6
Slope
analysis &
Grading
Earth shape and
earthwork
Topographic
map
Slope form
Slope analysis
Grading
Drawing illustrating the technique of slope profiling
(Source of drawing: Marsh, William M. Environmental Analysis for
Land use and Site Planning p. ..)
Topographic
Map
c o n t o u r
Topographic area represented by ABE, can be computed using slope data read from topographic contour maps.
Slope Form
Topographic contour map are composed of a series of line that designate the elevation of the land above sea level. Each line called contour line represents specific level (, elevation).
Contour Interval is the difference in elevation values between
two adjacent contours, so it indicates the elevation change from one contour line to the next one. Contour Interval is the same value for every elevation change in the same topography map.
source of illustrate: Environmental Analysis by William M.Marsh page 31
Maps disregard slope in representing land area, therefore in rough terrain, topographic area may be much greater
map area
Topographic area (surface area) Landform
Topographic Contour map
Slope form and topographic map
interpretation
Site Planning and Landuse Planning requires accurate slope information which is available in form of topographic map and aerial photography. The topographic contour map represents an elevation data to show landform in two-dimentional drawing
Graphical slope information can be generated by simple tech-niques from the contour map. Constructing a slope profile from a topographic contour map is to plot the elevation of contour lines on a two-dimentional graph.
• Contour interval: the height between each contour line. • Cross section show specific section of that shape
• X axis represents distance, Y axis represents level change Contours are set of lines of equal elevation above the same reference plane, the number indicated on each line referenced tothe DATUM PLANE, which is the level at “Mean Sea Level”. A CONTOUR INTERVAL is the verticle distance (Height) between contours.
Topographic model
Models are good mediums to give the feeling of the earth form and study the natural drainage pattern
Basic elements that should show on study model
Landform of the ground Group of existing trees Surface water body
The model of Doi Intanon shows landform of Royal project at Doi Intanon, Chiengmai and the surrounding area. which will help site planner to understand landform, drainage pattern, visual quality and the overall elevation relationship of the site and its surrounding source: 3rd year Architectural student Soa&D 2004
contour
characteristics
slope profile
Slope profile shows earth form
To know the characteristics of contours is important for their interpretation and essential to understand the nature of that land-form.
A Uniform slope is sndicateed by evenly spaced contour plan. A Ridge and Valley are shown similarity, but note that RIDGE with the higher contour inside (contour line pointing down to lower level), VALLEY with the lower contour inside (contour line point-ing up to higher level)
If two sides of VALLEY contour lines are quite closed, it indicates STREAM.
CONVEX and CONCAVE landforms are the most common landform found in nature and express the felling differently.
High point on SUMMIT or low point in a DEPRESSION are indicated by spot elevation.
Existing contour lines are shown in dashed line, proposed new Grade is shown in a set of solid lines.
Topography map: contour
characteristics
1. Same elevation on one contour line and same level change in between each contour line. (called contour interval)
2. Every contour closes on itself.
3. A summit or depression indicated by the elevation at highest, lowest points.
4. Contour lines never cross. 5. Uniform sloping surface 6. Convex slope 7. Concave slope 8. Valleys 9. Steep slope 10. Relatively level. 11. Ridge
Read the contour line
Natural drainage pattern : Water always flows in 90 degrees direction of contour line. Always check the topography of overall large scale drainage pattern besides the on-site topography.
Natural drainage pattern can be easily read from the topo-graphic model to see how criticle the drainage factor is in each particular area. In order to do a good site planning, we should try to avoid to disturb or change the major natural drainage pattern of the site.
Drainage
pattern
Runoff water flows downhill perpendicular to contour lines
Slope failures generally fall into 3 catagories
1. Grade: slopes that are too steep or too gentle for paricular landuses and inclined by undercutting by construction processes (cut-fill)
2. Erosion: slopes with steep inclinations, less vegetative cover, loose soil materials and eroded caused by waves, streams, heavy rainfall.
3. Failure: slopes that are composed of weak, soft material which have low bearing capacity and have tendency to mass movement problem such as mudflow, slides, sinking which worsen by increased or decreased ground water.
Mapping slope from Topography map
Slope compares the vertical distance to the horizontal dis-tance. This comparison can be expresses as an angle, a percent-age or as a ratio. the slope ratio is expressed by putting horizontal distance firse and vertical distance second such as a 4:1 slope means 1 metres of vertical rise in 4 metres of horizontal distancePercent of slope = elevation(in depth, height)*100 Distance (length)
Gradient
percent slope G=D/L*100 Horizontal distance L=D/G *100 Verticle distance D=GL/100 Grading formula Gradient percent = D/L*100 G= the gradient in percentD= the distance in elevation between two points L= the horizontal length between two points
Example of slope analysis
The topographic map of “Royal Project at Doi Intanon, Chiengmai” done on GIS shows contour lines, landuse, circulation.
Same project, the slope analysis was done to show percent slope which will be factor to determine constraints and opportunities of land development in each portion.
Interpreting slope
Slope analysis is the most basic crucial information in site analysis to determine the appropriate location for site develop-ment
Slope Analysis
Diagram show the use of graduated scale for mapping slope analysis(percentage of slope) from a contour map.
Source:
Slope analysis of 20.8 acre site. Diagram shows the use of
graduated scale for mapping slopes from a contour map.
slope Criteria
Recommended suitable slope for each use concerning possible cut-fill, mobility and drainage ability
Slope criteria
Slope ratios are determined by constraints such as design grade, soil stability, amount of planting, type of determined func-tion, program and circulation.
