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List of Modules
Construction Engineering
Part A Construction Plant and Techniques
Module 2 Part A
Earthmoving Operations
Objectives

Differentiate between bank, loose and
compacted soil states

Calculate swell, shrinkage and load factors

Estimate plant production for scrapers
and rollers
Soil may be in 3 states:

bank condition (as it occurs naturally)

loose condition (when it is excavated)

compacted condition (when spread and rolled
)
Soil volumes are measured
as:

bank cubic metres (Bm^{3})

loose cubic metres (Lm^{3})

compacted cubic metres (Cm^{3})
Clearly differentiate between:

volume

measured as cubic metres

mass

measures in tonnes or kilograms

density

measured as mass per cubic metre

units are t/m^{3} or kg/m^{3}
Attention !!!!  Important
Point

Always state the units of measurement
e.g.:

30 cubic metre scraper bowl

scraper tare mass (i.e. empty) 42,000
kg

density of a sample 1650 kg/m^{3}

haul truck that carries 40 tonne of shot
rock

and other units as required
Swell

is calculated as % by which loose volume
is greater when soil is dug

hence if one Bm^{3} swells to
fill a 1.4 m^{3 }bucket, then;

swell equals 40%

the ratio of expanded volume to bank volume
is inversely proportional to densities
Measure densities using
laboratory tests

Example

(in kg/m^{3}), density of a sample
is 1700 bank and 1200 loose; what is the value of swell?

Answer

41.7%, why?

Because 1700 is 41.7% greater than 1200
Why does soil or rock swell
when dug?

because the particles are broken up

particles take more space (especially
shot rock)

more air is admitted
Constant quantity has different
volumes

dig a one m^{3} hole, then:

without losing any material, or

changing the moisture content,

cart it, spread it and compact it

then  in all states the mass has
not changed
Our constant mass (say 1.63
tonne)

was 1 m^{3} in bank

swelled to say 1.35 m^{3} loose
in the scraper

was packed tighter than bank when compacted
with heavy rollers to say 0.86 m^{3}
We defined quantity by mass
 why?

for the given quantity of soil dug from
a hole of stated size

volume will change as it is handled

density will likewise change

the only thing that does not change is
mass

we need to consider the above things when
paying contractors
Payment for earthworks

in the field it is not practical to weigh
everything

if you design a road cutting

you could calculate bank volumes from
drawings

you could get a contractor’s quote per
Bm^{3}

when the job is done it would be simple
to agree the total price
But how to handle progress
pays?

suppose a quote is $8.50 to excavate road
cut in loam as per drawing

the job is 8 months (a large cut)

you have to pay monthly progress pays

the cut is too jagged to measure (survey)
easily

you’ve got a problem !!!!!
Progress payment based on
bank measure

it is traditional to schedule excavation
quantities in bank

hence final payment is Bm^{3}
times rate

progress pays should be based on Bm^{3}
as well

this is why we need to convert loose to
bank
Summary re payment

it is sound practice to monitor excavation
quantities in loose measure

do this by counting scraper (or truck)
loads of known volume when full

convert loose to bank measure before calculating
payment

check total pay against schedule (which
is in bank measure)
Load Factor (I)

to get bank volume, multiply loose volume
by load factor

remember:

Bm^{3} = I * Lm^{3}

bank volume will always be less than loose
volume

therefore Load Factor will always be less
than unity
Shrinkage Factor

to get compacted volume multiply bank
volume by Shrinkage Factor

remember:

Cm^{3} = Shrinkage Factor * Bm^{3}

Shrinkage Factor = bank density / compacted
density

ex: (1680 kg/Bm^{3}; 2085 kg/Cm^{3})
SF = 0.81
Summary  volume conversions

do lab tests on the three states of soil

find densities (bank, loose and compacted)

calculate Load Factor and Shrinkage Factor,
from these densities, or

for office estimating without soil samples,
get figures from tables