Cross Sections

1
Cross Sections

• CTC 440

2
Objectives

• Know what a cross section is and what is
  typically shown
• Know how to calculate areas and volumes
• Know how to use the simple stripping method to
  calculate areas
• Know the other ways to calculate areas
• Squares
• Planimeter
• CAD programs
• Know how to calculate volumes using the average
  end area method

3
Cross Sections

• A view, at a particular station, of all features
• Plotted perpendicular to the station
• Typical sections/cross sections are different
• A cross section is a snapshot at a particular
  location

4
Cross Sections - Use

• Earthwork quantities
• Drainage
• Driveways/intersecting roads
• Right-of-Way
• Cut/fill slopes
• Utilities

5
Cross Sections

• Show existing elevations (usually dashed)
• Show new features (usually solid)
• Road structure
• Ditches
• Sideslopes
• Drainage
• Utilities
• Guide railing

6
Cross Sections

• Example

7
Calculating Areas

• Various methods
• Stripping method
• Count squares
• Planimeter
• Computer software

8
Stripping Method

• Say you have a cross-section at a scale of 15
• Break area into 1 strips, measure the lengths of
  the center of the strips and add them up
• Multiply by 1 to get square inches
• Convert square inches to square feet

9
Calculating Volumes

• Most common method is the average end area method
• Take the sum of the areas at two different
  stations, average them, and then multiply the
  average by the length between the stations
• Calculate volumes 2 stations at a time dont try
  w/ 3 or 4 stations

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Calc. Volumes-Example

• At Sta 250 Area8 sf
• At Sta 275 Area20 sf
• Length between stations25
• There are 27 cubic ft per cubic yard
• Volume(820)/225350 cf
• Volume350cf/2713 cy

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Next Lecture

• Intersections