1 lesson 2: soils and aggregates cee 595 construction materials winter quarter 2008
TRANSCRIPT
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Lesson 2: Soils and Aggregates
CEE 595 Construction MaterialsWinter Quarter 2008
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Lesson 2: Soil and Aggregate Topics
• Soils– Soil classification systems– Soil related tests
• Aggregates– Aggregate Production– Aggregate Characterization
Soils
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Laterite Soil—Brazil—Aerial View
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Laterite Soil—Costa Rica--Close-up
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Soil Classification
• Two major soil classification systems used in the US– “AASHTO” Classification (ASTM D3282, AASHTO
M145)– Unified Soil Classification (USBR, 1973 and ASTM
D2487)
• Why classify a soil? (USBR)– Identifies and groups soils of similar engineering
characteristics.– Provides a “common language” to describe soils.– In a limited manner, soil classifications can provide
approximate values of engineering characteristics.
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Soil Classification
• How do classification systems work?– Determine gradation
• Is the dominant percentage of particles larger or “granular”
• Is the dominant percentage of particles “fine graded” (or silt-clay sizes).
– Perform Atterberg Limit tests (more on these tests shortly).
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Soil Classification—Highway Oriented System
• ASTM D3282 and AASHTO M145: Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes.
• Classification Groups split into– Granular Materials: Contains 35% or less
passing the No.200 sieve. These groups generally make good to excellent subgrades.
– Silt-Clay Materials: Contains more than 35% passing a No.200 sieve. These groups generally are fair to poor as subgrades.
Sieves used in ASTM D3282 and AASHTO M145
No.10 No.40 No.200
No. 10 Sieve—Close-up View
No. 40 Sieve—Close-up View
No. 200 Sieve—Close-up View
Soil Classification—Highway Oriented SystemSoil Group Granular
MaterialsSilt-Clay Materials
A-1 Well-graded mixture of stone fragments, gravel, and/or sand.
A-2 Silty or clayey gravel and sand.
A-3 Fine sand.
A-4 Silty soils.
A-5 Silty soils. Similar to A-4. Can be highly elastic.
A-6 Clayey soils.
A-7 Clayey soils. Similar to A-6 except for high liquid limits.
Soil Classification—Highway Oriented System
Soil Group
% Passing Sieve
Granular Materials
Silt-Clay Materials
A-1 No.10No.40No.200
--50% max25% max
A-2 No.10No.40No.200
----35% max
A-3 No.10No.40No.200
--51% max10% max
A-4 No.10No.40No.200
----36% min
A-5 No.10No.40No.200
----36% min
A-6 No.10No.40No.200
----36% min
A-7 No.10No.40No.200
----36% min
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Soil Classification—Highway Oriented System
• Additional tests required to perform classification grouping.– Liquid Limit (AASHTO T89, ASTM D4318): “The water
content, in percent, of a soil at the arbitrarily defined boundary between the liquid and plastic states.” See next image to view the device used to determine LL. The higher the LL, the poorer the soil.
– Plastic Limit (PL) and Plasticity Index (AASHTO T90, ASTM D4318): “The water content, in percent, of a soil at the boundary between the plastic and brittle states.” Plasticity Index (PI) is the “range of water content over which a soil behaves plastically.” PI = LL – PL. The higher the PI, the poorer the soil.
Liquid Limit Device
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Soil Classification—Unified Soil Classification System
• ASTM D2487: Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Classification Groups split into– Coarse-grained soils: More than 50%
retained on a No.200 sieve.– Fine-grained soils: 50% or more passes
the No.200 sieve.
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Soil Classification—Unified Soil Classification System
• Coarse-grained soils: More than 50% retained on a No.200 sieve.– Gravels: More than 50% of coarse
fraction retained on No.4 sieve.– Sands: 50% or more of coarse fraction
passes No.4 sieve.
• Fine-grained soils: 50% or more passes the No.200 sieve.– Silts and Clays: LL less than 50%.– Silts and Clays: LL 50% or more.
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Unified Soil Classification System—Additional Terminology
• Gravel: Particles of rock passing a 3 in. sieve but retained on a No.4 sieve.
• Sand: Particles of rock passing a No.4 but retained on a No.200.
