Jorge G. Zornberg, Ph.D., P.E. - Texas A&M University · 2017-01-04 · Jorge G. Zornberg, Ph.D.,...
Transcript of Jorge G. Zornberg, Ph.D., P.E. - Texas A&M University · 2017-01-04 · Jorge G. Zornberg, Ph.D.,...
Jorge G. Zornberg, Ph.D., P.E.The University of Texas at AustinImmediate Past-president, IGS
11 October 2016College Station, TX
Expansive Clays
Part of unit (generally less than 50%) consists of clay having high swelling potential
Part of unit (generally less than 50%) consists of clay having high swelling potential
Unit contains abundant clay having high swelling potential
Unit contains abundant clay having high swelling potential
Expansive Clays
Part of unit (generally less than 50%) consists of clay having high swelling potential
Part of unit (generally less than 50%) consists of clay having high swelling potential
Unit contains abundant clay having high swelling potential
Unit contains abundant clay having high swelling potential
Original ground profile
CL
Location of longitudinal cracks
Pavements on Expansive Clays
Source: Zornberg and Gupta (2009)
6
Pavements on Expansive Clays
7
Pavements on Expansive Clays
8
Pavements on Expansive Clays
9
Pavements on Expansive Clays
TxDOT Test Procedure Tex-124-E
TxDOT PDM Chapter 3 Section 2:
Tex-124-E, “Determining Potential Vertical
Rise,” is the recommended procedure for
determining PVR. A 15-foot soil column is
recommended for the analysis to determine
PVR. The least amount of PVR for design
is 1.5 inches for main lanes (2.0 inches for
frontage roads, when allowed), or as
established by the district SOP identifying
the requirements.
TxDOT Procedure Tex-124-E
TxDOT Test Procedure Tex-124-E
Minuses:
• Too many correlations:
- To define linear swell from
volumetric swell
- To define free volume change
from PI
- To define total volume change
from load
- To correct for unit weight
- To correct for % binder
• Problematic experimental data:
- Too little
- Too old
- Limits Extrapolated by Tex-124-E
TxDOT Procedure Tex-124-EPluses:
• Good practical
implications:
– Outcome (i.e. PVR) easy
to grasp by designers
– Can be used to relate to
performance
• Accounts for the
relevant variables:
– Soil characteristics
– Stratigraphy
– Initial moisture content
– Confining stresses
McDowell’s 1956 Method
McDowell’s 1956 Method
McDowell (1956) Tex-124-E
Tex-124-E Procedure
McDowell (1956) Tex-124-E
• ASTM D4546
• Conventional tests performed in consolidations
frames
Conventional Swell Testing (ASTM D4546)
• Samples
compacted, load
applied
• Samples
inundated
• Vertical
deflections
measured
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
0 50 100 150 200 250 300 350 400 450 500
Sw
ellin
g (
%)
Time (hr)
ASTM D4546Method
1 Day 1 Week ~20 Days
Conventional Swell Testing (ASTM D4546)
Effect of overburden pressure:
Conventional Swell Testing (ASTM D4546)
100 1000Seating load (psf)
0
5
10
15
20
Sw
ell
(%)
16.1
8.9
5.7
6048 Centrifuge-based Approach
Centrifuge axis
Ng
Large Centrifuge at the University of Texas at Austin
Centrifuge Characteristics:
– High-g centrifuge
– Permeameter and plumbing
– Low-flow rotary fluid union
– Data acquisition system
Measurements:
– Suction (tensiometers)
– Moisture content (TDR)
– Inflow (flow pump)
– Outflow (pressure transducer)
– Swelling (LVDT)
Large Centrifuge at the University of Texas at Austin
Centrifuge Characteristics:
– High-g centrifuge
– Permeameter and plumbing
– Low-flow rotary fluid union
– Data acquisition system
Measurements:
– Suction (tensiometers)
– Moisture content (TDR)
– Inflow (flow pump)
– Outflow (pressure transducer)
– Swelling (LVDT)
Small Centrifuges for Direct Measurement of Swelling
Centrifuge Device:– Floor mounted
– Low cost
– Can achieve very high g-levels
– In-flight data acquisition system
Measurements:– Six simultaneous specimens
tested at once
– Vertical displacements
– G-level
Small Centrifuges for Direct Measurement of Swelling
Centrifuge Device:– Floor mounted
– Low cost
– Can achieve very high g-levels
– In-flight data acquisition system
Measurements:– Six simultaneous specimens
tested at once
– Vertical displacements
– G-level
Small Centrifuges for Direct Measurement of Swelling
• Soil can be compacted in permeameter cup using kneading compaction
• Water ponded on top of soil and flows through to outflow chamber
• Cutting rings allow testing of either reconstituted or undisturbed specimens
• Stress controlled by gravitational level and bronze porous disks
• Can control initial moisture content using a glove box, scale, and unsaturated salt solution
Initial Equipment (v1)
• Mounted caliper used to measure
sample height
Problem: Discontinuous readings.
