Research thesis

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SHINSHU UNIVERSITY
A new apparatus for estimating Water
Retentivity and Shear Strength in
Unsaturated Clay during Precipitation
Umezaki lab
Ilavuna Erick KAGESI
2/10/2014

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Contents
Chapter 1: Introduction..............................................................................................................4
PREFACE .........................................................................................................................................4
RELATED RESEARCHES ................................................................................................................6
Chapter 2: Soil Properties .........................................................................................................7
Saturation......................................................................................................................................7
Water Retention...........................................................................................................................9
GENERAL ........................................................................................................................................9
PRINCIPLES OF MEASUREMENT ...............................................................................................11
Chapter 3: Experiments on Soil Properties.........................................................................12
Pre-Consolidation Test..............................................................................................................12
GENERAL ......................................................................................................................................12
TEST APPARATUS .........................................................................................................................13
TEST PROCEDURE........................................................................................................................14
Water Retention Test(Pressure Plate Method) ...................................................................19
GENERAL ......................................................................................................................................19
TEST APPARATUS .........................................................................................................................19
TEST PROCEDURE........................................................................................................................22
CALCULATIONS OF TEST RESULTS ...........................................................................................26
HIGH PRESSURE CELL PRESSURE PLATE METHOD................................................................29
Consolidated Undrained Triaxial Compression Shear Test ............................................32
GENERAL ....................................................................................................................................335
TEST APPARATUS .......................................................................................................................335
TEST PROCEDURE......................................................................................................................346
CALCULATIONS OF TEST RESULTS ...........................................................................................39
Constant Shear Test................................................................................................................402
GENERAL ....................................................................................................................................402
TEST APPARATUS .......................................................................................................................402
TEST PROCEDURE ..................................................................................................................413
CALCULATIONS OF TEST RESULTS .........................................................................................447
Chapter 4: Graphical presentations......................................................................................49
Chapter 5: Conclusion ............................................................................................................514
Acknowledgements..................................................................................................................525
References..................................................................................................................................536

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A new apparatus for estimatingwaterretentivity and shear strength in
clay during precipitation
降水時における粘土の保水特性とせん断強度を評価できる試験装置
平成 26 年 2 月 Erick KAGESI
要旨
目的
降水による斜面崩壊には，不飽和土の吸水により飽和度が上昇しサクションが低下して起こ
る場合がある．従来の試験方法では，透水距離が長いため供試体内の飽和度分布の不均一化と
試験時間の長期化等が問題となり，上記の現象の再現は困難である．そのため，供試体が薄く
均一な飽和度分布と時間短縮が期待される不飽和土用三軸スライスせん断試験装置が開発され
ている．本研究では，本装置を用いた保水性試験とせん断試験を実施し，基準試験と比較する
ことにより，その有効性について検討する．さらに，上記の現象を再現する試験も試みた。
方法
NSF(C) 粘土に対して，飽和粘土の排水・吸水過程における保水性試験（加圧板法）および
圧密非排水三軸スライスせん断試験を実施した．さらに，排水過程の加圧板法により不飽和状
態にした後に，初期せん断応力を負荷した状態で吸水させて飽和度を上昇させる試験も実施し
た．
結論
1. 新しく開発した試験装置を用いて加圧板法を実施することにより得られた粘土の排水・吸
水過程における水分特性曲線は，JIS に基づく試験方法により求めた結果とほぼ同じである．
2. 圧密非排水三軸スライスせん断試験を実施して得られた内部摩擦角は，JIS に基づく圧密非
排水三軸圧縮試験より求めた結果とほぼ同じである．
3. 不飽和土用三軸スライスせん断試験装置を用いることにより，粘土の保水特性およびせん
断強度を評価することができる．
4. 本装置を用いれば供試体を取り出すことなく，粘土の排水過程に続く吸水過程における飽
和度上昇によるせん断ひずみの増加やせん断強度の低下について連続的に評価することが
できる．
指導教員梅崎健夫准教授

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A new Apparatus for estimating Water Retentivity and Shear Strength
of Unsaturated Clay during Precipitation
Erick KAGESI 10/02/2014
Abstract
Objectives
During precipitation, water seeps into the soil and after a while, landslides and other
slope failure related disasters occur. Slope failure during precipitation can be explained in
two ways: one, seepage of water into clay increases its degree of saturation, and two, as the
pore water pressure increases (due to rise in ground water level), the ground effective stress
decreases resulting in shear failure. In order to understand and explain slope failure we
need to reproduce this phenomenon, which is difficult and extremely lengthy when one
employs standard tests due to problems like heterogeneous absorption of water. However,
using a Shinshu University newly developed triaxial slice shear test apparatus,
unsaturated clay water retentivity and shear strength decrease can be evaluated within a
reasonable time frame.
Method
Triaxial Slice Shear Test apparatus will carry out both the Water Retentivity Test by
Pressure Plate Method and the Shear Test of unsaturated clay in one experiment without
changing or removing the test specimen from the test apparatus. The behavior of the test
specimen during water absorption as well as drainage phase will be evaluated and the
results compared to other standard tests like the Standard Retentivity Test and the
Standard Triaxial Test. In this research, NSF(C) clay will be used as the test specimen.
Conclusion
1. The apparatus can be used to obtain a water retention curve by increasing suction in
the test specimen during the drainage phase and then reducing it during absorption
phase. The water Retentivity test result values were found to be close to other
approved test results.
2. The Slice Shear Test was carried out. From the test results, the internal angle of
internal friction was calculated, compared to, and found to be close to that from the
Standard Triaxial Test. These findings confirm the reliability of the Triaxial Slice Test
apparatus.
3. Using the Slice Triaxial Shear Test apparatus, we can measure the saturation
increase in unsaturated clay during the water absorption phase and also the shear
strength decrease with increase in shear strain.
Under the guidance of: Prof. Takeo UMEZAKI

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Chapter 1: Introduction
PREFACE
Japan is one of the countries with very high annual precipitation. These rains are the
biggest causes of landslides and other slope failure related disasters. When water is seeping
through soil pores, total head is dissipated as viscous friction producing a frictional drag,
acting in the direction of flow, on the solid particles1). This seepage forces coupled with
gravitational forces affect the effective normal stress and eventually causes the slope to fail
– slip.
Such slips (landslides) often occur after a period of heavy rain, when the pore water
pressure at the slip surface increases, reducing the effective normal stress and thus
diminishing the restraining friction along the slip line. This is combined with increased soil
weight due to the added groundwater. A 'shrinkage' crack (formed during prior dry
weather) at the top of the slip may also fill with rain water, pushing the slip forward. At the
other extreme, slab-shaped slips on hillsides can remove a layer of soil from the top of the
underlying bedrock. Again, this is usually initiated by heavy rain, sometimes combined
with increased loading from new buildings or removal of support at the toe (resulting from
road widening or other construction work).
The shear strength of soil with negative pore water pressure plays an important role in
the stability of a slope, particularly when the slip surfaces are shallow. Frendlund et al
(1978) shows this by the equation2)
𝜏 = 𝑐′ + ( 𝑢 𝑎 − 𝑢 𝑤) 𝑡𝑎𝑛𝜑 𝑏 + ( 𝜎 − 𝑢 𝑎) 𝑡𝑎𝑛𝜑′ (1.1)
Where,
c’ = cohesion interceptwhen the two stress variables are zero.
𝜑′ = Angle of internal friction with respect to changes in ( 𝜎 − 𝑢 𝑎) and 𝜑 𝑏
Bishop proposed the effective stress equation
𝜎 = ( 𝜎 − 𝑢 𝑎) + 𝜒( 𝑢 𝑎 − 𝑢 𝑤) (1.2)
Where,
𝑢 𝑎 = pore-air pressure
𝜒 = a parameter related to the degree of saturation of the soil
But when the effective stress equation was reevaluated, it was noted that a variation in
matric suction, ( 𝑢 𝑎 − 𝑢 𝑤), did not result in the same change. This suggests that suction
plays a pivotal role in the difference between characteristics of saturated and unsaturated
soils. With this in mind, several components were incorporated into the equation to explain
the effects of suction, water content and degree of saturation on slope failure in unsaturated
soils more comprehensively.

