CTC-375 Construction Methods

1. CTC-375 Construction Methods Earthwork

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3. 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

4. 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

5. 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

6. 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

7. Equipment planning • Cost per production unit = equip cost per working hour/equip production per hour • Table 2-1 show efficiencies

8. 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

9. 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

10. Soil And Rock • Moisture Content(%) = (moist wt – dry wt)/dry wt X 100 • Soil sample 120# • Dry weight 100# • MC = (120-100)/100X100 = 20%

11. 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

12. 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

13. 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

14. 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%

15. 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/compacted vol))X100 • Soil wt = 2800#/cy in bank • Soil wt = 3500#/cy compacted • Swell = (1-(2800/3500))X100 = 20%

16. 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/(1+swell) • Shrinkage factor = 1- shrinkage • Table 2-5

17. 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

18. 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

19. 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%

20. 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

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

22. 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

23. Estimating earthwork • Trench Excavations • V = x sectional area X length • Take x sections every 50 feet and compute volumes between x sections

24. Estimating earthwork • Large Areas • Use a grid to find volume