Expansive soils and practice in foundation engineering

Expansive soils and practice in foundation engineering

Jay X. Wang, Ph.D., P.E. Programs of Civil Engineering and

Construction Engineering Programs Louisiana Tech University

3/7/2016 2016 Louisiana Transportation Conference

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Facts about expansive soils

• Cracked foundations, pavements, floors and basement walls are typical types of damage done by swelling soils. Every year they cause billions of dollars in damage.

• The ASCE estimates that 1/4 of all homes in the United States have some damage caused by expansive soils. In a typical year in the United States they cause a greater financial loss to property owners than earthquakes, floods, hurricanes and tornadoes combined (USGS website).

• 60 percent of the 250,000 new homes built on expansive soils each year in the US experience minor damage and 10 percent experience significant damage (Holtz and Hart, 1978).


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• Expansive soils are not as dramatic as hurricanes or earthquakes and they cause only property damage, not loss of life.

• Expansive soils act more slowly and the damage is spread over wide areas rather than being concentrated in a small locality (Coduto et al., 2015).

• Swelling clays can exert uplift pressures of as much as 5,500 psf (Rogers et al.).

• Liquid limits exceeding 50 percent and plasticity index over 30, usually have high inherent swelling capacity.

• Expansive clay soils can be easily recognized in the dry season by the deep cracks, in roughly polygonal patterns, in the ground surface.


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Desiccation cracks in soil caused by drying

(UACE)

(Rogers et al.)


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Annual Damage in the US from expansive soils (Jones and Jones, 1987)

Category Annual Damage ($)

Highways and streets 4,550,000,000

Commercial buildings 1,440,000,000

Single family homes 1,200,000,000

Walks, drives and parking areas

440,000,000

Buried utilities and services 400,000,000

Multi-story buildings 320,000,000

Airport installations 160,000,000

Involved in urban landslides 100,000,000

Other 390,000,000

Total annual damages (1987) 9,000,000,000


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Swelling Clays Map of the Conterminous United States" (Olive et al., 1989)


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Approximate distribution of major montmorillonite clay deposits in the US

(Tourtelot, 1973)


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Damage cases on buildings and pavements


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A cost of $490,000 spent to repair this and other walls, ceilings, doors and windows, represented nearly one-third of the original cost of the six-year-

old building (Colorado Geological Survey)


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Building damage: displaced bricks and inward deflection of foundation (UACE)


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Differential settlement due to influence of trees (Clayton et al., 2010)


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Structural damage to house caused by ‘end lift’ (Peter Kelsey & Partners)


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Longitudinal cracks along pavement shoulders

(Sebesta, 2005) (Sawangsuriya et al, 2011)


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Longitudinal cracks in the middle of pavements


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http://www.capitalgeotechnical.com/pavementcracking.html

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=&url=http://www.pavementinteractive.org/article/dowel-bar-retrofit-construction-practices/&ei=0xpIVefpJIzUgwTKzYOoCg&bvm=bv.92291466,d.eXY&psig=AFQjCNGkD1L_cfn9-DQyP8zuxJfEhDAdFQ&ust=1430875220016398

Linear heave ridges

(Noe, 2007) (fhwa.dot.gov)


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http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http://coloradogeologicalsurvey.org/geologic-hazards/swelling-soils/definition/&ei=1hpIVb-LBYPysAWHsYDwDA&bvm=bv.92291466,d.eXY&psig=AFQjCNGkD1L_cfn9-DQyP8zuxJfEhDAdFQ&ust=1430875220016398

Differential heave from steeply dipping expansive bedrock


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Swimming pool in expansive soils (Rogers et al.)


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The layer of soil that has a fluctuating moisture content

(Coduto et al., 2015)


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Depth of the active zones in selected cities (O’Neill and Poormoayed, 1980)


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Profile of expansive soils from Denver International Airport, Denver, Colorado (CSU 2004; Chao 2007)


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Profile of expansive soils from Fort Sam Houston, San Antonio, Texas (Nelson et al., 2015)


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Annual fluctuation in moisture content on expansive soil (Elarabi)


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Idealized pore water pressure profile (Nelson et al., 2015)


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Soil-water characteristic curve for ordinary curves (Nelson et al, 2015)


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Identification, Testing and Evaluation of Expansive Soils

• Visual identification – Have significant clay content, CL or CH. – Dry expansive soils often have fissures, slickensides, or

shattering – When dry, the soils have cracks at the ground surface

• Determination of degree of expansiveness – A wide variety of testing evaluation methods

available, but none of them universally or even widely accepted.

