Tunnel project of Chilean capital Santiago
First publishedin World Highways
Tunnel construction in Chilean capital Santiago will help cut chronic congestion – Mauro Nogarin & Mike Woof write
Chile’s capital Santiago is a thriving city having benefited from the country’s economy growing strongly in recent years. The massive copper mining sector has helped boost the country’s GDP significantly in the past few decades, also aided by the growing international reputation of Chile’s large wine industry. The steady economic growth has resulted in an equally steady growth in average income, with Chile having been officially recognised as a developed nation in 2013.
This improvement has also fuelled both a major increase in the numbers of registered vehicles as well as a massive boost in infrastructure spending. Following its return to democracy in 1990, Chile’s transport infrastructure has seen steady investment from all of its governments. To cope with the increase in people movements, Chile’s highways have been extended while the country’s airports have been improved. Meanwhile capital Santiago now benefits from having one of the most extensive metro systems of any country in Latin America. The city has also grown, with work opportunities attracting more people both from outlying areas in Chile, and from neighbouring countries also. Along with the development of new industrial areas have come even greater levels of housebuilding to cope with Santiago’s expanding population.
However this combination of urban development and growth in vehicle numbers has resulted in serious traffic issues for Santiago. The problem has been further exacerbated by Chile’s general lack of investment in rail over the past few decades, with the result that bus transport is relied upon instead for long distance transportation. As many of these buses begin or end their journeys in Santiago, this has simply added to the number of vehicles using the city’s roads. Nestling in between the Andes, Santiago’s location also means that it can suffer heavily from pollution, as emissions from industry and vehicles can hang over the city at times when the winds are insufficient to clear the air.
A growing barrier to further development is that Santiago suffers chronic congestion, most particularly at peak periods. Some novel approaches have been made in the past, with the direction of flow being switched on some routes at different times of the day to account for commuter traffic for instance. Meanwhile major urban routes have been opened up, using sophisticated tolling technology so as not to impede traffic flow.
Yet even these moves are insufficient. A number of road tunnels are being built within the city so as to reduce the congestion issue.
The latest phase of this work is for the construction of the Kennedy Tunnel. Chile’s Ministry of Public Works began working on the East Downtown Santiago Building Program in 2013, in partnership with the North Coastal Highway. This programme is the latest in a series of works in Santiago. It involves extensive construction to decongest traffic in the main urban thoroughfares of the Chilean capital. The cost of this project is estimated at around US$500 million.
The first of these projects was the construction of overpasses over the Manquehue and Kennedy Avenues; improvement to the exit to Concepcion; and a tunnel to connect the North Coastal Highway and the Central Highway. These projects have all been completed and are in service today. And engineers are currently executing the second part of the Eastern Downtown Project, which includes the tunnel beneath Kennedy Avenue, expansion of the Southern Coastal Highway and its connection to the North Coastal Highway, which will include two tunnels under the Mapocho River. This second phase also includes improvements to the Lo Saldes/Zujovic Roundabout and an extension of the North Coastal Highway to Padre Arteaga.
1. In the Kennedy tunnel, Manitou telehandlers are used to carry out general tasks 2. The proven New Austrian Tunnelling Method (NATM) is being used to drive the Kennedy tunnel 3. The tunnels are being driven forward with very carefully controlled blasting rounds 4. Before each shot the equipment is moved away from the face 5. Tunnelling is an area in which Chilean engineers have significant experience to draw upon 6. A high advance rate is being achieved in this tunnelling project
One of the most important and complex feats of civil engineering is the Kennedy Tunnel, which is a tunnel with four lanes of traffic in an east-west direction below the existing Kennedy Avenue at about the height of the Perez Zujovic Roundabout and which exits at the Vespuci Knot. Construction of the 1.2km long tunnel begins at the Los Leones Golf Club in the neighborhood of Las Condes, where the entrance ramp begins with five lanes of traffic, covering an area of 250m² going in an easterly direction, which later reduces to four lanes of traffic and runs parallel to Kennedy Avenue. The Kennedy Avenue, once this project is completed, will run in a westerly direction and carry three express lanes of traffic and two local lanes of traffic.
