Atlas Copco drill rig's high-speed shaft drive

The rate of progress at a major shaft-sinking project under the village of Sedrun in Switzerland has amazed visiting engineers at the site.

An Atlas Copco shaft-sinking rig, equipped with six booms and COP A15 pneumatic rock drills, has driven an 800 m-deep shaft down to the planned route of the St. Gotthard Base Tunnel. The rig was also used to provide the cover drilling, a method of keeping the water away from the shaft.

How access is obtained to the multi-function St Gotthard Base Tunnel site.

And an advance rate of 3-3.5 metres/day was achieved with the rig. As a seven-day week was being worked on the project, this amounted to some 100 metres/month when the rig was working continually.

After solving the start-up problems, this high performance was maintained throughout the rest of the project, which - including four months of running-in time, preliminary work, rock reinforcement and final finishing-off work - spans a period of 18 months.

The consortium in charge of the construction of the Sedrun shaft consists of the four Swiss contractors Murer AG Erstfeld, Zschokke Locher AG Zuerich, Marti Tunnelbau AG Bern, CSC Impresa Costruzioni SA Lugano, and the South African company Shaft Sinkers Inter- national Ltd. Sandton.

The completed Sedrun shaft, nicknamed "the multi-function site", will be used for ventilation and maintenance. At its bottom, it holds an emergency railway station and emergency rooms for the train passengers.

Installed at the site was a hoist, which will later be rebuilt to suit tunnelling requirements. It lifts 10 tonne loads of rock in buckets at a speed of 11 metres/ second - or 700 metres/minute.

In order to maintain the high rate of progress, forming of the concrete lining was done in parallel with the general shaft sinking operation. Several other operations were also carried out in the shaft simultaneously.

Star performer in the Alps: The Atlas Copco six-boom shaft-sinking rig in the 800 m-deep shaft down to the St. Gotthard Base Tunnel.

A platform provided five working decks. The lower Deck 5 was for managing activities at the bottom of the shaft; the concrete forms were mounted from Deck 3 for final lining in six-metre stages; concrete was received through long pipes on Deck 2 to be remixed and formed; and all supply lines were assembled on Deck 1.


Round shafts

TShaft sinking is a speciality in South Africa because of the many deep mines in the country. So it follows that Atlas Copco South Africa has produced a series of drill rigs that are built for this purpose.

The rigs are designed for round shafts - the dominant choice and resemble the spokes in an umbrella. The "spokes" are the booms on the rig. There are three to nine booms and the rig works in shaft diameters of 6-12 m. The air-powered COP A15 rock drills fitted to the Atlas Copco rig at Sedrun were introduced in 1998 for shaft-sinking operations with water flushing of the drill hole.

Impact energy is 14 kW and the rock drill works with an air pressure of 6-bar, requiring 300 litres of air per second. It is designed for hole sizes of 51-102 mm and, at Sedrun, 51 mm was the choice with penetration at 1.5 metres per minute.

The hoist in the shaft: The muck bucket can take six cubic metres of waste.

The contractor considers that the rock of schistose gneiss made blasting difficult, as it required 2.9-3.6 kg of nitroglycerine-based explosive per cubic metre in an area of 58 m2.

The number of holes varied between 140 and 170 and they were normally drilled to a depth of 3.5 m to give the required advance of 3.2 m. The holes were vertical and in a circle. The opening was achieved by a parallel cut of three 102 mm holes placed in a triangle, and these larger holes were drilled with a DTH hammer placed in the centre of the rig. Each drilling period lasted about three hours.

The stage in the shaft: The platform structure has five decks from which a variety of essential tasks are carried out.

To control the inflow of water, continual pre-injection was carried out with 40 m-long holes drilled in a "trumpet" shape downwards, a method of cover drilling.

Before blasting took place, the entire shaft-sinking apparatus - called "the stage" - had to be lifted 60 metres above the bottom to avoid possible damage caused by flying rock.
Primary reinforcement was carried out during a pause in the loading cycle with 3 m-long Standard Swellex bolts and shotcrete. All the reinforcement work took up to six hours and the total time invested in each round was, at best, some 19 hours.

The planned rhythm of one round per day was achieved - but it took four months of running-in to reach the target.

"But producing the shaft, finished and lined, in 13 months is an achievement which in all probability exceeds what most people would consider possible."

The shaft has been constructed by the specialist company Shaft Sinkers of South Africa, and Senior Contracts Manager J.J. Kaalsen says the project was a difficult but interesting challenge. He continues: "It was pretty tough going in the beginning. There were so many nationalities involved here that it was quite a feat to get everything organised and set up.

A job well done: The Senior Contracts Manager J.J. Kaalsen (left) and Chief Site Supervisor Robert Meier say the going was tough - but successful.

"But the Atlas Copco equipment made a great contribution and, in the end everything was fine. The shaft-sinking rig worked well and the project went according to plan.