REALISTIC DYNAMIC ANALYSIS OF REALISTIC DYNAMIC ANALYSIS OF JOINTED ROCK SLOPES USING DDAJOINTED ROCK SLOPES USING DDA
Yossef H. HatzorDept. of Geological and Environmental Sciences, BGU
Funded by National Park and Nature Authority, Israel
Geological and Seismological Setting…
Seismicity along the Dead Sea Rift System
4.0 < ML < 4.95.0 < ML < 5.96.0 < ML
Topographic Site Effect in Masada
Spectral amplification of ground motions (Zaslavsky and Shapira, 2000)
Station 1Station 2
..
.Station 3
Typical Failure Modes
King Herod Palace: combined sliding (East face) and toppling (West Face ) leading to deterioration of entire slope segments
Snake Path Cliff: sliding, and “block slumping”, of large, removable key blocks + time dependentpropagation of tensile cracks
Rock Mechanics Considerations…
Mechanical Properties of Intact Rock
0
60
120
180
240
300
0 0.1 0.2 0.3 0.4 0.5Axial Strain (%)
Axi
al S
tress
(MP
a)
0
60
120
180
240
300
0 0.1 0.2 0.3 0.4 0.5Axial Strain (%)
Axi
al S
tress
(MP
a)
•Uniaxial Compressive Strength of intact Dolomite σc > 300 MPa;
•Elastic Modulus E = 43 GPa
•Poisson’s Ratio ν = 0.18
Shear Strength of Bedding Planes
An example of a natural, filled, bedding planeIn Masada dolomites
φ saw-cut = 28o
φ residual = 23o
Determination of residual friction angle using tilt testson “saw cut”, and “ground”surfaces
Triaxial Tests of Inclined, Filled, Saw-Cut
0
5
10
15
20
25
0 0.1 0.2 0.3 0.4 0.5 0.6
Axial strain (%)
Stre
ss D
iffer
ence
(MPa
)
)2.25.1
6.3
11.7
13
σ3 = 16.2 MPa
8.9
c = 0 MPaφ = 22.7o
0
5
10
15
20
25
0 0.1 0.2 0.3 0.4 0.5 0.6
Axial strain (%)
Stre
ss D
iffer
ence
(MPa
)
)2.25.1
6.3
11.7
13
σ3 = 16.2 MPa
8.9
0
5
10
15
20
25
0 0.1 0.2 0.3 0.40
5
10
15
20
25
0 0.1 0.2 0.3 0.4 0.5 0.6
Axial strain (%)
Stre
ss D
iffer
ence
(MPa
)
)2.25.1
6.3
11.7
13
σ3 = 16.2 MPa
8.9
c = 0 MPaφ = 22.7o
BB
Direct Shear Tests of Natural Bedding Planes
Direct Shear Tests for Rough Bedding Planes
0 0.4 0.8 1.2 1.6Shear Displacement (mm)
0
0.4
0.8
1.2
She
ar S
tress
(MP
a)
Normal Stress 1.38 MPa
1.2 MPa
1.03 MPa0.86 MPa0.7 MPa0.52 MPa
0.35 MPa
0.17 MPa
φ peak=41o
φ residual= 23o
0 5 10 15 20 25Normal Stress (MPa)
0
4
8
12
Shea
r Stre
ss (M
Pa)
Direct Shear of Natural Bedding PlanesTriaxial Shear of Filled Saw-cut
Summary: Mechanical Properties of Rock Mass
••Strength of intact rock > Strength of intact rock > 300 MPa300 MPa
••Elastic modulus = Elastic modulus = 43 43 GPaGPa
••PoissonPoisson’’s ratio = s ratio = 0.180.18
••Peak friction angle of bedding planes = Peak friction angle of bedding planes = 4141oo
••Residual friction angle of bedding planes = Residual friction angle of bedding planes = 2323oo
Measured keyblock Displacements…
Block 2Block 1
LVDT based “Joint Meter”
Joint Displacement Monitoring Devices
Flat Jack
Block 3 – the “control” block
Joint Meter Output - Block 3
-1
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
14 / 1
/ 98
18 / 1
/ 98
23 / 1
/ 98
27 / 1
/ 98
31 / 1
/ 98
4 / 2
/ 98
8 / 2
/ 98
12 / 2
/ 98
16 / 2
/ 98
21 / 2
/ 98
25 / 2
/ 98
1 / 3
/ 98
5 / 3
/ 98
9 / 3
/ 98
13 / 3
/ 98
18 / 3
/ 98
22 / 3
/ 98
28 / 3
/ 98
02/04
/9814
/ 4 / 9
827
/ 4 / 9
8 9
/ 5 / 9
8 21
/ 5 / 9
8 3
/ 6 / 9
8 15
/ 6 / 9
8 28
/ 6 / 9
8
Date
Rel
ativ
e D
ispl
acem
ent
0
50
100
150
200
250
Flat
jack
Pre
ssur
e
FJ 3
JM 10
JM 11
JM = Joint Meter(LVDT) FJ = Flat Jack
JM10
JM11
FJ3
Joint meter output - Blocks 1,2,3
Gulf of Eilat Seismicity???April 7, 98: M=4.4
