HighHigh --Precision Strength Evaluation of Rock Materials and Stability Analysis … 04 - Hiroki... · · 2011-11-01High-Precision Strength Evaluation of Rock Materials ... HighHigh

PWRIPWRI

1st International Symposium on Rockfill Dams1st International Symposium on Rockfill Dams1st International Symposium on Rockfill Dams1st International Symposium on Rockfill Dams

PWRIPWRI

High-Precision Strength Evaluation of Rock Materials and

Stability Analysis for Rockfill Dams

HighHigh--Precision Strength Evaluation of Rock Materials Precision Strength Evaluation of Rock Materials and and

Stability Analysis for Rockfill DamsStability Analysis for Rockfill Dams

HirokiHiroki SAKAMOTOSAKAMOTOResearch EngineerResearch Engineer

Public Works Research Institute, JAPANPublic Works Research Institute, JAPAN

PWRIPWRIPWRIPWRIPWRIPWRI

ContentsContentsContentsIntroductionIntroductionPurposesPurposesLaboratory testsLaboratory tests

MaterialMaterialTest methodTest methodTest resultTest result

Sliding stability analysisSliding stability analysisAnalysis methodAnalysis methodAnalysis resultsAnalysis results

ConclusionsConclusions


IntroductionIntroduction• The seismic performance evaluation method of rockfill dams in japan :

“Modified seismic coefficient method”

• Shear strength of rock materials :Evaluation of shear strength is defined by curvature approximation.

Low Confining Pressure Range

Normal Stress σ

She

ar S

tres

s τ

ϕϕϕϕ

C

0

Strength Curve

The triaxial compression test can’t measurer


D: Depth of slip circle

“Modified seismic coefficient method”

IntroductionIntroduction

slip circle

D > 5.0mD > 5.0m

1. Test’s precision2. The effect of shallow slip

failure

The shallow slip circle is disregardedThe minimum depth of slip circle is 5m

Test data by new equipment Stability analysis at shallow slip circle


PurposesPurposes

• Investigation of shear strength under low confining pressure condition;- Large-scale triaxial compression tests - Large-scale box shear tests

• Evaluation of shallow slip stability using above test results, in which the circle depth is less than 5m


Laboratory testsLaboratory tests

Material ADacite rock

Material BSandstone

currently used in the construction of a rockfill dam aggregate of crushed sandstone

MaterialsMaterials


Laboratory testsLaboratory tests

Material CDacite rock

currently used in the construction of a rockfill dam

MaterialsMaterials


Test methodTest method

Large-scale TriaxialCompression Tests (TCTs)

Large-scale TriaxialCompression Tests (TCTs)

Large-scale Box Shear Tests (BSTs)

Large-scale Box Shear Tests (BSTs)

( Specimen Size (cm) : L40×W40×H40 )( Specimen Size (cm) : φ30×H60 )


0

100

200

300

400

500

600

0 100 200 300 400 500 600Normal Stress σn (kPa)

Sh

ea

r S

tre

ss a

t F

ailu

re

τf

(kP

a)

Saturated

τf =3.2462･σn0.813

R2=0.997

Unsaturated

τf =4.968･σn0.759

R2=0.9973

● TCTs (Saturated)

○ BSTs (Saturated)

▲ TCTs (Unsaturated)

△ BSTs (Unsaturated)

・ Results can be plotted on a single power approximation curve.

Test resultsTest results ( Material A )( Material A )( Material A )


( Material A )( Material A )( Material A )

・ Internal friction angle ( φ0) has confining pressure dependency.

Test resultsTest results

φφ00==φφmaxmax=62.2=62.2°°

φφ00=62.2=62.2--11.6log10(11.6log10(σσnn/18.87)/18.87)

σσσσσσσσn0n0=18.9kPa=18.9kPa35

40

45

50

55

60

65

70

75

1 10 100 1,000Normal Stress　σn (kPa)

Inte

rnal

Fri

ctio

n A

ng

le 　 φ

0 (

°)

　●　　TCTs (Saturated) 　○　　BSTs (Saturated)　　　　　Semi-log approximation line


Test results Test results

• We confirm that shear strength of rock materials can be approximated by curvature approximation method at low confining pressure range in which box shear test results exist.

