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New Sandvik jumbos for Dakmi 4 hydropower plant in Vietnam

Delivery of two Sandvik DT820 jumbo drilling rigs to Vietnam’s Song Da will greatly assist in the contractor experiencing severe rock conditions getting back on schedule on the Dakmi 4 hydropower plant.

Drilling contractor Song Da on Vietnam’s Dakmi 4 hydropower plant has taken delivery of two purpose-ordered Sandvik DT820 jumbo drill rigs; which despite encountering severe rock conditions are proving the key to keeping the tunnelling contract on schedule. Both units were ordered by the local Sandvik dealer in Vietnam, Open Asia Heavy Equipment.

The proposed 172 MW hydropower plant is located some 2½ hours drive west of Vietnam’s third city, Da Nang and close to the Cambodian border and will include a 420 m long x 87 m high concrete dam to hold back the Dakmi river; creating a 1450 ha reservoir.

But it is rock conditions in the 3.37 km long tailrace tunnel which is creating major problems for main contractor, Ho Chi Minh City-based IDICO and Song Da.

Poor rock comprising sediment and badly fragmented and decomposed granite complying with Vietnamese standards of Class II, 1B, 1A2, 1A1 and edQ + eQ are being encountered.

At the power house portal conditions were particularly severe. With drilling starting at the beginning of May, advance rates were very slow and arduous.

Up to 40 x 4.5 m long rock bolts in two rows were installed at an angle of 15º together with steel mesh and shotcreteingplus erecting steel girders around the portal entrance.

The poor rock conditions continued to cause problems for Song Da ten metres into the tunnel. As a result the contractors opted to halt proceedings and open a new temporary adit 195.7 m long to allow access into the proposed main tunnel.

By the end of May the adit had been completed allowing Song Da to open two new faces – one towards the inlet portal and the second back to the power house and outlet portal.

Achieving advance rates of 4.5 m/day in the adit, Song Da are hoping to meet a similar schedule in the main tunnel.

Whilst rock conditions have improved in the new workings, some rock bolting is still required although the contractor is confident they can make-up lost time with the new Sandvik rigs.

Featuring two booms and a basket boom, the Sandvik D820’s are fitted with Sandvik 4.9 m shank adapters and couplings.

Throughout drilling at the 43.2 m2 tunnel faces at the outlet end, Song Da are drilling 115 holes including the three x 102 mm dia opening holes.

For these, Sandvik R32 reaming bits are being used.

“These,” according to Song Da Plant manager, Le Van Hung, “are far superior to the American bits being used for the remaining 44 mm dia blast holes.”

“We are in the process of changing over to Sandvik drill bits for all the drilling operations,” he said, adding, “The Sandvik cemented bits are far superior with longer life, ‘truer’ straight holes and increased productivity.”

Inlet tunnel

At the inlet end with a larger diameter 49.34 m2 tunnel cross section, drilling with the second Sandvik D820 has been halted following a tunnel collapse, having advanced 145 m.

Following the clean up of an earlier collapse, a second ‘cave in’ has resulted in a 40 m high hole to the surface with a 5 m diameter.

Currently 40 concrete segments 35 cm and 20 cm thick and meeting 250 MAC standards are being installed around the perimeter of the tunnel wall; advancing in 40 cm increments.

The final design, whether to infill the cavity with rock or concrete is still under discussion.

Song Da

Song Da as a tunnelling specialist with a large fleet of drill rigs is beginning to standardise with Sandvik rigs and rock tools.

In addition to the two DT820’s delivered earlier this year for Dakmi 4, two DX700 were also ordered for Sekaman 3 hydropower project in Laos.

The company also has a Sandvik DP1100, a Ranger 700 and CHA550 drill rigs.

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FOOTNOTE TO EDITORS

This press release is available on the Joem Promotions website:

Issued on behalf of Sandvik Mining and Construction by Joem Promotions.

For further details please contact:

John Hooper

Joem Promotions

The Court Yard, Sondes Road

Deal Kent CT14 7BW UK

Tel:+44 (0)1304 368688

Fax:+44 (0)1304 375181

email: john.hooper @joempr.demon.co.uk

The Sandvik DT820-C is a boom electro hydraulic jumbo for fast and accurate drilling in tunnelling and cavern excavation of 12 – 110 m2 cross sections.

The hydraulic controlled drilling system with added automatic functions and different optional instrumentation levels enable productive and high quality excavation.

The TB 90 universal booms have a large optimum shaped coverage and full automatic parallelism. The booms can also be used for cross-cutting and bolt hole drilling. A basket boom is used for bolting.

The powerful 4-wheel drive center articulated carrier ensures rapid and safe tramming with good balance.

The noise and vibration insulated safety cabin provides an ergonomic workplace with excellent visibility for both tramming and drilling.

Specification

Length14 900 mm

Width

Transportation2 500 mm

Tramming / Drilling3 000 mm

Height3 600 mm

Weight26 850 kg

Tramming speed

Horizontal16.0 km/h

14% = 1:7 = 8º5.4 km/h

Gradeability28% = 1:3,5 = 15º

Noise level (EN 791, free field condition)

In cabinLpA = 76 dB

EmittedLwA = 125 dB

TC 8 Carrier

Diesel engineMB OM904LA

110 kW (149 hp)

TransmissionClark 20 000 Hydrodynamic

AxlesClark-Hurth

Brakes

ServiceHydraulically operated wet disc brakes

Parking and emergencySAHR type, fail-safe wet disc brakes

Tyres14.00 – 24 PR 28

SteeringFrame steering, Orbitrol

Articulation± 37º

Rear oscillation± 8º

Ground clearance400 mm

Fuel tank150 l

Hydraulic jacks

Front2 x TJ60

Rear2 x TJ75

Safety cabinPressurized