Traxial CU-CD Test Sytems

Product Code

Triaxial Test Systems,    220-240 V 50-60 Hz


ASTM D2850, D4767, D7181; AASHTO T-297; BS 1377-7, BS 1377-8

Determining the mechanical properties of soils is a very important step to design foundations,

embankments and other soil structures. Building constructions, excavations, tunnelling and similar applications have several effects on the subsoil structures and these effects are successfully simulated with Triaxial Tests where the stress-strain relation of undisturbed soil specimen are investigated by subjecting the soil sample to different stress levels and drainage conditions.

The FALEX Triaxial Test System provides automated triaxial compression tests on cylindrical undisturbed and remolded soil samples. Unconsolidated undrained (UU), consolidated drained (CD) and consolidated undrained (CU) compression tests can be automatically run, controlled and reported using this apparatus.

Consolidated Undrained (CU) Test & Consolidated Drained (CD) Test

Peak effective strength parameters (c' and φ') may be determined either from the results of consolidated undrained (CU) triaxial compression tests with pore pressure measurement, or from consolidated drained (CD) triaxial compression tests. The consolidated undrained/ drained triaxial compression tests are normally performed in several stages, involving the successive saturation, consolidation and shearing of each of three specimens.

Saturation is carried out in order to ensure that the pore fluid in the specimen does not contain free air. Saturation is normally carried out by leaving the specimens to swell against an elevated back pressure. Back pressure (which is simply an imposed pore pressure) is applied through a volume change gauge to the top of the specimen, while a cell pressure of slightly higher value is also applied. Both cell pressure and back pressure are normally increased in increments, allowing time for equalization at each stage. The degree of saturation can be expressed in terms of Skempton's pore pressure parameter (Skempton, 1954):

           Δ u


          Δ σ3

where Δu is equal to change in pore pressure for an applied cell pressure change of Δ σ3. For an ideally saturated soil B is equal to unity. It is recommended by several standard test methods that  

a value of B greater than, or equal to, 0.95 must be achieved before the specimen may be considered as fully saturated and  the consolidation stage started. The consolidation stage of an effective stress triaxial test is carried out for two reasons. First, three specimens are tested and consolidated at three

different effective pressures, in order to give specimens of different strengths which will produce widely spaced effective stress Mohr circles. Secondly, the results of consolidation are used to determine the minimum time to failure in the shear stage. The effective consolidation pressures (i.e. cell pressure minus back pressure) will normally be increased by a factor of two between each specimen, with the middle pressure approximating to the vertical effective stress in the ground. When the consolidation cell pressure and back pressure are applied to the specimen, readings of volume change are made using a volume change device in the back pressure line. Pore pressure is measured at the specimen base, with drainage to the back pressure line taking place through a porous stone covering the top of the specimen. The coefficient of consolidation of the clay can be determined by plotting volume change as a function of the square root of time. Theoretical considerations indicate that the first 50% of volume loss during consolidation should show as a straight line on this plot. This straight line is extended down to cut the horizontal line representing 100% consolidation, and the time intercept at this point (termed “t ” by Bishop and Henkel) 100 can be used to obtain the coefficient of consolidation.

Consolidated Undrained (CU) Test:

Once consolidation is complete, the specimen is to be isolated from the back pressure and the rate of vertical movement of the compression machine platen set according to result of consolidation.. During the shear stage the vertical stress is increased by the loading ram, and measurements are made at regular intervals of deformation, ram load and pore pressure. These are converted to graphs of principal stress difference  (σ1- σ3) and pore pressure as a function of strain, and failure is normally taken as the point of maximum principal stress difference. The effective stress Mohr circles are plotted for the failure conditions of the three specimens which has been subjected to different consolidation level, and the gradient and intercept of a straight line drawn tangential to these circles defines the effective strength parameters c' and φ'.

Consolidated Drained (CD) Test:

The consolidated drained triaxial compression test, with volume change measurement during shear is carried out in a similar sequence to the consolidated undrained test, but during shear the back pressure remains connected to the specimen which is loaded sufficiently slowly to avoid the development of excess pore pressures. The shear stage of a drained triaxial test can be expected to take between 7 and 15 times longer than that of an undrained test with pore pressure measurement. Once shearing is complete, the results are presented as graphs of principal stress difference and volume change as  a function of strain, and the failure Mohr circles are plotted to give the drained failure envelope defined by the parameters cd' and φd' .Triaxial CD-CU-UU equipment is computer controlled, test values can be transferred to computer and data processing can be made with Triaxial software on Windows operating system. All data can be used on Excel programs. The load data and axial displacement data are transfered and recorded through BC 100 Unit to the software. Three pressure data (cell pressure, back pressure and pore pressure) from triaxial cell and volume change data transfered and recorded through the unilogger to the software.

