Drill and blast excavation is underway on six faces of the longest tunnel on the sprawling water conveyance system that will feed the Simplico hydro project in Brazil.

The top bench of the 6,030km long bore is being opened to 7.5m high by 15m wide, the standard width of all four tunnels on the scheme. The lower bench height of the “T3” tunnel will be 7.2m to give a final height of 15.7m.

Geology along all four tunnel alignments comprises gneiss with typical UCS of 200MPa. In recent months, as the excavation gets underway from the upstream and downstream portals and access tunnels a third of the way from each end, to give two faces each, the average advance has been 6m per day.

Contractor on the 36-month project is a joint venture of Odebrecht and Andrade Gutierrez. They have both ordered and are leasing a total of five Sandvik Axera jumbos – two T11 (now known as Sandvik DT11) and three T8 (Sandvik DT8), all of which have three booms. In addition, the rigs have the firm’s tools, including the 4.3m long R38-Hex32-R32 rods, 51mm diameter R32 bits and R38 shanks.

A T8 jumbo was used to open up the 7m by 8m access tunnels, and four of the five rigs on the project are being used to drive the tunnel.

The faces are on average advancing by 2.85m with each blast round. Typically, a total of 135 holes are drilled on the face, to 3m lengths, within about 2.5 hours. The drill pattern is 16 holes for the opening (including three cut holes reamed from 51mm to 102mm diameter), 14 foot holes, 39 contour holes and the remainder spaced at radii of 5.05m, 6.25m and 8m.

The excavation sequence has about three rounds per day, including up to 1.5 hours for charging, 40minutes for blasting and ventilation, and up to two hours for scaling and mucking out. The spoil from each round is approximately 264m3.

The JV contractor is achieving 300m with the drill bits, and achieving 6-7 regrinds with each. The average life of Sandvik tools on the project has been 5,000 drilled metres for the shank adaptor and 2,500m for the H32 rod.

The project is being built along the border of Minas Gerais and Rio de Janeiro states, and is to be completed in 2010.


Drill and blast works at Simplico Drill and blast works at Simplico