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 1”=5’ • 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; don’t try w/ 3 or 4 stations

10. Calc. Volumes-Example • At Sta 2+50; Area=8 sf • At Sta 2+75; Area=20 sf’ • Length between stations=25’ • There are 27 cubic ft per cubic yard • Volume=(8+20)/2*25=350 cf • Volume=350cf/27=13 cy

11. Next Lecture • Intersections