JGS 0551-2020

Japanese Geotechnical Society Standard (JGS 0551-2020)
Method for torsional shear test on hollow cylindrical specimens of soils
1

Scope

This standard specifies a test method to obtain the torsional shear strength in the drained state and in the
undrained state of soils that have been consolidated under isotropic or anisotropic stress conditions, and therelationship between the shear stress on a horizontal plane and the corresponding shear strain, using torsional
shear test apparatus. The standard is applicable to saturated cohesive and sandy soils.
Note 1: In this standard the shear stress on a horizontal plane of the specimen and the corresponding shear strain are
simply referred to as the “shear stress” and “shear strain”.
Note 2: The scope includes cohesive soils and sandy soils that have been saturated after specimen preparation. Also, thisstandard can be applied to other soil materials.

2

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).
JIS A 0207 Technical terms for geotechnical engineering
The specimen used in this test shall be prepared and installed in accordance with the following standard.
JGS 0550

Practice for preparing hollow cylindrical specimens of soils for torsional shear test

When implementing this test, refer to the following standards for matters that are not prescribed in this standard.
JGS 0523
JGS 0524

3

Method for consolidated-undrained triaxial compression test on soils with pore water pressure
measurements
Method for consolidated-drained triaxial compression test on soils

Terms and definitions

In addition to those specified in JIS A 0207, the main terminology and definitions used in this standard shall be
as follows.

3.1

Consolidated-drained (CD) torsional shear test

A shear test in which an axial stress, external pressure, internal pressure, and back pressure are maintained
constant on a hollow cylindrical specimen consolidated under an isotropic or specified anisotropic stress ratio,
and then a torsional force is applied to the horizontal plane of the specimen under drained states.

3.2̅̅̅̅̅) torsional shear test
Consolidated-undrained (CUA shear test in which an axial stress, external pressure, internal pressure, and back pressure are maintained
constant on a hollow cylindrical specimen consolidated under an isotropic or specified anisotropic stress ratio,
and then a torsional force is applied to the horizontal plane of the specimen under undrained states whilemeasuring the pore water pressure.

3.3

Axial stress

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

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JGS 0551-2020
3.4

External pressure and internal pressure

The pressure that is applied to the external surface of the specimen and the hollow part of the specimen,
respectively.

3.5

Lateral stress

The stress corresponding to the external pressure and the internal pressure, when they are equal. The value ofstress is defined at the mid-height of the specimen.

3.6

Back pressure

Pore water pressure applied to the specimen (refer to 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

3.7

Anisotropic consolidation stress ratio

The effective lateral stress divided by the effective axial stress when consolidation is completed.

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

Axial consolidation stress

The value of the consolidation stress on the specimen acting in the cylinder axial direction.

3.10 Lateral consolidation stress
The value of the consolidation stress on the specimen acting in the radial direction.

3.11 Torsional shear strength in the drained state
The maximum value of shear stress that can be applied to a horizontal plane of the specimen, based on theeffective stress at the time of completion of consolidation.

3.12 Torsional shear strength in the undrained state
The maximum shear stress that can be applied to a horizontal plane of the specimen, when entry or exit of thepore water is not permitted.

4Equipment

The torsional shear test equipment is configured from a pressure cell; a device for supplying external pressure,internal pressure, and back pressure; a device for applying torsional force and axial force; and a device formeasuring external pressure, internal pressure, torque, axial force, rotational angle, axial displacement,
specimen volumetric change, and pore water pressure, and shall satisfy the following conditions. An exampleof the torsional shear test equipment is shown in Figure 1.
Note:

It may include capability of measuring volume changes of the hollow part of the specimen.

a)

The equipment shall have sufficient durability and load resistance with respect to the maximum externalpressure, internal pressure, back pressure, and the maximum torque and axial force on the specimen. The
pressure cell shall be fixed to a loading platform, etc., so that the pressure cell does not rotate when thetorsional force is acting.

b)

The specimen shall be covered with a cap, a pedestal, and a rubber sleeve, the prescribed externalpressure, internal pressure, back pressure, torsional force, and axial force shall be capable of being applied

