ASTM D4186/D4186M-20e1

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.
´1
Designation: D4186/D4186M − 20
Standard Test Method for
One-Dimensional Consolidation Properties of Saturated
Cohesive Soils Using Controlled-Strain Loading
This standard is issued under the fixed designation D4186/D4186M; 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.
ε NOTE—Section references in 10.1 were editorially corrected in April 2021.
1. Scope* 1.8 This test method is most often used for materials of
relatively low hydraulic conductivity that generate measurable
1.1 This test method is for the determination of the magni-
excess base pressures. It may be used to measure the compres-
tudeandrate-of-consolidationofsaturatedcohesivesoilsusing
sion behavior of essentially free draining soils but will not
continuous controlled-strain axial compression. The specimen
provide a measure of the hydraulic conductivity or coefficient
is restrained laterally and drained axially to one surface. The
of consolidation.
axial force and base excess pressure are measured during the
deformationprocess.Controlledstraincompressionistypically
1.9 All recorded and calculated values shall conform to the
referred to as constant rate-of-strain (CRS) testing.
guideforsignificantdigitsandroundingestablishedinPractice
D6026, unless superseded by this test method. The significant
1.2 Thistestmethodprovidesforthecalculationoftotaland
digits specified throughout this standard are based on the
effective axial stresses, and axial strain from the measurement
assumptionthatdatawillbecollectedoveranaxialstressrange
of axial force, axial deformation, chamber pressure, and base
from 1% of the maximum stress to the maximum stress value.
excess pressure. The effective stress is computed using steady
state equations.
1.9.1 Theproceduresusedtospecifyhowdataarecollected/
recorded and calculated in this standard are regarded as the
1.3 This test method provides for the calculation of the
industry standard. In addition, they are representative of the
coefficient of consolidation and the hydraulic conductivity
significant digits that should generally be retained. The proce-
throughout the loading process.These values are also based on
dures used do not consider material variation, purpose for
steady state equations.
obtaining the data, special purpose studies, or any consider-
1.4 This test method makes use of steady state equations
ations for the user’s objectives; and it is common practice to
resulting from a theory formulated under particular assump-
increase or reduce significant digits of reported data to be
tions. Subsection 5.5 presents these assumptions.
commensuratewiththeseconsiderations.Itisbeyondthescope
1.5 The behavior of cohesive soils is strain rate dependent of this standard to consider significant digits used in analysis
andhencetheresultsofaCRStestaresensitivetotheimposed methods for engineering design.
rateofstrain.Thistestmethodimposeslimitsonthestrainrate
1.9.2 Measurements made to more significant digits or
to provide comparable results to the incremental consolidation
better sensitivity than specified in this standard shall not be
test (Test Method D2435).
regarded a non-conformance with this standard.
1.6 The determination of the rate and magnitude of consoli-
1.10 Units—The values stated in either SI units or inch-
dation of soil when it is subjected to incremental loading is
poundunits[giveninbrackets]aretoberegardedseparatelyas
covered by Test Method D2435.
standard. The values stated in each system may not be exact
1.7 This test method applies to intact (Group C and Group equivalents;therefore,eachsystemshallbeusedindependently
D of Practice D4220), remolded, or laboratory reconstituted of the other. Combining values from the two systems may
samples.
result in non-conformance with the standard. Reporting of test
results in units other than SI shall not be regarded as noncon-
formance with this standard.
1.10.1 The gravitational system is used when working with
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.05 on Strength and
inch-pound units. In this system, the pound (lbf) represents a
Compressibility of Soils.
unit of force (weight), while the unit for mass is slugs. The
Current edition approved Nov. 1, 2020. Published November 2020. Originally
ɛ1
rationalized slug unit is not given, unless dynamic (F = ma)
approved in 1982. Last previous edition approved in 2012 as D4186–12 . DOI:
10.1520/D4186_D4186M-20E01. calculations are involved.
*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
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D4186/D4186M − 20
1.10.2 Itiscommonpracticeintheengineering/construction Construction Materials Testing
profession to concurrently use pounds to represent both a unit D5720 Practice for Static Calibration of Electronic
of mass (lbm) and of force (lbf). This implicitly combines two Transducer-Based Pressure Measurement Systems for
separate systems of units; that is, the absolute system and the Geotechnical Purposes (Withdrawn 2018)
gravitational system. It is scientifically undesirable to combine D6026Practice for Using Significant Digits in Geotechnical
the use of two separate sets of inch-pound units within a single Data
standard. As stated, this standard includes the gravitational D6027Practice for Calibrating Linear Displacement Trans-
system of inch-pound units and does not use/present the slug ducers for Geotechnical Purposes
unitformass.However,theuseofbalancesorscalesrecording D6519Practice for Sampling of Soil Using the Hydrauli-
pounds of mass (lbm) or recording density in lbm/ft shall not cally Operated Stationary Piston Sampler
be regarded as non-conformance with this standard. D6913Test Methods for Particle-Size Distribution (Grada-
tion) of Soils Using Sieve Analysis
1.11 This standard does not purport to address all of the
D7015Practices for Obtaining Intact Block (Cubical and
safety concerns, if any, associated with its use. It is the
Cylindrical) Samples of Soils
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
3.1 Definitions:
1.12 This international standard was developed in accor-
3.1.1 Fordefinitionsofcommontechnicaltermsusedinthis
dance with internationally recognized principles on standard-
standard, refer to Terminology D653.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
3.2 Definitions of Terms:
–2
mendations issued by the World Trade Organization Technical
3.2.1 back pressure, (u (FL )), n—a fluid pressure in
b
Barriers to Trade (TBT) Committee.
