Correct Answer - Option 1 : (A) - (III), (B) - (I), (C) - (IV), (D) - (II)
Concept:
Section I (Alignment)
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Section II (Topography)
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A. Zig – zag alignment
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III. A slope with deep valleys
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B. Cross country alignment
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I. Sags and summits in succession
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C. Switch back development
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IV. One steep regular slope
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D.Valley alignment
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II. One slope of valley
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Tha alignment of a new railway line depends upon the topography of the country it traverses. The following few situations may arise :
Plain Alignment: When the topography is plain and flat, the alignment presents no problems and can pass through obligatory points and yet have very easy gradients
Valley Alignment: The alignment of a railway line in the valley is simple and does not pose any problem. If two control points lie in the same valley, a straight line is provided between these points with a single uniform gradient.
Cross Country Alignment: The alignment of a railway line in such terrain crosses the watersheds of two or more streams of varied sizes. As the levels vary in cross-country, the gradients are steep and varying and there are sags and summits.
Mountain Alignment: The levels in mountains vary considerably, and if normal alignment is adopted, the grades would become too steep, much more than the ruling gradient. In order to remain within the ruling gradient, the length of the railway line is increased artificially by the 'development process'.
The following are the standard methods for the development technique:
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Zig-Zag Alignment: In this method, the railway line traverses in a zig-zag alignment and follows a convenient side slope which is at nearly right angles to the general direction of the alignment. The line then turns about 180 degrees in a horseshoe pattern to gain height.
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Switch Back Development: In the case of steep side slopes, a considerable gain in elevation is accomplished by the switch-back method.
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Spiral Method: This method is used in a narrow valley where a small bridge or viaduct has been constructed at a considerable height to span the valley