Types of Railway Construction Surveys

Types of Surveys

Once a decision has been taken during preliminary investigations about the general feasibility and desirability of a railway line, surveys are undertaken before the construction of the new line. The following types of surveys are normally conducted:

(a)  Traffic survey

(b) Reconnaissance survey

(c)  Preliminary survey

(d) Final location survey

The details of these surveys are discussed in the following sections.

1 Traffic Survey

Traffic survey includes a detailed study of the traffic conditions in the area with a view to determine the

(a)  most promising route for the railway in the area,

(b) possible traffic the railway line will carry, and

(c)  standard of railway line to be followed.

Traffic surveys are normally undertaken in conjunction with reconnaissance or preliminary engineering surveys so that the technical feasibility and relative costs of alternative proposals can be formulated. The traffic survey team should work in close cooperation with the engineering survey team. The survey team should visit all trade centres in the area and consult local bodies, state governments, and prominent citizens regarding trade and industry and propose the most suitable alignment for the new line.

Traffic survey consists of an economic study of the area keeping in mind the following considerations, information on which should be collected in detail:

(a)  Human resources

(b) Agricultural and mineral resources

(c)  Pattern of trade and commerce

(d) Industries located and projected

(e)  Prospects of tourist traffic

(f)  Existing transport facilities

(g)  Locations of important government and private offices

(h) Planning for economic development of the area

The traffic survey team should make an assessment of the traffic likely to be carried by to the new line. While carrying out the survey, details of traffic likely to be offered by various government organizations, public bodies, or private enterprises should be gathered.

At the end of the survey, a report should be formulated by the officer-in-charge of the survey. The formation of the report is governed largely by the nature of the terms of reference and the investigations made. The traffic survey report should normally contain the following information:

(a)  History of the proposal and terms of reference

(b) General description

(c)  Potentials and prospects

(d) Industrial and economic development and traffic projections

(e)  Population projection and volume of passenger traffic

(f)  Existing rates and rates to be charged

(g)  Location of route or routes examined, alternate routes, and possible extensions

(h) Station sites and their importance

(i)  Train services, section capacity, and various alternative ways of increasing capacity

(j)  Coaching earnings

(k) Goods earnings

(l)  Working expenses and net receipts

(m) Engineering features

(n) Telecommunication facilities

(o) Financial appraisal

(p) Conclusions and recommendations

2     Reconnaissance Survey

This survey consists of a rapid and rough investigation of the area with a view to determine the technical feasibility of the proposal as well as the rough cost of one or more alternatives to the new line. The reconnaissance survey (RECCE) is normally based on contoured survey maps and other data already available without carrying out detailed investigations in the field. With the help of the maps, different alternative alignments of the new line are studied.

The general topography of the country is studied by the survey team and then field data are collected.

2.1 Survey Instruments

The reconnaissance survey is mostly conducted using survey instruments that rapidly measure approximate distances and heights. The survey instruments used are the following:

Prismatic compass  To get magnetic bearings of the proposed alignment.

Aneroid barometer To ensure relative heights of various points.

Abney level or hand level or clinometer To measure the gradients or angles of slopes.

Binocular To view the physical features.

Pedometer To get an idea of the total length traversed while walking.

2.2 Modern Surveying Instruments and Techniques

Modern surveying instruments make extensive use of infrared beams, laser beams, as well as computers. Using these instruments, it is possible to carry out fairly accurate surveying efficiently at all times, eliminating human error.

Electromagnetic Distance Measurement (EDM) Instruments

EDM instruments rapidly and automatically measure both horizontal and vertical distances. The readings can be displayed on built-in computer screens. Examples of such instruments are the geodimeter and the tellurimeter, which have been used in the past for electronic distance measurement of up to 80 km during day or night. Modern EDM instruments are much more advance and versatile.

Use of Computers

The results of the field survey are recorded in the form of angles and distances in the normal field book or electronic notebook. Using computers, it is possible to do all calculations as well as plot accurately. Thus, output from the EDM can be fed into the computer, which in turn can plot plans and sections.

Use of Laser in Surveying

Laser is an acronym for light amplification by stimulated emission of radiation. Its property of low diversion is used for alignment purposes. The invisible line of sight in ordinary survey instruments is replaced by the bright red beam of the Laser. This beam is intercepted by the target composed of light-sensitive cells connected to the display panel. Its most important aspect is that the beam is in a perfect straight line. Distances up to 70 km can be measured using laser. For short distances infrared beams are used.

2.3 Field Data

The following field data are collected during the reconnaissance survey.

