Viewing and Modifying the Moisture-Density Curve

Plot:

Determines whether the program plots the curve and test points, the curve only, or the test points only. See this section for further details.

Data-averaging curve

Selecting this option produces a smoother curve, but one that doesn't necessarily pass directly through every test point. Refer to this section for further details.

Similar Curves

Clicking this button causes the program to display moisture-density curves from the same project that have maximum dry density/optimum moisture contents close to the current test's maximum dry density and optimum moisture.

• The button is disabled for one-point tests because the program always shows the similar curves for these tests.

"+" and "-" buttons

Clicking on the "-" button increases the moisture and density scale steps (i.e., the chart is zoomed out), while the "+" button decreases the scale steps (i.e., the chart is zoomed in).

To reshape the curve by adding a shaping point:

The shape of the curve may be adjusted by forcing it to pass through a new point. To do this, select Curve then either Shape Curve (if the window shows a single curve) or Shape Corrected Curve or Shape Uncorrected Curve. Next, move the mouse cursor to the location desired for the curve to pass through, then click the left mouse button. The new point will be marked with a "+", which will not be shown on charts included on hardcopy reports.

To remove a shaping point:

Move the mouse cursor over the shaping point, then click the right mouse button and select Delete this Point from the popup menu.

You can also remove all shaping points by selecting Curve > Delete All Shaping Points.

To move a shaping point:

Once you've placed a shaping point you can move it: Place the mouse cursor over the shaping point, click the right mouse button and select Move this Point. Move the mouse cursor to the desired position for the shaping point then click the left mouse button.

• Shaping points cannot be added to data-averaged curves.

To move a test point:

Move the cursor over the test point then click the right mouse button and select Move this Point, then move the mouse cursor to the desired position for the test point then click the left mouse button.

• Note that the test point itself will continue to be shown in its original position, although the compaction curve will no longer pass through it. If you do not want to have the test point shown on the chart, use the procedure covered below.

To omit a test point from the chart:

Sometimes it may be necessary to remove a test point from the compaction chart because the testing data for the point is obviously not correct. To remove the point from the chart, move the mouse cursor over the bad point, right-click and select Include this Point on Curve to uncheck the option. (The point will still show up on the chart review window and on data summary reports, but it will not appear on chart reports.)

You can omit the curve from chart reports:

If your compaction curve cannot be modified into an acceptable shape you can choose to have LabSuite plot just the test points, omitting the curve. (You can then draw the curve by hand on the hardcopy report.) To omit the curve, select Curve > Plot Test Points Only. Note that this option also causes the calculated maximum dry density and optimum moisture values to be omitted from the report (you'll need to work out your own values based upon the curve you've hand-drawn).

You can omit the test points from chart reports:

Selecting Curve > Plot Curve Only omits the test points from the chart, leaving only the curve.

The compaction curve can be plotted using a data-averaging curve model:

If your test data doesn't form a smooth compaction curve, Curve > Data-Averaging Curve can be used to draw a compaction curve formed using a least-squares linear regression mathematical model. In simplified terms, these curves average the distance between the curve and each test point, making for a smoother curve, but one that may not actually pass directly through each test point. As an example, the following figure shows a compaction curve that's somewhat oddly-shaped because the points on the wet side of the curve do not make a smooth curve:

Note that the second curve does not exactly pass through each test point: For the top two points on the wet side of optimum moisture, the curve essentially "splits the difference" between the two points by passing on the right side of one and on the left side of the second. The resulting curve appears smoother.

• The data-averaging curve model is not a panacea for cleaning up all misshapen curves. Some curves may benefit more by moving test points, removing bad data points from the curve, or by adding curve shaping points. Additionally, curves with five or six test points do not tend to plot very well using the data-averaging approach.