Présentation du Professeur Thomas O'Rourke (Cornell University) - SCG Ouest Québec

CROSS CANADA LECTURE
Tom O’Rourke
Thomas R. Briggs
Professor
of Engineering
Cornell University
LESSONS LEARNED FOR
GROUND MOVEMENTS &
SOIL STABILIZATION ON
THE BOSTON CENTRAL
ARTERY

VALUE OF CASE HISTORIES
• They Are Real
• Involve Full Complexity of Real World
Conditions
• Provide Empirical Guidance
• True Test for Analytical/Numerical Models
• Surprising Insights

IMPORTANCE OF CASE HISTORIES
“Those who cannot
remember the past
are condemned to
repeat it.”
- George Santayana, 1905

TOPICS
•BOSTON CENTRAL ARTERY & TUNNEL
•DEEP SOIL MIXING TECHNOLOGY
•CASE HISTORIES
•LESSONS LEARNED

•BOSTON CENTRAL ARTERY
AND TUNNEL (CA/T)
TOPIC

1950s 1990s

I 93
I 90
• 260 lane-km of Interstate
Highways
• I-93 Underground Beneath
Boston
• I-90 Extension to Logan Airport
• Ted Williams Tunnel
• I-90/I-93 Interchange
• Extensive Frontage Roads
• Over 250 Construction
Contracts
Boston CA/T

I 93
I 90
Boston CA/T
1959:
$110 Million
2004:
$14.7 Billion

•DEEP SOIL MIXING
TECHNOLOGY
TOPIC

DEEP MIXING METHOD
In situ treatment
technology that blends
soil with cementitious
materials by means of
mixing shafts to create a
soil mix or soil cement
with higher strength and
lower compressibility
than those of the native
soil.

DEEP MIXING METHODS
GROUT
(W)
DRY
(D)
ROTARY
(R)
ROTARY + JET
(J)
ROTARY
(R)
SHAFT
(S)
END
(E)
END
(E)
END
(E)

TREATMENT PATTERNS

DMM APPLICATIONS
•Excavation Support Walls
•Stabilization of Deep Excavations
•Liquefaction Mitigation
•Hydraulic Cutoff Barriers
•Fixation of Contaminants

• CASE HISTORIES
TOPIC

CASE HISTORIES
•Bird Island Flats,
Contract C07A1
•Fort Point
Channel, Contract
C09A7
FORT POINT
CHANNEL
BIRD
ISLAND
FLATS

BIRD ISLAND FLATS Deep Boston
Marine Clay

PLAN VIEW

SUBSURFACE PROFILES

CEMENT DEEP SOIL MIX WALLS

WATER PRESSURE ON CDSM WALL

STEADY STATE SEEPAGE

WATER PRESSURE OBSERVATIONS
• Soil Mix Walls Often Regarded As Impervious
• Soil Mix K ~ 1 x 10-6 cm/s
• Soil Mix Wall May Be Relatively Pervious to In
Situ Clay
• Water Pressure Behind Wall Can Be Significantly
Less Than Hydrostatic

CLAY UNDRAINED STRENGTH PROFILE
Stress History and Normalized Soil Engineering Properties (SHANSEP)

EXCAVATION UNLOADING

LARGE GROUND DEFORMATION

FIELD VANE SHEAR STRENGTHS
Fill
Organic Silt
Marine Clay
Glacial Deposits

CIRCULAR STABILITY FOR
EXCAVATION UNLOADING
EFFECTS
POINT C
Excavation
Unloading
Negative
Porepressue
Su after
Unloading
Su Triaxial
Extension
Factor of Safety for Deep
Rotational Stability: 0.99 to 1.04
Critical Slip
Surface

DEEP SOIL MIX BUTRESS
115
98
82
66
49
33
0
16
12 6 0SOIL MIX
BUTRESSES
JET GROUT

DEEP SOIL MIX BUTRESS

CEMENT DEEP SOIL MIX

CEMENT DEEP SOIL MIX
CF = 4.7 kN/m3

FINITE DIFFERENCE MESH

Inclinometer
Measurements
DSM MODULUS

COMPARISON OF NUMERICAL RESULTS &MEASUREMENTS

FORT POINT CHANNEL

B
B’
SUBSURFACE CROSS-SECTION

DEEP SOIL MIX RIGS
M250 RIG 608 RIG

DEEP SOIL MIX INSTALLATION

DEEP SOIL MIX COMPOSITION
80-100% Spoil
CF = 2.9 kN/m3
CF = 2.2 kN/m3 CF = 4.7 kN/m3

