ASTM D1883-21

Standard Test Method for California Bearing Ratio (CBR) of Laboratory-Compacted Soils

SIGNIFICANCE AND USE
5.1 This test method can be used in a number of engineering applications such as to evaluate the potential strength of subgrade, subbase, and base course materials, including recycled materials for use in the design of flexible roads and airfield pavements.
Note 1: As with other laboratory test methods, the user should consider whether results from this test are appropriate for the intended design use. Considerations may include roadbed conditions, environmental conditions, soil saturation, drainage effects, seasonal effects, etc.  
5.2 For applications where the effect of compaction water content on CBR is small, such as cohesionless, coarse-grained materials, or where an allowance is made for the effect of differing compaction water contents in the design procedure, the CBR may be determined at the optimum water content of a specified compaction effort. The specified dry unit weight is normally the minimum percent compaction allowed by the using client’s field compaction specification.  
5.3 For applications where the effect of compaction water content on CBR is unknown or where it is desired to account for its effect, the CBR is determined for a range of water contents, usually the range of water content permitted for field compaction by using the client’s protocol or specification for field compaction.  
5.4 The criteria for test specimen preparation of self-cementing (and other) materials which gain strength with time must be based on a geotechnical engineering evaluation. As directed by the client, self-cementing materials shall be properly cured until bearing ratios representing long term service conditions can be measured.
Note 2: The quality of the results produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of ...
SCOPE
1.1 This test method covers the determination of the California Bearing Ratio (CBR) of laboratory compacted specimens. The test method is primarily intended for, but not limited to, evaluating the strength of materials having maximum particle size less than 3/4 in. (19 mm).  
1.2 When materials having a maximum particle size greater than 3/4 in. (19 mm) are to be tested, this test method provides for modifying the gradation of the material so that the material used for testing all passes the 3/4-in. (19-mm) sieve while the total gravel fraction (material passing the 3-in. (75-mm) sieve and retained on the No. 4 (4.75-mm) sieve) remains the same. While traditionally this method of specimen preparation has been used to avoid the error inherent in testing materials containing large particles in the CBR test apparatus, the modified material may have significantly different strength properties than the original material. However, a large experience database has been developed using this test method for materials for which the gradation has been modified, and satisfactory design methods are in use based on the results of tests using this procedure.  
1.3 Past practice has shown that CBR results for those materials having substantial percentages of particles retained on the No. 4 (4.75 mm) sieve are more variable than for finer materials. Consequently, more trials may be required for these materials to establish a reliable CBR.  
1.4 This test method provides for the determination of the CBR of a material at optimum water content or a range of water contents from a specified compaction test and a specified dry unit weight. The dry unit weight is usually given as a percentage of maximum dry unit weight determined by Test Methods D698 or D1557.  
1.4.1 The client requesting the CBR test may specify the water content or range of water contents and/or the dry unit weight for which the CBR is desired.  
1.5 Unless specified oth...

General Information

• Status: Published
• Publication Date: 14-Nov-2021
• ICS: 93.020 - Earthworks. Excavations. Foundation construction. Underground works
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.05 - Strength and Compressibility of Soils

Relations

• Refers: ASTM D4753-24 - Standard Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction Materials Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM C670-24a - Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
• Effective Date: 01-Feb-2024
• Refers: ASTM C670-24 - Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D2216-19 - Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
• Effective Date: 01-Mar-2019
• Refers: ASTM D2168-10(2018) - Standard Practices for Calibration of Laboratory Mechanical-Rammer Soil Compactors
• Effective Date: 01-Jul-2018
• Refers: ASTM D2487-17 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D2487-17e1 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D2488-17 - Standard Practice for Description and Identification of Soils (Visual-Manual Procedures)
• Effective Date: 15-Jul-2017
• Refers: ASTM D4318-17e1 - Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
• Effective Date: 01-Jun-2017
• Refers: ASTM D4318-17 - Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
• Effective Date: 01-Jun-2017
• Refers: ASTM D4753-15 - Standard Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction Materials Testing
• Effective Date: 01-May-2015
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM E11-13 - Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves
• Effective Date: 01-Oct-2013

Overview

ASTM D1883-21 - Standard Test Method for California Bearing Ratio (CBR) of Laboratory-Compacted Soils details the procedures for determining the California Bearing Ratio (CBR) of soil specimens that have been compacted in the laboratory. The CBR test is widely used in geotechnical engineering to evaluate the strength of subgrade, subbase, and base course materials - including recycled materials - primarily for the design of flexible pavements such as roads and airfields. The test is essential for understanding soil behavior and suitability for construction projects.

Key Topics

• Purpose and Significance

  • The CBR test measures the bearing resistance of soil by recording the pressure required for a piston to penetrate a compacted soil specimen.
  • Results help determine the potential strength of roadbed and pavement materials under traffic loading conditions.
  • Critical for the design and specification of flexible pavement layers in transportation infrastructure.

• Materials and Scope

  • Applies mainly to materials with a maximum particle size less than 3/4 inch (19 mm), but also provides procedures for larger materials using gradation modification.
  • Recognizes variability in CBR results with coarse-grained materials or soils containing significant gravel fractions.

• Test Parameters

  • Compaction is performed at the optimum water content or across a specified range of water contents and dry unit weights, based on project or client requirements.
  • Soaking procedures are included to replicate worst-case moisture conditions that may be encountered in the field.

• Quality Considerations

  • The accuracy of CBR results is heavily dependent on skilled personnel, proper equipment calibration, and facility qualification.
  • ASTM D3740 is referenced for minimum requirements for testing agencies.

Applications

• Pavement Design

  • Used extensively for the design of flexible pavements for highways, streets, parking lots, and airfields.
  • CBR values assist engineers in selecting suitable subgrade and base course materials, ensuring sufficient load-bearing capacity for anticipated traffic loads.

