AIRLIFT IN THE ANDES

Construction of 6,200 metres of tunnels which will form part of the new Chinango hydro power project in Peru is now complete.

Located in the towering Andes mountain range east of the capital city Lima, the three sites for the project were ideally suited for the production of hydro power.

But they are in a wild and remote area, inaccessible by road and subject to massive downpours during the rainy season. An attempt was made to build a supply road linking a small tunnel exit site, perched high on a mountainside, to an existing track 180 metres below. After five months, the project was abandoned when torrential rains and landslides washed the new road away.

Difficult option

Contractor Graña y Montero was faced with the problem of getting all the heavy construction equipment - drill rigs, construction vehicles, compressors and rock drills - to the site quickly in order to meet the just-in-time delivery requirements.

Difficult to access: The Valves Chamber site is carved out of the side of a mountain in the Peruvian Andes. Water pipes are hauled up from the project's base camp, located some 180 metres below the exit tunnel.

The only option available, although difficult and potentially hazardous because of strong winds gusting through the narrow ravine leading up the site, was to transport the equipment to the site by air, using a specially-adapted crane helicopter.

Jorge Fernandez, Head of Equipment for GyM, supervised a team of Atlas Copco technicians who dismantled the equipment so that loads would be within the safety limit of six tonnes per trip. Then the components were carefully flown up to the site and reassembled to start their various tasks.

Says Site Manager César Vera: "The risky operation was a success, although the setback delayed starting work on the tunnel by three months. However, due to the excellent performance and availability of the Atlas Copco equipment, we were able to recover the lost time. So much so that we now expect this part of the project to be completed a month ahead of schedule."

The USD 200 million Chinango project in the Chanchamayo valley region of Peru is a merger of two power stations which are under construction. The 40 MW Yanango plant is is scheduled for completion in mid-2000 and the 142 MW Chimay scheme will be ready a year later.

The completed project will draw on the fast-running waters of the Tarma, Yanango and Tulumayo rivers on the Atlantic watershed to generate a total of 1,217 GwH per year. (See separate article).

Tunnelling work started in April, 1998. Now, deep in the andesite rock, the headrace tunnel has a cross-section of 9.8 m2 and is 5,045 metres long, with secondary tunnels totalling over 1,000 metres.

Partners again

The GyM project team of Alfonso Gálvez, Operations Manager (Special Projects), Site Manager César Vera and David Vásquez, Head of Construction Works, chose Atlas Copco as the supplier of equipment for the project. Their decision was based on the success of previous partnerships between the two companies.

The specially-adapted crane helicopter, ready for its mission. It hoisted the equipment up to the Valves Chamber site without mishap.

Two contracts were signed by the partners: The first was a service contract for the maintenance of the Atlas Copco drill rigs, rock drills and vehicles on the project, guaranteeing mechanical availability of 90%. The second was a cost-per-drill-metre contract for rock drilling tools, which included bit grinding.

Drilling sites

Drilling was from three headings - the Tarma Tunnel, the Yanango Access and the Valves Chamber tunnel exit site, where the airlift took place. Atlas Copco equipment is in operation at all three worksites.

At the Tarma Tunnel: One Boomer H128 drill rig mounted with two COP 1238 rock drills, one Scooptram 3.5 LHD vehicle, an MT-420B truck, six BBC 16 rock drills and a Teroc 64 bit grinder.

At the Yanango Access: One Raildrill 322 rig equipped with two COP 1838 rock drills, four BBC 16 and three BBC 34 rock drills.

At the Valves Chamber: One Boomer 282 unit mounted with two COP 1238 rock drills, one Scooptram 3.5, one MT- 420B truck and eight BBC 16 rock drills.

Drill and blast operations at the three worksites consisted of 46 holes per round, using 14 ft-long rods and Teroc bit grinders. Drilling time was between 60 and 90 minutes and four blasts per day were accomplished.

César Vera is delighted with both the performance of the Atlas Copco equipment and the success of the service and maintenance contracts.

He says: "I want to emphasize that the high availability of the Atlas Copco equipment was the key to success in this operation. We would not have been able to perform major repairs at such an inaccessible site but availability was 95% and only minor repairs were required.

"The service and maintenance contracts also worked in a very positive way, thanks to our close relationship with the Atlas Copco people. There is mutual confidence and flexibility and we are always able to come to an agreement on any differences that occur."

He concludes: "We like working with companies that bring us solutions, not problems. And Atlas Copco is a first-class example. We are very happy with the price and quality of their services, their quick response and support. In this difficult project, things just had to work - and they did!"