JGS 0524-2020

Japanese Geotechnical Society Standard (JGS 0524-2020)
Method for consolidated-drained triaxial compression test on soils
1

Scope

This standard specifies a test method to determine the strength and the deformation characteristics of a soil
specimen when it is subjected to drained axial compression after isotropic consolidation. The test shall be
carried out on three or more specimens prepared from a same sample, under different consolidation stresses
within required consolidation stress range. In this test, the relationship between the volume change (and axial
displacement, if possible) during the consolidation process and time shall also be obtained. This standard
applies mainly to saturated cohesive soils.
Note 1:In this standard, it is assumed that the axial displacement is measured, but if the axial displacement is notmeasured, provisions relating to axial displacement may be ignored.
Note 2:2This standard is also applicable to unsaturated coarse-grained soil whose maximum particle size exceeds 20 mm.

Normative references

The following standards shall constitute a part of this standard by virtue of being referenced in this standard.
The latest versions of these standards shall apply (including supplements).
JGS 0520 Preparation of soil specimens for triaxial tests
JGS 0530 Preparation of specimens of coarse granular materials for triaxial tests

3

Terms and definitions

The terms and definitions used in this standard are as follows:Note:

The test covered by this standard can be referred to in abbreviated form as CD triaxial test.

3.1

CD

Shearing soil under the drained condition after consolidating it (Consolidated and Drained: CD).

3.2

Axial stress

The stress acting on the specimen in the cylinder axis direction.

3.3

Lateral stress

The stress acting in the radial direction of the specimen.

3.4

Principal stress difference

The difference between the axial stress and the lateral stress. The value of stress shall be defined at the midheight of the specimen.

3.5

Isotropic stress state

The stress state when the axial stress is equal to the lateral stress.

3.6

Cell pressure

The pressure applied to the triaxial pressure cell. The lateral stress is equal to the cell pressure.

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3.7

Back pressure

The pressure applied to the pore water within the test specimen (JIS A 1227).
Note:

In this standard, the back pressure means the pore water pressure applied to the specimen to achieve a higher

degree of saturation of the specimen while maintaining a constant effective stress.

3.8

Consolidation stress

The stress of soil element that induces consolidation.
Note:

In this standard, the consolidation stress means the difference between the externally applied stress on the specimen

and the back pressure during the consolidation process.

3.9

Drained compressive strength of soil

The maximum principal stress difference that can be applied to the specimen when subjected to the effective
lateral stress maintained after consolidation is completed.

4

Equipment

4.1

Triaxial compression test apparatus

The triaxial compression test apparatus shall consist of a triaxial pressure cell, a system for applying cellpressure, a compression device, and measurement devices for load, displacement, and volume change. The
apparatus shall satisfy the following conditions. Figure 1 shows an example of the configuration of triaxial
compression test apparatus. The back pressure burette, the back pressure gauge, and the double tube burette
indicated in Figure 1(a) in broken lines shall be required only when back pressure is used. The conditions that
this apparatus must satisfy shall be given in 4b), d). Figure 2 shows the schematic structure of the triaxialpressure cell: (a) is an example in which the piston and cap are rigidly connected, while (b) is an example inwhich the two are not rigidly connected. Both forms must allow for mounting of a specimen having the same
diameter as the cap and pedestal between the cap and pedestal, covered with a rubber sleeve, and sealed withan O-ring, etc. Note that, for testing unsaturated soil, the volume change measurement device shown in Figure1(b) shall be necessary, and the apparatus shall satisfy the requirements in 4g).
a)

The apparatus shall have sufficiently load-bearing strength and load capacity to handle the maximum cellpressure, back pressure, and maximum axial compression force to be applied to the specimen.

b)

The apparatus shall be capable of maintaining the cell pressure and back pressure within ±4 kN/m2 of atarget value for pressures up to 200 kN/m2, and within ±2 % of the target value for pressures of 200 kN/m2
or greater, for the duration of a single test.

c)

The apparatus shall be capable of applying and sustaining axial displacement up to 15 % or more of thespecimen height.

d)

The apparatus shall be capable of measuring the cell pressure and the back pressure with an allowable
tolerance of 0.1% 2 kN/m2 for pressures up to 200 kN/m2 and of 1 % for pressures of 200 kN/m2 or greater.

e)

The apparatus shall be capable of measuring the axial compression force up to the specimen’s maximum
axial compressive strength within an allowable tolerance of 1 %. If the test apparatus is set up such thatthe load cell is located outside the triaxial pressure cell, the frictional force at the point of sliding between
the piston and the triaxial pressure cell shall be measured. This friction value shall be used to correct themeasured value of axial compression force. If the load cell is located inside the triaxial pressure cell, theeffect of cell pressure shall be determined and the measured value of axial compression force shall becorrected.

f)

The apparatus shall be capable of measuring the axial displacement up to 15 % of the specimen height
within an allowable tolerance of 0.1 %.