• Material Evaluation

  • Helps assess both natural soils and improved or recycled materials intended for use in construction.
  • Applicable where project specifications demand reliable assessment of soil strength under compacted and potentially saturated conditions.

• Specification Compliance

  • Ensures that materials used in subgrade and aggregate base courses meet required strength and compaction specifications.
  • Supports consistency and reliability in construction practices by standardizing test procedures and interpretations.

Related Standards

• ASTM D698 - Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort
• ASTM D1557 - Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort
• ASTM D2216 - Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
• ASTM D2487 - Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• ASTM D3740 - Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock
• ASTM E11 - Specification for Woven Wire Test Sieve Cloth and Test Sieves

Additional related ASTM soil and geotechnical engineering standards may be considered depending on project scope.

---

In summary: ASTM D1883-21 offers a robust and standardized method for evaluating the CBR of laboratory-compacted soils, underpinning the design and quality assurance of flexible pavement systems. Adhering to this standard improves reliability in pavement performance by ensuring that soil and aggregate layers will support intended loads under varying moisture and compaction conditions.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D1883 − 21
Standard Test Method for
California Bearing Ratio (CBR) of Laboratory-Compacted
Soils
This standard is issued under the fixed designation D1883; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 1.4.1 The client requesting the CBR test may specify the
water content or range of water contents and/or the dry unit
1.1 This test method covers the determination of the Cali-
weight for which the CBR is desired.
fornia Bearing Ratio (CBR) of laboratory compacted speci-
1.5 Unless specified otherwise by the requesting client, or
mens.Thetestmethodisprimarilyintendedfor,butnotlimited
to, evaluating the strength of materials having maximum unlessithasbeenshowntohavenoeffectontestresultsforthe
material being tested, all specimens shall be soaked prior to
particle size less than ⁄4 in. (19 mm).
penetration.
1.2 When materials having a maximum particle size greater
1.6 Units—The values stated in inch-pound units are to be
than ⁄4 in. (19 mm) are to be tested, this test method provides
regarded as standard. The SI units given in parentheses are
for modifying the gradation of the material so that the material
mathematical conversions, which are provided for information
used for testing all passes the ⁄4-in. (19-mm) sieve while the
purposes only and are not considered standard. Reporting of
total gravel fraction (material passing the 3-in. (75-mm) sieve
test results in units other than inch-pound units shall not be
and retained on the No. 4 (4.75-mm) sieve) remains the same.
regarded as nonconformance with this test method.
While traditionally this method of specimen preparation has
been used to avoid the error inherent in testing materials 1.6.1 The gravitational system of inch-pound units is used
containing large particles in the CBR test apparatus, the when dealing with inch-pound units. In this system, the pound
(lbf)representsaunitofforce(weight),whiletheunitformass
modified material may have significantly different strength
properties than the original material. However, a large experi- is slugs. The slug unit is not given, unless dynamic (F = ma)
calculations are involved.
ence database has been developed using this test method for
materials for which the gradation has been modified, and
1.6.2 The slug unit of mass is almost never used in
satisfactory design methods are in use based on the results of
commercial practice; that is, density, balances, etc. Therefore,
tests using this procedure.
the standard unit for mass in this standard is either kilogram
(kg) or gram (g), or both.Also, the equivalent inch-pound unit
1.3 Past practice has shown that CBR results for those
(slug) is not given/presented in parentheses.
materials having substantial percentages of particles retained
1.6.3 It is common practice in the engineering/construction
on the No. 4 (4.75 mm) sieve are more variable than for finer
profession, in the United States, to concurrently use pounds to
materials. Consequently, more trials may be required for these
represent both a unit of mass (lbm) and of force (lbf). This
materials to establish a reliable CBR.
implicitly combines two separate systems of units; that is, the
1.4 This test method provides for the determination of the
absolutesystemandthegravitationalsystem.Itisscientifically
CBR of a material at optimum water content or a range of
undesirable to combine the use of two separate sets of
watercontentsfromaspecifiedcompactiontestandaspecified
inch-pound units within a single standard. As stated, this
dry unit weight. The dry unit weight is usually given as a
standard includes the gravitational system of inch-pound units
percentage of maximum dry unit weight determined by Test
and does not use/present the slug unit for mass. However, the
Methods D698 or D1557.
use of balances or scales recording pounds of mass (lbm) or
recording density in lbm/ft shall not be regarded as noncon-
formance with this standard.
1.6.4 The terms density and unit weight are often used
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.05 on Strength and
interchangeably. Density is mass per unit volume whereas unit
Compressibility of Soils.
weight is force per unit volume. In this standard, density is
Current edition approved Nov. 15, 2021. Published December 2021. Originally
given only in SI units. After the density has been determined,
approved in 1961. Last previous edition approved in 2016 as D1883–16. DOI:
10.1520/D1883-21. the unit weight is calculated in SI or inch-pound units, or both.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1883 − 21
1.7 All observed and calculated values shall conform to the Construction Materials Testing
guidelines for significant digits and rounding established in D6026Practice for Using Significant Digits and Data Re-
