INTORODUCTION BRIDGE:

Transcription

1 INTORODUCTION Transportation systems are backbone for the development of any country. There are mainly three type of surface transport system. Road Transportation system and Railway transportation system and Water transportation system. When it is required to intersect the two Transportation systems or even same Transportation system it will cross either at the same level or at different Label. The Bridges are constructed for intersecting two transport systems at different levels. BRIDGE: The bridge is a structure constructed to span the obstacles, such as water body, valley, Railway, or Road. The purpose bridge is to provide passage over the obstacle. The bridge may be classified based on purpose, site condition, construction material, loading standard and spans. The bridges are classified according to crossing in following three types. River crossing: The Bridge across a water body. Viaduct: The Bridge across a deep valley which is without perennial water is called a viaduct. Grade Separator: The Bridge built to cross another route of communication/ Transportation system passing at different level is called grade separator. When Railway and Road crossing at same level called Level crossing and when Railway and Road crossing at different level called grade separator. The grade separators are two types like over bridge or under bridge. The Railway and Roads are crossing at many locations by the means of Level crossing, Road under bridge or Road Over Bridge. The Road over bridge (ROB) are constructed where Road ali gnment crosses above the Railway alignment. ROBs are usually constructed where enough space is available for the approaches. The requirement of vertical clearance for Railway is more than Road section. Thus the more approach length is required in case of ROB. The vertical clearance requirement for Railway corridor of Dedicated freight corridor (DFC) and double stack container (8 to 9 meter) are much higher than present Railway system. Due to increased approach length the construction of ROB is not economical and viable. The Road under bridge (RUB) are constructed where Road alignment crosses Under the Railway alignment. The Road under Bridge is the most suitable structure

2 where the space is limited for the approaches specifically in urban areas. The less approach length is required in case of RUB, because the requirement of vertical clearance (maximum 5.5 meter) of Road is less than the Railway. The vertical clearance may be further reduced depends on type of road and vehicle used in that area. Normally The Rail level kept higher than the Road level. Roads are normally kept at average ground level but the Railway alignment designed much higher than ground level because of smoother gradient, higher radius curve and more clearance requirements. Thus, The construction of RUB will be more suitable where the Road level is lower than Rail level which is the normal condition. The RUB type structure is more suitable than ROB for energy consumption, fuel cost and carbon credit also due to lesser height of grade separation. Thus, The RUB is more economic and viable. Looking into the construction feasibility ROB construction is more easier than RUB. The ROB are constructed above the Railway track all activities of ROB construction are executed above the Rail level except foundation. The restriction to the Railway movement is very less during construction of ROB. Usually, no speed restrictions are required during construction of ROB. The most of the activities such as launching of superstructure may be executed during traffic block. In case of RUB construction, structure is constructed under the running Railway track. There are many serious failure were noticed during construction of RUB under the Railway track such as longitudinal moment of Railway track, disturbance of cross levels, sudden collapse of soil under the Railway track etc. This involve safety of running Railway structure, thus the continuous speed restriction, caution order and lookout man, close monitoring required during entire RUB construction under the track. The underground construction which is called Road under Bridge (RUB), Subway or underpass are the similar meaning for construction of grade separator Bridge under the Railway track. The construction of RUBs are discouraged by Railway Authorities due to various restrictions to Railway track in spite of RUBs are more feasible and useful than ROBs. Restriction of Railway traffic: Restriction of Railway traffic can be divided in following two Types: Speed restrictions.

3 Traffic block of certain duration. The speed restriction to Railway traffic imposed when the track geometry disturbed more than required parameters and tolerances. During underground construction below the Railway traffic, the soil below the track moved due to construction of foundation / bridge structure. This movement of soil may disturb the cross-levels, longitudinal level, and alignment or settlement of track. The train movement at normal speed is not possible under the disturbed track geometry. Thus the speed restriction required for the safe movement of trains. Most of the important Railway corridors are running on their optimum capacity. The time table of trains decided keeping a certain allowance of speed restrictions for the maintenance of Railway track known as Engineering allowance. If the speed restriction imposed beyond the Engineering allowance the punctuality of trains suffer. Due to optimum use of Railway track the Engineering Allowances (EA) are not sufficient for the maintenance activities only, whereas for construction of any new underground structure, the imposition of speed restrictions is very difficult for Railway to maintain punctuality. The late running of train affect the punctuality of complete train system which is loss of Railway earnings. Hence speed restrictions on Railway track is a very costly affair and loss full exercised for the Railways due to punctuality loss. When any construction or maintenance activity near or over the Railway track exercised by stopping complete train movement and after correcting the track geometry the train movement restored is known as Traffic block. The margin of 2 3 hrs. of traffic block are kept for maintenance of track on every Railway corridors. The construction activities of Bridge structure is not a regular maintenance activity, this is one time activity. The traffic block will be more suitable for construction of new structures. Even Railway may agree for long duration traffic block also for the construction of underpass, because one time activity. Thus the Traffic block is more useful for development of new infrastructure, than imposing speed restrictions to all trains of the section for long duration (many days) of entire foundation construction. The method of underpass construction: The method of underpass construction are mainly categorized in following methods: Cut and Cover method.

4 Inserting Restricted Head Girders (RH girders) and constructing the bridge below the Railway track by conventional method. By RCC Box pushing method. All of the above methods are required speed restriction for long duration to the Railway traffic whereas, cut and cover method required Traffic block of 6-8 hours. Speed Restriction for cut and cover method required for short duration for just to stabilize the track after inserting RCC Boxes under the track. Cut and Cover method is suitable for single line track only and not feasible for double line or multiple tracks. Construction of conventional bridge through RH girder method involves complete speed restriction for long duration (entire underground construction), because of temporary foundation support below the RH girder. That is why, this method is not usually suggested on busy routs. The RCC Box pushing method involves least restriction to the Railway traffic in comparison to both of above methods and most suitable for multiple Railway tracks also. However, this method also required speed restrictions during the pushing activities and there are many failures and difficulties also noticed during pushing activities. The box pushing methods are majorly used for under pass construction. In view of above, by designing a hybrid structure which reduce the requirement of speed restriction of Railway traffic, may be the most useful solution for the underpass construction. Five Why? Analysis: Five Whys is an iterative interrogative technique, which is used to explore the cause & effect relationships underlying a particular problem. The primary aim of the technique is to determine the root cause of a defect or problem by repeating the question "Why?". Each one of the question forms the basis of the next question. The five in the name derives from an empirical observation on the number of iterations typically required to resolve the problem. The technique was formally developed by Sakichi Toyoda. It was used within the Toyota Motor Corporation during the evolution of its manufacturing methodologies. In other companies, it appears in other forms such as Under Ricardo Semler, Semco practices "three whys" and broadens the practice to cover goal setting and decision making.

5 All problems have not a single root cause. If one wishes to uncover multiple root causes, the method must be repeated asking a different sequence of questions each time. The method provides no hard and fast rules about what lines of questions to explore, or how long to continue the search for additional root causes. Thus, even when the method is closely followed, the outcome still depends upon the knowledge and persistence of the people involved. The Five why analysis method will be used for developing the design of underpass structure resolving all difficulties, suitability and restrictions to Railway traffic during construction stage. In view of above, main aim of this study to control over the speed restrictions on the Railway traffic during underpass construction, to safeguard the Railways revenue loss, punctuality and smooth development of infrastructure for the country.