10th Asian Regional Conference of IAEG (2015)

Development of SPA-500 Type Unsaturated Soil-water Characteristics and HydraulicParameters Test System
Zhiqing LI(1,2), Feng HU(1), Ruiqiang YUE(3) and Tingting DU(4,1)(1) Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academyof Sciences, Beijing
E-mail:lizhiq-2002@163.com(2) State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water
Resources and Hydropower Research, Beijing, (3) Yunnan mengxin highway construction headquarter, Kunming,(4)China University of Mining & Technology, Beijing
Abstract
This manuscript describes the test system of SPA-500 unsaturated soil and water
characteristics and hydraulic parameters. The system contains double pressure chamber,pressure framework, pressurized cylinder, stress and strain measuring controller, backpressure and volume change measuring controller, underwater load sensor, displacement
sensor, pore pressure sensors etc. It can be used to research SWCC relating to moistureabsorption or dehumidifying and water (air) migration rules under triaxial pressure andsuction paths control. The load sensor is put inside the double pressure chamber. And thesample volume change measuring controller combined with the surrounding pressure device
is used in the system. The system can work independently by using high impedance linear
amplification technology, A/D conversion technology, stepper motor driving control
technique etc. The software programmed by Delphi language has capability of dataacquisition and real-time graphics by means of automatic control. The SPA - 500 type test
data is reliable based on the test results which show that the SPA - 500 type test data and
GDS test data have good comparability.
Keywords: unsaturated soil, soil and water characteristic curve (SWCC), permeability,
technical index, control precision
1.

Introduction

behavior characteristics. The pressure plate volume
meter apparatus and temple produced by American
Soil-moisture Equipment in 1985 can measure SWCC
of soil without overburden pressure. At the beginningof the 21st century, USA GCTS company produce thepressure plate apparatus of SDSWCC relating tostress, which can measure SWCC under the action of
axial stress. Ye invented a kind of soil permeameter,
which adopted GDS pressure controller to realize
control and measurement of fluid pressure andvolume, in order to obtain soil permeability under
different void ratio and stress conditions (Ye, 2005).
Miao invented a kind of consolidation and joint
measurement device for unsaturated soil, which canbe used for consolidation and SWCC (Miao, 2007).
Chen invented consolidation apparatus andpermeability gas meter of unsaturated soil to reveal
moisture migration rules of unsaturated soil andspecial soil (Chen, 2011). Li invented SPA - 500 typeof unsaturated soil water characteristics and hydraulicparameter experiment system (SPA experimental

The soil and water characteristic curve (SWCC) isa curve of soil matric potential with water content
change. It expresses the relationship between amountand energy of water in soil. It is important for SWCC
and moisture migration to predict mechanics
properties, shear strength, slope stability and slope
deformation of unsaturated soil (Agus, 2001). Li
invented SPA - 500 type of unsaturated soil water
characteristics and hydraulic parameter experiment
system (SPA experimental system) to attain SWCC,
permeability etc.
The SWCC of unsaturated soil can be attained byusing of the tension meter and heat conductivity
probe in-situ (Li, 2007). Indoor SWCC test methods
contain the pressure plate volume meter method(Fredlund, 1993), temple instrument method(Fredlund, 1993), the filter paper method (Ye, 2005)
and so on. But greater differences between SWCC
tests under different soil conditions show different

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10th Asian Regional Conference of IAEG (2015)

system) to attain SWCC, permeability etc. The
measurement details of pore-water pressures,volumetric water contents, temperatures, and relativeoxygen concentrations in unsaturated soil layers
under asphalt pavement, aeration slab, and turf cover,as well as weather conditions are described by field
instrumentation (Indrawan, 2012). The small
dual-probe sensors were used to measure heat andwater transport of unsaturated sandy soil which was
subjected to a wetting and drying cycle (Bristow,
1998). Watanabe et al measured liquid water content
and relative permittivity of various unsaturated soils
at above-zero and subzero temperatures by using
pulsed nuclear magnetic resonance (NMR) andtime-domain reflectometry (TDR) (Watanabe, 2009).
The unsaturated soil was tested in a modified triaxial
apparatus using independent stress state variables to
describe stresses in the specimen (Wulfsohn, 1998).
2.

