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Toledo Bend Project - STI Section 8Stability/Stress Analysis of Project Structures

SECTION 8

STABILITY / STRESS ANALYSIS

OF PROJECT STRUCTURES

8.1 GENERAL

8.1.1 Load Cases Analyzed

The load cases analyzed for the various structures over time in variousreports have been grouped by structure, then by report. Tables andfigures have been created to summarize all the data in the followingsections.

8.1.2 Stability Analyses Methodologies

a. Forrest & Cotton (1962). Serving as SRAs Engineer, Forrest &Cotton used the following methods for analyzing the stability of thestructures:

1) Main Embankment and Dikes (as reported in DesignMemorandum No 3). The main embankment and dikes wereanalyzed using the circular arc method.

2) Spillway (as reported in Design Memorandum No. 2). Handcalculations for sliding and overturning on three sections: theoverflow section, the low-flow section, and the non-overflowsection. Circular arc analysis was also performed on theoverflow section.

3) Powerhouse. To date, no information has been uncoveredthat describes the original powerhouse stability designmethodology.

b. Rone Engineers (1983). Serving as a geotechnical consultant,

Rone performed a liquefaction and stability analysis using thefollowing methods:

1) Main Embankment. The general subsurface of the mainembankment was tested by performing 16 standardpenetration sample borings. The stability analysis followedguidelines recognized by FERC. Using conservativeparameters, a maximum design earthquake acceleration of

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0.04 g resulted in a factor of safety greater than 1.15. Theliquefaction potential was also analyzed indicating that thereis no possibility for liquefaction.

2) A stability analysis was performed on Dike No. 2, whichindicated that the embankment was adequately stable.Recommendations were made for adding a small berm withan internal drainage system to control seepage areas.

c. Brown & Roots Toledo Bend Dam Stability Analysis (1988)

1) Main Embankment. The main embankment was analyzedon three separate cross sections using PCSTABL4 softwarewhich calculates the factor of safety against slope failureusing two-dimensional limit equilibrium methods. The factor

of safety was calculated using the Simplified Bishop methodof slices.

PCSTABL4 as used by Brown & Root for the 1988 analyses,was verified for a typical embankment section usingMCAUTO SLOPE ( McDonnell Douglas AutomationCompany product), which is a computer subsystem ofIntegrated Civil Engineering System (ICES). The run wasperformed for the embankment section at Station 116+30.

As reported in Toledo Bend Stability Analysis Verification ofPCSTABL4 Computer Program, dated November 1988 by

Brown & Root USA, Inc., the factor of safety calculated bythe PCSTABL4 program using the Simplified Bishop methodof slices correlated very well with that calculated usingMCAUTO SLOPE.

2) Spillway. Hand calculations were used in 1988 to calculatesliding stability for the spillway. The method of analysis wasa two-dimensional limit equilibrium approach, in accordancewith ETL-1110-2-256. Force equilibrium is satisfied in theapproach. Moment equilibrium was not analyzed. Theanalysis was performed on three different sections of the

spillway: the overflow section, the low-flow section, and thenon-overflow section.

3) Powerhouse. Slipcircle analysis was determined to be morecritical for the powerhouse, and therefore PCSTABL4 wasused to examine the stability of the powerhouse for slidingblock failure, using the simplified Janbu method of slices.The excavated intake channel slope was analyzed for

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sudden drawdown and earthquake conditions, also using thePCSTABL4 program.

c. Brown & Roots FERC Inspection Report (1998)

1) Spillway. Further analyses of the spillway only (overflow andlow-flow sections) were undertaken for this report to examinethe effect of the approach slab and drainage system on thestability of the structure against sliding and overturning. Themethod used was hand calculations using the two-dimensional limit equilibrium approach, similar to that used inthe 1988 Stability Analysis.

Note. There is no reference in the above to any analyses ontraining/retaining walls. These are less crit ical in the context

of publ ic safety and are therefore not inc luded in thisAppendix.