– Qualitative method; semi-quantitative method and quantitative method (Coduto et al., 2015)


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Qualitative Methods


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Correlations of swelling potential with common soil tests (Holtz, 1969)


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Correlations of swelling potential with common soil tests (Chen, 1988)


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Semi-quantitative evaluations

• In terms of swell potential, measured in some kind of loaded swell test

• Usually a laterally confined cylindrical specimen, initially dry specimen loaded with a surcharge, then soaked. The specimen swells vertically.

• This displacement divided by the initial height (immediately before soaking) is the swell potential, usually expressed as a percentage.


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Regular lab test to characterize expansive soils

• Standards for the performance of oedometer tests to measure expansion potential are set forth ASTM D4536.

• Two basic types of oedometer tests: the consolidation-swell (CS) test, and the constant volume (CV) test.

• The consolidation-swell test – Soil sample initially subjected to a prescribed vertical stress and inundated under that

constant vertical stress. – The vertical strain that occurs due to wetting is called percent swell. – After the swelling has been completed the sample may be subjected to additional vertical

load. The pressure that would be required to rescore the sample to its original height is termed the “consolidation-swell swelling pressure”.

• The constant volume test – Soil sample is initially subjected to a prescribed vertical stress. – During inundation the sample is confined from swelling and the stress that is required to

prevent swell is measured. – The stress is termed the constant volume swelling pressure.

• Results normally plotted in the form of vertical strain as a function of the applied stress in a logarithmic scale


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Determination of heave index CH


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ASTM Standard Loaded Swell Tests

• ASTM D4546-14 provides standards for the loaded swell test, Methods A, B and C.

• Method A – A sample of fill material from the project is compacted into

a lab specimen at the field specified dry unit weight and water content, placed in consolidometer.

– The specimen is loaded to a vertical stress, equal to the overburden stress at the depth of fill.

– The specimen is inundated in water and allowed to swell – Test is repeated with new specimens each loaded to

different overburden stress. – Potential swell calculated.


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Loading steps followed in Method A


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ASTM Standard Loaded Swell Tests (cont’d)

• Method B – Performed on undisturbed field specimens, specimens

can be from fill material or natural material depending on the project.

– Specimen is placed in a consolidometer. – The specimen is loaded to a vertical stress, equal to

the overburden pressure plus the induced stress from structural foundation loads, and its deformation is measured.

– The specimen is inundated in water and allowed to swell, and the deformation is measured.

– Potential swell calculated.


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Loading steps followed in Method B


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ASTM Standard Loaded Swell Tests (cont’d)

• Method C – A test is run after Method A or Method B. – An alternative way to determine the swell pressure,

that is the vertical stress at which the sample returns to its original height.

– After swelling has completed and the soil has reached Point B in the figure in next slide, and then a standard consolidation test is performed to determine the post swelling deformation versus stress curve.

– The magnitude of the swell pressure determined using Method C will be different than that determined using either Method A or B.


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Loading steps followed in Method C


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Summary of Test Parameters for Test Methods A, B and C specified in ASTM D4546 (Coduto et al., 2015)


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Typical classification of soil expansiveness based on loaded swell test, results at in-situ

overburden stress (Snethen, 1984)


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Expansion Index Test (ASTM D4829-11) • A soil specimen is remolded into a standard 102 mm (4.01 in)

diameter, 24.5 mm (1 in) tall ring at a degree of saturation of about 50 percent.

• A surcharge load of 6.9 kPa (1 lb/in2) is applied, and then the specimen is saturated and allowed to stand until the rate of swelling reaches a certain value or for 24 h.

• The percentage of free swell may be expressed as 𝑠𝑤 𝑓𝑟𝑒𝑒 % =ℎ

𝐻(100)

• The amount of swell is expressed in terms of the expansion index, EI


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Interpretation of Expansion Index Test Results (ASTM D4829-11)


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Empirical correlations between swell potential and different combinations of basic engineering properties (Vijayvergiya and

Ghazzaly, 1973)


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The free surface swell relationship developed by O’Neill and Poormoayed

(1980)

∆𝑆𝐹 = 0.0033 𝑍 𝑠𝑤 𝑓𝑟𝑒𝑒 %


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Ground heave prediction equations (adapted from Azam and Chowdhury, 2013)

