31 Geotechnical: Advanced soil testing - Welcome to ITL or Stress Path Triaxial System... · 31 127. . . . . . . . . . . . . . . . Geotechnical: Advanced soil testing SOIL MECHANICS

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Cyclic/Stress path triaxial system (continued)

Geotechnical: Advanced soil testing . . . . . . . . . . . . . . . .SOIL MECHANICS

31-WF7050

Dynamic triaxial system 50 kN load

frame, PC controlled with 20 bit

IMACS and 13 channels, 5 kN

actuator and air receiver. 110-240 V, 50-60 Hz, 1 ph.

31-WF7100

Dynamic triaxial system 100 kN load

frame, PC controlled with 20 bit

IMACS and 13 channels, 5 kN

actuator and air receiver. 110-240 V, 50-60 Hz, 1 ph.

General description and main features

The feedback controlled cyclic triaxial system applies cyclic or dynamic loading to the soil specimen. The system is a digitally control-led, servo-pneumatic (closed loop) system, which controls three parameters: axial load or displacement, confining pressure and back pressure.The base system incorporates an integrated Multi-Axis Control System (IMACS), a digit-ally controlled 5 kN actuator, TRITECH 50 load frame, auxiliary air receiver complete with two servo-valves for cell and back pres-sure control, two air filters and associated cables. The system is supplied complete with cyclic and stress path software. A double acting digitally controlled pneu-matic actuator applies axial load. This cyclic load can be applied in load (N), stress (kPa), displacement (mm) or strain (%). Digitally controlled pneumatic valves apply confining and back pressures. The dynamic tests are generally carried out in conjunction with static imposed conditions of stress to the soil samples.This means that the sample, in addition to the application of dynamic actions, can be saturated, consolidated upon different stress levels (isotropic, anisotropic, K0, etc.) and also carried out to failure under static monotonic conditions.

The Static and Dynamic Cyclic Triaxial sys-tem has been designed to perform the fol-lowing tests: - Standard triaxial tests (UU, CU, CD)

including saturation, isotropic and ani-sotropic consolidation with pore pressure and volume change measurements

- Stress path tests, including K0 consolida-tion

- Cyclic loading- Dynamic shear strength and deformation- Liquefaction potential- Shear modulus and damping ratio

The system can work with different models of triaxial cells for specimen sizes of 50, 70, and 100 mm (see accessories). Each of the two systems includes: • Load frame (50 or 100 kN capacity)• 5 kN actuator with coaxial displacement

transducer• IMACS for control and data acquisition• The software modules described above.

Transducers and triaxial cells (Tri-Cell Plus models) are not included with the base system and have to be ordered separately depending on the specimen characteristics. See pages 86 to 89.

Main features

- K0 consolidation

- Stress path testing

- Static and dynamic triaxial tests

on the same frame

- ± 5 kN cyclic loading

- Up to 25 kN in shear

- Actuator frequency 0-70Hz

- Measurement of liquefaction in

soil sands and silts

- Simulation of natural and

man-made seismic events

- Three closed loop control axes:

- vertical load or displacement

- cell pressure

- back pressure

31-WF7050 dynamic triaxial system with 28-WF4070/P TRI-CELL Plus

Testing equipment for the construction industry

N O T E 31-WF7101 Dynamic trixial system 100 kN load frame with 14 kN actuator is avai-lable on request. Contact our commercial department for further informations.

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Cyclic/Stress path triaxial system (continued). . . . . . . . . . . . . . . . Geotechnical: Advanced soil testingSOIL MECHANICS

Load frames

The basic standard triaxial machines Tritech 50 and Tritech 100 have been modified to include the pneumatic actuator mounted on the crosshead. The actuator has a specially designed locking mechanism, which will lock it in any position within its travel. Then shearing to load higher than the actuator capacity can be achieved using the Tritech load frame. This allows the specimen to be sheared at the end of the dynamic stage. When dynamic test is performed, the pneu-matic actuator is free to move vertically; for monotonic tests the actuator is locked to prevent it taking load.

Actuator

This is a digitally controlled, double acting pneumatic actuator. It requires a minimum air supply of 800 kPa for operation.Signals applied to the voltage/pressure con-verter from the IMACS enable computer controlled adjustment of the loads applied to the sample. The actuator has an integral displacement transducer, which allows tests to be run under load and displacement control. The actuator can generate frequencies up to 70 Hz. But the testing speed is really dependent on the type of sample being tested and test conditions. Soft materials will have greater displacement under load, which means the actuator has further to travel, stiff samples can require higher loads, which will reduce the frequency. This is not a problem when testing soils, especially if the testing is for liquefaction. In this case the loads and frequency will be very low.The servo-actuator high frequency perform-ance is shown in the following graph (see next page). It shows the maximum force obtainable at a given frequency for sinusoi-dal loading.

Integrated Multi-Axis Control System

(IMACS)

The IMACS is a compact self contained unit that provides all critical control, timing and data acquisition functions for the test and the transducers. The IMACS is linked to a personal computer through the USB com-munications link.