8.1.3 Properties of Materials

Material testing reports from the original construction have not beenlocated. Design properties and assumptions made for the variouscalculations have been collected. Concrete compressive and tensilestrength properties for the spillway are summarized in Section 8.2.1,paragraph h. Soil properties for the powerhouse are summarized in Table8.2.10. Soil properties for the main embankment are summarized in

Tables 8.3.3, 8.3.5, and 8.3.7 from the various reports. Soil properties forthe minor dikes are summarized in Tables 8.3.8, 8.3.10, and 8.3.12.

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8.2 GRAVITY STRUCTURES

8.2.1 Spillway

a. Sections, Loading Cases and Assumptions. Spillway sections areshown in Figures 8.2-01, 8.2-02, and 8.2-03. Loading conditionsand assumptions are shown in subsequent paragraphs of thereport.

1) Forrest & Cotton (1962). Stability analyses for the spillwayas given in the Forrest & Cotton Design Memorandum No. 2,dated August 1962 are summarized in Table 8.2.1. Thestability analysis calculations for the Intermediate PierMonolith (Figures 8.2-04 and 8.2-05), Low Flow ReleasePier Monolith (Figure 8.2-06), and the Non-Overflow Section

(Figure 8.2-07), are given in the respective figures. Thespillway chute stability analysis calculations are given inFigure 8.2-08.

2) Rone (1983). Stability analyses for the spillway as given inthe Rone Engineers report, Instrumentation and HydrostaticPressure Relief Systems, are summarized in Table 8.2.2 andshown in Figure 8.2-09.

3) KBR (1988). Stability analyses for the spillway as given inthe Brown & Root report, Toledo Bend Stability Analysis,

dated November 1988, are summarized in Table 8.2.3. Thestability analysis calculations are given in the followingfigures: Case A Overflow Section (Figure 8.2-10) Case B1 Overflow Section (Figure 8.2-11) Case B2 Overflow Section (Figure 8.2-12) Case C Overflow Section (Figure 8.2-13) Case B1 Low Flow Section (Figure 8.2-14) Case D Low Flow Section (Figure 8.2-15) Case A Non-Overflow Section Hydrostatic Loads

(Figure 8.2-16)

Case A Non-Overflow Section Soil Loads(Figure 8.2-17)

Case C Non-Overflow Section Hydrostatic Loads(Figure 8.2-18)

Case C Non-Overflow Section Soil Loads(Figure 8.2-19)

Main Embankment Showing Stability Sections(Figure8.2-20)

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4) KBR (1998). Stability analyses for the spillway as given inthe Brown & Root report, Toledo Bend FERC Stability

Analysis, dated October 1998, are summarized in

Table 8.2.4. Main Embankment Stability Section Locationsare shown in Figure 8.2-20. The stability analysiscalculations are given in the following figures:

Case 1 Overflow Section Sliding Analysis(Figure 8.2-21)

Case 1 Overflow Section Overturning Analysis(Figure 8.2-22X)

Case 2 Overflow Section Sliding analysis(Figure 8.2-23)

Case 2 Overflow Section Overturning Analysis(Figure 8.2-24)


Case 3 Overflow Section Overturning Analysis(Figure 8.2-26X)


Case 4 Overflow Section Overturning Analysis(Figure 8.2-28)

Case 1 Low Flow Section Sliding Analysis(Figure 8.2-29)

Case 1 Low Flow Section Overturning Analysis

(Figure 8.2-30) Case 2 Low Flow Section Sliding Analysis

(Figure 8.2-31) Case 2 Low Flow Section Overturning Analysis

(Figure 8.2-32)

b. Key Elevations. Table 8.2.5 gives the key elevations of thespillway.

c. Key Lateral Dimensions. Table 8.2.6 gives the key lateraldimensions of the spillway.

d. Piezometer and Drain Locations. Figure 8.2-33 shows the spillwaypiezometer and relief well locations for the spillway.

e. Foundation Shear Strength Parameters. Table 8.2.7 shows theshear strength parameters used in the different analyses conductedto spillway stability.

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f. Minimum Cohesion to Meet Stability Criteria. The minimumcohesion intercept providing acceptable factors of safety has notbeen determined, as such. However, due to concerns over thelong term strength parameters of the overconsolidated clays, a 50

percent reduction in cohesion was used in the 1988 analysis asindicated in Table 8.2.7.

g. Negative Crest Pressures on Spillway. Negative crest pressureshave not been addressed in any of the spillway stability analysesundertaken to date.