excess of atmospheric pressure that is applied to the drainage
boundary of a test specimen.
2. Referenced Documents
3.2.1.1 Discussion—Typically, the back pressure is applied
to cause air in the pore spaces to pass into solution, thus
2.1 ASTM Standards:
saturating the specimen.
D653Terminology Relating to Soil, Rock, and Contained
Fluids
3.2.2 consolidometer, n—an apparatus containing a speci-
D854Test Methods for Specific Gravity of Soil Solids by
men under conditions of negligible lateral deformation while
Water Pycnometer
allowing one-dimensional axial deformation and one direc-
D1587Practice for Thin-Walled Tube Sampling of Fine-
tional axial flow.
Grained Soils for Geotechnical Purposes
–2
3.2.3 excess pore-water pressure, ∆ (FL ), n—in effective
u
D2216Test Methods for Laboratory Determination ofWater
stress testing, the pressure that exists in the pore fluid relative
(Moisture) Content of Soil and Rock by Mass
to (above or below) the back pressure.
D2435Test Methods for One-Dimensional Consolidation
–2
3.2.4 total axial stress, σ (FL ), n—in effective stress
a
Properties of Soils Using Incremental Loading
testing, the normal stress applied to the axial boundary of the
D2487Practice for Classification of Soils for Engineering
specimen in excess of the back pressure.
Purposes (Unified Soil Classification System)
D2488Practice for Description and Identification of Soils 3.3 Definitions of Terms Specific to This Standard:
-2
(Visual-Manual Procedures)
3.3.1 average effective axial stress, σ’ (FL ), n—the
a
D3213Practices for Handling, Storing, and Preparing Soft effective stress calculated using either the linear or nonlinear
Intact Marine Soil
theory equations to represent the average value at any time
D3550Practice for Thick Wall, Ring-Lined, Split Barrel, under steady state constant strain rate conditions.
Drive Sampling of Soils
3.3.2 axial deformation reading, AD (volts), n—readings
D3740Practice for Minimum Requirements for Agencies
taken during the test of the axial deformation transducer.
Engaged in Testing and/or Inspection of Soil and Rock as
3.3.3 axial force transducer reading, AF (volts),
Used in Engineering Design and Construction
n—readings taken during the test of the axial force transducer.
D4220 Practices for Preserving and Transporting Soil
–2
3.3.4 base excess pressure, ∆u (FL ), n—the fluid pres-
Samples m
sure in excess (above or below) of the back pressure that is
D4318Test Methods for Liquid Limit, Plastic Limit, and
measured at the sealed boundary of the specimen under
Plasticity Index of Soils
conditions of one way drainage. The base excess pressure will
D4452Practice for X-Ray Radiography of Soil Samples
be positive during loading and negative during unloading.
D4753Guide for Evaluating, Selecting, and Specifying Bal-
ances and Standard Masses for Use in Soil, Rock, and
3.3.5 base excess pressure ratio, R (D), n—the ratio of (1)
u
the base excess pressure to (2) the total axial stress.This value
will be positive during loading and negative during unloading.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
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D4186/D4186M − 20
–2
3.3.6 base pressure, u (FL ), n—the fluid pressure mea- phase.Theconstantloadphaseallowsthebaseexcesspressure
m
sured at the sealed boundary (usually at the base of the to return to near zero prior to unloading. More extensive tests
consolidometer) of the specimen under conditions of one way can be performed by including more phases to obtain unload-
drainage. reload cycle(s).
3.3.7 base pressure reading, BP (volts), n—readings taken
4.4 The rate of deformation is selected to produce a base
during the test of the base pressure transducer.
excesspressureratiothatisbetweenabout3%and15%inthe
–2
normally consolidated range during the loading phase.
3.3.8 chamber pressure, σ (FL ), n—the fluid pressure
c
NOTE 1—The base excess pressure ratio typically decreases during
inside the consolidometer. In most CRS consolidometers, the
loading. The lower limit provides sufficient pressure to compute the rate
chamber fluid is in direct contact with the specimen. For these
parameters and the upper limit reduces the differences between the linear
devices (and this test method), the chamber pressure will be
andnonlinearmodelcalculations.Italsohelpsconstraindifferencesinthe
equal to the back pressure.
compression behavior when testing rate sensitive materials.