SPECIFICATION Continued

TECHNICAL SPECIFICATIONS

Frame model 31-WF7050 31-WF7100

Capacity 50 kN 100 kN Maximum vertical daylight 1000 mm 1040 mmMaximum horizontal clearance 335 mm 390 mmPlaten diameter 158 mm 158 mmMaximum monotonic loading 50 kN 100 kNMaximum monotonic displacement 100 mm 100 mm

Actuator and control system

Dynamic loading ± 5 kN with 0.1 kN resolution Dynamic displacement ± 15 mm 1 micron resolution Pressure 1000 kPa with 0.1 res. 1000 kPa with 0.1 res.Maximum actuator frequency 70 Hz 70 HzMaximum monotonic speed 9.99999 mm/min 9.99999 mm/minMinimum monotonic speed 0.00001 mm/min 0.00001 mm/min

Phisical specifications

Dimensions (hxwxd) 1460x503x380mm 1700x703x503mm Weight approx. 98 kg 330 kg

No. of digitally controlled axes 3 (vertical load or displacement, cell pressure, back pressure)No. of data acquisition channels 131/0 module processor 32 bit RISCCommunication ports USB or RS 232Data tranfer USB 10 Mb/sData transfer RS 232 115 Kb/s

Actuator

10

1

0.10 10 20 30 40 50 60 70

Forc

e (k

N)

Frequency (Hz)

Control system

The data acquisition module has 13 nor-malised (±10 V range) transducer input channels. These channels are digitised by accurate, high speed 20 bit (A/D) converters for data analysis and presentation.The control module has three channels for feedback control. One is dedicated to the actuator for vertical load/displacement, the second is dedicated to cell pressure, the third is for back pressure. The feedback control module and the data acquisition module have their own dedicated high speed USB 10 b/s or RS232 interface. This allows uninterrupted, simultaneous communication enabling increased speed of operation and flexibility.Supervised by the PC, the IMACS auto-matically controls the operation of loading for individual types of test. The IMACS directly controls the servo-valve to apply the requested loading rate or waveform, cell and back pressure. While the specimen is being subjected to loading forces, the IMACS cap-tures data from the transducers and trans-fers these, via the USB or RS232 link, to the PC for processing, display and storage.


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Multi testing Windows environment provid-ing the following software modules:

• ASTM D5311-2004 Standard test method for load controlled cyclic triaxial strength of soil

• ASTM D3999-2003 Standard test method for the determination of the modulus and damping properties of soils

• Cyclic stress test (standard sine, square, haversine, etc.)

• Cyclic strain test (standard sine, square, haversine, etc.)

• Playback function allowing user defined wave shapes of up to 40,000 points

• Liquefaction• Stress path: - with increase/decrease of radial stress - with increase/decrease of axial stress• Consolidation: - in a fixed or variable ratio - isotropic - anisotropic - K0 by radial stress increase - K0 by axial stress increase• Standard UU, CU, CD triaxial tests• Saturation: - with standard or automatic stepped

pressure increment with user input increment and differential values

- continuous saturation with B check option

• Monotonic test: - static compression with axial loading - static extension with axial loading.

This set up page for the cyclic triaxial give the following options:

SaturationIncremental pressure stepsContinuous saturation

ConsolidationIsotropic and AnisotropicK0 with radial or axial stress increase

Stress PathMean normal and deviator stress Effective mean normal and deviator stress Average and maximum shear stressEffective average and maximum shear stressLoad cell and back pressureDeviator stress and back pressure

Cyclic ShearASTM D5311, D3999 method A and B

Monotonic ShearDrained and undrained to BS 1377, ASTM D4767 or non standard

SaturationThis follows the incremental saturation as per BS 1377-1990 but is flexible and allows other methods to be used. The screen will let you apply cell and back pressure increments with B value displayed in the cell pressure stage.

Graph displaysCell pressure against timePore pressure against timeBack pressure against timeVolume change against time

Isotropic consolidationThis stage will allow the effective stress to be applied in incremental stages or in one stage by varying the cell or back pressure. The software allows you to apply pressure increments or back pressure decrements.

Graph displaysCell pressure against timePore pressure against timeBack pressure against timeVolume change against time

Anisotropic consolidationThis stage allows the axial stress to be increased or decreased in incremental stages. Graph displaysAxial stress against timeVolume change against time


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Cyclic/Stress path triaxial system (continued). . . . . . . . . . . . . . . . Geotechnical: Advanced soil testingSOIL MECHANICS

Continued

Cyclic The cyclic stage applies the specified cyclic loading to the specimen. This screen shows all the varying values during the cyclic stage.

Graph displaysAverage cyclic stress against timePeak stress in compression against cyclesPeak stress in extension against cyclesDeformation in compression against cyclesDeformation in extension against cycles

Transducers allocationTransducer can be allocated from the library into the test configuration.

LevelsThis part of the software shows all live readings of the transducers with serial number, name, span, and computer counts. Also used for calibrating the linear/non-linear transducers.