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In the previous attempt at this research, to examine the specimen’s increase in shearing
strain with decreasing shear strength during the water absorption phase, a thin “slice”
elliptical test piece was prepared. This ensured homogeneous water absorption in a
relatively short period of time due to the shortened infiltration distance. The test was
carried out using a newly developed Slice Triaxial Shear Test apparatus. A saturated clay
test specimen was prepared using a Pre-Consolidation Test Method, while an unsaturated
clay test specimen (required during Absorption Phase) was prepared using the Vacuum
Evaporation Method. The efficiency of the test apparatus to carry out a Water-Retention
Test during water absorption phase was examined. However, several problems arose during
the test: When the saturated ceramic disc fitted pedestal came into contact with the
unsaturated specimen, water from the ceramic disc was absorbed by the specimen, thus
affecting the expected results.
Using the Pressure Plate Method, the water retention curve (suction – water content and
suction – degree of saturation) was obtained. Later, after the drainage phase of the
saturated clay specimen, shear stress was introduced to the unsaturated specimen until the
specimen failed. This was very time effective as it enabled a one-move test, without the
need to prepare an unsaturated specimen using the Vacuum Evaporation Method. It also
helped solve the problem where the test piece drew water from the ceramic disk causing
water content disparity.
Fig 1.1 slip surface stress formation during seepage

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RELATED RESEARCHES
1.1.1. Influence of StressState on Soil-Water Characteristics and Slope Stability3)
A soil-water characteristic curve defines the relationship between the soil
(matric) suction and either the water content or the degree of saturation.
Physically, this soil-water characteristic is a measure of the water storage
capacity of the soil for a given soil suction. Conventionally, the soil-water
characteristic curves (SWCCs) are determined in the laboratory using a
pressure plate apparatus in which vertical or confining stress cannot be applied.
The net normal stresses considered in the apparatus are 40 and 80 kPa, which
are appropriate for many slope failures in Hong Kong. Experimental results
show that the soil-water characteristic of the soil specimens is strongly
dependent on the confining stress. Numerical analyses of transient seepage in
unsaturated soil slopes using the measured stress-dependent soil-water
characteristic curves predict that the distributions of pore-water pressure can
be significantly different from those predicted by the analyses using the
conventional drying SWCC. For the cut slope and the rainfall considered, the
former analyses predicted a considerably lower factor of safety than that by the
latter analyses. These results suggest that wetting stress-dependent soil-water
characteristic curves should be considered for better and safer assessment of
slope instability.
1.1.2. Slope Stability AnalysisIncorporating the Effect of Soil Suction4)
Clear appreciation has emerged regarding the influence of soil suction on the
stability of slopes. The shear strength equation has gained widespread
acceptance, and testing procedures have been proposed for measuring the shear
strength parameters for unsaturated soils. The new strength parameter is the
angle, 𝜑 𝑏 . This angle appears to be commonly of the order of 15 degrees.
However, further testing and research are required for a better understanding of
this soil parameter. More studies are needed of the season to season pore-water
pressure changes, and case studies are needed of stability problems in
unsaturated soils to promote confidence in analysis of the same.

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Chapter 2: Soil Properties
Saturation
Characteristics of saturation
When the soil pores are filled by more than one fluid, e.g. water and air, the
porous material is termed “unsaturated” with respectto the wetting fluid.
Fig 2.1 unsaturated soil structure
The water and air between the solid particles are known as pore-water and
pore-air respectively. Soil can be classified according to the ration of the
different fluids in its composition. e.g.
 Dry soil: consists of soil particles pore-air only (degree of saturation
Sr = 0% )
 Saturated soil: consists of soil particles and pore-water only (degree
of saturation Sr = 100% )
 Partially saturated soil: consists of soil particles and both pore-
water and pore-air
According to Skempton’s equation, increase in pore-water pressure Δu due to
earth stresses increase Δσ1 and Δσ3 can be given by,
∆𝑢 = 𝐵(∆𝜎3 + 𝐴(∆𝜎1 − ∆𝜎3)) (2.1)
Where,
B : Pore-water pressure co-efficient
Saturation level Degree of
saturation
Pore-water
pressure
Pore-air
pressure
B-value
Saturated = 100 ≥ 0 - = 1
Partial saturation < 100 ≥ 0 > 0 < 1
Pseudo saturation = 100 < 0 - = 1
Unsaturated < 100 < 0 = 0 < 1
Table 2.1 types of saturation

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Types of Saturation
i. Pendular saturation
The wetting phase exists in a pendular form of saturation.An adhesive fluid
film of the wetting phase coats solid surfaces, grain-to-grain contacts, and bridges
fine interstices or pore throats. The wetting phase might or might not be at
irreducible saturation. In the illustration, water in the “A” and “B” figures is
pendular.
ii. Insular air saturation
This can be described as a form of saturation in which the non-wetting phase
exists as isolated insular globules within the continuous wetting phase. A drop in
pressure might or might not cause the insular globules to collect into a continuous
phase. In figure 2.2, saturation in the “B” and “C” figures is insular.
iii. Funicular saturation.
This is a form of saturation in which the non-wetting phase exists as a
continuous web throughout the interstices. The non-wetting phase is mobile under
the influence of a hydrodynamic pressure gradient. The wetting phase might or
might not be at irreducible saturation. In figure 2.2, the saturation in the “A”
figure is funicular.
Fig 2.2 Types of saturation

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Water Retention
GENERAL
2.1.1.1. Suction (units: kPa)
a. Total Suction
Total soil suction is defined in terms of the free energy or the relative vapor pressure
(relative humidity) of the soil moisture7).
𝛹 = −
𝑅𝑇
𝑣 𝑊0 𝜔 𝑣
𝑙𝑛(
𝑢 𝑣
𝑢 𝑣0
) (2.2)
u v = partial vapor pressure of pore water vapor
u v0 = saturation vapor pressure of water vapor over flat surface of pure water
Total suction consists of two components:
 Matric suction (ua - uw)
 Osmotic suction (π).
Ψ = (ua - uw) + π (2.3)
Both components are due to differences in relative humidity of the soil vapor.
b. Matric Suction
When a meniscus forms at the soil-air interface, due to the surface tension, it results in
reduced vapor pressure in the water. As the vapor pressure decreases, it becomes more
negative, and the matric suction pressure increases as the radius of curvature of the
meniscus decreases. The size of the soil pores decreases with a decrease in soil particle size
which then affects the size of the radius of curvature and consequently the matric suction
pressure. The vapor pressure decreasesas the degree of saturation decreases.
 Direct measurementof Matric Suction8)
Matrix suction can be obtained through direct measurement of the negative
pore-water pressure. The pore-air pressure, usually equal to on-site atmospheric
pressure and matric suction, is the difference between air pressure and pore-
water pressure. The direct measurement of matric suction requires a separation
between water and air phase by means of a ceramic disk or a ceramic cup. The
maximum value of matric suction that can be measured is limited by the air
entry value of the ceramic disk used.
In this experiment, two ceramic diskswere used
1) 2.5 bar ceramic disk
2) 3.5 bar ceramic disk
A popular way to directly measure matric suction is utilizing suction probe.

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Suction probe
The direct measurement of matric suction is preferred in unsaturated soils
tests since measured pore-water pressures are more rapidly reflected. Ridley
and Burland (1993)11) developed a suction probe for measuring matric suction of
soil. The principle of making suction measurements using a suction probe is
based on the equilibrium between the pore-water pressure in the soil and the
pore-water pressure in the water compartment. Before equilibrium is attained,
water flows from the water compartment into the soil, or vice versa. The suction
probe measures the pore-water pressure (uw). The matric suction can be
computed since the applied air pressure (ua) is known, and the matric suction is
the difference between the pore-air pressure and the pore-water pressure (ua–
uw). Simply, a suction probe consists of a pressure transducer with a high-air
entry ceramic disk mounted at the tip of the transducer. The diaphragm of the
pressure transducer responds to the pressure applied. In the suction probe, the
volume of water reservoir beneath the ceramic disk or ceramic cup is minimized.
Water in the water reservoir is pre-pressurized such that the benefit of the high
tensile strength of water can be utilized (Marinho and Chandler, 1995).
Recently, Meilani et al. (2002) developed a mini suction probe for measuring
matric suction along the specimen’s height during a triaxial test on an
unsaturated soil.
2.1.1.2. Earth-water retention property
Soils can process and contain considerable amounts of water. They can take in water, and
will keep doing so until they are full, or the rate at which they can transmit water into and
through the pores is exceeded. Some of this water will steadily drain through the soil (via
gravity) and end up in the waterways and streams. But much of it will be retained, away
from the influence of gravity. The pores provide for the passage and/or retention of gasses
and moisture within the soil profile. The soil’s ability to retain water is strongly related to
particle size; water molecules hold more tightly to the fine particles of a clay soil than to
coarser particles of a sandy soil, so clays generally retain more water (Leeper and Uren,
1993).
From figure 1.2 (b), the radius of curvature of the meniscus of the crack water changes
depending on volume of crack, water pressure and crack air pressure. In other words, water
content varies according to volume of crack, water pressure and crack air pressure. In
addition, water content differs if the size of the soil particle is different even if the radius of
curvature of the meniscus is the same. The water content of unsaturated soil changes
depending on grain size distribution and crack diameter distribution. This property is
called earth-water retention properties.
2.1.1.3. Suction matric potential
Suction is expressed in terms of pressure, water-head or potential energy. The potential
energy of water refers to the chemical potential that a water unit has.
The main chemical potentials in earth-water are:
 gravitational potential
 matric potential
 osmotic potential
 air pressure potential
The sum of these is Total potential. Total potential is shown in the next expression.