• Clay: Soil passing a No.200 that exhibits plasticity (putty-like properties) within a range of water contents. Exhibits considerable strength when air dry.
• Silt: Soil passing a No.200 that is nonplastic or very slightly plastic and that exhibits little or no strength when air dry.
No.4 Sieve—Close-up View
Unified Soil Classification System—Additional Terminology
Soil Group Symbol Group Name
GW Well-graded gravel
GP Poorly graded gravel
GM Silty gravel
GC Clayey gravel
SW Well-graded sand
SP Poorly graded sand
SM Silty sand
SC Clayey sand
CL Lean clay
ML Silt
OL Organic silt or clay
CH Fat clay
MH Elastic silt
OH Organic silt or clay
Pt Peat
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Unified Soil Classification System
• As shown in the prior image, the primary goal of this classification system is to determine the group for a specific soil (such as CL, etc.). To fully describe how this is done is too detailed for this lesson—but the process is fully described in ASTM D2487. Basically, it is a combination of sieve analyses and Atterberg Limits (LL, PL, PI).
• The following table shows typical engineering characteristics associated with the Unified Soil Classification System (from USBR, 1973).
Unified Soil Classification SystemTypical Properties (USBR)Soil Group
Maximum Dry Density (pcf)
Optimum water content (%)
Permeability (ft per year)
GW >119 <13.3 27,000
GP >110 <12.4 64,000
GM >114 <14.5 >0.3
GC >115 <14.7 >0.3
SW 119 13.3 --
SP 110 12.4 >15.0
SM 114 14.5 7.5
SM-SC 119 12.8 0.8
SC 115 14.7 0.3
Unified Soil Classification SystemTypical Properties (USBR)Soil Group
Maximum Dry Density (pcf)
Optimum water content (%)
Permeability (ft per year)
ML 103 19.2 0.59
ML-CL 109 16.8 0.13
CL 108 17.3 0.08
OL -- -- --
MH 82 36.3 0.16
CH 94 25.5 0.05
OH -- -- --
Unified Soil Classification SystemTypical Properties (FAA)Soil Group
Maximum Dry Density (pcf)
Field CBR (%) Subgrade k (psi/in)
GW 125-140 60-80 300 or more
GP 120-130 35-60 300 or more
GM 130-145 40-80 300 or more
GC 120-140 20-40 200-300
SW 110-130 20-40 200-300
SP 105-120 15-25 200-300
SM 120-135 20-40 200-300
SM-SC -- -- --
SC 105-130 10-20 200-300
Unified Soil Classification SystemTypical Properties (FAA)Soil Group
Maximum Dry Density (pcf)
Field CBR (%) Subgrade k (psi/in)
ML 100-125 5-15 100-200
ML-CL -- -- --
CL 100-125 5-15 100-200
OL 90-105 4-8 100-200
MH 80-100 4-8 100-200
CH 90-110 3-5 50-100
OH 80-105 3-5 50-100
Unified Soil Classification SystemTypical Properties (FAA)Soil Group Value as a Foundation
When Not Subject to Frost Action
Potential Frost Action
GW Excellent None to Very Slight
GP Good to Excellent None to Very Slight
GM Good to Excellent Slight to Medium
GC Good Slight to Medium
SW Good None to Very Slight
SP Fair to Good None to Very Slight
SM Good Slight to High
SM-SC -- --
SC Fair to Good Slight to High
Unified Soil Classification SystemTypical Properties (FAA)Soil Group Value as a Foundation
When Not Subject to Frost Action
Potential Frost Action
ML Fair to Poor Medium to Very High
ML-CL -- --
CL Fair to Poor Medium to High
OL Poor Medium to High
MH Poor Medium to Very High
CH Poor to Very Poor Medium
OH Poor to Very Poor Medium
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Soil Related Tests
• Soil compaction• Strength or stiffness of soils
– Laboratory– Field
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Soil compaction
• Soil compaction is the process of “artificially” increasing the density (unit weight) of a soil by compaction (by application of rolling, tamping, or vibration).
• Standards are needed so that the amount of increased density needed and achieved can be measured.
• Two compaction tests are commonly performed to achieve this information.
