Dynamic response and tunnel damage from explosion loading.pdf
Transcript of Dynamic response and tunnel damage from explosion loading.pdf
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Dynamic Response and TunnelDamage from Explosion Loading
Dr Zhou YingxinDefence Science & Technology Agency
Singapore
Presented at the International Symposium on DefenceConstruction 2002, Singapore
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Explosives Storage Safety
• Design must consider accidental explosion(airblast, ground shock, debris, fire)
• Internal Safety– Chamber separation– Prevention of sympathetic detonation
• External Safety– Inhabited buildings– Public transport route– Workshops
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Large-scale Tests forUnderground Storage
Collaboration with SwedishDefence Research Agencyand Armed Forces HQ
Validation of undergroundfacility design■ Airblast propagation■ Door pressure and response■ Ground shock,■ Debris hazards■ Response of tunnels (atcriterion distances)
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Layout of Test Facility
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Barricade
Access Tunnel
Entrance Portal Existing Klotz Group Tunnel
Debris Traps
Detonation Chamber
Slot Tunnel
Debris Trap
Main Tunnel
Test Facility Layout – 3D View
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Chamber Sections
13 m
8.8 m
Explodingchamber
Adjacenttunnel
2 m
D=0.6Q1/3
100 m
Surface
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Considerations in Tunnel Design
• 10-ton explosives charge weight• Fragment loading (155 mm rounds)• Repeated blasts (3-4 year programme)• Safety considerations (need to go into
tunnel after test)
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Requirements for Tunnel Design
• Rock mass properties (can’t takeeverything for granite!)
• Ground shock prediction
• Tunnel damage criteria (if you know whatit means)
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Rock Mass Properties
Avg Q value: 15-20Rock mass quality
12.5 – 17.5 MPaUniaxial tensile strength (basedon point load tests)
200-250 MPaUniaxial compressive strength
2620 kg/m3Density
Red porphry syenite with greygranitic intrusion
Rock type
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Ground Shock Prediction
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Sources of Ground Shock
Low probabilityLarge charge weight
Low loading density
Ammo storage –accidentalexplosion
Illustration
Fully coupled chargeLow charge weight
Multiple delaysRepetitive blasting
Tunnelling /mining – blasting
CharacteristicsSources
Largest charge weight (kt or Mt)Large displacementGenerally indirect-induced shock
Nuclear weapons
Limited charge weight
Fully coupled or contact explosionPenetration & Cratering effects
Conventionalweapons –penetration bomb
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Empirical PPV Equation
V HR
QB
n
=
−
H = constant; B = scaling law;
n = attenuation coefficient
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Parameters for Coupled Explosions
H = (500/C2.17)/(ρC), mm/s
RockType
RockMass
Density, ρ,kg/m3
SeismicVelocity, C,
m/s
Initial Value,H (mm /
sec)
AttenuationCoefficient,
nD < 6
AttenuationCoefficient,
nD > 6
Good > 2600 5100-6000 5000 1.5 1.2
Fair 2300-2600
4100-5100 4000 1.8 1.5
Poor < 2300 3500-4100 3000 2.3 1.8
D = R/Q1/3, scaled range, m/kg1/3
Conservative estimate for spherical charges
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Correction Factors for PPV
• Charge geometry (distributed vsconcentrated charge)
• Decoupled explosions (explosives not infull contact with rock)
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PPV Correction Factor forDecoupled Explosions
0.00
0.20
0.40
0.60
0.80
1.00
0 50 100 150 200
Loading Density, kg/m3
Dec
oupl
ing
Fac
tor
Hultgren (1987)
McMahon (1992)
Joachim (1994)
Mandai Granite
LST: Loading density = 10 kg/m3
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PPV Prediction - Slot Wall
0.6 – 0.8PPV correction forcharge geometry
0.116 – 0.23Decoupling factor
10,760x0.6x(0.116-0.23)= 748-1,485 mm/s
Predicted PPV for slotwall (incipient)
5000(R/Q1/3)-1.5
= 5000(14/100001/3)-1.5
= 10,760 mm/s
Fully coupled PPV
10000 kgCharge weight
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Ground Shock Curves
1037
1729
0
1
10
100
1000
10000
100000
0.1 1 10 100Scaled horizontal distance, m/kg1/3
Pea
k pa
rtic
le v
eloc
ity, m
m/s Rock free field data
Tunnel Wall-AdjustedQuarry wall adjustedBest fit - DecoupledKlotz Group Test
0.6
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Tunnel Damage – What does itmean?
