chapter 2 teyba powerpoint.pptx

Chapter Two
Highway Survey And Route
Selection
2
Lecture
Two

Route Location and Survey
Main Objectives
 To perform specific studies for route location
survey
 To draw preliminary plans and profiles
 To undertake map study for all reasonable
alternative routes and to select the best route
Teyba .W(Msc) Highway Engineering I-Introduction 3

The road project cycle comprises of the following
 Stages:-
 Project Identification
 Route Selection
 Feasibility Study/Preliminary Design
 Detailed Design
 Construction
 Improvement/Upgrading
 Maintenance/Operation

The road project cycle comprises of the following
1. Project Identification
 Identification of the need for a new road, based on
strategic, economic and/or social/rural mobility
considerations.
 Definition of route corridor and identification of
fixed points through which route options must pass.

Stages:-
2. Route Selection
• Includes the identification of route options, desk &
field studies to yield comparisons of length, cost,
stability and geo-hazard, environmental and social
considerations, preliminary economic analysis.
Selection of preferred option.

Stages:-
3. Feasibility Study/Preliminary Design
• Preliminary design and economic analysis of
preferred route, including traffic studies, Economic
Internal Rate of Return (EIRR) to demonstrate
economic feasibility.

Stages cont.…
4. Detailed Design
• Detailed design involves geometric design, design of
earthworks, drainage, geo-hazard control,
environmental mitigation, land acquisition and
compensation, detailed Bill of Quantities (BoQ) and
cost estimate.

Stages cont.…
5. Construction
• Construction of designed alignment and ancillary
works.
• Inspection of ground conditions during excavations
to ensure compatibility.
• Redesign to take account of any unforeseen
conditions or unforeseen environmental effects.

Stages cont.…
6. Improvement/Upgrading
• This may require road realignment, either locally or
over longer distances, to allow for a higher
geometric specification.
• This could involve pre-feasibility level studies as
well as Feasibility Study and Design.

Stages cont.…
7. Maintenance/Operation
• Maintenance and operation of the constructed alignment

Highway Alignment
Definition: The position or the layout of the centre
line of the highway on the ground is called the
alignment.
 Horizontal alignment consists of straight paths and
curves
 Vertical alignment consists of grades and curves

Highway Alignment
 Improper alignment of a road facility implies capital loss
initially in construction as well as loss in costs of
maintenance and vehicle operation
 Once the road is aligned and constructed, it is not easy to
change the alignment due to increase in cost of adjoining
land and construction of costly structures by the road side.
 Hence careful considerations while finalising the alignment
of a new road need not be over-emphasised.
 In general, the aim of alignment selection process is to find a
location for the new road that will result in the lowest total
construction, land, traffic and environmental costs

Requirements of an ideal alignment
 Requirements of an ideal alignment between two terminals
include:
 Short
 A straight alignment would be the shortest, though
there may be several practical considerations which
would cause a deviation from the shortest path
 Easy
 Easy to construction
 Easy to maintain
 Easy for operation with easy grades and curves

Contd...
 Economical
 Design should consider initial capital cost, maintenance cost, and
operation cost
 Safe
 Safe enough for construction and maintenance from the view
point of stability of natural slopes, embankments, cut slopes, and
foundations
 Safe for traffic operations with easy geometric features such as
sharpness of curves, grades, side slopes and etc.

Factors Controlling Highway Alignment
 Obligatory Points
 Points through which the alignment is to pass
 Chosen Bridge Site, Intermediate town to be accessed
between the termini, a mountain pass, etc.
 Points which should be avoided
 Areas requiring costly structures, highly developed
expensive areas, marshes and low lying lands subject to
flooding, hilly terrain where there is a possibility of land
slides, etc.

Factors Controlling Highway Alignment (cont.)
Traffic
 The alignment should suit the traffic requirements
 Present and future travel patterns should be observed & forecasted
 Traffic “Desire line” should be drawn showing path of traffic flow
Geometric Constraints
 Design factors such as max. gradient, minimum radius of curve,
minimum available sight distance, maximum allowable super-
elevation, etc. should be within the limits of allowable design values
which are governed by the expected traffic speed

Factors Controlling Highway Alignment (cont.)
Economy
 Total transportation cost including initial construction cost,
maintenance cost, and operation cost
 Example :
 Deep cuttings, high embankments, no of bridges that need to be constructed, etc.
increases the initial cost of construction.
Other considerations
 Drainage considerations
 Hydrological factors
 Political considerations
 Monotony

