Clearing and Rough Grading the Site

Transcription

1 UNIT Clearing and Rough Grading the Site Objectives After completing this unit, you will be able to perform the following tasks: Identify work to be included in clearing a building site according to site plans. Interpret grading indications on a site plan. Interpolate unspecified site elevations. Property Boundary Lines The boundary lines of the building site are shown on the site plan. The direction of a property line is usually expressed as a bearing angle. The bearing of a line is the angle between the line and north or south. Bearing angles are measured from north or south depending on which keeps the bearing under 90, Figure 9 1. Angles are expressed in degrees ( ), minutes ( ), and seconds ( ). There are 360 degrees in a complete circle, 60 minutes in a degree, and 60 seconds in a minute. The point of beginning (P.O.B.) may or may not be shown on the site plan. If the point of beginning is not shown on the plan, start at a convenient corner. Figure 9 1. Bearing angles are always less than Unit 9

2 Corners are usually marked with an iron pin (I.P.) or some permanent feature. The approximate direction of the boundaries can be found with a handheld compass. This approximation should be accurate enough to aid in finding the marker (iron pin, manhole cover, concrete marker, or similar item) at the next corner. Proceed around the perimeter in this manner to find all corners. All construction activity should be kept within the property boundaries unless permission is first obtained from neighboring landowners. Figure 9 2. The winter sun passes through deciduous trees. Clearing the Site The first step in actual construction is to prepare the site. This means clearing any brush or trees that are not to be part of the finished landscape. The architect s choice of trees to remain is based on consideration of many factors. Trees and other natural features can be an important part of architecture not only for their natural beauty, but for energy conservation. For example, deciduous trees, which lose their leaves in the winter, can be used to effectively control the solar energy striking a house. In the winter, the sun shines through the deciduous trees on the south side of a house, Figure 9 2. In the summer, the trees shade the south side of the house, Figure 9 3. The Lake House offers a good example of the importance of the selection of trees to remain on a site. This house gets a large part of its heat from its passive-solar features. The passive-solar features are described more fully later. Trees that are to be saved are shown on the plot plan by a symbol and a note indicating their butt diameter and species, Figure 9 4. Areas that are too densely wooded to show individual trees are outlined and marked woods, Figure 9 5. Removal of unwanted trees may require felling and stump removal, or may be accomplished with a bulldozer and dump truck. In either case, care must be exercised not to damage the trees that are to be saved. Figure 9 3. The summer sun is shaded by deciduous trees. Figure 9 4. Typical note and symbol for individual tree. Grading Grading refers to moving earth away from high areas and into low areas. Site grading is necessary to ensure that water drains away from the building properly and does not puddle or run into the building. In some cases, grading may be necessary for access to the site. For example, if Figure 9 5. Typical note and symbol for wooded area. Clearing and Rough Grading the Site 59

3 Figure 9 6. Spot elevations for specific locations. the site has a steep grade, it may be necessary to provide a more gradual slope for a driveway. Grade is measured in vertical feet from sea level or from a fixed object such as a manhole cover. This vertical distance is called elevation. The term elevation to denote a vertical position should not be confused with elevation drawings that show the height of objects. The elevations of specific points are given as spot elevations. Spot elevations are used to establish points in a driveway, a walk, or the slope of a terrace, Figure 9 6. Spot elevations are often given for trees that are to be saved. The grade of a site is shown by topographic contour lines. These are lines following a particular elevation. The vertical difference between contour lines is the vertical contour interval. For plot plans this is usually 1 or 2 feet. When the land slopes steeply, the contour lines are closely spaced. When the slope is gradual, the contour lines are more widely spaced. The builder must be concerned with not only the grade or contour of the existing site, but also that of the finished site. To show both contours, two sets of contour lines are included on the plot plan. Broken lines indicate natural grade (N.G.), and solid lines indicate finished grade (F.G.), Figure 9 7. When the natural-grade elevation is higher than the finished-grade elevation, earth must be removed. This is Figure 9 7. Two sets of contour lines show that this site will be graded to be more level in the area of the building. referred to as cut. When the natural grade is at a lower elevation than the finished grade, fill is required. To determine the amount of cut or fill required at a given point, find the difference between the natural grade and the finished grade, Figure Unit 9

4 Figure 9 8. Cutting is required where N.G. is above F.G. Fill is required where N.G. is below F.G. Interpolating Elevations Sometimes it is necessary to find an elevation that falls between two contour lines. This can be done by interpolation. Interpolation is a method of finding an unknown value by comparing it with known values. Example: To interpolate the elevation of the tree at point A in Figure 9 9, follow the listed steps of the procedure using the information shown in the illustration and the numbers enclosed in parentheses. Step 1. Step 2. Step 3. Step 4. Scale the distance between the two adjacent contour lines (12 feet). Scale the distance from the unknown point to the nearest contour line (4 feet). Multiply the contour interval by the fraction of the distance between the contour lines to the unknown point. (Contour interval 2 feet; fraction of distance between contour lines 4/12 1/3. Therefore, 2 1/3 2/3 feet.) If the nearest contour line is below the other one, add this to it. If the nearest contour line is above the other one, subtract this amount. (Nearest contour 48. This is below the other contour line at 50, so 2/3 is added to 48. 2/ ) Figure 9 9. Interpolate the elevation of the tree. Clearing and Rough Grading the Site 61

5 CHECK YOUR PROGRESS Can you perform these tasks? Determine the bearings and lengths of property lines. Identify each tree to be removed from a site. Give the natural grades and finished grades of all points on a site. Explain which direction water will naturally run from any point on a site. ASSIGNMENT Refer to the site drawings of the Lake House (in the packet) to complete the assignment. 1. What are the lengths of the north, east, and west boundaries of the Lake House? 2. Which of the compass points shown in Figure 9 10 corresponds with the north boundary of the Lake House? Which compass point corresponds with the east boundary? 3. How many trees are indicated for removal? 4. How many trees are to remain on the site? (Do not include wooded areas.) 5. What is the finished-grade elevation at the tree nearest the Lake House? 6. What is the natural-grade elevation of the most easterly tree to be saved? Figure What is the elevation of the tree to be saved nearest the lake? 8. What is the natural-grade elevation at the southwest corner of the Lake House? Do not include the deck as part of the house. 9. What is the finished-grade elevation at the southwest corner of the house? 10. How much cut or fill is required at the entrance of the garage? 11. Is cut or fill required at the southwest corner of the house? How much? 12. What is the elevation at the northeast corner of the site? 62 Unit 9