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JGS 0551-2020

to this, and water shall be capable of being supplied to or drained from the top and bottom ends of thespecimen. The external diameter and the internal diameter of the cap and the pedestal shall be the sameas the external diameter and internal diameter of the specimen as standard. The two surfaces of the cap
and the pedestal shall be flat and parallel to each other, and shall be normal to the axial direction of theloading piston. A porous plate with metal ribs and having sufficiently high water permeability shall be usedat the drainage surface, and when necessary appropriate filter paper shall be placed there. However,sliding shall not occur between the specimen and the cap or the pedestal, and another format may be usedprovided excessive disturbance is not caused to the specimen.
c)

It shall be possible to continuously apply the prescribed external pressure, internal pressure, back pressure,and axial stress to within ±2 kN/m2 for less than 200 kN/m2, and within ±1% for 200 kN/m2 and higher.

d)It shall be possible to apply torsion continuously to the specimen until the shear strain in the horizontal
direction exceeds 22.5%.

e)

It shall be possible to measure the external pressure, internal pressure, and porewater pressure to anallowable tolerance of 2 kN/m2 for less than 200 kN/m2, and 1% for 200 kN/m2 and higher. The performanceof the pore water pressure measuring device shall comply with Section 4.1d) of JGS 0523 Method for̅̅̅̅̅) triaxial compression test on soils.
consolidated-undrained (CUf)

It shall be possible to measure the torque acting on the specimen using a torque meter installed within thepressure cell, to an allowable tolerance of 1% of the maximum torque. The interference with the output of
the torque meter due to changes in the external pressure or axial force shall not exceed 1% of the capacityof the torque meter.

g)

It shall be possible to measure the axial force acting on the specimen using a load cell installed within thepressure cell, to an allowable tolerance of 1% of the axial force when consolidation is completed. Theinterference with the output of the load cell due to changes in the external pressure or the torque shall not
exceed 1% of the capacity of the load cell.

h)

It shall be possible to measure the rotational angle of the specimen using a rotational angle measuring
device to an allowable tolerance of 1% of the maximum rotational angle. If the rotational angle of thespecimen is measured with a rotational angle measuring device installed outside the pressure cell, thenthe deformation of the loading piston, torque meter, load cell, etc., located between the rotational angle
measuring device and the specimen shall be 1% or less of the rotational angle of the specimen. Theinterference with the output of the rotational angle measuring device due to changes in the externalpressure shall be not more than 1% of the maximum rotational angle, and the change in the calibration
value shall be not more than 1%.

i)

It shall be possible to measure the axial displacement and the volumetric change of the specimen to anallowable tolerance of 0.02% and 0.05% of the height and volume of the specimen, respectively. The
volumetric change of the specimen during isotropic or anisotropic consolidation or during drained torsional
shear shall be measured using a burette, or a measuring device having equal or better performance. If thevolumetric change of the hollow part of the specimen is measured, it shall be capable of being measured
to an allowable tolerance of 0.05% of the hollow part volume.

Note:

The burette shall have a structure to enable back pressure to be applied, and it is desirable that it shall have astructure such that the water level within the burette does not vary due to changes in the back pressure.

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JGS 0551-2020

5

Test method

5.1

Preparation and installation of the specimen

Preparation and installation of the specimen shall be carried out by the method prescribed in JGS 0550 Practicefor preparing hollow cylindrical specimens of soils for torsional shear test.

5.2

Checking the specimen saturation

The pore water pressure coefficient B (B value) shall be measured in the last stage of back pressure application.
a)

Close the drainage valve.

b)

Apply an increment σ to the lateral stress σr for 1 to 2 minutes, while maintaining the isotropic stress state.
As standard σ shall be about 10-50 kN/m2. However, the lateral stress after applying σ shall not exceed
the lateral stress when the specified consolidation is completed.

c)Measure the increment of pore water pressure u when the pore water pressure has stabilized to a constantvalue.

d)Open the drainage valve after increasing the back pressure by the same amount as σ.

5.3

Consolidation process

Isotropic consolidation or anisotropic consolidation shall be carried out in accordance with the objectives of thetest. The axial displacement of the specimen Hc (mm) and the volumetric change of the specimen Vc (mm3)due to consolidation shall be measured. During consolidation, the back pressure ub (kN/m2) shall be constant.
Completion of primary consolidation of the specimen shall be confirmed by the method described in Section
5.2 d) of JGS 0522 Method for consolidated-undrained triaxial compression test on soils.
a)b)Isotropic consolidation process1)

Under drained states, the lateral stress shall be increased by maintaining the isotropic stress state up
to the value at completion of the prescribed consolidation.

2)

Consolidation shall be continued at least until completion of primary consolidation.