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Soil Compaction: Moisture-Density Tests
• Moisture-density testing as practiced today was started by R.R. Proctor in 1933. His method became known as the “standard Proctor” test.
• This test (today described by ASTM D698 and AASHTO T99) applied a fixed amount of compaction energy to a soil at various water contents. Specifically, this involves dropping a 5.5 lb weight 12 inches and applying 25 “blows” per layer in 3 layers in a standard sized mold. Thus, 12,375 ft-lb per ft3 of compaction effort is applied.
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Soil Compaction: Moisture-Density Tests
• US Army Corps of Engineers developed “Modified Proctor” or “Modified AASHTO” to accommodate compaction needs associated with heavier aircraft used in WW 2.
• ASTM D1557 and AASHTO T180: “Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lb/ft3)”
• Refer to relative location of compaction curves on the next image. The higher the compaction energy, the lower the optimum water content and the higher the dry density.
Water Content (%)
Dry Density (lb/ft3)
Typical Compaction Curves
Typical for Modified
Compaction
Typical for Standard
Compaction
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Soil Compaction—Typical Compaction Specification
• Section 2-03.3(14)C, Method C: “Compacting Earth Embankments”– “Each layer of the entire embankment shall be
compacted to 95 percent of the maximum density as determined by the compaction control tests described in Section 2-03.3(14)D. In the top 2 feet, horizontal layers shall not exceed 4 inches in depth before compaction. No layer below the top 2 feet shall exceed 8 inches in depth before compaction.”….
– “Under Method C, the moisture content shall not vary more than 3 percent above or below optimum determined by the tests in described in Section 2-03.3(14)D.”….
– Go to next image.
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Soil Compaction—Typical Compaction Specification
• Section 2-03.3(14)D: “Compaction and Moisture Control Tests”– “The maximum density and optimum moisture for
materials with less than 30 percent, by mass, retained on the US No.4 sieve shall be determined …[by]… AASHTO T99.”
– The are many more requirements that relate to specifying soil compaction but these two images provide a quick but focused example.
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Strength or Stiffness of Soils
• Typical tests of soil strength are:– Shear strength tests– Index types of tests
• California Bearing Ratio (CBR)• Modulus of subgrade reaction (k)• Stabilometer Test (Hveem method)• Cone penetrometers
– Resilient modulus test– CBR, R-value, cone penetrometers, and
resilient modulus tests will be briefly covered.
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California Bearing Ratio
• The CBR test is a relative measure of shear strength for unstabilized materials and the results are stated as a percentage of a high quality crushed limestone—thus all results are shown as percentages. A CBR = 100% is near the maximum possible. CBRs of less than 10% are generally weak soils.
• The test was originally developed by O. J. Porter of the California Division of Highways in 1928. The widespread use of the CBR test was created by the US Corps of Engineers during WW 2.
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California Bearing Ratio
• The CBR test can be reviewed in the WSDOT Pavement Guide, Module 4 (Design Parameters), Section 2 (Subgrade)--http://hotmix.ce.washington.edu/wsdot_web/index.htm
• The CBR test is only conducted on unstabilized materials (soils or aggregates).
• The test is most always done in the laboratory; however, a field test is available but rarely conducted.
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California Bearing Ratio
Test apparatus and specimen. Photo by ELE International
Standard methods: ASTM D1883, AASHTO T193.
Correlations between CBR, AASHTO and Unified classification systems, the DCP, and k.
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R-value
• This test was developed in California by Hveem and Carmany in the late 1940’s.
• In effect, it is a relative measure of stiffness since the test apparatus operates somewhat like a triaxial test.
• The test is mostly used by western states for highway base and subgrade characterization.
• Use of this test is likely declining a bit.• ASTM D2844 and AASHTO T190: “Resistance R-
Value and Expansion Pressure of Compacted Soils”
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Stabilometer Device (R-value)
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Dynamic Cone Penetrometer (DCP)
• Originally developed in the Republic of South Africa (RSA). South Africans have used and developed related tools and analyses for over 25 years.
• Standard test method– ASTM D6951: “Use of the Dynamic Cone
Penetrometer in Shallow Pavement Applications”– Equipment can come with different hammer weights
—which can effect correlations.
