Volume calculation bw two surfaces using a slope

[Openantics]

i am learning how to calculate volumes from sediment removal efforts, and I use two TIN surfaces. i create a surface from the design grade and call it "Datum", and then use the volume tool and compare to the existing surface. however, this project wants a 3:1 slope which is the basis of my question.

 

So I propose:

 

1. create an offset polyline that defines the new TOE of slope (X,Y), make it a feature line and then set its elevation to the desired elevation.

2. then create the "datum" surface from this feature line (and compare it to the condition survey

 

question:

 

1. How do i efficiently determine the position of the new toe and

2. will the volume tool work the same and compare surfaces, even though they have different footprints?

 

thanks!

OA

[BIGAL]

Q1 you determine

 

Q2 Your surfaces need to be contained within each other the design surface needs to fit within the eixtsing, you can not really have a surface outside a surface if you want correct volumes.

[Openantics]

BIGAL - thanks for the quick reply

 

Just to make sure I understand you explanation: My assumption/hope is that C3D will calculate the volume from the trapezoid defined by the current surface, the 3:1 slope, and the design grade (The design surface is marginally smaller because of the slope requirements) however, you are suggesting this is not the case, and the volume tool will generate a rectangle bw the design grade surface and the current, and ignore the slope area.

 

did i interpret your response OK?

 

thanks

OA

[Bill_Myron]

What you can do is use grading tools to create the slope. Create your feature line and assign it elevations. Create a grading tool that is 3:1 slope to surface. add it do your design surface.

 

Compare the 2 surfaces.

[Openantics]

Bill - great advice, the Grading Tools were very straight forward (well, eventually became so!) and I was able to build exactly what I was hoping with relative efficiency. I am unfortunately stuck trying to calculate the volume of my "bowl", that is, what is the cut volume to get from the base surface to the grade.

 

To learn how the Grading Tools work I created a dozen or so points (with varying, believable elevations), and then used the Grade To Elevation criteria (since i know both slope and grade elevation) which resulted in a second surface. I performed several spot checks around the grade and all the trig worked out great. However when I initially created the points for the base surface i wasn't paying attention to my scale, and my resultant surface was about 17 million square feet! obviously this is not consequential for learning how to use the grade tools, however, the Volume Calculations are showing a cut of 4500 cubic yards, which is not the volume of the that needs to be removed.

 

Actually, I think I mis-read your instructions.

[Bill_Myron]

Create a Feature line that wiil be the outer boudary of your pond. When you create it, you can assign elevations from surface. Assign the elevations from your existing surface.

 

Use the grading tools to create your slope. Grade to elevation would work if you know both.

 

Create featurelines from the bottom of your grading objects.

 

 

Add the Feature lines to a new surface. Compare the surfaces.

 

Make sure you set up the units for volume un the drawing settings.

[Openantics]

worked perfect! thank you for your prompt replies and good advice!