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Damage of Unlined Tunnels – aSample of Definitions
• Slight damage• Medium damage• Severe damage• Intermittent failure• Local failure• General failure• Tight closure• Blow out
• Incipient swelling• Incipient damage• Dislodge of rock
section• Large displacement• Minor damage• Damage!
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Damage by Earthquakes
Calculated PPV andassociated damage tounderground excavationsby earthquakes, Brady,1991
Slot wall: PPV = 0.75-1.5 m/s
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Damage of Swedish Hard Rock(Persson, 1997)
Peak ParticleVelocity (mm/s)
Tensile Stress(Mpa)
Strain Energy(J/kg)
Typical effect
700 8.7 0.25 Incipientswelling
1000 12.5 0.5 Incipient damage
2500 31.2 3.1 Fragmentation
5000 62.4 12.5 Goodfragmentation
15,000 187 112.5 crushing
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Tunnel Damage (Li & Huang,1994)
Rock Rock Parameters Peak Particle Velocity, mm/s
Type UnitWeight(g/cm3)
Comp.strength
(Ppa)
TensileStrength(MPa)
NoDamage
SlightDamage
(slightcracking)
MediumDamage(partialcollapse)
SeriousDamage(large
collapse)
Hard 2.6-2.7 75-110 2.1-3.4 270 540 820 1530
Rock 2.7-2.9 110-180 3.4-5.1 310 620 960 1780
2.7.-2.9 180-200 5.1-5.7 360 720 1110 2090
Soft 2.0-2.5 40-100 1.1-3.1 290 580 900 1670
Rock 2.0-2.5 100-160 3.4-4.5 350 700 1070 1990
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1-D Elastic Calculations (Zukas,1982)
• A saw-tooth wave pulse travelling along arock bar
Cppv
CV DTDTm
SP ρσ
ρσσ
−=−
= 22
VSP = velocity of the first spall; s m = magnitude of incipientstress; σDT = dynamic tensile strength of rock; ρ = rock massdensity, kg/m3; C = seismic wave velocity in rock, m/s.
)( Cppvm ρσ =
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1-D Spall Calculations
0.1
1.0
10.0
100.0
0.1 1.0 10.0 100.0
Free-field Radial Peak Particle Velocity (ppv), m/s
Thi
ckne
ss o
f Firs
t Spa
ll
0
10
20
30
40
50
60
Num
ber
of S
palls
Assumptions: Density = 2650 kg/m3
Seimic velocity = 5500 m/s Dynamic tensile strength = 21.5 Mpa Dominat frequency = 100-500 hz
100 Hz200 Hz300 Hz400 Hz500 Hz
5-m rock bolt
Threshold PPV = 0.5σT/(ρC) = 0.5(21.5x106)/(2650x5500) = 0.74 m/s
Slot wall: PPV = .75-1.5 m/s
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UET Tests, Sandstone (afterHendron, 1977)
Damage Zone 1 2 3 4 Damage tight
closure General failure
Local failure
Intermittent failure
Free-field radial strain NA 40 13 3-6 Free-field ppv, m/s NA 12 4 0.9-1.8 Calculated thickness of 1st spall, m
0.3-1.4 1-4.2 2-18.5
Calculated number of spalls 11 4 1
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1-D Spall Calculation for UET
18.5
4.2
1.4
9.259
2.083
0.694
1
4
11
0.1
1.0
10.0
100.0
0.1 1.0 10.0 100.0
Free-field Radial Peak Particle Velocity (ppv), m/s
Thi
ckne
ss o
f Firs
t Spa
ll
0
2
4
6
8
10
12
Num
ber
of S
palls
Assumptions: Density = 2400 kg/m3 Seimic velocity = 2500 m/s Dynamic tensile strength = 8 Mpa Dominat frequency = 100-500 hz
100 Hz
200 Hz300 Hz400 Hz500 Hz
Calculated Threshold
Zone 1Zone 3Zone 4
Zone 2
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Explosive Testing of TunnelResponse (Dowding, 1984)
40.00.8Complete failure
7.40.15Local failure
1.3Displacement of cracks
1.00.02Cracking of liner
Lined tunnel:
0.1Complete closure
3.60.04Local failure
2.00.015Intermittent failure
0.3Joint movement, fall of loose rock
Unlined tunnel:
PPV, m/sStrain%Type
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Design of Tunnel Support
• Unlined tunnel can sustain ground shock of PPV= 1.0-2.0 mm/s before damage begins
• Static support design specified fibre-reinforcedshotcrete and rock bolts for increasedperformance against dynamic loads
• Swedish Armed Forces HQ Requirements: allmilitary facilities in rock must use dynamic rockbolts
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Swedish Dynamic Rock Bolts