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𝜑 𝑇 = 𝜑 𝑔 + 𝜑 𝑜 + 𝜑 𝑚 + 𝜑 𝑎 (2.4)
Where,
𝜑 𝑇 : Total potential
𝜑 𝑔 : Gravitational potential
𝜑 𝑜 : Osmotic potential
𝜑 𝑚 : Matric potential
𝜑 𝑎 : Air pressure potential
Gravitational potential is also called potential energy. When carrying out calculations, it
is possible to disregard the air pressure potential ( 𝜑 𝑎 = 0), as one has to assume it under
atmospheric pressure. Osmotic potential varies depending on chemical compounds in earth-
water. Also, when the chemical substances in the pore-water and soil particle surface such
as in unsaturated soil, it is disregarded ( 𝜑 𝑜= 0) as the value is minute. Matric potential is
chemical potential without osmotic potential. It is the soil’s ability to attract water.
PRINCIPLES OFMEASUREMENT
2.1.1.4. Pressure Plate Method
The Pressure Plate Method uses the axis-translation technique, which reverses the
reference air pressure from atmospheric to above atmospheric causing the pore water
pressure to change as it comes to equilibrium with the pore air pressure

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Chapter 3: Experiments on Soil Properties
Pre-Consolidation Test
GENERAL
3.1.1.1. Preparation of the soil specimen
(a) This preparatory consolidation aims to prepare a saturated test piece with an
objective water content wobj approximately twice the liquid limit water content
wL of the soil sample. Keeping in mind the objective water content wobj, NSF(C)
clay (ρs = 2.723 kgf/cm2, wL = 57.5%) and pure water are put in a mixing bucket.
The soil sample – pure water ratios are shown in the table below.
(b) The soil sample and water are first mixed using a spatula before a motor
propelled mixer is employed to mix the mixture to a homogenous solution. The
water content wn is measured.
(c) This mixture is covered and kept in a temperature regulated room for more than
24 hours.
(d) To obtain the objective water content, the following formula to calculate the
amount of pure water Mw required is used.
Mw = {(wobj – wn)/ (100+wn)} ×M (3.1)
Where,
wobj: objective water content(%)
wn : water content after mixing (%)
M : total mass of mixture and mixing bucket (g)
(e) After 24 hours the mixture is mixed again and water added if needed. The
measured water contentis the objective water content.
Soil sample and pure water masses
Consolidation force NSF(C) clay mass (g) Objective water
content wo bj (%)
Pure water mass (g)
1.0 kgf/cm2 3500 115 4025

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Fig 3.1: NSF (C) clay soil
TESTAPPARATUS
The test apparatus includes:
 Acryl consolidation column
 Upper and Lower Column Cover
 Consolidation piston
 Consolidation pressure regulator gauge
 Vacuum pump
 Drainage tubes and pressure delivery couplers.
 Vertical displacement gauge

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TESTPROCEDURE
3.1.1.2. Preparatoryconsolidation apparatussetup
(a) 4 felt fabrics are placed in a de-aeration vacuum desiccator more than 24 hours
before the start of consolidation.
(b) To remove any particles that might block the flow of water and air during
consolidation, an air-gun is used to blow out any particle sediments in the upper
and lower column covers.
(c) Grease the rubber O-rings using green airtight grease and place one in the O-
ring sheath on the lower column cover (LCC)
(d) Pure water is injected into the LCC at the opening on top and allowed to flow out
from the side nozzle. The nozzle valve is closed while the water runs. This
ensures all air is expelled from the water passage.
(e) The Metal shaft is fixed and passed through the upper column cover (UCC). The
UCC is placed on a wooden stand with the top facing up.
(f) A short bearing is greased properly on the inner side and placed atop a greased
rubber plate on the top side of the UCC. The bearing is then fastened into place
using the shorter screws.
(g) A circular plastic plate handle is fastened onto the top of the metal shaft.
(h) The UCC is then turned upside down, with the shaft still in the middle, and
placed again atop the wooden stand.
(i) Similar to the LCC the other greased rubber O-ring is placed into the O-ring
sheath of the UCC.
(j) A greased small rubber ring is placed into the grooving on the translucent plastic
O-ring, slid down the metal shaft and onto the UCC.
(k) A brass alloy plate is placed onto the translucent plastic and fastened into place
using the longer screws.
(l) An aluminum propeller agitation plate is fixed onto the bottom end of the shaft.
(m)Green grease is applied to the inner side of the acryl cell column to reduce
friction and also act as an airtight barrier on the column sides.
(n) The greased acryl cell column is mounted onto the LCC and properly fixed so
that its edges fit into the O-ring sheath.
(o) Two of the de-aired felt fabrics are removed from the desiccator after 24 hours
and placed properly at the bottom of the acryl column cell.
3.1.1.3. De-aeration of NSF(C) clay - water mixture
(a) The NSF(C) clay - water mixture is mixed one last time and carefully poured into
the cell column ensuring no air pockets are formed.
(b) The UCC is then placed carefully on top of the acryl cell column and rotated
slightly to ensure the cell fits into the sheath perfectly. The metal shaft is then
carefully lowered into the clay mixture.
(c) Fasten the UCC and the LCC tightly in place with screw rods.

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(d) Close the water drainage valve on the UCC.
(e) The vacuum pump coupler is connected to the nozzle on the UCC and the
vacuum pump is switched on.
(f) Agitate the mixture by moving the propeller fixed shaft up and down until the
swelling settles. NSF(C) has high swelling tendency so one ought to be extra
careful.
(g) After swelling settles, de-aeration continues for at least 3 hours. To remove any
air bubbles trapped in the mixture, agitation after every 30 minutes is important.
(h) After 3 hours of de-aeration, the vacuum pump is switched off and the coupler
disengaged from the air nozzle on the UCC.
3.1.1.4. PreparatoryConsolidation
(a) Using a depressurizing coupler, push the air valve inside the nozzle on the UCC
to release trapped pressure from the column cell.
(b) Screw rods are unfastened and removed. Be careful so as not to allow air into the
mixture while scooping off the mixture from the propeller as it falls back into
column cell.
(c) Using a rubber squeegee, remove any extra mixture sticking on the sides of the
column cell. Clean it further using a clean piece of cloth and pure water.
(d) Apply more green air tight grease on to the surface.
(e) Using a spatula, level the mixture and then place the remaining 2 felt fabrics
carefully on top.
(f) Remove the UCC and unfasten the propeller. Dismantle and clean both the UCC
and the metal shaft.
(g) Reassemble the UCC as in (2) 5. ~ (2) 11.
(h) Take a circular pressure piston; fit a greased rubber O-ring into the sheath along
its circumference.
(i) At the bottom end of the shaft where the propeller was removed, fasten the
pressure piston firmly.
(j) Connect the pressure plate water outlet with the UCC water valve via a bourdon
water tube.
(k) Open the water valve on the UCC.
(l) Carefully holding the piston and shaft in place, lower the piston into the cell
column and fix the UCC properly onto the column cell.
(m)Fasten the UCC and the LCC tightly with the screw rods.
(n) Connect and fasten tightly water tubes onto the water valves on the UCC and
the LCC. The open end of the tubes is to be inserted into a bucket half filled with
water. This is to help prevent drying of the test piece on either end.
(o) Connect a double coupler bourdon tube to the pressure nozzle on the UCC and
the pressure regulator.

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(p) Gradually increase the pressure inside the cell until the piston comes into
contact with the mixture and felt fabric. This is to force out any air between the
mixture and the pressure piston.
(q) Close the water valve on the UCC and then fix a vertical change dial gauge atop
the circular plastic plate handle.
(r) Set the pressure to the required amount.
(s) At the same time with the start of a timer, open the upper water valve (on the
UCC) and lower water valve (on the LCC). This is the start of the consolidation.
(t) Determine the consolidation duration time using the 3t-method. The
consolidation carried out by step loading. In this test the step loads are:
0.5kgf/cm2 and then 1.0kgf/cm2
(u) When the consolidation time ends, with the pressure regulator at 1.0kgf/cm2,
close both water valves. Remove the bourdon tubes from both valves and let the
test piece and the apparatus rest for more than 24 hours. This helps prevent
swelling and also reduces water content disparity along the height of the test
piece.
(v) After more than 24 hours the pressure is gradually reduced to zero.
(w)Remove the bourdon tube coupler from the pressure nozzle.
3.1.1.5. Extraction of the test piece
(a) Using a depressurizing coupler, push in the air valve inside the nozzle on the
UCC to release trapped pressure from the column cell.
(b) Unfasten the screw rods.
(c) Place one of the two special rectangular vinyl chloride plates (VC plate
henceforth) on top of the UCC and fasten it on firmly with the screw rods. The
VC plate has a circular hole in the middle whose circumference is just a little
bigger than the acryl column cell.
(d) Overturn the whole apparatus and place it upside down on top of two tables in
close proximity such that the plate is held in position on top of either table
without any obstacles around the circular opening.
(e) Unfasten the screw rods again.
(f) Open the water valve on the LCC and remove it from the column cell.
(g) Fasten the other VC plate into position around the top of the cell column making
sure the inner circumference of the cell is well inside the VC plate’s inner
circumference.
(h) Connect the pressure regulator again to the pressure nozzle on the UCC.
(i) Increase the pressure slowly as the test piece is pushed out of the cell column.
Remove it and carefully place it on a saran wrapped glass slab. Note the original
upper side of the test piece.

17
(j) On a trimmer, cut the test piece into four equal quarters. From the middle part
of each of the quarters cut a thin strip, divide it into 3 and put them into three
separate beakers: top, middle and bottom part of the test piece. Measure the
water content.
(k) Wrap the quarters using saran wrap taking note of the top and bottom sides.
Using a felt pen, note the date of packaging, consolidation load (e.g. 1.0kgf/cm2),
type of test piece (e.g. NSF(C)) and the side (which side is top). Arrange the
packaged and marked test pieces in a storage desiccator and cover them with wet
cloth. Cover the desiccator and store it in a temperature controlled room.