April 10, 98: M = 4.3
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
14 / 1
/ 98
18 / 1
/ 98
23 / 1
/ 98
27 / 1
/ 98
31 / 1
/ 98
4 / 2
/ 98
8 / 2
/ 98
12 / 2
/ 98
16 / 2
/ 98
21 / 2
/ 98
25 / 2
/ 98
1 / 3
/ 98
5 / 3
/ 98
9 / 3
/ 98
13 / 3
/ 98
18 / 3
/ 98
22 / 3
/ 98
28 / 3
/ 98
02/04
/9814
/ 4 / 9
827
/ 4 / 9
8 9
/ 5 / 9
8 21
/ 5 / 9
8 3
/ 6 / 9
8 15
/ 6 / 9
8 28
/ 6 / 9
8 12
/ 7 / 9
8
Date
Rel
ativ
e D
ispl
acem
ent
Bedrock
Block 1
Block 3
Block 2
Influence of climatic fluctuations– Block 3
Summary: Joint Monitoring Program
•• The monitored The monitored keyblockskeyblocks exhibit dynamic exhibit dynamic behaviorbehavior
•• Periodic Periodic keyblockkeyblock displacements with amplitude displacements with amplitude of up to 1mm and period of 6 months of up to 1mm and period of 6 months –– most likely most likely climatically controlledclimatically controlled
••High High keyblockkeyblock sensitivity sensitivity –– most likely due to most likely due to limiting state of static equilibriumlimiting state of static equilibrium
Limit Equilibrium Analysis…
Representative Keyblock in the East Face (Block 1)
ψ
H = 15mV
W
U
bA A’
J1J3
J2
A
A’
Plan view of Block 1
N
5 m
α=2oo
DDATUM, Zw = 0
Influence of Water Head in “Tension Crack” on Factor of Safety Against Sliding and Rotation – Block 1
φ φ availableavailable = 22.7= 22.7oo
True Geometry of Block 1
Elements of 3D Graphical Solution
Static Solution Pseudo - Static Solution
Total Required Support Force (Ton) for Block 1
0
500
1000
1500
2000
2500
3000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7PEAK HORIZONTAL GROUND ACCELERATION (g)
SU
PPO
RT
FOR
CE
Dry Case
Saturated Case
FACTOR OF SAFETY = 1 . 5
Summary:Limit Equilibrium Analysis
•• Fully three dimensional analysis is required when Fully three dimensional analysis is required when stability of individual, prismatic, stability of individual, prismatic, keyblockskeyblocks is of is of concern.concern.
•• Dominant failure mode in east slope of mountain Dominant failure mode in east slope of mountain is block slidingis block sliding
•• Relatively small water head will induce sliding of Relatively small water head will induce sliding of critical critical keyblockskeyblocks
Support Installation…
Support installation in progress Preparations for support installation
Horizontal Drilling
The Final “Product” in the Snake Path Cliff
Fully Dynamic DDA…
Upper Terrace of King Herod’s Palace
Joint Trace Map Generation…
Joint Spacing and Orientation – North Palace
0102030405060
0.15
2.78
5.42
8.05
10.69 More
Joint Length (m)
Freq
uenc
y
N = 100Mean = 2.7m
05
10152025
0.15 0.61 1.08 1.54
Bed Spacing (m)
Freq
uenc
y N = 59Mean = 60cm
0
10
20
30
2.82 11.11 19.41 27.70 MoreJ2 Spacing (cm)
Freq
uenc
y
N = 80Mean = 14 cm
0
5
10
15
3.00 10.93 18.87 26.80 More
J3 Spacing (cm)
Freq
uenc
y N = 69Mean = 16.8 cm
J1 (bedding)
J2
J3
A Synthetic Joint Trace Map Model
A Photo-geological Discontinuity Trace Map
- E - - W -
DC Realization of Digitized Photo-geological Map
- W -- E -
Discontinuous Deformation Analysis (Shi, 1993)
• A Discrete Element Method (Completely Discontinuous)
• A Rigorous Contact Detection Algorithm
• Normal and Shear Springs at Contact Points Between Blocks
• No Tension / No Penetration Between Blocks
• Sliding Deformation Modeled Using Coulomb’s Law
• Solution for Displacement Obtained by Minimization of Total Potential Energy (as in FEM).