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g)

The apparatus shall be capable of measuring the volume change of the specimen up to its maximum value
within an allowable tolerance of 0.1 % of the specimen’s initial volume. When testing saturated soil, thevolume change of the specimen shall be determined as the amount of water expelled from the specimen
during the test measured using a burette or other devices with equivalent or higher measurement accuracy.
When testing unsaturated soil, and if a volume change measuring device is used to measure the volume
change of the specimen, the relationship between the cell pressure and the expansion of the triaxialpressure cell shall be determined in advance, and the volume change of the specimen shall be correctedaccordingly.

5

Test method

5.1

Preparation and set-up of test specimen

Preparation and set up of the test specimen shall be in accordance with JGS 0520 Preparation of soil specimens
for triaxial tests or JGS 0530 Preparation of specimens of coarse granular materials for triaxial tests. Additionally,
the specimen shall have a height not less than twice its diameter.

5.2

Consolidation process

The test shall be carried out in accordance with the following requirements for consolidation.
a)Install the displacement transducer, and make zero adjustments. Also, take the initial reading of the burette.

Note:

When testing unsaturated soils, check and adjust the zero point of the volume change measuring device.

b)

Close the drainage valve connected to the burette. Increase only the isotropic stress so that the difference
between the isotropic stress and the back pressure is equal to the desired value of consolidation stress. If
the loading piston is not rigidly connected to the cap, set the load cell, the piston, and the cap in contact
with each other before this process. If back pressure is used, apply it in accordance with Section 5.2b) of
JGS 0520 Preparation of soil specimens for triaxial tests or JGS 0530 Preparation of specimens of coarse
granular materials for triaxial tests.

c)Open the drainage valve to start consolidation.

d)Record readings of the volume change ΔVt (mm3) and if possible also the axial displacement ΔHt (mm) of
the specimen at appropriate time t intervals, and plot them. Consolidation shall be continued at least until
the end of primary consolidation. Measure the volume change ΔVc (mm3) and the axial displacement
ΔHc (mm) of the specimen due to consolidation. The termination of consolidation shall comply with Section
5.2(d) of JGS 0522 Method for consolidated-undrained (CU) triaxial compression test on soils. If the axial
displacement cannot be measured during consolidation because the loading piston is not rigidly connectedto the cap, carefully bring the piston into contact with the cap, while observing the load cell reading suchthat no additional force is applied to the specimen. Then take the reading of the displacement transducer.
This measured value is to be taken as the axial displacement ΔHc (mm) due to consolidation. If unsaturated
soil is tested, the value of the reading for volume change due to consolidation shall be corrected for
expansion of the triaxial pressure cell and the movement of the loading piston, and this value shall be taken
to be the volume change due to consolidation ΔVc (mm3).

5.3

Axial compression process

The axial compression shall be carried out in accordance with the following procedure.
a)

Check and adjust the zero reading of the load cell and deformation transducer.

b)Compress the specimen continuously with a constant strain rate keeping the cell pressure constant. If theaxial strain εaf (%) at the peak principal stress difference can be estimated, the axial strain rate ε̇ a (%/min)shall not exceed the value calculated from the following equation. However, the axial strain rate shall not
exceed 0.5 % per minute regardless of the value calculated from the above equation.

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ε̇ a =

εaf
15tc

where
tc:
c)

Consolidation time (min)Record the axial compression force P (N), the axial displacement ΔH (mm), and the volume change
ΔV (mm3) during compression. When testing unsaturated soil, the volume change shall be corrected for theamount of the loading piston intrusion into the triaxial cell.

Note:

If the axial compression force, the axial displacement, and the pore water pressure are not recorded continuously,

the measurement time intervals should be sufficiently small to enable smooth curves for the principal stress difference - axial
strain curve and the pore water pressure – axial strain to be drawn. It is recommended, for example, to measure the axial
deformation at a maximum interval of 0.2 mm up to the maximum value of the axial compression force, and thereafter at
maximum intervals of 0.5 mm.

d)Terminate the compression either when an axial strain of more than 3 % has been reached since themaximum axial load reading, when the load reading has been fallen to about 2/3 of its peak value, or whenan axial strain of 15 % has been reached.

e)Remove the specimen from the triaxial pressure cell, and observe and record its deformed shape, failuremode, and other features. The observation shall be made in the direction that captures the features offailure most clearly. If a slip surface is found, observe it from the direction in which the steepest gradient isdetermined and record it so that the gradient angle can be approximately read. Any heterogeneity of thespecimen and the presence of any foreign materials shall be observed and recorded.

f)Measure the oven-dried mass of the specimen ms (g).

Note:This step in the process may be omitted if the water content of the specimen is determined from the trimmed wasteof the sample, or if the water content of the specimen is determined from a representative sample of the sample taken fromthe specimen after completion of compression.

6

Processing test results

6.1

Initial state of the specimen before consolidation

Refer to Section 6.1 of JGS 0522 Method for consolidated-undrained (CU) triaxial compression test on soils forthe initial state of the specimen before consolidation.

6.2

Consolidation process

Refer to Section 6.2 of JGS 0522 Method for consolidated-undrained (CU) triaxial compression test on soils forthe method of calculation for the consolidation process. If the amount of penetration of the rubber sleeve
associated with loading of the cell pressure is measured or estimated, the volume change of the specimen due
to consolidation, Vc (mm3) shall be corrected accordingly.

