulletin - Summer 2017 - 42
Canadian Dam Association Bulletin - Summer 2017 - 43
Canadian Dam Association Bulletin - Summer 2017 - 44
Canadian Dam Association Bulletin - Summer 2017 - 45
Canadian Dam Association Bulletin - Summer 2017 - CDA Directors & Officers - Call for Nominations
Canadian Dam Association Bulletin - Summer 2017 - 47
Canadian Dam Association Bulletin - Summer 2017 - 2017 CDA Awards - Call for Nominations
Canadian Dam Association Bulletin - Summer 2017 - 49
Canadian Dam Association Bulletin - Summer 2017 - CDA Developing New Ways to Distribute Guidelines
Canadian Dam Association Bulletin - Summer 2017 - 51
Canadian Dam Association Bulletin - Summer 2017 - 52
Canadian Dam Association Bulletin - Summer 2017 - Notice of Annual General Meeting
Canadian Dam Association Bulletin - Summer 2017 - Time to Renew Your Membership
Canadian Dam Association Bulletin - Summer 2017 - Buyers' Guide and Trade List
Canadian Dam Association Bulletin - Summer 2017 - 56
Canadian Dam Association Bulletin - Summer 2017 - 57
Canadian Dam Association Bulletin - Summer 2017 - 58
Canadian Dam Association Bulletin - Summer 2017 - 59
Canadian Dam Association Bulletin - Summer 2017 - 60
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