Special considerations on Hilly Roads
 Slope Stability
 a common problem in hill roads is land slide. Special care should be taken to
choose the side that is more stable
 Drainage
 Numerous hill-side drains to adequately drain the water across the road should be
provided
 But, attempts should be made to align the road where the number of cross-
drainage structures are minimized
 Geometry
 Different standards of grades, curves, sight distances, speeds and other related
features are followed in hill roads
 Resisting Length
 The resisting length should be kept as low as possible. Thus, the ineffective rise
and excessive fall should be kept minimum

Special considerations on Flat Roads
 In flat country the route line might be straight
between terminal points,but frequently a change of
direction is introduced
 to reach some of the strategic or compulsory points, to
relieve monotony of driving or
 to avoid certain areas necessitating costly or undesirable
property

Route Selection
• Route selection involves the following steps
 Project Identification
 selection of the corridor
 identification of route options within the corridor
 selection of the preferred route option

Project Identification
• Potential road projects are initially identified in a
number of ways:
 through ERA’s strategic road network planning
analysis
 via the initiatives of other ministries
 from proposals by regional governments
 from requests by community representatives.

Selection of Corridor
• A route corridor is defined as the length and width of an
area of terrain that needs to be studied in order to be able to
identify route options within it.
• Corridor selection involves a range of traffic forecasting,
connectivity, economic and strategic environmental land
engineering issues and should take into account the intended
road function within the classification system of the existing
network.

• There are no minimum or maximum dimensions to the width
of the corridor, as this is determined usually by the
geographical structure of the existing road network, intended
road purpose, or road category, topography and the envisaged
constraints imposed by social and environmental factors.

The data resources available for identifying a
corridor are:
 existing topographic and other specialized mapping,
including those for national
 parks and other protected areas
 satellite imagery
 site reconnaissance
 local information
 government and regional development plans.

The outcome of corridor identification process is:
the definition of the start and end points of the
project corridor
the identification of any other defined intermediate
control points (e.g. towns and villages) through
which various route options are required to pass
the definition of any constraints (topographical,
environmental or administrative) that might dictate
where route options cannot be located.

Route Option Identification
• Route options are defined as approximate
alignments within the route corridor that are
compared in order to select the preferred route.

Route option identification is usually undertaken by consultants on
behalf of ERA, and should take into account:
• ease of topography
• practicality of designing an alignment according to the required
geometric standard within the topography
• avoidance (or mitigation) of areas of known geo-hazard, including
landslides,flooding and problematic soils
• avoidance of environmentally protected areas and other sensitive
habitats

Route option identification is usually undertaken by consultants on
behalf of ERA, and should take into account:
• avoidance of the location or areas of cultural heritage value
(including archaeological sites, sites of historical
importance, religious sites and other locations of ethnic or
community value)
• the need to maximise connectivity of villages and towns and
improve rural mobility
• the need to maximise traffic connectivity and access to
economic resources andmarkets
• the need to select the shortest distance alignment, bearing in
mind the factors givenabove.

Route Location Surveys
 In order to select the best road corridor, the following
engineering surveys are usually carried out:
 Reconnaissance Surveys
 Preliminary Surveys
 Detailed (Location) Surveys

Reconnaissance Surveys
Highway Eng. I , Route Selection 34
 1st phase of Reconnaissance: Desk Study
 Involves an examination of a relatively large area between
terminal points for the purpose of determining a broad corridors
through which a road alignment may pass
 Usually such survey is made by the use of available maps and
Aerial Photographs (stereoscopy)
 Probable Alignment is identified on the map by:
 Avoiding valleys, ponds, etc.;
 Avoiding river bends where bridges should not be
located;
 Keeping in view of geometric standards (e.g.
avoiding steep topographies, etc)

Reconnaissance Surveys
Highway Eng. I , Route Selection
35
 2nd phase of Reconnaissance: Field Study
 Involves inspection of each band (identified during the desk study) to determine
the most feasible route based on some basic criteria
 A survey party inspects a fairly broad stretch of land along the proposed
routes identified on the map during the 1st phase and collects all relevant
details not available on the map
 Some of the details include:
 valley, ponds, lakes, marshy land, ridge, hills, permanent structures, &
other obstructions;
 gradient, length of gradient, and radius of curves;
 number & types of cross-drainage structures, and maximum flood level;
 soil types from field identification;
 sources of construction materials, water and location stone quarries;
 geological formation, type of rock, depth of strata, seepage flow, etc to
identify stable sides of a hill
A rapid field study of the area, especially, when it is vast and the terrain is
difficult may be done by aerial survey

General criteria used in route selection
 The relative length of the alternatives was considered. mostly the shortest is
selected
 The average and mean gradient was computed for each route. Normally the
least severe grade alternative is preferred. However, minimum grade mostly
give larger length.
 Route more closely follow an existing road or track are preferred.
 Routes face least severe terrain type was considered.
 Route remain longer on the crest of the terrain minimize drainage structure.
 Alignment minimizes for land acquisition and demolition of buildings and
houses are preferred.
 Trial number of cross drainage structures is considered.
 Routes result in least environmental disturbance is preferred.
 Route with least overall project cost are preferred.

