Contour Gradient, Field Location of Contour Gradient By Abney Level

Contour Gradient:
During preliminary survey for roads during a hilly area, the specified points are first established along the gradient. the road joining these points is understood because the contour gradient or grade contour.

Initially, the points are established approximately by an Abney level , then accurately fixed by a levelling instrument.

Suppose it's required to locate the center line of a road during a hilly area with a ruling gradient of 1 in 20. Let the start line A get on a 94.00 m contour . Since the contour interval is 2 m and gradient is 1 in 20, the horizontal distance between A and therefore the point on subsequent contour (96.00 m) is 2 x 20 40 m.

With the center at A and radius adequate to 40 m (taken on an equivalent scale), an arc is drawn cutting the contour of 96.00 at the purpose B Taking # because the center and with an equivalent radius, another arc is drawn to urge subsequent point C. the opposite points are located during a similar manner.

Field Location of Contour Gradient By Abney Level:
The Abney level (Fig. 6.17) is nothing but an improved sort of clinometer. Abney level consists of a telescope and spirit bubble. A mirror is provided over the bubble at an angle of 45º to assist observe the image of the bubble. The bubble tube is attached to the vernier arm which may be rotated by a worm-and-wheel arrangement. to repair the contour gradient, the index of the vernier is about to the angle like the given gradient. The Abney level is held over the starting station A against a pole at an appropriate height C. A mark D is formed on another pole at an equivalent height. This pole is held over subsequent point of gradient. It is made to maneuver up or down along Capitol Hill slope until the mark D is bisected at point B; at an equivalent time the bubble should be at the center of its run.

Now the road joining the station point A to the purpose B is practically parallel to the road of sight and thus on the given gradient. The points A and B are marked on the bottom with pegs.

The Abney level is then shifted and persisted the purpose D. subsequent point of the gradient is fixed consistent with the previous procedure. the opposite points are fixed on the gradient in similar fashion.