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h. Concrete Compressive and Tensile Strength: The following pagestaken from Forrest & Cotton Design Memorandum No. 2, dated

August 1962, provide the concrete design parameters for thespillway. Actual test results from samples taken during constructionare not available.

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5-05. Concrete, general. The symbols, nomenclature, and abbreviations used

herein with respect to plain, reinforced, and prestressed concrete are those used by the

American Concrete Institute. For purposes of referencing working stresses as pertainingto the various concrete components of the spillway, the stresses have been separated

into three groups, as follows:

GROUP I stresses: Applies to miscellaneous concrete not included

under Group II and III stresses.

GROUP II stresses: Applies to concrete in structures that will besubjected to submergence, wave action, and spray.

Included will be most of the mass concrete in the

weirs, piers, non-overflow sections and theretaining walls. Exceptions will be the approach

apron and all prestressed concrete.GROUP III stresses: Applies to prestressed concrete as proposed for the

bridge girders and the trunnion anchorage.

5-06. Strength of concrete. For design purposes, it was assumed that theultimate compressive strength of the concrete in the different components of the

spillway would be as follows:

Spillway component

Ultimate compressive

strength at 28 days in psi

1. General structural concrete 3,000

2. Prestressed trunnion anchorage and bridge girders 5,000

3. Bridge deck 4,000

4. Fill concrete and for other purposes where strength is

not a required property of the material

2,000

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5-07. Allowable unit stresses, plain concrete. The allowable flexure (fc) stress for plainconcrete with assumed Group A loading will be as follows:

Design Strength of Concrete

Nature of Stress

f 'c

proportion

Unit stress for

3000 lb. concrete in psi,

n = 10

Extreme fiber stress in tension:

GROUP I 0.03 f 'c 90

GROUP II 0.02 f 'c 60

5-08. Allowable unit stresses, reinforced concrete. The allowable unit stressesfor reinforced concrete with Group A loading will be as is given in the following

paragraphs:5-08a. Flexure, fc. The allowable flexure stress, fc, for reinforced concrete for

assumed Group A loading will be as follows:


Nature of Stress

f 'c

proportion

Unit stress for

3000 lb. concrete in psi,n = 10

Extreme fiber stress in compression:

GROUP I 0.45 f 'c 1,350

GROUP II 0.35 f 'c 1,050

5-08b. Shear, Vc. Allowable shear stresses, Vc, as a measure of diagonal tension,

for assumed Group A loading will be as follows. These stresses are within the GROUP I

stress classification and are all in accordance with the American Concrete Institute

specifications.

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Nature of Stress

f 'cproportion

Unit stress for3000 lb. concrete in psi,

n = 10

a. Beams with no web reinf. (1) 0.03 f 'c 90

b. Beams with longitudinal bars

and stirrups or bent bars

0.08 f 'c 240

c. Beams with longitudinal bars

and stirrups plus bent bars (2)

0.12 f 'c 360

d. Punching shear 0.075 f 'c 225

e. Footings 0.025 f 'c 75

(1) Where calculations indicate Vc is not exceeded, nominal vertical stirrups will

be provided throughout the full span of the beam. The minimum stirrup will be #3 barsand the maximum spacing will be one half the beam depth.

(2) The bent bars are to be bent up and suitable to carry at least 0.04fc.

5-08c. Bond, u. The allowable bond, u, for assumed Group A loading will be asfollows. These stresses are all within the GROUP I stress classification.


Nature of Stress

f 'c

proportion

Unit stress for


n = 10

Deformed ASTM A-305 bars (3):

Top bars 0.07 f 'c 210

In two-way footing except top

bars

0.08 f 'c 240

All others 0.10 f 'c 300

Plain bars hook required (4)

Top bars 0.03 f 'c 90In two-way footing except top

bars

0.036 f 'c 108

All others 0.045 f 'c 135

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5-08f. Combined bending and direct stresses. The allowable combined axial and

bending stresses for reinforced concrete columns and walls will be determined inaccordance with the American Concrete Institute Code (ACI-3l8-56).

