ROAD BRIDGE ON THE RIVER.
A giant Leap towards the development of the North-East India. The most striking feature of the picturesque North Eastern region, the hills and rivers, is the all-pervasive presence of the majestic Brahmaputra. This masculine river not only splits the state of Assam along its length but also cuts off the seven sister states of the North-East from the rest of the country.
Above: Sunset view of the Kaliabhomora bridge.
The river having a catchments area of 3.8 lakh sq.km flows in the most unpredictable manners, occupying 12 km to 16 km of space at places and poses a challenge to the bridge engineers. Despite the pioneering efforts of the Railways at SaraiGhat, the Northeast continued to suffer from the long-felt lack of transporation network. Quarter of a century later, INDIAN RAILWAYS have turned yet another dream into reality. The 2nd Brahmaputra Bridge has greatly accelerate march of the North eastern states towards 21st century.
Above: View at day time from the river side.
Brahmaputra, one of the longer rivers in Asia with a total length of 2880 km – 920 km of which lie in India – had been bridged only at one place, the only link between the North Eastern states with the rest of the country. This 1.3 km rail-cum-road bridge, completed in 1962, was also constructed by INDIAN RAILWAYS. RAILWAY- CUM-ROAD BRIDGE, GUWAHATI.
Above: Diagrammatic view of location of the bridge,
Out of 27 foundations, 25 are open wells. The North abutment and pier No.1 are on raft foundations. The wells have been sunk to 56 m below L.W.L, mainly from scour and seismic considerations. The strata encountered were dense sand mixed with pebbles. During sinking, obstructions in the form of wooden logs and boulders were overcome; this was possible with armoured well curb having shoe-brackets and 12 mm thick steel plates.
Above: Well work in progress for the Bridge pillar.
With elaborate monitoring at each stages of sinking, it has been possible to position all the wells within permissible limits of tilt (1 in 80) and shift (150 mm) each well costing of Rs. 80 lakh and involving 5,000m of concrete was completed within an average period of 90 days.WELL FOUNDATION.
Two of the well foundations required launching of Caissons in depth of water ranging from 8 m to 12 m 290 t of steel was required to be fabricated for these caissons. Water-ballasting of sinking-pontoons. To ferry across the construction materials, for simultaneous working on a number of foundations, a large fleet of marine craft was deployed. it consisted of tugs, 20 barges and a number of country boats. For concreting , batching plants of 950 m3/day capacity were installed. 9 SLD cranes, 3 crawler cranes and stand cutter – dredger pumps were used for sinking of well foundations.
Above: Well work in progress for the Bridge pillar.
Pier No.1 founded on a 2m thick R. C. C raft, which is held down with 96 rock-anchors on North and 6 R.C.C bored piles of 1.5 m dia on South. These piles were driven with CASSAGRADE pile-driving equipment.
Substructure is hollow circular R. C. C piers of 12.5 Metre height constructed with concrete of grade M-300 . It being a navigable river, the height of the piers has been determined to cater to the navigational clearances. R. C. C feeders have been provided to protect the piers from any possible damage due to impact of stray vessels. The pier-cap is made 6.5 m square, to facilitate the construction pier-head.
While sinking the well for pier No.2 near Bhomoraguri hill, boulder stratum at a depth of 26 m below L.W.L was met with. services of deep-sea divers were utilized for sinking the well through this stratum, by under-water blasting.
This well has been secured by 1.5 m diameter R.C.C bored piles along with protection work in the form of a 60m diameter boulder apron.
The distance of 120m between consecutive pier-center is spanned by two 52.5m long balanced cantilever from the Piers and a 15m long suspended span in the middle. The Cantilever portion is a single-cell P.S.C, Box-girder in concrete of grade M-425 using special cement, post- tensioned with 90 nos. of 24x 8 mm dia, H.T.S cables. The cantilever arm has been constructed in 11 segments of different lengths. Diaphragms have been provided at pier head and 11th segment to impart tensional rigidity to the cantilever arm. Considering the unpredictable nature of the river and short working season available, cast-in-situ method of segmental construction by Traveler from-work has been preferred to pre-cast segment launching system. The entire cantilever construction having 275 segments, has been constructed at and average rate of 7m / day which favorably compares with internationally accepted standards.
Above: The 15 meter section in between two cantilever of 52.5 meters being fitted in place.
Above: Cantilever section work under progress.
Above: View of work inside a box section of cantilever.
For the construction of the cantilevers, the BRIDGE_BUILDER system has been imported from Norway for the first time in India. An average cycle time of 5 days has been achieved here for segment construction, as against the accepted international average of 7days.FREYSSINET system has been adopted for pre-stressing. Careful detailing of reinforcement and a cable profile was necessitated to achiever good quality and to minimize construction time. In order to place concrete through dense reinforcement and cable assembly, use of super plasticisers has been made. For manufacture and placing of large volumes of high grade concrete, electronically controlled automatic ELBA batching plants along with concrete pumps, were imported from West Germany. The total installed concreting capacity was of the order of 1000 m3/day.
