Shani Wallis, TunnelTalk
- Other than superficial damage to surface structures and stations, the Santiago Metro, the large majority of which is built underground, has survived well the 8.8 magnitude earthquake that shook the southern part of Chile last Friday night at 3.30am into Saturday morning (26-27 February 2010). A report from Ing. Carlos Mercado, Manager of New Line Extensions for the Metro corporation, confirmed that the underground structures performed well. The first cut-and-cover line, cut-and-cover stations, and NATM mined stations and double-track running tunnels all withstood one of the largest earthquakes on record, an event that caused destruction of buildings and elevated highways on the surface, tsunamis along the coastline, and a dreadful rising death toll.
Devastation on the surface...
- Tunnels and underground structures are well know as being resilient to earthquake activity and the building codes applied to infrastructure and urban construction in Chile are recognised as being a significant reason why destruction was not more devastating under such a heavy event. After inspection of the system during Saturday, the city's metro system was up and running again by Sunday with only one station reported closed for repair of damage to the exit and entrance structures and superficial damage at the depots continuing around the operating system. The city's Costanera Norte highway, part of which is built in cut-and-cover tunnels under the bed of the River Mapocho, also survived unharmed.
- Underground expansion
At present, Santiago's Metro consists of 101km in operation comprising 59.1km and 67 stations underground, 20.4km and 17 stations at grade, and 21.2km and 20 stations elevated. From a start of construction in the early 1970s using cut-and-cover, it was in the 1994 that NATM excavation of running tunnels and stations was
- introduced to keep construction underground and eliminate the social disruption of cut-and-cover works. The geology under Santiago is particularly suited to the application of the open face sequential method of excavation and the engineers and contractors working on design and construction of the system have become masters of the technique. A study in 2002 to compare the cost effectiveness and risk scenarios of using shield TBMs and segmental linings for planned construction of Line 4 concluded that NATM was more appropriate as it was less expensive, generated more benefits to the local industry and posed fewer risks for the project schedule. The Dr. Sauer Corporation and Geoconsult of Austria were instrumental in introducing the technique to the Metro's construction programme.
- As the last section of the Line 5 extension prepares to open to the public this summer and draws to a close several decades of continuous metro expansion, plans are advancing for a new Line 6. Cutting diagonally under the city from northeast to southwest, and will relieve congestion on the existing Line 1.
Metro system and planned Line 6
- The new 14.8km long line with 12 new stations was planned as a combination of at-grade, elevated and underground elements but strong objection by the mayors of different districts resulted in having the line placed mostly underground.
- The project was promoted by the Chilean federal administration of President Michelle Bachelet that lost office in the recent elections. The incoming administration of President-elect Sebastián Piñera has not cancelled the project but has said that it will be examined in great detail given the tight economic environment in Chile and that three alternatives, including a possibility of constructing the line in parts and of perhaps altering the alignment, are being considered. In the meantime, site investigation studies have been scheduled to start in the coming months.
- City and national projects
Another major tunnelling project planned for under the streets of Santiago is a new 30km highway to the north that includes sections of cut-and-cover and mined tunnels. The project is currently in the basic design phase, which is scheduled to conclude for the start of the procurement process by the end of the year. Although not yet confirmed, it is anticipated that the project will be realised as another in Chile's long list of highway concession projects with construction of the tunnels progressed under a design-build arrangement most likely with members of the successful concession group. The tunnelling works pass through a mountain and very cost to operating metro structures.
NATM Metro station construction
- In the hydro world and among other projects, the Astaldi-Fe Grande JV has launched its rock TBM for the 2.5km long drive for the Chacayes hydro scheme which involves construction of more than 6km of tunnels in a complex water conveyance system, as part of the Alto Cachapoal development project which is being developed by the Australian group Pacific Hydro.
- For Chile's enormous mining industry, several major tunnelling projects are advancing. High in the Andes, at nearly 4,000m elevation, Seli operating a 4.5m diameter double-shield TBM as a subcontractor to the Dragados-Besalco Consortium to excavate an 8km long inspection tunnel for the El Soldado copper mining company.
- For Codelco's vast El Teniente copper mining operation, proposals for award of the design-build contract to build twin 9km long access tunnels to a new production level are underway. International contractors known to be interested in bidding the work include Dragados, Besalco, Seli, Strabag, Mas Errazimus, Jaegar, Hochtief, Frontier Kemper, and Redpath.
- Another huge project in basic design for the Codelco is the development work to establish an underground mining operation to continue extraction of copper ore after exhaustion of the open pit operation. The overall project is the aggregation of about 10 big projects in their own right. These include two large access tunnels of 9km long, ventilation and extraction and ingress shafts of up to 800m deep, and caverns for various processing and staging operations. Currently in basic design, the owners schedule is to have access work tendered by the end of 2010 and construction work underway by early 2011.
TBM launch for the Chacayes hydro scheme
- "There is a lot of work going on in Chile at the moment," said Alexandre Gomes, Ingeniero Civil Gerente General for Geoconsult in Chile when TunnelTalk made contact after the earthquake, initially by e-mail and later by telephone. "Last year, the economic downturn cancelled many jobs, particularly in the mining industry, but all has picked up this year to create a workload that is like two years in one. Just as when you take a day off from the office there is two days of work to get through the day you return. The problem," said Gomes, who is a regular participant with the Chilean delegation to the ITA Congresses, "is finding the right people for all the necessary tasks. If Spanish speaking engineers or experienced tunnelling managers are looking to relocate, Chile has a job for them - and we can assure them that we will not have another big shake for the next 25 years or so!"
Designed for seismic survival - TunnelTalk, Sept 2009
Chilean mine invites access project proposals - TunnelTalk, Nov 2009
Santiago Metro goes underground with NATM - TunnelTalk, Apr 2003
Optimized NATM designs for Santiago Metro - TunnelTalk, Apr 2003
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