Friday, December 15, 2017

Project Focus

Hydro oomph

The Uri-II Hydel Power Project is a triumph of engineering resilience an organisational trait which Hindustan Construction Company can proudly lay claim to. The inauguration of the 240 MW Uri Stage-II Hydro Electric Project (HEP) by Prime Minister early last month is expected to give a major boost to the country’s power sector contributing 240 MW of electricity to the Northern Grid. Located in the Uri area of Baramullah district in Northern Kashmir, around 18 km away from the LOC, the run-of-the-river scheme has been constructed by Hindustan Construction Company for the National Hydroelectric Power Corporation (NHPC). This is the second project to be constructed on the Jhelum River and is a downstream development of Uri-I which is already in operation.

 

Ambuj Jain, Chief Operating Officer, HCC, is led to say, “Overcoming challenges has always been a speciality of our engineers. We triumphed over every obstacle posed by difficult geographical conditions, freezing temperatures and constant floods, with a single objective – to successfully execute this project of vital importance to the nation.” 

 

PROJECT BACKGROUND

HCC received the LOA for the Uri-II Project on September 21, 2005. Immediately after mobilisation  the project team faced several technical challenges due to unpredictable geology and inconsistency of the rock mass of this region and frequent flooding of River Jhelum, both seasonal and non-seasonal.  On October 8, 2005, a devastating earthquake measuring 7.4 on the Richter scale hit the region, resulting in massive damage to life and property in the area. With all access roads to the work site damaged due to landslides and mudflows triggered by the high intensity quaver the execution schedule was disturbed. HCC had five teams trained by RedR at the Uri site. Their first action was to assess needs in one part of the disaster zone; they then opened roads to 21 villages and distributed basic necessities like, clothing, tents and shelter materials. About one-fifth of the $76,000 cost in staff time, equipment use and materials was covered by donations from the company’s employees across India. Despite challenging conditions, the project team successfully completed the 337 meter long diversion tunnel for facilitating the dam construction on January 11, 2007, on the contractual date. During the second phase, HCC worked with an Indian NGO, SEEDS, to design and build several hundred temporary shelters in the 12 weeks before winter hit the disaster zone. As a result of this disaster, initial project mobilisation and start of the project was impacted for a period of six months. Despite this initial delay, the Uri-II project team remained steadfast in their efforts and application.

 

 

PROJECT DETAILS

The scope of work for the Uri-II project included construction of a concrete gravity dam, diversion tunnel, head race tunnel, surge shaft, pressure shaft, power house complex and tail race tunnel. The River Jhelum was channelised through a diversion tunnel having a diameter of 8.8 m and length of 337 m to facilitate the construction of the concrete dam. The total catchment area at the dam site is 13,400 km2. The concrete gravity dam is 52 m in height and 157 m in length. The project’s head race tunnel is 4.23 km in length and 8.4 m in diameter. Other structures include a restricted orifice type surge shaft of 25 m diameter and a 3.61 km long tail race tunnel. There are four spillways of nine metres each in the dam which will help divert the water to the tunnel for power generation. An underground power house 133 m in length, 15 m in width and 40 m in height will accommodate four turbines of 60 MW capacity each, which is anticipated to generate 1,123 million electricity units annually.
 

UNPREDICTABLE GEOLOGY OF THE TERRAIN

The project lies in the eastern part of the Kashmir syntaxial bend of the Northwest Himalaya and is occupied by quaternary deposits and sedimentary rocks of upper Murree Formation comprising sandstone, siltstone and shale sequence which are folded and faulted. In order to ensure the success of activities such as tunneling in adverse geological conditions, the HCC project team carried out detailed investigations, and appropriate rock support (Wire mesh, Shotcrete, Steel Rib, Rock Bolt and Rock anchor) methods were used to safeguard against the poor geological portion. In many ways, achieving work progress was not easy, and each day was a new beginning for the project engineering team. During project execution, the Uri-II team encountered frequent flooding of River Jhelum, (both seasonal and non-seasonal), which resulted in the washing away of both upstream and down steam cofferdams almost every season. Despite these circumstances, the project team successfully completed the dam structure with a total concrete quantity of 1.00 lakh cubic metre during March 2011, except for the apron structure, that carries water from the dam to the head race tunnel.  In order to adhere to the Indus water treaty agreement executed between the Government of India and Pakistan, there was a requirement for impounding the reservoir before August 20, 2011. Subsequently, NHPC requested HCC to complete the apron structure of the dam during the monsoon of June 2011, within target duration of 25 days.

