- Drill+blast excavation is virtually complete at India's first crude oil storage caverns at Vizag. Four Sandvik DT 820 jumbos and two Sandvik DX 700 surface rigs for benching work have been operated by Indian contractor Hindustan Construction Co Ltd (HCC) to produce in excess of 1.8 million tonne of rock spoil and more than 6km of tunnel headings to create the strategic underground storage facility.
Layout of the complex and its water curtain galleries
- The project is being constructed under a US$75.5 million contract with Mumbai-based HCC for Indian Strategic Petroleum Reserves, a subsidiary of the Oil Industry Development Board of India under the Petroleum Ministry. Located at a hill known as Dolphin's Nose, on land belonging to the Eastern Naval Command in Visakhapatnam, usually abbreviated to Vizag, the scheme will have a storage capacity of 1.33 million tonne of crude oil. Vizag, on the nation's east coast and considered the eastern gateway to India, was selected for the facility because it has a large seaport for the import of oil. Adjacent to the site is South East Asia's first underground LPG storage cavern on which Sandvik jumbos were also used during construction.
- HCC began work on the oil storage cavern in 2008 and excavation within the 36-month schedule is on track to be completed on schedule this month (March 2011).
- The completed facility is scheduled for hand over in August 2011. HCC's contract covers detailed engineering and design, storage cavern excavations, access tunnels, water curtain galleries, shafts and associated underground civil works.
- HCC's Project Manager, Ramana Rao, explained that the complex comprises five caverns for crude storage, all 30m high and 20m wide. Three caverns are 840m long and connected at one end to form a 'w' shape. Two shorter caverns of 370m long are also joined to form a 'u' shape.
- The Sandvik DT 820 is a two-boom electro hydraulic jumbo with full automatic boom parallelism for fast and accurate drilling in faces of 12m2 to 110m2 cross sections. It is equipped with a HLX5 rock drill on each TB 90 universal boom, which gives a large area of optimum coverage. The booms can also be used for cross-cutting and bolt hole drilling. An optional basket boom for hole chanrging and bolting and utility works is available. The four-wheel-drive, centre articulated carrier ensures rapid and safe tramming with good balance.
Water curtain works
Excavation work included advance of two 6m x 6.5m x 1.3km long water curtain galleries. Once completed boreholes of 102mm diameter and 75m long were drilled horizontally at 10m intervals from both sides of the galleries to cover the caverns. These were sealed and connected to a continuous recirculating pumping system injecting water to a pressure of 6 bar to seal any fissures in the rock around the caverns. As an essential part of the project, the water will prevent seepage of crude fumes through the fissures to eliminate the possible risk of explosions. Similarly, the strictly enforced smooth finish specification of the gallery walls, with just 400mm tolerance either side of the tunnels, is set to reduce the risk of voids in the caverns and the possible build-up of fumes and once again preventing the risk of explosions.
- The floors of the caverns are 80m below mean sea level and beneath a hill that rises above the site to an elevation of about 130m.
- Access into the caverns is via an inclined access adit at ground level and two large shafts have been sunk to house the operating equipment for the caverns.
- Project Manager Rao said that the rock strata is Khondalite, a form of sandstone that follows an arc through India's southern and eastern states and which has been used throughout the subcontinent's history for architectural construction and ornamentation.
- Excavation advanced on several fronts and the contractor's four Sandvik jumbos worked simultaneously for much of the time. "Our logistics were designed to supply power and water to four headings simultaneously," he said. "The four jumbos worked within the cycle of drilling, blasting, rock removal and support installation."
- With profiles of 11m x 8m, the jumbos drill at least 150 holes per blast cycle, at 2m to 4m deep, depending on the location in the works, and taking on average two minutes to drill each hole. Charge holes in the larger 11m x 8m faces are loaded with a total 480kg of explosives. A 10m x 8m profile requires 473kg/round, and a smaller 8m x 8m profile takes 365kg/round.
- Power Bulk Drive-T liquid explosives, supplied by Orica Mining Services, have been used for only the second time on a construction project in India. The key advantages of the product are improved safety, faster cycle times, and better blasting control to ensure the specified smooth finish of the tunnel walls.
Isometric view of the bench excavation sequence
- Drilling for each blast cycle takes around three hours with loading of the charge holes being undertaken simultaneously from the jumbo's fixed basket boom. Once the drilling is complete, the jumbos are moved out and washed down. With the blasted rock removed and the support installed, the jumbos are moved back into heading to start the next 16hr cycle. With work proceeding 24hr/day, the production cycle allows three blasts over a two-day period, said Project Manager Rao, with each blast advancing the heading by 3.5-3.8m.
- HCC's project mechanical engineer Kaushal Kumar Sharma said that the machines are hosed down at the washing area next to the access portal between cycles and that routine maintenance is undertaken once a week. "We inspect the hoses and linkages and the drill bits, and oil and lubricate the machines. Our own staff does this and Sandvik's on-site presence works closely with our maintenance and operating teams."
- The jumbos were supplied to HCC by Sandvik India, whose senior engineer on site, Harish Pokharkar, says that spare parts are supplied via the company's Pune headquarters.
- The two Sandvik DX 700 surface drill rigs are drilling vertical charge holes for excavation of three benches in the high caverns. This minimises consumption of explosives and increases advance rates. Sandvik Engineer Pokharkar said that both machines are fitted with 45mm R32 drill bits, with an R 38 shank adapter and R 38 and R 32 drifter rods. "The DX 700s are drilling holes to depths of 21m on all three benches," he says. "We have a grinding facility for the drill bits installed at the site, and we have recorded that by grinding we are achieving 30% extra life with the bits. We have also ascertained that machine availability has been slightly more than 96% per month."
- The crude oil cavern installation at Vizag is one of three such caverns being built by the Indian Government, the other two located at Mangalore and Padur. With a total capacity of 5.3 million tonne, the crude stored at the facilities will act as a buffer in the event of emergencies or disruptions in supply. All three projects are scheduled to be operational by 2013.
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