CTC-375 Construction Methods

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CTC-375 Construction Methods

• Earthwork

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Construction Order

• There is an order to all projects
• What activities get done first
• What activities need to be done in a specific
  order
• What activities can be done at any point in time

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Start at beginning

• Earthwork
• Moving rock or soil from one location to another
• Processing it to meet location, elevation,
  density moisture content, etc
• Efficient earthwork requires accurate estimating
  of work quantities and conditions, proper
  equipment, competent job mangement

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Equip Selection

• Proper equipment has major impact on efficiency
  and profitablility
• Can equipment perform required work
• Also look at profitablility, other uses for
  equipment, return on investment, availability of
  parts and services, effect of downtime on other
  construction equip

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Equipment planning

• Need to plan to effectively use equipment
• Production of equipment
• Production Volume per cycle/cycles per hour
• Cycles per hour is based on efficiency of equip
• Swing angle and elevation to truck bed
• Soil hardness and Soil type
• Room to manuever

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Equipment planning

• Cost per production unit equip cost per working
  hour/equip production per hour
• Table 2-1 show efficiencies

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Soil And Rock

• General Soil Characteristics
• Trafficability ability of soil to support
  weight of vehicles under repeated traffic
• Controls traffic on unimproved access roads
• Also gives measure of how earthmoving equip will
  operate
• Primarily function of moisture conditions and
  soil type
• Loadability how difficult to excavate and haul
  a soil
• Granular high
• Compact cohesive - low

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Soil And Rock

• Unit Soil Weight
• Pounds /cy
• Depends on soil type, moisture content, degree of
  compaction
• Relation between soil weight and bearing capacity
• So soil weight is used as a measure of compaction
• Soil weight is also a factor in hauling

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Soil And Rock

• Moisture Content() (moist wt dry wt)/dry wt
  X 100
• Soil sample 120
• Dry weight 100
• MC (120-100)/100X100 20

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Soil ID

• Boulders
• Cobbles over 3 diameter
• Gravel 1/4 3 diameter
• Sand 0.7mm (200 sieve) ¼ diameter
• Silt 0.002 0.7 mm
• Clay less than 0.002mm
• Organic Matter decaying organic matter
• Soils classified using these types

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Soil Classification Systems

• Unified System
• All material 3 removed
• Separates soils into two main groups- Fine
  grained and coarse grained
• Table 2-2, Figure 2-1
• AASHTO System
• 7 classes of soil
• Based on suitability of soil for subgrade
• Table 2-3
• Table 2-4

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Soil Volume Change Characteristics

• Soil Conditions
• Bank material in natural state before
  disturbance Bank cubic yard
• Loose material that has been excavated or
  loaded loose cubic yard
• Compacted material after compaction compacted
  cubic yard

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Soil Volume Change Characteristics

• Swell
• Soil increases in volume when it is excavated
• Soil grains are loosened and air fills voids
• So 1 unit of soil in bank is smaller than the
  soil once it is excavated
• Swell() ((weight/bank vol)/(weight/loose
  vol)-1)X100
• Soil wt 2800/cy in bank
• Soil wt 2000/cy loose
• Swell ((2800/2000)-1)X100 40

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Soil Volume Change Characteristics

• Shrinkage
• Soil decreases in volume when it is compacted
• Air is forced out of soil
• So 1 unit of soil compacted is smaller than the
  soil in the bank or once it is excavated
• Shrinkage() (1-(weight/bank vol)/(weight/compac
  ted vol))X100
• Soil wt 2800/cy in bank
• Soil wt 3500/cy compacted
• Swell (1-(2800/3500))X100 20

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Soil Volume Change Characteristics

• Load and Shrinkage Factors
• Need a common unit of measure for earthwork (get
  rid of calculations )
• Can use any of the three measures
• Called pay measure in contract
• Load factor 1/(1swell)
• Shrinkage factor 1- shrinkage
• Table 2-5

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Spoil Banks

• Material removed from excavation
• Longer than wide spoil bank triangular x
  section
• Conical spoil pile
• To determine the size of the bank or pile need
  swell and angle of repose for soil
• Angle of repose angle that soil on side of bank
  naturally form
• Varies with moisture content and type
• Table 2-6

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Spoil Banks

• Spoil bank
• Vol X-sect area x length
• B (4V/(L x tan R))1/2
• H (B x tan R)/2
• B base width
• H height
• L length
• R angle of repose
• V volume

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Example

• You have to store 30,000 BCY of soil in an area
  no wider than 80 feet
• How long is the spoil bank?
• Swell 25

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Spoil Banks

• Spoil pile
• Vol 1/3 p(D/2)2 X H
• D (7.64V/tan R)1/3
• H D/2 x tan R
• D diameter of base
• H height
• R angle of repose
• V volume

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Estimating earthwork

• 3 types of excavations
• Small pit
• Trench
• Large areas
• Roadways
• Find cut and fill using cross sections
• Mass diagram

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Estimating earthwork

• Pit Excavations
• Area X average depth
• Depending on size and ground may break into
  several geometric shapes to get volume
• Give bank volume

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Estimating earthwork

• Trench Excavations
• V x sectional area X length
• Take x sections every 50 feet and compute volumes
  between x sections

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Estimating earthwork

• Large Areas
• Use a grid to find volume