Above: The joints between two section of cantilever.
The suspended span consists of two R.C.C girders placed on the tips of cantilevers along with a cast-in-situ R.C.C deck. The purpose of providing the suspended span is to minimise damage to the pier during and earthquake, by structurally isolating the piers. The R.C.C girders of suspended spans are cost on the cantilevers and launched in position.
The bearing at the interface of a cantilever and a suspended span is specially designed to cater to complex seismic movements. These consist of a combination of spherical knuckle and P.T.F.E stainless steel sliding surface for free end bearings and spherical knuckle cum electrometric pad for fixed end bearings. Electrometric type of expansion joints are provided for to cater to large seismic movements and to give a smooth riding surface. The bridge deck is provided with 25 mm thick layer of Mastic Asphalt.
Above: The Hollow cantilever box section , inside view.
GUIDE-BUND AND SOUTH APPROACH BANK.
In the absence of any firm control point on the South Bank at the bridge alignment, the river had a tendency to shift towards south. To regulate this tendency and to guide the flow of river within the waterway provided, a massive Guide Bund of 2 km. length along with a 1.7 km. long approach bank was constructed after extensive hydrological studies. The Guide Bund has a 3m thick launching apron made with G.I.Wire crates filled with man-size boulders. Its width varies from 78 m at mole head to 54 m in the shank portion. The total quantum of work involved 8.2 lakh m3 boulder work and 19-lakh-m3-earth work using local river sand.
Above: Approach road from south bank and the guide bund ( diagram)
Above: Bull Dozer closing the guide bund in full flow.
SOUTH APPROACH BANK
To start the work of Guide-bund, it was required to close the active South channel, separating main work area from the high South bank. The channel was closed by continuous dumping of boulders, after diverting the flow with the help of river training works provided in the form of permeable and diverting spurs.
To complete the work of Guide-bund and South Approach Bank in the short period available, average daily progress rate of 13,000 m3 for earthwork and 6,000 m3 for boulder work was required.
To meet this target, a large fleet of earth-moving equipments consisting of scrapers dozers, hydraulic excavators, tippers & loaders along with a strong work-force of 3000 men, were pressed into service.
Preparatory works are the launching pad from which a successful project takes off. The extent of preparatory and ancillary works, connected with such a project is to be seen, to be believed. Procurement of construction material forms a major part of such work.
The requirement of aggregates for the bridgework met with from a reverie quarry on the North bank. For the Guide-bund the required quantity of man-size boulders was collected from hill quarry on the South bank, for which 30 t of explosives were used. Both these quarries were 50-60 km away from the work site and this necessitated deployment of a large fleet of trucks for transpiration. 14 km of permanent approach roads had to be developed for this purpose. At work site, to produce large quantities of different sizes of aggregates for verifying grades of concrete, a fully mechanized aggregate processing plant of 150 t/hours capacity was set-up.
The project site is situated in are mote corner of the country. Due to non-availability of adequate quality of steel and cement in the proximity, their procurement involved long leads in distance and time. Therefore, large storage capacity to the tune of 24,000 t for cement and 14,000 t for steel, had to be developed. To feed electrical power to the work site, power supply network was developed consisting of 33KVA overhead transmission lines for a length of 30 km along with four major sub-stations. River-crossing was arranged by laying underwater X.L.P.E cables. Necessary infrastructure was development at work site, to house 4,000 Workmen including Engineers and Supervisors.
Precision survey for laying long base lines and fixing up bridge-alignment with astronomical observations was carried out with sophisticated equipment like DISTOMAT, T-3 Theodolite, Geodometer etc. Extensive river survey was also carried out with Echo sounder for conducting model studies. Well-equipped quality control laboratories were set up for exercising stringent quality control at all stages of construction.
By completing this intricate task well ahead of scheduled time.
Railway engineers and worksmen reconfirmed their reputation and
scaled new height of excellence in the field of bridge-construction.
The KALIBHOMORA BRIDGE, named after the illustrious Ahom General, is truly a landmark of Northeastern States progress. Before this, the entire region was connected to the rest of the country through a rail-cum-road bridge at Saraighat- the only bridge on entire 920 KM length of the river Brahamaputra. INDIAN RAILWAYS constructed the bridge in 1962.
The need for a second bridge was long felt, for rapid development of the area. 1975 the North Eastern Council entrusted the work of conducting feasibility studies to M/S. RAIL INDIA TECHNICAL & ECONOMIC SERVICES LIMITED – a public sector undertaking and a subsidiary of INDIAN RAILWAYS.