measure triaxial shear strength and volume change ofunsaturated and saturated soil via the double pressurechamber and back pressure device. It can be used tomeasure vertical stress changes of sample by using
the built-in high precision pressure sensor. Also, it
can be used to test axial deformation of sample
through the high precision displacement sensor.
2.3 Working principle
SPA experiment system is a kind of doublepressure chamber with a built-in load sensor and axial
load applied as one of the test device. It can be used
to accurately measure principal stress difference andthe total volume change of specimen. The insidepressure chamber is mounted within the interiorchamber, and will be filled with water. The change ofthe sample volume will cause the changes of waterlevel in the pressure chamber by connecting insidepressure chamber and volume change reference tube.
The volume change is measured by the high precisiondifferential pressure sensor and volume change
measurement control. The high intake value clay
plate is installed on sample base. And the porous
plate is installed on pressure cap. The air intake andwater inflow are respectively set up corresponding
channels to provide matrix suction to realize pore airpermeability, pore water infiltration and SWCC
measurement of unsaturated soil. The matrix suction
can be controlled in the range of 0.1 to 500kPa byaxis-translation technique. The confining pressure canbe controlled automatically by adopting the precise
electric proportional valve. The total volume change
can be controlled automatically by using volume
change tube device. Software system can realize thereal-time data acquisition and graphical display, andcontrol the test process according to the given stop
conditions.

Experimental System

2.1 Instrument composition
SPA experiment system is a new type of doublepressure chamber suction control system which
relates to stress using to measure soil water
characteristic curve and permeability. The system
consists of double pressure chamber (a), pressure
framework (b), pressurized cylinder, stress and strain
measurement controller (c), back pressure andvolume change measurement controller (d),underwater load sensor, displacement sensor, porewater pressure controller (e) etc. as shown in Fig. 1.

(a)
(c)

(d)

(b)

(e)

2.4 Main technical indicators
Axial force range: 0 ~ 6 kN. Control modes: (1)the strain control with 0.002 ~ 4mm/min, control
accuracy ±10%, (2) stress control with 0 ~ 6kN,
control accuracy ±1%. Dimension of soil sample:
Φ61.8mm x 20mm, 61.8mm x 40mm or Φ61.8mm x
120mm. Confining pressure range: 0 ~ 1.0MPa,
control precision with1.0kPa. Pressure range of porepressure controller: 0 ~ 0.8MPa, control precision
with 1.0kPa. Gas volume change measuring range: 0~ 400ml, 1.0 mm3 resolution. The pore water pressure
controller pressure range 0 ~ 1.0MPa, control
accuracy with 1.0kPa. Water change measuring
range: 0 ~ 400 ml, 1.0 mm3 resolution. Pressure rangeof pore pressure sensor: 0 ~ 1MPa, the control
precision
with1.0kPa.
Displacement
sensormeasurement range: 0 ~ 30mm. Sample volume
change range: 0 ~ 200ml. Clay plate inlet value:
500kPa and 1500kPa. Pressure chamber uses doublepressure chamber structure.

Fig. 1 SPA-500 unsaturated soil and water
characteristic and hydraulic parameters test system
2.2 Main functions
The system can be used to study soil and water
characteristic curves (SDSWCC) and water phase(gas phase) permeability rules (WAPC) of
unsaturated soil which are related to dry-wet stressunder the action of independent triaxial stress andsuction path. The specific functions include many
functions, such as, measuring SWCC under theconditions of desorption and wet by theaxis-translation technique. It can measure pore water
permeability coefficient and pore gas permeability
coefficient of unsaturated soil through flexible stresscontrol and suction path. It can measure the highpressure consolidation coefficient of unsaturated soil
through the consolidation test base. It can be used to2

10th Asian Regional Conference of IAEG (2015)

3.

Design of Experimental System

software control. The devices issue instructions,acquire data and process according to the software
requirements. The character-oriented synchronization
protocol is used in the instruction model to solve thecommunication security problem of test control. It
ensures the security and integrity of system datatransmission. And it avoids that distractions (such as
electromagnetic) may cause information error.

