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CBR By Plate Loading Test [UK In-House Method]

CBR By Plate Loading Test [UK In-House Method]

Applies to QESTField, QEST Web App

This article describes how to use the CBR Plate Loading Test worksheet, which is based on an in-house variant of BS 1377-9:1990 Clause 4.1.

Qest ID: 110471

Contents

Overview

The CBR by Plate Loading Test worksheet can be used to determine equivalent CBR values of insitu soils. It is based on the methodology of the Plate Loading Test (BS 1377-9:1990 Clause 4.1) but has been modified to only provide equivalent CBR values.

This article provides information on how the various choices available within the QEST Web App version of this test method provide the required pathways to deal with the variations within the test.

 

 

 

Embedded Tests

General functionality is described in the article Associated Test Results.

The following associated test method is embedded in this worksheet:

 

Data Entry

Preparation

Selection

Action

Default - user input expected, but not required.

“Data Not Supplied” reported as value.

Default - user input expected, but not required.

“Data Not Supplied” reported as value.

Default - No action required

User input is required to satisfy a reporting requirement.

  • The full list of equipment items used on the worksheet can be found below.

  • Data entry requirements for equipment are as follows.

Additional Plate

Selection

Action

Default - only one Plate equipment item available on worksheet.

Adds an additional Plate equipment item to worksheet.

  • A checkbox is provided to allow the use of a second plate.

  • This second plate is sometimes used on top of the test plate to ensure stiffness of the plate. E.g. a 600mm plate could have a 450mm plate on top.

It is assumed by the worksheet that the additional plate will be placed on top of the first plate. Therefore, it is an error if the diameter of the additional plate is larger than that of the first plate.

Plate

  • The diameter and mass of the plate used can be imported from the selected equipment item or entered manually.

  • Area is automatically calculated from the diameter.

Jack

  • The mass of the jack used can be imported from the selected equipment item or entered manually.

Load Cell

A load cell can either provide a direct reading in units of force (e.g. kN), or an indirect reading (e.g. gauge divisions or volts) that requires a conversion factor to convert the reading into force units.

The worksheet provides for the following options:

  • A load cell is expected to be selected from the equipment list but can be left without making a selection.

  • If a load cell is not selected, Factor is available for numeric data entry.

  • If a load cell is selected, a value for Factor will be imported, if available.

  • If a load cell is selected and Factor is blank, the readings will be assumed to be direct readings in kN.

  • If not a direct reading, Factor is still available for numeric data entry.

  • A value of 1 for Factor will also provide the direct reading result.

The mass of the load cell cannot be imported or recorded here. If it is desired to include the mass of the load cell as part of the total load applied, it will need to be included in the calculation of the Combined Mass, below.

Combined Mass

This is the combined mass of any additional equipment used that should be considered as part of an initial load. This may include all spacers used as well as the load cells and/or displacement gauges (if desired).

Apply Equipment Load to Readings

Selection

Action

Default - No action required

The Combined Equipment Load, will be calculated and added to the load that is read from the load cell.

The calculated load of the equipment is based on its mass. Calculated as:

Where g = force due to gravity (9.80665)
mP = mass of plate
mJ = mass of jack
mAdd = Combined Mass

Displacement Gauge

The worksheet provides data recording for three displacement gauges for recording the deformation of soil during testing.

A displacement gauge can either provide a direct reading in mm, or an indirect reading (gauge divisions) that requires a conversion factor to convert the reading into mm.

The worksheet supports the following options:

  • A displacement gauge is expected to be selected from the equipment list but can be left without making a selection.

  • If a displacement gauge is not selected, Factor is available for numeric data entry.

  • If a displacement gauge is selected, a value for Factor will be imported, if available.

  • If a displacement gauge is selected and Factor is blank, the readings will be assumed to be direct readings in mm.

  • If not a direct reading, Factor is still available for numeric data entry.

  • A value of 1 for Factor will also provide the direct reading result.

 

Initial Seating Readings

If the average initial seating reading is not zero, a checkbox is provided to allow the initial reading to be automatically subtracted from the various settlement readings.

