Project Understanding
39~/142763
October 29,2010
Mr. Henry Taylor . Duke Energy Carolinas, LLC Mail Code EC 111 526 South Church Street Charlotte, NC' 28285 SUBJECT:
.
Marshall Steam Station Stability Evaluation Revised Report of Static Slope Stability Evaluation
Dear Mr. Taylor: . HDR Engineering, Inc; of the Carolinas, (HDRIDTA) is pleased to submit this revised .report for a static slope stability analysis of the main embankment section at the :ash basin at Marshall Steam Station near Terrell, North Carolina. The scope of work included analysis of the static steady-state seepage loading condition using infomiation provided by Duke Energy Carolinas, . LLC (Duke Energy). Subsequent to submitting the previous report dated September 15,2010, HDRjDTA was informed by Duke Energy that certain dimensions contained in the provided information did not represent actual field conditions. This report summarizes the results of a revised analysis based on the corrected dimensions and a profile that is more representative of actual field conditions.
Project Understanding Marshall Steam Station is located near Terrell, North Carolina, in the southeast section of Catawba County. HDRIDTA understands that the ash basin is classified as active but only receives water that is unsuitable for direct release but does not contain sluiced ash. The section analyzed represents the maximum section of the main embankment, the downstream slope of which is essentially a part ofthereservoir rim of Lake Norman. A representation of the profile section ' analyzed is shown on Figure 1. HDRIDT A understands that this evaluation is in response to a: request by the Environmental Protection Agency (EPA) regarding re-evaluation of the static stability of the earthen embankment at this facility. The main embankment is approximately 90 feet tall and consists of a rolled fill interior section with a dumped fill berm and spoils berm on the upstream and downstream sides of the interior section, respectively. Details about the placement methodology of the dumped and spoil fill were not provided at the time ofthis analysis, and it is assumed that no mechanical compaction was performed and the material is only consolidated under its own weight. A shear strength judged appropriately conservative given the uncertainty regarding the materials was assigned' to the dumped and spoil materials ·in the analysis. The design slopes of the embankment are HDR IOTA HDR Engineering,lnc. olthe Carolinas
400 S Tryon Street Suite 2401 Charlotte, NC 28285-0106
Phone: (704) 377-4182 Fax: (704) 377·4185 www.hdrinc.com
Mr. Henry Taylor October 29,2010 Page 2 2 horizontal (H): 1 vertical (V), but survey data shows that the slopes are inconsistent and range anywhere between approximately 1.75H:1V and 2.2H:1V (Ref 3). The slopes for the analysis were set at 2H: 1V in the analysis, but the variations of the slope inclination from the design value would generally result in higher safety factors for flatter slopes and lower safety factors for steeper slopes than those calculated in the analysis. The crest width of the embankment varies depending upon the station, with a crest width of 80 feet at an elevation of approximately 800 feet mean sea level (msl) used for the analysis section. The crest length of the ups,tream dumped fill berm was set at a width of 76 feet at an elevation of approximately 755 feet msl, and the crest length of the downstream spoils berm was set at a width of 160 feet at an elevation of approximately 780 feet msl. The dimensions and crest width of the downstream spoils berm were based on field observations and surveys by others (Ref 3). The dimensions and crest width of the upstream dumped fill berm were based on information provided by Duke Energy.
Evaluation Procedures and Assumptions The analysis section is based on a profile section developed from information given on Figure 3 of Reference 2 and survey information from Reference 3. Full pond reservoir elevations of 790 and 760 feet mean sea level (msl) were used for the water levels within the ash basin and Lake Norman, respectively. The phreatic surface within the embankment was assumed to be represented by a straight line within the embankment connecting the intersections with the embankment profile of the full pond elevation within the ash basin on the upstream side and the full pond elevation within Lake Norman on the downstream side; This assumption is used in the analysis as there is no instrumentation within the embankment from which to base a phreatic surface. A detailed description of the main embankment can be found in Reference 2. Shear strengths for materials comprising the embankment and foundation were based on data provided by Duke Energy and engineering judgment where applicable. Laboratory test data pertaining to the compacted embankment materials and residual foundation materials were compiled from the data contained in Reference 5. Test data for in-place embankment fill were. not provided and it was assumed that the materials described as borrow were used for construction of the embankment, and that the shear strengths from tests performed on compacted borrow samples are representative of the shear strengths of materials within the existing embankment. As no test data was provided for the dumped and spoils materials in the upstream and downstream berms, a shear strength judged to be conservative was assigned to the materials in the analysis. The shear strength for the partially weathered rock was based on engineering judgm,ent and the assumption that failure surfaces would not pass through this material. Although the raw data from the individual tests were not examined, the test results provided in Reference 5 generally appeared to be reasonable for drained shear strengths of regional materials. Conservative values of the drained shear strengths were selected based on the collection of shear strength envelopes provided for each material type from test data and HDRIDTA HDR Engineering, Inc , altha Carolinas
Mr. Henry Taylor October 29,2010 Page 3 engineering judgment to select a representative design envelope for each material type. The design shear strength envelopes used in the analyses are labeled on Figures 2 and 3. The shear strengths used in the analysis for each material type are given in Table 1.
