CE 276 Site Design

1. CE 276Site Design Wes Marshall, P.E. University of ConnecticutMarch 2007 Chapter 7 – Earthwork

2. Chapter 7Earthwork

3. Definitions

4. Definitions • Subgrade • The top of the material on which the surface material is placed • Top of a fill situation & bottom of a cut • Compacted subgrade must attain a specified density • Undisturbed subgrade has not been changed or excavated

5. Definitions • Typically a course or fine aggregate • Base / Sub-base • Imported material that is typically placed under pavements

6. Definitions • Finished Grade • Final grade after all landscaping has been completed (i.e. top surface of lawns, pavements, etc.) • Typically designated with contours and spot elevations on a grading plan

7. Definitions • The relationship of FFE to the exterior grades depends upon the type of construction • Finished Floor Elevation (FFE) • Typically the elevation of the first floor of a structure • However, it can be used for any floor

8. plan section Cut & Fill

9. Cut & Fill plan section Other Definitions Cut • Cut • The process of removing soil • Proposed contours extend across existing contours in the uphill direction

10. Cut & Fill plan section Other Definitions Fill Cut • Fill • The process of adding soil • Proposed contours extend across existing contours in the downhill direction

11. Other Definitions • Compaction • The densification of soil under controlled conditions, sometime with a specified moisture content • Topsoil • Typically the top layer of a soil profile that can range from ~ one inch up to ~ one foot • Highly organic & subject to decomposition • Therefore not suitable for structures • Borrow • When fill material needs to be imported to a site, it is sometimes referred to as borrow

12. Cut & Fill • Factors that influence your cut & fill grading decisions… • Cost • Nature of the site including size & shape • Aesthetics • Intricacy of the grading plan • Soil types & suitability for use • Surrounding uses & elevations

13. Cut & Fill • In situations where you cannot balance cut & fill… • It is generally better to use more cut than fill (unless there are very specific soil requirements such as with an athletic playing field)

14. Cut & Fill • Why? • Importing soil tends to be more expensive than removing soil • A fill condition is usually structurally less stable and more susceptible to erosion & settlement

15. Calculating Cut & Fill 3 methods of estimating cut & fill volumes • Average End Area Method • Contour Area Method • Grid Method

16. Calculating Cut & Fill • Earthwork volumes are typically measured in cubic yards… • Keep in mind that cubic feet (ft3) must be divided by 27 ft3/yd3to convert to cubic yards (yd3)

17. Average End Area Method • Take cross sections at regular intervals indicating both existing & proposed contours • Calculate the amount of cut & fill at each cross-section based upon existing & proposed grades • Multiply average of two adjacent cross-sections by the length between them

18. Average End Area Method V = [(A1 + A2) / 2] x L V = Volume A1, A2 = Cut/Fill area of cross sections L = Distance between A1 & A2

19. Average End Area Method • Keep in mind that the vertical scale is usually exaggerated by 5 or 10 times • This is needed because the vertical change is usually a lot smaller than the horizontal scale • It helps you see what is really going on

20. Average End Area Method • The Average End Area Method is best used in linear situations such as: • Roads • Paths • Utility work

21. Contour Area Method Using the grading plan with existing & proposed contours: • Establish the “no cut - no fill” limit line • Separate the area of cut from the area of fill • Keeping cut & fill separate… Measure the horizontal area of change for each contour line within limit line

22. Contour Area Method V = A1h/3 + (A1+A2)h/2 + … + (An-1+An)h/2 + Anh/3 V = Volume A1, A2 , An = Area of horizontal change for each contour h = Vertical distance between areas

23. Contour Area Method If h equals i (the contour interval)Then the equation can be simplified as follows: V = i(A1 + A2 + … + An) V = Volume A1, A2 , An = Area of horizontal change for each contour i = Contour interval This form of the equation often overestimates volumes…

