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Triaxial Testing System Setup Part 2

Mar 18 2014

Part one of our Triaxial testing system setup guide explained the initial installation required that involves the System Setup, Sample Preparation and Test Creation. Now that Steps 1 and 2 (Hardware Setup and Specimen Details) of the wizard have been completed we will guide you through the necessary stage setup required for Saturation testing, Consolidation testing and Shear testing.

Soil Testing – Triaxial Testing Part 2 – Saturation, Consolidation and Shear Setup

Saturation testing:

Selecting the Saturation Method step (3) from the wizard will display the Saturation setup screen as shown below.

The saturation stage consists of:

  • The number of schedules set up
  • Incremental Cell and Back Pressure steps to saturate the specimen
  • A B-value measurement of the specimen until the desired saturation is achieved.

Each schedule consists of:

  • A Ramp or Step to a pre-defined stress point
  • Set effective pressure
  • A check to see whether the desired B-Check value is achieved

For an inexperienced technician, it is usual to tick the ‘Request manual intervention in between increments to control other equipment or carry out manual adjustments’ checkbox to avoid unexpected occurrences and a warning message will be displayed to Open or Close the Back Pressure Valve as necessary when starting a schedule.

If the technician is experienced and happy with the Test setup, the Saturation sequence is as follows:

  • Automated testing can be implemented using an Automatic Solenoid Valve that is controlled by the computer.
  • The Back Pressure valve will be opened and closed automatically
  • The whole Saturation process can be completed without manual intervention, leaving the technician free to perform other duties.

Data Logging can be at a specified cyclic rate or using time values specified in a table as shown below. A predefined table may be used to log data (either square root or logarithmic) selected from the drop down menu, or a new one created by the technician using the ‘Edit’ facility.

 

The stopping condition for each B-check step will be dependent upon how the Back Pressure is applied. If the Back Pressure is applied to one end of the specimen and the PWP is measured on the other end, set up and use the PWP change stopping condition. If the Back Pressure controller is connected to both ends of the specimen, set up and use the Volume change stopping condition.

If the User requires this increment to remain running for a certain time, this can be set up and the checkbox ticked. The Saturation stage will be terminated when the B value is above the specified level (which may be changed from the standard value (0.95) if necessary). The Stopping Condition options are illustrated below.




 

The ‘Advanced’ tab is not normally required by most Users, but enables ALL increments to be run irrespective of the B-Value check being satisfied and/or maintain the Back Pressure obtained at the end of the previous phase for the subsequent phase.

Consolidation testing:

Selecting the Consolidation Method step (4) from the wizard will display the Consolidation setup screen as shown below.

 

When initiating the Consolidation stage, either enter a value for the Back Pressure to be held at, or use the (rounded) last value achieved during the Saturation stage and specify the Effective Pressure to be maintained.

If the Cell and Back pressures need to be established before commencing the Consolidation test, tick the ‘Wait for the Effective Pressure to be established' selection box. If the Pore Water Pressure needs to be stable before commencing Consolidation, then a Pore Water Pressure Value and Time Interval can be entered when the second checkbox is ticked. If an audible warning is required when the Cell and Back pressures are established before data logging commences, tick the ‘Request manual intervention before proceeding’ selection box.

The ‘Data logging’ screen enables drainage corrections to be input if required as shown below. They can be selected by clicking the appropriate radio button

  • No Corrections
  • Corrections from one end only
  • Corrections from both ends
  • From the radial boundary and one end
  • From the radial boundary and both ends.

Consolidation testing data Logging can be at a specified cyclic rate or using time values specified in a table as shown below. A predefined table may be used to log data (either square root or logarithmic) selected from the drop down menu, or a new one created by the technician using the ‘Edit’ facility.

The Consolidation stage will terminate when the first of up to 3 selectable criteria is satisfied as shown below. They are:

  • When the Pore Water Pressure dissipation exceeds a specified percentage
  • When a specified maximum time is exceeded
  • When the Volume changes by less than a specified amount within a selected time period

Shear testing:

Selecting the Shear Method step (5) from the wizard will display the Shear setup screen as shown below.

The Starting Conditions to be input for the Shear stage are;

  • The Test Control Pressure - this can either be the current Cell Pressure or new manually input values of Cell and Back Pressure
  • The Shear Machine Speed - which can either be a manually input value or the Shear Speed calculated at the end of the Consolidation Stage (limited to a maximum specified value)
  • The thickness of the membrane in use

The ‘Data logging’ screen enables the Engage Speed data to be input as well as data logging details as shown;

The Engage Speed data to be input consists of:

  • The initial Speed of the frame
  • The minimum Load change required
  • The reverse travel speed following overshoot (if applicable)
  • The specified Load change to be reached

Shear testing data Logging can either be at an input time interval or on a specified Axial Strain percentage change. If required, the technician can also specify that Cell and Back Pressures are established before data logging commences and that manual intervention is required before starting the Shear stage.

The Stopping Criteria screen is shown below;

UP TO five Stopping Criteria for Shear stage completion may be specified. When the first of those selected is satisfied the Stage will terminate. The first three are:

1) When the Maximum Deviator Stress falls by the specified percentage and optionally, the stage carries on for an additional Shear strain percentage

2) When the Maximum Stress Ratio falls by the specified percentage

3) When the calculated Stress Ratio falls by the specified number of times

However, there is a checkbox option to ignore these first three conditions until a specified minimum Strain has been reached which is important to avoid premature Test termination due to initial erratic readings.

4) When the Axial Strain extends beyond the specified percentage

5) When the specified Maximum time has been exceeded

Part 3 will cover executing and monitoring Tests with the Live Data Views, Graphs and Tables that are available to the technician, as well as the creation of personalised examples.

Speak To The Experts At VJ Tech

If you would like any further information or assistance with Triaxial testing then please do not hesitate to call us +44 (0) 118 945 3737+44 (0) 118 945 3737 or Email: service@vjtech.co.uk


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