Typical configuration of system for different tests (UU-CU-CD)

Product Code





Multiplex Universal Electromechanic Test Machine*




Load Cell 5 k N





Triaxial Cell**




Block with One Connection Line for Triaxial Test Cells,




Block with 3 Connection Lines for Traxial Test Cells




Pressure Transducer




Oil and Water Constant Pressure System




Automatic Volume Change Unit




Static Unilogger4 Channels




Software to Perform UU Triaxial Tests




Software to Perform CU-CD Triaxial Tests



FIS-1330 and


De-Airing Water Tank, 7 L. and Hose



*Supplied complete with FIGM-0025 50 kN Load Cell, FIGM-0062 25 mm Linear Potentiometric Transducer and  UTC-4930 BC 100 Data Acquisition and Control Unit.

**Choose the suitable cell for the specimen size (FIS-0400: 38-50 mm dia. samples / FIS-0401: 70-100 mm dia. samples).  For cell accessories and sample prepatarion accessories see next page.

Optional apparatus for de-airing water see page 8.

Multiplex Universal Electromechanic Test Machine

The FIM-0108 Multiplex Universal Electromechanic Test Machine is a Servo Controlled Multiplex Machine supplied complete with FIGM-0025 50 kN Load Cell, FIGM-0062 25 mm Linear Potentiometric Transducer and UTC-4930 BC 100 Data Acquisition and Control Unit. 5 kN Loadcell should be ordered separately for Triaxial Tests.

The Frame capacity is 50 kN. This versatile digital loading frame features a microprocessor controlled drive system with an advanced servo motor enabling the operator to easily set any test speed via the membrane keyboard. The keyboard comprises adjustment buttons such as “start”, “increase”, “automatic”, “manual”, “down”, “up”. The testing speed can be set between 0,00001 mm/min to 51mm/min. The test automatically stops when load and displacement is reached to 99% value of the set measuring range. See page 243 to 245 for details.

Load and displacement values are collected by BC 100 and transferred to PC for further processing with the FIS-0416 UU and FIS-0417 CU-CD Software.


550x650x1100 mm

Weight (approx.)

95 kg


750 W

BC 100 Unit

BC100 TFT unit is designed to control the machine and processing of data from load-cells, pressure transducers or displacement transducers which are fitted to the machine.

All the operations of BC100 are controlled from the front panel consisting of a 800x480 pixel 65535 color resistive touch screen display and function keys 4 analogue channels are provided for load-cells, pressure transducers or displacement transducers.

BC100 has easy to use menu options. It displays all menu option listings simultaneously, allowing the operator to access the required option in a seemless manner to activate the option or enter a numeric value to set the test parameters.The BC100 digital graphic display is able to draw realtime "Load vs. Time", "Load vs. Displacement" or "Stress vs. Time" graphics.

BC100 unit offers many addition unique features. You can save more than 10000 test results in its internal memory. BC100 unit has support for various off-the-shelf USB printers, supporting both inkjet and laser printers(ask for compatible models). Thanks to its built-in internet protocol suite, every aspect of BC100 device can be controlled remotely from anywhere around the world.

Main Features
  • Can make test with displacement or load control.
  • Real time display of test graph.
  • CPU card with 32-bit ARM RISC architecture
  • One analog channel for high capacity load cell, one analog channel for low capacity load cell, one analog channel for displacement transducer and one analog channel for cell pressure (only for UU tests)
  • Programmable digital gain adjustment for load-cell, pressure transducers, strain-gauge based sensors, potentiometric sensors, voltage and current transmitters
  • 1/256000 points resolution per channel
  • 10 data per second sample rate for each channel
  • Ethernet connecting for computer interface
  • 800x480 resolution 65535 color TFT-LCD industrial touchscreen
  • 4 main function keys
  • Multi-language support
  • 3 different unit system selection; kN, Ton and lbf
  • Real-time clock and date
  • Test result visualization and memory management interface
  • Remote connection through ethernet
  • USB flash disc for importing test results and for firmware
  • USB printer support for inkjet and laser printers (ask for compatible models)
  • Camera support for real-time video recording during test (ask for compatible models)
  • Free of charge PC software for the test control and advanced report generation
Data Acquisition & PC Software

The CU-CD triaxial test is a complicated test needs load data, diplacement data 3 pressure data from triaxial cell and volume change data. Load data and displacement data are transfered and recorded  through BC 100 Unit to the  software. 3 pressure data from triaxial cell and volume change data transfered and recorded through  the unilogger  to  the software.