0
20
40
60
80
100
120
12.6 13.5 14.4 15.4 16.3 17.3 18.2 19.2 20.1 21.0 22.0
Total Unit Weight (kN/m3
)
Frequency
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
CumulativePercentage
Frequency
Cumulative
n = 775
mean = 16.3 kN/m3
stdev. = 1.2 kN/m3
COV = 7%
All Core Samples
0
100
200
300
400
500
600
11.0 11.9 12.9 13.8 14.8 15.7 16.6 17.6
Total Unit Weight (kN/m3
)
Frequency
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Frequency
Cumulative
n = 3319
mean = 15.2 kN/m3
stdev. = 0.8 kN/m3
COV = 5%
All Wet Grab Samples
UNIT WEIGHT FROM CORES MEAN = 16.3 kN/m3UNIT WEIGHT FROM WET GRAB MEAN = 15.2m3
DEEP SOIL MIX PROPERTIES

1178
1024
584
364
196
90 60
24 13 6 3 3 0 0
0
200
400
600
800
1000
1200
1400
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Unconfined Compressive Strength (MPa)
Frequency
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Frequency
Cumulative
n = 3545
Mean = 3.95 MPa
Median = 3.03 MPa
All Wet Grab Samples
0
500
174
65
34
17 7 6 9 2 1 3 2 2 1
0
100
200
300
400
500
600
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Unconfined Compressive Strength (MPa)
Frequency
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Frequency
Cumulative
n = 823
Mean = 2.68 MPa
Median = 1.59 MPa
All Core Samples
qU FROM CORES MEAN = 2.68 MPaqU WET GRAB MEAN = 3.95 MPa
DEEP SOIL MIX PROPERTIES

0
20
40
60
80
100
120
140
160
180
2 3 4 5 6 7 8 9 10
Ln of Unconfined Compressive Strength, ln(qu), (kPa)
Frequency
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Frequency
Cumulative
n = 823
Mean = 1450 kPa
Median = 1590 kPa
Core Samples
Ln-Normal Distribution
Distribution Function
All Core Samples, Ln Distribution
0.0
0.2
0.4
0.6
0.8
1.0
1 2 3 4 5 6 7 8 9 10
Ln of Unconfined Compressive Strength, ln(qu), (kPa)
CumulativeProbability
Empirical
Kolmogorov-Smirnov Test Dnmax = 0.04
LOGNORMAL DISTRIBUTION K-S TEST FOR GOODNESS OF FIT
STATISTICAL CHARACTERISTICS

SAMPLING
•Wet Grab Sampling Biased Against
Unmixed Soil: Low Unit Weights &
High qu
•75-mm Triple Tube & 80-mm Double
Tube Coring Gave Best Results

y = -7E-05x + 1.7
r2
= 3E-05
0.01
0.1
1
10
0 100 200 300 400 500 600
Age (days)
UnconfinedCompressiveStrength(MPa)
CF = 2.91 kN/m3, w/c = 0.7
Linear (CF = 2.91 kN/m3, w/c = 0.7)
Cell 3
DEEP SOIL MIX STRENGTH VS TIME

0.01
0.1
1
10
1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0
Cement Factor (kN/m3
)
CF = 1.86 kN/m3
CF = 1.93 kN/m3
CF = 2.32 kN/m3
CF = 2.91 kN/m3
1.93 Median
2.32 Median
2.91 Median
Trendline
Cell 1
w/c = 0.7
y = (44.7e1.04x
)/1000
r2
= 0.92
qu vs WATER/CEMENT RATIO qu vs CEMENT FACTOR
0.01
0.1
1
10
0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95
Water:Cement Ratio
w/c = 0.7
w/c = 0.8
w/c = 0.9
0.7 Median
0.8 Median
0.9 Median
Trendline
Cell 3
CF = 2.32 kN/m3
y = (16.4e5.1x
)/1000
r2
= 0.99
DEEP SOIL MIX STRENGTH VS W/C & CF

FORT POINT CHANNEL QUALITY CONTROL
• Min/Max 56-day qu = 2.1 and 6.9 MPa
• Triple tube core barrels with 75-mm core for sampling
• ≤ 2% horizontal deviation of soil mix wall panels
• Restroking augers at bottom of panels & 0.3 m
penetration of glacial deposits
• Minimum soil mix unit weight = 16.5 kN/m3