Anisotropic consolidation process
Anisotropic consolidation shall be carried out by the following method as standard.
1)

An axial stress shall be applied that satisfies the prescribed anisotropic consolidation stress ratio
corresponding to the effective lateral stress in the initial isotropic consolidation state.

2)

σr shall be obtained by dividing the difference in the effective lateral stress between the initialconsolidation stress state and the final consolidation stress state into 5 or more equal increments.
However, σr shall not exceed 20 kN/m2.

3)

The lateral stress shall be increased by σr in steps.

4) The axial stress shall be increased until the prescribed anisotropic consolidation stress ratio is reached.

4

5)

Repeat the operation in 3) and 4) until the final consolidation stress state is reached.

6)

As a guide the loading rate of the axial stress and the lateral stress during isotropic consolidation
should be such that the axial strain rate is 0.1%/min or less, then proceed to the next stage.

7)

Consolidation shall be continued at least until completion of primary consolidation.

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JGS 0551-2020
5.4

Torsional shear process

Either drained torsional shear or undrained torsional shear shall be carried out, in accordance with the purposeof the test.
a)Consolidated-drained (CD) torsional shear
1)

Check that the state is the prescribed isotropic or anisotropic consolidation state.

2)

Continuously apply torsion to the specimen so that the shear strain rate is constant, maintaining theexternal pressure, internal pressure, back pressure, and axial stress constant. Instead of controllingthe axial stress during torsional shear to be constant, the axial force may be controlled to within arange of variation of ±5% of the axial force when consolidation is completed. If it is possible to predict
the shear strain γf (%) at the maximum shear stress, the shear strain rate γ̇ (%/min) shall not exceed
the value calculated from the following equation.
γ̇ =

γf
15tc

where
tc:

Consolidation time (min)However, the shear strain rate shall not exceed 1% per minute, regardless of the value calculated from theabove equation.
3)

During torsional shear, the torque T (N･m), the axial force P (N), the rotational angle θ (rad), the axial
displacement H (mm), and the volumetric change V (mm3) shall be measured.

4)

Shearing shall be continued for an additional 5% or more shear strain after the torque meter reading
reaches a maximum, or shearing shall be terminated when the shear strain reaches 22.5%.

Note: If the torque, axial force, rotational angle, axial displacement, and volumetric change are not continuously recorded,
their measurement intervals shall be such that it is possible to smoothly draw the shear stress-shear strain curve and thevolumetric strain-shear strain curve.

b)̅̅̅̅̅) torsional shear
Consolidated-undrained (CU1)

Check that the state is the prescribed isotropic or anisotropic consolidation state.

2)

Close the drainage valve.

3)

Continuously apply torsion to the specimen at a constant shear strain rate, maintaining the externalpressure, internal pressure, and axial stress constant. As a guide the shear strain rate should be
0.5%/min. for sandy soil, 0.2%/min. for specimens with a large quantity of silt, and 0.1%/min. for
specimens with a large quantity of clay, in order that the pore water pressure distribution within thespecimen becomes uniform. For controlling the axial stress, the conditions described in Section 5.4a)2) apply.

4)

During torsional shear, the torque T (N･m), the axial force P (N), the rotational angle θ (rad), the axial
displacement H (mm), and the pore water pressure u (kN/m2) shall be measured.

Note:

If there is no continuous record of the torque, axial force, rotational angle, axial displacement, and pore waterpressure, their measurement intervals shall be such that it is possible to smoothly draw the shear stress-shear strain curve
and the pore water pressure-shear strain curve.

5)

Shearing shall be continued for an additional 5% or more shear strain after the torque meter reading
reaches a maximum, or shearing shall be terminated when the shear strain reaches 22.5%.

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5.5

State of the specimen after the test

The state of the specimen after testing shall be determined as follows.
a)

The deformation and failure state of the specimen, etc., shall be observed and recorded. The deformationand failure state of the specimen after torsional shear shall be observed and recorded from the direction atwhich their state is most distinct. Also, if a slip plane is evident, it shall be observed from the direction atwhich the slope is steepest, and recorded so that the angle can be approximately read. Heterogeneity or
foreign matter in the specimen shall be observed and recorded.

b)

The oven-dried mass ms (g) of the specimen shall be measured.

