jorge g. zornberg, ph.d., p.e. - texas a&m university · 2017-01-04 · jorge g. zornberg,...

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

Original ground profile

CL

Location of longitudinal cracks

Pavements on Expansive Clays

Source: Zornberg and Gupta (2009)

6


7


8


9


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


Effect of overburden pressure:


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)

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


0

1

2

3

4

5

6

7

8

9

10

11

0 1 2 3 4

Ax

ial

Str

ain

(%

)

Test Duration (Days)


0

5

10

15

20

25

30

1 10 100 1000

Standard

Centrifuge

Resulting swell vs. stress trend significantly

higher for centrifuge


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


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


Developed based on open source

hardware platform Arduino

Takes readings from LVDT and stores

values on SD card


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)


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


0.00%

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.


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

0.00%

1.00%

2.00%

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

0.0%

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%


Test #

Predicted Liquid Limit, LL

Selected Liquid Limit, LL

Plastic Limit, PL

Plasticity Index, PI



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%


Test #



Plastic Limit, PL




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 )


ZAV

S = 90%

S = 80%

S = 70%

S = 60%

S = 50%

Site 6: FM 1976 [HB-1976] - 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 (

%)


2V - NL

Centrifuge Results

Free Swell Results

Site 6: FM 1976[HB-1976] - Assumed Soil Profile


Description

Liquid

Limit

Plastic

Limit

Plasticity

Index

Water Content

[%]

Unit Weight

[pcf]

Average

Pressure

From To [psf] [psi]

- +1.5 0*Asphalt +


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


Site 6: FM 1976 [HB-1976] - PVR Comparison



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)


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%


Test #



Plastic Limit, PL




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 (

%)


2V - NL

Centrifuge Results

Free Swell Results

Site 8: FM2924 [MC] - Assumed Soil Profile


Description

Liquid

Limit

Plastic

Limit

Plasticity

Index

Water Content

[%]

Unit Weight

[pcf]

Average

Pressure

From To [psf] [psi]

- +1.5 0*Asphalt +


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


Site 8: FM2924 [MC] - PVR Comparison



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

jorge g. zornberg, ph.d., p.e. - texas a&m university · 2017-01-04 · jorge g. zornberg,...

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