37
After evaluating the alternative routes proposed, one or more
routes will be recommended. If more than one routes passed
the reconnaissance survey detail study is made to choose one
best route in the preliminary survey.

Preliminary Surveys
38
 Consists of running an accurate traverse line along
the routes already recommended as a result of
reconnaissance survey in order to obtain sufficient
data for final location
 Objectives
 Survey and collect necessary data (topography, drainage,
soil, etc.) on alternate alignments
 To estimate quantity of earthwork, material, … of
different alternatives
 Compare alternate alignments
 Finalize the best alignment from all considerations

Preliminary Survey
39
 The preliminary survey may be carried out by
one of the following two methods:
 Modern: Aerial Survey – using photo interpretation
techniques, information on topography, soil, geology,
etc. can be obtained
 Conventional: a survey part carries out surveys using
the require field equipment taking measurements,
collecting topographical and other data and carrying
out soil survey

Conventional Method
40
 Establishing primary Traverse following the line recommended in the
reconnaissance survey
 Record all topographical features
 Levelling work: to determine the Centre Line, Profile & Typical Cross-sections
(just sufficient to approximate earthwork)
 Hydrological Data: to estimate type, number, & size of cross-drainage
structures, and the grade line is decided based on the hydrological and drainage
data
 Soil Survey: the suitability of proposed alignment is to be finally decided based
on the soil survey data. The soil survey at this stage helps to workout details of
earthwork, slopes, suitability of materials, sub-soil and surface drainage
requirements, pavement type and approximate thickness requirements
After finishing the preliminary survey, Select the most suitable alignment by
conducting a comparative study considering economy, geometry, etc.

Final Location Survey
Purpose
to fix the centre line of the selected alignment and
collect additional data for the design and preparation of
working drawings. If extensive data is collected earlier
the survey work here might be limited.

Tasks during Final Location Survey
42
1. Pegging the centre line: usually done at stations
established at 30m intervals with reference to
preliminary traverse/ base line (if used earlier) or
a control survey (if aerial survey was used).
2. Centre-line Levelling: at the stations and at
intermediate points between stations where there
is a significant change in the slope to obtain the
representative profile of the ground

Tasks (cont.)
3. Cross-section Levelling: at each station (!) and at
points with significant change in ground slope
4. Intersecting Roads: the directions of the centre
line of all intersecting roads, profiles, and cross-
sections for some distance on both sides
5. Ditches and Streams: horizontal alignment,
profile, and cross section levelling of the banks
of the stream/river

Steps in route location
44
 Know the termini points of the scheme.
 From the study of a map of the area, identify
and locate:
 National parks
 Any ancient relics, castles and the likes
 Existence of monasteries
 Mining sites
 Existing transport facilities
 Other public facilities (electricity, water)
 Location of construction materials

Steps in route location (cont…)
45
 Conduct preliminary and reconnaissance surveys and
collect information on pertinent details of topography,
climate, soil, vegetation, and any other factors.
 Based on the information collected in the previous two
steps select a corridor.
 Identify a number of possible centerlines within the
corridor.
 Make a preliminary design for the possible alternative
alignments and plot on a base map.
 Examine each of the alternative alignment with respect to
grades, volume of earthwork, drainage, crossing
structures, etc to select the best alternative route.
 Make final design and location of the selected best
alternative route.

Drawings & Reports
46
 The data, after the necessary investigation and final
location survey, is sent to the design office to be used for
 geometric design, pavement design, and design of drainage and
other structures, preparation of drawings, reports, and specifications
 A complete sets of drawings for a road design includes:
 Site plan of proposed alignment
 Detailed Plan & Profile
 Cross-sections for Earth work
 Typical Roadway sections at selected locations (e.g. junctions)
 A mass-haul diagram
 Construction details of structures like bridges, culverts, ….

47

Quize
1. What are general objective of the chapter ??
Teyba .w(Msc) Highway Engineering I-Introduction 49

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