Method Equation Material Parameter Description

Fredlund et al. ∆𝐻 = 𝐶𝑠

𝐻

1 + 𝑒0𝑙𝑜𝑔

𝑃𝑓

𝑃𝑠

𝑃𝑓 – Final stress state,

𝑃𝑠 – Corrected swelling pressure

H – Thickness of soil layer

e0 – initial void ratio

Cs – Swelling index

Vanapalli and

Lu ∆𝐻 = 𝐶𝑠

𝐻

1 + 𝑒0𝑙𝑜𝑔

𝐾𝑃𝑓

10𝐶𝑠𝐶𝑤

∆𝑤

𝐶𝑤 = 0.019𝑒0.0343𝐼𝑝

𝐾 = 0.0039𝑒0.64(∆𝑤)

Ip – Plasticity index

Cw - Suction modulus ratio

∆𝑤 – Change in water content

Briaud et al. ∆𝐻 = 𝐻𝑓 ∆𝑤 − 𝐸𝑤 𝐸𝑤 = ∆𝑤 ∆𝑉/𝑉𝑜

𝐻𝑓 – Thickness of expansive soil layer

𝐸𝑤 – Shrinkage-swell modulus

Dhowian ∆𝐻 = 𝐻

𝛼𝐺𝑠

1 + 𝑒0𝑤𝑓 − 𝑤𝑖

𝐺𝑠 – Specific gravity

𝛼 – Volume compressibility factor

𝑤𝑓 − 𝑤𝑖 – Water content change

Snethen ∆𝐻 = 𝐻

𝐶𝜏

1 + 𝑒0𝐴 − 𝐵𝑤0 − 𝑙𝑜𝑔 𝜏𝑚𝑓 + 𝛼𝜎𝑓

𝐶𝜏 = 𝛼𝐺𝑠/100𝐵

𝐶𝜏 – Suction index

𝑤0 – Initial water content

A – Y-intercept of gravimetric SWCC

B – Slope of gravimetric SWCC

𝜏𝑚𝑓 – Final matric suction

𝛼 – Compressibility factor

𝜎𝑓 – Final applied pressure


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Summary of Empirical Heave Prediction (Nelson et al., 2015)


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Contours plot of Swelling Potential in

Louisiana (1)

SP = 0.00216IP2.44

Swelling potential % Percentage of soil swell from optimum moisture content to the saturated moisture content IP = Plasticity index


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Contours plot of Swelling Potential in Louisiana (2)


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Characterization of expansive soils in Northern Louisiana


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Soil Sampling

2833 Viking Dr, Bossier City, LA 71111 First United Pentecostal Church


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Boring log from adjacent area (Ben Fernandez, LA DOTD, 08/15)


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Soil Compaction Lab Tests

1.25

1.30

1.35

1.40

1.45

1.50

1.55

0 5 10 15 20 25 30 35 40 45

Dry

den

sity

, ρ

d (

gm

/cm

³)

Moisture content, w(%)

Dry unit weight vs moisture content

Zero air void unit weight standard proctor test

γd(max) = 1.48 gm/cm3

Liquid limit (LL)

Plastic Limit (PL)

Plasticity Index (PI)

Activity (Ac)

77 28 49 1.23


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WP4-T test for dry side of SWCC

Undisturbed soil sample (left), soil getting saturated before introducing to pressure plate (middle), saturated soil inside the pressure plate extractor (right)


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SWCC curve for Moreland clay in Northern Louisiana

0

10

20

30

40

50

60

1 10 100 1000 10000 100000 1000000

Mois

ture

(%

)

Suction (kPa)

Gravimetric Moisture (%)

Volumetric moisture (%)


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Consolidation test

Swelling pressure Ps = 170 kPa, The compression index Cc = 0.36, and the swelling index Cs = 0.11.


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Prediction of soil heave


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Case history of a slab-on-grade floor on Regina clay, Canada (Vu and Fredlund, 2004)

Investigation of volume change problems associated with the heave of a floor slab of a light industrial building in north-central Regina, Saskatchewan, Canada. Construction of the building and instrumentation took place during the

month of August 1961. Instrumentation installed at the site included a deep benchmark, vertical

movement gauges, and a neutron moisture meter access tube. Vertical ground movement was monitored at depths of 0.58, 0.85, and 2.39 m

below original ground level. The building owner noticed heave and cracking of the floor slab in early

August 1962, about a year after construction. The owner also noticed an unexpected increase in water consumption of

approximately 35 000 L. The loss of water was traced to a leak in a hot-water line beneath the floor slab, which was subsequently repaired.

The location of the cracking and contours of heave for the floor slab are shown in next slide.


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Geometry and boundary conditions (Vu and Fredlund, 2004)


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Seepage analysis model (Vadose/W)

• Vadose/W model for seepage analysis.