18
3.1.1.6. 3-t method
This method is vital in determining when the consolidation test has reached completion.
This helps avoid over-consolidation as this research’s scope of application is normally
consolidated clay.
(a) After exerting 0.5 kgf/cm2 consolidation pressure on the soil specimen for about 1
hour, the upper and lower water valves are closed.
(b) Increase the consolidation pressure to 1.0 kgf/cm2.
(c) Connect a vertical displacement transducer on top of the consolidation piston.
(d) Start the computer data logger and monitor. Configure the interval
measurements timer to 3 minutes.
(e) Simultaneously start the interval measurements timer and open the upper and
lower water valves.
(f) Use the data logger obtained data to plot a vertical displacement – time graph.
Time (x-axis) is displayed in log values.
(g) Find the highest gradient between two points on the graph.
(h) Plot a line with the same gradient but translated 3 times the original x value to
the right.
(i) When the plotted vertical displacement – time curve crosses the straight line,
close both upper and lower valves.
(j) Let the apparatus stay for more than 24 hours before reducing the consolidation
pressure to zero.

19
Water RetentionTest(Pressure Plate Method)
GENERAL
The determination of soil water retention curves requires the volume to be measured
in order to calculate the void ratio and degree of saturation. The volume change of the
sample during drainage and absorption phases in the Water Retention Test is obvious
and vital, especially for soils with deformability. The soil water retention curve is
generally influenced by the volume change of soil specimens. However, in general, many
apparatus that are used for soil water retention testing cannot measure the volume
change during the test process. In this study, a modified experimental system, which
can measure and record volume change during the test, and also can control the entire
testing process via computer, is employed to determine the soil water retention curve.
The new system has several advantages over existing apparatus. Notable amongst them
is that it can automatically determine both the drainage and the absorption
characteristics with high accuracy, and can measure volume change during the test,
using only one sample. Water retention characteristics of clay are briefly tackled in this
experiment. Then the effect of pore-water volume change and suction on shear strength
of clay is briefly discussed.
TESTAPPARATUS
For this experiment, the following were used:
 Ceramic disk. The ceramic disks should be placed inside pure water
and in a de-airing desiccator for a minimum of 24 hours before the
start of the experiment. For this research, the two ceramic disks
used were:
 AEV 250kPa
 AEV 500kPa
 Rubber membrane
Internal diameter 50 mm × length 180 mm × thicknesses 0.25mm
 Membrane setter
 2 rubber O-rings
 O-ring setter
 Double-duct burette
 De-aeration tank
 Dry set vacuum pump

20
 Test specimen preparation kit
 Trimmer
 Trim waste collection tray
 Wire saws
 Cutter
 Vernier scale
 Acryl specimen shaper (has 3 parts: upper, middle (slice cover)
and the lower part)
 Glass slab and saran wrap
 3 beakers
 Filter paper
 Triaxial slice shear test apparatus
 Triaxial pressure chamber (in the acryl water tight cylinder)
 Cell and back pressure supply/control systems
 Axial compression device
 Axial displacement transducer
 Lateral displacement analog laser sensor
 Triaxial pressure chamber (acryl water tight cylinder)
 Axial confining pressure weights plate
 Shaft and top cap weight cancelling bells.

21
空気圧
間隙水圧計
スライダー
供試体
セラミック付き
ペデスタル
DP
グラスファイバー
付きキャップ
吸水，間隙水圧増加
ギャプセンサー
メンブレン
Oリング
Confining
Pressure
Displacement sensor laser
Glass fiber fit Top cap
Rubber O-ring
Rubber membrane
Ceramic disk mount
Pedestal
Pore-water Pressure
gaugeAbsorption,
Increase in pore-water pressure
Test
specimen
Slider

22
TESTPROCEDURE
3.1.1.7. Preparation of the test Specimen
(a) Make sure the dehumidifier is turned off in the preparation room. Switch off
the ventilation fan and sprinkle water on the floor. This helps raise the
humidity thereby reducing the risk of the test specimen drying up before the
trimming procedure ends.
(b) Prepare a setting glass slab; wrap it with saran wrap, measure its weight and
record the data. Mark out the rubber membrane for use during image
analysis.
(c) Cut out the filter paper according to the required test specimen size and, for
this too, note down its weight.
(d) Before taping together the 3 parts of the slice shaper, record the weight of the
middle (slice cover) part.
(e) Prepare for measuring the water content of the test specimen. Take the mc of
the 3 beakers.
(f) Remove the NSF(C) clay from the storage desiccator and unwrap it. Place it
on the trimmer and set the trimmer diameter to 5mm.
(g) Using the thickest wire saw, systematically trim off the outer parts of the soil
specimen.
(h) Take a part of the untouched inner region and place it in one of the beakers
allocated to measuring water content.
(i) When the soil specimen takes on a more defined cylindrical shape, change to
a smaller wire saw for a smoother finish.
(j) Cut out saran wrap, just enough to wrap around the trimmed soil specimen.
Carefully slide the acryl shaping tube down the wrapped soil specimen.
(k) Remove the tape connecting the upper to the middle and the lower parts and
remove only the upper part of the shaping tube. Using a cutter, cut out the
exposed saran wrap from the edge of the middle part of the shaping tube and
remove the wrap being careful not to deform the structure of the specimen.
(l) Raise the remaining parts of the shaping tube to a level higher than the cut
out part of the saran wrap.
(m) Carefully place the soil specimen and the shaping tube horizontally on the
saran wrapped glass slab.
(n) Using the smallest wire saw, carefully cut out the protruding soil specimen in
small slices, take a slice cut closest to the edge of the shaping tube; place this
inside one of the beakers allocated to measuringwater content.
(o) Carefully slice off the remaining part of the protruding soil specimen. Repeat
this trimming until the soil specimen and the edge of the shaping tube are
one smooth plane.
(p) Carefully place the cut out filter paper onto the soil specimen part avoiding
the shaping tube surface.
(q) Place the specimen on the slab on the filter paper surface.
(r) Remove the tape connecting the middle (slice cover) part from the bottom
part. Remove the exposed saran wrap and dispose it.
(s) Repeat stages (n) and (o). Use the Vernier calipers to measure the thickness,
long diameter and the short diameter of the elliptical final slice – test
specimen.

23
(t) Cover the test specimen to avoid surface drying.
3.1.1.8. TestApparatusPreparation
(a) Calibrate the test apparatus measuring peripherals (pore-water pressure
gauge, pore-air pressure gauge, double-duct burette, lateral displacement
sensor gauge, vertical displacement transducer and confining pressure gauge)
(b) To avoid air bubbles forming when the water delivery tubes are inundated,
flood the pipesapproximately 24 hours before performing a dry set.
(c) Preparation of a de-aired water tank.
 Fill the de-aeration tank three quarter way full and place it on the de-
aeration station.
 Make sure all valves on the tank are closed. Connect the vacuum pump
coupler.
 This takes about 48 hours for a complete and proper de-aeration.
(d) The ceramic disk mounted pedestal saturation and mounting.
 The base surface of the ceramic disk mount pedestal being smooth and
flat is pivotal in the success of the experiment. Therefore, at a frequency
of once a year, the base surface should be smoothened out using sand
paper (#1000 or #1200)
 Submerge the ceramic disk mounted pedestal in a beaker with pure water.
 Place the beaker in a vacuum pump desiccator, place the desiccator lid on
and turn on the vacuum pump.
 On the vacuum pressure dial, the degree of vacuum should be over 95kPa.
 De-air for at least 2 days before preparing for mounting.
(e) Switch on the computer and data logger; start the measurements monitor.
Check the measurement settingsand adjust the items to be measured.
(f) De-aeration of the water delivery tubes.
 Disengage the de-airing tank from the vacuum pump coupler at the de-
aeration station. Place the tank next to the test apparatus.
 Connect valve 1 to the de-aeration tank valve. Place the tank lying
horizontally on a flat surface making sure that the two holes on either
side of the tank are above the water level. Connect it to the dry set
vacuum pump and switch on the pump.
 Fasten a cap on the pedestal holder; place the de-airing tank lying

24
horizontally on the working table.
 Open valve 1 and the valve on the de-airing tank.
 Turn on the vacuum pump and gradually increase the negative pressure
to maximum.
 On the data logger the negative pressure should be about -98kPa. Let this
set up stay for at least 3 hours.
 Make sure there is no more water in the water tubes before standing the
de-aeration tank upright, reducing the negative pressure and inundating
the same.
 Stand the de-airing tank upright and disengage the dry set vacuum pump
from the de-airing tank.
 Switch off the dry set vacuum pump and disconnect the connecting
coupler. Open the top valve on the de-airing tank.
 Holding the de-aeration tank at a higher level than the pedestal height,
unfasten the pedestal holder cap and let water flow and form a meniscus
on the top of the pedestal holder.
 Make sure all the water delivery tubes are properly flooded up to the
center and the outer pore-water pressure gauges.
(g) Close valve 1.
(h) Remove the ceramic disk from the desiccator and carefully place it atop the
pedestal being careful not to allow air to escape into the ceramic disk. Place a
piece of saran wrap on the still wet ceramic disk to avoid drying. It is because
of this reason that, the test specimen should be prepared and ready to be
mounted onto the ceramic disk before removing the ceramic disk from the
beaker to install it on the pedestal.
(i) Fit the O-rings and the membrane onto the O-ring setter and membrane
setter respectively and place them down the pedestal shaft in that order.
(j) Make sure the top cap shaft is firmly clamped in position. Remove the saran
wrap from the ceramic disk.
(k) Using a specimen extractor, extract the test specimen from the middle (slice
cover) part and place the test specimen as accurately as possible on the
ceramic disk. Close valve 1 to avoid water seeping into the test specimen.
(l) Unclamp the top cap, slowly lower and position it on top of the test specimen.
Clamp the shaft again in this position.
(m)Set the rubber membrane to cover the slice test specimen, ceramic disk,
pedestal and the top cap. Fit the rubber O-rings at the upper and lower end
of the rubber membrane.
(n) Connect the pore-air pressure Ua tube to the top cap.
(o) Install the triaxial pressure chamber (acryl water tight cylinder) onto the test
apparatus. Bolt it in position and flood it to the marked water level.
(p) Fasten the axial confining pressure weights plate on top of the shaft. Connect
the shaft weight cancelling bells.
(q) Fix the vertical displacement transducer and the lateral displacement sensor
laser in position.
(r) Connect the confining pressure coupler atop the test apparatus. Check the
burette water level (about 0.0ml mark).
(s) Start the data logger and perform an initialize data check on all
measurement components.