6

Processing test results

Note: If the volumetric change of the hollow part of the specimen is measured during the consolidation process and thetorsional shear process, the external diameter and the internal diameter of the specimen may be calculated using thesevalues. However, this shall not be carried out for sandy soils if it is not possible to appropriately evaluate the effect ofpenetration of the rubber sleeve.

6.1

State of the specimen prior to consolidation

The state of the specimen prior to consolidation shall be obtained from the following equations.
a)

The volume of the specimen prior to consolidation V0 (mm3) shall be calculated from the following equation.
V0 = Vi − ∆Vi
where
Vi :
∆Vi :

b)

Initial volume of the specimen (mm3)Volumetric change in the specimen produced from the initial state until prior to consolidation(mm3), where compression is defined to be positive

The height of the specimen H0 (mm) prior to consolidation shall be calculated from the following equation.
H0 = Hi − ∆Hi
where
Hi :
∆Hi :

c)

Initial height of the specimen (mm)Axial displacement of the specimen produced from the initial state until prior to consolidation(mm), where compression is defined to be positive

The external diameter Do0 (mm) and the internal diameter Di0 (mm) of the specimen prior to consolidation
shall be calculated from the following equations.
Do0 = Doi × √(1 − εvi /100)/(1 − εai /100)
Di0 = Dii × √(1 − εvi /100)/(1 − εai /100)
where
Doi: Initial external diameter of the specimen (mm)Dii: Initial internal diameter of the specimen (mm)εvi: Volumetric strain (%) produced from the initial state until prior to consolidation (=Vi /Vi), wherecompression is defined to be positiveεai: Axial strain (%) produced from the initial state until prior to consolidation (=Hi /Hi), wherecompression is defined to be positive

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6.2

Pore water pressure coefficient B

The B value of the specimen shall be calculated as follows and rounded to two significant digits.
B=

∆u
∆σ

where

σ:
u:

Increment of isotropic stress (kN/m2)
Increment of pore water pressure associated with σ (kN/m2)

Note: The B value need not be calculated for consolidated drained torsional shear tests.

6.3

Consolidation process

The method of calculating and analyzing the consolidation process shall be as follows.
a)

The volume of the specimen Vc (mm3) after consolidation shall be calculated from the following equation.

Vc = V0 − Vc
whereVc: Volumetric change due to consolidation (mm3), where compression is defined to be positiveb)

The specimen height Hc (mm) after consolidation shall be calculated from the following equation.

Hc = H0 − HcwhereHc: Axial displacement due to consolidation (mm), where compression is defined to be positivec)

The specimen cross-sectional area Ac (mm2) after consolidation shall be calculated from the following
equation.

AC =
d)

VC
HC

The specimen external diameter Doc (mm) and internal diameter Dic (mm) after consolidation shall becalculated from the following equations.
Doc = Do0 × √(1 − εvc /100)/(1 − εac /100)
Dic = Di0 × √(1 − εvc /100)/(1 − εac /100)
where
εvc:
εac:

e)

Volumetric strain (%) due to consolidation (=Vc /V0), where compression is defined to be positive
Axial strain (%) due to consolidation (=Hc /H0), where compression is defined to be positive

The dry density ρdc (Mg/mm3) of the specimen after consolidation shall be calculated from the following
equation, and rounded to two digits after the decimal point.
ρdc =

ms
× 1000
Vc

where
ms:

Oven-dried mass of the specimen (g)© JGS 2018 – All rights reserved

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JGS 0551-2020

Note 1:

If necessary, the void ratio ec and the relative density Drc of the specimen after consolidation shall be calculated

from the following equations.

ec =Vc /1000 × ρs
−1
ms

Dr c =

emax − ec 100emax − emin

where
ρs:
Soil particle density (Mg/m3)
emax: Void ratio of the sample from the minimum density test
emin: Void ratio of the sample from the maximum density test

6.4

Torsional shear process

The method of calculation and analysis of the torsional shear process shall be as follows.
a)Consolidated drained (CD) torsional shear
1)

The axial strain εa (%) of the specimen shall be calculated from the following equation.
εa =

∆H
× 100
Hc

where

H : Axial strain in the torsional shear process (mm), where compression is defined to be positive2)

The volumetric strain εv (%) of the specimen shall be calculated from the following equation.
εv =

∆V
× 100
V0

where

V : Volumetric change in the torsional shear process (mm3), where compression is defined to
be positive3)

The external diameter Do (mm) and the internal diameter Di (mm) of the specimen shall be calculated
from the following equations.
Do = Doc × √(1 − εv /100)/(1 − εa /100)
Di = Dic × √(1 − εv /100)/(1 − εa /100)

4)

The shear strain γ (%) of the specimen shall be calculated from the following equation.
γ=∆θ(ro + ri )
× 100
2H

where

θ:
ro:
r i:
H:
Note:

8

Rotational angle of the specimen (rad)External radius of the specimen (mm) (=Do/2)
Internal radius of the specimen (mm) (=Di/2)
Specimen height (mm) (=Hc−H)

The shear strain γ (%) may be alternatively calculated by the following equation.

