contours, grades & slopesnkissoff/pdf/cet-2030... · 2018. 8. 10. · contours, grades &...
TRANSCRIPT
CONTOURS, GRADES & SLOPES
CET-2030 Construction Graphics
• Plans need to show elevations and ground shapes on flat 2D medium
• Magnitude of slopes need to be specified on plans• Proper drainage is dependent upon properly
designed and specified slopes:• On the ground surface• In gravity utility systems (channels & pipes)
The Earth is not flat!!!
CONTOURS & SPOT ELEVATIONS
CET-2030 Construction Graphics
•Denote lines of equal elevation•Encapsulate higher or lower elevations•Quickly show that the ground has a slope and shape•What is shown? A rise or depression?
Contours
Spot Elevations •Single point elevation of ground surface •Existing ground to 0.1’•Proposed pavement to 0.01’
CONTOURS
CET-2030 Construction Graphics
Slope Steepness•The closer the contours, the steeper the slope!
CONTOURS
CET-2030 Construction Graphics
What do you think about this island?
•Do you think the beaches are wide, flat and sandy? •Is the center a tall steep mountain peak?
CONTOURS
CET-2030 Construction Graphics
Contour shapes show terrain features
CONTOURS
CET-2030 Construction Graphics
Closed Depressions: Contours include hachure marks to indicate the closed depression
RULES OF CONTOURS
CET-2030 Construction Graphics
• Contours form closed loops and thus..
• Contours NEVER cross, split or merge!!
• The steepest slope is between closest contours
• The direction of the steepest slope is perpendicular to the contours
RULES OF CONTOURS
CET-2030 Construction Graphics
Contours have equal vertical separation (a set contour interval) Topographic plans may contain major and minor contour intervals
Contour interval = 10’ Major contour interval = 50’
RULES OF CONTOURS
CET-2030 Construction Graphics
What do you think?
Major contour interval = ???
Contour interval = ???
RULES OF CONTOURS
CET-2030 Construction Graphics
Spot elevations between contours can be interpolated using the distance between the contours as a guide. Approximation may be adequate for most cases.
Spot = 32.9’
What would you think would be the elevation at the star?
CONTOURS
CET-2030 Construction Graphics
What do you think? What is the contour elevation of X(a) & X(b)?
Is this a hill or depression?
Is the slope from the southeast uniform?
What is the highest that a spot elevation at X(c) could be ??
SLOPES (SLOPE RATIO)
CET-2030 Construction Graphics
•The steepness of a slope needs to be quantified:
• For comparisons to standards • For specifications on sites
•Slope Ratios are use to specify slopes that are “steep”
Slope Ratio = Run : Fall= X : 1
X = Horizontal distance to fall 1’X could be thought of as the horizontal distance between 1’ contours
CALCULATING SLOPE RATIOS
CET-2030 Construction Graphics
•Set up the calculation using a slope triangle to find your known values. •Run is always measured horizontally NOT along the slope•Fall is the difference between the top and bottom slope elevations
Fall
Run
Top Elevation
Bottom Elevation
•Use a “Slope Circle” to help calculate your missing values.•Use the positioning of your known values as a guide to multiply or divide the known values.
Run
Fall Slope Ratio
Slope Ratio =Fall
Run
RFS
CALCULATING SLOPE RATIOS
CET-2030 Construction Graphics
•What if you are given a top and bottom of slope elevation and a slope ratio and need to find the length (run) of the slope?
Run??
Fall Slope Ratio
Fall = Top – Bottom
Slope Ratio
Run = Fall x Slope Ratio
Run
Fall?? Slope Ratio
•What if you are given a slope ratio and need to find how much the slope falls over a given length?
RunFall =
SLOPE PRACTICE PROBLEMS
CET-2030 Construction Graphics
GRADES
CET-2030 Construction Graphics
•10:1 and Steeper >>>> Use a Slope Ratio•Natural slopes, embankment or cut slopes to existing ground or along roadside
•10:1 or Flatter >>>> Use a G%•Pavements, roads, walks
•G% indicates the number of feet of fall over 100’ of length
Flatter slopes are usually expressed using a % Grade. (G%)
CALCULATING GRADES
CET-2030 Construction Graphics
•Again set up the calculation using a slope triangle to find your known values. •Run is always measured horizontally NOT along the slope
Flatter slopes are usually expressed using % Grade (G%)
Run
Fall
G
Fall
Run
Top Elevation
Bottom Elevation
G =Fall
Run
FRG
= Gradient (ft/ft)
G% = Gx100 = %G% is what is normally found on plans!!
CALCULATING GRADES
CET-2030 Construction Graphics
•What if you are given a top and bottom of slope elevation and a G% and need to find the length (run) of the slope?
Run??
Fall
G
Fall = Top – Bottom
G
G = G% / 100
•Remember, Grade (G%) is often specified on plans. G is needed in your calculations!!!!•Roadway plans in some circumstances will use G without the %. If you see 0.016 without the %, that is a Gradient G (ft/ft)
FallRun =
GRADE OR SLOPE CIRCLE: HOW DO YOU KNOW?
CET-2030 Construction Graphics
Run
Fall
G
FRG
Run
Fall Slope Ratio
RFS
Frogs hop on flat areas. Grades are flat.
Roofs are steep because they are sloped.
SLOPES & GRADES-OTHER NOMENCLATURE
CET-2030 Construction Graphics
•Some short slopes may be specified by Inches/Feet (“/ft) •Cross-slopes of streets and walks may use this convention•Any “/ft need to be converted to G to be incorporated into calculations of the FRG slope circle
(“/ft) / 12 = G (ft/ft)
GRADES PRACTICE PROBLEMS
CET-2030 Construction Graphics