25
3.1.1.9. Drainage Phase
(a) The confining pressure and the pore-air pressures are increased in stages
when the volume of water displaced from the test specimen becomes too
minimal i.e. less than 0.00125ml/h (this figure was arrived at after
calculations). The loading stages are 10, 20, 40, 80, 160 and 200kPa for the
2.5 bar ceramic disk and 100, 200 and 300kPa for the 5 bar ceramic disk. (For
purposes of explanation,A5 bar ceramic disk is employed in this description).
(b) Before the drainage phase commences, make sure valve 3 and valve 5 are
closed.
(c) Set the timer properties, depending on the data interval requirements. Start
the data logger Excel worksheet.
(d) Raise the ua + σ3 confining pressure dial to 100kPa. Place 1.0 kgf/cm2 weights
on the weights plate on top of the loading shaft.
(e) Record the initial double-duct burette reading.
(f) Unclamp the loading shaft, open valve 5 (pore-air pressure valve). Start the
interval timer and open valve 3 (burette valve) simultaneously with the timer
when it beeps.
(g) Keep recording volume displacements from the readings on the double-duct
burette; record these next to the excel data.

26
(h) When the volume change becomes lower than the minimum limit, increase
the ua + σ3 confining pressure dial to 200kPa and repeat the subsequent
procedure.
N.B: When changing the confining and pore-air pressures to the next stage,
stop the data logger timer, clamp the shaft in position and close valve 5 before
commencing the next phase of loading.
(i) At the end of the drainage phase, save the data obtained for analysis.
3.1.1.10. Absorption Phase
(a) The absorption phase is the mirror reverse of the drainage phase. The
unloading is also done systematically in stages, just as it was during
drainage phase.
(b) Record the initial double-duct burette reading.
(c) At intervals take burette readings (ml)
(d) Check the test apparatus, making sure there is no air or water leakage.
(e) Change the loading pressures and weights at the end of every stage, closing
valves 3, 5 and clamping the shaft before every change.
(f) When the experiment reaches the final stage i.e. minimal change in the
volume of displaced water from the double-duct burette (the reading change
is less than 0.00125ml/h), close valves 3 and 5.
(g) Clamp the loading shaft.
3.1.1.11. Dismantling the test apparatus
(a) Gradually reduce all the pressure dials back to zero.
(b) Expel water from the triaxial pressure chamber (acryl water tight cylinder).
(c) Dismantle all the apparatus peripherals.
(d) Just like at the beginning of the experiment, take measurements and the
weight of the test specimen.
(e) Measure the final water in the test specimen.
(f) Clean the working area after completion.
CALCULATIONS OF TEST RESULTS
After the experiment has reached completion, the recorded data is to be analyzed in
order to obtain the relationship between suction, water content, degree of saturation
and shear strength in clay.
Here the calculations for the initial, intermediate and final conditions, drainage and
absorption phase of The Water Retention Test (Pressure Plate Method) on saturated
clay are recorded.
3.1.1.12. Initial conditions
The initial water content wo (%), according to Japanese Industrial Standards, was
obtained by calculating the average water content of the soil specimen during trimming
of the soil specimen.
𝑤 =
𝑚 𝑎−𝑚 𝑏
𝑚 𝑏−𝑚 𝑐
× 100(%) (4.1)

27
𝑚 𝑎 : Specimen mass before drying + container (g)
𝑚 𝑏 : Specimen mass after drying + container (g)
𝑚 𝑐 : Container mass (g)
The initial volume V0 (cm3) was obtained from calculations using the dimensions of
the test specimen.
i. Initial surface area of ellipse Ao (cm2)
𝐴0 = 𝜋 ×
𝐷0
2
×
𝑑0
2
(4.2)
𝐷0 : Long diameter (cm)
𝑑0 : Short diameter (cm)
ii. Initial volume of ellipse V0 (cm3)
𝑉0 = 𝐴 𝑜 × 𝐻0 (4.3)
𝐻0 : Initial test specimen thickness (cm)
3.1.1.13. Intermediate and Final conditions
i. Drainage phase (Suction (= pore-air pressure) stages: 100, 200, 300)
Particular water content wn (%) is calculated based on the initial water content, wo (%).
𝑤 𝑛 =
(𝑚 𝑤𝑜±∆𝑚 𝑤𝑛 )
𝑚 𝑠
× 100(%) (4.4)
𝑤 𝑛 : Water content at a particular suction stage (%)
𝑚 𝑤𝑜 : Initial conditions test specimen water mass (g)
∆𝑚 𝑤𝑛 : Drained or absorbed water mass (g)
The volume at a particular suction stage (Sn) is given by
𝑉𝑛 = 𝑉𝑜 + ( 𝑣𝑜 − 𝑣 𝑛) (4.5)
𝑉𝑛 : Volume of test specimen at Sn (cm3)
𝑉𝑜 : Initial volume of test specimen (cm3)
𝑣𝑜 : Initial Double-ductburette reading (cm3)
𝑣 𝑛 : Double-duct burette reading at Sn (cm3)
Void ratio is calculated by the following formula:
𝑒 = {𝐺𝑠 (1 +
𝑤 𝑓
100
)
𝜌 𝑤
𝜌 𝑡
}− 1 (4.6)
And, Degree of saturation shall be obtained by:

28
𝑆 𝑟 =
𝐺𝑠
𝑒
(4.7)
𝜌𝑡 : Wet density (g/cm3)
𝑤 𝑓 : Final water content (%)
𝑒 : Final void ratio
𝐺𝑠 : Specific particles density (g/cm3)
𝜌 𝑤 : Water density (g/cm3)
𝑆 𝑟 : Final degree of saturation (%)
When Suction (pore-air pressure) value changes, the following error revision values are
added to the value of 𝑉𝑛 calculated in equation (4.5).
10 → 20 kPa : + 0.08
20 → 50 kPa : + 0.07
50 → 100 kPa : + 0.06
100 → 200 kPa : + 0.05
200 → 300 kPa : + 0.04
ii. Absorption phase (Suction stages : 300, 200, 100 kPa)
𝑉𝑛 = 𝑉𝑜 + ( 𝑣𝑜 − 𝑣 𝑛) (4.8)
When the Suction (pore-air pressure) value changes, the following error revision values
are added to the value of 𝑉𝑛 calculated in equation (4.5).
200 → 100 kPa : - 0.04
100 → 50 kPa : 0.0
50 → 20 kPa : - 0.01
20 → 10 kPa : + 0.06
10 → 5 kPa : + 0.1
5 → 0 kPa : 0.0
The above values were arrived at after test apparatus performance approval tests were
carried out.

29
HIGH PRESSURE CELL PRESSURE PLATE METHOD
3.1.1.14. Preparation of the test Specimen
(a) Test specimen preparation is the same as in 3.1
(a) Connect the various water and air delivery pipes to their respective receptacles.
(b) To avoid air bubbles forming when the water delivery tubes are inundated, flood
the pipes approximately 24 hours before performing a dry set.
aeration station.
coupler.
paper (#1000 or #1200)
 Submerge the ceramic disk mounted pedestal to be used in a beaker with
pure water.
(e) Switch on the computer and data logger; start the measurements monitor. Check
the measurements settings and adjust the items to be measured.
to maximum.
de-aeration tank and reducing the negative pressure and inundating the
same.

30
(g) Close valve 1.
piece of saran wrap on the still wet ceramic disk to avoid drying. It is because of
this reason that, the test specimen should be prepared and ready to be mounted
onto the ceramic disk before removing the ceramic disk from the beaker to install
it on the pedestal.
(i) Fit the O-rings and the membrane onto the O-ring setter and membrane setter
respectively and place them down the pedestal shaft in that order.
(j) Make sure the top cap shaft is firmly clamped in position. Remove the saran
wrap from the ceramic disk.
cover) part and place the test specimen as accurately as possible on the ceramic
disk. Close valve 1 to avoid water seeping into the testspecimen.
(l) Unclamp the top cap, and slowly lower and position it on top of the test specimen.
Clamp the shaft again in this position.
(m)Set the rubber membrane to cover the slice test specimen, ceramic disk, pedestal
and the top cap. Fit the rubber O-rings at the upper and lower end of the rubber
membrane.
apparatus. Bolt it in position and flood it to the marked water level.
(p) Fasten the axial confining pressure weights plate on top of the shaft. Connect the
shaft weight cancelling bells.
laser into position.
(s) Start the data logger and initialize all measurement components. The test is
ready to commence.
3.1.1.16. Drainage phase
2.5 bar ceramic disk and 100, 200 and 300kPa for the 5 bar ceramic disk. (for
purposes of explanation, a 5 bar ceramic disk is employed in this description.
closed.

