CONTOURS, GRADES & SLOPESnkissoff/pdf/CET-2030... · 2018. 8. 10. · CONTOURS, GRADES & SLOPES CET-2030 Construction Graphics • Plans need to show elevations and ground shapes

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


•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


Slope Steepness•The closer the contours, the steeper the slope!

CONTOURS


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


Contour shapes show terrain features

CONTOURS


Closed Depressions: Contours include hachure marks to indicate the closed depression

RULES OF CONTOURS


• 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


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


What do you think?

Major contour interval = ???

Contour interval = ???

RULES OF CONTOURS


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


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)


•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


•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


•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


GRADES


•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


•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


•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?


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


•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


Documents

CONTOURS, GRADES & SLOPESnkissoff/pdf/CET-2030... · 2018. 8. 10. · CONTOURS, GRADES & SLOPES CET-2030 Construction Graphics • Plans need to show elevations and ground shapes