presa bennet columbia británica 1
DESCRIPTION
Presa BennetTRANSCRIPT
-
1Detection and Assessment of Internal Erosion atWAC Bennett Dam
Steve Garner, BC Hydro
182 m high2 km longZoned Earthfill Dam
-
2WAC Bennett DamLocation
Vancouver
WAC Bennett Dam
On the Peace River in North-eastern British Columbia
Williston Reservoir is 70 x 109 m3
Prince George
British
Columbia
-
3Working HypothesisGradations of Construction Materials
All materials come from moraine pits, deficient in medium sands Wide, blended till-like core, internally unstable Transition and Filter gap-graded in medium sand range
-
4Reservoir El 672
CoreSilty Transition
SandstoneShale
Shale
Scale: 0 30 60 90 m
Shell
Drain
TransitionFilter
Permeable Shales and Sandstones
Instrument Plane in Canyon Area
EP-06 EP-07 EP-08
1964
1965
1966
1967
Reservoir El 2205 ft (672 m)
Observation Well
Riser Pipe
-
5Observation Wells
8 leaky Observation Wells installed downsteam of dam axis
Includes an Observation Well near each Instrument Plane
Part of Instrument Island near Riser Pipes
-
6Performance Of Embankment Piezometers
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
1965 1970 1975 1980 1985 1990 1995 2000 2005
G
r
a
d
i
e
n
t
EP08 TO TRANSITION
UPSTREAM SHELL TO EP06
BETWEEN EP'S
540
560
580
600
620
640
660
680
700
1965 1970 1975 1980 1985 1990 1995 2000 2005
E
l
e
v
a
t
i
o
n
H
e
a
d
(
m
)
RESERVOIR
PIEZOMETER TIPS
EP06
EP07
EP08
-
7Canyon Area (1974)
EP502032
EP511976
EP522160
EP532072
Res El 2205.6
2163 2065?
2145? 2115 2053?
2080 2055 1995
2165 2110?
( )
2163 2065?
2145? 2115 2053?
2080 2055 1995
2165 2110?
Instrument Plane 11974
Canyon Area1974
-
8Canyon Section (1978)
EP502019
EP511964?
EP522126
EP5320482160? 2065??
2150 2130 2050??
2085 2060 2010
2130? 2075?
Instrument Plane 11978
Canyon Section1978
-
9Canyon Section (1988)
2053
1991
1865
2057
2012
1946
EP501958
EP511888
EP522137
EP5320532140 2045
2140 2085 2020
1998 1905 1845
2145 2075
2140 2045
2140 2085 2020
1998 1905 1845
2145 2075
2140 2045
2140 2085 2020
1998 1905 1845
2145 2075
Instrument Plane 11988
Canyon Section1988
-
10
Canyon Section (1996)
( )
2049
1973
1842
2060
2002
1911
EP50 EP511843
EP522126
EP532030
( )
2132 2010
2120 2050 1975
1980 1880 1810
2130 2075
Instrument Plane 11996
Canyon Section1996
-
11
OW Flowmeter Measurements
0 0.2 0.4
2000
2050
2100
2150
2200
OW10
0 0.2 0.4
OW9
0 0.4 0.8 1.2
1700
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
OW2
0 0.4 0.8 1.2 1.6
1700
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
OW7
0 0.4 0.8 1.2 1.6
1900
1950
2000
2050
2100
2150
2200
October 1996December 2000September 2002September 2004September 2004 (verification)
OW5
0 0.4 0.8 1.2 1.6
1850
1900
1950
2000
2050
2100
2150
2200
OW4
End of 1966 Construction
End of 1965 Construction
End of 1964 Construction
-
12
OW Cross-hole Seismic Results
500 1000 1500 2000
2000
2050
2100
2150
2200
OW10 OW9
5001000150020002500
1700
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
OW2
5001000150020002500
1700
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
OW7
5001000150020002500
1900
1950
2000
2050
2100
2150
2200
OW5
5001000150020002500
1850
1900
1950
2000
2050
2100
2150
2200
OW4
ANALYSIS REPORT
DATE:
Fig. 3-42CDREPORT No.: E301
WAC Bennett Dam Oct. 2004SV
SHEAR WAVE VELOCITY PROFILESummary of OW Results
End of 1966 Construction
End of 1965 Construction
End of 1964 Construction
500 1000
1500
2000
-
13
2111 1994
2090.5 2010 1915
1966.5 1859.5 1789
2122 2066
InstrumentIsland
( )Res El 2192.6
1956.5
1919
Winter 1966/67
Winter 1965/66
Instrument Plane 12004 Seepage Model, Flowmeter and Seismic
