Missing CBR Design Value on Reports
There's several reasons why the "CBR at x% Design" box will be missing from CBR chart reports:
- You have not entered a Maximum Dry Density, or the value that you entered is not correct: Select "Window" > "Sample Info.", then check the "Maximum Dry Density" field to make sure that you've entered a valid density. (The units for this value are those specified by the "Density units" selection on the program's configuration dialog -- "Options" > "CBR Setup".)
- The design density percentage that you've chosen is incorrect: Check the "Max. Dens. Percent" selection in the left-hand toolbar to make sure that you've chosen the correct design percentage.
- The calculated design density falls outside the range of densities
that you tested: Take your maximum dry density value and multiply
by your design percentage, then divide by 100. Does the value you calculated
fall within the range of densities for the samples that you tested?
If it is, then the program will not calculate your design CBR. (A quick
way to check this is to select "Window" > "CBR Curve"
and look to see if your calculated design density is to the left of
the first curve point, or to the right of the last curve point.)
Our rationale for not calculating the CBR for a point that does not fall within the range of the CBR vs. density curve is that the program has no basis for deciding how the curve acts outside the range of the soil that you actually tested. If you think you can decide for the program how the curve shape can extend to either side of the existing testing points, you can use the program's shaping point facility to extend the range of the curve -- select "Curve" > "Add Shaping Point", then move the mouse to where you think the curve should extend, then click the left mouse button.