• Suction based initial condition has been used with 888 kPa at surface and 12 kPa at bottom. A linear interpolation has been adopted to specify conditions along the depth profile.

q= 3.12 X 10-9 ms-1 Uw = -888 kPa Uw = -888 kPa

Uw = -12 kPa

q= 0 q= 0

q= 0 q= 0

60 3/7/2016 2016 Louisiana Transportation Conference

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Calibration/Validation

• Model has been calibrated by comparing results with Vu and Fredlund et al. (2004) findings.

• Suction along depth at various times obtained from Vadose/W analysis (top) shows close approximation with FlexPDE results (bottom).

Pore water pressure profile for various times with depth

0 sec

432000 sec

1728000 sec

4320000 sec

Ele

va

tio

n (

m)

Pore-Water Pressure (kPa)

0

0.5

1

1.5

2

2.5

3

-100-200-300-400-500-600-700-800-900 0

Initial

5 days

20 days

50 days


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Heave Analysis Model

• Heave Analysis model without slab load.

• Same initial and boundary conditions as seepage analysis have been used. Structural support has also been used to ensure no horizontal or vertical movement.

Uw = -888 kPa Uw = -888 kPa

q= 3.12 X 10-9 ms-1

Uw = -12 kPa

q= 0

q= 0 q= 0

q= 0

Horizontal displacement= 0

Vertical displacement= 0


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Heave Analysis Result

Resulted heave dominated near the leak location.

The contour is showing the heave.

63

Leak water line

Occurred heave


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Heaves at different times after leak

Heave at surface (without slab load)

0 sec

43200 sec

1728000 sec

4320000 sec

He

ave

/ ve

rtic

al-D

isp

lace

me

nt

(m)

Distance (m)

-0.01

0

0.01

0.02

0.03

0.04

0.05

5 10 15

64

Initial

5 days

20 days

50 days


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Verification of Prediction models on the field performance of Geosynthetic Reinforced Pavements over Expansive Clay Subgrades

65

Brief descriptions of the field investigation program • Field investigation -- A comprehensive field program involving 32

pavement test sections with various combinations of reinforcements. • Texas Farm-to-Market Road No.2 (FM 2), located in the Grimes

County, southeast part of Texas. • The field testing program included unreinforced and reinforced

sections. The reinforced section further consisted of one of the three types of geosynthetic reinforcements i.e., geogrid type 1 (G1) or geogrid type 2 (G2) or a geotextile (G3).

• The field program includes moisture sensor profiles, which were installed in both horizontal and vertical direction below the pavement during its construction.

(Zornberg, et al. 2010)

3/7/2016 2016 Louisiana Transportation Conference Baton Rouge 02/28 - 03/02/16

Moisture sensor (a) Horizontal profile (b) Vertical profile below the pavement


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Seepage analysis model (Vadose/W)

• Vadose/W model for seepage analysis.

• Suction based initial condition has been used. Suction value at surface to 4m depth with a 0.5m interval obtained from Zornberg et al. paper used as initial condition.

• Hydraulic boundary has been forced by time dependent climate data and unit flux of 3.935e-8 m/s at two ditches. At all other locations no flux boundary condition has been used.

q= 0 q= 0

Climate boundary

Unit flux = 3.935e-8 m/s

67

Unit flux = 3.935e-8 m/s

Climate boundary

q= 0

q= 0

q= 0


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Water Content result(Ongoing research):

• The purpose of this study is to validate the measured gravimetric water content at various depth at field with numerical simulation by Vadose/W.

• The top and bottom parts of numerical simulations result closely validate with field data.

• The validation for rest of the curve is under current research.

68

Gravimetric water content profiles from the boreholes: Station 199

0

0.5

1

1.5

2

2.5

3

0 0.05 0.1 0.15 0.2 0.25 0.3

De

pth

(m

)

Gravimetric water Content

Gravimetric Water Content Profile (Station 199)

January

August


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Development of a Mechanistic-based

Design Method for Geosynthetic-Reinforced Pavement on Expansive

Soils


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https://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=https://failures.wikispaces.com/Expansive+Soils+Failures+Overview&ei=bR1IVamhB4HnsQW19oCYAQ&bvm=bv.92291466,d.eXY&psig=AFQjCNGkD1L_cfn9-DQyP8zuxJfEhDAdFQ&ust=1430875220016398

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=https://failures.wikispaces.com/Expansive+Soils+Failures+Overview&ei=bR1IVamhB4HnsQW19oCYAQ&bvm=bv.92291466,d.eXY&psig=AFQjCNGkD1L_cfn9-DQyP8zuxJfEhDAdFQ&ust=1430875220016398

Heave-vertical load relationship


Baton Rouge 02/28 - 03/02/16 71

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Expansive soils and practice in foundation engineering

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