Controls Group Dynamic pneumatic triaxial systems DYNATRIAX Dynamic pneumatic triaxial systems DYNATRIAX
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Soil mechanics

Dynamic pneumatic triaxial systems DYNATRIAX

ASTM D5311
Main features

  • Capability to perform Static (effective stress and stress path), Dynamic and Unsaturated soil triaxial tests
  • Three axis closed loop control for axial load or displacement, cell and back pressure
  • Automatic compensation of cell/back pressure during dynamic stage
  • Nominal operating frequency up to 10 Hz (depending on the test condition) 
  • Complete test automation of all test stages using an high sensitivity closed loop P.I.D. feedback 
  • Dynamic load/displacement options: up to ±25 mm with ±5 kN double-effect actuator
  • Available upgrade for Bender element testing and Local strain measurement
  • Standard and user defined wave shapes also derived from in situ measurements (from violent earthquakes to sedate ocean waves)
  • Test set-up by unique programmable Multi stage test procedure: during the test run, acces to all controls to expand and modify the stages according to the response of the soil specimen
  • Manual and automatic Emergency air shut-off function

General description
General description
DYNATRIAX apparatus is a computer controlled servo-pneumatic systems, designed to perform the static and dynamic stages of a triaxial test. The systems manage three closed loop axis:
  1. Vertical load/displacement:
    - up to ± 25 mm (± 5 kN double-effect actuator)
  2. Cell pressure up to 1000 kPa
  3. Back pressure up to 1000 kPa
The base system includes:

Triaxial load frame Tritech 50
The Tritech digital loading frames feature a microprocessor controlled drive system, specifically designed to perform both static or dynamic tests.
  • Static load capacity: 50 kN ( 100 kN available on request)
  • Static vertical displacement: up to 100 mm (machine travel)
The double acting pneumatic actuators are digitally controlled and includes an integrated LVDT displacement transducer to control the position and the displacement of the piston during the test.
  • Dynamic load capacity: ±5 kN 
  • Dynamic vertical displacement ±25 mm
  • Nominal operating frequency: up to 10 Hz (depending on test conditions)
  • Maximum servo-valve frequency: 70 Hz
  • Min. air supply: 800 kPa

Data Acquisition, process & control system 
The unit manages the three closed loop axis (vertical load/displacement, cell and back pressure) with a control loop rate of 10 kHz. It provides the automatic control of the system and drives the servo-valve units of the three axis and two on/off valves, one connected to the drainage line and one connected to the air main supply of the triaxial cell. The CDC communicates with the PC through an Ethernet communication link (1 Gbit/s). The CDC has sixteen transducer input channels using 16 bit ADC.

PID control
An extremely efficient algorithm with larger gain ranges gives enhanced sensitivity, making it easier to tune the system and achieving a more accurate waveshape.
New features include manual and automatic amplitude controls which compensate for small changes that may occur in the system during cycling, ensuring that the required peak and valley levels are consistently maintained.
The improved tuning panel, with its more user-friendly interface, provides all the tools necessary to optimise system control during static and cyclic test stages.  

Multitasking, user-friendly Windows-based software is pre-installed on the computer provided with the system. The software provides control of the following utilities and stages of a cyclic triaxial test:
  • Saturation
    - Cell pressure increments with B value check
    - Back pressure increments with volume change measurement
    - Cell and back pressure ramp
  • Consolidation
    - Isotropic consolidation with continuous volume change measurement
  • Ko consolidation
    Vertical displacement loading with sample diameter control using either:
    - Direct measurement by radial belt with on-sample transducers
    - Measurement of sample volume change and height
  • Stress path
    - Horizontal and Vertical Stress
    - s, t (average stress and shear stress)
    - p, q (mean normal stress and deviator stress)
    - Vertical stress using strain control
  • Monotonic shear
    - Strain controlled static shear stage, drained or undrained
    - Loading in compression or extension, using the vertical actuator or the Tritech
    Any or all of the above stages can be performed in “Automatic mode” where the test parameters are entered at the start of the test or stage and the software takes control of managing the stages using predefined criteria.
  • Cyclic loading
    - ASTM D5311 Load Controlled Cyclic Strength
    - ASTM D3999 Load Controlled Modulus & Damping
    - ASTM D3999 Displacement Controlled Modulus & Damping
    - Non Standard Single or multi cycle test
    - User defined or imported Waveshape
  • Transducer limits
    - An air shut-off valve can be programmed to be activated using defined channel limits
  • Calibration
    - Digital calibration using linear fit, polynomial fit or linearization
    - Transducer verification option
More +