3.3.9 chamber pressure reading, CP (volts), n—readings 4.5 During loading and unloading, the measurements are
taken during the test of the chamber pressure transducer.
first evaluated in order to be sure transient effects are small as
defined by the steady state factor. Steady state equations are
3.3.10 constant rate-of-strain, CRS, n—a method of con-
thenusedtocomputetheone-dimensionaleffectiveaxialstress
solidating a specimen in which the surface is deformed at a
versusstrainrelationship.Duringtheloadingphase,whenbase
uniform rate while measuring the axial deformation, axial
excess pressures are significant and transient effects are small,
reaction force, and induced base excess pressure.
the measurements are used to compute both the coefficient of
3.3.11 equilibrated water, n—test water that has come to
consolidation and hydraulic conductivity throughout the test.
equilibrium with the current room conditions including
4.6 It is possible to interpret measurements made during the
temperature, chemistry, dissolved air, and stress state.
test when transient effects are significant, but these equations
3.3.12 linear theory (calculation method), n—a set of equa-
are complicated and beyond the scope of this standard test
tions derived based on the assumption that the coefficient of
method. Interpretation of transient conditions does not consti-
volume compressibility (m ) is constant (the soil follows a
v
tute non-conformance of this test method.
linear strain versus effective stress relationship).
5. Significance and Use
3.3.13 monofilament nylon screen, n—thin porous synthetic
woven fabric made of single untwisted filament nylon.
5.1 Information concerning magnitude of compression and
3.3.14 nonlinear theory (calculation method), n—a set of rate-of-consolidation of soil is essential in the design of earth
equations derived based on the assumption that the compres-
structuresandearthsupportedstructures.Theresultsofthistest
sion index (C ) is constant (the soil follows a linear strain method may be used to analyze or estimate one-dimensional
c
versus log effective stress relationship).
settlements, rates of settlement associated with the dissipation
of excess pore-water pressure, and rates of fluid transport due
3.3.15 steady state condition, n—in CRS testing, a time
to hydraulic gradients. This test method does not provide
independent strain distribution within the specimen that
information concerning the rate of secondary compression.
changes in average value as loading proceeds.
5.2 Strain Rate Effects:
3.3.16 steady state factor, F (D), n—a dimensionless num-
5.2.1 It is recognized that the stress-strain results of con-
ber equal to the change in total axial stress minus the base
solidation tests are strain rate dependent. Strain rates are
excess pressure divided by the change in total axial stress.
limited in this test method by specification of the acceptable
3.3.17 transient condition, n—in CRS testing, a time depen-
magnitudesofthebaseexcesspressureratioduringtheloading
dentvariationinthestraindistributionwithinthespecimenthat
phase. This specification provides comparable results to the
is created at the start of a CRS loading or unloading phase or
100 % consolidation (end of primary) compression behavior
when the strain rate changes and then decays with time to a
obtained using Test Method D2435.
steady state strain distribution.
5.2.2 Field strain rates vary greatly with time, depth below
the loaded area, and radial distance from the loaded area. Field
4. Summary of Test Method
strain rates during consolidation processes are generally much
4.1 In this test method the specimen is constrained axially
slower than laboratory strain rates and cannot be accurately
between two parallel, rigid boundaries and laterally such that
determinedorpredicted.Forthesereasons,itisnotpracticalto
the cross sectional area remains essentially constant. Drainage
replicate the field strain rates with the laboratory test strain
isprovidedalongoneboundary(typicallythetop)andthefluid
rate.
pressureismeasuredattheothersealedboundary(typicallythe
5.3 Temperature Effects:
base) of the consolidometer.
5.3.1 Temperature affects the rate parameters such as hy-
4.2 Aback pressure is applied to saturate both the specimen
draulic conductivity and the coefficient of consolidation. The
and the base pressure measurement system.
primary cause of temperature effects is due to the changes in
4.3 The specimen is deformed axially at a constant rate pore fluid viscosity, but soil sensitivity may also be important.
while measuring the time, axial deformation, reaction force, This test method provides results under room temperature
chamber pressure, and base pressure. A standard test includes conditions, corrections may be required to account for specific
one loading phase, one constant load phase, and one unloading field conditions. Such corrections are beyond the scope of this
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D4186/D4186M − 20
test method. Special accommodation may be made to replicate conductivity. In this case, the average effective axial stress is
field temperature conditions and still be in conformance with equal to the total axial stress and the results are independent of
this test method. model.