3.1 Precision realization of axial load, confiningpressure and suction control
The axial load control technology of theexperimental system based on step motor as thesource of power to drive screw nut mechanism, whichmakes rolling diaphragm cylinder to obtain pressure,is used to apply axial load on sample by stressapproaches or strain rate. Rolling diaphragm cylinder
has the performance characteristics of rolling friction
and low friction resistance. The precision of strain
rate and stress control is greatly improved for low
friction cylinder, step motor technology and built-in
load sensor technology.
The electrical proportional valve which is made inJapanese company SMC is used in confining pressure
control and improving pressure control precision to
be less than 1kPa. The exchange between gas andwater is achieved by volume change tube. The gas
equaling to confining pressure enter into theinterlayer of dual chamber pressure chamber. The
water equaling to confining pressure enter into insidepressure chamber to apply confining pressure on
sample. And at the same time, the volume of water,
namely the total volume change of sample can bemeasured.
The electrical proportional valve of SMC
Company is also used in the air volume controller,
which provides the pore air pressure. The controller
using the high precision pressure sensor produced inUSA, controls the inlet value 1kPa precision andmeasure air volume change of in and out of the gas
volume controller at the same by controlling back the
stepping motor driven actuators. Moisture absorption
control adopts stepper motor to drive screw nut
mechanism, which promotes the oil cylinder tocontrol the water pressure. So water pressure can beapplied on the top and bottom of sample in constantflow or equal water pressure. The precision pressure
sensors are used to control the water pressure with
precision of 1kPa and the water volume with
precision of 1 ml by controlling back stepping motor
driven actuators.

3.3 Realization of volume change measurement for
double pressure chamber
In order to ensure the accuracy of total volume
change measurement of sample, the built-in load
sensor is used in double pressure chamber structure of
the system. The confining gas and water respectively
enter into the isolation layer and the inner chamber ofthe pressure chamber to ensure that the inner pressurechamber can endure balanceable pressure and reducethe deformation. The accuracy of the volume change
measurement can be carried on by calibrating
confining pressure and the relationships between in
and out of the water.
3.4 Implementation of sensor measurement
accuracy and stability
The system adopts precision pressure sensor madein the Meas-Spea company in USA. It also uses thehigh impedance linear amplification and A/Dconversion technology to ensure the stability andprecision of the measurement requirements. The
mathematical model of simple moving averagemethod is adopted in the software to solve thestability problem of the sensor measurement data inthe static measurement.
3.5 System software programming
According to GB/T50123-1999 "test procedures"and BS1377 (1990) test method, the Delphi language
is used for computer control oriented programming toensure automatic test according to the parameters of
the experiment requirement. Software provides realtime curve display to facilitate participants todetermine whether a test process is normal.
The test data is stored in access database to ensure
the reliability of the datum. After test the datum canbe output in the form of Excel. The treatment methodof anomalies such as power outage is designed in thesoftware. The test will continue after connecting thedatum of last test when the abnormal situation is dealt.
The control parameter values in the software can bechanged any time in the process of normal test. And
the test will continue on the basis of the new control
values.

3.2 Test control method and the realization of datatransmission accuracy
The system consists of two sets of pore gas
control device, two sets of pore water control device,a set of axial force of control device and the confiningpressure control device. The devices can work
independently according to the parameters set by thehuman. The system uses the computer software
programming technique and software design for test
method. It reduces the working strength and improves
the working efficiency. Control mode of the system
uses multiple computer communication technology.
The devices are organized together by the

3.6 The advanced nature of the instrument
Multifunction flexible control method used in thissystem, not only can accomplish triaxial tests(including UU, CU, CD test) and penetrant tests of3

10th Asian Regional Conference of IAEG (2015)

saturated soil, but also can complete all kinds of testsof unsaturated soil, such as triaxial shear test under
the condition of matric suction control, moistureabsorption test.
The system uses double pressure chamber
structure with a built-in load sensor, and soil sample
volume change measurement system combined withthe surrounding pressure device. The axial force
device uses the rolling diaphragm cylinder actuator toensure the realization of the strain and stress control
mode. The air intake value of pore air control device
can reach a minimum of 2 MPa. The pore water
control device can control the water pressure
precision of 1kPa and flow measuring resolution of 1
ml. The clay plate at the bottom of sample base is set
up the spiral groove structure to effectively eliminate
the bubbles of clay accumulation at the bottom of theplate. The system uses high precision sensors toensure the accuracy and stability of the test
measurement data. The advanced communication
technology is used to ensure the accurate test
instructions and secure receive of data. Test method
oriented programming technique, which is easy to bemodified, ensures that the test can be carried on
automatically according to the requirement.
4.

