DEVELOPMENT OF LATERAL DISPLACEMENT METER AND ITS APPLICATION IN
TRIAXIAL TEST
三軸試験における横変位測定装置の開発とその応用
Student: Fedallisa Ahmad
Advisor: Hirofumi TOYOTA
Abstract:
The soil deformation characteristic in small strain region (less than 1%) has become important
especially in soil deformation prediction during the tunnel construction and dynamic analysis. There is muchresearch, which has been done regarding the measurement of small strain by using proximeter on triaxial test
(Atkinson, 1993). The research on axial displacement in small strain had been worked out well but there are a
few studies about displacement in lateral direction.
Therefore, in this study, three types of lateral displacement meters (LDM) were developed to measure
the radial displacement during triaxial test. The CU and CD tests on Yoneyama sandy silt were conductedemploying the proximeter to detect the soil deformation during the tests and the comparison on accuracy ofeach type of LDM was done to determine the most accurate LDM. As the result, LDM type 3 showed the mostreliable result. Besides, it was also shown that the influence of consolidation hours on Poisson’s ratio needed tobe considered as the result showed different value at different consolidation hours.
1.Types of LDMs and the new triaxial test apparatus
Three types of LDMs have been suggested in this study. The shape of each type is shown in Figs. 1.1,
1.2 and 1.3. In LDM type 1, two proximeters were employed and two standing rod were needed to set theseproximeters for measuring lateral displacement. In type 2 and type 3, only one proximeter was needed but theglue used to attach the LDM considerably strong enough to keep the position of LDM. The proximeter, which
was used in the test, is AEC-5505 with sensor PU-05. It can measure soil deformation less than 2mm by using
the current eddy loss principle.
In the previous triaxial apparatus, the de-aired water was supplied up to the top cap and air pressure
was applied to the top of the cell water. The degree of saturation decreases during long-term test because the air
dissolved in the cell water and the dissolved air went into the specimen via rubber membrane.

TargetTargetTargetProximeter 1
SampleProximeter 1

SampleTargetProximeter 2

Fig 1.1 LDM type 1

Proximeter 2

SampleTargetProximeterFig 1.2 LDM type 2

SampleTargetProximeterFig 1.3 LDM type 3

Fig 1.4 The new triaxial apparatus

While, in the latest apparatus, the triaxial cell was filled with de-aired water, then the cell pressure
was applied through a water tank filled with some de-aired water and olive oil at the top layer, where the olive
oil played the role in guarding the air dissolved in the water. The description of the latest triaxial apparatus isshown in fig 1.4.
2. Test material and outline (Toyota et al., 2003):a) Material
The material used in this experiment was Yoneyama sandy silt. The soil grain size was controlled tobe smaller than 840μm and the soil consisted of 23.6%, sand 19.4% and silt 57%. The properties of this soil
are liquid limit(ωL)=52.4%, plastic index (Ip)=22.5% and specific gravity 2.746 g/cm3, which was defined by
the Japanese Standard Association.
The soil (550g) was mixed with distilled water (1000 g) and kept for one night so that it would bemixed well. Then, the air was removed from this slurry to get good saturation during vacuuming process and thesoil was consolidated under vertical pressure 80kPa for about two days until it turned into soil block. This soil
block was trimmed into 5 cm diameter and 12.5 cm height cylindrical specimen.
b) Experiment
The experiment started with saturating process where the soil specimen was fully saturated and thesaturation ratio was confirmed by the B-value which is more than 0.95. After the B-value check process, thetargets and proximeters were attached to the specimen and the data will be recorded from this stage. Then thebackpressure was applied to achieve a good saturation, and then the specimen was isotropically consolidated.

Finally, the specimen was compressed until the shear failure occurs. During the compression process, the test
was conducted with two different condition; Consolidated-Drained (CD) and Consolidated- Undrained (CU).
The data was recorded and calculated by computer program. Comparison on each LDM result was done todetermine the most accurate LDM. The effect of consolidation time on soil stiffness also was examined.
3. Experimental resultsprocess
Figure 3.1 shows the axial strain andradial strain during isotropic consolidation ofsaturated soil specimen. The results of each LDM
types were assembled in one graph and thencompared to the isotropic line, which wasconsidered as ideal behaviour during this process.

0.3 Yoneyama sandy silt

Radial strain, εｒ (%)

3.1 Comparison during isotropic consolidation

等方線

type1:p' =200 ～400 kPa
type2:p' =300 ～350 kPa

0.2

type3:p'=300 ～350 kPa

Type1
Type2

0.1
Type3

All the lines show that the radial displacement
occurred during the consolidation and it increased

00.0with an increase of axial strain. When the0.10.2

Local axial strain ,ε a (%)

uniformity of the specimen is assumed during theprocess, the soil specimen is uniformly deformed inboth vertical and horizontal directions. In this case,Fig 3.1 Relationships between axial strain and radial

the LDM type 3 came out with the result

strain during saturated isotropic consolidation

approximately to the isotropic line.

It can beconsidered that the most accurate LDM is type 3 in

–0.5

3.2 Comparison during Consolidated -Undrained
shearing processThe data during CU shearing test was also
compared for each type of LDM. During theshearing process, the volumetric strain which isdefined as εv=εa+2εr are supposed to be zero
because of undrained condition. According to therelationship between axial strain and radial strain,
the measured data was plotted to confirm theaccuracy of LDMs in which the line plotted should

Radial strain, εｒ (%)

this condition.

Yoneyama sandy silt

–0.4
–0.3

Type1Type3εa+2εr=0–0.2
Type2–0.1
00.00.5

Local axial strain ,ε a (%)

be inclined of –0.5 with the negative value of radialstrain since the specimen was expanding to theFig 3.2 Relationships between axial strain and radial

lateral directions during the compression process

strain during consolidated-undrained shearing test

(refer fig 3.2). As the result, it also confirmed that
the LDM type 3 showed the most reliable result.

1.0

3.3 Effects of consolidation time on Poisson’s ratio
The tests were also conducted with different hours (3 hrs, 6 hrs, 12 hrs and 48 hrs) of consolidation
process under the same mean effective stress p’=300 kPa. The consolidation time of this specimen is 3 hrs based
on 3t method. The result shows that the Poisson’s ratio ν increases with the extension of the time duringconsolidation process. From this result, it is affirmed that the stiffness of cohesive soil easily changes by theconsolidation time.

νPoisson’s ratio

12 hrs

3 hrs

48 hrs

6 hrs

Local axial strain εa(%)
Fig 3.3 Relationships between axial strain εa and Poisson’s ratio ν4. Conclusion
From the test results, the final observation can be concluded as follows:① LDM type 3 was found to be the most accurate lateral displacement meter for measuring small strain.
② Triaxial test apparatus was improved not to decrease the saturation degree of saturated specimens duringlong-period experiment.
③ The consolidation time affects the stiffness of cohesive soil where the stiffness increase as the period ofconsolidation process increase.
References:
1) John Atkinson (1993): An Introduction to the Mechanics of Soils and Foundations Through Critical State
Soils Mechanics, McGraw-Hill International Series in Civil Engineering.
2) Toyota, H., Nakamura, K., Sakai, N. and Sramoon, W. (2003): Mechanical Properties of Unsaturated
Cohesive Soil in Consideration of Tensile Stress, Soils and Foundations, Vol. 43, No. 2, pp. 115-122.