Practice D6026. cords in Geotechnical Data
1.7.1 Theproceduresusedtospecifyhowdataarecollected/ D6913/D6913MTest Methods for Particle-Size Distribution
recorded or calculated in this standard are regarded as the (Gradation) of Soils Using Sieve Analysis
industry standard. In addition, they are representative of the E11Specification forWovenWireTest Sieve Cloth andTest
significant digits that generally should be retained. The proce- Sieves
dures used do not consider material variation, purpose for
obtaining the data, special purpose studies, or any consider-
3. Terminology
ations for the user’s objectives, and it is common practice to
3.1 Definitions:
increase or reduce significant digits of reported data to be
3.1.1 Fordefinitionsofcommontechnicaltermsusedinthis
commensuratewiththeseconsiderations.Itisbeyondthescope
standard, refer to Terminology D653.
of this standard to consider significant digits used in analytical
3.2 Definitions of Terms Specific to This Standard:
methods for engineering design.
3.2.1 water content of the compaction specimen, w ,
i
1.8 This standard does not purport to address all of the
n—watercontentinpercentofmaterialusedtocompactthetest
safety concerns, if any, associated with its use. It is the
specimen.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- 3.2.2 water content top 1 in. (25-mm) after soaking w ,
s
n—water content in percent of upper 1 in. (25 mm) of material
mine the applicability of regulatory limitations prior to use.
1.9 This international standard was developed in accor- removed from the compacted specimen after soaking and
penetration.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
3.2.3 water content after testing, w,n—water content in
f
Development of International Standards, Guides and Recom-
percent of the compacted specimen after soaking and final
mendations issued by the World Trade Organization Technical
penetration; does not include material described in 3.2.2.
Barriers to Trade (TBT) Committee.
3.2.4 dry density as compacted and before soaking, ρ ,
di
n—dry density of the as compacted test specimen using the
2. Referenced Documents
measured wet mass and calculating the dry mass using the
2.1 ASTM Standards:
water content defined in 3.2.1.
C670Practice for Preparing Precision and Bias Statements
for Test Methods for Construction Materials
4. Summary of Test Method
D653Terminology Relating to Soil, Rock, and Contained
4.1 The California Bearing Ratio (CBR) is an index of the
Fluids
bearing resistance of a compacted soil by forcing a circular
D698Test Methods for Laboratory Compaction Character-
piston at a constant rate of penetration into the soil and
istics of Soil Using Standard Effort (12,400 ft-lbf/ft (600
measuring the force during penetration. The CBR is expressed
kN-m/m ))
as the ratio of the unit force on the piston required to penetrate
D1557Test Methods for Laboratory Compaction Character-
0.1in.(3mm)and0.2in.(5mm)ofthetestmaterialtotheunit
istics of Soil Using Modified Effort (56,000 ft-lbf/ft
force required to penetrate a standard material of well-graded
(2,700 kN-m/m ))
crushed stone.
D2168Practices for Calibration of Laboratory Mechanical-
Rammer Soil Compactors
4.2 This test method is used to determine the CBR of a
D2216Test Methods for Laboratory Determination ofWater
material compacted in a specified mold. It is incumbent on the
(Moisture) Content of Soil and Rock by Mass
requesting client to specify the scope of testing to satisfy the
D2487Practice for Classification of Soils for Engineering
client’s protocol or specific design requirements. Possible
Purposes (Unified Soil Classification System)
scope of testing includes:
D2488Practice for Description and Identification of Soils
4.2.1 CBR penetration tests can be performed on each point
(Visual-Manual Procedures)
of a compaction test specimen prepared in accordance with
D3740Practice for Minimum Requirements for Agencies
either Method C of Test Methods D698 or D1557. The CBR
Engaged in Testing and/or Inspection of Soil and Rock as
mold with the spacer disk specified in this standard has the
Used in Engineering Design and Construction
same internal dimensions as a 6.000-in. (152.4-mm) diameter
D4318Test Methods for Liquid Limit, Plastic Limit, and
compaction mold.
Plasticity Index of Soils
4.2.2 Another alternative is for the CBR test to be per-
D4753Guide for Evaluating, Selecting, and Specifying Bal-
formed on material compacted to a specific water content and
ances and Standard Masses for Use in Soil, Rock, and
density so as to bracket those anticipated in the field. A water
contentrangemaybestatedforoneormoredensityvaluesand
will often require a series of specimens prepared using two or
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
three compactive efforts for the specified water contents or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
over the range of water contents requested. The compactive
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. efforts are achieved by following procedures of Test Methods
D1883 − 21
cautioned that compliance with Practice D3740 does not in itself ensure
D698 or D1557 but varying the blows per layer to produce
reliable results. Reliable results depend on many factors; Practice D3740
densities above and below the desired density.
provides a means of evaluating some of those factors.
5. Significance and Use
6. Apparatus
5.1 Thistestmethodcanbeusedinanumberofengineering
6.1 Loading Machine—The loading machine shall be
applications such as to evaluate the potential strength of
equippedwithamovableheadorbasethattravelsatauniform
subgrade, subbase, and base course materials, including re-
(not pulsating) rate of 0.05 60.01in. (1 60.2mm)⁄min for
cycled materials for use in the design of flexible roads and
useinpushingthepenetrationpistonintothespecimenoverthe
airfield pavements.
range of forces developed during penetration.
NOTE 1—As with other laboratory test methods, the user should
6.1.1 Axial Load Measuring Device—The machine shall be
consider whether results from this test are appropriate for the intended
equipped with a load-indicating device matched to the antici-
design use. Considerations may include roadbed conditions, environmen-
