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.
4.6.1 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
4.6.2 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.
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.
4.6.4 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.
(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
4.6.5 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)
(c) Detailed plans and sections
(d) Plans of station yards
(e) Plans of junction arrangements