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JGS 0551-2020γ=
5)2∆θ(ro3 − ri3 )3H(ro2 − ri2 )× 100

The amount of correction (amount of reduction) in the shear stress due to the tension in the rubber
sleeve 𝜏m (kN/m2) shall be calculated from the following equation.

 m =

2Emtm (ro3 + ri 3 )r(ro3 − ri 3 ) (ro + ri ) 100

where
Em: Young’s modulus of the rubber sleeve (kN/m2)
tm: Thickness of the rubber sleeve (mm)6)

The shear stress 𝜏 (kN/m2) shall be calculated from the following equation.
𝜏=

3T
2π(ro3 − ri 3 )× 106 − ∆𝜏m

where
T:
7)

Torque (N∙mm)

The axial stress σa (kN/m2), the maximum principal stress σ1 (kN/m2), and the minimum principal stress
σ3 (kN/m2) shall be calculated from the following equations.
σa =P 1 − εa /100
×× 1000Ac 1 − εv /100

σ1 =σa + σr √(σa − σr )2 + 4𝜏 2
+
2
2

σ3 =

σa + σr √(σa − σr )2 + 4𝜏 2
−
2
2

where
P:
σr:

Axial force acting on the specimen (N)Lateral stress acting on the specimen (kN/m2)

8)

The shear stress-shear strain curve and the volumetric strain-shear stress curve shall be drawn withthe shear strain on the horizontal axis.

Note 1:

If necessary the major effective principal stress σ'1 (kN/m2) and the minor effective principal stress σ'3 (kN/m2)

shall be calculated from the following equations, and the effective principal stress ratio (σ'1 /σ'3 ) – shear strain curve shall bedrawn, with the shear strain on the horizontal axis.

σ'1 = σ1 − uσ'3 = σ3 − uNote 2:

If necessary, the axial stress – shear strain curve and the axial strain – shear strain curve shall be drawn with theshear strain on the horizontal axis.

9)

Obtain the maximum value of the shear stress within the range 0< γ ≤22.5% from the above curves,
and rounded to three significant digits to obtain the drained torsional shear strength 𝜏d (kN/m2). The
shear strain at this time shall be rounded to one digit after the decimal point and taken to be γf (%).

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Note:

If necessary the major effective principal stress σ'1f (kN/m2) and the minor effective principal stress σ'3f (kN/m2)

when the shear stress is maximum are calculated from the following equations.

σ'1f = σ1f − uf
σ'3f = σ3f − ufwhere
σ1f : Major principal stress when the shear stress is maximum (kN/m2)
σ3f : Minor principal stress when the shear stress is maximum (kN/m2)
uf : Porewater pressure when the shear stress is maximum (kN/m2)
10) The ratio of the drained torsional shear strength 𝜏d and the axial consolidation stress σ'ac shall beobtained as 𝜏d /σ'ac after being rounded to three significant digits. The axial consolidation stressσ'ac (kN/m2) shall be obtained from the following equation, and rounded to three significant digits.
σ'ac = σac − ub
where
σ'ac : Axial stress when consolidation is completed (kN/m2)
ub :

b)

Back pressure̅̅̅̅̅) torsional shear
Consolidated-undrained (CU1)

The axial strain εa (%) of the specimen shall be obtained from the following equation.
εa =

∆H
× 100
Hc

where

H:
2)

Axial displacement in the torsional shear process (mm), where compression is defined to bepositive

The external diameter Do (mm) and the internal diameter Di (mm) of the specimen shall be calculated
from the following equation.
Do = Doc × √1/(1 − εa /100)
Di = Dic × √1/(1 − εa /100)

3)

The shear strain γ (%) of the specimen shall be calculated from the following equation.
γ=∆θ(ro + ri )
× 100
2H

where

θ:
ro:
r i:
H:
Note:

The shear strain γ (%) may be alternatively calculated by the following equation.

