estimating for excavation works

8/13/2019 estimating for excavation works

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Topic:

Excavation works estimation

P RINCIPLES OF E STIMATING FOR B UILDING

WORKS 1 (AQS 1193)

1



The nature of the work included in theexcavation section of the bills of quantitiesfalls broadly into seven categories:

1. Site preparation(e.g. removing hedges, clearing undergrowth, removing

trees, removing tree stumps, lifting turf, excavating topsoil)

2. Excavation(e.g. excavating to reduce level, excavating pits, excavatingtrenches)

3. Earthwork support(e.g. sheet piling, diaphragm wall, close timber piling) 2



4. Disposal of water

(surface water and water in the ground)

5. Disposal of excavated materials(e.g. disposal of excavated material on site, disposal ofexcavated material off site, handling and disposal of topsoil)

6. Filling(e.g. filling to excavation, filling to make up levels)

7. Surface treatment(e.g. levelling, compacting bottoms and trimming of sides ofexcavation, and anti-termite treatment) 3



1. Weather conditionsDry or wet conditionsDisposal of water (e.g. diversion or pumping of surface water)

Efficiency of mechanical plant

2. BulkingExcavation is measured ‘net’ in the BQ i.e. the quantity stated

being that ‘in the ground’ before excavation However, after being excavated, soil increases in volume(bulks) to a greater or lesser depending on the nature of thegroundThis bulking factor affects the pricing of the ‘disposal’ itemsmeasured in the BQ

FACTORS AFFECTING THE COST OF EXCAVATION WORKS

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2. Bulking (cont’d)

Average increases in bulk of various types of ground after

excavation (Schedule of Rates JKR, 2011):

Type Per centGravel 10Sand 12 ½Ordinary earth 25Clay 33 1/3Chalk 33 1/3Rock 50

FACTORS AFFECTING THE COST OF EXCAVATION WORKS (CONT ’D)

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3. Type of excavation and volume

Methods of carrying out the work for each type of excavation

The choice is normally to adopt method which results in thefastest rate of progress at the lowest possible cost

Under certain conditions, (such as existing underground services and treeroots) the use of machinery may be restricted and demand hand

digging, or maybe some combination of the two

The use of mechanical plant may not be economical if the totalvolume of excavation is insufficient (i.e. when the cost of transportingthe machinery is too high in relation to the amount of work to be done) 6



4. The nature of the ground

Mechanical plant is capable of excavating in all normal

ground, although the output will vary

Output may be reduced and at great cost for excavatinghard rock

The exact nature of the ground will affect the actualexcavating operations, the need, or otherwise, for anyearthwork support (e.g. a loose sandy soil may require continuous closeboarding or steel sheet piling to support sides of excavation)


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5. Distance to a tip

Location of the tip

Tipping fees (if any)

Transport (type and number of vehicles neededfor disposal to the tip)


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EXAMPLE 1

Build-up the rate for cutting down hedges (per m) including itsdisposal.

Assumptions:

1. The work will be carried out by a gang comprising of three(3) general workers for cutting down the hedges includinggrubbing up the roots by hand.

2. The gang can clear and load 10 meters of hedges in 1 hour.

3. A lorry is required for removing the materials to a tip nearby.4. General worker: RM 50.00 per day.

5. All-in-rate for lorry and driver is RM 400 per day.

Make other reasonable assumptions where necessary.10



Answer:

Hourly cost RMA gang of worker = 3 x RM 50 ÷ 8 = 18.75

Lorry and driver = RM 400 ÷ 8 = 50.0068.75

Total hedges per hour = 10 m

Rate per meter

1 hour : 10 m = RM 68.751 m = RM 68.75 ÷ 10 = 6.88

ADD overhead and profit say = 1.03Rate (per m) = 7.91

15%

EXAMPLE 1 ( CONT ’D)

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EXAMPLE 2

Build up the rate for excavating to reduce level (per m3)

Assumptions:

1. The excavation work will be carried by excavator with a

labour as attendance.2. The output of the excavator including digging and loading

directly into a waiting lorry is 20m 3 per hour.

3. All-in-rate for excavator and driver is RM 75 per hour.

4. Labour rate for attendance : RM 50.00 per day

Make other reasonable assumptions where necessary.

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EXAMPLE 2 ( CONT ’D) Answer:

Hourly cost All-in-rate for excavator and driver = RM 75Labour (as attendance) = RM 50 ÷ 8 = RM 6.25

RM 81.25

Total excavation per hour = 20 m3

Rate per m 3

1 hour : 20 m 3 = RM 81.25

1 m 3 = RM 81.25 x 1

= RM 4.06

Add overhead and profit say 15% = RM 0.61

Rate (per m 3) = RM 4.67

20

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EXAMPLE 3

Build up the rate for excavating trenches to receivefoundations starting from reduced level maximum depth notexceeding 0.25 meter (per m 3)

Assumptions:1. The excavation work will be carried by excavator with a

labour as attendance.

2. The output of the excavator including digging and loading

directly into a waiting lorry is 17m 3 per hour.3. All-in-rate for excavator and driver is RM 75 per hour.