31
interval timer and open valve 3 (burette valve) simultaneously when the
timer beeps.
procedure.
commencing the next phase of load.
3.1.1.17. Absorption phase
(a) The absorption phase is the mirror reverse of the drainage phase. The
unloading is also done systematically in stages, just as it was during the
drainage phase.
(c) At intervals take burette readings (ml)
(d) Check the test apparatus, making sure there is no air or water leakage.
(e) Change the loading pressures and weights at the end of every stage, closing
valves 3, 5 and clamping the shaft before every change.
(f) When the experiment reaches the final stage i.e. minimal change in the
volume of displaced water from the double-duct burette (the reading change
is less than 0.00125ml/h), close valves 3 and 5.
(g) Clamp the loading shaft.

32
Consolidated Undrained Triaxial Compression Shear Test (CU -
S Test)

33
GENERAL
3.1.1.19. Purpose of Test
This test is carried out to determine the strength and the deformation
characteristics of a soil specimen when it is subjected to undrained triaxial
compression after isotropic consolidation, and to obtain the effective stresses
at the maximum principal stress difference.
3.1.1.20. Scope of Application
This standard will apply mainly to saturated cohesive soils (e.g. NSF(C) clay).
TESTAPPARATUS
The apparatus consists of a triaxial pressure chamber (acryl water tight cylinder),
cell and back pressure supply/control systems, and axial compression device and
measurement systems for axial displacement and volume change.
Other test tools include:
used were:
 AEV 250kPa
 AEV 500kPa
 Rubber membrane
 Membrane setter
 O-ring setter
 Trimmer
 Wire saws
 Cutter
 Vernier scale
and the lower part)
 3 beakers
 Filter paper

34
 Note: For this test, the valve settings were changed:
i. Ua (center) and Ua (outer) were interchanged.
ii. The tube connecting to the top cap was changed in that instead of air, it
now supplies water to the top cap. Therefore, the air tube on the Ua valve
(valve 5) is left open.
iii. A new valve (valve 6) was installed to control flow of air to allow complete
flooding of water in the top cap.
iv. Water flow between the burette, top cap and the pedestal (Ua (center) and
Ua (outer)) was joined.
TESTPROCEDURE
3.1.1.21. Adjustment of Pore Water Pressure gauge (Ua (center))
(a) Without installing the pedestal, flood the pedestal base with de-aired pure
water (use the pressure pumps, if needed, to force the water through the
tubes). Close valve 1 after water starts to overflow from the top of the
pedestal base. This ensures complete flooding of the tubes.
(b) Connect the de-aired water tank to the double-duct burette and raise the
water level to a fixed level.
(c) Install the water tight cylinder onto the apparatus and flood it with water.
(d) Open the double-duct burette valve (valve 3) and wait for the water levels in
the pressure cell and the burette to equalize. Close the valve at the bottom of
the double-duct burette.
(e) Zero-set the Ua (center)gauge reading on the monitor.
(f) Expel water from the pressure cell and remove the cell from the apparatus.
3.1.1.22. Drying of Drainage Tubes
(a) Install the Shear test pedestal and top cap and set up for the test by
connecting the now water tube (connect Ua pressure tube to the top cap
during the Water Retention Test) with the top cap. The new valve (valve 6)
connecting the water tube to the burette and the pedestal is left open. Since
Ua (outer) valve is not needed for this test, valve 4 is closed all through the
experiment. Keep valve 2 (Ua (center)) open.
(b) Connect valve 1 to the de-aired water tank and lay the tank on a flat surface.

35
Open valves 2, 3 and 6 and connect a Partial Vacuum Control Unit.
(c) Connect consolidation pressure coupler (Ua + σ3) to the Convum Side
Internal Cell Pressure Regulator and set the consolidation air pressure at
about 196kPa (2.0kgf/cm2). Leave the pore water pressure gauge and the
tubes to dry for approximately 3 hours.
NB: drying of drainage tubes, pedestal and top cap is vital for partial vacuum
pressure to work.
3.1.1.23. Setting of TestSpecimen
 This happens after complete drying of the pore water pressure gauge and the
drainage tubes.
(a) Place a rubber O - ring mounted O ring setter at the base of the pedestal. Make
sure the rubber rings are properly greased.
(b) Place the 0.25mm thick rubber membrane setter on top of the O ring setter. Be
careful not to scratch the rubber membrane.
(c) This step requires two people. Place the slice test specimen onto the pedestal and
hold it in place while the other person releases the shaft and aligns it on top of
the specimen before fastening it in position once again.
(d) Lift the rubber membrane setter at the base of the pedestal and fit it accurately
making sure it is covering the specimen on both upper and lower sides. Roll the
membrane onto the top cap and subsequently the pedestal; unclasp the
membrane setter and put it away.
(e) Take the O ring setter and, just like with the membrane, fit the rubber O - rings
on the top cap and the pedestal making sure nothing tampers with the soil test
specimen.

36
3.1.1.24. Partial Vacuum
(a) Mount and fit the acryl water tight cylinder tightly onto the triaxial test
apparatus and move the apparatus to the required position. Connect the
necessary tubes.
(b) Mount the shaft counter weight onto the counter weight saddles. Making sure
the shaft holder is tightly fit and the power water pressure gauge valve (valve 2)
is closed, flood the cylinder to the required water level. Connect the Partial
Vacuum Control Unit: the vacuum pump pressure gauge valve to the vacuum
pump.
(c) Open valve 2: Ua (center) tube connecting to the pedestal, valve 3: connecting the
double duct burette to Ua (center) and valve 6: connecting the top cap to valves 2
and 3. Make sure the shaft is tightly fixed in position; the pressure release valve
at the top of the cylinder is closed. Open the valve coupled with the vacuum
pump (at the vacuum pump pressure gauge).
(d) Connect Ua + σ3 pressure tube and raise the air pressure on the Ua pressure
gauge dial to 392kPa (4.0kgf/cm2). On the Partial Vacuum Control Unit, raise the
convum side regulator to -4.9kPa (-0.05kgf/cm2) and the vacuum pump pressure
regulator acting on the internal of the test specimen, to -19.6kPa (-0.2kgf/cm2).
While maintaining effective confining pressure load of +19.6kPa (+0.22kgf/cm2)
on the test specimen, increase the negative pressures on the convum regulator
and the vacuum pump regulator gauges to -73.5kPa (-0.75kgf/cm2) and -93.1kPa
(-0.95 kgf/cm2) to de-air the test specimen.
(e) After 3 hours of continuous de-aeration, stand the de-aired water tank upright.
(f) Do the inverse of step d) making sure the effective confining pressure load is
maintained. This allows de-aired water to slowly flow into the drainage tubes,
pore water pressure gauge, filter papers and finally to the test specimen. To
ensure maximum saturation, this process should be done slowly to take about 15
minutes.
(g) Disengage couplers and remove the Partial Vacuum Control Unit. Connect the
Ua + σ3 pressure tube to the valve on top of the cylinder on the test apparatus.
2.5 bar ceramic disk and 100, 200 and 300kPa for the 5 bar ceramic disk. (for
purposes of explanation, a 5 bar ceramic disk is employed in this description.
closed.
(f) Unclamp the loading shaft, and open valve 5 (pore-air pressure valve). Start
the interval timer and open valve 3 (burette valve) simultaneously when the
timer beeps.

37
procedure.
commencing the next phase of loading.
CALCULATIONS OF TESTRESULTS
3.3.4.1. Initial conditions
The initial water content wo (%), according to Japanese Industrial Standards, was
obtained by calculating the average water content of the soil specimen during trimming
of the soil specimen.
𝑤 =
𝑚 𝑎−𝑚 𝑏
𝑚 𝑏−𝑚 𝑐
× 100(%) (5.1)
The initial volume V0 (cm3) was obtained from calculations using the dimensions of the
test specimen.
i. Initial surface area of ellipse Ao (cm2)
𝐴0 = 𝜋 ×
𝐷0
2
×
𝑑0
2
(5.2)
𝐷0 : Long diameter (cm)
𝑑0 : Short diameter (cm)
ii. Initial volume of ellipse V0 (cm3)
𝑉0 = 𝐴 𝑜 × 𝐻0 (5.3)
𝐻0 : Initial test specimen thickness (cm)
3.3.4.2. Consolidation process(Drainage phase)
i. The volume of the specimen during and after consolidation, 𝑉𝑐 (cm3), can be
obtained by
𝑉𝑐 = 𝑉𝑜 − ∆𝑉𝑐 (5.4)
∆𝑉𝑐 : Volume change of the specimen due to consolidation (read from the double-
duct burette) (cm3)
𝑉𝑐 : Volume change of the specimen after consolidation (cm3)