pated maximum penetration load. The axial load measuring
tal conditions, soil saturation, drainage effects, seasonal effects, etc.
device shall be a load ring, electronic load cell, hydraulic load
5.2 For applications where the effect of compaction water
cell, or any other load-measuring device with an accuracy of
content on CBR is small, such as cohesionless, coarse-grained
1% of the load from 0.100 in. (2.5 mm) penetration to at least
materials, or where an allowance is made for the effect of
0.500 in. (13 mm) penetration or failure.
differing compaction water contents in the design procedure,
the CBR may be determined at the optimum water content of
6.2 Penetration Measuring Device—The penetration mea-
a specified compaction effort. The specified dry unit weight is
suringdevice(suchasamechanicaldialindicatororelectronic
normally the minimum percent compaction allowed by the
displacement transducer) shall be capable of reading to the
using client’s field compaction specification.
nearest 0.001 in. (0.02 mm) and provided with appropriate
mounting hardware. The mounting assembly of the deforma-
5.3 For applications where the effect of compaction water
tion measuring device shall be connected to the penetrating
content on CBR is unknown or where it is desired to account
piston and the edge of the mold providing accurate penetration
for its effect, the CBR is determined for a range of water
measurements.Mountingthedeformationholderassemblytoa
contents, usually the range of water content permitted for field
stressed component of the load frame (such as tie rods) will
compaction by using the client’s protocol or specification for
introduce inaccuracies of penetration measurements.
field compaction.
6.3 Mold—The mold shall be a rigid metal cylinder with an
5.4 The criteria for test specimen preparation of self-
inside diameter of 6.000 6 0.026 in. (152.4 6 0.66 mm) and
cementing (and other) materials which gain strength with time
a height of 7.000 6 0.018 in. (177.8 6 0.46 mm). It shall be
must be based on a geotechnical engineering evaluation. As
provided with a metal extension collar at least 2.0 in. (51 mm)
directed by the client, self-cementing materials shall be prop-
in height and a metal base plate having at least twenty-eight
erly cured until bearing ratios representing long term service
⁄16-in. (1.59-mm) diameter holes uniformly spaced over the
conditions can be measured.
plate within the inside circumference of the mold. When
NOTE 2—The quality of the results produced by this standard is
assembled with the spacer disc placed in the bottom of the
dependent on the competence of the personnel performing it, and the
mold, the mold shall have an internal volume (excluding
suitability of the equipment and facilities used. Agencies that meet the
3 3
extension collar) of 0.0750 6 0.0009 ft (2100 6 25 cm ). A
criteria of Practice D3740 are generally considered capable of competent
and objective testing/sampling/inspection/etc. Users of this standard are moldassemblyhavingtheminimumrequiredfeaturesisshown
TABLE 1 SI Equivalents for Figs. 1-5
Inch-Pound SI SI SI
Inch-Pound Inch-Pound
Units, in. Equivalent, Equivalent, Equivalent,
Units, in. Units, in.
mm mm mm
1 1
1.954 49.63 1 ⁄4 31.8 4 ⁄2 114.3
3 3
2.416 61.37 1 ⁄8 34.90 4 ⁄4 120.7
1 1 7
⁄16 1.59 1 ⁄2 38.1 5 ⁄8 149.2
1 3 15
⁄4 6.4 1 ⁄4 44.5 5 ⁄16 150.8
3 1
⁄8 9.53 1 ⁄8 28.58 6.000 152.4
7 7
⁄16 11.11 2 50.8 6 ⁄32 158.0
1 1
⁄2 12.70 2 ⁄8 53.98 7.000 177.8
5 3 1
⁄8 15.9 2 ⁄4 69.85 7 ⁄2 190.5
3 3
⁄4 19.1 3 76.20 8 ⁄8 212.7
1 1 3
1 ⁄8 28.58 4 ⁄4 108.0 9 ⁄8 238.1
Inch-Pound SI Inch-Pound SI
Units, in. Equivalent, mm Units, psi Equivalent, MPa
0.10 2.5 200 1
0.20 5.1 400 3
0.30 7.6 600 4
0.40 10 800 6
0.50 13 1000 7
1200 8.4
1400 9.8
D1883 − 21
in Fig. 1.Acalibration procedure shall be used to confirm the 6.7 Surcharge Weights—These “weights” are actually
actual volume of the mold with the spacer disk inserted. “masses” converted to a force. One or two annular metal
Suitable calibration procedures are contained in Test Methods weights having a total weight of 10 6 0.05 lbf (equivalent to
D698 and D1557. a mass of 4.54 6 0.02 kg) and slotted metal weights each
having a weight of 5 6 0.05 lbf (equivalent to a mass of 2.27
6.4 Spacer Disk—A circular metal spacer disc (see Fig. 1)
7 15
6 0.02 kg).The annular weight shall be 5 ⁄8 to 5 ⁄16 in. (149.2
having a minimum outside diameter of 5 ⁄16 in. (150.8 mm)
to 150.8 mm) in diameter and shall have a center hole of
but no greater than will allow the spacer disc to easily slip into
approximately 2 ⁄8in. (53.98 mm) (see Fig. 3).
the mold. The spacer disc shall be 2.416 6 0.005 in. (61.37 6
0.13 mm) in height. 6.8 Penetration Piston—A metal piston 1.954 6 0.005 in.
(49.63 6 0.13 mm) in diameter and not less than 4 in. (101.6
6.5 Rammer—Arammer as specified in eitherTest Methods
mm) long (see Fig. 3).
D698 or D1557 shall be used to compact the soil specimen to
the desired density. 6.9 Balance—A class GP5 balance meeting the require-
ments of Specifications D4753 for a balance of 1-g readability.
6.6 Expansion-Measuring Apparatus—An adjustable metal
stemandperforatedmetalplate,similarinconfigurationtothat 6.10 Drying Oven—Thermostatically controlled, preferably
7 15
shown in Fig. 2. The perforated plate shall be 5 ⁄8 to 5 ⁄16 in. of a forced-draft type and capable of maintaining a uniform
(149.2 to 150.8 mm) in diameter and have at least forty-two temperature of 230 6 9°F (110 6 5°C) throughout the drying
⁄16-in. (1.59-mm) diameter holes uniformly spaced over the chamber.
plate. A metal tripod to support the dial gauge for measuring
6.11 Sieves— ⁄4in.(19mm)andNo.4(4.75mm),conform-
the amount of swell during soaking is also required. The
ing to the requirements of Specification E11.
expansion measuring apparatus shall not weigh more than 2.8
6.12 Filter Paper—A fast filtering, high grade hardened,
lbf or a mass of 1.3 kg.
low ash filter paper, 6.000 in. (152.4 mm) diameter.
6.6.1 Swell Measurement Device—Generally mechanical
dialindicatorscapableofreadingto0.001in.(0.025mm)with 6.13 Straightedge—Astiff metal straightedge of any conve-
a range of 0.200-in. (5-mm) minimum. nient length but not less than 10.0 in. (254 mm). The total
NOTE 1—See Table 1 for SI equivalents.