No. I 2
3 4 5
Description PWR Foundation - Saturated Compacted Fill - Saturated Com~acted Fill - Moist Dumped Fill / Spoils Fill
Table 1 Unit Weight (pcO 125 120 120 120 100
Shear Stren2th
c' (psO
:
-
L
----_.
c'-O sf p ;3r
==
~~:-I-----==:J:~-=--. ' , -~ ~I ==--J-----=="I:1 =c=l1===1 II
-j---
'- "
Effective ConfIDing Stress (psf)
'
.
;
L gwer Bouud
I
.
-
___
.-
..
3,000
.I
---
=-.....
_
]
2,000
---'
---
-..--' , ~,,~~ ' ------
---
; -. l ; _
-
.
_.7P ='
_,
1,000
,
.
,='==:;:} -:=~~--=- ,f--~ _J _ ..-~ ....~7_"'" ..,...---:
f---: :~I~ '" .. ~ ~ ~. ~ ". .,.
;.
.
-
' ~ l ~~' ~~ ---"l.' ; ;;~~~~ ~~~ _2~_~ ~:7.;L~ · -·--: ;: ~ >; ~~~~1 ~ --- ~- ------~ rL ;:::;4 - . ". ~ ~ - -=1
' --I-
- ~-.. . . . ~---, ~ ../'~ ".... ~,.. -/. -= . ~ ~ ~r:7 _ -----~~ ~ ,-
_
r
'
--------,------
., -
, ''
___ __ _+ ____ __ ,Bound,;;;: ,_ _ ----=---= · --.-
~ ~L~~. , ----=~~~" ~ ~ __
-
r:::------ -]
-
, ~ ' .--7--1 ~ :: -=- -r 7--~ " -: ---
_ --
~======~-=~~= t l _ = == ___==::==.~up~~er ~ ~ __ _ ' :::::-s '-
r---
2,000
=
.
---1-
_ 1,____
I
3,000
-,
,,__ -I- -=- _
- 1 -
1
'
-
i
-
___
L
,
---
"
C - - 'r-----
---=~========J[==------'----1 .
'
_1L
-
,
'L
___,__ . ____
7,000
----- .
--
-,
--
8,000
.
----
9,000
10,000
Figure 3 Triaxial Shear Test Results - Fill Soil 9,000
---- .--
UOO
71
7,000
6,000
~r'
7 /
s;.;-s;::::~
1- - -
Ii CL
-! l it
- . ---
5,000
....
~
~- I
.. 4,000
.t:.
."
3,000
- -'- - - --
-
=a psf
CD' =32.6·
.~
- --
2,000
c'
,
~r=.--I=--
1----:- -I
Lower Bound
1,000
o
- - -1 -- - - 1 -
~
o
1,000
2,000
3,000
4,000
5,000
Effective Stress (psI)
6,000
7,000
8,000
9,000
10,000
1000
900
Factor of safety: 2.511 Side force Inclination: -6.71 degrees
i ii
E
tc
800
o
®
';:l
5 ii:i 700
600
CD
500 ~,---------------------------------------------------------------------------300 -100 o 100 200 300 400 -400 -200
Distance (ft)
Figure 4. Slope Stability Analvsis Results - Max. Section- Downstream Slope
000
100
Factor of safety: 0.859 Side force Inclination: -11.56 degrees
i ii
tE
100
c o ;:;
@
E iii '-00
G>
6000
500
~I----------------~------------------------------------------------------~~
- 400
-2QO
o
2 00
Distance (ft)
Figure 5. Slope Stability Analysis Results - Max. Section- Downstream Slope
400
1000
900
Factor of safety: 1.517 Side force Inclination: 4.23 degrees
Oii
E
tc
800
o
i
®
~
ii:i
700
600
CD
500 ~'-----------------------------------------------------------------------100 100 400 o 200 300 -300 -200 -400 Distance (ft)
Figure 6. Slope Stability Analysis Results - Max. Section- Upstream Slope
1000
900
Factor of safety: 0.997 Side force Inclination: 1.14 degrees 800
i ii
E .t:• c
0
~ III
.d
7
/
~
@
®
700
> G/
W
October 29,2010
Mr. Henry Taylor . Duke Energy Carolinas, LLC Mail Code EC 111 526 South Church Street Charlotte, NC' 28285 SUBJECT:
.
