Calculating AS 1289.3.9.1 Cone Liquid Limit test

[BioBloke]

Just a quick question on the calculation of the cone liquid limit test. In the past we have been using natural log on a computer program, NATA has come back saying this i wrong. I have adjusted the program to use Log base 10 but still need a bit of help with the full caculating of the test. Can someone out there please in laymans terms describe how to calculate it on paper and if possible on a excel spreadsheet- I am no scientist and have no idea about log or anything like that just starting to learn it.

Thanks in advance

 

[woofar]

Hi BioBloke,

Sounds like NATA (along with many people in the industry) are getting this confused.

The standard requires the points to be plotted on a chart with linear scale for moisture contents and log base 10 scale for the number of blows. It then specifies to draw a straight line of best fit through the data. Alternatively, through Note 12, it allows you to calculate to that line of best fit.

To calculate a straight line of best fit on a semi log chart you need to use log natural, with the equation y=(c*LN(x))-b .

If you were to use a linear equation, y=m*x-b, through the data, it would plot as a curve and thus not be compliant with the requirement to draw a straight line.

To see how to plot this on an Excel chart, take a look at this website

http://spreadsheetpage.com/index.php/tip/chart_trendline_formulas/

If you need any help getting it going, post back here.

HTH
Michael

 

[woofar]

There is a typo with both those equations. They should be
y=(c*LN(x))+b
and
y=m*x+b