Design height is determined by aesthetics and functional requirement for each particular uses. Stability is related to angle
of repose of each natural material and soil. Slope stability is
also affected by water and wind.
Slope Criteria is suitable & recommended slope for each use concerning mobility, possible cut-fill, maintenance and drain-age ability. In addition, for some specific uses such as sport field, tennis lawn, basketball field, we must try to follow the slope cri-teria to get the acceptable standard.
Slope Ratio for suitable uses
Angles of repose for various types of slope materials.
(Angles are given in degrees.)
• Maximum angle for earth material that it can be in-clined, and it will fail if beyond.
A standard from: Marsh, William M. : Environmental Analysis for Land Use
and Site Planning P.56, Mcgraw-Hill, NY)
Angles of
Designing a level plane on steeply sloping site.
Source: LANDSCAPE ARCHITECTURE, John Ormsbee Simands.
Designing a level plane on steeply
sloping site.
Avoid grading on the following conditions (From Grade Easy by Richard Untermann)
1. Grading that results in radical loss of vegetation and topsoil
2. Grading that interrupts the natural drainage 3. Grading that results in aesthetic degradation 4. Grading on difficult slopes (excess of 25%)
5. Grading in environmental unique condition; floodplain, bogs,
6. Grading in areas effected by natural disaster; mudslides or along earthquake fault lines
When not to
Grade
Grading
Grading
Grading : is the modification of existing land form. It is one of the most important items in site planning, landscape design and construction. Grading serves three main purposes:
1. To create a level to put something on; for a house, car, sport play field, a hotel, etc.
2. To create circulation ways; road way, loading ramp, handi-capped ramp, bicycle track, etc.
3. To create special effect and solve special problem ; make a mound to hide parking lot or reduce sound, prevent erosion and landslide, aesthetic or psychological purposes.
However, to make a land usable, all three purposes must concern drainage factor and grading is essential to direct water away from building and outdoor surfaces and conducted to drain-age channel.
(see chapter 7 Drainage)
Manipulating contour line
To do the grading plan is to manipulate contour for that pur-pose. The grading plan should show both existing and revised contours so we will see how much the grade has been changed.
By cutting only
– the soil is stable – require less cost for foundation construction
– be able to do very steep slope
– cost to transport earth from the site
Grading: making an area level to put
something on
Purposes
Cutting procedure
souce of drawing: Brook, Gene R., Site Planning, Environmental process and Development, p. 149-153
By filling only
– easier to make a very level elevation
– good for low land, flood problem area.
– Unstable earth, needs a compaction.
– Cost of transporting earth into the site
– Soil cost
Filling procedure
By the combination of cut and fill
– balance earth in the site, no transportation cost.
– Less earth cost – Machine cost – Must has good con-struction schedule and man-agement
Balance cut-fill procedure
By the combination of cut and fill: plan of slab on sloping topography
Grading: making a proper slope for
circulation
Circulation routes should be level as possible.Two ways to travel up slope terrain
(maximum slope for local street is 8%)
The normal grading method is something between the two extremes with roads or paths climbing and falling
Circulation routes cross-ing level country are relatively easy to grade— providing uniform surface and assuring the roadway drains properly.
1. A uniform surface means smoothing out the bumps by spacing contours evenly.
2. Draining the level road sometimes requires creating artificial high and low points for water flow direction. These can be shown graphi-cally with contours, spot elevations, or sections.
Section through road with CROWN
Road sloped from side to side
The picture shows shortest distance but results extensive cutting and would have erosion problem at the road bank.
The natural slope is steep, the road crosses series of contour will causes a very steep bank since it needs UNIFORM slope. We should try to compromise the cut and fill along the centerline.
To Design the road centerline aligned with or parallel to the contour lines with minimal grading and smoothly change in slope from one contour line to another
Center line crown
The most common way if existing topography is NOT to steep and the road is not too long, the method is to select the contour in the middle of the road and cut half the contour above,
When grading by
CUT-TING , begin with the lowest
contour and work up, by
FILLING, begin with the top
contour and work down. Contours are spaced according to the gradient of the proposed route typically expressed in percent. For 10% slope, one meter interval contours would be spaced 10 m. apart
cutting
Additional
technique
If cut/fill creates a steep bank, a heavy rainfall can cause erosion. Proper retaining wall with good drain must be used on the high side of the slope along with the consideration to sepa-rate road way into two levels.
Road crosses drainage swale, the problem concerning the intersection between road and topographical depression, the use of BOX CULVERT or BRIDGE would be chosen depend on the length and depth of the swale and the image of the design.
Source of drawing: Brook, Gene R., Site Planning, Environmental
process and Development
Reference books
1. Prof. Untermann, Richard K. ,Grade Easy,Department of Landscape Architecture, University of Washington, Seattle
2. Brooks,Gene R.,Site Planning : Environmental
pro-cess and development P.129-171, , Prentice Hall N.J. 07632
3. Boomkum, Decha, Site Planning p.83-106, Lecture sheet , Chulalongkorn University, Thailand
4. Marsh, William M., Environment Analysis for Land
use and Site Planning, Mcgraw-Hill Company, NY.
Source of drawing: Marsh, William M. Environmental Analysis for Land
use and Site Planning
Source of drawing: Untermann, Richard K.: Grade Easy
Source of drawing: Brook, Gene R., Site Planning, Environmental process