Plain shotcrete Reinforced shotcrete
Anchor Section
Smooth Section
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Tunnel Support for LST
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Tunnel Support for LST
Dynamic rock bolts
Dynamic rock bolts
SFR Shotcrete
Chamber
Slot Tunnel
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LST - Instrumentation
Organisation Gauge Type 2000 2001 RemarksAir Blast – Chamber 3 3
Airblast – Tunnel 21 21Airblast – External 8 8
Ground Shock 40 40Strain 8 8
Temperature 1 12 New - 11
FOI
Smoke puffs 0 0 Consider for future testsAir Blast 11 11
Ground Shock 16 16Airblast InducedGround shock
0 2 New
NDCS
Geophones 8 8Chamber – Pressure 2 2Chamber – Bargauge 2 2Pressure – External 4 8 Stings (4)
Accelerometer 8 12Radar – Fragment Vel. 1 2
DTRA
Time of Arrival 0 15 New133 170
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Ground Shock Gauges
Detonating Chamber
Access Tunnel
Slot Tunnel Horizontal
Borehole
Vertical Borehole
Rock-Soil Interface
Soil Surface
NS
2-D Accelerometers
1-D Accelerometers
Detonating Chamber
Access Tunnel
Slot Tunnel Horizontal
Borehole
Vertical Borehole
Rock-Soil Interface
Soil Surface
NS
2-D Accelerometers
1-D Accelerometers
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Shotcrete Pannels in Slot Tunnel
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PLAN VIEW
ELEVATION
TNT Bare Charge (Test #3)
TEST NO.
NEQ (KG)
CHARGE TYPE
OBJECTIVES/ DESCRIPTION
1 10 Bare charge
Ground shock calibration
2 500 Bare charge
Loading density 0.5 kg/m3
3 10000 Bare charge
Loading density 10 kg/m3
4a 2500 Bare Charge
Loading density 2.5 kg/m3
4b 10000 Cased Charge
Cased charge Test Loading density 10 kg/m3
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Vide of Test #3 - 10000 Kg TNT
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Chamber
• 10 craters in floor underneath charge• No rock fall from roof!
CraterOverview of Chamber
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Video Of Slot During Test #3
Slot Tunnel
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Slot Tunnel
• No visible damage of tunnel wall• Slight soil movement on floor
Shotcrete WallSoil Movement
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Slot Tunnel• Lights (and all other fixtures) fully
functional after detonation
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3/16/01
Time, ms
Pre
ssur
e, k
Pa
LST Test#3 - NEQ=10,000 kgGauge No.: DP1 and DP2
15.6 16.8 18 19.2 20.4 21.6 22.8 24 25.2 26.4 27.6-30,000
-15,000
0
15,000
30,000
45,000
60,000
75,000
90,000
105,000
120,000
135,000
150,000
Pressure @ 7.2 mPressure @ 24.6 mBargauge @ 24.6 m
Chamber Pressure
Equivalent PPV = [115 Mpa/(2620x5000)] = 8.8 m/s
P = 115 Mpa
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VERTICAL BOREHOLE
Ground Surface and Soil-Rock Interface3x2-D at -4.4m, 64m and 12m from Chamber Wall
AccessTunnel
SlotTunnel
DetonatingChamber
VerticalBorehole
NS
Time, ms
Acc
eler
atio
n, g
LST Test #3 - NEQ = 10000kgLocation: Vertical Borehole @ 16m from Chamber Roof (Vertical)
Guage No.: G4
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5-1,200
-900
-600
-300
0
300
600
900
Time, ms
Vel
ocity
, m/s
Dis
plac
emen
t, E
-03
m
LST Test #3 - NEQ = 10000kgLocation: Vertical Borehole @ 16m from Chamber Roof (Vertical)
Guage No.: G4
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5-0.25 0
0 0.6
0.25 1.2
0.5 1.8
0.75 2.4
1 3
1.25 3.6
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HORIZONTAL BOREHOLE
Horizontal BoreholeAccessTunnel
SlotTunnel
DetonatingChamber
NS
3/16/01
Time, ms
Acc
lera
tion,
g
LST Test #3 - NEQ = 10000kgLocation: Horizontal Borehole @ 18m from Chamber Wa ll (Horizontal)
Guage No.: G10
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20-240
-160
-80
0
80
160
240
320
400
480
560
640
720
3/16/01
Time, msV
eloc
ity, m
/s
Dis
plac
emen
t, E
-03
m
