The accompanying map, located on the back page of Section A, shows ground contours at 5 metre vertical intervals. ABC is the centreline of a proposed roadway and line DE is the centreline of a proposed motorway overpass. The roadway ABC has the following specification: (i) The section of the roadway between A and B is level at an altitude of 40m (ii) The section from B to C has a gradient of 1 in 10 falling. Using slope ratios of 1 in 1 for the cuttings and 1 in 1.5 for the embankments, complete the earthworks necessary to accommodate the roadway ABC on its northern side. Note: The earthworks on the southern side of the roadway have already been completed. (b) It is proposed to construct a motorway overpass, as shown in the image on the right, along the line DE. In the space provided to the right of the map, draw a vertical section (profile) on line DE. The section should show the profile of the ground after the earthworks for the roadway AB have been completed but before the overpass DE has been constructed. (c) On the map, points P, Q and R are three points on the surface of the earth. Vertical boreholes drilled at these points show the surface of the earth in the space provided above the map. They reveal the top surface of a stratum at distances of 5m, 35m and 10m below P, Q and R, respectively. (i) Draw the plan and elevation of the top surface of the stratum. (ii) Determine the strike and dip of the stratum.

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The accompanying map, located on the back page of Section A, shows ground contours at 5 metre vertical intervals - Leaving Cert DCG - Question C-1 - 2013

Question C-1

The accompanying map, located on the back page of Section A, shows ground contours at 5 metre vertical intervals. ABC is the centreline of a proposed roadway and li... show full transcript

Worked Solution & Example Answer:The accompanying map, located on the back page of Section A, shows ground contours at 5 metre vertical intervals - Leaving Cert DCG - Question C-1 - 2013

Step 1

Earthworks between A and B (Level) - Cutting (i)

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Answer

To draw the parallel lines at 5m intervals for the roadway section between points A and B, start at altitude 40m and mark lines at 35m, 30m, 25m, etc., down to the last line corresponding to the lowest point in the area.

Step 2

Earthworks between A and B (Level) - Cutting (ii)

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Answer

Identify the intersections of these lines with the given contours. Each intersection represents a point where the roadway will affect the existing ground level.

Step 3

Earthworks between A and B (Level) - Embankment (iii)

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Answer

Draw parallel lines at 7.5m intervals starting from point A and mark these lines upwards according to the highest point in the proposed embankment.

Step 4

Earthworks between A and B (Level) - Embankment (iv)

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Answer

Identify the intersections of the 7.5m intervals with contours to establish potential earthworks needed for the embankment.

Step 5

Earthworks between B and C (Falling) - Cutting (v)

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Answer

Draw the required lines for the falling section of the roadway as per the gradient of 1 in 10.

Step 6

Earthworks between B and C (Falling) - Cutting (vi)

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Answer

Draw parallel lines at 5m intervals along the slope indicating the fall from the section at B towards C.

Step 7

Earthworks between B and C (Falling) - Cutting (vii)

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Answer

Identify the intersections with contours for this fall section to calculate cut and fill requirements.

Step 8

Intersection between level and rising earthworks (viii)

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Answer

To establish additional points, analyze the contours and mark points along the lines that intersect with the proposed roadway levels.

Step 9

Intersection between level and rising earthworks (ix)

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Answer

Complete the intersection bridge between the prior road levels and the projected earthworks, ensuring smooth transitions.

Step 10

Profile on DE (x)

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Answer

Measure and draw the height lines at 5m intervals from the map data for section DE.

Step 11

Profile on DE (xi)

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Answer

Project intersections from line DE to the established contours to visualize the relationship of the overpass to the existing ground.

Step 12

Profile on DE (xii)

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Answer

Draw a complete outline of the profile ensuring dimensional accuracy and scale matching.

Step 13

Profile on DE (xiii)

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Answer

Finalize the profile by incorporating edge views of the cut surfaces post earthwork completion.

Step 14

Strike and Dip (xiv)

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Answer

Draw triangle PQR in plan and elevation to visually depict the areas of interest based on elevation differences.

Step 15

Strike and Dip (xv)

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Answer

Determine the strike line by assessing the angles from points P and Q as referenced by the borehole data.

Step 16

Strike and Dip (xvi)

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Answer

Draw XY perpendicular to the strike line to assist in further calculations of angle and direction.

Step 17

Strike and Dip (xvii)

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Answer

Determine the dip of the stratum using the angle measurements obtained from the elevations at points P, Q, and R.

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