Atterberg Analysis (lab testing)

 

ATTERBERG table (none are Modifiable or have an associated Lookup):

Field Name

Description

PointID

 

Depth

 

Liquid_Limit

Will be calculated from the readings data, if the data exist.

Plastic_Limit

Will be calculated from the readings data, if the data exist.

Organic

Affects ASTM classification

 

ATTB READINGS table (none are Modifiable or have an associated Lookup):

Field Name

Description

PointID

 

Depth

 

Reading

Arbitrary Counter

WC_Wt_Wet

Water Content Determination: Weight Wet Soil + Tare, any consistent units

WC_Wt_Dry

Water Content Determination: Weight Dry Soil + Tare, any consistent units

WC_Wt_Tare

Water Content Determination: Weight Tare, any consistent units

Water_Content

%; Will be calculated if the data exists.

Number_Blows

Liquid Limit: Casagrande cup method. Leave blank for plastic limit determination readings.

Cone_Pen_Initial

mm; Liquid Limit: Cone Penetrometer Method. Leave blank for plastic limit determination readings.

Cone_Pen_Final

mm; Liquid Limit: Cone Penetrometer Method. Leave blank for plastic limit determination readings.

 

Liquid Limits and Plastic limits can be input into those fields in the parent record. If readings data exist, Liquid and Plastic limits will be calculated.

You can have as many Liquid and Plastic limits readings as desired. The program distinguishes between the two types by the Number_Blows and Cone_Pen_xxx fields. If these have values, then the reading is taken as a Liquid Limit reading, otherwise it is assumed to be a Plastic Limit reading.

You can use the Casagrande rotating cup method of Liquid Limit determination by filling in values for the Number_Blows field. Use the cone penetrometer method by filling in Cone_Pen_Initial and _Final fields.

You are allowed to input just the Liquid Limit points or just the Plastic Limit points in the lower grid. The program automatically inserts a "0" into the upper grid for the item that is not input in the lower grid, for example, if Liquid Limit points are input in the lower grid but no Plastic Limit points, the calculated Liquid Limit will be inserted in the upper grid and "0" will be inserted for the Plastic Limit.

This is to accommodate ASTM specification D 4318 (Liquid Limit, Plastic Limit, and Plasticity Index of Soils), section 20.1.4 which states in part: "If the Liquid Limit or Plastic Limit tests could not be performed, or if the Plastic Limit is equal to or greater than the Liquid Limits, report the soil as nonplastic, NP."

In southeastern Alaska there are soils where the Liquid Limit test can be performed and yields values in the range of 20 but the Plastic Limit test cannot be run. Your first reaction might be to input a value of "0" and expect the ASTM functions to classify such a soil as a clay since the PI would be 20. Section 20.1.4 says otherwise, that is, since the Plastic Limit test could not be run the soil is non-plastic and therefore a silt. The ASTM Classification function in gINT accommodates this condition.

Calculations:

Casagrande Method Liquid Limit

If only one reading exists, the ASTM D4318 one point method is used. If two readings, two one-point method calculations are averaged. If three or more, a best fit line through a graph of logarithm of blows vs. arithmetic water contents is used and the Liquid Limit is defined as the water content at 25 blows on this best fit line.

Cone Penetrometer Liquid Limit

The  liquid limit determination allows for the one point method as per BSI 1377. This requires that the penetration be between 15 and 25 millimeters, inclusive. If there are two liquid limit determinations, two one point calculations are run and the average is used as the liquid limit. With three or more liquid limit determinations the liquid limit is determined as the moisture content at a penetration of 20 millimeters as taken from a best fit straight line through a graph of arithmetic penetration vs. arithmetic water contents

Plastic Limit

Only one reading is required. The average of all the Plastic Limit readings is used as the final Plastic Limit value.