From the reconnaissance survey of the area, suitable routes are selected and details selected with the instrument are conducted to prepare an accurate topographic map of the selected belts. The field work generally consists of traveling by total station along the selected routes.
Distance heights and angles between traverse stations are measured accuracy
The basic product of preliminary survey in terms of route survey is the location of base line, which are:
Series of straight lines that run along or near what will be the center line of the final route.
The strip or belt should be of sufficient width to accommodate any on expected variation in the position of the final line. Then the preliminary survey is conducted with the same accuracy, as that is required for the final location survey.
The Main Objectives of the Preliminary Survey
The following lists are the objectives of the preliminary survey
1. To survey the various alternate alignment proposed or supposed after the reconnaissance and to collect all the necessary physical information and details of topography, drainage and soil.
2. To compare the different proposals in view of the requirements of a good alignment.
3. To estimate quantity of earth work materials and other construction aspects to work out the cost of alternate proposals.
4. To finalize the best alignment from all considerations
The information thus collected from the field work is used in the preparation of plan. What ever methods be used in making the map, is should show the following information.
• Ground elevation and coordinated is needed.
• The commercial, industrial and other building.
• Feces walls and gravel pits.
• Wells, hydrants and man holes.
• Rail road crossing.
• Existing drainage structures.
• Extents of cultivated area.
• National water courses, ponds, swamps etc
Final location & detailed survey
Final location survey
Locating the proposed line on preliminary map on the ground. The preliminary map may also be an aerial photo or any topographic map available. Marking on the ground will conduct with the help of peg. This process is carried out in two stages:
A-Office location survey.
B -Field location survey.
A- Office location survey: After careful study of the topography of the terrain final location of the route is drawn on the detail map by trial and error method. The new line of alignment projected on the preliminary map or plan is called paper location or office location.
The step that we follow here is that:-
I- Draw the straights along the most suitable alignment of the route.
II- Draw curve by means of radius of curve with known degree of curvature.
III- Prepare a profile along the new line from the contour on the map & make the grade line on the profile.
In our case, the paper location is not conducted on paper rather it is conducted based on computer so, there is no usage of locating the new line on paper with pencil. While choosing the proper location of the route, the following factors should be considered to select the most economical route:-
I- Minimum gradient.
II- Minimum curvature.
III- Proportion of earth work.
IV- Heavy earth work.
V- Minimum no. of expensive bridge.
VI- Minimum no. of retaining &breast walls.
The new line of the route and its corresponding profile are further study to improve, if possible. Repeated trials are made till a well balanced location line is obtained. Before starting the actual construction the center line of the road first marked on the map &then on the site.
The following points are considered while aligning the proposed route:-
I- The alignment that crossed the river/stream should minimum.
II- As far as possible alignment should not pass through built up area of cultivated land.
III- The alignment should be easy gradient &smooth curve.
IV- Unnecessary zigzag in alignment should be avoided.
The recommended minimum radius for highway curve:-
TERRIAN RADIUS OF CURVE(m)
Hilly steep 11
B –Field location survey: It is carried out to set out on the ground the alignment of the route finally decided on the preliminary plan. This includes horizontal alignment (plan view) and vertical alignment (profile view) minor changes are permissible to be made in the field at this stage if necessary. The center line of the projected line is set out on ground as follows:
1. From preliminary map, scale of the position of the various points to be transferred on the ground .To do this; perpendicular offset may be made from the traverse line. The chain age of the intersection of the line with main traverse may be ascertained and if necessary angels and distance may also be used.
2. Prolong the adjoining tangents and find their points of intersection measure the angel of intersection carefully.
3. Knowing the radius of the curve and the angel of intersection of tangents, computer the necessary data for setting out the simple curve.
4. Drive stakes at every 20m intervals and hubs at all intermediate theologize stations, intersection points of tangents and the points of the tangencies of the curves give their proper reference the book.
5. Draw sketches with paper dimension for important feature such as roads railways streams etc on the right hand side of the field books.
6. Carryout the leveling over the located line. Prepare profile & establish a suitable grade line on the profile.
7. Plot the finally located line known as field location on the preliminary plan & complete the profile.
8. Show vertical curves on the final profile.
9. Calculate the appropriate quantities of the earth work by drawing cross section of the location line on the preliminary map.
10. Depict all important features in the close proximity of the line, all the points where hubs are set, all bench marks& the boundaries of private properties on the preliminary plan
1. Center line of the Alignment
Locating the route along which the center line of the rood is well done on the plan, is called alignment of center line. Bettor staring of the virtual constriction the center line of the rood is first marked on the map and on the route of the site.
Consideration while aligning the proposed
1. The alignment crossed the river or stream should minimum and good and durable foundations are possible for construction of a bridge over culvert.
2. Their minimum number of crossing bridge or culvert in argument of proposed route.
3. As far as possible alignment should not pass through soils up area of cultivated land.
4. The alignment should be easy gradient and smooth curves.
5. Unnecessary zigzag in allayment should be avoided.
2. Making Center line of our Alignment
Instrument: – Computer accessed civil survey software
Before the actual alignment of the center line is selected different center line on the alignment are examined for this consideration the following points are kept in mind at the time of study. There is a map by carefully examining of this map; the final center line is selected.
The proposed center line may be placed in the detail location.
3. Draw the Center Line in Plan
In drawing the center line alignment in plan it is good foe using on selecting a correct or current alignment in project. An allayment can be on or more drawing files even though there is only one current alignment at a time.
When definer is defining several alignments, the debugger must be sure that the correct alignment is the current alignment. At a time when designer is defining several alignments the designer must be sure that the correct alignment is the current alignments. The current alignment controls or loops on the generation of profiles and sections if we want to select to define the alignment in the computer, you should have to go to the dialog list and select define alignment. That means if we want the horizontal alignment we can select alignment from dialog list and select define alignment from entities and then select the first entity /tangent/ see the point of beginning.
4- Drawing the Road way centerline Curves
Having done selecting center line alignment the next activities that we should have to focus on the next step is adding curves and spiral segments. The process that we focus to do on this, we connect the first and second tangents, the second and third tangents. The transition from tangent to tangent will be accomplished by a drawing a spiral in to a curve. If it present transition curve in the alignment selected in this description select align-curves-spiral-curve-spiral.
This selection completes the formation of the road way centerline click here view the creation or illustration.
5-Defining Horizontal Alignment
Incase of defining horizontal alignment that we have drawn all of the entities that create the centerline alignment, that we need to define an alignment the entities that we need are grouped and arranged and we can assign a name, a description, and station information. In the civil survey there are two commands from the define alignment menu for defining horizontal alignment.
From entities: Separate entities, such as line, curves comprise the alignment from poly line. The one continuous poly line comprises the alignment is made up of separate entities, we will use the from entities command.
Select align, define alignments, and from entities pick a point near the upper (north-westerly) end of the first tangent that we drew. This can be taken as a point of beginning. In this process some thing is focused properly that is the entities that makes up our alignment must meet exactly end to end. The form entities command ends the alignment at any point it tails to find a connecting entity. Accept the default reference point, which is the beginning of the alignment select reference point (enter for start): (press enter). The define alignment dialog box is displayed since this is the first alignment defined it is assigned the number.