Selection

Action

Default - No action required

The average initial seating reading will be subtracted from settlement readings.

 

Load Increments

  • Six load increments are automatically provided on the worksheet. They are identical in their requirements.

  • Increments can be deleted individually or new ones can be added as required.

 

Desired Settlement

  • Default settlement values are provided for each of the initial load increments.

  • The default values can be edited if required.

 

Measured Settlement

  • Each load increment is required to have at least two rows of measurements for settlements.

  • The worksheet initially provides three rows at one minute intervals, with the first row’s Elapsed Time set at “0”.

  • Additional rows may be added through the use of the plus button under the final row of measurements.

  • Any newly added row will get an automatically populated time of one minute more than the previous row.

  • It is possible to modify the Elapsed Time of any row after the first row. New values must be whole numbers.

For example, for longer running tests, 5 minute (or longer) intervals, rather than 1 minute intervals, may be preferred.

  • Any row, after the second row, may be deleted through the use of a delete button next to each row.

 

Laboratory Moisture Content

Selection

Action

Default - No action required

Provides a set of radio buttons to make the results of a laboratory moisture content test (BS 1377-2:1990 Clause 3.2) available.

Default - Makes an embedded laboratory moisture content test (BS 1377-2:1990 Clause 3.2) available.

For further details on using this section, refer to the Moisture Content Test documentation page.

Selecting Import from another test as the determination method allows the results from another test to be made available for data entry, as per Associated Test Results | Import from Another Test.

Selecting External source as the determination method causes the standard fields for an external source, as per Associated Test Results | External Source, to be made available for data entry.

The dry masses in the embedded water contents test will be available for dry mass data entry in the Dry Mass Entry grid.

Equipment List

For equipment to be available for selection in equipment dropdown boxes, the equipment item must first be created in QESTLab’s Equipment List. Refer to the article Creating Equipment.

The following equipment items can be selected on the worksheet:

Worksheet Equipment Item

Equivalent to Qest Equipment Item (Qest ID)

Balance

Balance (30005)

Displacement Gauge

Deflection Gauge (30098)

Jack

Cylinder Jack (30091)

Load Cell

Load Cell (30078)

Plate

Plate (30109)

Some equipment on this worksheet imports equipment properties or calibration values. Ensure that these properties and values are set on the relevant equipment in order to avoid having to enter these values every time.

Results

Results are shown as both graphs and numeric values.

The progress of the test is shown in the following graphs:

  • Settlement vs. Applied Pressure

  • Settlement vs. Time

 

Numeric values are shown for the following, where applicable:

  • Maximum Applied Pressure (kN/m²)

  • Maximum Deformation (mm)

  • Pressure at 1.25 mm Settlement (kN/m²)

  • Modulus of Subgrade Reaction (MN/m²/m)

  • Equivalent CBR (%)

  • Moisture Content (%)

 

Reporting

The results from this worksheet can be reporting on the following test report.

Plate Loading Test Report

As this report is a “child report” of the test, it will be automatically added to the sample when the worksheet is added.

Properties

QESTID

110274

Name

Plate Loading Test Report

Child Of

Test (110471)

 

Reported Values

Field

Unit

Precision

Condition

Field

Unit

Precision

Condition

Pressure at 1.25 mm Settlement

kN/m²

3 s.f.

Always

Modulus of Subgrade Reaction

MN/m²/m

3 s.f.

Always

Equivalent CBR

%

2 s.f.

Always

Moisture Content

%

Nearest 0.1

Conditional

 

Batch Update Support

This worksheet is not supported on the batch update page.

 

Work Progress and Complete Status

The work progress rules noted below are the default set of rules for this test, these may be overwritten by system administrators and therefore behave differently on each QEST Platform instance.

Progress (%)

Criteria

Progress (%)

Criteria

0%

Sample has been created and this test has been added.

75%

All load increments are complete, AND, if a Laboratory Moisture Content Sample has been taken, the Moisture Content drying is incomplete.

100%

Test is complete

 

 

 

 

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