5.4 Saturation Effects: 5.8 The procedures presented in this test method assume a
high permeability porous disk is used in the base pressure
5.4.1 This test method may not be used to measure the
measurementsystem.Useofalowpermeabilityporousdiskor
properties of partially saturated soils because the method
high-air entry (>1 bar) disk will require modification of the
requires the material to be back pressure saturated prior to
equipment specifications and procedures. These modifications
consolidation.
arebeyondthescopeofthistestmethodandarenotconsidered
5.5 Test Interpretation Assumptions—The equations used in
a non-conformance.
this test method are based on the following assumptions:
NOTE 3—The quality of the results produced by application of this
5.5.1 The soil is saturated.
standard is dependent on the competence of the personnel performing it,
5.5.2 The soil is homogeneous. and the suitability of the equipment and facilities.Agencies that meet the
criteria of Practice D3740 are generally considered capable of competent
5.5.3 The compressibility of the soil particles and water is
and objective testing/sampling/inspection/etc. Users of this standard are
negligible.
cautioned that compliance with Practice D3740 does not in itself assure
5.5.4 Flow of pore water occurs only in the vertical direc-
reliable results. Reliable results depend on many factors; Practice D3740
tion. provides a means of evaluating some of those factors.
5.5.5 Darcy’s law for flow through porous media applies.
6. Apparatus
5.5.6 The ratio of soil hydraulic conductivity to compress-
ibility is constant throughout the specimen during the time
6.1 Overview—Fig. 1 presents an overview of the arrange-
interval between individual reading sets.
ment of components for a device used to perform the constant
5.5.7 The compressibility of the base excess pressure mea-
rate of strain consolidation test. This figure is provided to aid
surement system is negligible compared to that of the soil.
thereaderanddoesnotdescribeanyspecificdevice.Thefigure
shows the essential components and one of many possible
5.6 Theoretical Solutions:
configurations. Other arrangements meeting the individual
5.6.1 Solutions for constant rate of strain consolidation are
componentspecificationsoutlinedinthefollowingsectionsare
available for both linear and nonlinear soil models.
equally acceptable.
5.6.1.1 Thelinearmodelassumesthatthesoilhasaconstant
coefficientofvolumecompressibility(m ).Theseequationsare
6.2 Electronics—This test method requires the use of elec-
v
presented in 13.4. tronic transducers along with the necessary apparatus to
5.6.1.2 The nonlinear model assumes that the soil has a energize (power supply) and read (digital multimeter) these
constant compression index (C ). These equations are pre- transducers. In addition, automatic data acquisition will be
c
sented in Appendix X1. necessary to achieve the required reading frequency.
6.2.1 Transducers are required to measure the base pressure
NOTE 2—The base excess pressure measured at the boundary of the
(or base excess pressure), the chamber pressure, the axial
specimenisassumedequaltothemaximumexcesspore-waterpressurein
deformation, and the axial force. Each transducer must meet
the specimen. The distribution of excess pore-water pressure throughout
the specimen is unknown. Each model predicts a different distribution.As
the accuracy and capacity requirement specified for the par-
the magnitude of the base excess pressure increases, the difference
ticular measurement. The capacity of the force and pressure
between the two model predictions increases. At a base excess pressure
transducers will depend on the stiffness of the soil and
ratio of 15%, the difference in the average effective stress calculation
magnitude of the back pressure.
between the two models is about 0.3%.
6.2.2 Apowersupplyisrequiredtoenergizethesetransduc-
5.6.2 The equations for the linear case are used for this test
ers. The specific type of power supply will depend on the
method. This test method limits the time interval between
detailsoftheindividualtransducers.Ideally,allthetransducers
readingsandthemaximumbaseexcesspressureratiotovalues
will operate using the same power supply. Some data acquisi-
that yield similar results when using either theory. However, it
tion systems provide transducer power.
is more precise to use the model that most closely matches the
6.2.3 The calculations presented in this standard assume
shape to the compression curve.
thatthetransducersproducealinearnormalizedvoltageoutput
5.6.3 ThenonlinearequationsarepresentedinAppendixX1
as a function of the parameter being measured as specified in
andtheiruseisnotconsideredanon-conformancewiththistest
D5720 and D6027. Many other types of transducers exist and
method.
areacceptableoptionsforthisstandardprovidedthattheymeet
5.6.4 The equations used in this test method apply only to
the accuracy and capacity requirements. These transducers
steady state conditions. The transient strain distribution at the
mayproducecurrentratherthanvoltage,havenon-linearrather
start of a loading or unloading phase is insignificant after the
than linear outputs, or may not require normalization to the
steady state factor (F) exceeds 0.4. Data corresponding to
excitation voltage.
lower steady state factors are not used in this test method.
6.2.4 Recording Devices:
5.7 This test method may be used to measure the compres- 6.2.4.1 Adigital multimeter is useful in setting up tests and
sion behavior of free draining soils. For such materials, the obtaining zero readings, but conducting a test requires far too
base excess pressure will be zero and it will not be possible to many readings (frequency and duration) to be collected manu-
compute the coefficient of consolidation or the hydraulic ally.
