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HAND BOOK FOR BRIDGE WORKS
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INTRODUCTION
A bridge project from its conception to completion involves various stages of
planning, design, approval/sanction, tendering and execution. Also inspections,
maintenance and repairs are continuing activities for enhancing the service life of
the structure. This pocket book has been specifically aimed at giving the
practicing engineers the basic information on these aspects.
A bridge project from conception to construction and final completion of the
bridge involves a number of major activities which can be summarized as
follows.
PROJECT PREPARATION
Preparation of a detailed project report is a pre-requisite for proper evaluation of
the project, its approval by competent authority and finally its execution. Properly
prepared project report is very helpful in ensuring timely completion of project
thereby ensuring fullest advantage of the project avoiding time and cost
overruns. Project preparation activity can be divided into the following three
broad stages:-
(1) Feasibility Study
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(2) Preliminary Project Report
(3) Detailed Project Report
For detailed guidelines reference may be made to Special Publication
No.54-“Project Preparation Manual for Bridges” published by Indian
Congress.
Feasibility Study
The project preparation for a bridge work starts with the identification of the
project. This phase is known as the pre feasibility stage. For this stage, broad
features of the project are identified, the possible locations, nature of crossing,
traffic dispersal system for different alternatives are identified. The effect of
implementation of the project on the traffic scenario in immediate vicinity is also
considered. This reconnaissance visit to the area of the intended site is sufficient at
this stage.
In the feasibility stage, preliminary surveys, data collection and
investigations are carried out. Alternative site are investigated, design and rough
cost estimates for various alternatives are made. The feasibility report covering
the recommended alignment including alternative considered, span
arrangement, preliminary cost estimates, economic and financial viability is
prepare. Feasibility study should also cover the following aspects.
i. the main purpose of the bridge project i.e. the trunk route,
economic or interstate importance, access to ports, tourism,
agriculture development etc. the place of the project in the road
development programme and the priority assigned to.
ii. The geographic features of the area such as size, economic
(industrial and agricultural), other traffic generated activates in
the area, main population centers, their size projections and
growth rates, and government’s economic programme for the
developments.
iii. Measurable and non measurable benefits should be listed. The
former may consider reduction in operation costs, reduction in
travel time for goods and passengers, reduction in maintenance
cost in case a old bridge is replaced. The latter may include
social and economic development of the adjacent area
consequent to the construction of the bridge.
iv. A cost benefit analysis should be enclosed and results critically
discussed. For calculation of cost benefit analysis, a reference
may be made to IRC SP -30: 1993. “Manual on Economic
Evaluation of Highway Projects in India (First Revision)
Preliminary Project Preparation
Preliminary project preparation involves various stages like recognition of the
need, study of maps, reconnaissance survey leading to selection of alternative
site, preliminary survey and investigation including subsoil investigation and
collection of hydraulic data leading to final site selection and all these activities
has to be systematically planned and carried out in their logical sequence.
Preliminary subsoil investigation
( i) Preliminary subsoil investigations should include adequate number
of trial bores/trial pits for obtaining realistic data for deciding the span
arrangement, type of foundation and scour level as specified in 1RC:78
for making the preliminary design of the bridge. The exploration shall
cover the entire length of the bridge and also extend at either side for
a distance of about twice the depth below bed of the last main
foundations.