(a)  General topography of the country

Approximate heights of the different points falling on the alignment

(c)  Positions of rivers, streams, and some hydrological details of the same

(d) Positions of roads and highways

(e)  Nature of soil at different places

(f)  Rough location of various station sites

(g)  Controlling points on the alignment, through which the railway line must pass

(h) Facilities for construction

2.4Project Report for Reconnaissance Survey

Based on the above data, a report should be prepared by the engineer in charge of the project bringing out clearly from the financial point of view whether or not the prospects of the line surveyed are such as to make it worthwhile to undertake further investigations to construct the line. The project report should be accompanied by an abstract estimate of the cost of the line.

The report and estimate should be accompanied by a map of the area on a scale of 20 km to 1 cm and an index map of 2.5 km to 1 cm.

3 Preliminary Survey

The preliminary survey consists of a detailed instrumental examination of the route to be selected as a result of the reconnaissance survey in order to estimate the cost of the proposed railway line. Based on the preliminary and traffic survey reports, the railway administration decides whether or not the proposed railway line is to be constructed.

3.1 Instruments for Preliminary Survey

The instruments to be used for a preliminary survey will depend on the topography of the country and its flora. The survey instruments normally used are the following.

(a)  Theodolite for traversing and pegging the centre line

(b) Tacheometer for plotting the main features

(c)  Dumpy level for taking the longitudinal and cross levels

(d) Plane table for getting details of various features

(e)  Prismatic compass for measuring the magnetic bearings of a particular alignment

3.2 Field Survey

The route selected is surveyed in greater detail in the preliminary survey. The survey normally covers a width of 200 m on either side of the proposed alignment. The following survey work is carried out.

(a)  An open traverse is run along the centre line of the proposed alignment with the help of a theodolite, tacheometer, or a compass.

(b) Longitudinal and cross levelling on the proposed route for a width of 200 m on either side in order to make an accurate contour map.

(c)  Plane tabling of the entire area to obtain various geographical details.

(d) Special survey of station sites, level crossings, and bridges using the plane table.

3.3 Data

The following information should normally be collected during a preliminary survey.

(a)  Geological information such as type of soil strata and the nature of rocks.

(b) Source of availability of construction materials such as sand, aggregate, bricks, cement, and timber.

(c)  Facilities for construction such as the availability of labour and drinking water.

(d) Full details of the land and buildings to be acquired.

(e)  Details of existing bridges and culverts along with information about proximity of tanks, bunds, etc., which may affect the design of bridges.

(f)  Details of road crossings along with the angles of crossing and the traffic expected on the level crossings.

(g)  High flood level and low water level of all the rivers and streams falling on the alignment.

(h) Full details of station sites along with the facilities required.

3.4     Preparation of Project Report

A report based on the preliminary survey is prepared after obtaining an estimate of the cost. The project report should contain the following details.

(a)  Introduction

(b) Characteristics of the project area

(c)  Standard of construction

(d) Route selection

(e)  Project engineering including cost estimate and construction schedule

(f)  Conclusions and recommendations

3.5     Cost Estimate

The report should be accompanied by cost estimate. The estimate based on the preliminary report should be sufficiently accurate to enable a competent authority to take a decision regarding the construction of the new line. The estimate should contain the following details.

(a)  An abstract cost estimate of the line surveyed accompanied by an abstract estimate of junction arrangements.

(b) Detailed estimates of land, tunnels, major bridges, minor bridges, one kilometre of permanent way, rolling stock, and general charges.

The report and estimate should be accompanied by the following drawings.

(a)  Map of the area (scale 20 km = 1 cm)

(b) Index plan and section (scale 0.5 km to 1 cm horizontal and 10 m to 1 cm vertical)

(d) Detailed plans and sections Plans of station yards

(e)  Plans of junction arrangements

4.Preliminary Engineering-cum-traffic Survey

In practice, and quite often, both the traffic survey and the preliminary engineering survey are carried out simultaneously in order to expedite the project. In such cases techno-economic survey reports based on preliminary-cum-traffic surveys are compiled. Such techno-economic survey reports contain the following details.

(a)  Introduction

(b) Traffic projections

(c)  Analysis of alternatives

(d) Characteristics of project area

(e)  Standards of construction (for new lines, multiple tracking schemes, gauge conversions)

(f)  Route selection and project description

(g)  Project engineering (for new lines, multiple tracking schemes, and gauge conversions)

(h) Cost, phasing, and investment schedules

(i)  Financial appraisal

(j)  Recommendations

5.Final Location Survey

Once a decision has been taken for a particular railway line to be constructed, a final location survey is done. The instruments used are generally the same as in the case of the preliminary survey. Final location survey is done to prepare working details and make accurate cost estimates in certain cases. The principal differences between the preliminary survey and the final survey are as follows.