• Solution Progresses by a Time-Step Marching Scheme
• First Order Displacement Approximation
• Simply Deformable Blocks
DDA Validation…
Block on an Incline:Gravitational Loading - Constant Acceleration
(MacLaughlin and Sitar, 1997)
0
1
2
3
4
5
6
7
0 0.5 1 1.5 2 2.5TIME (s)
DIS
PLA
CEM
ENT
(m)
φ=5
DDA, g1=0.002φ=10
DDA, g1=0.005φ=15
DDA, g1=0.05φ=20
DDA, g1=0.1
Block on an Incline – Dynamic Loading(Hatzor and Feintuch, 2001)
0 1 2 3 4 5
Time (sec)-5
0
5
10
15
20
a (m
/s2 )
, v (m
/s),
s (m
)
AccelerationVelocityDisplacementDDA displacement
a(t) = 2sint + 3sin2t
Shaking Table Experiments (Wartman, 1999)
Shaking Table
11.37o
45 in
48 in
Inclined Plane
Rigid Block
1
2
34
5
No. Instrument Direction of Measurement 1 accelerometer parallel to plane 2 accelerometer parallel to plane 3 accelerometer horizontal 4 displacement transducer horizontal 5 displacement transducer parallel to plane
Comparison Between Shaking Table and DDA (Tsesarsky, Hatzor, and Sitar 2002)
-0.3
-0.2
-0.1
0
0.1
0.2
Acc
eler
atio
n (g
)
0 1 2 3 4 5Time (sec)
0
0.02
0.04
0.06
0.08
0.1
Dis
plac
emen
t (m
m)
ay(φ = 16o) = 0.08g
ty(φ = 16o) 0.64sec
Measuredk01 = 1k01 = 0.985k01 = 0.98k01 = 0.975K01 = 0.95
Summary:Validation Study•• Good agreement between numeric and analytical Good agreement between numeric and analytical solutions solutions -- provided that the control parameters provided that the control parameters (g01, g02) are optimized in constant acceleration (g01, g02) are optimized in constant acceleration cases.cases.
•• Similar results are found for time dependent Similar results are found for time dependent acceleration.acceleration.
•• When comparing time dependent acceleration When comparing time dependent acceleration analysis with physical models (e.g. shaking table) analysis with physical models (e.g. shaking table) some velocity damping must be introduced in order some velocity damping must be introduced in order to get good agreement. For a single block problem to get good agreement. For a single block problem the optimal value of velocity damping seems to be the optimal value of velocity damping seems to be not greater than 2%.not greater than 2%.
The Real Case…
The Nueiba 7.1 Earthquake of Nov. 1995Fill Response (Eilat)
0 10 20 30 40 50 60Time (sec)
-0.08
-0.04
0
0.04
0.08
0.12
Accl
. (g)
-0.08
-0.04
0
0.04
0.08
0.12
Accl
. (g)
Vertical
E - W
-0.12
-0.08
-0.04
0
0.04
0.08
0.12
Acc
l. (g
) N-S
De-convolution: Bed-Rock Response (Zaslavski, Shapira, and Arzi, 2000)
0 5 10 15 20 25 30 35 40 45 50 55 60Time (sec)
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
Acc
l. (g
)
E-W
-0.08
-0.04
0
0.04
0.08
Acc
l. (g
)
N-S
Convolution: Topographic Site Effect
0 5 10 15 20 25 30 35 40 45 50 55 60Time (sec)
-0.12
-0.08
-0.04
0
0.04
0.08
Acc
l. (g
)
-0.08
-0.04
0
0.04
0.08A
ccl.
(g)
N-S
E-W
Predicted Damage by DDA
No Energy Dissipation2.5% Kinetic Damping5% Kinetic Damping
Rock Bolt Reinforcement:Modified Record Normalized to a 0.6g PGA
Dense Bolting Pattern: L = 6m, s = 2mSparse Bolting Pattern: L = 6m, s = 4m
Conclusions•• The DDA method can be used to perform a fully The DDA method can be used to perform a fully dynamic analysis of a jointed rock slope.dynamic analysis of a jointed rock slope.
•• Historical evidence indicate that the modeled slope has Historical evidence indicate that the modeled slope has sustained at least 4 episodes of PGA = 0.2g earthquakes sustained at least 4 episodes of PGA = 0.2g earthquakes in the past.in the past.
•• This historical evidence is confirmed by DDA.This historical evidence is confirmed by DDA.
•• DDA with no energy dissipation clearly over predicts DDA with no energy dissipation clearly over predicts damage due to shaking.damage due to shaking.
•• On the basis of historical performance we believe that On the basis of historical performance we believe that a reasonable damping value for a multi block problem in a reasonable damping value for a multi block problem in DDA should be in the order of 2% .DDA should be in the order of 2% .