38
ii. The height (thickness) of the specimen during and after consolidation, 𝐻𝑐 (cm),
can be obtained by
𝐻𝑐 = 𝐻𝑖 − ∆𝐻𝑖 (5.5)
𝐻𝑐 : Height (thickness) of test specimen after consolidation (cm3)
∆𝐻𝑖 : Height (thickness) change of test specimen due to consolidation (cm)
iii. The cross-sectional area of the test specimen after consolidation, 𝐴 𝑐 (cm2), shall
be calculated by
𝐴 𝑐 = 𝑉𝑐/𝐻𝑐 (5.6)
iv. Dry density of the test specimen after consolidation, 𝜌 𝑑𝑐 (g/cm3), shall be
calculated by
𝜌 𝑑𝑐 = 𝑚 𝑠 𝑉𝑐⁄ (5.7)
𝑚 𝑠 : Dry weight of the test specimen (g)
3.3.4.3. Pore-pressure co-efficient, B-value
B-value of the specimen after consolidation shall be consolidated by the following
equation:
𝐵 =
∆𝑢
∆𝜎
(5.8)
∆𝜎 : amount of isotropic stress increment (kPa)
∆𝑢 : amount of pore pressure increment (kPa) caused by ∆𝜎
3.3.4.4. Vertical compression process
i. Vertical strain of the specimen, 𝜀 𝑣 (%), shall be calculated by the following
equation:
𝜀 𝑣 =
∆𝐻𝑣
𝐻𝑐𝑣
× 100 (5.9)
∆𝐻𝑣 : Vertical strain of the test specimen (cm)
ii. Principal stress difference, (𝜎1 − 𝜎3) (kPa), and Pore-water pressure increment,
𝑢 𝑒 (kPa), at vertical strain of 𝜀 𝑣 shall be calculated by:
𝜎1 − 𝜎3 =
𝑃
𝐴 𝑐
(1 −
𝜀 𝑣
100
) × 10 (5.10)
𝑢 𝑒 = 𝑢 − 𝑢 𝑏 (5.11)

39
𝑃 : Vertical compression force (kgf) at the vertical strain of 𝜀 𝑣 (%), setting 𝑃 = 0
during isotropic consolidation
𝜎1 : Vertical stress acting on the specimen (kPa)
𝜎3 : Lateral stress acting on the specimen (kPa)
𝑢 : Pore-water pressure in the test specimen (kPa)
𝑢 𝑏 : back pressure (kPa)

40
Constant Shear Test
GENERAL
This test explains in a simple but very vivid way how slope failure occurs. A slope
fails when a fault of weakness forms in the ground when the subsurface soil cannot
hold dead weight of the overlying soil. After precipitation, the ground water level
slowly rises and increased water pressure causes the slope to fail when it cannot
support the dead weight of the overlying ground, along faults of weakness, which is
mostly the ground water level surface.
TESTAPPARATUS
The apparatus consists of a triaxial pressure chamber (acryl water tight cylinder),
cell and back pressure supply/control systems, and an axial compression device and
measurement systems for axial displacement and volume change.
Other test tools include:
used were:
 AEV 250kPa
 AEV 500kPa
 Rubber membrane
 Membrane setter
 O-ring setter
 Trimmer
 Wire saws
 Cutter
 Vernier scale
and the lower part)
 3 beakers
 Filter paper

41
 A 5-bar ceramic disk was used for this experiment
TESTPROCEDURE
(a) Calibrate the test apparatus measuring peripherals (pore-water pressure
gauge, pore-air pressure gauge, double-duct burette, lateral displacement
sensor gauge, vertical displacement transducer and confining pressure gauge)
(b) To avoid air bubbles forming when the water delivery tubes are inundated,
flood the pipesapproximately 24 hours before performing a dry set.
aeration station.
coupler.
paper (#1000 or #1200)
 Submerge the ceramic disk mounted pedestal to be used in a beaker with
pure water.
(e) Switch on the computer and data logger; start the measurements monitor.
Check the measurements settings and adjust the items to be measured.

42
to maximum.
de-aeration tank and reducing the negative pressure and inundating the
same.
(g) Close valve 1.
piece of saran wrap on the still wet ceramic disk to avoid drying. It is because
of this reason that the test specimen should be prepared and ready to be
mounted onto the ceramic disk before removing the ceramic disk from the
beaker to install it on the pedestal.
(i) Fit the O-rings and the membrane onto the O-ring setter and membrane
setter respectively and place them down the pedestal shaft in that order.
(j) Make sure the top cap shaft is firmly clamped into position. Remove the
saran wrap from the ceramic disk.
cover) part and place the test specimen as accurately as possible on the
ceramic disk. Close valve 1 to avoid water seeping into the test specimen.
(l) Unclamp the top cap, slowly lower and position it on top of the test specimen.
Clamp the shaft again into this position.
(m)Set the rubber membrane to cover the slice test specimen, ceramic disk,
pedestal and the top cap. Fit the rubber O-rings at the upper and lower end
of the rubber membrane.
apparatus. Bolt it into position and flood it to the marked water level.
(p) Fasten the axial confining pressure weights plate on top of the shaft. Connect
the shaft weight cancelling bells.
laser into position.

43
(s) Start the data logger and initialize all measurement components. The test is
ready to commence.
calculations). The loading stages were 150 and 300kPa for the 5 bar ceramic
disk.
closed.
(d) Raise the confining pressure ( 𝑢 𝑎 + 𝜎3 ) dial to 100kPa. Place 1.0 kgf/cm2
weights on the weights plate on top of the loading shaft.
interval timer and open valve 3 (burette valve) simultaneously with the timer
beeps.
the (𝑢 𝑎 + 𝜎3) confining pressure dial to 200kPa and repeat the subsequent
procedure.
stop the data logger timer, clamp the shaft into position and close valves 3
and 5 before commencing the next phase of loading.
(i) At the end of the drainage phase, close valve 3 and 5, clamp the loading shaft
and save the data obtained for analysis.
3.4.1.3. Absorption Phase
(a) Before the absorption phase commences:
i. While maintaining the pore-air pressure at 300 kPa, the confining
pressure is raised further to 450 kPa.
ii. Add confining pressure weights on the loading shaft to 4.5 kgf/cm3
(about 450 kPa)
iii. Make sure valves 3 and 5 are closed.
(c) Configure the data logger timer’s measurements settings to a minimum of
about 10 second’s interval.
(d) Record the initial burette reading.
(e) At intervals take burette readings.
(f) Check the test apparatus, making sure there is no air or water leakage.
(g) Align the loading shaft with bellphram piston and bring the loading piston
into contact with the loading shaft receptacle.

44
(h) Increase the vertical shearing stress to 2.0 kgf, unclamp the loading clamp;
start the data logger timer and open valve 3 and 5.
(i) Increase the vertical shearing load by multiples of 2, changing when the
vertical displacement remains constant until about 25 kgf. After 25 kgf,
increase the load by 0.5 kgf until a shearing stress of 30 kgf is reached.
(j) With this constant shearing stress, reduce the confining pressure from
450kPa to 300 kPa. For this maneuver, (𝑢 𝑎 + 𝜎3) (kPa) pressure dial is used
(it ensures that, as the confining pressure drops to 300kPa, the pore-air
pressure 𝑢 𝑎 (kPa) drops at the same rate thereby maintaining a difference of
150 kPa all through the phase).
(k) Change the loading pressures and weights at the end of every stage, closing
valve 3, 5 and clamping the shaft before every change.
(l) Reduce the confining pressure (𝑢 𝑎 + 𝜎3) (kPa) dial from 450 kPa → 300 kPa
→ 160 kPa each time allowing the test specimen to absorb water , raising its
water content to its point of failure.
(m)When the experiment reaches the final stage i.e. the test specimen fails, close
valves 3 and 5.
(n) Clamp the loading shaft. Record and save the timer data for analysis.
(o) Measure the final water content of the test specimen by dividing it into three
pieces for a more accurate observation.
 Sometimes the pore-water pressure 𝑢 𝑎 (kPa) within the test specimen is too low to
absorb water from the double-duct burette. When this happens, back pressure can
be applied in stages of small amounts (about 10kPa each stage) to the burette and
force the water content to increase in the test specimen. Increasing back pressure to
the burette is dependenton whether the test specimen begins absorption or not.
CALCULATIONS OF TEST RESULTS
iii. Drainage phase (Suction (= pore-air pressure) stages: 100, 200, 300)
Particular water content wn (%) is calculated based on the initial water content, wo (%).
𝑤 𝑛 =
(𝑚 𝑤𝑜±∆𝑚 𝑤𝑛 )
𝑚 𝑠
× 100(%) (3.1)
𝑤 𝑛 : Water content at a particular suction stage (%)
𝑚 𝑤𝑜 : Initial conditions test specimen water mass (g)

45
∆𝑚 𝑤𝑛 : Drained or absorbed water mass (g)
The volume at a particular suction stage (Sn) is given by
𝑉𝑛 = 𝑉𝑜 + ( 𝑣𝑜 − 𝑣 𝑛) (3.2)
Void ratio is calculated by the following formula:
𝑒 = {𝐺𝑠 (1 +
𝑤 𝑓
100
)
𝜌 𝑤
𝜌 𝑡
}− 1 (3.3)
And, Degree of saturation shall be obtained by:
𝑆 𝑟 =
𝐺𝑠
𝑒
(3.4)
𝜌𝑡 : Wet density (g/cm3)
𝑤 𝑓 : Final water content (%)
𝑒 : Final void ratio
𝐺𝑠 : Specific particles density (g/cm3)
𝜌 𝑤 : Water density (g/cm3)
𝑆 𝑟 : Final degree of saturation (%)
Figure 3.3 stress and strain forces acting on the test specimen