5-08g. Moduli and coefficients. The modulus of elasticity, Ec, and the coefficient

of expansion of 3,000 pound concrete will be as follows:

Modulus of elasticity, Ec. - 3,000,000 psi

Coef. of expansion - 0.000006 per F.

5-09. Allowable unit stresses, prestressed concrete. Working stresses forprestressed concrete used in trunnion anchorage and. bridge girders will be in accordance

with applicable specifications listed. in paragraph 5-01. The allowable unit stresses for

assumed Group A loading will be as follows. These stresses are all within the GROUP IIIstress classification.


Nature of Stress

f 'c i

proportion

Unit stress for


n = 6

TEMPORARY STRESSES:

Compression in extreme fiber 0.60 f 'c i 2,400

Tension 0.05 f 'c i 200

STRESSES: UNDER DEAD, LIVE AND IMPACT LOADSCompression in extremefiber 0.40 f 'c i 2,000

Tension in extreme fiber 0 0

ANCHORAGE BEARING STRESSES:

Trunnion anchorage fcp = (0.6 f 'c i) times the cube root of Ac/Ab

The strength of concrete at the time of prestress of trunnion anchorage will be 4,000 psi.

The strength of concrete at the time of cable release will be 4,000 psi.

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i. Alkali Aggregate Reactivity (AAR) Potential. AAR has not beenaddressed in any of the previous reports.

1) Cement with high alkaline content can react with theaggregate in a wet environment. Reactive aggregates aregarnet or silica. The aggregate decomposes into a greatervolume that the original causing the concrete to craze, crackand spall.

2) There is no known preventive or remedy when thesecharacteristics are present.

8.2.2 Powerhouse

a. Sections, Loading Cases and Assumptions: Powerhouse sectionsare shown in Figure 8.2-34. Loading conditions and assumptionsare provided in subsequent paragraphs of the report.

1) Forrest & Cotton (1962). No data is available for Forrest &Cottons analyses of the powerhouse. However, a note onthe Power Plant Stability Analysis from the Rone (1983)report states that data on this plate from the power plantstability analyses performed by Forrest & Cotton, Inc.,Consulting Engineers, in 1963.

2) Rone (1983). Stability analyses for the powerhouse asgiven in the Rone Engineers report, Instrumentation andHydrostatic Pressure Relief Systems, are summarized inTable 8.2.8. The stability analysis calculations are given inFigure 8.2-35.

3) KBR (1988). Stability analyses for the powerhouse as givenin the Brown & Root report, Toledo Bend Stability Analysis,dated November 1988 are summarized in Table 8.2.9. Soilproperties used in the stability analysis are given in Table8.2.10. The powerhouse plan view showing the location of

the stability sections used for calculations is given in Figure8.2-36. The stability analysis calculations are given in thefollowing figures:

Powerhouse Sliding Stability Normal Pool(Figure 8.2-37)

Powerhouse Stability Normal Pool (Figure 8.2-38) Powerhouse Seismic (Figure 8.2.39)

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Powerhouse Surcharge Pool (Figure 8.2-40)

b. Key Elevations. (Not available)

c. Key Lateral Dimensions. (Not available)

d. Piezometer and Drain Locations. Figure 8.2-41 shows thepowerhouse piezometer and relief well locations for the spillway.

e. Foundation Shear Strength Parameters. Refer to Table 8.2.10.

f. Minimum Cohesion to Meet Stability Criteria. Refer to paragraph8.2.1f.

g. Negative Crest Pressures on Spillway. (Not applicable)

h. Concrete Compressive and Tensile Strength. (Not available)

i. Alkali Aggregate Reactivity (AAR) Potential. Refer to paragraph

8.2.1i.

8.2.3 Intake and Outlet Works

There are no intake or outlet works associated with this project. Alldischarges from the reservoir are made through the spillway or the

powerhouse.

