transportation engineering i (chapter ii/iii

7/25/2019 Transportation Engineering I (chapter II/III

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1 Dr. P. B Shahi. Transportation engineering I

TRANSPORTATION ENGINEERING I

Chapter: II Highway Surveys

Map study:

By careful study of topographical maps, it is possible to have an idea of several alternate routes so that furtherdetails of these may be studied later at the site. The probable alignment can be located on the map from thefollowing details available on the map.

Alignment avoiding valleys, ponds or lakes. Possibility of crossing through a mountain pass. Avoiding bend of the river for crossing rivers. Keeping the permissible gradient.

Reconnaissance:

The second stage of surveys for highway location is the reconnaissance to examine the general character of thearea for deciding the most feasible routes for detailed studies. Some of the details to be collected duringreconnaissance are given below.

Valley, ponds, lakes, ridge, hills, permanent structures and other obstructions along the route which arenot available in the map.

Approximate values of gradient, length of gradient and radius of curves of alternate alignment. Number and types of cross drainage structure, maximum flood level and natural water level. Soil type and observation of geological features.


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Sources of construction materials, water and location of stone quarries. Type of rocks, seepage flow, and dip of strata may observe when the road passes through hilly or

mountainous terrain.

Preliminary surveys:

The main objectives of the preliminary survey are;

To survey the various alternate alignments proposed after the reconnaissance. To collect all the necessary physical information and details of topography, drainage, and soil. To compare the different proposals in view of the requirements of a good alignment. To estimate quantity of earth work. To finalize the best alignment.

Detailed survey;

The alignment finalized at the design office is to be located on the field by establishing center line. The center line stakes are driven at suitable intervals (50m intervals in plain and rolling terrain and 20 m

intervals hilly terrain.) Bench marks are fixed at interval of about 250m and all drainage and under pass structures. Levels along the final center line should be taken at all staked points. The cross section levels are taken up to the desired width. All river crossing, valley etc. should be surveyed in detail Detailed soil survey is carried out The data during the detailed survey should be complete for preparing detailed plans, design and

estimate of the project.

Highway Alignment:

The position or the layout of the centre line of the highway on the ground is called alignment.

Horizontal alignment (straight path, curves, horizontal deviations)

Vertical alignment (Changes in gradient and vertical curves)

Disadvantages of improper alignment:

Increase in construction cost Increase in maintenance cost Increase in vehicle operation cost Increase in accident rate.

The basic requirements of an ideal alignment should be;

Short It is desirable to have a shortest alignment between two terminal stations. Easy The alignment should be such that it is easy to construct and maintain easy with minimum

problems. Safe The alignment should be safe enough for construction and maintenance from the view point of

stability of natural hill slopes, embankment and cut slopes and foundation of embankments. It should besafe for the traffic operation with safe geometric features.

Economical If the total cost including initial cost, maintenance cost and vehicle operation cost is lowthe road alignment could be considered economical.


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Factors controlling the highway alignment

a) Obligatory pointsb) Trafficc) Geometric designd) Economye) Others

In hill roads addition care has to be given for;

StabilityDrainageGeometric standard of hill roads

a) Obligatory point: Points through which the alignment is to pass

Bridge siteIndustrial areaHill passIntermediate town

Points through which the alignment should not passWaterlogged areaHistorical or archeological siteRestricted zone for defense/national securityDensely populated areaVery costly structures

b) TrafficThe alignment should suit traffic requirements. Origin and destination study should be carried out in thearea.

c) Geometric designThe geometric design of a highway deals with the dimensions and layout of visible features of thehighway such as such as gradients, radius of curve, sight distance, and super elevation etc. Whilealigning a new road, the gradient should be flat and less than design gradient.

d) EconomyThe alignment should also be economical

e) OthersVarious other factors such as drainage, hydrological factors, political considerations, monotony, Sub-surface water level, seepage flow and high flood level are to be keeping in view.


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Alignment along a hill side pass

Connecting intermediate town

A

BLake

Alignment avoiding an intermediate area

Alignment to suit proper location of bridge.

transportation engineering i (chapter ii/iii

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