6 Slope analysis & Grading Earth shape and earthwork Topographic map Slope form Slope analysis Grading 81
Topographic Map Topographic Contour map 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. contour map area Landform Topographic area represented by ABE, can be computed using slope data read from topographic contour maps. Topographic area (surface area) Maps disregard slope in representing land area, therefore in rough terrain, topographic area may be much greater source of illustrate: Environmental Analysis by William M.Marsh page 31 Slope Form 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 Drawing illustrating the technique of slope profiling (Source of drawing: Marsh, William M. Environmental Analysis for Land use and Site Planning p...) 82
Graphical slope information can be generated by simple techniques 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 83
contour characteristics Slope profile shows earth form To know the characteristics of contours is important for their interpretation and essential to understand the nature of that landform. 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 pointing 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. slope profile Source of drawing: Untermann, Richard K.: Grade Easy 84
source of drawing: Untermann, Richard K: GRADE EASY Topography map: contour characteristics Read the contour line 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 85
Drainage pattern 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 topographic 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. Runoff water flows downhill perpendicular to contour lines slope Problem 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. 86
Mapping slope from Topography map Slope compares the vertical distance to the horizontal distance. This comparison can be expresses as an angle, a percentage 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 distance Gradient Grading formula Gradient percent = D/L*100 G= the gradient in percent D= the distance in elevation between two points L= the horizontal length between two points Percent of slope = elevation(in depth, height)*100 Distance (length) percent slope G=D/L*100 Horizontal distance L=D/G *100 Verticle distance D=GL/100 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. 87
Slope Analysis Interpreting slope Slope analysis is the most basic crucial information in site analysis to determine the appropriate location for site development Slope analysis of 20.8 acre site. Diagram shows the use of graduated scale for mapping slopes from a contour map. Diagram show the use of graduated scale for mapping slope analysis(percentage of slope) from a contour map. Source: 88
slope Criteria Recommended suitable slope for each use concerning possible cut-fill, mobility and drainage ability 89
Slope criteria Slope Ratio for suitable uses Slope ratios are determined by constraints such as design grade, soil stability, amount of planting, type of determined function, 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 drainage ability. In addition, for some specific uses such as sport field, tennis lawn, basketball field, we must try to follow the slope criteria to get the acceptable standard. Angles of Repose Angles of repose for various types of slope materials. (Angles are given in degrees.) Maximum angle for earth material that it can be inclined, 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) 90
Designing a level plane on steeply sloping site. Designing a level plane on steeply sloping site. Source: LANDSCAPE ARCHITECTURE, John Ormsbee Simands. 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 91
Grading Purposes 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, handicapped 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 drainage channel. (see chapter 7 Drainage) Manipulating contour line To do the grading plan is to manipulate contour for that purpose. The grading plan should show both existing and revised contours so we will see how much the grade has been changed. souce of drawing: Brook, Gene R., Site Planning, Environmental process and Development, p. 149-153 Grading: making an area level to put something on 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 Cutting procedure 92
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 construction schedule and management Balance cut-fill procedure By the combination of cut and fill: plan of slab on sloping topography 93
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 94
Circulation routes crossing 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 graphically with contours, spot elevations, or sections. Section through road with CROWN Road sloped from side to side crown 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. Center line 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 95
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 Filling 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, fill half of the contour below. 96
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 separate road way into two levels. Additional technique 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 p.149-153 97
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 and Development p.149-153 Reference books 1. Prof. Untermann, Richard K.,Grade Easy,Department of Landscape Architecture, University of Washington, Seattle 2. Brooks,Gene R.,Site Planning : Environmental process 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. 98