RITES conducted initial reconnaissance of nine probable sites, selecting four for detailed investigations. The final site at Bhomoraguri Tezpur, 135 km upstream of Guwahati was judged as the best site form techno-economic considerations.
The project connects N.H. 52 and N.H. 37 on South –bank, through a 23 km long link. Though the entire scheme is a road project, construction of prestigious 3 km Road Bridge along with Guide-bund and South Approach Bank over Brahmaputra, was entrusted to the RAILWAYS, in recognition of the fact the Railways have vast experience of successful bridging of all the major rivers of the country, including the Brahmaputra.
The total scheme costing Rs.89 cores was divided in to three parts, for the purpose of execution, as follows:
1) Construction of 3 km long road bridge with its 2 km Guide-bund and 1.7 km South Approach Bank by N.F. Railway Construction Organization, at a total cost of Rs.73.5 crores.
2) Construction of 18 km approach road by Assam P. W. D at a total cost of Rs.11 Crores.
3) Construction of Jia-bharali River protection-works by Brahmaputra flood control Commission, at total cost of Rs.4.5 crores.
Northeast Frontier Railway construction organization took up the challenging task in 1979 and work started on war footing. Finalisation of design of this major project was done in consultation with the leading institutions/agencies of the country and all the preparatory works were completed by 1981. Actual work started in October 1981 and has been completed in a period of only 64 months.
|Maximum concreting done in one day||950 M3|
|Maximum sinking done in one day||19 Meter|
|Average rate of sinking of wells||1.3 M/day|
|Maximum amount of work done for bridge in one day (Contractor’s payment )||Rs.6.5 lakh|
|Maximum concreting done in one season||71,000 M3|
|Maximum cement consumed in one season||23,800mt|
|Maximum sinking done in one season||703m|
|Maximum number of cantilever segments done in one month||28|
Maximum amount of earth-work done in one day
|Maximum amount of boulder-work done in the one day||9,350m3|
|Maximum amount of work done for Guide-bund in one day : (Contractor’s payment)||Rs.11.6 Lakh.|
The river offers only 135 days for normal river-bed working, as compared to 180-210 days for other major rivers of India. This necessitated large-scale mechanization for foundations and elaborate arrangements for superstructure works even during high-floods. The Guide-bund, involving 19 lakh m3 of earth-work and 8.2 lakh m3 of boulder-work, was required to be completed within 135 days and needed deployment of machinery worth Rs.11 Crores for the work. The actual time of completion of each work, is as follows : -
|Structural details :-
1) Spans : 24 spans of 120m and two shore-spans discharge of 67.5 m
2) Total length : 3015m
3) Main span : Balanced cantilever Pre Stressed concrete box –girder of 52.5m site with central R. C. C suspended span of 15 Meter.
4)Clear carriage way : 7.5m
5)Footpath :1.5m wide on either side.
6) Sub-structure: : 12.5m high hollow Circular R.C.C pier with Square pier-cap.
7)Navigational clearance : 12.0m for central 90m.
8) Foundation : 56 m deep 12m dia.
b) Guide-bund :
1) Length : 1633m on U/s and 405 m on D/S.
2) Shape : Elliptical
3) Sausage crate size : 2.55m x 1.5 m (0.90 to 1.05)
4) Top level : R.L 71.10 m
5)Top width : 9.0 m
6) Side slopes : 2.5 : 1.
7) Pitching on front slop : 1.2 m thick grouted with 1:3:6 concrete over 0.3 m thick filter.
8) Pitching on rear slope : 0.3 m thick boulders over 0.15 m
c) South Approach Bank :
i) Length : 1678 m
ii) Top width : 12.0 m
iii) Side slopes : 2.5: 1
| Hydraulic data
1) Maximum design : 92,278 Cumecs.
2) Minimum discharge : 4,000 cumecs.
3) Design H.F.L : R.L.67.5m
4) Maximum mean Velocity : 4m/sec.
5) Average L.W.L : R.L 610m.
6) River width at bridge : 4,683m
7) Maximum design scour level a) Normal condition : R.L.24.76m b) Seismic condition : R.L.29.03m
a) Bridge :
1) Total concrete quality : 1,70,000 m3
2) Total reinforcing steel : 12,000 mt
3) Cement : 82,000 mt
4) Coarse aggregate : 1,50,000m3
5) Sand :75,000m3
b) Guide-bund and South Approach Bank
1) Earth-work : 19 lakh m3
2) Stone –work : 8.2 lakh m3
3) G.I wire : 5300mt
a) Main Bridge : Rs.44 crores.
b) Guide-bund and South Approach Bank : Rs.29.5 crores.
a) Main Bridge : M/S Hindustan Construction Company Ltd, Bombay.
b) Guide-bund and South Approach Bank : M/s.Jai Prakash Associates, New Delhi.
c) Bridge bearings and Expansion joints : M/S Metal Engineering & Treatment Co.(P) Ltd, Calcutta.