July 25, 2019

Constant Rate of Strain Test – Checklist

The following checklist is designed to help a new user complete all the necessary tasks required before starting a Constant Rate of Strain test using the Multi-Purpose Cell from VJTech.

The test can be performed with either an ACONS Pro or a TriSCAN Pro load frame. The following guide refers to the procedure followed on an ACONS Pro load frame. The user should also reference the local standard for additional steps and detail on how to undertake certain steps below.

  1. Ensure a supply of de-aired water.
  2. Place the porous disc inside a tray with de-aired water and leave to saturate.
  3. Clean the base of the MP cell and slightly grease O-ring in base groove.
  4. Flush the de-airing block.
  5. Check pore water pressure transducer calibration and recalibrate if necessary. The calibration needs to be performed to the instrument that the sensor is connected to (look at point 17 below).
  6. Flush the Back Pressure and Pore Pressure lines. Leave a small water bubble on the pedestal.
  7. Check Back Pressure line for leaks.
  8. Attach the base pedestal required for CRS tests in the MPC base. Make sure that the two holes at the bottom of the pedestal are aligned with the holes at the bottom of the cell (figure 1). Use the 5 bolts to tighten it up firmly.
Figure 1. Fitting the base pedestal onto the MP Cell. For Constant Rate of Strain Test
  1. Weigh the empty cutting ring and prepare the sample (disturbed or undisturbed). Then, weigh the sample & ring and calculate the net weight of the sample. Place any trimmings of the soil in the oven to dry and to determine its moisture content.
  2. Remove the porous disc from the tray and place it onto the base pedestal.
  3. Place the sample on the base pedestal and make sure that the ring is in contact with the O-ring. Then, place on the clamping ring and firmly fix in place using the screws (figure 2 (L)). Place on the top cap (figure 2 (R)).
Figure 2. Fitting the sample on the base pedestal.

Place on the top of the MP cell while keeping the loading ram up, so that it does not yet come into contact with the top cap. The ram should be held in place using the LSCT bracket. Tighten the three bolts to secure the cell Top Plate tightly (figure 3).

Figure 3. Tightening the Top Plate of the MP Cell for a constant rate of strain test
  1. Connect the solenoid valve to the Back Pressure line and the Pore Pressure transducer to the Pore Pressure line through the quick-release valves.
  2. Create a junction in the Back Pressure line, placed behind the solenoid valve, to split it between the Cell (CP) and the Back (BP) valves using a T-piece on the pipe (figure 4).
Figure 4. Splitting the Back Pressure Line
  1. Open the CP valve and close the BP valve. Fill the cell by opening the access to the de-aired water tank through the distribution panel.
  2. Connect the Load Cell and the Displacement transducers to the back of the ACONS Pro instrument, using the designated ports. If a digital displacement transducer is to be used, connect it to the digital port at the back of the ACONS Pro instrument.
  3. Connect the Pore Water Pressure transducer to the External Channel port of the APCH. If the test is conducted using a TriSCAN Pro load frame, the PWP transducer can be connected to one of the spare instrument ports.
  4. Connect the loading ram to the frame’s cross beam (figure 5).
  5. Loosen the LSCT bracket to leaving the loading ram to move freely when the instrument operates. Fix the LSCT in place.
  6. Press Engage on the instrument front panel to engage the loading ram with the sample. The instrument will stop loading as soon as the load changes by the value set up as the Engage Level in the instrument menu. 3 N has been proved to work well in most cases.
  7. Program the test in Clisp studio.
  8. Before starting, make sure that:
  • The PWP, CP and BP valves on the cell are open;
  • The release valve for the de-airing block of the PWP sensor is closed;
  • The sample is properly engaged with a very small load (2-3 N);
  • BP controller is at a value of approximately 0 kPa.
  • The LSCT bracket is positioned so that is free to move downwards during the test, without hitting any part at the top of the cell.
Figure 5. Connecting the loading ram to the cross beam for a constant rate of strain test

  Start the Test.

For more information about our Constant Rate of Strain equipment, please contact us.