The Compression Curve

After you've entered a couple of loading increments the software displays a graph of percent change, void ratio or deformation vs. log10(pressure) in the top-left portion of the screen. You can use this display to adjust the construction lines used to determine preconsolidation pressure (Pc) and the compression index (Cc), change the type of data used on the chart (percent change, void ratio or deformation, and D100 or final dial reading) and modify the chart's scales.

Selecting the Compression Curve Type

The Curve is box at the right of the compression curve box selects between plotting the compression curve as log10(pressure) vs. either void ratio, percent strain or deformation.

Using D100 Values to Plot the Compression Curve

If you've taken time-rate data for some of your loading increments you can have the program use the deformation/void ratio/percent strain value calculated at D100 for these: increments as the point that the compression curve passes through instead of the result at the increments' final dial reading. (Doing so ignores the effects of secondary consolidation on the curve.) Loading increments without time-rate data (those for which a D100 value could not be calculated) would still be marked at the deformation/void ratio/percent strain value produced by their final dial reading.

Construction Line Adjustment

The compression curve chart features two construction lines:

A blue line

This line is used to determine the compression index (Cc). It should be adjusted to be tangent to the steep, linear portion of the compression curve.

A vertical red line

This line is used to determine the Pc value. It should be adjusted left or rightwards until it intersects the point of maximum curvature on the compression curve.

Both construction lines can be adjusted by dragging on their endpoints with the mouse while holding down the left mouse button. If you don't like the result, you can reset the construction line placement by clicking on the Reset Constructions button.