• Unable to see swell trend unless
centrifuge is stopped multiple times
Initial Equipment (v1)
0
1
2
3
4
5
6
7
8
9
10
11
0 1 2 3 4
Ax
ial
Str
ain
(%
)
Test Duration (Days)
Initial Equipment (v1)
0
5
10
15
20
25
30
1 10 100 1000
Standard
Centrifuge
Resulting swell vs. stress trend significantly
higher for centrifuge
Initial Equipment (v1)
Due to substantial swell occurring
before measurement of sample
height, in-flight data acquisition
system explored further.
In-flight Proof of Concept (v2)
Sensor mount
Initial DAS
In-flight Proof of Concept (v2)
Designed from scratch based on open
source hardware platform Arduino
Takes readings from LVDT and stores
values on SD card
Battery powered
Able to fit inside centrifuge cup
In-flight Proof of Concept (v2)
Developed based on open source
hardware platform Arduino
Takes readings from LVDT and stores
values on SD card
In-flight Proof of Concept (v2)
Improvements needed:
• Increase resolution
• Add accelerometer to measure g-
level directly
• Send sensor data outside
centrifuge so it can be viewed in
real time
In-flight Prototype (v3)
24 bit
ADC
250g accelerometer
New Arduino w/ RF12 radio
Stored to file
(Labview)
In-flight Prototype (v3)
W
Sample LPS 1, 2,
3, 4
250g
acceleromete
r
1
2
24-bit ADC
Values merged into
packet & given to RF12
radio
3
Centrifuge
USB
connection
5
6
Wireless
transmission
4
In-flight Prototype (v3)
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5.00%
10.00%
15.00%
20.00%
25.00%
30.00%
0 5 10 15 20 25 30 35 40 45 50
Swe
llin
g (%
)
Time (hr)
Improvements allow:
• Much higher resolution in
measurement: 0.0005 mm
• Real time viewing of data while
testing
• Direct measurement of g-level.
In-flight Prototype (v3)
Misc. improvements:
• Lower power consumption
• Less noise
• Detachable sensors
• No wires (to break)
• Replaced centrifuge rotor
increasing slots from 4 -> 6,
allowing 4 simultaneous samples
(one used for DAS, one for
batteries)
Final In-flight DAS (v4)
Most Recent Improvements• Vastly improved quality and
accuracy of collected data
• Measurements taken while under desired stress level
• Measurements taken continuously throughout test
• Can control initial moisture content using a glove box, scale, and unsaturated salt solution
0.0%
1.0%
2.0%
3.0%
4.0%
5.0%
6.0%
7.0%
8.0%
9.0%
0 100 200 300 400 500 600
Swe
llin
g (%
)
Time (hr)
Centrifuge - Corrected
Typical Swell Test Results
TestActual ωi (%)
Actual γd (kN/m3)
θi θf S,i S,fEnd of Swell
Water Content (%)
Max Swell (%)
Swell (%)
Time to
Swell (hr)
Equiv. Stress (psf)
FS 19.3% 15.93 0.313 0.702 73% 100% 34.57% 8.02% 7.06% 18.50 125
DI 19.6% 15.67 0.313 0.635 72% 100% 32.29% 8.03% 7.88% 16.61 133
0.0%
1.0%
2.0%
3.0%
4.0%
5.0%
6.0%
7.0%
8.0%
9.0%
0 100 200 300 400 500 600
Swe
llin
g (%
)
Time (hr)
FS - 1-14
Centrifuge - Corrected
Typical Swell Test Results
TestActual ωi (%)
Actual γd (kN/m3)
θi θf S,i S,fEnd of Swell
Water Content (%)
Max Swell (%)
Swell (%)
Time to
Swell (hr)
Equiv. Stress (psf)
FS 19.3% 15.93 0.313 0.702 73% 100% 34.57% 8.02% 7.06% 18.50 125
DI 19.6% 15.67 0.313 0.635 72% 100% 32.29% 8.03% 7.88% 16.61 133
Swell-stress Curve for Eagle Ford Clay
Comparison with Results from Standard Swell Tests
Testing of Undisturbed Soil Specimens
Specimens Provided Trimmed Specimens
Typical Result using Undisturbed Soil Specimens
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3.00%
4.00%
5.00%
6.00%
0 5 10 15 20 25 30
Ve
rtic
al S
trai
n (
%)
Time (hr)
Sample 1 - In-Situ
Sample 2 - In-situ
Moisture Adjusted
Swell-stress Curve for Cook Mountain Clay
