Soil Testing – Automatic Consolidation Testing Part 1 – System and Test Setup

Consolidation Testing – Part 1 will describe the initial setup for a Consolidation Test involving the system setup and test creation using an Automatic CONSolidation (ACONS) Instrument.

Consolidation testing (or Oedometer test) is one of the most common tests performed to determine the suitability of the ground on which a structure is to be built. This post will give an overview of VJ Tech hardware and software to perform Consolidation Testing including how to connect everything up, configure the test, control it, see the data and get your results out at the end.

Hardware & Software Required:

The instruments required for Consolidation Testing are the ACONS Load Frame (with integrated 15kN Load Cell), a Consolidation Cell suitable for the sample size to be tested and a junction box to connect the Digital Dial Gauge Displacement Transducer to the computer. If an LSCT Transducer is being used, it can be connected directly to the back of the ACONS. A compressed air supply is also required.

VJ Tech’s primary software module for Consolidation Testing is csOedo and the entire test can easily be automated.

Connections:

The Displacement Transducer is positioned using the necessary bracket and adaptor and then the tubing connected from the compressed air supply. The following schematic illustrates the electrical and pneumatic connections when using a Digital Dial Gauge. If an LSCT Transducer is being used, the junction box will not be required.

Once the system has been correctly connected Clisp Studio should then be started and the Instrument(s) added using the menus. It should be noted that all instruments supplied by VJ Tech are factory calibrated, but it is still important to check that calibration is still correct periodically.

Sample Preparation:

The sample is prepared to the correct cylindrical dimensions (using a sample trimmer if necessary) and then placed in the Consolidation Cell. The Load Cell is then lowered onto the top of the Consolidation Cell.

Test Creation:

When carrying out consolidation testing using csOedo, right click on the sample and select csOedo from the CRS, Consolidation and Permeability Tests pull-down menu. There are a number of International Geotechnical Standards available, select the required standard, name the test and then a wizard will be displayed to help to guide you through the test.

If a swelling test is not required, un-tick the ‘Include a Swelling stage’ checkbox. If the complete sequence is to be automated (i.e. no manual intervention), tick the ‘Automate the complete sequence’ checkbox.

The first step is to select the Instrument and Channel to be used for the Transducer and Controller Inputs required for the test setup. This is done using pull down menus from the Hardware setup (Step 1) window selected from the wizard, which lists the relevant Transducer and Controller Instruments and Channels as shown below.

The second step is to set up the Specimen Details (Step 2), again selectable from the wizard. When the specimen's initial Height, Diameter, Weight and Swelling are input, the related calculations for area, volume and bulk density will adjust accordingly. Select the Moisture tab to input the specimen's initial wet and dry weight and the tin weight, the related calculations for moisture, dry density voids ratio and degree of saturation are calculated automatically as shown below.

If a Swelling Stage is required, Click on the 'Swelling Test' icon (Step 3) in the ’Assistant’ window to display the ‘Swelling’ setup window shown below.

Select one of two ‘Data Starting Conditions’, either based on a time delay or on a specified swelling load, the rate at which data is to be logged and specify up to 3 ‘Stopping Conditions’ from the following:

1) If the specimen stress has changed by less than a certain amount within a specified interval.

2) If the settlement has changed by a specified amount within a given time period.

3) If a specified time has been exceeded.

For safety reasons, a maximum swelling pressure should be specified. If an e-mail is required when the Consolidation testing is complete tick the ‘Send email when completed’ selection box (e-mail must have been enabled in the customisation menu).

Finally, click on the Step 4 icon to set up the test Conditions. Select the ‘Increments’ tab and us the ‘Add’ and ‘Delete’ buttons to adjust the number of Consolidation Increments (or decrements) for your requirements. An example is shown below.

Click on the ‘Criteria’ tab to return to the Consolidation testing setup. The ‘Starting Conditions, ‘Data Logging’ rates and ‘Stop Criteria’ need to be set up for each Consolidation Increment (or decrement) that has been entered. One of three ‘Starting Conditions’ needs to be selected for each Consolidation increment (or decrement), either:

1) When a specified time has been exceeded.

2) When the Vertical stress is within a specified band of the target stress level.

3) When the Vertical settlement has changed by a specified amount.

A checkbox can be ticked to ensure a reading is taken at the very start of the increment.

One of three ‘Data Logging Rates’ needs to be selected for each Consolidation increment (or decrement), either:

1) At a specified data rate.

2) Using a pre-defined logging table or a User defined table specified using the ‘Edit’ button.

3) When the Vertical settlement has changed by a specified amount.

UP TO two ‘Stop Criteria’ can be selected for each Consolidation increment:

1) When the settlement changes by a specified amount within a given period.

2) When a maximum entered time has been exceeded.

The technician can also tick a checkbox to request that Vertical Stress be maintained at a specified level in order to prevent the sample from swelling. An e-mail may be requested upon completion if required (as long as the e-mail option has been setup).

The values entered in this section will be reflected in the Test Plan which governs the execution of the test procedure. The following example shows selection of the first increment; please remember that ALL increments have to be set up.

Part 2 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.