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D4186/D4186M − 20
FIG. 1 Overview of Primary Components of a CRS Apparatus
6.2.4.2 A data acquisition system is required to collect and other force-measuring device capable of the accuracy pre-
store data during the test. The specifications (bit precision and scribedinthisparagraphandmaybeapartoftheaxialloading
input range) of the data acquisition system must be matched to device. The axial force-measuring device shall have an accu-
the individual transducers in order to obtain the capacity racy of 0.25% (or better) of full range and a readability
necessaryfortheindividualtestandreadabilityrequirementfor equivalent to at least 4 significant digits at the maximum force
eachdevice.Theserequirementswilldependonthestiffnessof applied to the specimen.
the soil, the magnitude of the back pressure, and the output
6.4.1 For a constant rate-of-deformation to be transmitted
characteristics of the specific transducers.
from the axial loading device through the force-measuring
6.2.4.3 A reading set must contain a measurement of base
device, it is important that the force-measuring device be
pressure (or base excess pressure), chamber pressure, axial
relatively stiff. Most electronic load cells are sufficiently stiff,
force, axial deformation, transducer excitation (if using nor-
while proving rings are typically not stiff (that is, they are
malized conversion equations), and elapsed time (or time).
compressible).
Whendeterminingthehydraulicconductivityorthecoefficient
6.5 Chamber Pressure Maintaining Device—This device is
of consolidation, time must be recorded to three significant
used to back pressure saturate the specimen and base pressure
digits of the reading interval and the reading set must be
measuring system. It must be capable of applying and control-
completed within 0.1 s if the measurements are made sequen-
lingthechamberpressuretowithin 62%ofthetargetpressure
tially. The reading interval will depend on the strain rate.
throughout the test. This device may consist of a single unit or
6.3 Axial Loading Device—Thisdevicemaybeascrewjack
separateunitsconnectedtothetopandbottomofthespecimen.
driven by an electric motor through a geared transmission, a
Thedevicemaybeapressurizedhydraulicsystemorapartially
hydraulic or pneumatic loading device, or any other compres-
filledreservoirwithagas/waterinterface.Thebottomdrainage
sion device with sufficient force and deformation capacity. It
lines shall be connected to the bottom drainage valve and shall
must be able to apply a constant rate of deformation as well as
be designed to minimize dead space in the lines. This valve,
maintainaconstantforce.Duringasingleloadingorunloading
when open, shall permit the application of the chamber
phase of the test, the deformation rate shall be monotonic and
pressure to the base of the specimen; when closed, it shall
shallnotvarybymorethanafactorof5.Theratecangradually
prevent the leakage of water from the specimen base and base
changeduetothesystemstiffness,butshallnothavemorethan
pressure measuring device. However, if a high air entry stone
610% cyclic variation. During a constant load phase of the
is used on the nondrainage boundary of the specimen, then
test, the load must be maintained to 62% of the target value.
different means will be required to keep the system saturated.
Vibration due to the operation of the loading device shall be
6.5.1 A pressurized hydraulic system may be activated by
considered sufficiently small when there are no visible ripples
deadweight acting on a piston, a gear driven piston with
in a glass of water placed on the loading platform when the
feedback control, a hydraulic regulator, or any other pressure-
device is operating at the typical test speed.
maintaining device capable of applying and controlling the
6.4 Axial Force Measuring Device—This device may be a chamber pressure within the specifications stated above. The
load ring, strain-gauge load cell, hydraulic load cell, or any system shall be filled with equilibrated test water.
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D4186/D4186M − 20
6.5.2 Apressurereservoirpartiallyfilledwithtestwaterand appliedbackpressureplus50%ofthemaximumappliedaxial
having a gas/water interface may be controlled by a precision stress, and a readability equivalent to at least four significant
pressure regulator. As much as practicable, the device should digits at the maximum applied axial stress.
minimize the air diffusion into the chamber water. All gas/
NOTE 6—Typically, pressure transducers with a capacity of 1500 kPa
water interfaces should be small in area relative to the volume 2
[200 lbf/in. ] will meet these requirements.
of water in the reservoir and the reservoirs connected to the
6.8 Deformation Measuring Device—Theaxialdeformation
consolidometer by a length of small diameter tubing. Any
of the specimen is usually determined from the travel of the
water remaining in the reservoir shall be flushed out after each
piston acting on the top platen of the specimen. The deforma-
test and replenished with equilibrated water.
tion measuring device may be a linear variable differential
6.5.3 The bottom drainage valve may be assumed to pro-
transformer (LVDT), a digital dial gauge (DDG), an
duce minimum volume change if opening or closing the valve
extensometer, a linear strain transducer (LST), or other elec-
in a closed, saturated pore-water pressure system does not
tronicmeasuringdeviceandshallhavearangeofatleast50%
induce a pressure change of greater that 1 kPa [0.1 lbf/in ].All
of the initial height of the specimen. The device shall have an
valves must be capable of withstanding applied pressures
accuracyof0.25%(orbetter)offullrangeandareadabilityof
without significant leakage.
at least 4 significant digits at the initial specimen height.