The FALEX software  for CD-CU tests  is compatible with FALEX FIG-0320 datalogger and BC 100 unit. FALEX unilogger can be connected  to PC by RS232 port.  All channel gains can be set manually and accuracy of the reading can be increased.

Triaxial Software is a modular software that when a new test wanted to do, it directs the user step by step. First the software wants to input initial measurements such as diameter, heigth, sample weigth etc. On this stage the user decides CU or CD test will be done and enters cell pressure increment steps, back pressure differential pressure and effective stress that will be used on consolidation.

After the initialization is completed, the user goes to Saturation Cell Pressure increment stage. Cell presure must be incremented to the pressure entered at initialization stage. During this stage the software calculates B and pore pressure and submits their graph respect to time. When B value saturates this stage must be ended. Generally value of B would not reach to 0.95, therefore a back presuure increment stage must be implemented. On the saturation back pressure increment stage, prior to the start of this stage software commands what back pressure must be applied respect to initial settings. The software draws volume change and pore pressure data during this stage.

Saturation stages can be done recursively at most of 10 cycles. The relevant data of each stage is written to respective files for further investigation and report facilities. When the saturation is completed the consolidation stage can be implemented.On this stage the software commands to adjust both cell and back pressure to apply effective stress. On the consolidation stage Volume change,pore pressure and pore pressure disssipation percent is drawn as graphs. When the stage is completed, the next stage will be shear stage of CU or CD. The software suggest the shear speed respect to the results found on consolidation stage. Axial displacement and force must be tared prior to the start of shearing.

On the shear stage deviator stress, pore pressure, ơ' versus ơ'3 and s' versus t' graphs are drawn. 4 different test specimen can  be configured in same file. All the results are used for drawing mohr circles. The data is evaluated with respect to specimen shear end condition. This condition  can be selected as constant pore pressure, constant volume change effective prime deviator ratio etc. With the final measurements one set of data is closed.

The raw data can be exported to Microsoft Excel. Without using Microsoft Excel environment all reports can be printout which includes summary of each stage with relevant graphs.

Triaxial Cells & Sample Preperation

FIS-0400            Standard Triaxial cell for 38 and 50 mm dia. samples
FIS-0401            Standard Triaxial cell for 70 and 100 mm dia. samples

The cell has been designed and treated to minimize corrosion. Particular attention has been paid to the quality of finish between the piston and the head. Final assembly includes the fitting of       an O-ring seal and the use of a special lubricant to reduce friction to a minimum and eliminate water leakage. The piston load capacity is designed to accept high axial loads which may be present during the final stages of a test.

Each cell has five take-off positions drilled in the base for top drainage/back pressure, pore water pressure and bottom drainage. Three no volume change valves and anvil for displacement transducer are supplied complete with the cell. Each cell will accept a range of base adaptors and various accessories for testing a wide range of specimens.

The cell capacity is designed to tolerate confining pressures as high as 1700 kPa which is enough for simulating most in-situ conditions.

For cell accessories and sample prepatarion accessories see next page.





160x160x400 mm

210x210x550 mm

Weight (approx.)

4.5 kg

12 kg

Cell Accessories

Sample Diameter(mm)









Base Adaptor







Porous Top Cap







Nylon Tubing for Drainage







Pair of Porous Discs







Rubber Membrane







Membrane Placing Tool (Strecher)







0 Ring (10pcs.)







0 Ring Placing Tool







Leteral Filter Paper (50 pcs.)







Filter Paper Discs (100 pcs.)







Plastic Discs (2 pcs.)







Sample Preperation Accessories

Sample Diameter

38 mm

50 mm

70 mm

100 mm

Split Sand Former





Split Mould










Aliminium Dolly





Oil and Water Constant Pressure System

Product Code

FIS-0408            Oil and Water Constant Pressure Unit, 1700 kPa220-240V, 50-60Hz, 1ph
FIS-0409            Digital Pressure Gauge, 1700 kPa (250 psi)
FIGM-0110       Pressure Transducer, 2000 kPa

The Oil and Water Constant Pressure Unit is extremely versatile and can be used in conjunction with a wide range of test equipment. The unit provides continuous variable pressure up to 1700 kPa. Pressure is increased or decreased simply by turning a control wheel.

The Unit is used for providing cell/back pressure in triaxial tests. The apparatus is supplied without a gauge for those customers who have suitable pressure monitoring equipment.

