Page 14 - ebook_soil engineering practical workbook_15112021

1.5.3 Contour Mapping

- The land area to be made mapped should be laid out in grid pattern

(25m x 25m).
- Starting to the corner where the two bases line meet, measure the

interval of 5m x 5m. The interval should be marked as shown below.

- Set up the levelling instrument somewhere in the field where the entire

field can be seen through the telescope tube.
- Take a back sight on a bench mark, some other point of known

elevation, or a sight on a permanent object which is given an arbitrary
elevation of 128.4m.
- With a grid system located on the ground, the elevations of a various

point are determined by profile levelling. Points are identified in the

field notes by lettering each grid points on the east-west base line and
numbering each grid point on the north-south base line. Each grid point
then is identified by a combination of one letter and one number that

corresponds to its location on the map.
- To draw the contour map, reproduced the grids on graph paper. The

scale should conform to one of those found on the engineer’s scale.
Show the elevation on each grid point on map. Contour lines are usually

given values in even numbers.
- Draw the contour lines by determine its interpolations between

adjacent grid points.

6 | Soil Engineering Practical Workbook