retrofitting of irrigation structures- Prakasam Barrage, Andhra Pradesh,

-A case Study

Dr. I Satyanarayana Raju,FIE,Ph.D.Former Chief Engineer, Irrigation Dept.(AP)Chairman, Institution of Engineers (India)

APState Centre, Hyderabad,Telangana State

Preamble

• In early twentieth Century engineers devoted more time to develop methods of analysis and construction of different kind of structures but spared very little time in repair/retrofitting/rehabilitation of Structures.

• New construction of Dams, Highways, Sea Ports, Airways, Industries, and other Infra-structural facilities was focused for long term development and economic growth as a global scenario.

• In the second half of twentieth century the structures earlier built had passed half of their life span and situation demanded repairs, rehabilitation and retrofitting.

• Structures during their service life have a specified level of safety and serviceability under the design working load and anticipated condition of use.

• The deterioration structures may be due to inadequate design, deficient construction, overloading, inadequate maintenance, weathering, unforeseen events (Natural disasters)etc.,

• Repair, Rehabilitation, retrofitting and strengthening of structures needed due to any one or combination those reasons.

What is Retrofitting ?

• Retrofitting is method or process for the strengthening of a structure.

• It is a Technique used to enhance the safety against any likely damage to save the structure.

• The retrofitting avoids the expenses for a new structure and prolongs life of structure.

• Reasons for retrofitting : -Change in the intended use of structure (Ex: Increase in

loading pattern).-Change in prevailing Codes- Ex: Grades of concrete.-Damage to structure due to aging.-Protect from disasters.-Add additional strength to structure.

Rehabilitation: It is act of restoring some thing to its original position after damage by an external or internal force. It denotes repairing damaged structure during service or by natural disaters.

Vulnerability of Irrigation Structures: • These are more vulnerable to natural disasters such as Floods, Cyclones,

Tsunamis, Earthquakes, Volcanoes etc.• The Design Standards BIS or International Standards are dynamic and

change due to passage of time by updating.• The Irrigation Structure built with certain standards are needing stability

analysis against modified standards in life span.• Earlier Max. Design Flood of 100yrs/500yrs/1000yrs are now needed to check

for passage of PMF( Probable Max Flood) as per latest BIS.• For safety point of all such Irrigation Structures needs rechecking for their

stability with Present standards.• Some of the Structures due to their proneness for floods and cyclones could

have effected and damaged requiring rehabilitation.• Hence the retrofitting or rehabilitation of Irrigation structures is a common

phenomenon, a case study of barrage is Presented.• The Case study taken is Prakasam barrage across Krishna River in

Vijayawada town ( Famous for Goddess Kanakadurga and South central Railway hub of many trains passing in all directions south,north,east and west of India).

• It was basically an Anicut conceived by sir Arthur Cotton during in mid 19th century and upgarded as barrage in mid 20th century.

• The Rehabilitation carried out ( By Author) is presented and very interesting.

CONCLUSIONS• Post Barrage Rehabilitation Impacts:• The Barrage with stood Historic Krishna flood -2009 of 10.60 lakhs

Cusecs.• The downstream boils of Post rehabilitation of -7M is changed to

+0.00M indicating positive sign due to execution of sheet pile cut-off on upstream and down stream of Barrage.

• The Expert Committee suggested to go in for second line of sheet pile cut off on downstream.

• The barrage life sustained by rehabilitation works carried out during 2002-2004.

• Vulnerability to Vijayawada City of Prakasam Barrage minimised, otherwise the 2009 floods to Krishna could have created scare among Public.

• The Hydro-mechanical components(Gates) are periodically getting painted to avoid corrosion and Gates upkeeping.

• The New upstream KLRao Pulichintala Project relieved pressure on Prakasam barrage during floods becoming an intermittent flood moderation Dam.