Marshall Steam Station Stability Evaluation Revised Report of Static Slope Stability Evaluation
Dear Mr. Taylor: . HDR Engineering, Inc; of the Carolinas, (HDRIDTA) is pleased to submit this revised .report for a static slope stability analysis of the main embankment section at the :ash basin at Marshall Steam Station near Terrell, North Carolina. The scope of work included analysis of the static steady-state seepage loading condition using infomiation provided by Duke Energy Carolinas, . LLC (Duke Energy). Subsequent to submitting the previous report dated September 15,2010, HDRjDTA was informed by Duke Energy that certain dimensions contained in the provided information did not represent actual field conditions. This report summarizes the results of a revised analysis based on the corrected dimensions and a profile that is more representative of actual field conditions.
Project Understanding Marshall Steam Station is located near Terrell, North Carolina, in the southeast section of Catawba County. HDRIDTA understands that the ash basin is classified as active but only receives water that is unsuitable for direct release but does not contain sluiced ash. The section analyzed represents the maximum section of the main embankment, the downstream slope of which is essentially a part ofthereservoir rim of Lake Norman. A representation of the profile section ' analyzed is shown on Figure 1. HDRIDT A understands that this evaluation is in response to a: request by the Environmental Protection Agency (EPA) regarding re-evaluation of the static stability of the earthen embankment at this facility. The main embankment is approximately 90 feet tall and consists of a rolled fill interior section with a dumped fill berm and spoils berm on the upstream and downstream sides of the interior section, respectively. Details about the placement methodology of the dumped and spoil fill were not provided at the time ofthis analysis, and it is assumed that no mechanical compaction was performed and the material is only consolidated under its own weight. A shear strength judged appropriately conservative given the uncertainty regarding the materials was assigned' to the dumped and spoil materials ·in the analysis. The design slopes of the embankment are HDR IOTA HDR Engineering,lnc. olthe Carolinas
400 S Tryon Street Suite 2401 Charlotte, NC 28285-0106
Phone: (704) 377-4182 Fax: (704) 377·4185 www.hdrinc.com
Mr. Henry Taylor October 29,2010 Page 2 2 horizontal (H): 1 vertical (V), but survey data shows that the slopes are inconsistent and range anywhere between approximately 1.75H:1V and 2.2H:1V (Ref 3). The slopes for the analysis were set at 2H: 1V in the analysis, but the variations of the slope inclination from the design value would generally result in higher safety factors for flatter slopes and lower safety factors for steeper slopes than those calculated in the analysis. The crest width of the embankment varies depending upon the station, with a crest width of 80 feet at an elevation of approximately 800 feet mean sea level (msl) used for the analysis section. The crest length of the ups,tream dumped fill berm was set at a width of 76 feet at an elevation of approximately 755 feet msl, and the crest length of the downstream spoils berm was set at a width of 160 feet at an elevation of approximately 780 feet msl. The dimensions and crest width of the downstream spoils berm were based on field observations and surveys by others (Ref 3). The dimensions and crest width of the upstream dumped fill berm were based on information provided by Duke Energy.
Evaluation Procedures and Assumptions The analysis section is based on a profile section developed from information given on Figure 3 of Reference 2 and survey information from Reference 3. Full pond reservoir elevations of 790 and 760 feet mean sea level (msl) were used for the water levels within the ash basin and Lake Norman, respectively. The phreatic surface within the embankment was assumed to be represented by a straight line within the embankment connecting the intersections with the embankment profile of the full pond elevation within the ash basin on the upstream side and the full pond elevation within Lake Norman on the downstream side; This assumption is used in the analysis as there is no instrumentation within the embankment from which to base a phreatic surface. A detailed description of the main embankment can be found in Reference 2. Shear strengths for materials comprising the embankment and foundation were based on data provided by Duke Energy and engineering judgment where applicable. Laboratory test data pertaining to the compacted embankment materials and residual foundation materials were compiled from the data contained in Reference 5. Test data for in-place embankment fill were. not provided and it was assumed that the materials described as borrow were used for construction of the embankment, and that the shear strengths from tests performed on compacted borrow samples are representative of the shear strengths of materials within the existing embankment. As no test data was provided for the dumped and spoils materials in the upstream and downstream berms, a shear strength judged to be conservative was assigned to the materials in the analysis. The shear strength for the partially weathered rock was based on engineering judgm,ent and the assumption that failure surfaces would not pass through this material. Although the raw data from the individual tests were not examined, the test results provided in Reference 5 generally appeared to be reasonable for drained shear strengths of regional materials. Conservative values of the drained shear strengths were selected based on the collection of shear strength envelopes provided for each material type from test data and HDRIDTA HDR Engineering, Inc , altha Carolinas
Mr. Henry Taylor October 29,2010 Page 3 engineering judgment to select a representative design envelope for each material type. The design shear strength envelopes used in the analyses are labeled on Figures 2 and 3. The shear strengths used in the analysis for each material type are given in Table 1.