Make other reasonable assumptions where necessary. 14



EXAMPLE 3 ( CONT ’D) Answer:

Hourly cost All-in-rate for excavator and driver = RM 75Labour (as attendance) = RM 50 ÷ 8 = RM 6.25

RM 81.25

Total excavation per hour = 17m 3

Rate per m 3

1 hour : 17 m 3 = RM 81.25

1 m 3= RM 81.25 x 1

= RM 4.78

Add overhead and profit say 15% = RM 0.72


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REMOVAL OF EXCAVATED MATERIAL FROM SITE

The optimum level of efficiency will be achieved when the number ofvehicles assigned for disposal is sufficient for the excavator to beable to work continuously.

Ideally, an empty vehicle drawing in through the site gates as aprevious one becomes fully loaded and is about to leave the site forthe tip.

In practice, this situation is almost impossible to achieve.

However, in this theory, the optimum number of vehicles can becalculated as:Number of vehicles = time taken to load + total journey time and tipping

time taken to load 16



Solution

1) Lorry capacity

1.60 tonnes = 1 m 3

10 tonnes = 1 x 101.60

= 6.25 m 3

Allow for bulking of earth (25%)

125% = 6.25 m 3

100% = 6.25 x 100125

= 5 m 3

2) Time taken to load 5m 3 of earth

10 m 3 = 60 mins5 m 3 = 60 x 5

10

= 30 mins

3) Nos. of lorry required

Outward journey 20 minutes

Return journey 15 minutesTotal journey time 35 minutes

Add tipping time 5 minutes

Total journey and tipping time 40 minutes

Nos.of lorries required = time taken to load + total journey time + tipping time

time taken to load

= (30 + 40)

30

= 2.33

Say, 3 lorries

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Solution (cont’d)

4) Total hourly cost of operation

All-in rate for lorry and driver is RM 75 per hour

3 lorries = 3 x RM 75= RM 225

5) Cost of removal (per m 3)

Quantity of excavated material per hour is 10 m 3

1 hour, 10 m 3 = RM 225

1 m 3 = RM 225

10

= RM 22.50

Add overhead and profit, say 10% = RM 2.25


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TUTORIAL Q UESTIONS

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QUESTION 1

A specific size of backhoe was selected to performexcavation works. Estimate the equipment (backhoe) cost(per m 3) for the excavation works.

Assumption:

1. The cost of the backhoe (rental) is RM 600 per day (8hours).

2. The hourly production rate of the backhoe was 12m 3.Make other reasonable assumptions where necessary.

21



QUESTION 2

Build-up the rate for cutting down hedges (per m) including itsdisposal.

Assumptions:

1. The work will be carried out by a gang comprising of two (2)general workers for cutting down the hedges includinggrubbing up the roots by hand.

2. The gang can clear and load 9 meters of hedges in 1 hour.

3. A lorry is required for removing the materials to a tip nearby.4. General worker: RM 55.00 per day.

5. All-in-rate for lorry and driver is RM 450 per day.

Make other reasonable assumptions where necessary.22



QUESTION 3

Build up the rate for excavating to reduce level (per m3)

Assumptions:

1. The excavation work will be carried by excavator with a

labour as attendance.2. The output of the excavator including digging and loading

directly into a waiting lorry is 15m 3 per hour.

3. All-in-rate for excavator and driver is RM 550 per day.



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QUESTION 4

Build up the rate for excavating trenches to receivefoundations starting from reduced level maximum depth notexceeding 0.25 meter (per m 3)

Assumptions:1. The excavation work will be carried by excavator with a

labour as attendance.

2. The output of the excavator including digging and loading

directly into a waiting lorry is 20m3 per hour.

3. All-in-rate for excavator and driver is RM 80 per hour.


Make other reasonable assumptions where necessary. 24



QUESTION 5

Build up the rate for extra over trench excavation forexcavating in rock (provisional) (per m 3)

Assumptions:

1. The work will be carried out by a gang comprising of three(3) general workers for excavating in rock by hand.

2. The gang can excavate 1m 3 rock in 4.50 hours.

3. General worker: RM 55.00 per day.


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Build up the rate for removal of unsuitable excavatedmaterial (per m 3) from site.

Assumptions:

1. The excavator is loading directly into 7-tonne lorries.

2. All-in rate for lorry and driver is RM 60 per hour.3. Ordinary earth weigh 1.60 tonnes per m 3.

4. The bulking of earth is 25 per cent.

5. Excavator output is assumed at 9m 3 per hour.

6. Journey time: Outward journey, say 45 minutes.

Tipping time, say 10 minutes.

Return time, say 35 minutes.


QUESTION 6

26



Build up the rate for filling to excavation with imported earth(per m 3).

Assumptions:

1. The cost of imported earth delivered to site is RM 27 per m 3

2. Allow 25% additional cost of material for compacting andwastage.

3. The work will be carried out by a gang comprising of two (2)general workers for spreading, leveling and compacting theearth.

4. The gang can spread, level and compact 1m 3 earth in 0.75hour.

5. General worker: RM 55.00 per day.

Make other reasonable assumptions where necessary

QUESTION 7

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estimating for excavation works

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