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Earthworks quantities (GRD Part 3 Chpt. 8)

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• Process of excavating existing land to a suitable level so that pavement construction can commence

• Earthworks normally consist of both cuts and fills• Aim is to minimise earthwork quantities• Seek to achieve a balance in cut and fill quantities

Earthworks

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• On urban projects or rural works on flat terrain difficult to obtain a balance

• In rolling terrain earthwork balance is more readily achieved after making adjustments for:– stripping– depth of top soil removed– removal of unsuitable road construction materials– use of materials for pavement– photogrammetric bias– compaction and bulking factors

• Information to provide the adjustment factors can be obtained from geotechnical investigations

Earthwork balance

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• E Easy digging - loose free running soils e.g. sands, fine gravels.

• M Medium - denser cohesive soils e.g. clayey gravel, low PI clays

• M-H Medium to hard – e.g. broken rock, wet heavy clay, gravel with boulders

• H Hard - material requiring blasting and hard high PI clays

Excavation of material – ease of digging

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Excavation increases the volume of material. It is therefore necessary to use a bulking factor to determine the volume of material that will be created by excavation.

Bulking factor is defined as:

Bulking factor = volume after excavation/volume before excavation

Shrinkage factor is defined for the compaction of a soil at its final destination:

Shrinkage factor = volume after compaction/volume before excavation

Bulking/compaction of excavated material

6Bulking and shrinkage factors (Part 7 Table 4.1)

Material Loose volumeCompacted

volume

Solid rock 1.60 1.25

75%/25% rock/soil mixture

1.45 1.20

50%/50% rock/soilmixture

1.35 1.10

25%/75% rock/soil mixture

1.25 1.05

Granitic sand and gravel

1.10 0.90

Dune sand 1.15 0.95

Sandy clay 1.25 0.93

Expansive clay (basaltic)

1.45 0.90

Topsoil 1.45 0.95

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• Using average end area method

Estimating earthwork quantities

natural surface

natural surface

A1

A2

Volume = (A1+A2)* L

2

L

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• For a cut or fill on horizontal ground

Earthwork calculations

Assuming a cut such as the one above, the cross sectional area is given by:

Area = h.2b + 2nh²/2 = h(2b + n.h)

Note: Actual volumes may vary from estimates by 5 – 10%

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• For a cut or fill on sloping ground

Earthworks calculations

Assuming a cut such as the one above, the cross-sectional area is found firstly by calculating WL and WG:

WL = S(b+nh)/(S+n)WG = S(b+nh)/(S-n)

Area = ½(h + b/n)(WL + WG) - b²/n

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Mass haul diagram

-100,000.0

-80,000.0

-60,000.0

-40,000.0

-20,000.0

0.0

20,000.0

40,000.0

60,000.0

0.0 300.0 600.0 900.0 1,200.0 1,500.0 1,800.0

Chainage

Vo

lum

es

m3

Mass haul

Mass haul diagrams

The mass haul diagram is simply a plot of cumulative volume against chainage. Areas below the line represent net fill and areas above the line represent net waste. The following points are worth noting:

– a rising curve indicates an increasing volume (cut)

– a maximum point on the curve represents the end of a cut

– a falling curve represents a decreasing volume (fill)

– a minimum point represents the end of a fill

– areas at the end of the diagram represent a waste or a deficit.

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Earthwork Balance

-10.0

-5.0

0.0

5.0

10.015.0

20.0

25.0

30.0

35.0

40.0

0.0 200.0 400.0 600.0 800.0 1,000.0 1,200.0 1,400.0 1,600.0

Chainage

Le

ve

ls

Ground levelRoad level

Mass haul diagram example

Mass haul diagram

-100,000.0

-80,000.0

-60,000.0

-40,000.0

-20,000.0

0.0

20,000.0

40,000.0

60,000.0

0.0 300.0 600.0 900.0 1,200.0 1,500.0 1,800.0

Chainage

Volu

mes

m3

Mass haul

12Questions?

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QUESTIONS?

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