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Figure 8.2-01

SPILLWAY SLIDDIN STABILITY

TYPICAL PIER SECTIONS


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Figure 8.2-02

UPSTREAM ELEVATION

OVERFLOW SECTION


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Figure 8.2-03

UPSTREAM ELEVATION

LOW FLOW SECTION


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Figure 8.2-04

INTERMEDIATE PIER MONO

STABILITY ANALYSES

Sheet 1 of 2


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Figure 8.2-05

INTERMEDIATE PIER MONO

STABILITY ANALYSES

Sheet 2 of 2


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Figure 8.2-06

LOW FLOW RELEASE PIER MO

STABILITY ANALYSES


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Figure 8.2-07

NON-OVERFLOW SECTION

STABILITY ANALYSES


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Figure 8.2-08

SPILLWAY CHUTE

STABILITY ANALYSES


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NOTE:

THE BASE DRAWING INFORMATION ON THIS SHEET WAS TAKEN FROM:

FERC COMMISSION ON INSPECTION OF PROJECT WORKS THAT MI GHT ENDANGER PUBLIC SAFETY

B&R - 1998, APPENDIX D-65

Figure 8.2-09

SPILLWAY STABILITY ANALYSES

OPERATIONAL PROCEDUURES


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TOLEDO BEND DAM STABILITY

ANALYSIS, B&R - 1988

Figure 8.2-10

CASE A - OVERFLO

SECTION


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Figure 8.2-11

CASE B1 - OVERF

SECTION


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Figure 8.2-12CASE B2 - OVERFL

SECTION


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Figure 8.2-13

CASE C - OVERFLOW

SECTION


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Fig 8.2-14

CASE B1 - LOW FLOW

SECTION


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Figure 8.2-16

CASE A - NON -

OVERFLOW SECTION

HYDROSTATIC LOAD


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figure 8.2-17

CASE A - NON-OVERFLO

SECTION SOIL LOADS


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Figure 8.2-18

CASE C - NON-OVERFL

SECTION HYDROSTA

LOADS




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Figure 8.2-20

MAIN EMBANKMENT STABILITY

SECTION LOCATIONS


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CASE1

OV

ERFLOWS

ECTION-SLIDINGANALYSIS

NOTE:

THE BASE DRAWING

INFORMATION ON THIS

SHEET WAS TAKEN FROM:

FERC COMMISSION ONINSPECTION OF PROJECT

WORKS THAT MIGHT

ENDANGER PUBLIC SAFETY

B&R - 1998

APPENDIX D-54

Figure 8.2-2

CASE1

OVERFLOW SEC

SLIDING ANALY


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CASE1

OV

ERFLOW

SECTION-OVERTURN

ING

ANALYSIS

A p p r o a c h S l a b N o t E f f e c t i v e

NOTE:

THE BASE DRAWING INFORMATION ON

THIS SHEET WAS TAKEN FROM:

FERC COMMISSION ON INSPECTION

OF PROJECT WORKS THAT MIGHT



Figure 8.2-22

CASE1

OVERFLOW SECTION -

OVERTURNING ANALYSIS


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CASE2

OVER

FLOW

SECTION-SLIDINGANA

LYSIS

ApproachSlabEffective

Figure 8.2-23

CASE 2

OVERFLOW SECTI

SLIDING ANALYSNOTE:

THE BASE DRAWING INFORMATION

ON THIS SHEET WAS TAKEN FROM:






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CASE2

OVERFLOW

SECTION-OVERTURNINGA

NALYSIS


NOTE:



FERC COMMISSION ON INSPECTION OF

PROJECT WORKS THAT MIGHT



Figure 8.2-24

CASE 2

OVERFLOW SECTION



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CASE3

OVE

RFLOW

SECTION-SLIDINGAN

ALYSIS

ApproachSlabNotEffective

Figure 8.2-25

CASE 3

OVERFLOW SECTI)

SLIDING ANALYSNOTE:








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CASE3

OVERFLOW

SECTION-OVERTURNINGANALYSIS


NOTE:







Figure 8.2-26

CASE 3

OVERFLOW SECTION

OVERTURNING ANALYS


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CASE4

OOVERFLOW

SECTION-SLIDINGANA

LYSIS


NOTE:







Figure 8.2-27

CASE 4

OVERFLOW SECTI

SLIDING ANALYS


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CASE1

LOW

FLOW

SECTION-SLIDINGANALYSIS


S

i l W t

1 2 0

f

NOTE:

THE BASE DRAWING INFORMATION ON THIS SHEET

WAS TAKEN FROM:

