Volumes By Triangulation is a volume method that compares two triangulation networks. This method is different from the grid based volume routines (Volumes By Layer, One Surface Volumes, Two Surface Volumes, Stockpile Volumes, etc.) and the cross section volume routine (Calculate Section Volume). Volumes by Triangulation calculates faster in most cases than the other methods, and it is the most accurate because it uses true TIN to TIN prismoidal volumes. This added accuracy in general is very small. The grid resolution is usually sufficient to model the surface for the grid based volumes. The Volume By Triangulation accuracy applies well when there is a feature like a 5 foot wide ditch. Then the grid resolution would need to be less than 5 feet to model the ditch which might be difficult on a large site.
The disadvantage to this routine is that it lacks the output options that help the analysis of the volume such as Difference Contours. Also Volumes by Triangulation does no extrapolation and stops calculating volume at the perimeter of the smaller of the two triangulation networks. Volumes By Triangulation is better when used with point data instead of contour data because contour data requires triangulating all the contour polylines as breaklines which creates a large triangulation network and is slower.
The triangulation networks to compare are defined in .tin or .flt files that are created by Triangulate & Contour with the Write Triangulation File option. Note that while both file formats are supported, the newer binary triangulation file format (.tin) is twice as fast to load and save, and half the size, of the .flt triangulation file format. For this reason, the .tin file format is recommended. Before using this command, run Triangulate & Contour twice to create an triangulation (.TIN or .FLT) file for each surface. The volume calculation is limited by either the extent of the triangulation networks or by an inclusion/exclusion perimeter(s). These perimeters must be closed polylines.
Output data includes area, tons by density, average thickness, shrink and swell, ratio, and total volume.
An optional aspect of the Volumes by Triangulation routine is the ability to supply either a Cut "Swell" Factor and/or a Fill "Shrink" Factor to the results of the volume calculation. Having a solid understanding on the ramifications of each factor is important for determining how (and when) the values should be used for earthwork considerations.
The factors are commonly expressed as decimal differences from
the "factor neutral" value of 1.00. In most cases, surface models
are representations of what currently exists in the field or what
is desired to exist after construction. Consider the following
examples:
Excavating a
Pit
Suppose you are given the task of designing a below ground storage
pit. Based on your design surface model, the amount of Cut has been
determined to be 1,000
C.Y.Cut Swell Factor > 1
(example 1.15)
Supplying a Cut Swell Factor greater than 1 would usually be taken
to mean "How much volume will my 1,000 C.Y. of material occupy when
it comes out of the ground?" With a 15% swell factor (1.15)
applied, the 1000 C.Y. of excavated material would now occupy 1,150
C.Y. of space.
Cut Swell Factor < 1 (example
0.85)
Supplying a Cut Swell Factor less than 1 would usually be taken to
mean "How much volume will 1,000 C.Y. of material occupy in this
hole when it has been compacted?" With a 15% compaction factor
(0.85) applied, the 1000 C.Y. of material getting compacted would
now occupy 850 C.Y. of the hole space.
Working with a
Stockpile
Suppose you have a stockpile of material that is suitable for
building purposes. Based on your design surface model, the amount
of material has been determined to be 1,000 C.Y.
Fill Shrink Factor > 1 (example
1.10)
Supplying a Fill Shrink Factor greater than 1 (see NOTE below)
would usually be taken to mean "How much volume would this 1,000
C.Y. of material occupy if it were picked up and deposited
elsewhere?" With a 10% swell factor (1.10) applied, the 1000 C.Y.
of stockpile material would occupy 1100 C.Y. of space.
Fill Shrink Factor < 1 (example
0.90)
Supplying a Fill Shrink Factor less than 1 would usually be taken
to mean "How much volume will 1,000 C.Y. of stockpile material
occupy when it has been compacted?" With a 10% compaction factor
(0.90) applied, the 1000 C.Y. of material getting compacted would
now occupy 900 C.Y. of the hole space.
Select EXISTING Surface Triangulation File Choose an
.flt or .tin file
Select FINAL Surface Triangulation File Choose an .flt
or .tin file
Select Inclusion polylines.
Select objects: select objects that form a perimeter
around the area of study
Select Exclusion polylines.
Select objects: select objects that form an exclusion
area within the area of study
Cut Swell Factor:
Supply an appropriate factor by which the
calculated Cut volume should be
multiplied.
Pulldown Menu Location(s):
Civil > Surface > Volumes by
Triangulation, Survey > Surface > Volumes by
Triangulation
Keyboard Command: trivol
Prerequisite: Two .flt or .tin files