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2.0%
4.0%
6.0%
8.0%
10.0%
12.0%
14.0%
10 100 1000
Ver
tica
l Str
ain
(%
)
Effective Stress (psf)Centrifuge - 6048 ASTM D4546 - Method A Stress-Swell Curve
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
30.0%
100 1000
Ver
tica
l Str
ain
(%
)
Effective Stress (psf)Centrifuge - 6048 ASTM D4546 - Method A Stress-Swell Curve
Swell-stress Curve for Eagle Ford Clay
Benefits of the Centrifuge Testing Approach
• Expeditious
• Highly repeatable
• Generates swell data from multiple soil specimens in a single spin
• Requires comparatively small laboratory space
• Provides direct measurement of swelling:
– No need of using correlations with index properties
– Generates soil-specific, project-specific data
• Data suitable for generation of soil-specific databases
• Results can be readily used for prediction of PVR
6048(A) Methodology
• Run centrifuge tests at three different stress levels (5g, 25g, 100g)
• Generate Swell-stress curve using the centrifuge test results
• Discretize the soil profile into sub-layers:
– Soil type, initial moisture content
– Effective stresses on top and bottom of each sub-layer
• Determine swelling for each sub-layer
• Multiply by height to determine PVR contribution of each sub-layer
• Add PVR contributions to define total PVR
Site 5: Loop 1604 & Graytown Rd [HB-Gray] - Location & Identification
• Retrieved soil samples using Auger on Graytown Rd. near Loop 1604 on Northeast side of Bexar County
• USDA map identified soil as Houston Black Clay
Site 5: Loop 1604 & Graytown Rd [HB-Gray] - Soil Characterization
Test # 1 2 3 4
Predicted Liquid Limit, LL 64.5% 63.1% 62.9% 66.5%
Selected Liquid Limit, LL 64.0% 63.0% 62.5% 66.0%
Plastic Limit, PL 22.1% 22.4% 21.1% 21.4%
Plasticity Index, PI 41.9% 40.6% 41.4% 44.6%
Averaged Liquid Limit, LLavg 64%
Averaged Plastic Limit, PLavg 22%
Averaged Plasticity Index, PIavg 42%
OPTIMUM WATER
CONTENT [%]26.5
MAX DRY UNIT WEIGHT
[kN/m³]14.2
MAX DRY UNIT WEIGHT
[pcf]90.4
Tex-124-E Dry = 25.0%
Tex-124-E Avg = 32.3%
Tex-124-E Wet = 39.6%
DMS-C DOPT = 21.0%
1 2 3 4
81% 82% 78% 81%
81% 81% 78% 81%
21% 21% 23% 23%
60% 60% 55% 58%
Averaged Plasticity Index, PIavg 58%
Test #
Predicted Liquid Limit, LL
Selected Liquid Limit, LL
Plastic Limit, PL
Plasticity Index, PI
Averaged Liquid Limit, LLavg 80%
Averaged Plastic Limit, PLavg 22%
12.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
16.0
16.5
17.0
14 16 18 20 22 24 26 28 30
Dry
Un
it W
eig
ht
(kN
/m3 )
Gravimetric Water Content (%)
ZAV
S = 90%
S = 80%
S = 70%
S = 60%
S = 50%
Site 5: Loop 1604 & Graytown Rd [HB-Gray] - Centrifuge/Free Swell Results
0.00%
2.00%
4.00%
6.00%
8.00%
10.00%
12.00%
14.00%
16.00%
18.00%
20.00%
10 100 1000
Ve
rtic
al S
we
ll (%
)
Effective Stress (psf)
2V - NL
Centrifuge Results
Free Swell Results
Site 5: Loop 1604 & Graytown Rd [HB-Gray] - Assumed Soil Profile
LayerDepths [ft] Soil
Description
Liquid
Limit
Plastic
Limit
Plasticity
Index
Water Content
[%]
Unit Weight
[pcf]
Average
Pressure
From To [psf] [psi]
- +1.5 0*Asphalt +
Base Material0 0 0 - Varies 223 1.55
1 0 1
Houston Black
Clay80 22 58 23.5 112
274 1.90
2 1 2 391 2.72
3 2 3 507 3.52
4 3 4 623 4.33
5 4 5 739 5.13
6 5 6 854 5.93
7 6 7 969 6.73
8 7 8 1085 7.53
9 8 9 1200 8.33
10 9 10 1315 9.14
*Asphalt + Base Material Pressure is Assumed as a Total Applied Surcharge Load on Top of Soil Layer
Site 5: Loop 1604 & Graytown Rd [HB-Gray] - PVR Comparison
Layer Calculations DMS-C Tex-124-E
Layer Number Thickness [ft]
Top Stress
[psf]
Bottom Stress
[psf])
Avg. Stress
[psf] DOPT Dry Adj.