FERC COMMISSION ON INSPECTION OF PROJECT

WORKS THAT MIGHT ENDANGER PUBLIC SAFETY


Figure 8.2-29

CASE 1

LOW FLOW SECTION

SLIDING ANALYSIS


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NOTE:

THE BASE DRAWING INFORMATION

ON THIS SHEET WAS TAKEN FROM:





Figure 8.3-30

CASE 1 - LOW FLOW SECTION


CASE1

LOW

FLO

WS

ECTION-OVERTURNINGA

NALYSIS


S

i l W t

1 2 0

f


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NOTE:

THE BASE DRAWING INFORMATION ON THIS SHEET WAS

TAKEN FROM:

FERC COMMISSION ON INSPECTION OF PROJECT WORKS

THAT MIGHT ENDANGER PUBLIC SAFETY


CASE2

LOW

FLOW

SECTION-SLIDINGANALYSIS


S

i l W t

1 2 0

f

Figure 8.2-31

CASE 2

LOW FLOW SECTION

SLIDING ANALYSIS


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NOTE:

THE BASE DRAWING INFORMATION ON THIS SHEET WAS

TAKEN FROM FERC COMMISSION ON INSPECTION OF

PROJECT WORKS THAT MIGHT ENDANGER PUBLIC

SAFETY, B&R - 1998, APPENDIX D-66

CASE2

LOW

FL

OW

SECTION-OVERTURNINGANALYSIS


Figure 8.2-32

CASE 2

LOW FLOW SECTION



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Figure 8.2-33

PLAN OF

SPILLWAY PIEZOMETER


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Figure 8.2-34

POWRHOUSE PLAN

& SECTIONS


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Source: INSTRUMENTATION AND

HYDROSTATIC PRESSURE RELIEF

SYSTEMS, RONE ENGINEERS, INC., 1983

Figure 8.2-35

POWER PLANT STABILITY ANAL

OPERATIONAL PROCEDURE


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Figure 8.2-36

POWER HOUSE STABILI

SECTION LOCATIONS


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Figure 8.2-37

POWER HOUSE

SLIDING STABILITY


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Figure 8.2-38

POWER HOUSE NORMAL PO


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Figure 8.2-39

POWER HOUSE

SEISMIC


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Figure 8.2-40

POWR HOUSE

SURCHARGE POOL


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Figure 8.2-41

PLAN OF POWRE HOUSE

PIEZOMETERS


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8.3 EMBANKMENT STRUCTURES

The Toledo Bend Dam embankment structures are identified inTable 8.3.1 with their corresponding key dimensions, elevations, andslopes.

8.3.1 Main Embankment

a. Sections, Loading Cases and Assumptions: A section of the MainEmbankment is shown in Figure 8.3-01. This section is taken fromFinal Design, Volume 2, by Forrest & Cotton (1962).

1) Forrest & Cotton (1963). Stability analyses for the mainembankment as given in the Forrest & Cotton DesignMemorandum No. 3, dated January 1963, are summarizedin Table 8.3.2. Soil properties used in the stability analysisare given in Table 8.3.3. The slope stability analysis for theembankment and dike are shown on Figure 8.3-02. Theembankment stability analysis is given in Figure 8.3-03.

2) Rone (1983). Stability analyses for the main embankmentas given in the Rone Engineers report, Liquefaction andStability Analysis, are summarized in Table 8.3.4. Soil

properties used in the stability analysis are given in Table8.3.5. The stability analysis calculations are given in Figure8.3-04.

3) KBR (1988). Stability analyses for the main embankment asgiven in the Brown & Root report, Toledo Bend Stability

Analysis, dated November 1988, are summarized in Table8.3.6. Soil properties used in the stability analysis are givenin Table 8.3.7. The embankment plan view showing thelocation of the stability section used for calculations is givenin Figures 8.3-05 and 8.3-06.

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The stability analysis calculations are given in the following figures:

Main Embankment Stability Steady SeepageSta. 116+30 (Figure 8.3-07)

Main Embankment Stability Surcharge Pool Sta.