• Shear strength of rock materials have confining pressure dependency.


Sliding stability analysisSliding stability analysis

1: 2.10

　

1:0.2

1:0.2

1: 2.75

1: 2.10

　

1:0.2

1:0.2

コアロックロック1: 2

.751: 2.10

　

1:0.2

1:0.2

▽

h=92m

H=100m

6m2m 2m

Rock RockCore

Analysis method ：Modified seismic coefficient method

Analysis model

y: Elevation gap from dam crestH: Dam heightk : Seismic force of dam bodykF: Design seismic intensity of ground

Seismic force coefficient

0

0.2

0.4

0.6

0.8

1

0 1 2 3k/kF

y/H

0 1 2 31

0.8

0.6

0.4

0.2

0

1.40

1.76

2.50



Evaluation method of shear strength : φφφφ0 method

0

20

40

60

80

100

0 20 40 60 σ n (kPa)

τf (k

Pa) Straight line

0

100

200

300

400

500

600

0 100 200 300 400 500 600Normal Stress σn (kPa)

She

ar

Str

ess

at

Fa

ilure

τ

f (k

Pa

)

Curvature line

○○○○

○○○○

○○○○

○○○○

○○○○

○○○○○○

15~20 15~20 kPakPa ≒≒1m earth covering1m earth covering



Material property for analysis

φφφφm axm axm axm ax

（°）（°）（°）（°）aaaa

σσσσn0n0n0n0

(kN /m (kN /m (kN /m (kN /m 2222))))c (kN /mc (kN /mc (kN /mc (kN /m 2222)))) φ （°）φ （°）φ （°）φ （°）

AAAA 62.262.262.262.2 11.611.611.611.6 18.8718.8718.8718.87 ---- ---- 20.220.220.220.2 19.119.119.119.1

BBBB 71.271.271.271.2 10.7110.7110.7110.71 12.3212.3212.3212.32 ---- ---- 23.423.423.423.4 21.921.921.921.9

CCCC 69.169.169.169.1 12.8712.8712.8712.87 18.3718.3718.3718.37 ---- ---- 22.722.722.722.7 21212121

---- ---- ---- 0000 35353535 21.921.921.921.9 21.821.821.821.8

W etW etW etW etW eightW eightW eightW eight

（kN /m（kN /m（kN /m（kN /m 3333))))

D ryD ryD ryD ryW eightW eightW eightW eight

（kN /m（kN /m（kN /m（kN /m 3333))))

C oreC oreC oreC ore

M aterialM aterialM aterialM aterial

φφφφ0 0 0 0 M ethod M ethod M ethod M ethodM ohr-C oulom b'sM ohr-C oulom b'sM ohr-C oulom b'sM ohr-C oulom b'sFailure C riterionFailure C riterionFailure C riterionFailure C riterion

R ockR ockR ockR ock


Sliding stability analysisSliding stability analysisAnalysis results

AAAA BBBB CCCC

upstreamupstreamupstreamupstream 15.615.615.615.6 27.427.427.427.4 33.533.533.533.5

donw streamdonw streamdonw streamdonw stream 30.930.930.930.9 30.530.530.530.5 40.140.140.140.1

upstreamupstreamupstreamupstream 1.1561.1561.1561.156 1.6421.6421.6421.642 1.4641.4641.4641.464

donw streamdonw streamdonw streamdonw stream 1.3931.3931.3931.393 1.8421.8421.8421.842 1.6401.6401.6401.640

M aterialM aterialM aterialM aterial

　SF　SF　SF　SFm inm inm inm in

　D at SF　D at SF　D at SF　D at SFm inm inm inm in (m ) (m ) (m ) (m )

・ Shallower slip circle than 5m don’t have minimum safety factor.

SFmin: Minimum Safety Factor

slip circleD: Depth of slip circle


ConclusionsConclusions

• We confirm the distribution of shear strength of rock materials can be approximated by curvature approximation method at low confining pressure range.

• It is made clear that shallower slip circles than 5m don’t have minimum safety factor.


