The soil sample you will test will have been prepared before the lab starts. It was
conditioned to a certain preconsolidation stress, then allowed to relax back to a relatively
The goal of this experiment is to determine the compression index, Cc, the
preconsolidation stress, σp, and the coefficient of consolidation, cv. To do this you will
monitor the change in height of the soil sample resulting from a sequence of vertical
stresses imposed. The stress levels will start at 1 ton per square foot (tsf), progressing to
2 tsf, 4 tsf, 8 tsf and 16 tsf. Then there will be a progression of reduced stresses
(unloading) to 8 tsf, 4 tsf and finally 1 tsf. For each stage you should ensure that the load
remains until the rate of change in height approaches zero before going to the next load
step. Using Gentest, the results at each load level will be recorded and stored to an
individual data file for data reduction and analysis.
CAUTION: BE AWARE OF WHAT IS GOING ON WITH THE EQUIPMENT AT
ALL TIMES. KEEP FINGERS AWAY FROM THE CONSOLIDATION DEVICE
WHILE CONNECTING OR ADJUSTING THE COMPRESSED AIR SOURCE AND
THE CONSOLIDOMETER CONTROLS.
Gentest data acquisition workstation Consolidation device with soil
sample loaded in the consolidometer
The loaded consolidometer under
Older model Newer model
Older model: LDT sensor tip resting on edge of consolidometer wall. This photo was taken
near the end of the test.
Newer model: LDT sensor tip rest at the top center of the crosshead.
At the beginning of the test the LDT position should be adjusted so there is ample range for the
tip to travel.
The following procedure steps assume the test setup has been prepared before the lab for
the preconsolidation phase. This means the load on the sample is less than 1 tsf and the
LDT has been installed but not yet adjusted for the test. There should be a nominal load
on the sample. Have the Instructor or TA check the setup before you proceed.
1. Set the Load/Unload selector on the consolidation device to OFF. Adjust the
regulator on the consolidation device for the pressure (read on the pressure
transducer's digital readout) corresponding to 1 tsf load. DO NOT APPLY THE
2. Adjust the LDT so the sensor tip has at least 0.3 inches of movement available.
Secure the LDT by tightening the locking screw. Do not overtighten.
Older model: The sensor tip rests squarely on the consolidometer wall . The tip
should travel toward the body of the LDT during the loading phase of the test so
the sensor tip should be almost fully extended.
Newer model: The LDT sensor tip should travel away from the body so the LDT
position should be adjusted so that the sensor tip is near the transducer barrel.
3. Start Gentest, select the 1-D Consolidation Test.
4. Click the Check Transducer Operation tab and observe that the computer is
reading the LDT transducer signal conditioner readout correctly.
5. Select the Run Test tab. Verify that the small readout (black background, green
numbers) shows the correct LDT value.
6. In the Description textbox, enter a description about the load increment for which
Gentest will collect and store the data.
7. In the Save to File textbox, enter a filename about the load increment for which
Gentest will collect and store the data. Use the following pattern for the filename:
where 'g' represents the group number, 's' is the section number, 'x' should
be "L" for loading or "U" for unloading, and the last one or two digits
represents the applied stress in tsf. For example, "G1S1L16", means
Group 1, Section 1, Loading at 16 tsf. "G1S1U4" means Group 1, Section
1, Unloading at 4 tsf.
8. To start the test, simultaneously turn the Load/Unload selector switch to LOAD
and click the Begin button on Gentest to start data collection. The sampling rate
is based on a rate of ten samples per log decade. This means that for each log
period, e.g. 0.1 to 1.0, 1.0 to 10, and so on about ten samples will be collected.
9. Allow the test to run until the change in LDT movement slows to about 0.0002
inch or less between sample intervals.
10. Turn the Load/Unload selector switch to OFF. Click the STOP SAMPLING
button on Gentest to stop data collection and close the data file. NOTE: Do not
leave the Load/Unload selector in the OFF position for more than a few minutes.
To do so would allow the applied load to relax slightly which will introduce data
11. Adjust the regulator for the next load step.
12. Repeat steps 6 through 11 for the specified load and unload values. Be sure to
change the description and filename each time.
13. After the final unload step, remove the compressed air source and let the
consolidometer base drop to its lower position. Retrieve the soil sample and
consolidometer ring and measure the final height of the soil sample.
14. Measure the moisture content of the soil sample.
15. Copy the data files and finish the calculations.