• Equipment can be purchased from companies such as Salem Tool Co., Salem, MI; Kessler Soils Engineering Products, Inc; or Dynatest Inc for about $1000--$2000.
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Dynamic Cone Penetrometer (DCP)
• Standard test method– ASTM D6951: “Use of the Dynamic Cone
Penetrometer in Shallow Pavement Applications”– Equipment can come with different hammer
weights:• 8 kg (17.6 lb.)• 4.6 kg (10.1 lb.)
– USACE CBR—DCP correlations are contained in the ASTM standard test method (see correlations in subsequent images).
Dynamic Cone Penetrometer
Rod
Reference
Mass
Engine
Data Recorder
Positioning System
DCP As Developed in the RSA
Semi-Automatic DCP
Photos of Florida DOT equipment (June 2004). This type of DCP saves time and labor.
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DCP
• Examples of DCP use by the Minnesota DOT– Pavement rehabilitation strategy
determination.– Locate layers in pavement structures.– Supplement foundation testing for design.– Identify weak spots in constructed
embankments.– Use as an acceptance testing tool.– Location of boundaries of required
subcuts.
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DCP
• Assumption: A correlation exists between the strength of a material and its resistance to penetration.
• Typical measure is DCP Penetration Index (DPI)
• Measured in mm/blow or inches/blow• Maximum depth for the DCP 800 mm• Correlations follow
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DCP (if CBR > 10) Correlation
• Correlation developed by the US Army Corps of Engineers (USACE)
1.12DPI
292CBR
Where
CBR = California Bearing Ratio (if CBR > 10)
DPI = Penetration Index (mm/blow)
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DCP (if CBR < 10) Correlation
• Correlation developed by the US Army Corps of Engineers (USACE)
Where
CBR = California Bearing Ratio (if CBR < 10)
DPI = Penetration Index (mm/blow)
2)(DPI)][(0.017019
1CBR
CBR Examples (based on USACE Correlation)
DPI(mm/blow)
CBR(%)
5 48
10 22
20 10
DCP Values and Subgrade Improvement (Illinois DOT)
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DCP Correlation
• CBR Correlation developed in South Africa (for values of DN>2 mm/blow)
1.27410(DN)CBR Where
DN = Penetration of the DCP through a specific pavement layer in mm/blow. The DN is a weighted average. DN is similar to DPI.
CBR Examples (based on RSA Correlation)
DN(mm/blow)
CBR(%)
5 53
10 22
20 9
40 4
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DCP Correlation
• Modulus Correlation developed in South Africa
(DN)1.06166log3.04758logEeff
Where
R2 = 76% and n = 86 data points
Eeff = Effective elastic modulus for a 40 kN load.
DN = Weighted average DCP penetration rate in mm/blow.
E-value Examples (based on RSA Correlation)
DN(mm/blow)
Eeff
MPa (psi)5 202 (29,000 psi)
10 97 (14,000 psi)
20 46 (7,000 psi)
40 22 (3,000 psi)
Typical DCP Plot (from RSA)
RSA Design Curves
Note: MISA is the same as ESALs.
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DCP Testing Frequency (based on RSA recommendations)
• Existing paved road– 8 DCP tests randomly spaced over the
length of the project in both the outer wheelpath and between the wheelpaths.
• Gravel road– 5 DCP tests per kilometer with the tests
staggered between the outer and between wheelpaths.
– Perform additional test at significant locations identified via visual distress survey.
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DCP—Supplemental Information
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Modulus Background
• What is it?• Nomenclature?• What affects values?• Typical values?