116+30 (Figure 8.3-08) Main Embankment Stability Rapid Drawdown

Sta. 116+30 (Figure 8.3-09) Main Embankment Stability Seismic Sta. 116+30

(Figure 8.3-10) Main Embankment Stability Steady Seepage

Sta. 130+50 (Figure 8.3-11) Main Embankment Stability Surcharge Pool Sta.


Sta. 130+50 Figure 8.3-13) Main Embankment Stability Seismic Sta. 130+50

(Figure 8.3-14) Main Embankment Stability Steady Seepage

Sta. 151+70 (Figure 8.3-15) Main Embankment Stability Surcharge Pool Sta.


Sta. 151+70 (Figure 8.3-17) Main Embankment Stability Seismic Sta. 151+70

(Figure 8.3-18)

Main Embankment Stability Steady SeepageSta. 178+20 (Figure 8.3-19) Main Embankment Stability Seismic Sta. 178+20

(Figure 8.3-20)

b. Potential for Uncontrolled Seepage at Toe. The embankment isdesigned with a pervious drainage blanket to control seepage.Relief wells have been installed to control the piezometricpressures of the foundation soils.

c. Summary of Liquefaction Analysis. The liquefaction potential was

previously evaluated by Rone Engineering, Inc., in their reporttitled, Liquefaction and Stability Analysis, Toledo Bend Dam,dated July 1983. The liquefaction potential was not found to be anissue.

d. Summary of Deformation Analysis. Soil deformation analysis dueto stability induced strains has not been performed as the

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conventional analysis factors of safety are satisfactory, based onstrength parameters derived by commonly accepted procedures.

e. Procedures Used to Determine Soil Properties.

The shear strength properties of soils were determined asdescribed in the following paragraphs. Soil classification tests forthe 1988 investigations included moisture control, dry density, andplasticity index.

f. Procedures Used to Determine Soil Strengths.

1) Soil shear strength parameters used in the 1988 stabilityanalysis by B&R were obtained from the MRA geotechnicalreport prepared by McBride & Ratcliff, titled Geotechnical

Investigation Toledo Bend Dam, dated November 1988.The tests were performed as consolidated, undrained tiaxialtests with pore pressure measurements on samples from thespillway, powerhouse, and embankment areas.

2) FERC and COE guidelines for steady seepage stabilitycases analyzed require use of the shear strength defined bythe S-curve (effective stress envelope) up to the normalstress where the S-curve and R-curve (total stress envelope)intersect, which is the point of the mobilized pore pressure.Thereafter, the shear strength defined by the average of theR-curve and S-curve was used.

3) Cohesive embankment zones for the steady seepage caseswere subdivided to delineate the depths below whichstrength parameters defined by the average of the total andeffective stress envelopes became effective. This transitiondepth was based on the normal stress at which the R-curveand S-curve presented in the MRA report intersected foreach material type.

4) The minimum shear strength obtained from the combined S-curve and R-curve was used for the rapid drawdown cases.The same shear strength was used for the earthquake

analysis as was used for steady seepage cases.5) Cohesive foundation strata were assigned appropriate

strength values in a similar manner, depending on normalstress and material type. The derivation of the angle ofinternal friction for granular soils is presented in the report byMRA. The same angle was used for all stress conditions.

g. Shear Strength Parameters

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8.3.2 Dike Nos. 1, 2 and 3

a. Sections, Loading Cases and Assumptions. A section of theTypical Embankment Saddle Area is shown in Figure 8.3-21. Thissection is taken from Final Design, Volume 2, by Forrest & Cotton(1962).

1) Forrest & Cotton (1963). The analyses that were conductedby Forrest & Cotton on the dikes are unknown. Thefollowing extract from the Forrest & Cotton DesignMemorandum No. 3, Embankment and General ConstructionSchedule, dated January 1963, is the only informationavailable related to the original dike design. Soil propertiesused in the stability analysis are given in Table 8.3.8.

4-21. Dike design. A typical trial section similar to the embankmentsection was initially selected for design analysis. The stability analysis of the

typical dike section was made, assuming the strength of the compacted materials

to be the same as adopted for compacted materials in the main embankmentsection. The strength of the foundation material was assumed to have a cohesion

of 1400 psf and an angle of internal friction of zero degrees. The analysis for the

maximum section of the dike, height of about 66 feet, indicates that a factor ofsafety of 1.33 would be obtained at the end of construction condition. Adopted

dike sections are shown on Plate I-7. The adopted section differs slightly from the

section used in the slope stability analysis. However, the stability of the adoptedsection will obviously be equal to, or greater than, the section analyzed.

