1. Estimation 1
Lesson 4 - Excavation

2. Excavation
Excavation is the biggest unknown element in construction and therefore has a high risk for additional costs in terms of variations.
Estimating the cost of excavation is highly specialized and therefore this lesson will only touch on the basic understanding

3. Excavation

4. Excavation

5. Excavation Ability to read plans and specifications
Understanding of surveying and civil engineering terminology
Understanding of environmental and legal requirements
Ability to estimate quantities based on m3 i.e cut and fill

6. Excavation The estimate is separated into two types of quantities
General quantities – work where you can use motorised equipment such as scrapers, hoes and loaders and it is based on production rates
Special quantities – ie anything that reduces production rates and requires extra care
Rock excavation
Excavation around sewer pipes, existing buildings

7. Excavation Quantities in excavation are mainly m3
The cost of excavation is on labour and equipment (cost/hour) needed to complete the work i.e It is based on the (volume) m3 of material moved
Programme of works- time is important factor and is a huge consideration for the type of equipment you are going to use

8. Excavation
The most expensive equipment (cost/hr) is the most productive. However the machine with the largest capacity isn't always the best to use
Good equipment selection will help reduce costs

9. Excavation Considerations when estimating excavation Desk top study
Site visit

10. Excavation – Desk top study
Review plans and specifications
Existing utilities lines
How accurate
Phone the companies to locate the lines for you. Need to give them advanced notice
Check what permits are required
Resource consent
Aborist report/permits
Sediment control

11. Excavation Review plans and specifications
Public records might give additional information
Soil conditions
Water problems
Abandoned utility lines

12. Excavation Setting out carried out by the engineer Under cutting
If not cost to get the site surveyed
Under cutting
Might need to remove dirt from below the existing finishing line if in rock
Underground services – may have to cut the trench deeper for the bedding of the pipe

13. Excavation Cut and fill
Consider is there enough fill on site from the spoil heaps.
If not where will you transport it from ?
Is it available?? – Snapper rock subdivision
Conversely will you have to transport excess fill off site
If so.. Where will you transfer it to?
How much are tipping fees?

14. Excavation Top soil requirements Special excavation
Is there enough on site ?
Can you keep it in spoil heaps on site ?
Will you have to bring additional material in?
Special excavation
Rock ? Hire of specialist equipment
Removal of existing structures

15. Excavation Review utility lines –
Not only new lines but connection to existing
Review drainage, new roads, parking lots and consider the base, sub bases for estimating
Review the building/basement structure for estimating

16. Excavation – site visit
Accessibility
Location of the site –
How remote ? Are the roads undeveloped or narrow ? Can you get the equipment you want on site? Bream Bay Sub division
If you are having to bring the dirt out – what is the best route to the tipping site? – Can the trucks use that route

17. Excavation
If the surrounding area is heavy traffic. Will you require additional traffic management ? Do you require a wheel wash facility (Kensington Park)
Noise restriction – if the site is in a built up area are there noise restrictions
Are there any bridge weight restrictions in the area which will affect what equipment you use

18. Excavation Degree of Difficulty
Are there steep slopes on site that need different equipment – slopes that are steeper than 1 in 3 will need track machines which are slower.
Other considerations are buildings, trees, underground services, overhead electricity lines.

19. Excavation Surface Conditions
Drainage – what happens to the water across the site. It can’t flow into the existing roads
Sediment control is important
Permit/consents are required
Silt ponds
Sand bags
Protect existing waterways

20. Excavation Surface Conditions Trees Consents are required
Do you have to protect trees
If they are to be removed – who will take them? Can they be sold for firewood? Are you allowed burning on site?

21. Excavation Sub surface Conditions Geotech reports
These reports are expensive. They show the soil conditions however the bore readings taken maybe limited - Ibis Hamiliton, Snow planet
If you are working below the water table level you may have to pump the water… Where is this water going to go

22. Excavation Sub surface Conditions
Some site have been used as fill sites… these areas will need to be removed and new fill imported
Soft spots can be found in any excavation… make sure you either make allowances or tag it out your tender – Ibis Rotorua

23. Excavation
Utilities
Utility lines may not be in the correct location and if they are hit by a digger it becomes expensive
Check manholes are in the right location and they are at the correct depth and have the right no of inlets/outlets
Check overhead lines. Can you machines get under them. Get the electricity company to put sleeves on the lines or flags – Current roadworks in Remeura.
If Utilities need to be moved – check out how much and how long it will take.

