‘Learning from failures’, VIDC getting Gosikhurd LBC reconstructed
   Date :12-Oct-2020

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The completed work of lining and water in the LBC of Gosikhurd irrigation project presents a
refreshing sight. (File photo)
 
 
 
By Kartik Lokhande :
 
For years, Gosikhurd irrigation project was in the headlines over poor quality of work and inordinate delays. In the past few years, the picture has been changing. The construction of Left Bank Canal (LBC) of Gosikhurd project had come in for sharp criticism in official reports also. However, over the years, ‘learning from failures’, Vidarbha Irrigation Development Corporation (VIDC) is getting the entire 23.93 km LBC reconstructed. Gosikhurd national irrigation project comprises two main canals -- LBC and Right Bank Canal (RBC). The total length of LBC is 22.93 kms. The work of construction up to 11 km was given to one contractor, and that of remaining portion to another contractor.
 

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The LBC has irrigation potential of 31,577 Ha. However, soon, the problems in construction quality of LBC came in for criticism. The officials inspection conducted in the year 2010 revealed cracks in canal lining. H T Mendhegiri Committee had pointed out reasons behind cracks in lining and had recommended reconstruction of the entire lining at the cost of the contractor concerned. Pravin Zoad, who was Executive Engineer (Gosikhurd LBC) with VIDC when the reconstruction work commenced and made progress, recently made a presentation on how it was done and deficiencies were removed while ‘learning from failures’. Zoad, who is presently Executive Engineer, Pench Irrigation Division, told ‘The Hitavada’ that it was a challenging task.
 
“Till June 2019, the work has been completed in 1-10 km critical patches of LBC lining at the original cost of contractor concerned. As much as 70 per cent of the work of reconstruction of canal lining in 11-23 km stretch has been completed. The remaining is being done and is expected to be completed in this financial year. It would also have been done but COVID-19 has affected the pace of work,” Zoad said. The inspection of Gosikhurd LBC had identified several reasons behind the canal lining developing cracks. These included poor quality of lining concrete resulting in low density and lower strength of concrete. Insufficient and improper curing, lesser thickness than design and insufficient core strength of concrete at some locations, improper compaction of base material as well as cohesive non-swelling (CNS) layer resulting in settlement of subgrade (layer of rock or earth levelled and graded for a foundation) and formation of gap between lining and subgrade were other important reasons. Further, it was found that minimum thickness of CNS layer was lesser than required.
 
The longitudinal and transverse joints with PVC strips were not placed properly as per specifications. There was increase in surcharge load on either side of canal due to dumping of spoil material. Since reconstruction was to be done, existing faulty lining was dismantled, existing CNS layer was removed completely, canal section was excavated below lining to provide murrum of sufficient thikcness required to cater swelling pressure and discharge of canal, steps/benches were provided in the slopes of canal in cutting to provide a good bond between CNS layers and expansive soil and to also prevent contact slides between CNS materials and expansive soil. CNS material was laid in layers and mechanised compaction was done. Proper moisture was added to CNS material and expansive soil. The final subgrade was made thoroughly moist with fine spray nozzles to a depth of about 15 cm, before placement of concrete to prevent it from absorbing water from the freshly laid concrete.
 
Zoad said that one complete monsoon season was allowed to pass after the work of murrum filling was completed, for consolidation. In addition to designed thickness of CNS layer, 15 cm or more of extra thickness (pride) was provided to take extra care of damage due to rainfall and weathering action. The ‘pride’ was removed just prior to placement of lining (not exceeding three days). Sufficient drainage was provided below lining. Transverse seepage drains were provided in canal slope, and longitudinal seepage drains were provided in 1-3 rows in bed depending on bed-width. PVC perforated pipes were provided at central portion for collection and disposal of water. In the original work, Pressure Relief Valves (PRVs) were provided in sloping portion and Non Return Valves (NRVs) in bed portion. However, these were either stolen or became non-functional, resulting in creation of problems of under-drainage.
 
Against this backdrop, porous plug of certain specifications were proposed instead of PRV/NRV. Apart from several other technical measures, contraction joints were cut using groove cutters attached to pavers. Proper curing was done, and contraction joints were proposed in transverse direction. Filling of joints was taken up after minimum period of 28 days of setting of cement-concrete lining. Grooves were cleaned thoroughly using brush, air-jet, water-jet etc and dried to ensure good adhesion to the sealant. Various tests were done and concrete cores were taken from the site to evaluate the quality of concrete lining laid in respective reaches. As per Zoad’s presentation, all the core samples satisfied the criteria specified by IS 456:2000 as per concrete core test conducted at VNIT.
 
“No settlement or hogging of lining and cracks was observed after discharging water for irrigation during Kharif agricultural season for last five years,” Zoad said. He said that best results were achieved and many experts visited the site to know and see how it was done. Learning from failures, modifications had to be carried out. He felt that proper compaction needed to be done. Otherwise, settlement results in development of cracks. Concrete panelling has to be done properly through grooves. Soil nature, CNS layer, or murrum filling hold the key to longevity of the construction of canal lining, he added. Summing up, Zoad said, “The work has to be executed after studying area of work, sub-base, soil properties. One set formula does not apply everywhere. There are guidelines, but we need to consider and make modifications as per the local variations.”