NOTE 4—Ball valves have been found to provide minimum volume-
6.9 Consolidometer—Thisdevicemustholdthespecimenin
change characteristics; however, any other type of valve having suitable
a confinement ring sealed to a rigid base, with porous disks on
volume-change characteristics may be used.
each face of the specimen and contained within a pressure
6.6 Chamber Pressure Measuring Device—A pressure
vessel. The pressure vessel must contain the chamber pressure
transducer arranged to measure the applied chamber pressure
andprovidealignmentandapressuresealforthepiston.Ahigh
shall have an accuracy of 60.25 % (or better) of full range, a
air entry stone can be used in place of the porous disk on the
capacity in excess of the applied chamber pressure, and a
bottom of the specimen provided that the high air entry stone
readability equivalent to at least 4 significant digits at the
is saturated prior to setting up the specimen. The top platen
maximum applied axial stress.
shall be attached to the piston and rigid enough to uniformly
distribute the axial load to the top stone. Any potentially
6.7 Base Pressure Measuring Device—This device can be a
differential pressure transducer referenced to the chamber submerged parts of the consolidometer shall be made of a
materialthatisnoncorrosiveinrelationtothesoilorotherparts
pressure or a separate pressure transducer measuring pressure
at the base of the specimen. If a separate pressure transducer is of the consolidometer. The bottom of the confinement ring
shall form a leak proof seal with the rigid base capable of
used, then it’s zero value must be adjusted to give the same
pressure reading as the chamber pressure transducer at the end withstanding the base excess pressure. The consolidometer
shall be constructed such that placement of the confinement
of back pressure saturation and with the bottom drainage valve
open.Thedeviceshallbeconstructedandlocatedsuchthatthe ring(withspecimen)intotheconsolidometerwillnotentrapair
water pressure at the base of the specimen can be measured at the base of the specimen. The axial loading device and
with negligible drainage from the specimen due to changes in chamberpressuremaintainingdevicemaybeanintegralpartof
pore-water pressure. To achieve this requirement, a stiff elec- the consolidometer. A schematic drawing of the essential
tronic pressure transducer must be used.The compliance of all components of a generic CRS consolidometer is shown in Fig.
the assembled parts of the base pressure measurement system 2.
relative to the total volume of the specimen shall satisfy the 6.9.1 Axial Loading Piston—The axial loading piston trans-
following requirement:
fers force to the specimen and passes through the pressure
26 2 25 2 vessel.
~∆V/V!/∆u ,3.2 310 m /kN @2.2 310 in /lbf# (1)
m
6.9.1.1 Thepistonshallbeconstructedofhardenedstainless
where:
steel with surface roughness and tolerance meeting the speci-
∆V = change in volume of the base measurement system
fications set by the bushing manufacturer. The external end of
3 3
due to a pressure change, mm [in ],
thepistonshallbeconcaveorconvextomatewiththemoment
3 3
V = total volume of the specimen, mm [in ], and
break. The internal end shall connect rigidly to the top platen.
∆u = change in base excess pressure, kPa [lbf/in ].
m
6.9.1.2 The axial load piston seal must be designed so the
NOTE 5—To meet this compressibility requirement, tubing between the
variation in axial load due to friction does not exceed 0.05 %
specimen and the measuring device should be short and thick-walled with
of the maximum axial load applied to the specimen.
small bores. Thermoplastic, copper, and stainless steel tubing have been
used successfully.
NOTE 7—The use of two linear ball bushings to guide the piston is
recommended to minimize friction and maintain alignment.
6.7.1 A differential pressure transducer shall have an accu-
racy of 60.25 % (or better) of full range, a capacity of at least
6.9.1.3 The external end of the piston shall be fitted with a
50%ofthemaximumappliedaxialstress,aburstpressurethat shear and moment break. This element allows precise align-
exceeds the applied back pressure plus 50 % of the maximum
ment of the loading piston with the load cell while preventing
appliedaxialstress,andareadabilityequivalenttoatleastfour transfer of either a bending moment or lateral force.
significant digits at the maximum applied axial stress.
6.9.2 Specimen Confinement Ring—The confinement ring
6.7.2 Aseparate pressure transducer shall have an accuracy shall be made of a material that is noncorrosive in relation to
of 60.25 % (or better) of full range, a capacity of at least the the soil and pore fluid. The inner surface shall be polished and
´1
D4186/D4186M − 20
FIG. 2 Example of a CRS Consolidometer
coated with a low-friction material (silicone/vacuum grease). D6913.If,aftercompletionofatest,itisfoundbasedonvisual
The inside diameter of the ring shall be fabricated to a observation that oversize (> 2 mm [0.075 in.]) particles are
tolerance of at least 0.1 percent of the diameter. present, indicate this information in the report of test data.