1 1 223 334 273 0.79 0.62 0.63
2 1 334 446 386 0.70 0.59 0.61
3 1 446 557 498 0.64 0.54 0.56
4 1 557 669 611 0.60 0.51 0.53
5 1 669 781 723 0.56 0.47 0.49
6 1 781 892 835 0.54 0.45 0.47
7 1 892 1004 947 0.51 0.41 0.43
8 1 1004 1116 1058 0.50 0.39 0.41
9 1 1116 1227 1170 0.48 0.36 0.38
10 1 1227 1339 1282 0.47 0.34 0.36
Total PVR [in] 5.79 4.67 4.87
Site 6 : FM 1976 [HB-1976] - Location & Identification
• Retrieved soil samples using auger on FM 1976 near Miller Rd. on Northeast side of Bexar County (Close to Graytown Rd.)
• USDA map identified soil as Houston Black Clay
Site 6 : FM 1979 [HB-1976] - Soil Characterization
OPTIMUM WATER
CONTENT [%]24.0
MAX DRY UNIT WEIGHT
[kN/m³]14.6
MAX DRY UNIT WEIGHT
[pcf]92.8
Tex-124-E Dry = 24.0%
Tex-124-E Avg = 30.6%
Tex-124-E Wet = 37.3%
DMS-C DOPT = 21.0%
1 2 3 4
75.5% 74.6% 75.4% 77.0%
75.0% 74.0% 75.5% 76.0%
20.6% 21.6% 20.6% 20.9%
54.4% 52.4% 54.9% 55.1%
Averaged Plasticity Index, PIavg 54%
Test #
Predicted Liquid Limit, LL
Selected Liquid Limit, LL
Plastic Limit, PL
Plasticity Index, PI
Averaged Liquid Limit, LLavg 75%
Averaged Plastic Limit, PLavg 21%
12.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
16.0
16.5
17.0
14 16 18 20 22 24 26 28 30
Dry
Un
it W
eig
ht
(kN
/m3 )
Gravimetric Water Content (%)
ZAV
S = 90%
S = 80%
S = 70%
S = 60%
S = 50%
Site 6: FM 1976 [HB-1976] - Centrifuge/Free Swell Results
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2.00%
4.00%
6.00%
8.00%
10.00%
12.00%
14.00%
16.00%
18.00%
20.00%
10 100 1000
Vert
ical
Sw
ell (
%)
Effective Stress (psf)
2V - NL
Centrifuge Results
Free Swell Results
Site 6: FM 1976[HB-1976] - Assumed Soil Profile
LayerDepths [ft] Soil
Description
Liquid
Limit
Plastic
Limit
Plasticity
Index
Water Content
[%]
Unit Weight
[pcf]
Average
Pressure
From To [psf] [psi]
- +1.5 0*Asphalt +
Base Material0 0 0 - Varies 223 1.55
1 0 1
Houston Black
Clay75 21 54 21 112
273 1.90
2 1 2 387 2.69
3 2 3 500 3.47
4 3 4 613 4.26
5 4 5 726 5.04
6 5 6 839 5.83
7 6 7 951 6.61
8 7 8 1064 7.39
9 8 9 1177 8.17
10 9 10 1289 8.95
*Asphalt + Base Material Pressure is Assumed as a Total Applied Surcharge Load on Top of Soil Layer
Site 6: FM 1976 [HB-1976] - PVR Comparison
Layer Calculations DMS-C Tex-124-E
Layer Number Thickness [ft]
Top Stress
[psf]
Bottom Stress
[psf])
Avg. Stress
[psf] DOPT Dry Adj.