24. Excavation Project size
Check if the site is large enough to store all the equipment and spoil heaps
Traffic Control
Traffic management systems are becoming paramount – they are very expensive

25. Excavation
Security
Check the security issues of leaving the big machines on site. They wont take the machines but they will take the batteries !! Bream Bay
Do you need to hire security ??
Do you have to fence the site for public safety??

26. Excavation Time of year works are completed
Existing and imported soils
Earthworks are carried out in the spring and summer
If the weather is wet then the machines are slower, wet and heavy soil costs more to move than dry light soils
Compaction of the soil is very important and this is affected by the moisture content.
If the soil doesn’t dry out by natural means then additives such as lime has to be used
Conversely if the soil is too dry, then water trucks have to be used

27. Excavation – types of machines
Excavator with back actor and front loading bucket
available on wheels or track
Capable of trench, basement and foundation excavation. Can load spoil into trucks

28. Excavation Face shovel
Particularly suitable working against banks, forming cuttings and embankments

29. Excavation
Grab
Used to load loose material into spoil heaps on site

30. Excavation
Graders
Level out deposit fill

31. Excavation
Rollers
Used for compaction

32. Excavation Compaction and bulking factors
bulking factor compaction factor
In place
loose
Compacted

33. Excavation
Bulking factors % by volume Gravel 10% Sand 12.5% Ordinary earth 25% Clay 33% Chalk 33.3 % Rock 50%

34. Excavation
By hand factors Ordinary ground has a value of 1 Type of ground multipler Sand 0.75 Stiff clay 1.25 Compacted gravel 1.50 Soft chalk 2.50 Soft rock 4.00

35. Excavation - calculations
Excavate to reduced levels Requirements – excavator with a banksman The output of the excavator includes digging and loading directly onto a waiting truck Say Banksman is $20.00/hr Excavator and driver is $40.00/hr Hourly cost of operation – excavator $40.00 Banksman $ TOTAL $60.00/hr

36. Excavation
Excavate to reduced levels – cont’d Output of excavator - $15m3/hr So cost/m3 = $60.00/15 = $4.00/m3

37. Excavation
Excavate trenches Requirement 90% completed by machine, 10% completed by hand. Banksman required for machine All in hourly rate is as before - $60.00/hr Assume excavator is 9m3/hr Cost for excavation = $60/9 = $6.67/m3

38. Excavation
Excavate trenches – cont’d Hand digging – labour = $15.00/hr 1 labour digs 1 m3 in 2.5 hours Cost/m3 = $15.00 x 2.5 =$37.50/m3 Total cost 90% of machine cost – 90% x $6.67 = $ % of hand digging – 10% x $37.50 = $3.75 TOTAL = $9.75/m3

39. Excavation
Disposal of water Requirement – 2 pumps for 8 weeks of excavation Labour – ½ a day in attendance Labour - $15.00 /hr Hire of a pump $150/week Cost of fuel/pump $20/week Total cost of pump $170/week

40. Excavation
Disposal of water – cont’d Hire of pump – 2 x $170 x 8 weeks = $2, Cost of labour 0.50 hour x (8 x 5) days x $15.00/hr =$2, TOTAL = $5,140.00

41. Excavation
Removal of excavated material Requirement – the excavation is loaded directly onto 10 tonne lorries The cost of the excavation is included in the excavation rate For the excavator to work efficiently, once one truck is loaded another one comes through the gate.

42. Excavation
Removal of excavated material – cont’d No of vehicles = time taken to load + total journey time time taken to load Lorry and driver = $95/hr Tipping fees = $ 40/load

43. Excavation
Removal of excavated material – cont’d Weight of earth = 1.60tonnes/m3 so a 10 tonne lorry with a full load takes 10 tonnes/1.6 = 6.5m3 Allow for bulking factor of 25% 6.5m3 = 6.5m3 x 100/125 = 5 m3

44. Excavation
Removal of excavated material – cont’d Time taken to load 5 m3 assume the excavator is 9m3/hr = 5/9 = 33 mins Assume tip is 10k from site Outward journey 15 mins Tipping time 5 mins Return journey 12 mins Total time 32 mins

45. Excavation
Removal of excavated material – cont’d Therefore no of lorries needed are 33 mins + 32 mins = 2 no aprox 33 mins Cost of operation = 2 no lorries x $95/hr = $190

46. Excavation
Removal of excavated material – cont’d Excavator is working continously and the quantity of excavated material removed in 1 hour is 9m3 Cost /m3 = $190/9 = $21.11/m3 Tipping charge $40/load Cost/m3 = 40/5m3 = $8.00/m3 Total cost/m3 = $ $8.00 = $29.11/m3

47. Excavation
References Estimating excavation – Deryl Burch Estimating and tendering building works – R.C Smith