No. I 2
3 4 5
Description PWR Foundation - Saturated Compacted Fill - Saturated Com~acted Fill - Moist Dumped Fill / Spoils Fill
Table 1 Unit Weight (pcO 125 120 120 120 100
Shear Stren2th
c' (psO
:
-
L
----_.
c'-O sf p ;3r
==
~~:-I-----==:J:~-=--. ' , -~ ~I ==--J-----=="I:1 =c=l1===1 II
-j---
'- "
Effective ConfIDing Stress (psf)
'
.
;
L gwer Bouud
I
.
-
___
.-
..
3,000
.I
---
=-.....
_
]
2,000
---'
---
-..--' , ~,,~~ ' ------
---
; -. l ; _
-
.
_.7P ='
_,
1,000
,
.
,='==:;:} -:=~~--=- ,f--~ _J _ ..-~ ....~7_"'" ..,...---:
f---: :~I~ '" .. ~ ~ ~. ~ ". .,.
;.
.
-
' ~ l ~~' ~~ ---"l.' ; ;;~~~~ ~~~ _2~_~ ~:7.;L~ · -·--: ;: ~ >; ~~~~1 ~ --- ~- ------~ rL ;:::;4 - . ". ~ ~ - -=1
' --I-
- ~-.. . . . ~---, ~ ../'~ ".... ~,.. -/. -= . ~ ~ ~r:7 _ -----~~ ~ ,-
_
r
'
--------,------
., -
, ''
___ __ _+ ____ __ ,Bound,;;;: ,_ _ ----=---= · --.-
~ ~L~~. , ----=~~~" ~ ~ __
-
r:::------ -]
-
, ~ ' .--7--1 ~ :: -=- -r 7--~ " -: ---
_ --
~======~-=~~= t l _ = == ___==::==.~up~~er ~ ~ __ _ ' :::::-s '-
r---
2,000
=
.
---1-
_ 1,____
I
3,000
-,
,,__ -I- -=- _
- 1 -
1
'
-
i
-
___
L
,
---
"
C - - 'r-----
---=~========J[==------'----1 .
'
_1L
-
,
'L
___,__ . ____
7,000
----- .
--
-,
--
8,000
.
----
9,000
10,000
Figure 3 Triaxial Shear Test Results - Fill Soil 9,000
---- .--
UOO
71
7,000
6,000
~r'
7 /
s;.;-s;::::~
1- - -
Ii CL
-! l it
- . ---
5,000
....
~
~- I
.. 4,000
.t:.
."
3,000
- -'- - - --
-
=a psf
CD' =32.6·
.~
- --
2,000
c'
,
~r=.--I=--
1----:- -I
Lower Bound
1,000
o
- - -1 -- - - 1 -
~
o
1,000
2,000
3,000
4,000
5,000
Effective Stress (psI)
6,000
7,000
8,000
9,000
10,000
1000
900
Factor of safety: 2.511 Side force Inclination: -6.71 degrees
i ii
E
tc
800
o
®
';:l
5 ii:i 700
600
CD
500 ~,---------------------------------------------------------------------------300 -100 o 100 200 300 400 -400 -200
Distance (ft)
Figure 4. Slope Stability Analvsis Results - Max. Section- Downstream Slope
000
100
Factor of safety: 0.859 Side force Inclination: -11.56 degrees
i ii
tE
100
c o ;:;
@
E iii '-00
G>
6000
500
~I----------------~------------------------------------------------------~~
- 400
-2QO
o
2 00
Distance (ft)
Figure 5. Slope Stability Analysis Results - Max. Section- Downstream Slope
400
1000
900
Factor of safety: 1.517 Side force Inclination: 4.23 degrees
Oii
E
tc
800
o
i
®
~
ii:i
700
600
CD
500 ~'-----------------------------------------------------------------------100 100 400 o 200 300 -300 -200 -400 Distance (ft)
Figure 6. Slope Stability Analysis Results - Max. Section- Upstream Slope
1000
900
Factor of safety: 0.997 Side force Inclination: 1.14 degrees 800
i ii
E .t:• c
0
~ III
.d
7
/
~
@
®
700
> G/
W
