CASE STUDY.docx

CASE STUDY  STUDY 

COFFERDAM CONSTRUCTION AND DEWATERING TAUNSA BARRAGE REHABILITATION PROJECT

INTRODUCTION

Taunsa Barrage is located on the river of Indus river in the region of Punjab, India. The irrigation system is connected to all the rivers through a series, this process is done by diverting the river water in sequence to barrages then releasing the water into main canals and eventually to the network where water is distributed to small channels. The taunsa barrage was built in !"# in such a way that four main canals were constructed with two canals on either side of the barrage. The barrage consist of $" gates which were divided with a thickness of % feet piers with a total width of the structure constituting to &,'&$ feet and was designed in a way that ,(((,((( cusecs of flood can pass through the barrage.

)igure* Taunsa Barrage PROJECT DESCRIPTION

The civil work contractor for the project was +escon ngineering -imited +-/ in association with 0hina 1a2ooba 0orporation 0110/ and they were selected under international competitive bidding. bidding. The  process of rehabilitation rehabilitation was planned in a way way such that in first year year they construct half of the weir weir and rehabilitate half bays of the barrage. This rehabilitation work consist of strengthening the old concrete at chute and basin floor, for this the cofferdam was built on the upstream and downstream of the restoration site.

)igure* arly stage of 0onstruction

)igure* 0onstruction of 0offerdam at front and back of the enclosure

It was constructed in such a way that the barrier across the barrage could resist to a greater ma3imum observed flood of '((,((( cusecs for non4monsoon and monsoon seasons. Thus taking this kind of   precautions made all satisfactory factor of safety to divert and also the height of the cofferdam. There was also a periodic monitoring of the rise of water level and flow of river, which made them to build the head across the barrage within " ft and design head being at 5& ft across the barrage.

The major cost region of the project was estimated to be at 6$( million and other works like maintenance of dam and securing of water was estimated to be around 6 & million. 7est all schedules and planning was done to get all those materials and equipment8s to the site at right time.

CONSTRUCTION PROCESS OF COFFERDAM

In the initial stage of the construction materials like stone and earth fill was brought to the site to dump in the upstream and downstream of the river in large quantities to construct the sub weir. In this kind of  construction the major equipment8s used are e3cavators, do2ers and dumpers. These dumpers dump the stone on top of the embankment whereas do2ers move across the flowing water and also the earth fill material was dumped from top so that it settles down. But during the built up of the cofferdam it should  be monitored keenly time to time thus to safe guard the area as well as to place the materials over the settled area. The major advantage while constructing the cofferdam was the continual supply of the materials like stone and earth fill which were maintained at the site with a scheduled supply. 9s the construction work  approached the center of the river channel there was a constant rise in the velocity which required more materials timely to make sure the progress was going in a planned way. This is because of having limited time to build the cofferdam, activity of constructing the cofferdam became a major priority and no other  activity is carried out till the completion of the cofferdam.

)igure* +umper unloading stones

:aterial quantities for constructing a cofferdam* ;tone

4

((,((( cft '(((m '/

;heet piles

4

55&,((( sft 9rea/, '" < &( ft +epth/

;and bags

4

$(,((( =o

arth filling

4

.&$ : cft '5&,'!& m '/

DEWATERING

In the process of construction of coffer dam, the ne3t step is dewatering. +ewatering method requires a lot of pumping of water with certain measures like maintain the water levels to a desired point. The main equipment8s used for dewatering are tube wells, pumps and screens for concreting at required different areas of the compound. ;heet piles analysis and overall stability is calculated in a software called ;P>? for cofferdam section seepage. Thus a realistic model is available where for different parameters sensitivity analyses is done. ventually based on these results a sheet pile is installed. In the primary phase of work, single enclosure for construction of sub weir has been planned. 9fter a keen analysis for the flow conditions across the barrage it was decided to construct a four %(( ft wide enclosures instead of having a one single enclosure of 5#(( ft length. ;ubsequently, to lower down the water table "( to $( tube wells were required in each enclosure of %(( ft. Being large portioned area in spite of having pumps and generators there was e3tra capacity provided for keeping the project to run swiftly. 1eneration of power supply being a challenged task, the pumps required ' :? for which eight generators of sets '%" k@9 was provided. 9s two generators required for dewatering there was stand by generator provided thus making sure that there is no interruption of power supply. Thus the pumped water  was directed to the surrounding water bodies.

)igure* 0onstruction of ;ub < ?eir 

)igure* 0offerdam with sheet piles during dewatering

EQUIPMENTS USED

Aeavy equipment8s were used during the construction of the cofferdams, such as • • •

-oaders and +ump trucks +o2ers Backhoe

• •

+ewatering pumps < tube wells along with pumps and screens @ibrating pile hammer 

ach machinery used constitute a weight around ( < " tons which can move freely on newly constructed embankment. sually stone dump was built then was followed by earth fill dump. The stone is dump in reverse on top of the embankment by the dumper during the construction.