Estimation 1 Lesson 4 - Excavation

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

Excavation

Excavation

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

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

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

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

Excavation Considerations when estimating excavation Desk top study Site visit

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

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

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

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?

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

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

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

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

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.

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

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?

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

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

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.

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

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??

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

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

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

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

Excavation Graders Level out deposit fill

Excavation Rollers Used for compaction

Excavation Compaction and bulking factors bulking factor compaction factor 1.00 1.25 0.90 In place loose Compacted

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

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

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 $ 20.00 TOTAL $60.00/hr

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

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

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 = $6.00 10% of hand digging – 10% x $37.50 = $3.75 TOTAL = $9.75/m3

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

Excavation Disposal of water – cont’d Hire of pump – 2 x $170 x 8 weeks = $2,720.00 Cost of labour 0.50 hour x (8 x 5) days x $15.00/hr =$2,420.00 TOTAL = $5,140.00

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.

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

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

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

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

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 = $21.11 + $8.00 = $29.11/m3

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