Construction Challenges For Bridges In Hilly Area.docx
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Construction Challenges For Bridges In Hilly Area
Himalaya since Vedic times have been considered a vast repository of valuable medicinal herbs, minerals, forest resources etc. Vedic literature followed by the writings of Charaks, Susruta, Dhanwantri, Nagarjuna, Parashar, Balmiki and various other saints, bear testimony to it. "Alexander, The Great", who was much influenced because of its scenic beauty, bracing climate and agroclimatic conditions, made a great publicity of the Himalayan Herb Science in Yunan and Rome during middle ages (Anonymous, 1977; Chauhan, 1988). This potential, however, remained unexploited especially in higher reaches due to inadequate means of communication. After independence, Govt. of India, gave a special emphasis on road construction in order to bring socio-economic upliftment of tribal inhabitants. But due to lack of proper planning it resulted in serious ecological imbalances.
Society has now become aware of the environmental consequences resulting from road construction in hill areas. Right from the days of Vedas, our country has an age-old tradition of environment consciousness. During Samrat Ashok�s days social forestry was at its full swing having shady trees along the roads and fruit plants on the wastelands. In this paper efforts have been made to incorporate the latest techniques for protecting the environment after extensive survey of literature (Lone et al., 1992 and Chauhan
Hilly region pose unique problem for bridge construction. In a restricted hilly area itself climatic conditions, geological features and hydrological parameters vary considerably. Keeping in view the bridge site and various constraints, type of bridge and method of construction are to be selected carefully for safe, economical and successful completion of bridge construction.
Various challenges that come across while constructing bridges in hilly area are
1. Construction of bridge across deep gorges
2. Construction of bridge on rivers with bouldary beds
3. Construction of bridges in extreme temperature zones
4. Construction of bridges on sharp turn on highway
5. Landslide or Debris flow
Deep gorges, rivers with bouldary beds, extremely low temperature condition, high winds, landslide etc. in hilly regions require special attention to complete the activities of bridge planning and construction in a systematic way and are discussed here in.
Bridge Construction Overview
Planning and monitoring is basically what is to be done in due course of time, and how it is to be executed in the planned/allotted period for the particular bridge. All the pros and cons of the likely problems in the anticipated period need to be examined. Also the records of important points are made available at site with executives as follows:
• Why the particular site was selected for the bridge.
• Why particular type of bridge is proposed. (structural arrangement)
• Site data
• Proposal for preparation drawing.
• Soil strata in the form of bore log.
• Model study detail if already done for scour assessment.
• Salient features of the bridge and quantities of each items involved.
• Upto date approved structural drawings.
• Details of all meetings and up to date decision if at all taken.
• Decision making mechanism in case of any dispute i.e. Dispute Review Borad (DRB) be already finalized.
Bridge Foundation and Substructure
Foundation construction for any large bridge takes time. Problems encountered during construction of foundation depend upon type of foundation, soil strata encountered, equipment/plant deployed and logistic problems. Construction difficulties anticipated during the execution be kept in view while planning the works/ period for the job. Foundation can be opened foundation, pile foundation, well foundation or any other types of foundation. In case of well foundation, the various type of soil are encountered and it becomes difficult to give any clear time schedule about the sinking of wells unless the soil details are very clear and the anticipated profile matched with the actual encountered. In case of bouldery and clayey soil the rate of sinking schedule is likely to be slow when compared with the sandy soil. Also there may be requirement of pneumatic sinking technique subsequent to open grabbing due to difficulties in sinking of well. As the cost of pneumatic sinking is very high, this should be deployed judiciously. In such cases, there is need to keep the details of all the sinking difficulties in a systematic order and this can be reviewed in consultation with decision making authority. Review of soil parameter if required be given more attention and wherever required the details may be referred to material testing laboratory but within the time schedule. This may be helpful to recommend revision in foundation level, wherever possible based on soil data report. Tough strata in the foundation stage should be considered as engineering friendly
For particular site there are numerous structural arrangements possible. Final proposal be made based on the greater examination of site condition may be technical, aesthetic and construction methodology. Special care need to be taken in case of deep gorge where there is sizable difference between soffit level and bed level. This may pose difficulties for staging and shuttering. Proposal recommended for site should be well read in advance. After the proposal has been finalized for particular bridge, the construction can be planned. The quantities of each items involved and execution method be listed. Basically method statement should be kept ready for overall execution including job estimate. This data will be kept to ensure smooth progress of project.
Management of Construction Activities
Management of bridge construction demands that construction manager to reorient all the resources in such a way that the project is completed without any time/cost over run. Output of the work depend upon how best the activities are managed which will vary from site to site based on many factors. Based on the experience, various aspects be identified for efficient construction management. Schedule of construction based Critical Path Method (CPM) be prepared along with major milestone and Bar Charts. Latest software management tool can be used for this in case of a major bridge project. Design of Bridge is a post sanction in case of departmental construction and after tendering action in case of bridges throughout contract. It is necessary that design must be preceded by at least six to eight months or say 50% ahead of execution of concerned event. It has to be ensured that this should be completed well in time. Reviseddesign if any should be updated and clarified without delay. Observation on the approved design drawing if any be passed to design office immediately to make the changes. This is most important in case of foundation where design soil parameter needs to be adhered to. These may vary on actual execution and require review of design. To keep details with design office it is necessary that progress of foundation work be well informed to the design office.
Requirement of equipment/plant be assessed systematically and accordingly action may be taken to arrange this for a particular job.
• Quantum of work covering all the items with specifications
• Time available for work excution
• Details of equipment and also minimum requirement as per job position.
• Rated capacity of equipment/ plant
• Assessed capacity
• Schedule of maintenance
• Inventory of spare parts required
• Repair cover to equipment/plant
The layout should ensure minimum movement of material, equipment and personnel of the area is an essential condition, for operation of some equipment for example tower crane operation not possible at heavy winds speed. Stone crusher if required for site should be suitably located. Supporting facilities such as generator, office, stores should not be located in the path of dust, flow. The service road should be properly maintained. Receipt and despatch of equipment be kept in proper format to keep of details of its utilisation at site.
After staff has reported at site necessary action should be taken to utilise all the equipment. The required facilities for servicing and repair must be established to meet requirements.
Material management is a parallel activity along with start of the Project. This cover procurement of camp material, office equipment, major purchased items, such as aggregates, sand, cement, steel, structural steel, shuttering consumables, electrical fittings. Forecasting of quantities and cost of various items on monthly basis must be done at least three to six months in advance which should be regularly reviewed.
No project or project management can be meaningful without this. In case of Government work the manager should get his budget fixed on monthly basis, on the basis of work done or minimum to be fed at site, on the decision of higher authorities. Key to measure financial planning lies in taking all above action and taking suitable measures at appropriate times to ensure that individual inputs are achieved to the maximum and capital investment kept at the lowest level.