Thank youfor your kind attention!

Thank youfor your kind attention!


ReferenceReference


Low Confining Pressure Range

BackgroundBackgroundThe design Shear strength of rock materials :

・Base on Mohr-Coulomb’s failure criterion.・Cohesion is zero, only internal friction angle is used for design value.

Normal Stress σ

She

ar S

tres

s τ

ϕϕϕϕ

C

0

ϕϕϕϕ (Design value)


BackgroundBackgroundThe problem of evaluation of shear strengthThe problem of evaluation of shear strength

The triaxial compression test, (which is the most common strength test for rock materials,) can’t assure the test precision under very low confining pressure condition. (σ3< 100kPa )

So, we couldn’t check these strength distribution under low pressures is actually like this picture.

Develop the method of measurering the shear strength under low confining pressure condition

&Eevaluate shear strength of rock materials

considering the confining pressure dependency


0

20

40

60

80

100

0.01 0.1 1 10 100

Material AMaterial BMaterial C

Silt FineSand

MediumSand

CoarseSand

FineGravel

CoarseGravel

MediumGravel

0.075 0.250 0.850 4.75 19 752

Material A B C

Maximum Grain Size(mm)

37.5 37.5 63.0

UniformityCoefficicent

13.6 28.3 40.0

Coefficient ofCurvature

1.0 0.4 2.5

Dry Density 2.391 2.661 2.607

Water Absorption(%)

4.66 0.66 0.88

Grain size distribution curves of test materialsGrain size Grain size distribudistribution curves of test materialstion curves of test materials

Grain SizeGrain Size (mm)(mm)

Per

cen

tag

e F

ines

Per

cen

tag

e F

ines

(%)

(%)


Large-scale Triaxial Compression Tests (TCTs)Large-scale Triaxial Compression Tests (TCTs)

Test Condition

8590

C

49,98,196,294,392,588,785(saturated)49,98,196, 392(unsaturated)

C

49,98,196,294(saturated, unsaturated)

A,B

Confining Pressure(kPa)

A,BRelative Density (%)

φ30×H60Specimen Size (cm)

CD conditionSaturated / Unsaturated

Test and Specimen Condition


Large-scale Box Shear Tests (BSTs)Large-scale Box Shear Tests (BSTs)

σnVerticalRoller

τ

ReactionPlate

WaterproofSheet

SpecimenWater Tank

WaterproofSheet

Water

Water40cm

40cm

Horizontal Adjustment Bar

Loading Plate

Normal Stress

Shear Stress

HorizontalRoller

Spacer

Test Condition

15,25,49,98,196,294Normal Stress

(kPa)

90Relative Density

(%)

L40×W40×H40Specimen Size

(cm)

Constant Pressure Condition,Saturated / Unsaturated

（Removed friction around the shear box）

Test and SpecimenCondition


Special Safety Inspection of Damsby Site Officers

Special Safety Inspection of DamsSpecial Safety Inspection of Damsby Site Officersby Site Officers

Primary Inspection (Visual Inspection) :410 dams

Secondary Inspection (Detailed Visual Inspection & Safety Check Based on Measured Behavior) :

323 dams

Should be conducted immediately after“Earthquakes that generate earthquake motion with maximum acceleration of 25 gal or more observed at the dam foundation or earthquake with Japan Meteorological Agency seismic intensity of 4 or higher”


Results of Special Safety InspectionResults of Special Safety InspectionResults of Special Safety Inspection

• No severe damage which affects the safety of dams was reported.

• Cracks generated at dam crest and/or spillway, and increase in leakage/seepage through dam bodies and/or their foundation were reported at several dams.

• Dam owners continued careful monitoring of dam behavior, and made detailed investigation and repair of their damage.


Fujinuma-ike(After Tohoku earthquake)

Fujinuma-ike(After Tohoku earthquake)

View from left abutment toward the breached portion

Documents

HighHigh --Precision Strength Evaluation of Rock Materials and Stability Analysis … 04 - Hiroki... · · 2011-11-01High-Precision Strength Evaluation of Rock Materials ... HighHigh