Tuesday, 24 April 2012

Windfarm Access Roads - Volumes Calculations

When calculating the earthworks volumes for the site there will usually be a number of subsurface layers that we will need to take into account. For example a typical site might consist of 3 layers; a peat layer overlying an intermediate layer of reusable material under which there is a rock layer. All of these will probably be intersected by your proposed access road surface at some point and volumes calculations will involve comparisons between two or more of these surfaces.
In calculating the volumes we will look at two methods; Volume Surfaces and Materials from Cross Sections. While using volume surfaces is a great method for calculating volumes I have found that using materials is more flexible. You define a material as the volume you wish to calculate. For example I might create a material called Volume of Rock Cut and define it using the access road proposed surface and the top of rock surface. Materials are particularly useful where you have more than two surfaces bounding your desired volume. It also allows you to generate a cumulative volumes report for each material on a per cross section basis.

Volumes to be Calculated:

1.   Volume of Peat to be Stripped from Site
This is straight forward. Create a volume surface using the existing ground surface as the base and bottom of peat surface as the comparison. Extract the border from your final corridor top surface to give you a polyline representing the extents of the works. Add this polyline to the volume surface as a boundary (This can be added from the Toolspace).

2.   Volume Of Rock Cut
This is the volume bounded by the top of rock and the access road proposed surfaces. Create a material (Sections menu<Compute Materials) using these two surfaces. Set the Quantity Type and the Conditions as below:
The conditions in this case are telling Civil 3D that we want everything above the formation surface and below the rock surface.

3.   Volume of Rock Fill
This is the volume bounded by the bottom of peat and access road proposed surfaces. Create a material using these materials. Conditions are everything Below the proposed surface and Above the peat surface. Quantity Type is Fill. See completed material below.
Volume Cut/Fill Rock Materials on Cross Sections:

4.   Volume Reusable Material Cut
Between the bottom of peat and top of rock layers on this project there was a layer of material that was deemed competent enough to be reused as fill elsewhere. The volume required in this case is bounded by three surfaces; Proposed surface, top of rock and bottom of peat.

Create another material as before adding in the three surfaces. The Conditions are everything below bottom of peat and above the other two surfaces, Quantity Type is Cut. See below:
Volume Reusable Material on Cross Sections:
Once you have your materials calculated you can generate a volume report – Sections menu<Generate Volume Report and select the report template you wish to use. This provides an easy to read cumulative volume report for each of the cross sections.

No comments:

Post a Comment