1 1 223 335 273 0.58 0.60 0.66
2 1 335 447 387 0.50 0.56 0.62
3 1 447 560 500 0.44 0.52 0.58
4 1 560 672 613 0.40 0.48 0.54
5 1 672 785 726 0.37 0.45 0.51
6 1 785 897 839 0.34 0.42 0.48
7 1 897 1009 951 0.32 0.39 0.46
8 1 1009 1122 1064 0.30 0.36 0.42
9 1 1122 1234 1177 0.29 0.33 0.39
10 1 1234 1347 1289 0.27 0.31 0.37
Total PVR [in] 3.80 4.41 5.04
Site 8: FM2924 [MC] - Location & Identification
• Retrieved soil samples using Auger on FM2924 near Fashing in the Southeastern most portion of Atascosa County
• USDA map identified soil as Monteola Clay
Site 8: FM2924 [MC] - Soil Characterization
OPTIMUM WATER
CONTENT [%]24.0
MAX DRY UNIT WEIGHT
[kN/m³]13.4
MAX DRY UNIT WEIGHT
[pcf]85.3
Tex-124-E Dry = 25.0%
Tex-124-E Avg = 32.3%
Tex-124-E Wet = 39.6%
DMS-C DOPT = 23.5%
12.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
16.0
16.5
17.0
14 16 18 20 22 24 26 28 30 32D
ry U
nit
We
igh
t (k
N/m
3)
Gravimetric Water Content (%)
ZAV
S = 90%
S = 80%
S = 70%
S = 60%
S = 50%
1 2 3 4
82.1% 80.2% 82.0% 78.2%
82.0% 79.5% 82.0% 78.0%
24.4% 22.7% 23.3% 23.8%
57.6% 56.8% 58.7% 54.2%
Averaged Plasticity Index, PIavg 56%
Test #
Predicted Liquid Limit, LL
Selected Liquid Limit, LL
Plastic Limit, PL
Plasticity Index, PI
Averaged Liquid Limit, LLavg 80%
Averaged Plastic Limit, PLavg 24%
Site 8: FM2924 [MC] - Centrifuge/Free Swell Results
0.00%
2.00%
4.00%
6.00%
8.00%
10.00%
12.00%
14.00%
16.00%
18.00%
20.00%
10 100 1000
Vert
ical
Sw
ell (
%)
Effective Stress (psf)
2V - NL
Centrifuge Results
Free Swell Results
Site 8: FM2924 [MC] - Assumed Soil Profile
LayerDepths [ft] Soil
Description
Liquid
Limit
Plastic
Limit
Plasticity
Index
Water Content
[%]
Unit Weight
[pcf]
Average
Pressure
From To [psf] [psi]
- +1.5 0*Asphalt +
Base Material0 0 0 - Varies 223 1.55
1 0 1
Monteola
Clay80 24 56 21 103
269 1.87
2 1 2 374 2.60
3 2 3 478 3.32
4 3 4 581 4.04
5 4 5 685 4.76
6 5 6 788 5.48
7 6 7 892 6.19
8 7 8 995 6.91
9 8 9 1099 7.63
10 9 10 1202 8.35
*Asphalt + Base Material Pressure is Assumed as a Total Applied Surcharge Load on Top of Soil Layer
Site 8: FM2924 [MC] - PVR Comparison
Layer Calculations DMS-C Tex-124-E
Layer Number Thickness [ft]
Top Stress
[psf]
Bottom Stress
[psf])
Avg. Stress
[psf] DOPT Dry Adj.
1 1 223 326 269 1.02 0.59 0.65
2 1 326 429 374 0.89 0.57 0.63
3 1 429 532 478 0.80 0.52 0.58
4 1 532 635 581 0.73 0.49 0.55
5 1 635 739 685 0.68 0.47 0.53
6 1 739 842 788 0.64 0.43 0.49
7 1 842 945 892 0.61 0.40 0.45
8 1 945 1048 995 0.58 0.38 0.44
9 1 1048 1151 1099 0.56 0.36 0.42
10 1 1151 1255 1202 0.54 0.32 0.38
Total PVR [in] 7.05 4.53 5.10
Remarks on PVR Determination using Centrifuge Testing
• Procedure is consistent with PVR determination using Tex-124-E
• Uses soil-specific and project-specific experimental data
• Does not require corrections (e.g. volumetric swelling, stress level, unit weight, % binder)
• Predictions using Tex-124-E may result in significant errors, sometimes on the conservative, sometimes on the unconservative side
Conclusions• The concept of PVR is useful and considers the appropriate
variables
• PVR prediction using Tex-124-E involves a significant number of correlations, defined using dated and extremely scarce data
• The use of centrifuge technology leads to the direct determination of soil swelling in an expeditious, repeatable manner
• Swelling results obtained using centrifuge testing match excellently those obtained using conventional swell tests
• Centrifuge testing is particularly suitable to define project-specific swell-stress relationships, which can be directly used for prediction of the PVR
Jorge G. Zornberg, Ph.D., P.E.The University of Texas at AustinImmediate Past-president, IGS
11 October 2016College Station, TX