24. Contour Area Method

25. Step 1No Cut - No Fill Line

26. Step 2Line Between Cut & Fill

27. Step 3Measure Area of Cut & Fill for each contour line fill cut

28. For the 72’ Contour Line • Approximate area of Cut = 284 ft3 • Approximate area of Fill = 1,056 ft3 Repeat for Each Contour Line

29. Total Cut & Fill • Approximate Total Cut = 1,280 ft3 • Approximate Total Fill = 3,216 ft3 Divide by 27 ft3/yd3to find square yards Cut = 47.4 yd3 Fill = 119.1 yd3

30. Contour Area Method The Contour Area Method is best used for large, relatively uncomplicated grading plans as well as for calculating the volume of water in lakes or ponds

31. Grid Method Also known as the Borrow Pit Method • Create a grid over the area to be graded • Smaller cells → More accurate • For each grid cell • Find the average change in elevation by determining the elevation difference for all four corners of the grid cell • The volume is calculated by • Adding the averaged cut & fill volumes separately • Then multiplying by the area of one grid cell

32. Step 1Create Grid

33. Step 2Find Avg. Change in Elevation (existing spot) proposed spot

34. Step 2Find Avg. Change in Elevation Vavg = (h1 + h2 + h3 + h4) / 4 Vavg = 3.5+4.4+2.6+3.3 4 Vavg = 3.45 feet of cut Repeat for each grid cell…

35. Step 3Add Cuts/Fill Separately& Multiply by Grid Cell Area Grid Cell #1 = 3.45 feet cut Grid Cell #4 = 2.30 feet cut Grid Cell #2 = 3.48 feet cut Grid Cell #5 = 2.35 feet cut Grid Cell #3 = 2.50 feet cut Grid Cell #6 = 1.78 feet cut • Add cuts & fills separately • In this case, the site is all cut • Total of Grid Cells = 15.85 feet cut • Multiply by the Area of one Grid Cell • 15.85’(100’)(100’) = 158,500 ft3 → 5,870 yd3

36. Grid Method The Grid Method is best used for complex grading projects and urban conditions

37. Adjusting Cut & Fill Volumes • For estimating purposes • Cut & fill volumes are determined for the volume in between existing & proposed subgrades (not the finished grades) • Since grading plans depict finished grade, we typically make adjustments…

38. Adjustment Principles • The depth of the proposed surfacing material (i.e. pavement, topsoil, etc.) • Increases the amount of Cut needed • Decreases the amount of Fill needed

39. Adjustment Principles • The removal of existing surfacing (i.e. pavement, topsoil, etc.) • Decreases the amount of Cut needed • Increases the amount of Fill needed

40. Adjusting Cut & Fill Volumes • If we remove topsoil… • Multiply the area by the depth • For example… • 6” of topsoil over 60,000 ft2 of area = 30,000 ft3 less cut or more fill • If we are installing a pavement… • Multiply the area by the depth • For example… • 6” concrete slab w/ 4” gravel base = 49,800 ft3 more cut or less fill

41. Adjusting Cut & Fill Volumes • If the depth of the • Removed surface & proposed surface are the same • Then no adjustment is needed... They cancel each other out

42. Adjusting Cut & Fill Volumes • Another factor affecting cut & fill volumes is compaction • Cut volumes (existing in-place soil) will typically yield less than their full volume when used as fill by 10 to 20% • This means that 100 yd3 of material cut will only result in 80 to 90 yd3 of fill

43. Adjusting Cut & Fill Volumes Therefore, for estimating purposes, fill volumes should be increased by 10 to 20%(depending on the type of soil)

44. Balancing Cut & Fill • Balancing cut & fill on-site is often a goal of the grading process… It saves money and is the most energy efficient option

45. Balancing Cut & Fill On a balanced site, no earth needs to be hauled to or from a site

46. Balancing Cut & Fill • Taking into account compaction, we would then require a cut to fill ratio between 1.1 & 1.2 • Achieving this is typically a process of trial & error