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TEST DATA

Cyclic test on a 38 mm sandy

silt material

Test graphs showing the cyclic

deformation of a sample

Data from Dr T. Higuchi, Durham UniversityFinal reading of measured parameters:

Loading time (hh:mm:ss) 00:04:20 pulse count 26Average cell pressure (kPa) 299.1 mean consolidation area (mm?) 1092.68Max. excess pore pressure (kPa) 85.6 consolidation height (mm) 73.49Effective consol. stress (kPa) 99.9 peak cyclic load [comp] (N) 33.2Pore pressure ratio (%) 0.86 peak cyclic load [extn] (N) 34.3Cyclic deformation [comp] (mm) 2.342 peak stress [comp] (kPa) 30.4Cyclic deformation [extn] (mm) 6.19 peak stress [extn] (kPa) 31.4Peak axial strain [comp] (%) 3.187 average cyclic stress (kPa) 30.9Peak axial strain [extn] (%) 8.424 cyclic stress ratio (%) 0.155Double amplitude strain (%) 11.61 average stress ratio (%) 0.035

Test graphs showing the

behaviour of a saturated

sand


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Triaxial cells for cyclic test

The Tri-cell Plus model 28-WF4150/P, 28-WF4100/P, 28-WF4070/P, and accessories for different sample size and sample prepa-ration described on page 88 are required.

TRIAXIAL

Load cells

31-WF7115 Submersible load cell 5 kN with in-line calibration module

31-WF7116 Submersible load cell 25 kN with in-line calibration module

These load cells are fitted inside the triaxial cell and measure the load applied to the sample, independent of the cell pressure. The load cell is fitted with an in-line calibra-tion module, allowing the transducers to be changed or moved within the data acquisi-tion system without the need to re-calibrate them.

Displacement transducer

31-WF7120 Axial displacement transducer with in-line calibration module

This ± 25 mm displacement transducer has in-line signal conditioning. It measures the sample displacement and can also be used as the control transducer for the cyclic strain test. Accuracy is 1 micron.

Volume change transducer

31-WF7125 Volume change transducer 100 cc with in-line calibration module

100 cc volume change transducer with in-line signal conditioning, which monitors the water entering or leaving the sample. Fitted with a change over valve system, it provides unlimited volume change measurements.

Pressure transducers

31-WF7130 Pressure transducer 1000 kPa cell and back pressure with in-line calibration module

31-WF7131 Pore pressure transducer 1000 kPa with in-line calibration module

31-WF7115 Submersible load cell

31-WF7120 Displacement transducer

31-WF7131 Pore water pressure transducer

Water distribution panel

31-WF4334 Triaxial panel, two pressure lines, complete with digital pressure gauge.

Optional, to be used as a water distribution panel to fill, easily the air water bladders and the triaxial cells.

Detail of solenoidal valve for B check

In line calibration module for transducers used

in dynamic test systems

31-WF4334


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Bender elements

ApplicationsBender elements allow to measure the maxi-mum shear modulus (Gmax) of a soil sample and from this data to evaluate the stiffness of a soil. Gmax is generally associated with shear strain levels of about 0.001% and is a key parameter in small strain dynamic analy-ses, such as those to predict soil behaviour or soil structure interaction during earth-quakes, explosion or machine and traffic vibrations.For more information see page 90.

Continued

Bender elements

On sample transducers for dynamic

testing specifications:

Linearity: ± 0.25%Temp. coefficient: ± 0.01%/FS/deg CResolution: 1 micron

On sample strain transducers

ApplicationOn sample transducers consist of radial and axial strain belts. In conventional triaxial testing the determination of axial stiffness is based on external measurements. This method brings errors due to sample bedding effects of the porous stones on either end of the sample and to the loading system and load measuring system. Furthermore the two ends of the specimen are subjected to restraint, differently from the middle third of the sample, where the strain transducers are mounted and where the realistic deformations occur.Axial and radial strain transducers give the opportunity to measure with high accuracy the deformations directly on the triaxial test specimen. These transducers have to be used with our TRI-CELL PLUS models of triaxial cells. (see page 88).

BENDER ELEMENTS. (FOR USE WITH TRI-CELL PLUS MODELS TRIAXIAL CELLS ONLY)

TRI-CELL Plus Sample size Top cap and base pedestal

of triaxial cell with bender elements Vacuum type

for extension tests

28-WF4070/P 50 mm 28-WF4058/B70 mm 70 mm 28-WF4078/B

28-WF4100/P 70 mm 28-WF4078/B1100 mm 100 mm 28-WF4108/B

28-WF4150/P 150 mm 28-WF4158/B150 mm

31-WF4079/KD On sample transducer kit for 70 mm samples with 2 linear and 1 radial transducers used with dynamic test systems, including in-line calibration module




ShearStrain

Bender Element

Machine Foundations

Ocean Wave Loading

Earthquake

Cyclic TrixialCyclic Simple Shear

Torsional ShearHollow Cylinder

Documents

31 Geotechnical: Advanced soil testing - Welcome to ITL or Stress Path Triaxial System... · 31 127. . . . . . . . . . . . . . . . Geotechnical: Advanced soil testing SOIL MECHANICS