γ=

10

Rotational angle of the specimen (rad)External radius of the specimen (mm) (=Do/2)
Internal radius of the specimen (mm) (=Di/2)
Specimen height (mm) (=Hc−H)2∆θ(ro3 − ri3 )3H(ro2 − ri2 )× 100© JGS 2018 – All rights reserved

JGS 0551-2020

4)

The amount of correction (amount of reduction) of the shear stress due to the tension in the rubber
sleeve 𝜏m (kN/m2) shall be calculated from the following equation.

 m =

2Emt m (ro3 + ri 3 )(ro3 − ri 3 ) (ro + ri ) 100

where
Em: Young’s modulus of the rubber sleeve (kN/m2)
tm: Thickness of the rubber sleeve (mm)5)

The shear stress 𝜏 (kN/m2) shall be calculated from the following equation.
𝜏=

3T
2π(ro3 − ri3 )× 106 − ∆𝜏m

where
T:
6)

Torque (N∙m)

The axial stress σa (kN/m2), the maximum principal stress σ1 (kN/m2), the minimum principal stress
σ3 (kN/m2), and the increment of porewater pressure ue (kN/m2) associated with the torsional shear
shall be calculated from the following equations.
σa =

P
εa
(1 −
) × 1000
Ac
100

σ1 =

σa + σr √(σa − σr )2 + 4𝜏 2
+
2
2

σ3 =

σa + σr √(σa − σr )2 + 4𝜏 2−22

ue = u − ub
where
P:
σr:
u:
ub:
7)

Axial load acting on the specimen (N)Lateral stress acting on the specimen (kN/m2)
Pore water pressure acting on the specimen (kN/m2)
Back pressure (kN/m2)

The shear stress – shear strain curve and the porewater pressure increment – shear strain curve shallbe drawn with the shear strain on the horizontal axis.

Note 1: When necessary the major effective principal stress σ'1 (kN/m2) and the minor effective principal stress σ'3 (kN/m2)
shall be calculated by the following equations, and the effective principal stress ratio (σ'1 /σ'3 ) – shear strain curve shall bedrawn with the shear strain on the horizontal axis.

σ'1 = σ1 − uσ'3 = σ3 − uNote 2: Note 2 in Section 6.4a) 8) applies.

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JGS 0551-2020

8)

Obtain the maximum value of the shear stress within the range 0< γ ≤22.5% from the above curves,
and rounded to three significant digits to obtain the undrained torsional shear strength 𝜏u (kN/m2). The
shear strain at this time shall be rounded to one digit after the decimal point and taken to be γf (%).

Note: If necessary the major effective principal stress σ'1f (kN/m2) and the minor effective principal stress σ'3f (kN/m2)
when the shear stress is maximum are calculated from the following equations.

σ'1f = σ1f − uf
σ'3f = σ3f − uf
where
σ1f :
σ3f :
uf :

Major principal stress when the shear stress is maximum (kN/m2)
Minor principal stress when the shear stress is maximum (kN/m2)
Pore water pressure when the shear stress is maximum (kN/m2)

The ratio 𝜏u /σ'ac of the undrained torsional shear strength 𝜏u and the axial consolidation stress σ'ac
shall be obtained after being rounded to three significant digits.

9)

The axial consolidation stress σ'ac (kN/m2) shall be obtained according to Section 6.4 a) 10).

Note:

10)

The effective axial stress σ'a (kN/m2) in the undrained torsional shear process shall be calculated fromthe following equation, and a diagram of the effective stress path shall be drawn with 𝜏 on the verticalaxis and σ'a on the horizontal axis.
σ'a = σa − u7Reporting

The following items of the test results shall be reported.

7.1

Consolidated-drained (CD) torsional shear test

For the consolidated-drained (CD) torsional shear test, the following items of the test results shall be reported.
a)Method of preparation of specimensb)Specimen dimensions prior to consolidationc)

If measured, the B value and its measurement methodd)Volumetric change (mm3) and axial displacement (mm) due to consolidation. If consolidation required along period of time, such as for cohesive soils, etc., the relationship between time (min) and the axial
displacement (mm) or the volumetric change (mm3) shall also be reported.