6.9.2.1 Ring Rigidity—The ring shall be stiff enough to 6.9.3.3 The maximum height-to-diameter ratio shall be 0.4.
prevent significant lateral deformation of the specimen
6.10 Porous Disks—The porous disks at the top and bottom
throughout the test. The rigidity of the ring shall be such that,
of the specimen shall be made of silicon carbide, aluminum
underhydrostaticstressconditionsinthespecimen,thechange
oxide, or other material of similar stiffness that is not corroded
in diameter of the ring will not exceed 0.04 percent of the
by the specimen or pore fluid. The disks shall have plane and
diameter under the greatest load applied.
smooth surfaces and be free of cracks, chips, and nonunifor-
mities. They shall be checked regularly to ensure that they are
NOTE 8—For example, a ring thickness (for metallic rings) of 3.2 mm
[ ⁄8 in.] will be adequate for stresses up to 6000 kPa [900 lbf/in ] for a
not clogged. For fine-grained soils, fine-grade porous disks
specimen diameter of 63.5 mm [2.5 in.].
shall be used. The disks shall be fine enough that the soil will
6.9.3 Specimen Geometry—The test specimen dimensions not penetrate into their pores but have sufficient hydraulic
shall conform to the following specifications. conductivity so as not to impede the flow of water from the
6.9.3.1 The minimum diameter shall be about 50 mm [2.0 specimen. The disk thickness and hydraulic conductivity
in.]. should result in an impedance factor of at least 100.
6.9.3.2 Theminimumheightshallbeabout12mm[0.5in.],
NOTE 9—The impedance factor is defined as the ratio of the hydraulic
but shall not be less than 10 times the maximum particle
conductivity of the stones times the drainage thickness of the soil to the
diameter as determined in accordance with Test Method hydraulic conductivity of the soil times the thickness of the stone.
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D4186/D4186M − 20
6.10.1 The diameter of the top disk shall be 0.2 to 0.5 mm be rigid and larger in diameter than the outside diameter of the
[0.01 to 0.02 in.] less than the inside diameter of the confine- confinement ring. One surface of the disc shall have a
ment ring. protrusion that is about 0.1 mm [0.005 in.] less than the inside
diameter of the confinement ring, a step height of at least 1.2
6.10.2 The surfaces of the disks, as well as the bearing
mm [0.050 in.] and a flatness tolerance of 6 0.03 mm [0.001
surfaces in contact with them, shall be flat and rigid enough to
in.].
prevent breakage of these disks.
6.10.3 The disks shall be regularly cleaned by ultrasonifi-
6.16 Specimen Measuring Device—The specimen height
cation or boiling and brushing and checked routinely for signs
may be computed from the height of the confinement ring and
of clogging. Disks will last longer if stored in water between
therecessspacerormeasureddirectly.Ifapplicable,thedevice
testing.
to measure the height of the specimen shall be capable of
measuringtothenearest0.01mm[0.001in.]orbetterandshall
6.11 Filtering Element—To prevent intrusion of material
beconstructedsuchthatitsusewillnotpenetratethesurfaceof
into the pores of the porous disk, a filtering element must be
thespecimen.Thespecimendiametermaybeassumedequalto
placed between the top porous disk and the specimen. The
the inside diameter of the confinement ring.
element shall have negligibly small hydraulic impedance. A
fine monofilament-nylon screen mesh or high grade hardened,
6.17 Temperature Maintaining Device—Unless otherwise
low ash filter paper may be used for the filtering element.
specified by the requesting agency, the standard test tempera-
NOTE 10—Filtering elements should be cut to approximately the same
ture shall be in the range of 22 6 5°C. In addition, the
shape as the cross section of the test specimen. Soak the filter paper, if
temperatureoftheconsolidometer,testspecimen,andreservoir
used, in a container of test water to allow it to equilibrate before testing.
of pore fluid shall not vary more than 62°C. Normally, this is
6.12 Balance—The balance(s) shall be suitable for deter-
accomplishedbyperformingthetestinaroomwitharelatively
miningthemassofthespecimenplusthecontainmentringand
constant temperature. If such a room is not available, the
for making the water content measurements. The balance(s)
apparatus shall be placed in an insulated chamber or other
shall be selected as discussed in Specification D4753. The
device that maintains a temperature within the tolerance
mass of specimens shall be determined to at least four
specified above.
significant digits.
6.18 Test Water—Water is necessary to saturate the porous
6.13 Sample Extruder—When the material being tested is
stones, fill the pressure chamber and the back pressure system.
contained in a sampling tube, the soil shall be removed from
Ideally, this water would be similar in composition to the
the sampling tube with an extruder. The sample extruder shall
specimenporefluid.Optionsincludeextractedporewaterfrom
be capable of extruding the soil from the sampling tube in the
the field, potable tap water, demineralized water, or saline
same direction of travel that the soil entered the tube and with
water. The requesting agency should specify the water option.
minimum disturbance of the soil. If the soil is not extruded
In the absence of a specification, the test shall be performed
vertically, care shall be taken to avoid bending stresses on the
with potable tap water.
soilduetogravity.Conditionsatthetimeofsoilextrusionmay
6.19 Water Content Containers—In accordance with Test
dictate the direction of removal, but the principle concern is to
Method D2216.
avoid causing further sample disturbance.