2) Rone (1983). Stability analyses for Dike No. 2 as given inthe Rone Engineers report, Liquefaction and Stability

Analysis, are summarized in Table 8.3.9. Soil propertiesused in the stability analysis are given in Table 8.3.10. Thestability analysis calculations are given in Figure 8.3-22.

3) KBR (1988). Stability analyses for Dike No. 2 as given in the

Brown & Root report, Toledo Bend Stability Analysis, datedNovember 1988, are summarized in Table 8.3.11. Soilproperties used in the stability analysis are given in Table8.3.12. Dike No. 2 plan view showing the location of thestability section used for calculations is given in Figure8.3-23. The stability analysis calculations are given in thefollowing figures:

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Dike No. 2 Stability Steady Seepage (Figure 8.3-24) Dike No. 2 Stability Surcharge Pool (Figure 8.3-25) Dike No. 2 Stability Rapid Drawdown (Figure 8.3-26) Dike No. 2 Stability Seismic (Figure 8.3-27)

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b. Potential for Uncontrolled Seepage at Toe. (Not available)

c. Summary of Liquefaction Analysis. (Not available)

d. Summary of Deformation Analysis. (Not available)

e. Procedures Used to Determine Soil Properties. (Not available)

f. Procedures Used to Determine Soil Strengths. (Not available)

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Figure 8.3-03

EMBANKMENT

STABILITY ANALYSIS


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Figure 8.3-06

MAI EMBANKMENT AND

SPILLWAY STABILITY

SECTION LOCATIONS


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Figure 8.3-07

MAIN EMBANKMENT

STEADY SEEPAGE

STATION 116+30


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Figure 8.3-09

MAI EMBANKMENT RAPID

DRAWDOWN

STATION 116+30


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Figure 8.3-10

MAIN EMBANKMENT SEISM

STATION 116+30


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Figure 8.3-13

MAIN EMBANKMENT

RAPID DRAWDOWN

STATION 130+50


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Figure 8.3-15

MAIN EMBANKMENT STEAD

SEEPAGE

STATION 151+70


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Figure 8.3-16

MAIN EMBANKMENT

SURCHARGE POOL

STATION 151+70


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Figure 8.3-17

MAIN EMBANKMENT

RAPID DRWDOWN

STATION 151+70


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Figure 8.3-18

MAIN EMBANKMENT

SEISMIC

STATION 151+70


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Figure 8.3-19

MAIN EMBANKMENT

STEADY SEEPAGE

STATION 178+20


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Figure 8.3-20

MAIN EMBANKMENT

SEISMIC

STATION 178+20


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Figure 8.3-22

DIKE NO. 2

STABILITY ANALYSES

SUMMARY OF RESULTS

Source: Liquefaction aStability analysis, Rone

Engineers, Inc., 1983


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Figure 8.3-23

DIKE NO. 2 STABILITY

SECTION LOCATION


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Figure 8.3-24

DIKE NO. 2

STEADY SEEPAGE


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Figure 8.3-26

DIKE NO. 2

RAPID DRAWDOWN


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Figure 8.3-27

DIKE NO. 2

SEISMIC


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8.5 WATER CONVEYANCE SYSTEM

No water conveyance systems are associated with the Toledo Bend Dam.

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8.6 SUMMARY OF FACTORS OF SAFETY ACHIEVED

8.6.1 Gravity Structures

a. See Section 8.2.1 for the summary of factors of safety, materialproperties, and hydrostatic conditions assumed for the spillway.

b. See Section 8.2.2 for the summary of factors of safety, materialproperties, and hydrostatic conditions assumed for thepowerhouse.

8.6.2 Embankment Structures

a. See Section 8.3.1 for the summary of factors of safety, materialproperties, and hydrostatic conditions assumed for the mainembankment.

b. See Section 8.3.2 for the summary of factors of safety, materialproperties, and hydrostatic conditions assumed for the Dikes 1, 2,and 3.

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