(a)  In the final location survey, the alignment is fully staked with the help of a theodolite, whereas it is not obligatory to do so in the case of preliminary survey.

(b) In the final location survey, a more detailed project report is prepared and submitted.

(c)  All working drawings are prepared in the final location survey.

The following tasks are carried out in the final location survey.

(a)  The centre line is fully marked by pegs at 20 m. At each 100 m, a large peg should be used.

(b) Masonry pillars are built at tangent points of curves and along the centre line at intervals of 500 m.

(c)  Longitudinal and cross levelling is done to ascertain the final gradient of the alignment. All gradients are compensated for curves.

(d) The sites for station yards are fully demarcated.

In the final location survey, the following set of drawings is prepared.

(b) General map of the country traversed by the project at a scale of about 20 km to 1 cm Index map, scale about 2.5 km to 1 cm

(c)  Index plan and sections

(d) Detailed plans and sections

(e)  Plans and cross section

(f)  Plans of station yards

(g)  Detailed drawings of structures

(h) Plans of junction arrangements

5.1 Objectives

The following broad objectives should be kept in mind when selecting the best possible alignment in the final location survey.

(a)  Correct obligatory points

(b) Easy grades and flat curves

(c)  Minimum cost of construction

(d) Minimum adverse effect on environment

(e)  Ease of construction

(f)  Potential for high speeds

(g)  Avoidance of constraints for future expansion

(h) Minimum maintenance cost

5.2-Project Report

A final project report is prepared based on the final location survey. The report consists of the following.

Introduction

In this segment of the report, the following details are covered.

(i)  Object of investigation and background

(ii)  Programme and methodology of investigation

(iii) Special features of investigation

Characteristics of the Project Areas

In this segment the topographical outline of the areas and geographical features of the country are given to the extent to which these are likely to affect the alignment, probable stability of the line, cost of construction, working expenses, or future prospects of the proposed line. Climatic and rainfall characteristics and environmental characteristics such as the presence of corrosive factors, pollution, etc., which may have an effect on the design and maintenance of structures and bridges, are also brought out.

Standard of Construction

This segment gives details of the following.

Gauge The gauge adopted for the proposed line and the reasons, if any, for adopting it. Category of line The category of the line, the maximum speed potential of the line, the maximum axle load, the loading standard of bridges, and the basis for adopting the same.

Ruling gradient  The gradient adopted and the basis for its selection.

Curves The sharpest degree of curvature adopted, the basis for its adoption, and its impact on the projected speed compatible to the category of line.

Permanent way The rail section adopted, the decision as to whether welding of the rails will be carried out or not, and the type and density of sleepers provided in the project estimate.

Ballast The type and depth of ballast cushion provided.

Stations Spacing of stations in the case of new lines, provision for future intermediate stations, and the scale of facilities contemplated at stations.

Signalling and telecommunication The standard of signalling adopted and the scale of communication facilities provided.

Traction The type of traction proposed.

Other details Road crossings, station machinery, residential accommodation, service and maintenance facilities, etc.

Route Selection

This segment provides relevant information and data related to the various alternative routes examined and gives an insight into the factors influencing the choice of the route adopted for the project.

Project Engineering

This section furnishes information and data for the project manager to enable him to understand the scope and extent of the project and to assist him in formulating the strategy for the execution and management of the project. It must focus on the problems likely to be encountered, identify the areas requiring special attention, and place the knowledge and information gathered at the investigation stage for evolving optimal solutions.

Estimation of Cost and Construction Schedule

This segment gives a cost estimate of preliminary expenses, land, formation, bridges, permanent way, station building and residential quarters, road crossings, station equipment, signalling and interlocking, rolling stock, etc. The schedule of' construction as well as investment is also given. A network should be developed for projects costing above Rs 5 million.

Project Organization

This section details the organizational structure for the execution of the project, the proposed headquarters of the project manager and other construction officers, as well as the allocation of the various construction activities. Health and hygenic conditions provided to the staff as well as the provision of necessary medical establishments may be indicated, along with suggested plans providing for the housing of staff and labour and the construction of temporary office buildings. Comments regarding the availability of water for construction purposes and its suitability for drinking purposes may also be given. The purpose and final cost allocation of such plans may also be indicated.

Tabulated Details

The report is accompanied by tabulated details of curve abstract, gradient abstract, bridge abstract, important bridges, stations, machinery, stations, and station sites.

Arrangement of Documents in the Report

All the documents pertaining to a final location survey report should be in the following order.

1.  Covering note

2.  Index

3.  Report

4.  A list of drawings accompanying the report

5.  Appendices to the report

(a)  Historical and geographical aspects

(b) Location report

(c)  Rates for construction work