FIG. 1 Mold with Extension Collar and Spacer Disk
D1883 − 21
NOTE 1—See Table 1 for SI equivalents.
FIG. 2 Expansion-Measuring Apparatus
length of the straightedge shall be machined straight to a 7.2 The specimen(s) for compaction shall be prepared in
tolerance of 60.005 in. (60.13 mm). The scraping edge shall accordance with the procedures given in Method C of Test
be beveled if it is thicker than ⁄8 in. (3 mm). Methods D698 or D1557 for compaction in a 6.000-in.
(152.4-mm) mold except as follows:
6.14 Soaking Tank or Pan—Atankorpanofsufficientdepth
7.2.1 Ifallmaterialpassesa ⁄4-in.(19-mm)sieve,theentire
and breadth to allow free water around and over the assembled
gradationshallbeusedforpreparingspecimensforcompaction
mold.Thetankorpanshouldhaveabottomgratingthatallows
without modification. If material is retained on the ⁄4-in.
free access of water to the perforations in the mold’s base.
(19-mm) sieve, the material retained on the ⁄4-in. (19-mm)
6.15 Mixing Tools—Miscellaneous tools such as mixing
sieve shall be removed and replaced by an equal mass of
pan, spoon, trowel, spatula, etc., or a mechanical device for
material passing the ⁄4-in. (19-mm) sieve and retained on the
thoroughly mixing the sample of soil with water.
No. 4 (4.75 mm) sieve obtained by separation from portions of
the sample not used for testing.
7. Sample
8. Test Specimens
7.1 Do not reuse soil that has been previously compacted in
8.1 Bearing Ratio at Optimum Water Content Only—Using
the laboratory. The reuse of previously compacted soils may
material prepared as described in 7.2, conduct a control
yield a greater maximum dry unit weight.
compaction test with a sufficient number of test specimens to
establish the optimum water content for the soil using the
compaction method specified, either Test Methods D698 or
Johnson, A. W., and Sallberg, J.R., Factors Influencing Compaction Test
D1557. A previously performed compaction test on the same
Results, Highway Research Board, Bulletin 318, Publication 967, National Acad-
emy of Sciences-National Research Council, Washington, DC, 1962, p. 73. material may be substituted for the compaction test just
D1883 − 21
NOTE 1—See Table 1 for SI equivalents.
FIG. 3 Surcharge Weights and Penetration Piston
described, provided that if the sample contains material re- 95% of maximum dry unit weight is desired, specimens
tained on the ⁄4-in. (19-mm) sieve, then soil prepared as compacted using 10-blows, 25-blows, and 56-blows per layer
described in 7.2.1 is used for the CBR test. is satisfactory. Penetration shall be performed on each of these
specimens.
NOTE 3—Maximum dry unit weight obtained
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D1883 − 16 D1883 − 21
Standard Test Method for
California Bearing Ratio (CBR) of Laboratory-Compacted
Soils
This standard is issued under the fixed designation D1883; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers the determination of the California Bearing Ratio (CBR) of pavement subgrade, subbase, and base
course materials from laboratory compacted specimens. The test method is primarily intended for, but not limited to, evaluating
the strength of materials having maximum particle size less than ⁄4 in. (19 mm).
1.2 When materials having a maximum particle size greater than ⁄4 in. (19 mm) are to be tested, this test method provides for
modifying the gradation of the material so that the material used for testing all passes the ⁄4-in. (19-mm) sieve while the total
gravel fraction (material passing the 3-in. (75-mm) sieve and retained on the No. 4 (4.75-mm) sieve) remains the same. While
traditionally this method of specimen preparation has been used to avoid the error inherent in testing materials containing large
particles in the CBR test apparatus, the modified material may have significantly different strength properties than the original
material. However, a large experience database has been developed using this test method for materials for which the gradation
has been modified, and satisfactory design methods are in use based on the results of tests using this procedure.
1.3 Past practice has shown that CBR results for those materials having substantial percentages of particles retained on the No.
4 (4.75 mm) sieve are more variable than for finer materials. Consequently, more trials may be required for these materials to
establish a reliable CBR.
1.4 This test method provides for the determination of the CBR of a material at optimum water content or a range of water
contentcontents from a specified compaction test and a specified dry unit weight. The dry unit weight is usually given as a
percentage of maximum dry unit weight determined by Test Methods D698 or D1557.
1.4.1 The client requesting the CBR test may specify the water content or range of water contents and/or the dry unit weight for
which the CBR is desired.
1.5 The client requesting the test may specify the water content or range of water contents and the dry unit weight for which the
CBR is desired.
1.5 Unless specified otherwise by the requesting client, or unless it has been shown to have no effect on test results for the material
being tested, all specimens shall be soaked prior to penetration.
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.05 on Strength and
Compressibility of Soils.
Current edition approved March 1, 2016Nov. 15, 2021. Published March 2016December 2021. Originally approved in 1961. Last previous edition approved in 20142016
as D1883 – 14.D1883 – 16. DOI: 10.1520/D1883-16.10.1520/D1883-21.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1883 − 21
1.7 For the determination of CBR of field in-place materials, see Test Method D4429.
1.6 Units—The values stated in inch-pound units are to be regarded as standard. The SI units given in parentheses are
mathematical conversions, which are provided for information purposes only and are not considered standard. Reporting of test
results in units other than inch-pound units shall not be regarded as nonconformance with this test method.
1.6.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In this system, the pound (lbf)
represents a unit of force (weight), while the unit for mass is slugs. The slug unit is not given, unless dynamic (F = ma) calculations
are involved.