test， and SPA - 500 type equipment. The basic
physical and mechanical properties of the soil are
shown in table 1. The soil and water characteristic
curves are obtained by test as shown in figure 2. The
datum is fitted by the polynomial. The results showthat the SPA - 500 type test data and GDS test data
have good comparability. So the SPA - 500 type test
data is reliable.

Fig. 2 Comparison between GDS data and SPA
data

Deformation Test Instrument

The purpose of instrument deformation test is toensure the accuracy of the soil sample volume
variation and reduce instrument deformation effect on
measured result. The standard specimen rigidity is putin the pressure chamber filled with water. Then thespecimen is carried on the confining pressure of 100
kPa, 200 kPa, 400 kPa, 600 kPa, 800 kPa respectively.
A mathematic model of the surrounding pressure andbody variables is established by measuring waterchange in volume change tube. The model is used tocorrect the volume change variables in the practicalunsaturated soil test to obtain accurately total
deformation of soil sample.
5.

6.

Conclusions

The system can be used to research soil and water
characteristic curves relating to dry and wet stress,
water and gas migration regularity of unsaturated soil
under the independent triaxial stress and suction path.
The system controller uses A/D conversion
technology, high impedance linear amplification
technology and stepper motor drive control
technology. It is able to work independently. Also it
can be controlled to acquire data by computer
software. It has many characteristics such as highmeasuring accuracy, stable control, convenient
operation etc.
The system uses double pressure chamber
structure with a built-in load sensor. The confininggas pressure and water pressure respectively enter
into the isolation layer and the inner chamber of theExperimental Data Analysis

The expansive soil in a highway in Hubei is used
to test SWCC respectively by the British commercial
GDS instrument，which is famous in unsaturated soil

Table 1 The physical and mechanical parameters of samplesTyped / g·cm-3

wo/ % wp/ %

wL/ %

IP

ef / %

c/ kPaφ/ºExpansive
1.55
22.0 24.8
50.4
25.6
60～80
32.0
22.4
soil
d —Dry density；wo — initial water content; wp —liquid limit; wL— plastic limit; IP— plastic index; ef—free expansion ratio; c —cohesive force; φ — internal friction Angle4

10th Asian Regional Conference of IAEG (2015)

pressure chamber to ensure that the inner pressurechamber can endure balanceable pressure and reducethe deformation. The accuracy of the volume change
measurement can be carried on by calibrating therelationships between confining pressure and in andout of the water.
Test method oriented programming technology isused in the system to ensure the test automaticallyaccording to customer’s parameter requirements. The
test data is stored by Access database, and the system
can display the data real-time graphics.
The SPA - 500 type test data is reliable based on
the test results which show that the SPA - 500 type
test data and GDS test data have good comparability.

Watanabe, K. and Wake, T. (2009): Measurement of
unfrozen water content and relative permittivity offrozen unsaturated soil using NMR and TDR, Cold
Regions Science and Technology, Vol. 59, pp. 3441.
Wulfsohn, D., Adams, B.A. and Fredlund, D.G.
(1988) : Triaxial testing of unsaturated agriculturalsoils, J. agric. Engng Res. , Vol. 69, pp. 317-330.
Ye, W.M., Chen, B. and Bai, Y. (2005) :Soil
infiltration
meter,
Chinesepatent,
ZL200510024691X.

Acknowledgements
This research is financially supported by theStrategic Priority Research Programof the Chinese
Academy of Sciences, Grant No. XDB10030102;
National Natural Science Foundation of China, Grant
No. 41330643); the Open Research Fund of StateKey Laboratory of Simulation and Regulation of
Water Cycle in River Basin (China Institute of Water
Resources and Hydropower Research), Grant No:
IWHR-SKL-201217.
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