OW
2
End of 1966 Construction
End of 1965 Construction
1000
1200
1400
1600
1800
2000
2200
2400
Shear Wave Velocity (feet/s)
1650
1700
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
OW2 OW7Flowmeter
-
14
WAC Bennett Dam - 1996
Sinkhole 1(BM 1)
Sinkhole 2(BM 2)
-
15
Sinkhole 1
2.5 m diameter at crest
7 m deep sinkhole
extremely loose zone to 80 m depth
variable zone to 125 m depth
-
16
Splitter Dikes
Splitter Dike 1
Splitter Dike 2
Splitter Dike 3
Splitter Dike 4
Sinkhole 1
Sinkhole 2
-
17
Splitter Dike Gradation
ShellTransition
Drain
Filter
Transition
Core
Crest of Dike
Splitter Dike
3" 1 1/2 " 3/4" 3/8" #4 #20#10 #40 #60 #100 #200
0
10
20
30
40
50
60
70
80
90
100
0.010.1110100
GRAIN SIZE (millimetres)
P
E
R
C
E
N
T
F
I
N
E
R
T
H
A
N
GRAVEL
COARSE FINE
SAND
COARSE MEDIUM FINESILT
U.S. STANDARD SIEVE SIZES
Drain
Transition and Splitter Dike
Sandstone/Shale Foundation
#20#4 #10
Flow Test
-
18
Slice 15 (590 mm)Local Collapse Near Rigid Cell
-
19
Slice 50 (30 mm)Loss of Fines Between Nested Particles
-
20
1850 1875 1900 1925 1950 1975 2000 2025
Working HypothesisSurmised Internal Erosion
Internal Erosion
Benchmark Tube
OW-6OW-5
-
21
1850 1875 1900 1925 1950 1975 2000 2025
Working HypothesisSurmised Present Condition
Remaining Damaged Area
Locally Remediated Area
Limit of Core at Crest
OW-6OW-5
-
22
500 1000 1500 2000 2500 3000 3500 4000 4500Shear Wave Velocity (feet/s)
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
E
l
e
v
a
t
i
o
n
(
f
e
e
t
)
Oct. 2000Aug. 2001Aug. 2002Sept. 2003Oct. 2003Sept. 2004Oct. 2005Core ecs-0.1
Core ecs-0.07
Transition ecs-0.05
500 1000 1500 2000 2500 3000 3500 4000 4500Shear Wave Velocity (feet/s)
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
E
l
e
v
a
t
i
o
n
(
f
e
e
t
)
Oct. 2000Aug. 2001Aug. 2002Sept. 2003Oct. 2003Sept. 2004Oct. 2005Core ecs-0.1
Core ecs-0.07
Transition ecs-0.05
500 1000 1500 2000 2500 3000 3500 4000 4500Shear Wave Velocity (feet/s)
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
E
l
e
v
a
t
i
o
n
(
f
e
e
t
)
Oct. 2000Aug. 2001Aug. 2002Sept. 2003Oct. 2003Sept. 2004Oct. 2005Core ecs-0.1
Core ecs-0.07
Transition ecs-0.05
500 1000 1500 2000 2500 3000 3500 4000 4500Shear Wave Velocity (feet/s)
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
E
l
e
v
a
t
i
o
n
(
f
e
e
t
)
Oct. 2000Aug. 2001Aug. 2002Sept. 2003Oct. 2003Sept. 2004Oct. 2005Core ecs-0.1
Core ecs-0.07
Transition ecs-0.05
500 1000 1500 2000 2500 3000 3500 4000 4500Shear Wave Velocity (feet/s)
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
E
l
e
v
a
t
i
o
n
(
f
e
e
t
)
Oct. 2000Aug. 2001Aug. 2002Sept. 2003Oct. 2003Sept. 2004Oct. 2005Core ecs-0.1
Core ecs-0.07
Transition ecs-0.05
500 1000 1500 2000 2500 3000 3500 4000 4500Shear Wave Velocity (feet/s)
1750
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
E
l
e
v
a
t
i
o
n
(
f
e
e
t
)
Oct. 2000Aug. 2001Aug. 2002Sept. 2003Oct. 2003Sept. 2004Oct. 2005Core ecs-0.1
Core ecs-0.07
Transition ecs-0.05
Transition PlaneChanges in Shear Wave Velocities
850 ft/s(259 m/s)
-
23
MP-Data and Shear Wave Velocities
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
E
l
e
v
a
t
i
o
n
(
f
e
e
t
)
X-Hole Seismic MP Pressure Head
1800
1850
1900
1950
2000
2050
2100
2150
2200
2250
-10 -5 0 5 10 15 20 25Pressure Head (ft)
E
l
e
v
a
t
i
o
n
(
f
t
)
Oct-00
Aug-01
Aug-02
Sep-03
0
-
24
Tack(Thank You)
Conventional instrumentation can detect internal erosion
Conventional instrumentation can accelerate internal erosion
Cross-hole seismic has been used successfully for detecting and tracking internal erosion