Technical specifications

  • Dynamic load capacity: ±5 kN 
  • Static load capacity: 50 kN ( 100 kN available on request) 
  • Nominal operating frequency: up to 10 Hz (depending on soil and  test conditions)
  • Max diameter sample: up to 150 mm  
  • Max cell and back pressure: depending on max working pressure of air supply

Ordering info

DYNATRIAX 50/5, PC controlled automatic dynamic triaxial system, including  ±5 kN double acting pneumatic actuator, 50 kN cap. load triaxial frame, CDC Compact Dynamic Controller 16 channels cap., testing software and PC. 110-240 V, 50-60 Hz, 1 pf.


Triaxial load frame TRITECH
Triaxial cells for advanced applications. Tri-Cell plus models for 70, 100 or 150 mm dia. specimens
Double wall triaxial cells for unsaturated tests
Submersible load cells 
Air/Water pressure system and controls panels. Bladder air/water pressure cylinders.
Axial strain displacement transducers. LVDT linear transducer ±25 mm travel
Pressure transucers for triaxial test.
Automatic volume change transducer for remote flow control
Mini On-sample transducers for local strain measurement in triaxial testing

Water distribution panel.
Two pressure lines, complete with digital pressure gauge and hand pump.

Air compressor, 10 bar max. pressure, 200 l capacity, 5.5 kW.
400 V, 50 Hz, 3 ph.
220 V, 60 Hz model available on request.

Air treatment unit for the dehumidification of air, comprehending: air dryer, particle filter 5M, oil filter 0.01 M. 230 V, 50-60 Hz, 1 ph.

Air treatment unit for the dehumidification of air, comprehending: air dryer, particle filter 5M, oil filter 0.01 M. 110 V, 60 Hz, 1 ph.

Note: for more information on the above components clic to the relevant positions.

Additional Information

Typical configuration of a dynamic system
Cyclic system and load frame
DYNATRIAX - Dynamic Triaxial System 50kN-5kN 31-WF7005 1
Submersible Load Cell 25 kN 31-WF7119 1
Axial Displacement Transd LVDT 31-WF7121 1
Pore Pressure Transducer 1000kPa 28-WF6300 3
de-airing blok 28-WF6310 1
Automatic volume change 29-WF4412 1
70mm sample triaxial cell and accessories
Triaxial cell 28-WF4070 1
Base pedestal 28-WF4071/7 1
Vacuum top cap 28-WF4072/AV 1
Pair of porous stone 28-WF4074 1
Rubber membrane 28-WF4075 2
O-ring 28-WF4076 1
Suction device 28-WF4071/A 1
O-ring placing tool 28-WF4071/B 1
2 part split former 28-WF4071/D 1
Filter drains 28-WF4071/E 2
Filter discs 28-WF4071/F 1
Hand sampler 28-WF4071/G 1
2 part split mould with vacuum attachment 28-WF4071/H 1
Bender elements option
bender elements 70mm dia 28-WF4078/B 1
Wave generator  28-WF4190 1
Advanced kit for Triaxial cell model WF4070 28-WF4070/ADV 1
Pressure system
Bladder air/water interfa 28-WF4320 2
Triaxial panel two way pressure 28-WF4335 1
Air Compressor 10 bar 145 31-D2015/A 1
Air treatment unit 86-D2019 1
De airing system
Air drying unit 86-D2005 1
Silica gel dessicant with indicator 86-D0819 1
De airing tank, 23lt capacity 28-WF4221/A 1
Valve panel por use 28-WF4225 1
Portable vacuum pump. 28-WF2001 1
Rubber tube dia 6,5 x 12mm 28-WF2064 1




Unsaturated soil testing package.
The package includes the additional servo-valve for air pressure control, prressure transducer and the software to automatically perform the test stages using the axis translation method:
  • Simultaneous and independent control of air pressure, pore water pressure and axial stress
  • Performance of consolidation, saturation soil water curve and shear stages
  • Test data recording for each stage
Triaxial cell and test accessories have to be ordered separately.


Resilient modulus determination on compacted samples.
This package provides software for performing the test according to AASHTO T307 standard, two 10 mm displacement transducers, and mounting brackets to fit the transducers to the piston of the triaxial cell.
The software includes:
  • Two standard sequences of dynamic cyclic stress and static confining stress for subgrade soils and base/sub-base materials
  • The possibility to set up customized sequences that the user can save and replicate automatically
  • Continuous monitoring in real time of recorded and processed data of each single sequence


Partner's Documents