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

Note: If necessary, the void ratio and relative density (%) after consolidation shall be reported.

f)

The magnitude of the axial stress (kN/m2), external pressure (kN/m2), internal pressure (kN/m2), and backpressure (kN/m2) after consolidationg)

The axial consolidation stress σ'ac (kN/m2), the lateral consolidation stress σ'rc (kN/m2), and if necessary
the anisotropic consolidation stress ratio σ'rc /σ'ac (= K)h)Shear strain rate (%/min) during the torsional shear processi)

Method of measurement of torque, axial load, and rotational angle during torsional shear, and the positionsof the torque meter, load cell, and rotational angle measurement device within the pressure cell.

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JGS 0551-2020

j)Shear stress versus shear strain curve, and volumetric strain versus shear strain curve

Note: When necessary, the effective principal strain ratio (σ'1 /σ'3 ) – shear strain curve, the axial stress – shear strain curve,
and the axial strain – shear strain curve shall be reported.

k)

The drained torsional shear strength 𝜏d (kN/m2), the shear strain γf (%) at the maximum shear stress, themajor and minor effective principal stresses at the maximum shear stress, and 𝜏d /σ'ac .

l)Failure state of the specimenm) When tests have been carried out on multiple specimens of the same material, the drained torsional shear
strength – axial consolidated stress relationship. Draw either a graph with the drained torsional shear
strength (kN/m2) on the vertical axis, and the axial consolidation stress (kN/m2) on the horizontal axis, or,a Mohr circle for σ'1f and σ'3f at 𝜏d .
n)

If a method that partially differs from this standard was used, give details of the points of difference.

o)Other reportable matters, including the following.
1)

An overview of the testing equipment, the method of saturating the specimen, and the material,
thickness, and Young’s modulus of the rubber sleeve.

2)

The dimensions, positions, and number of the metal ribs embedded in the porous plate, or the statusof the slip prevention used instead of the metal ribs.

̅̅̅̅̅) torsional shear test
Consolidated-undrained (CU7.2̅̅̅̅) torsional shear test, the following items of the test results shall be reported.
For the consolidated-undrained (CUa)

Method of preparation of specimensb)Specimen dimensions prior to consolidationc)

The B value and its measurement methodd)Volumetric change (mm3) and axial displacement (mm) due to consolidation. The instructions of Section
7.1d) applies.

e)

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

Note: The Note at Section 7.1e) applies.

f)

The magnitude of the axial stress (kN/m2), external pressure (kN/m2), internal pressure (kN/m2), and backpressure (kN/m2) after consolidationg)

The axial consolidation stress σ'ac (kN/m2), the lateral consolidation stress σ'rc (kN/m2), and if necessary
the anisotropic consolidation stress ratio σ'rc /σ'ac (= K)h)Shear strain rate (%/min.) during the torsional shear processi)

Method of measurement of torque, axial load, and rotational angle during torsional shear. The instructionof Section 7.1i) applies.

j)

Shear stress versus shear strain curve, and pore water pressure increment versus shear strain curve.

Note:

k)

The instruction of Note at Section 7.1 j) applies.

The undrained torsional shear strength 𝜏u (kN/m2), the shear strain γf (%) at the maximum shear stress,
the major and minor effective principal stresses at the maximum shear stress, and 𝜏u /σ'ac .

Note:When necessary the values of σ'1 and σ'3 when the effective principal stress ratio is the maximum shall bereported.
© JGS 2018 – All rights reserved

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JGS 0551-2020l)

The effective stress path diagramm) The failure state of the specimenn)When tests have been carried out on multiple specimens of the same material, the undrained torsional
shear strength – axial consolidated stress relationship. Draw either a graph with the undrained torsional
shear strength (kN/m2) on the vertical axis, and the axial consolidation stress (kN/m2) on the horizontal axis,
or, a Mohr’s stress circle for σ'1f and σ'3f at 𝜏u .

o)

If a method that partially differs from this standard was used, give details of the points of difference.

p)

Other reportable matters

Note: The instructions at Section 7.1o) apply.

14© JGS 2018 – All rights reserved

JGS 0551-2020

Axial load application device

Torque application device
Loading frame

Axial displacement gauge

Pressure (airpressure)
Load cell, torque meter
Rotational angle measuring device

Cap
Pedestal

Cell waterSpecimen

Double-walled tube burette

Double-walled tube buretteInternal pressure(air pressure)

Back pressure(air pressure)Internal pressure
measuring device

Pore water pressure
measuring device
Loading platform

Figure 1 Example of torsional shear test equipment© JGS 2018 – All rights reserved

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