1.6.2 The slug unit of mass is almost never used in commercial practice; that is, density, balances, etc. Therefore, the standard unit
for mass in this standard is either kilogram (kg) or gram (g), or both. Also, the equivalent inch-pound unit (slug) is not
given/presented in parentheses.
1.6.3 It is common practice in the engineering/construction profession, in the United States, to concurrently use pounds to
represent both a unit of mass (lbm) and of force (lbf). This implicitly combines two separate systems of units; that is, the absolute
system and the gravitational system. It is scientifically undesirable to combine the use of two separate sets of inchpoundinch-pound
units within a single standard. As stated, this standard includes the gravitational system of inch-pound units and does not
use/present the slug unit for mass. However, the use of balances or scales recording pounds of mass (lbm) or recording density
in lbm/ft shall not be regarded as nonconformance with this standard.
1.6.4 The terms density and unit weight are often used interchangeably. Density is mass per unit volume whereas unit weight is
force per unit volume. In this standard, density is given only in SI units. After the density has been determined, the unit weight
is calculated in SI or inch-pound units, or both.
1.7 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice
D6026.
1.7.1 The procedures used to specify how data are collected/recorded or calculated in this standard are regarded as the industry
standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not
consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives,
and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations.
It is beyond the scope of this standard to consider significant digits used in analytical methods for engineering design.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.9 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C670 Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials
D422 Test Method for Particle-Size Analysis of Soils (Withdrawn 2016)
D653 Terminology Relating to Soil, Rock, and Contained Fluids
3 3
D698 Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft (600 kN-m/m ))
D1557 Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft (2,700
kN-m/m ))
D2168 Practices for Calibration of Laboratory Mechanical-Rammer Soil Compactors
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D2487 Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
D2488 Practice for Description and Identification of Soils (Visual-Manual Procedures)
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
D1883 − 21
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D4318 Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
D4429 Test Method for CBR (California Bearing Ratio) of Soils in Place (Withdrawn 2018)
D4753 Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction
Materials Testing
D6026 Practice for Using Significant Digits and Data Records in Geotechnical Data
D6913/D6913M Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis
E11 Specification for Woven Wire Test Sieve Cloth and Test Sieves
3. Terminology
3.1 Definitions:
3.1.1 For common definitions of common technical terms used in this standard, refer to Terminology D653.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 water content of the compaction specimen, w —, n—water content in percent of material used to compact the test specimen.
i
3.2.2 water content top 1 in. (25.4-mm)(25-mm) after soaking w —, n—water content in percent of upper 1 in. (25.4(25 mm) of
s
material removed from the compacted specimen after soaking and penetration.
3.2.3 water content after testing, w —, n—water content in percent of the compacted specimen after soaking and final penetration;
f
does not include material described in 3.2.2.
3.2.4 dry density as compacted and before soaking, ρ —, n—dry density of the as compacted test specimen using the measured
di
wet mass and calculating the dry mass using the water content defined in 3.2.1.
4. Summary of Test Method
4.1 The California Bearing Ratio (CBR) test is used in evaluating subgrade, subbase and base materials as an aid to the design
of pavements. The laboratory test usesis an index of the bearing resistance of a compacted soil by forcing a circular piston to
penetrate material compacted in a mold at a constant rate of at a constant rate of penetration into the soil and measuring the force
during penetration. The CBR is expressed as the ratio of the unit loadforce on the piston required to penetrate 0.1 in. (2.5(3 mm)
and 0.2 in (5.1in. (5 mm) of the test material to the unit loadforce required to penetrate a standard material of well-graded crushed
stone.
4.2 This test method is used to determine the CBR of a material compacted in a specified mold. It is incumbent on the requesting
client to specify the scope of testing to satisfy the client’s protocol or specific design requirements. Possible scope of testing
includes:
4.2.1 CBR penetration tests can be performed on each point of a compaction test performed specimen prepared in accordance with
either Method C of Test Methods D698 or D1557. The CBR mold with the spacer disk specified in this standard has the same
internal dimensions as a 6.000-in. (152.4-mm) diameter compaction mold.
4.2.2 Another alternative is for the CBR test to be performed on material compacted to a specific water content and density.
Alternatively, a density so as to bracket those anticipated in the field. A water content range may be stated for one or more density
values and will often require a series of specimens prepared using two or three compactive efforts for the specified water contents
or over the range of water contents requested. The compactive efforts are achieved by following procedures of Test Methods D698
or D1557 but varying the blows per layer to produce densities above and below the desired density.
5. Significance and Use
5.1 This test method is used can be used in a number of engineering applications such as to evaluate the potential strength of
subgrade, subbase, and base course materials, including recycled materials for use in the design of road flexible roads and airfield
pavements. The CBR value obtained in this test forms an integral part of several flexible pavement design methods.
