cut and fill volumes for earthworks projects _ grid method, cross section method, earthworks...

12/23/2015 How to Estimate Cut and Fill Volumes for Earthworks Projects | Grid Method, Cross Section Method, Earthworks Software

https://www.kublasoftware.com/knowledgebase/cutandfill/estimatingearthworks.html 1/4

The example project which will be used in thisarticle. This is a (fictional) platform being addedto Alcatraz Island in San Francisco Bay. Theproject includes cut (shaded red) and fill (blue)

Sections are drawn at equal intervals through theproject. For each section line the cut area and thefill area is determined. The volume between twosections is determined as the average area of the

How to Estimate Cut and Fill Volumes forEarthworks Projects

Introduction

On construction projects it is often necessaryto modify the existing ground levels to createplatforms to build on. Accurately calculatingthe volumes of soil that must be removed(cut) or added (fill) to create the final groundlevels is an essential part of the planningprocess.

In this article we are going to describe howthese volumes can be calculated. We will takean example project, and use three of the mostcommon methods to estimate cut and fillvolumes. The three methods that we will gothrough are:

The crosssection methodThe grid methodUsing specialist software

The examples described in this article have been worked through for each of these three methodwith an excel spreadsheet which is available here. You may wish to download this spreadsheet andwork through the examples yourself to aid understanding of the methods described. The spreadsheetalso contains a number of formulas which automate certain aspects of these methods describedbelow, so you may find it useful for implementing these methods on your own project.

CrossSection Method

The cross section method involves plottingcross sections of the existing and proposedlevels at regular intervals across the projectsite. For each of the cross sections, the cutarea and the fill area is determined. Thevolume between each pair of sections isestimated by multiplying the average cut orfill area of the two sections by the distancebetween them. Once these volumes have beencalculated for each pair of sections the totalcut and fill volumes are obtained by addingthem all together.

There areseveral

https://www.kublasoftware.com/knowledge-base/cut-and-fill/calculations.xlsx



two sections multiplied by the distance betweenthem. By adding together the volumes betweenall of the sections the total cut and fill volumesare obtained.

An example calculation forthe volumes between twosections of the exampleshown opposite. Thiscalculation is repeated for allof the sections, and thevalues are added together toget the total cut and fillvolumes.

The average cut or fill depths are determined foreach cell in the grid. From these depths thevolumes of each grid cell can be calculated, andby adding the cell volumes together the total cutand fill volumes are obtained

differentmethodsused todeterminethe areas ofcut and fill once the sections have been plotted. Perhaps thesimplest (but most time consuming) method is to plot the sectionson gridded paper and count the grid cells of the cut and fill areas.Multiplying the cell count by the area represented by each of thegrid cells gives the cut or fill area for the section. Other methodsinclude drawing the sections in CAD and exporting areas orcalculating areas mathematically using the trapezoidal rule. Thespreadsheet included with this article includes formulae whichhave automated the process of calculating section areas using thetrapezoidal rule. This can save a great deal of time if you areusing the cross section method.

The accuracy of the cross section method depends to a largedegree on the distance you choose to set between the sections.Closer sections improve the accuracy of the estimate, but takelonger to estimate. A balance has to be made between accuracy on

the one hand, and speed of generating the estimate on the other.

One of the great advantages of this method is that cross sections are generated in the process. Theseprovide a useful visual summary of the estimation, which present the cut and fill depths across theproject in a very clear way. One of the disadvantages off the method is that it can be extremelylaborious to extract cross sections from the drawing, and to determine the areas of the sections.

Grid Method

The grid method involves drawing a uniformgrid onto a plan of the earthworks project, andtaking off the existing and proposed groundlevels at each node of the grid. With thesevalues the average depth of cut or fill requiredon each cell of the grid is calculated, and thevolume for each cell is obtained bymultiplying the depth by the cell area. Byadding the volumes for each cell together thetotal cut and fill volumes for the project canbe estimated.

The cut or fill depth for each cell is found bysubtracting the average existing level of thecell from the average proposed level. If theresultant depth is positive then this is a fill



An example calculation ofthe volume for one of thegrid cells in the example onthe right

A screen shot from Kubla Cubed, which issoftware for estimating earthworksvolumes. As well as calculating volumesautomatically, the cut and fill depths areshaded.

cell, while a negative value indicates a cut cell. In either case, the volume is calculated bymultiplying the cut of fill depth by the area of the grid cell.

Once the volume has been calculated for each grid cell, all of thecut cells are added together to obtain the total cut volume. Thesame is done for the fill cells to get the total fill volume.

As with the crosssection method, the accuracy of the grid methoddepends upon the size of grid cell which is used. A compromisehas to be made between the accuracy which is required, and thetime which will be taken to produce the estimate.

An advantage of the grid method are that the basis of the estimatecan be fully summarised on the site drawings, which presents avery clear summary of the calculations for others to check. One ofthe disadvantages are no graphical summary is generated for theestimation. Also, like the section method, the grid method is timeconsuming and tedious to implement.

Software

Modern computer software allows earthworksvolumes to be calculated quicker and moreaccurately than either of the two manual methodsdescribed above. There are a number of softwareproducts available for this purpose. These productsvary greatly in terms of complexity and price.

The first stage of producing an estimate usingsoftware is to import the existing terrain. Once thisis done the proposed terrain is drawn, and thesoftware automatically calculates the cut and fillvolumes required.

Different software products use different methodsto generate the estimate. Some will essentiallyapply the grid method described above on a fineresolution grid, whereas others use a triangulationof the terrain to calculate volumes directly. In anycase, the processing power of modern computersmeans that a high level of accuracy can be achieved in a fraction of the time it would take toproduce a manual estimate.

There are many advantages to using software to calculate earthworks volumes, and most companieswhich estimate earthworks on a regular basis will use software to do so. Perhaps the principaladvantage of software is that it is much quicker to produce a more accurate estimate when comparedwith the manual methods described above. Another major advantage is that most modern softwareproducts of this type will have useful display options which can be exported for presentations.Shading cut and fill depths across the project is a particularly useful facility. Rightly or wrongly,people tend to be more impressed by computergenerated images than they are by hand calculations,and trust them more. This is particularly important when presenting your estimates to a client as part



of a tender.

The primary disadvantage of using software to produce estimates is the cost of the software licence,which varies between around $200 to several $1000s. While this cost should be offset against thetime saved by using the software as well as the improved chance of winning bids with computervisualisations, it can nevertheless be a cause of concern for a company that does not need to producemany earthworks estimates.

Summary

There are a number of methods available for estimating cut and fill quantities, three of which aredescribed here. The best method for a particular organisation will depend on a number of factors,including:

The number and complexity of the projects which you need to estimateThe presentational requirements for the estimationThe level of accuracy requiredThe time you have available to produce the estimateThe money you have available to buy software licences

This article is written by an employee of Kubla Ltd. who are the makers of Kubla Cubed, a softwareproduct which is mentioned in this article.

This article, including the images, are the copyright of Kubla Ltd. They may be used by educatorsprovided attribution is given. In all other cases you must contact Kubla before using thiscopyrighted material.

The topographic data used in the example in this article is provided courtesy of the NOAA.

If you have any feedback on this article please email [email protected]

cut and fill volumes for earthworks projects _ grid method, cross section method, earthworks...

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