NOTE 11—Removing the soil from a short section of the tube will
6.20 Drying Oven—InaccordancewithTestMethodD2216.
reducetheamountofforcerequiredtoextrudethesampleandhencecause
less disturbance.This can be done by cutting a section from the tube with
6.21 Miscellaneous Equipment—Specimen trimming and
a band saw or tube cutter prior to extrusion. When using a tube cutter, it
carving tools such as spatulas, knives, and wire saws, data
will be necessary to provide additional support to prevent ovalization of
sheets, and wax paper or polytetrafluoroethylene (PTFE) sheet
thetube.Thistechniqueisveryeffectivewhencombinedwithradiography
as required.
to nondestructively examine the soil and select test locations.
6.14 Specimen Trimming Devices—Atrimming turntable or
7. Calibration
a cylindrical cutting ring may be used for cutting the cylindri-
7.1 Apparatus Constants—The following information is
cal samples to the proper specimen diameter. The cutting ring
required to determine the physical characteristics to the speci-
maybepartoftheconfinementringoraseparatepiecethatfits
men.
on the confinement ring. The cutter shall have a sharp edge, a
highly polished surface, and be coated with a low-friction
7.1.1 Measure diameter (D ) and height (H ) of the confine-
r r
material. Alternatively, a turntable or trimming lathe may be ment ring to the nearest 0.01 mm [0.001 in.].
used. In either case, the cutting tool must be properly aligned
7.1.2 The cross sectional area (A) of the specimen may be
to form a specimen of the same or slightly larger diameter as
computed from the inside diameter of the confinement ring to
2 2
that of the confinement ring.The top and bottom surface of the
four significant digits in cm [in. ].
specimen may be rough trimmed with a wire saw. All flat
7.1.3 Applyathincoatofgreasetotheinsideperimeterand
surfacesmustbefinishtrimmedwithasharpenedstraightedge
measure the mass of the confinement ring plus one filtering
and shall have a flatness tolerance of 6 0.05 mm [0.002 in.].
element and the recess spacer (M ) to the nearest 0.01 g
r
–7
[7×10 ] slugs.
6.15 Recess Spacer—A disc (usually made of acrylic) used
to create a gap between the top of the specimen and the top 7.1.4 Measure the thickness of the recess spacer plus one
edgeoftheconfinementring.Thediscshallbethickenoughto filtering element (T ) to the nearest 0.01 mm [0.001 in.].
rs
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D4186/D4186M − 20
7.2 Miscellaneous Loading Elements—Determine the cu- 7.4.4 Compute the effective area of the piston (A)inm
p
mulative mass (to the nearest 0.001 kg) of the top porous disk [in. ] as the slope of this line and the effective piston weight
plus any other apparatus components that rest on the specimen (W ) in kN [lbf] as the intercept with the force axis.
p
and are not counterbalanced by the load frame, M .
a
7.5 Piston Seal Dynamic Friction—If the design of the
7.3 Consolidometer Deflection—The consolidometer de- consolidometerissuchthatthefrictioninthepistonsealaffects
flects due to both changes in axial load and chamber pressure, the axial force measuring device, then the axial force shall be
referred to as apparatus compressibility. The apparatus com- corrected whenever the piston friction exceeds 0.5% of the
pressibility must be subtracted from the measured deforma- maximum axial stress applied to the specimen. This is the
tions in order to correctly compute the specimen axial strain. dynamic friction of the piston seal.
7.3.1 Correction due to Axial Load—During consolidation, 7.5.1 Assemble the apparatus without a specimen and apply
the measured axial deformations shall be corrected for appa- a typical chamber pressure used during testing.
ratus compressibility whenever the equipment deformation 7.5.2 Record readings of chamber pressure (CP ) and axial
n
exceeds 0.10 % of the initial specimen height. If the correction force (AF ) while advancing the piston at the typical test
n
iswarrantedatanypointduringthetest,thenitshallbeapplied displacement rate.
to all measurements throughout the test. 7.5.3 Compute the increment in axial force (∆f)asthe
n
difference between the measured axial force and the piston
7.3.1.1 Assemble the apparatus with a copper, steel, or
aluminum disk of approximately the same size as the uplift force.
7.5.4 Compute the dynamic seal friction force (∆f)inkN
specimen, the filtering element and the porous disks.
s
7.3.1.2 Record readings of the axial deformation (AD ) and [lbf] as the average of the increment in axial force.
n
axialforce(AF )astheaxialforceisincreasedfromtheseating
n
8. Sampling
value to its maximum value and then returned to the seating
value.
8.1 Intact samples having satisfactory quality for testing by
7.3.1.3 Use these data to establish the relationship between
this test method may be obtained using sampling procedures
apparatus deformation (δ ) in mm [in.] as a function of net
and apparatus described by Practices D6519, D1587 and
af
force (F ) in kN [lbf].
D3550. Specimens may also be trimmed from large intact
a
7.3.2 Correction due to Chamb
...