Project Manager R Rajendrakumar, Project Manager, elaborates, “The project team took up this challenge and mobilised all additional resources required to complete the apron structure within this stipulated timeline. To construct this apron, we were required to excavate for the foundation at EL 1196m and the excavated muck had to be disposed at EL 1220 m,( with the level difference of 24m), in the absence of haul roads, and with limited space. We deployed seven excavators in a series from bottom to the top, to transfer the excavated muck from the foundation to the disposal area, and completed the excavation and concreting of the apron structure. Another major challenge encountered was seepage from the downstream cofferdam. To tide over this seepage, we deployed 20 units of 50 HP capacity dewatering pumps, each with a discharge capacity of 6,000 litres per minute. Each pump was run continuously for 25 days to avoid any obstruction during construction of the apron structure. With total commitment, the project team completed this apron structure within the 25 day duration and the reservoir was impounded during the first week of August 2011.”  Another challenge was encountered during the excavation of the Tail Race Tunnel through Adit-IV upstream and downstream during the monsoon periods. It was clearly envisaged from the construction drawings that the bottom level of the tunnel would be lower than the river bed level. Even after adverse geological and project conditions, the Uri-II team was able to successfully complete the major works for commissioning of the project.

 

 

TUNNELING THROUGH ADVERSE GEOLOGY

While excavating for the headrace tunnel, the rock encountered was of class 3 and 4, the tailrace tunnel engineers encountered riverine materials for a length of 223 m. This consists of earth mixed with boulders, together with heavy seepage of about 15,000 litre per minute.

  • To excavate in these very loose earth strata the following methods were adopted:
  • Only exposed boulders on the face were removed by blasting, subsequently the earth surrounding the boulders was removed using excavators.
  • Shotcrete and Consolidation Grouting on the face were carried out to stabalise the tunnel face.
  • Dewatering pumps were deployed to a capacity of 600 hp, in stages to tackle the seepage.
  • To avoid loose fall from the crown, specialised pipe roofing using Mai anchors were installed on the crown of the tunnel as umbrella. This pipe roofing with Mai Anchors were installed by drilling holes with self sacrificing drill bits, for a length of 18m, along with perforated pipes and the same was grouted with cement grout.
  • Advancement of tunnel was carried out cautiously to avoid any mishap with rib support and back fill concreting after the activities mentioned above.
  • Finally, the entire stretch of the tail race tunnel (with a poor geological zone) was lined with reinforced concrete. To mitigate this delay in excavation in tailrace tunnel, an additional face was identified from downstream surge gallery.

 

 

DEWATERING

The seepage encountered in the Tail Race Tunnel, Power House and dam area was huge, as the nallahs that were crossing over the TRT alignment and the crown of the underground Power House was designed 22m below the river water level. The project team ensured uninterrupted dewatering in the TRT, Power House and Dam area till the completion of the project. Total dewatering quantity in this project was 345 million kilowatt hours. Total electrical cables used to maintain this dewatering arrangement in tunnels was 15,000m.

 

 

SOCIAL CHALLENGES

During the course of project execution there were calls for stoppage of work due to bandhs and strikes and a continuous curfew was imposed in the state for months together, especially in Baramulla district, where the project was located.  Further the absence of traffic on NH 1A affected the supply of vital construction materials. With fear psychosis in the state affecting local labour skilled manpower was drawn from outside J&K thus allowing the project team to sustain work progress.

 

 

PROGRESS

The dam structure involving 100,000 cubic metres of concrete was completed in March 2011 and the construction of the power house and switchyard as well as key tunnelling works was carried out thereafter. The four units were commissioned in phases with Unit No. 1 and Unit No. 3 synchronised in September 2013, Unit 2 in November 2013 and Unit 4 in February 2014. With the commissioning of this project, the total installed capacity of NHPC Power Stations in Jammu and Kashmir will go up by 240 Mega Watts. The other projects of NHPC in Jammu and Kashmir are the 690-MW Salal, 480-MW Uri-I, 390-MW Dulhasti and 120-MW Sewa-II. NHPC has also commissioned the 45-MW Chutak in Kargil and 44-MW Nimo Bazgo in Leh, both built by HCC.

 

 

HCC SAGA

With an engineering heritage of nearly 100 years, HCC has executed a majority of India's landmark infrastructure projects, having constructed 25 per cent of India's Hydel Power generation and over 50 per cent of India's nuclear power generation capacities, over 3,500 lane km of expressways and highways, more than 280 km of complex tunneling and over 350 bridges. HCC’s landmark projects include the Bandra Worli Sea Link, Mumbai − India's first and longest open sea cable-stayed bridge; the Kolkata Metro, Farakka Barrage and India's largest nuclear power plant at Kudankulam - Tamil Nadu, to name a few. The company in J&K: Various projects built by HCC in Jammu & Kashmir, have not only helped create a robust infrastructure in the difficult terrains of the valley but have also touched lives of millions of people in the region. In the hydro electricity domain HCC has also developed other NHPC projects in J&K, such as the 690-MW Salal, the 45-MW Chutak in Kargil and 44-MW Nimo Bazgo near Leh. The company is also credited with constructing the 10.96-km Pir Panjal tunnel, the longest rail tunnel in India and Asia’s second longest. The tunnel is part of the Udhampur-Srinagar-Baramulla rail link, which provides an alternative and reliable transportation system to Jammu & Kashmir (J&K) by joining the Kashmir Valley with the Indian Railways network. This railway line will strengthen available transport facilities to J&K and provide an all-weather means of transport in an area that is snowbound for a significant part of the year. Similarly, HCC has successfully completed the ambitious Mughal Road project, located at an altitude of more than 10,000 ft and passing through the heart of the Himalayan mountains.




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