D1883 − 21
NOTE 1—As with other laboratory test methods, the user should consider whether results from this test are appropriate for the intended design use.
Considerations may include roadbed conditions, environmental conditions, soil saturation, drainage effects, seasonal effects, etc.
5.2 For applications where the effect of compaction water content on CBR is small, such as cohesionless, coarse-grained materials,
or where an allowance is made for the effect of differing compaction water contents in the design procedure, the CBR may be
determined at the optimum water content of a specified compaction effort. The specified dry unit weight is normally the minimum
percent compaction allowed by the using client’s field compaction specification.
5.3 For applications where the effect of compaction water content on CBR is unknown or where it is desired to account for its
effect, the CBR is determined for a range of water contents, usually the range of water content permitted for field compaction by
using the client’s protocol or specification for field compaction.
5.4 The criteria for test specimen preparation of self-cementing (and other) materials which gain strength with time must be based
on a geotechnical engineering evaluation. As directed by the client, self-cementing materials shall be properly cured until bearing
ratios representing long term service conditions can be measured.
NOTE 2—The quality of the results produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the
equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective
testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself ensure reliable results.
Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
6. Apparatus
6.1 Loading Machine—The loading machine shall be equipped with a movable head or base that travels at a uniform (not
pulsating) rate of 0.05 in.0.05 6 0.01 in. (1 6 0.2 mm) (1.3 mm)/min ⁄min for use in pushing the penetration piston into the
specimen. The load rate of 0.05 in. (1.3 mm)/min shall be maintained within 620% specimen over the range of loadsforces
developed during penetration. The minimum capacity of the loading machine shall be based on the requirements indicated in Table
1.
6.1.1 Axial Load Measuring Device—The machine shall be equipped with a load-indicating device matched to the anticipated
maximum penetration load. The load-indicating axial load measuring device shall have a minimum accuracy of: 10 lbf (44 N) or
less for a 10,000 lbf (44 kN) capacity; 5 lbf (22 N) or less for 5,000 lbf (22 kN) and 2 lbf (9 N) or less for 2,500 lbf (11 kN).be
TABLE 21 SI Equivalents for Figs. 1-5
Inch-Pound SI SI SI
Inch-Pound Inch-Pound
Units, in. Equivalent, Equivalent, Equivalent,
Units, in. Units, in.
mm mm mm
1 1
1.954 49.63 1 ⁄4 31.8 4 ⁄2 114.3
3 3
2.416 61.37 1 ⁄8 34.90 4 ⁄4 120.7
1 1 7
⁄16 1.59 1 ⁄2 38.1 5 ⁄8 149.2
1 3 15
⁄4 6.4 1 ⁄4 44.5 5 ⁄16 150.8
3 1
⁄8 9.53 1 ⁄8 28.58 6.000 152.4
7 7
⁄16 11.11 2 50.8 6 ⁄32 158.0
1 1
⁄2 12.70 2 ⁄8 53.98 7.000 177.8
5 3 1
⁄8 15.9 2 ⁄4 69.85 7 ⁄2 190.5
3 3
⁄4 19.1 3 76.20 8 ⁄8 212.7
1 1 3
1 ⁄8 28.58 4 ⁄4 108.0 9 ⁄8 238.1
Inch-Pound SI Inch-Pound SI
Units, in. Equivalent, mm Units, psi Equivalent, MPa
0.10 2.5 200 1.4
0.10 2.5 200 1
0.20 5.1 400 2.8
0.20 5.1 400 3
0.30 7.6 600 4.1
0.30 7.6 600 4
0.40 10.2 800 5.5
0.40 10 800 6
0.50 12.7 1000 6.9
0.50 13 1000 7
1200 8.3
1200 8.4
1400 9.7
1400 9.8
D1883 − 21
a load ring, electronic load cell, hydraulic load cell, or any other load-measuring device with an accuracy of 1 % of the load from
0.100 in. (2.5 mm) penetration to at least 0.500 in. (13 mm) penetration or failure.
6.2 Penetration Measuring Device—The penetration measuring device (such as a mechanical dial indicator or electronic
displacement transducer) shall be capable of reading to the nearest 0.001 in. (0.025(0.02 mm) and provided with appropriate
mounting hardware. The mounting assembly of the deformation measuring device shall be connected to the penetrating piston and
the edge of the mold providing accurate penetration measurements. Mounting the deformation holder assembly to a stressed
component of the load frame (such as tie rods) will introduce inaccuracies of penetration measurements.
6.3 Mold—The mold shall be a rigid metal cylinder with an inside diameter of 6.000 6 0.026 in. (152.4 6 0.66 mm) and a height
of 7.000 6 0.018 in. (177.8 6 0.46 mm). It shall be provided with a metal extension collar at least 2.0 in. (50.8(51 mm) in height
and a metal base plate having at least twenty eight twenty-eight ⁄16-in. (1.59-mm) diameter holes uniformly spaced over the plate
within the inside circumference of the mold. When assembled with the spacer disc placed in the bottom of the mold, the mold shall
3 3
have an internal volume (excluding extension collar) of 0.0750 6 0.0009 ft (2124(2100 6 25 cm ). A mold assembly having the
minimum required features is shown in Fig. 1. A calibration procedure shall be used to confirm the actual volume of the mold with
the spacer disk inserted. Suitable calibration procedures are contained in Test Methods D698 and D1557.
6.4 Spacer Disk—A circular metal spacer disc (see Fig. 1) having a minimum outside diameter of 5 ⁄16 in. (150.8 mm) but no
greater than will allow the spacer disc to easily slip into the mold. The spacer disc shall be 2.416 6 0.005 in. (61.37 6 0.13 mm)
in height.
6.5 Rammer—A rammer as specified in either Test Methods D698 or D1557 except that if a mechanical rammer is used it must
be equipped with a circular foot, and when so equipped, must provide a means for distributing the rammer blows uniformly over
NOTE 1—See Table 21 for SI equivalents.
FIG. 1 Mold with Extension Collar and Spacer Disk
D1883 − 21
the surface of the soil when compacting in a 6.000-in. (152.4-mm) diameter mold. The mechanical rammer must be calibrated and
adjusted in accordance with Test Methods shall be used to compact the soil specimen to the desired density.D2168.
6.6 Expansion-Measuring Apparatus—An adjustable metal stem and perforated metal plate, similar in configuration to that shown
7 15 1
in Fig. 2. The perforated plate shall be 5 ⁄8 to 5 ⁄16 in. (149.2 to 150.8 mm) in diameter and have at least forty-two ⁄16-in.
