What is highway alignment?
A highway alignment may be defined as a position occupied by the centerline of the road on the ground.
Classification of highway alignment
- Horizontal alignment
- Verticle alignment
Without right alignment of the road there may occur accident between vehicles and loss of economy so, to have highway alignment economical and safe we have to survey all the possible rout of road and then we have started to the construct.
So, friends here I have given a different stage of highway alignment survey read carefully to get the full concept.
Stage of highway alignment
- Map study
- Preliminary survey
- Detailed survey
1) Map Study
it is the first step of the survey
In the first step, all the readymade (updated) topographical maps, geological maps, and Hydrological maps are carefully studied and the best possible alternative routes are located on a topographical map.
During the study of the prepared map, the following points are considered.
* Obligatory points
* Geometric design features
* Composition of vehicles …
* Availability of resources
* Socio-economic impact etc.
It is the second step or stage of the survey
in this stage, group of people i.e. teams are walked along all the alternative routes, selected during map study.
Each team carries simple instruments like Tape, Abney level, digging tools, etc.
In this stage of the survey, survey teams collect the topographical, geological data, and hydrological data that were not available in readymade maps studied during map study.
At this stage, the engineer should have sufficient physical information which, when taken in combination with the traffic, economic, social & political data, will enable them to trace one or more paper location of feasible routes.
When the extent & quality of data’ gathered is sufficient, it may be possible to make the necessary economic to aid in the selection.
3) Preliminary survey
The preliminary survey is a large scale study of one or more feasible routes. It Consists of running an accurate traverse line, usually called baseline along the route already recommended after a reconnaissance survey in order to obtain sufficient data for the final location.
The” preliminary survey is made for the purpose of collecting all the physical information that may affect the location of highway alignment
There are two approaches for preliminary survey mapping,
- Aerial survey
- Ground survey
As its name, Aerial survey is the survey done from the air with the help of remote sensing or picture of an aerial view.
separating or in combination, the ground method is best one to use in the situation where the alignment is well defined, has the narrow right of way & less man-made features in following circumstances aerial survey is desirable
Where the reconnaissance was unable to approximate closely the final alignment such as an entirely new location in rugged, mount anion terrain.
Where a wide right of way such as that for high type road is necessitated.
Where it is desirable to prevent the premature or erroneous disclosure of the details of the probable location. In case of a ground survey, highway engineer may or may be compelled to locate the alignment through particular locality which is not possible in the aerial survey.
Steps of Ground Survey
1) Preparation of baseline traverse:-
Open traverse is run following the route suggested after reconnaissance. All the linear & angular measurements are taken to prepare a topographical survey.
2) Leveling along baseline:-
TO furnish data for profile and cross-section, the level should be taken at all marked stations (Peg interval), as well as at all important breaks On the ground. Elevation of existing roads, invert of streams or other control elements & critical points should be noted.
3)collecting topographical and other data:
All necessary data required for the topographical map is taken. The linear or angular method may be adopted.
4) Preparation of preliminary survey map:–
with all thoroughly controlled checked survey data, the preliminary topographical map is prepared, showing spot height, traverse line other features. Contours may be drawn manually & the Digital terrain model (DTM) of the ground may be prepared based on preliminary survey data.
5) Paper location or preliminary design:–
Now depending upon the types of road, all geometric elements are designed.
4.) Detailed survey or final location survey:
This survey serves the dual purpose of definitely fixing the line of the road, while at the same, physical data are collected which are necessary for the preparation of complete construction plans, profile, cross-section & road structures.
General features of Detailed survey or final location survey
1) Pegging the center line:-
The centerline established on the ground at this stage should follow closely to the paper location of the preliminary survey map conforming as much as possible to the major & minor control points & alignment prescribed.
The centerline is pegged with references to the preliminary traverse or baseline by any suitable method described in a survey textbook
2) Centerline leveling:-
Profile levels are taken along the centerline at regular intervals & at each point of chainage where ground configuration changes. This profile should generally be extended 150 — 200 m beyond the origin & endpoints, so as to allow for transition from a given road
3) Cross section:-
Cross-sections should be taken at each station, at all points of significant change ¡n the ground slope & for a reasonable distance beyond the beginning & endpoints. The width of the cross-section depends upon the type of highway& topography.
4) Property lines:–
The position of all property corners, lines, fences, buildings, the boundary of land, nature of ownership including name at landowner & kitty number, types of land, other manmade features are accurately determined & note during final location survey.
These data gives an idea about the compensation that should be paid.
5) Temporary watercourse & stream detail:-
All temporary watercourse & streams within the area of constriction should be carefully located. In addition, streambed profiles should be taken for some distance up and down each stream. Cross-sections are also be taken to provide the information required for the hydraulic design.
6) Intersecting roads: –
The direction with respect to the pegged centerline of all intersecting roads should be measured. Profile & cross-section of intersecting roads should be taken for Some length.
7) Material site survey:-
Location of all available sand, stone, boulder queries Should be referenced With respect to the center in either side of the road.
8) Special site survey:–
in order to obtain the detailed information needed for the design of culverts interchanges & other complex intersections or structures, a special site Survey is Carried out.
Hence, these are the different stages and Classification of Highway Alignment.
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