6.3

Axial compression process

The method of calculation for the axial compression process shall be as follows.
Note:

If necessary, the void ratio of the specimen at the maximum principal stress difference shall be calculated from thefollowing equation, which shall be rounded to the two digits after the decimal point.

ef =

4

Vf /1000 × ρs
−1
ms

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where
Vf:
a)

Volume of the specimen at the maximum principal stress difference (mm3)The axial strain of the specimen εa (%) shall be calculated from the following equation, where compression
is defined to be positive.
εa =

∆H
× 100
Hc

where
ΔH:
b)

Axial displacement of the specimen in the axial compression process (mm), where compression
is defined to be positive

The volumetric strain εv (%) (compression positive) when the axial strain is εa (%) shall be calculated fromthe following equation, where compression is defined to be positive.
εv =

∆V
× 100
V0

where
ΔV:
c)

volume change of the specimen in the axial compression process (mm3), where compression isdefined to be positive

The principal stress difference (σa – σr) (kN/m2) at axial strain of εa (%) shall be calculated from the following
equation.
σa − σr =P 1 − εa /100
×× 1000Ac 1 − εv /100

where
P:
σa:
σr:

Axial compression force (N) applied to the specimen at the axial strain of εa (%), where P=0 in
the isotropic stress state
Axial stress (kN/m2) acting on the specimen
Lateral stress (kN/m2) acting on the specimend)Draw graphs of the principal stress difference – axial strain curve and the volumetric strain – axial strain
curve.

e)

Obtain the maximum value of the principal stress difference (σa – σr)max in the range 0 < εa  15 % from thegraph, and the corresponding value of axial strain shall be taken as the strain at failure (%), which shall be
rounded to one digit after the decimal point. The value of this maximum principal stress difference shall betaken as the compressive strength, which shall be rounded to three significant digits.

7

Reporting

The following test results and other items shall be reported.
a)Method of specimen preparationb)

Dimensions of the specimen before the consolidationc)

Magnitude of the cell pressure (kN/m2) and the back pressure (kN/m2)d)Relationship between the volume change (mm3) and time (min) in the consolidation process© JGS 2015 – All rights reserved

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JGS 0524-2020

Note:

e)

Report the relationship between axial displacement and time in the consolidation process, if necessary.

Oven-dried mass (g) of the specimen and the dry density (Mg/m3) after consolidation

Note:

Report the void ratio of the specimen after consolidation and at the maximum principal stress difference, if necessary.

f)Strain rate (%/min) in the axial compression processg)Compressive strength (kN/m2) and strain at failure (%)h)

Principal stress difference versus axial strain curve and volumetric strain versus axial strain curvei)

Failure condition of the specimenj)Compressive strength – consolidation stress relationship, which shall be shown by drawing a graph withthe compressive strength on the vertical axis and the consolidation stress on the horizontal axis, or by
drawing a Mohr’s stress circle of (σa – ub) and (σr – ub) at (σa – σr)max, where ub is the back pressure. If
necessary, report the Mohr’s stress circle envelope, and the angle of shear resistance, ød (o), and theintercept on the vertical axis, cd (kN/m2), obtained from the envelope.

k)

If the method used deviates in any way from this standard, give details of the method used.

l)

Other reportable matters

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Air pressure(To vacuum regulator)

Load cell (where installedinside the pressure cell)
Axial displacement gauge(mainly for use in axial
compression process)

Cell pressure(hydraulic or
pneumatic)Specimen

Axial displacement gauge (mainfor use in consolidation process)Double-tube burette (forsaturated specimens)

Cap

Water

Axial displacement gauge (mainly foruse in consolidation process)

Tank for supplying de-aired water

Triaxial pressure cell
Rubber sleeve

Volume change
measurement device

Water

Specimen

Triaxial pressure cell

Water

Cell pressuregaugeSingle-tube burette

Displacement
gauge

Regulator

Load cell (where
installed outside thepressure cell)(Back pressure gauge)(Double-tube burette)

Load cell(Back pressure regulator)

Compression device

Porousplate

O-ringBase plate

Compression
deviceFilter (where needed)(a) Small-scale apparatus (broken lines: backpressure supply device)Pedestal

Seating for triaxial compression(b) Large-scale apparatus for coarse-grained soil
whose maximum grain size exceeds 20 mm

Figure 1 Example of the configuration of CD triaxial test apparatus

Loading piston

Loading piston
Air releasevalve

Air release
valve
Upper
plate

Cap

Upper
plate

O-ringO-ringRubber sleeve

Rubber sleeve

Post

Pressure cylinder
Post

Porous plate

Path of applying
pressure to cell

Path of drainage
water

Specimen

Specimen

Pressure cylinder
Pedestal
Path of applying
pressure to cell
Base plate

Cap

Path of drainage
water

Pedestal(a) Case in which loading piston and cap are rigidly
connected

Porous plate

Path of drainage water
Base plate

Path of drainage water(b) Case in which loading piston and cap are notrigidly connected

Figure 2 Schematic structure of the triaxial pressure cell

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