(1.59-mm) diameter holes uniformly spaced over the plate. A metal tripod to support the dial gauge for measuring the amount of
swell during soaking is also required. The expansion measuring apparatus shall not weigh more than 2.8 lbf or a mass of 1.3 kg.
6.6.1 Swell Measurement Device—Generally mechanical dial indicators capable of reading to 0.001 in. (0.025 mm) with a range
of 0.200-in. (5-mm) minimum.
6.7 Surcharge Weights—These “weights” are actually “masses” converted to a force. One or two annular metal weights having a
total weight of 10 6 0.05 lbf (equivalent to a mass of 4.54 6 0.02 kg) and slotted metal weights each having a weight of 5 6
7 15
0.05 lbf (equivalent to a mass of 2.27 6 0.02 kg). The annular weight shall be 5 ⁄8 to 5 ⁄16 in. (149.2 to 150.8 mm) in diameter
and shall have a center hole of approximately 2 ⁄8 in. (53.98 mm) (see Fig. 3).
6.8 Penetration Piston—A metal piston 1.954 6 0.005 in. (49.63 6 0.13 mm) in diameter and not less than 4 in. (101.6 mm) long
(see Fig. 3).
6.9 Balance—A class GP5 balance meeting the requirements of Specifications D4753 for a balance of 1-g readability.
NOTE 1—See Table 21 for SI equivalents.
FIG. 2 Expansion-Measuring Apparatus
D1883 − 21
NOTE 1—See Table 21 for SI equivalents.
FIG. 3 Surcharge Weights and Penetration Piston
6.10 Drying Oven—Thermostatically controlled, preferably of a forced-draft type and capable of maintaining a uniform
temperature of 230 6 9°F (110 6 5°C) throughout the drying chamber.
6.11 Sieves— ⁄4 in. (19 mm) and No. 4 (4.75 mm), conforming to the requirements of Specification E11.
6.12 Filter Paper—A fast filtering, high grade hardened, low ash filter paper, 6.000 in. (152.4 mm) diameter.
6.13 Straightedge—A stiff metal straightedge of any convenient length but not less than 10.0 in. (254 mm). The total length of
the straightedge shall be machined straight to a tolerance of 60.005 in. (60.13 mm). The scraping edge shall be beveled if it is
thicker than ⁄8 in. (3 mm).
6.14 Soaking Tank or Pan—A tank or pan of sufficient depth and breathbreadth to allow free water around and over the assembled
mold. The tank or pan should have a bottom grating that allows free access of water to the perforations in the mold’s base.
6.15 Mixing Tools—Miscellaneous tools such as mixing pan, spoon, trowel, spatula, etc., or a mechanical device for thoroughly
mixing the sample of soil with water.
D1883 − 21
7. Sample
7.1 Do not reuse soil that has been previously compacted in the laboratory. The reuse of previously compacted soils may yield
a greater maximum dry unit weight.
7.2 The specimen(s) for compaction shall be prepared in accordance with the procedures given in Method C of Test Methods D698
or D1557 for compaction in a 6.000-in. (152.4-mm) mold except as follows:
7.2.1 If all material passes a ⁄4-in. (19-mm) sieve, the entire gradation shall be used for preparing specimens for compaction
3 3
without modification. If material is retained on the ⁄4-in. (19-mm) sieve, the material retained on the ⁄4-in. (19-mm) sieve shall
be removed and replaced by an equal mass of material passing the ⁄4-in. (19-mm) sieve and retained on the No. 4 (4.75 mm) sieve
obtained by separation from portions of the sample not used for testing.
8. Test Specimens
8.1 Bearing Ratio at Optimum Water Content Only—Using material prepared as described in 7.17.2, conduct a control compaction
test with a sufficient number of test specimens to establish the optimum water content for the soil using the compaction method
specified, either Test Methods D698 or D1557. A previously performed compaction test on the same material may be substituted
for the compaction test just described, provided that if the sample contains material retained on the ⁄4-in. (19-mm) sieve, then soil
prepared as described in 7.17.2.1 is used.used for the CBR test.
NOTE 3—Maximum dry unit weight obtained from a compaction test performed in a 4.000-in. (101.6-mm) diameter mold may be slightly greater than
the maximum dry unit weight obtained from compaction in the 6.000-in. (152.4-mm) compaction mold or CBR mold.
8.1.1 For cases where the CBR is desired at 100 % maximum dry unit weight and optimum water content, compact a specimen
using the specified compaction procedure, either Test Methods D698 or D1557, from soil prepared to within 60.5 percentage point
of optimum water content determined in accordance with Test Method D2216.
8.1.2 Where the CBR is desired at optimum water content and some percentage of maximum dry unit weight, compact three
specimens from soil prepared to within 60.5 percentage point of optimum water content and using the specified compaction but
using a different number of blows per layer for each specimen. The number of blows per layer shall be varied as necessary to
prepare specimens having unit weights above and below the desired value. Typically, if the CBR for soil at 95 % of maximum dry
unit weight is desired, specimens compacted using 56, 25, and 10 blows 10-blows, 25-blows, and 56-blows per layer is satisfactory.
Penetration shall be performed on each of these specimens.
8.2 Bearing Ratio for a Range of Water Contents—Prepare specimens in a manner similar to that described in 8.1 except that each
specimen used to develop the compaction curve shall be penetrated. In addition, the complete water content-unit weight
relationship for the 10-blows, 25-blows, and 56-blows per layer compactions shall be developed and each test specimen compacted
shall be penetrated. Perform all compaction in the CBR mold. In cases where the specified unit weight is at or near 100 %
maximum dry unit weight, it will be necessary to include a compactive effort greater than 56-blows per layer.
NOTE 4—Where the maximum dry unit weight was determined from compaction in the 4.000-in. (101.6-mm) mold, it may be necessary to compact
specimens as described in 8.1.2, using 75 blows per layer or some other value sufficient to produce a specimen having a unit weight equal to or greater
than that required.
NOTE 5—A semi-log log plot of dry unit weight versus compactive effort usually gives a straight-line relationship when compactive effort in ft-lb/ft is
plotted on the log scale. This type of plot is useful in establishing the compactive effort and number of blows per layer needed to br
...