As optional equipment for monitoring the pressure of the  unit;

  • The Digital Pressure Gauge (FIS-0409) or
  • The pressure transducer(FIGM-0110) which can be used with FALEX BC100 TFT Unit on the Multiplex Universal Electromechanic Test Machine (FIM-0108) for only UU test or
  • The pressure transducer(FIGM-0110) which should be used with the datalogger (FIG-0320) for CU-CD tests

can be used and prefered optional equpment should be ordered separately.

The machine features a clear hydraulic/water interface reservoir and up to 1 liter capacity of water is available under pressure. Supplied complete with 2 liters of No.46 regular hydraulic oil.

Product Code





300x250x250 mm

7.5 kg

35 W


150x150x100 mm

0.6 kg


Volume Change Measurement

Product Code

FIS-0415            Automatic Volume Change Unit

The Unit  consists of a piston connected to a 25 mm travel linear transducer which is sealed against a precision machined calibration chamber so that the linear movement of the piston is exactly proportional to the volume of water in the calibration chamber.

The apparatus creates an electrical signal proportional to the volume of water flowing through the unit. By connecting it to the data acquisition system the measured volume change will be used by software during the test and in final report.

Capacity                              : 100 cm3

Transducer Input            : up to 12 V DC

Accuracy                             : ± 0.1 ml


260x260x400 mm

Weight (approx.)

5 kg

Pressure Transducer and Connection Block for Pore Water Pressure Measurement and De-Airing

Product Code

FIGM-0110       Pressure Transducer, 2000 kPa
FIS-0405            Blockwith One Connection Line for Triaxial Test 
FIS-0406            Block with Three Connection Lines for Triaxial Test 

The Pressure Transducer is used for the measurement of cell or back or pore pressure of water in triaxial test systems and also should be used with an FALEX BC100 TFT Unit (UTC-4930) or a datalogger (FIG-0320)

The Block for triaxial test cells is used for connection of the pressure transducers and de-airing in the water hoses.

De-Airing Water

Product Code

FIS-0418            De-Airing Water Apparatus, 230V, 50Hz, 1ph
FIS-1330            De-Airing Water Tank, 7 L.
FIGE-3580         Vacuum Control and Water Connection Panel with Regulator and Vacum Gage Manometer
FIGE-3585         Connection Panel for Vacuum and Water with Vacuum Gage Manometer
FIGE-3505         Vacuum Pump 51 L/min. Capacity,220-240 V 50-60 Hz
FIGG-2015        Filter Flask 2000 ml
FIGE-3570         Air Drying Unit / Water Trap, Vacuum Type
FIGP-1140         Plastic Hose, Ø8mm, 6m

The FIS-0418 De-Airing Water Apparatus is a compact and self-contained equipment which can de-air water quickly and efficiently down to levels of dissolved oxygen acceptable for geotechnical test methods.The apparatus used in conjunction with the de-airing tank (FIS-1330). Air is removed from the water by a vacuum system. De-airing tank should be ordered separately.

The first option for de-airing water;

  • De-Airing Water Apparatus FIS-0418
  • De-Airing Water Tank(FIS-1330)
  • Vacuum Control and Water Connection Panel with Regulator and Vacum Gage Manometer(FIGE-3580) or Connection Panel for Vacuum and Water with Vacuum Gage(FIGE-3585) (These panels are optional)
  • Plastic Hose (FIGP-1140 )

The second option for de-airing water;

  • Vacuum Pump (FIGE-3505),
  • Filter Flask (FIGG-2015) or Air Drying Unit / Water Trap (FIGE-3570)
  • De-Airing Water Tank (FIS-1330)
  • Vacuum Control and Water Connection Panel with Regulator and Vacum Gage Manometer (FIGE-3580) or Connection Panel for Vacuum and Water with Vacuum Gage(FIGE-3585) (These panels are optional)
  • Plastic Hose (FIGP-1140 )

By using FIGE-3580 Vacuum Control and Water Connection Panel, vacum pressure degree can be regulate.

By using FIGE-3585 Connection Panel for Vacuum and Water with Vacuum Gage Manometer and FIGE-3580 Vacuum Control and Water Connection Panel with Regulator, de-aring water equipment can be used without repeated assembling the hoses.

Product Code


Weight (approx.)


465x240x340 mm

15 kg


450x150x500 mm

7 kg


250x250x250 mm

2.7 kg


120x120x220 mm

0.5 kg


300x150x240 mm

8.5 kg


70x80x170 mm

0,5 kg

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