Elastic Modulus
S
tres
s
Strain
Figure 1.2 Illustration of a Stress-Strain Plot and the Difference in the Elastic Range of a Material and
Strength
Strength is generally a measure associated with the failure of a material
Elastic Range of a
Material
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Pavement Modulus Abbreviations
• EAC = Asphalt Concrete
• EPCC = Portland Cement Concrete
• EBS = Base course
• ESB = Subbase course
• ESG or MR = Subgrade
Stress Stiffening
Stress Softening
Comparison of Moduli for Various Materials
Material E, psi (MPa)
Rubber 1,000(7)
Wood 1.0-2.0 million(7,000-14,000)
Aluminum 10,000,000(70,000)
Steel 29,000,000(200,000)
Diamond 170,000,000(1,200,000)
Moduli for Various Materials Pavement Materials
Material E, psi (MPa)
HMA (0C) 3,000,000(21,000)
HMA (20C) 500,000(3,500)
HMA (50C) 50,000(350)
Portland Cement Concrete
3-6 million (20-40,000)
Crushed Stone Base 20-100,000 (150-750)
Subgrade Soils 5-30,000 (35-210)
Summary of National Pavement Practices
State DOT Flexible Pavement Design Subgrade Inputs
Summary of National Pavement Practices
State DOT Rigid Pavement Design Subgrade Inputs
Resilient Modulus (MR)
• Measure: stress-strain• Units: psi, MPa• Typical Values
– Subgrade: 3,000 to 40,000 psi
– Crushed rock: 20,000 to 50,000 psi
– HMA: 200,000 to 500,000 psi at 70°F
Picture from University of Tokyo Geotechnical Engineering Lab
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Modulus Correlations
• Use with caution
MR = (1500) (CBR)
Fine-grained materials with soaked CBR ≤ 10
MR = 1,000 + (555)(R-value)
Fine-grained soils with R-Value ≤ 20
MR = (2555)CBR0.64
New AASHTO Design Guide
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Modulus—CBR Correlation
• Modulus Correlation developed by TRRL
Where
E = Elastic modulus (MPa)
CBR = California Bearing Ratio
0.64(17.6)CBR E
Aggregates
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Aggregate Production
• Aggregate production in the US is large—some annual production figures include:– Natural aggregates
• Sand and gravel: 1.13 billion metric tons• Crushed stone: 1.49 billion metric tons
– Recycled aggregates: 200 million metric tons produced from demolition wastes (includes roads and buildings).
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Aggregate Production
• Sand and gravel (estimated for 2003)– 1.13 billion metric tons of sand and gravel
produced in the US in 2003.– Value $5.8 billion – Produced by 4,000 companies from 6,400
operations in all 50 states. Leading production states are: California, Texas, Michigan, Arizona, Ohio, Minnesota, Washington, Wisconsin, Nevada, and Colorado.
– How were these aggregates used?• 53% unspecified• 20% concrete aggregates• 11% road bases and road stabilization• 7% construction fill• 6% HMA and other bituminous mixtures• 3% other applications
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Aggregate Production
• Crushed stone (estimated for 2003)– 1.49 billion metric tons of crushed stone
produced in the US in 2003.– Value $8.6 billion – Produced by 1,260 companies from 3,300
operations in 49 states. Leading production states are: Texas, Florida, Pennsylvania, Missouri, Illinois, Georgia, Ohio, North Carolina, Virginia, and California.
– How were these aggregates used? 35% was for unspecified uses followed by construction aggregates mostly for highway and road construction and maintenance, chemical and metallurgical uses (including cement and lime production), agricultural uses, etc.
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Aggregate Production
• Crushed stone—cont.– Of the crushed stone produced it was
composed of these source rock types:• Limestone and dolomite: 71%• Granite: 15%• Traprock: 7%• Sandstone, quartzite, marble, etc: 7%
View “Lesson 2a Aggregate Production at Glacier NW”
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Aggregate Production
• Perspective– The eruption of Mt. St. Helens in 1980
was estimated to produce 3.7 billion yd3 of debris. This amounts to about 5.6 billion metric tons of material (assuming a unit weight of 125 lb/ft3). The total annual production of sand and gravel, crushed stone, and recycled aggregates amounts to about 50% of the St. Helens debris.
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Aggregate Production
• Recycled aggregates (1999)– 200 million metric tons of recycled
aggregates produced (or generated) in the US in 2000.
– 100 million metric tons of recycled asphalt paving materials recovered annually. 80% of this material is recycled with the other 20% going to landfills. Of the 80% that is recycled—2/3 used as aggregates for road base and 1/3 reused as aggregate for new HMA.