46
Shear stress 𝜏 and normal stress 𝜎 𝑁 shall be obtained by the following equations:
𝜏 = (
∆𝑃
𝐴 𝑐
) 𝑠𝑖𝑛𝛽 ∙ 𝑐𝑜𝑠𝛽 (3.5)
𝜎 𝑁 = (
∆𝑃
𝐴 𝑐
) 𝑐𝑜𝑠2 𝛽∙ 𝜎𝑐 (3.6)
𝜎𝑐 : Consolidation stress (kPa)
𝛽 : Slice angle of slant (= 45°)
The test specimen surface 𝐴 𝑐′ area during shearing is calculated by:
𝐴 𝑐′ =
𝐴 𝑐∙𝐻𝑐∙(1−𝜀 𝑉/100)
𝐻𝑐−|∆𝑑 𝑉−∆𝑑 𝐻 𝑡𝑎𝑛𝛽|
(3.7)
𝐻𝑐 : Height of test specimen after consolidation (cm)
𝐻𝑐 = 𝐻0 − ∆𝐻
𝐴 𝑐 : Specimen surface area after consolidation (cm2)
𝐴 𝑐 =
𝑉𝑜−∆𝑉𝑐
𝐻𝑐
(3.8)
𝜀 𝑉 : Volumetric strain during shearing
𝜀 𝑉 =
∆𝑉𝑠
𝑉𝑐
Shearing strain 𝛾 is obtained by:
𝛾 =
∆𝑑 𝛽
𝐻𝑐∙𝑐𝑜𝑠𝛽
× 100 (%) (3.9)
∆𝑑 𝛽 =
∆𝑑 𝐻
𝑐𝑜𝑠𝛽

47
Chapter 4: Graphical presentations
1) Water Retention Test(Pressure Plate Method)
a) Suction – water content curve
0 10 20 30 40 50 60
1
10
100
1000
10000
100000
1000000
SuctionS(kPa)
Water content w (%)
NSF(C)Clay
σn=98.1kPa
・Drainage Phase
Pressure Plate Method(FDPG)
Pressure Plate Method（Expt data）
1cm slice: Pressure Plate Method（Expt data）※SS
Vapor Pressure Method
・Absorption Phase
Pressure Plate Method(FDPG)
1cm slice: Pressure Plate Method（Expt data）※US
1cm slice: Pressure Plate Method（Expt data）※US
wS=35.7%
wL=57.5%
Fig 4.1 a graph showing water content – suction relationship in NSF(C) clay
Suction values (the same as pore-air pressure, Ua) were plotted against water
content from the drainage through the end of the absorption phase. The shaded plots
are data obtained in this research while the unshaded plots are data obtained from
experiments and test procedures already accepted by the Japanese Industrial
Standards. From these graphs similar water retentivity properties can be deduced.
This goes to support the reliability of the Triaxial Slice Shear Test apparatus.

48
b) Suction – degree of saturation curve
0 10 20 30 40 50 60 70 80 90 100
1
10
100
1000
10000
100000
1000000
Suction　S(kPa)
Degree of Saturation　Sr (%)
・Drainage Phase
Pressure Plate Method
Vapor Pressure Method
・Absorption Phase
Sr1=67.8
Sr1=55.8
Sr1=28.8Pressure plate exp 1
Pressure plate exp 2
Pressure plate exp 3
Pressure Plate exp 3
Similarly, suction values (the same as pore-air pressure, Ua) were plotted against
degree of saturation from the drainage through the end of the absorption phase. The
shaded plots are data obtained in this research while the unshaded plots are data
obtained from experiments and test procedures already accepted by the Japanese
Industrial Standards. In this research, the ceramic disk used can only withstand
suction to a maximum of about 450 kPa. This, therefore, did not allow the test
specimen to be subjected to higher suction forces to cause the degree of saturation to
drop to remarkable values (as seen in the cases of standard tests). Nevertheless,
from the available data, similar water retentivity properties can be deduced. This
also supports the reliability of the Triaxial Slice Shear Test apparatus.

49
2) Consolidated Undrained Triaxial Compression Shear Test
0 100 200 300
0
50
100
150
φ' = 23.9°
φ' = 20.3°
Effective normal stress σN' (kPa)
Shearstressτ(kPa)
Standard Triaxial Shear Test
Triaxial Slice Shear Test
Using the Triaxial Slice Shear Test apparatus, a Triaxial Consolidated Undrained Shear
Test was carried out. From the test, the internal angle of shearing friction was calculated
and found to be about 20.3 degrees. The internal angle of shearing friction from standard
tests recognized by the JIS law is 23.9 degrees. Since there was only one successful test, no
concrete conclusion can be deduced, but looking at the values, it’s not completely wrong to
say that they are close. On carrying out further tests, a more absolute answer can be given.
However, this shows that, with a few corrections and more experiments, the Triaxial Slice
Shear Test apparatus can also be used to obtain the internal angle of shearing friction in
clay soil.

50
3) ConstantShear Test
The graph shows the relationship between shear stress and shear strain in the test
specimen.
The blue plots show the behavior of the test specimen when it was subjected to shearing
stress during the water absorption phase until it reaches failure. The orange data shows
the test after the drainage phase. After the drainage phase, it was subjected to
consolidation force (hence requires more shearing stress to fail) and then specified initial
shearing stress was introduced to the specimen. The shearing stress is kept constant while
the water content was increased (the densely populated horizontal plots) which in turn
increased the pore-water pressure and the degree of saturation until the test specimen
reached failure, hence the spaced out horizontal plots.
This can help to understand the soil’s water retention properties vis-a-vie the soil’s shear
strength properties, which is very vital in understanding what really happens during slope
failure.
0 10 20 300
20
40
60
80
100
Constant Shear Test
CU-bar Triaxialslice Shear Test
InitialShearing
stress introduced
Shear strain (%)
Shearstress(kN/m2)
Sro = 98.9%
Sro = 98.4%
water content
raised untilfailure

51
Chapter 5: Conclusion
1. The Triaxial slice shear test apparatus can be used to obtain a water retention
curve by increasing suction in the test specimen during the drainage phase and
then reducing it during absorption phase. The Water Retentivity Test result values
were found to be close to other approved test results.
2. The Slice Shear Test was carried out. From the test results, the internal friction
angle was calculated, compared to, and found to be close to that from Standard
Triaxial Test. These findings confirm the reliability of the the Triaxial Slice Test
apparatus.
3. On completion of the drainage phase, a constant shearing stress can be applied to
the test specimen and the same is allowed to absorb water – absorption phase.
With the increase in water content and thus pore-water pressure, slowly the test
specimen reaches its deformation limit and fails. This can be done in one
experiment without changing or removing the test specimen from the test
apparatus.

52
Acknowledgements
First, I would like to extend my sincere gratitude to my professors: Assoc Prof. Takeo
Umezaki and Asst. Prof. Takashi Kawamura for their unwavering support and
encouragement. Both were pivotal from the start to the end of this research thesis. I
am grateful for the many hours they spent advising and pushing me to broaden my
spectrum.
Secondly, I want to extend my appreciation to my lab mates: Mr. Atsushi Tone, Mr.
Yuuta Kobayashi, Mr. Daiki Arai, Ms. Anna Ooishi, Mr. Toshiaki Mizutani, Mr.
Takahisa Ishida, Mr. Kenji Matsuda and Mr. Taguchi Ryuuji for moral support and
helping to keep me in perspective.
I also would like to thank our laboratory attendant Mr. Noriyuki Toya for ensuring
our laboratory equipment was in good condition. He helped prepare the necessary
materials and was there, readily giving advice then called upon.
Finally, I cannot discount my siblings’ support. Living abroad, far away from family
and friends in a country with a foreign language is not easy. My siblings have always
supported and encouraged me through thick and thin. I am grateful for that.

53
References
1) Soil Mechanics 3rd Edition R. F. Craig. Department of Civil engineering, University of
Dundee
2) The shear strength of unsaturated soils, Canadian Geotechnical journal 15: 313-321
3) Ng, C. and Pang, Y. (2000). ”Influence of Stress State on Soil-Water Characteristics and
Slope Stability.” J. Geotech. Geoenviron. Eng., 126(2), 157–166.
4) Slope Stability Analysis Incorporating the Effect of Soil Suction D. G. Fredlund.
Department of Civil Engineering, University of Saskatchewan, Saskatchewan, Canada
S7N 0WO
5) 梅崎健夫，落合英俊，林重徳，内田浩平：粘土の鋼矢板の接触面における摩擦特性，九州大
学工学州集報，第 65 巻，第 6 号，pp.565-572,1992.
6) 宮林佳裕：保水性試験の効率化における真空蒸発法の適用―蒸気圧法における初期含水比と
初期質量の影響―，信州大学卒業論文，2011．
7) 川上浩・岩崎公俊・西垣誠：ジオテクノート５不飽和土，土質工学会，1993．
8) 安藤幸二：不飽和粘性土の変形・強度に及ぼすサクションと拘束圧の影響，信州大学修士論
文，pp．1-3，1996
9) Aitchison，G．D．：The Strength of Quasi-saturated and Unsaturated Soils in Relation
to the Pressure Deficiency in the Pore Water，Proc．4th．Int．Conf．on SMFE，Vol.1，
pp.135-139，1957．
10) Skempton，A．W．：The Pore-pressure Coefficients A and B，Geotech，No.4，pp.143-
147，1954．
11) Jennings，J．E．and Burland，J．B．：Limitations to the Use of Effective Stresses in
Partly Saturated Soils，Geotechnique，Vol.12，pp.125-144，1962．
12) Lofgren，B．E.：Land Subsidence due to the Appliciation of Water，USGS Publications，
Reviews in Engineering Geology Ⅱ．

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