PRELIMINARY SURVEY

PRELIMINARY SURVEY

The __________ is carried out to collect all the physical information which are necessary in connection with the proposed highway alignment.

• The main objectives of the preliminary survey are:

(i) To survey the various alternate alignments proposed after the reconnaissance and to collect all the necessary physical information and details of topography, drainage and soil.

(ii) To compare the different proposals in view of the requirements of a good alignment.

(iii) To estimate quantity of earth work materials and other construction aspects and to work out the cost of alternate proposals.

(iv) To finalize the best alignment from all considerations.

(a) Conventional approach

(b) Modern rapid approach

The PRELIMINARY SURVEY may be carried out by any one of the following methods:

CONVENTIONAL APPROACH

in which a survey party carries out surveys using the required field equipment, taking measurements, collecting topographical and other data and carryout soil survey.

MODERN RAPID APPROACH

by serial survey taking the required aerial photographs and by photogrammetric methods and photointerpretation techniques for obtaining the necessary topographic and other maps including details of sol and geology.

• PRIMARY TRAVERSE

• TOPOGRAPHIC FEATURES

• LEVELING WORK

• DRAINAGE STUDIES AND HYDROLOGICAL

• SOIL SURVEY

• MATERIAL SURVEY

• TRAFFIC SURVEY

• DETERMINATION OF FINAL CENTRE LINE

The procedure of the CONVENTIONAL METHODS of preliminary survey is given in following steps:

PRIMARY TRAVERSE

The first step in the preliminary survey is to establish the primary traverse, following the line recommended in the reconnaissance.

TOPOGRAPHIC FEATURES

After establishing the centre lines of preliminary survey, the topographical features are recorded. All geographical and other manmade features along the transverse and for a certain width on either side are surveyed

LEVELING WORK

The levelling work in the preliminary survey is kept to a minimum just sufficient to obtain the approximate earth work in the alternate alignments.

DRAINAGE STUDIES AND HYDROLOGICAL

drainage investigations and hydrological data are collected so as to estimate the type, number and approximate size of cross drainage structures

SOIL SURVEY

Soil survey is an essential part of the preliminary survey as the suitability of the proposed location is to be finally decided based on the soil survey data.

MATERIAL SURVEY

the survey for naturally occurring material like stone aggregates, soft aggregates, etc. and identification of suitable quarries should be made. Also, availability of manufactured materials like cement, lime, brick etc. and their locations may be ascertained.

TRAFFIC SURVEY

traffic surveys conducted in the region form the basis for deciding the number of traffic lanes and roadways width, pavement design and economic analysis of highway project.

DETERMINATION OF FINAL CENTRE LINE

after completing the preliminary surveys and - conducting the comparative studies of alternative alignments the final centreline of the road is to be comparative studies of alternative alignments the final centre line of the road is to be decided in the office before the final location survey.

Aerial photographic surveys

are very much suited for preliminary surveys, especially when the distance and aera to be covered are vast. The survey may be divided into following steps:

• (a) Taking aerial photographs of the strip of land to be surveyed with the required longitudinal and lateral overlaps.

• (b) The photographs are examined under stereoscopes and control point are selected for establishing the traverses of the alternate proposals.

• (c) Using stereo-pair observations, the spot levels and subsequently contour lines may be obtained.

• (d) Photo-interpretation methods are used to assess the geological features, soil conditions, drainage requirements etc.

FINAL LOCATION AND DETAILED SURVEY

The alignment finalized at the design office after the preliminary survey is to be first located on the field by establishing the centre line.

LOCATION

This is done using a transit theodolite and by staking of the centre line. The location of the centre line should follow as closely as practicable, the alignment finalized after the preliminary surveys.

DETAILED SURVEY

Temporary bench marks are fixed at intervals of about 250 metre and at all drainage and under pass structure. Levels along the final centre line should be taken at all staked points. Levelling work is for great importance as the vertical alignment, earth work calculations and drainage details are to be worked out form the level notes.