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Aggregate Production
• Recycled aggregates (1999)—cont.– 100 million metric tons of recycled
concrete is recovered annually. • 68% of recycled concrete reused as road
base.• 9% aggregate for HMA mixes• 6% aggregate for new PCC mixes• 3% riprap• 7% general fill• 7% other applications
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Aggregate Production
• Recycled aggregates (1999)—cont.– Only 15% of recycled aggregates reused in
HMA or PCC mixes—why?—Due to quality issues (the lack thereof).
– Economics of recycling according to USGS (1999 data)• Capital investment for an aggregate recycling
facility about $4.40 to $8.80 per metric ton of annual capacity.
• Processing costs: Range from $2.76 to $6.61 per metric ton. Average production of fixed site processing facilities is 150,000 ton/year.
• Prices best for aggregate-poor southern states.
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Aggregate Characterization
• Aggregate Physical Properties– Maximum Aggregate Size– Gradation– Other Aggregate Properties
• Toughness and Abrasion Resistance• Specific Gravity• Particle Shape and Surface Texture• Durability and Soundness• Cleanliness and Deleterious Materials
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Aggregate Characterization
• Maximum Aggregate Size– Maximum size
The smallest sieve through which 100 percent of the aggregate particles pass.
– Nominal maximum size The largest sieve that retains some of the
aggregate particles but generally not more than 10 percent by weight.
Aggregate Gradation
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0.45 Power Curves
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Calculation of the Max Density Curve
n
D
dP
where P = % finer than the sieve
d = aggregate size being considered
D = maximum aggregate size being used
n = parameter which equals 0.45—represents the
maximum particle packing
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Gradations and Permeability
• Uniformly graded- Few points of contact- Poor interlock (shape dependent)- High permeability
• Well graded- Good interlock- Low permeability
• Gap graded- Only limited sizes- Good interlock- Low permeability
Types of Gradations
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Other Aggregate Properties
• Los Angeles Abrasion• Soundness• Sand Equivalent
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Los Angeles Abrasion Test
Start with fraction retained on No. 12 sieve
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Sample submerged in magnesium or sodium sulfate—causes salt
crystals to form in the aggregate pores
Soundness Test
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Sand Equivalent
SE = (Height of Sand/Height of Clay)100
Photo Courtesy of Caltrans
This is a test to determine the amount of clay in fine aggregate.
Aggregate passing a No. 4 sieve is agitated in a water-filled transparent cylinder. Liquid is water and flocculating agent. After settling, the sand separates from the flocculated clay. Measure each.
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Virtual Superpave Laboratory
Aggregate tests done for HMA are featured in the Virtual Superpave Laboratory (VSL). The VSL will be used in subsequent lessons but it is appropriate to briefly examine the aggregate section now. To do this, go to http://guides.ce.washington.edu/UW/VSL
and look under “Aggregate Tests.” Access to the VSL will require your UW NetID and password.
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Lesson 2: Discussion Forum
• Assume that you are participating in a toll road design-build project and the site is new—no previous soil or aggregate source data is readily available. Please discuss the following question—What exploration, sampling, and testing would you recommend so that the soils underlying the new pavements could be reasonably characterized? It is understood that the content of this Lesson will not answer this question fully.
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Lesson 2: References
• USGS (2004), “Mineral Commodity Summaries,” US Geological Survey, January 2004.
• USGS (1999), “Natural Aggregates—Foundation of America’s Future,” USGS Fact Sheet—FS 144-97, Reprinted February 1999.
• WSDOT (2003),“WSDOT Pavement Guide Interactive,” Washington State Department of Transportation, URL: http://guides.ce.washington.edu/UW/WSDOT
• USBR (1973), “Design of Small Dams,” Second Edition, US Department of the Interior, Bureau of Reclamation.
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Lesson 2: References
• FAA (1996), “Airport Pavement Design and Evaluation,” Advisory Circular 150/5320-6D, Federal Aviation Administration, January 30, 1996. http://www.faa.gov/arp/pdf/5320-6dp1.pdf
• PCA (1992), “PCA Soil Primer,” Publication EB007.05S, Portland Cement Association, Skokie, Illinois.
• WSDOT (2004), “Standard Specifications for Road, Bridge, and Municipal Construction,” M41-10, Washington State Department of Transportation. http://www.wsdot.wa.gov/fasc/EngineeringPublications/Manuals/SS2004.PDF