PRESSUREMETER
PLATE LOAD
TESTS
SHEAR WAVE
VELOCITY
DEEP SOIL MIX FIELD TESTS

PRESSUREMETER

0
100
200
300
400
500
600
700
800
900
1000
0.001 0.01 0.1 1 10
Radial Strain or Engineering Shear Strain, /2 (%)
Gsec(MPa)
Depth=19.6m (Hole No. 7325C4)
Depth=18.8m (Hole No. 7325A2)
Depth=29.5m (Hole No. 7325A2)Upper Bound Gmax
from Seismic Velocity
Test Results
Lower Bound Gmax
from Seismic
Velocity Test Results
PRESSUREMETER
Digital filtering
of pressuremeter
data
> 30 m depth
< 30 m depth
Wang, Y. and T.D. O’Rourke, “Interpretation of Shear Modulus
Degradation Characteristics from Pressuremeter Tests” (2007),
Journal of Geotechnical and Geoenvironmental Engineering,
ASCE, Vol. 133, No. 12, Dec., pp. 1556-1566

0
100
200
300
400
500
600
0.001 0.01 0.1 1 10
Radial Strain or Engineering Shear Strain, /2 (%)
Gsec(MPa)
Gmax from
Seismic Velocity
Test Results
Pressuremeter
Test Results
Laboratory
Test Results
Plate Load
Test Results
BIF Buttress
DEEP SOIL MIX SHEAR MODULUS VS SHEAR
STRAIN

DEEP SOIL MIX EXCAVATION STABILIZATION

SYSTEM STIFFNESS
~0.05%

• LESSONS LEARNED
TOPIC

LESSONS
• Clay Undrained Shear Strength Is Key Parameter for
Evaluation of Excavation Base Stability
• SHANSEP Method, DSS, and FVST Preferred for
Evaluating Clay Undrained Shear Strength
• Excavation Unloading and Dissipation of Negative Pore
Pressures Can Reduce Undrained Strength
• Soil Structure Can Play a Critical Role in Undrained
Strength Reduction
• Need to Evaluate the Effects of Excavation Unloading
on Base Stability in Clay

LESSONS
• Deep Soil Mix Walls Can Be Relatively Pervious in Clay
• Steady State Seepage Reduces Water Pressure on DSM
Walls
• Soil Mix Buttresses 35% Soil Mix Coverage Were
Successful in Stabilizing Against Deep Rotational
Failure
• Significant Deformation & Strain Were Observed for
35% Coverage Buttresses
• Anchored Buttress Preferable to Floating Buttress

LESSONS
•Wet Grab Sampling Tends to Screen Out
Untreated Soil from Deep Soil Mix Resulting
in Relatively High qu and Low Unit Weight
•DSM Unit Weight Normally Distributed
•DSM qu Lognormally Distributed
•Statistical Distribution Affects QC/QA
Decisions

LESSONS
•qu Increases with Water /Cement Ratio &
Cement Factor When Water Needed for
Mixing
•Pressuremeter Valuable for Defining Gsec vs
Shear Strain Relationship
• Gsec vs Shear Strain for In Situ Soil Mix at
Fort Point Channel

LESSONS
•Wall and Ground Deformation Well Controlled
at Fort Point Channel to ≤ 12 mm (0.5 in.)
•Very Favorable Agreement Between
Analytical and Measured Movements When
Gsec vs Shear Strain Relationship Used
•Very Stiff Walls with Base Stabilization
Promote Elastic Response with Wall
Moments ≈ 0.05%

LESSONS
•Bird Island Flats: Deep Soil Mix with high
shear strains ~ 0.6%, Gsec = 10% Gmax
and strength mobilized at 50% qu
•Fort Point Channel mobilized very low
shear strains ≈ 0.015% with Gmax
controlling performance

BOSTON ARTERY COST INCREASES

MEGA-PROJECTS
• Menai Bridge
• Brooklyn Bridge
• Panama Canal
• Trans-Alaska Pipeline
• Channel Tunnel
• Superconducting
Super Collider
• Actual Costs/Completion
• Average 2.5x Cost at Start of
Construction
• 2-4 Years Late
• Benefits
• Societal Improvements
• Economic/Commercial
Advantages
• Technology Advancement

AMERICAN INSURANCE GROUP
$182 Billion Bailout 2008/09

URBAN REGENERATION

Présentation du Professeur Thomas O'Rourke (Cornell University) - SCG Ouest Québec

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