LST Test #3 - NEQ = 10000kgLocation: Horizontal Borehole @ 18m from Chamber Wa ll (Horizontal)
Guage No.: G10
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20-0.2 0
0 0.3
0.2 0.6
0.4 0.9
0.6 1.2
0.8 1.5
1 1.8
1.2 2.1
1.4 2.4
1.6 2.7
1.8 3
2 3.3
2.2 3.6
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1/18/01
Time, ms
Acc
eler
atio
n, g
LST Test#3 - NEQ=10,000 kg26.4 m from back of slot - Shotcrete 100 mm - Fibre 60 kg/m3
Gauge No.: DA6
19.2 20.4 21.6 22.8 24 25.2 26.4 27.6 28.8 30 31.2-300
-150
0
150
300
450
600
750
900
1,050
1,200
1,350
1,500
1/18/01
Time, ms
Vel
ocity
, cm
/s
Dis
plac
emen
t, cm
LST Test#3 - NEQ=10,000 kg26.4 m from back of slot - Shotcrete 100 mm - Fibre 60 kg/m3
Gauge No.: DA6
18 21 24 27 30 33 36 39 42 45 48-60 -0.02
-40 0
-20 0.02
0 0.04
20 0.06
40 0.08
60 0.09999999
80 0.12
100 0.14
120 0.16
140 0.18
160 0.2
180 0.22
VelocityDisplacement
Ground Shock on Slot Walls
Acceleration
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PPV’s from Test #3
100
1000
10000
1 10 100
Distance from Chamber Wall / Roof, m
Pea
k P
artic
le V
eloc
ity, m
m/s
Horizontal Hole
Vertical Hole
Slot Wall Peak
Slot wall - Predicted
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Strain on Rock Bolts (T3)11/16/01
Time, sec
stra
in
LST - Test#3Rock Bolt
Strain - TT6
111.632 111.656 111.68 111.704 111.728 111.752 111.776-1E-4
-8E-5
-6E-5
-4E-5
-2E-5
0
2E-5
4E-5
6E-5
8E-5
1E-4
0.00012
0.00014
11/16/01
Time, s
Str
ain
LST Test#3Rock Bolt 2
Gauge No.: TT7
111.65 111.665 111.68 111.695 111.71 111.725 111.74-0.00012
-0.000105
-9E-5
-7.5E-5
-6E-5
-4.5E-5
-3E-5
-1.5E-5
0
1.5E-5
3E-5
4.5E-5
6E-5Strain = 0.00011
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Fragment Loading (Test #4b)
PLAN VIEW
ELEVATION
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Video of Test #4b
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Damage in Chamber
• Spalling of shotcrete layer• Still no rock fall from roof!
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Slot Tunnel
• Lights (and fixtures) still fully functional duringand after the test
• Damaged shotcrete fell off to floor
Shotcrete Panels
Light Fixtures
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Comparison of PPV’s
PPVTNT = 0.94(R/Q1/3)-1.3
PPV155 = 0.72(R/Q1/3)-1.3
0.01
0.1
1
10
0 1 10
Scaled Distance from Center of Charge, m/kg 3
Pea
k P
artic
le V
eloc
ity, m
/s
Measured 10-ton TNT Charge
Measured 10-ton Cased Charge
Best Fit for Test#4b - 10-ton Cased Charge
Best Fit for Test#3 - 10-ton TNT ChargeBare TNT
Cased charges
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Effects of Fragment Loading
Mostly fragments from outer row of rounds wereloading the tunnel walls
Items Test #3 Test #4b Min PPV, m/s 0.94 0.62 Ratio of Min PPV 1.00 0.66 Max PPV, m/s 1.70 1.84 Ratio of Max PPV 1.00 1.09 Average PPV, m/s 1.39 0.98 Ratio of Avg PPV 1.00 0.70 Equivalent TNT Ratio
1.00 0.54
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Computed Seismic Velocity
Test and Charge Peak Chamber Pressure, MPa
Average PPV on Tunnel Wall,
mm/s
Time of Arrival, Ms
Calculated Seismic
Velocity, m/s
Test 1 – 10 ton bare TNT
100 1390 3.07 4,636
Test 2 – 2.5 ton bare TNT
622 3.26 4,268
Test 3 – 10 ton TNT (1450 155mm shells)
50 977 3.28 4,294
Ratio of Seismic Velocity after Test 2
--- 0.93
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Conclusions
• Fresh rock damage appears to begin at PPV’s of1-2 m/s
• At incipient PPV’s of 2-4 m/s, static support withrock bolts and fibre-reinforced shotcrete sufficientfor tunnels in competent rock
• For low loading densities (10 kg/m3), tunnels sitedat 0.6Q1/3 in hard rock can remain fully functionalagainst ground shock loading
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Finally,
If in doubt . . .
. . . build in rock
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THANK YOU
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THANK YOU