The project also envisions an improvement in the connectivity to the highway with the existing urban infrastructure through traffic solutions, pedestrian access and an expansion of the Americo Vespuci Park (at its intersection with Kennedy Avenue) which does not yet exist.
The area where the Kennedy tunnel project is being built is one of the most congested parts in the entire metropolitan area of Santiago. It is also an area which is expected to grow dramatically in the future with increased building of residential and commercial buildings.These public works seek to reduce travel times in the area, while improving traffic conditions and the quality of life of users and local residents, who will benefit from shorter journey times while commuting. These improvements are also an attempt to deal with the increase in the number of vehicles being driven in this area.
The material the tunnel must traverse is the typical gravel found in the Santiago area, from its start at the Perez Zujovic Roundabout to its conclusion at the Mapocho River. At the Paocho end the tunnel route encounters ancient marine seafloor, at a minimum of 10m depth. The water table also varies from 2m at the start to completely disappearing halfway through the length of the tunnel. The five-lane section has a maximum width of 21m and a height of 11.28m, which is gradually reduced to four lanes during the first 150m of the tunnel.
Because of the ground conditions, the Kennedy Tunnel is being excavated using the New Austrian Tunnel Method (NATM).The primary coating for the four-lane section of the tunnel, with no groundwater seepage, consists of a Primary normal coating of 30mm deep Shotcrete SH 35 as a seal and then placing rolled frames spaced every 120m, finishing with the placement of 230mm of an additional Shotcrete SH-35 for a total fill of 300mm of primary coating.
For the area with groundwater filtration a PVC coating has been placed between the primary and secondary layers of Shotcrete. This PVC coating has a depth of 1.5mm and is made of a geotextile with a 500gm/m2 plus an Acma C-116 mesh. The secondary coating for the section with groundwater seepage consists of 400mm of Shotcrete SH-35 with a stainless steel grid made of 12mm transversal rods spaced 150mm apart and a longitudinal grid of 16mm steel rods spaced 15mm apart, with a secondary steel grid of 12mm transversal rods spaced 150mm apart and a longitudinal grid of 22mm rods spaced 100mm apart. Finally a 100mm coating of Shotcrete SH-35 with 2kg/m3 of polypropylene fibres has been laid down to provide fire protection.
The tunnel builders are using drilling rigs at both ends, with very carefully controlled rounds, while dump trucks take away the debris. A Roboshot machine is used to apply the shotcrete, while two Manitou telehandlers are used for placing the HE 120 frames and steel mesh. There are also topographical and instrumentation control by inclinometers, caskets subsidence and convergence plates, which are used continuously to measure deformation.
1. The blasting pattern is optimised to suit the conditions 2. Effective ventilation is essential to ensure that the tunnel crews can work easily 3. With effective ventilation, machines can operate right at the face 4. Bus transportation is used by many in Santiago as well as across Chile as a whole 5. A downside of Santiago's geographic location and its reliance on vehicle transport is that it suffers frequent problems with smog 6. Santiago has a well-developed metro system yet roads provide a vital transport link for many commuters
The main difficulties facing the construction team are not associated with the construction of the civil works itself however. Instead, the biggest challenge is one of logistics, given the need to make detours and major interventions in an area of high traffic flow. It is important to remember that this section of Kennedy Avenue usually handles a vehicular flow of 1.27 million vehicles going east to west and 1.21 million vehicles going west to east, in other words about 2.5 million vehicles/day, without even considering the vehicle flow from adjacent streets. The area where the construction work is taking place is also a densely populated urban area. And this has required several other additional tasks to mitigate the impact of the construction on the residents in the immediate area. These tasks include erecting noise attenuation barriers in nearby warehouses to reduce the noise from the construction, as well as systems to reduce airborne dust and particulate emissions from the construction and excavation activities.
This current tunnel construction job has followed in the path of an earlier project in the city, to build the San Cristóbal tunnels. The first bore of this previously constructed link was completed in July 2008, with both tubes then being opened to traffic in December 2008. The San Cristóbal project was carried out under the build, operate, transfer (BOT) model and managed by Chile’s Public Works Ministry (MOP).
This project was for the twin tube San Cristóbal tunnels measuring 1.8km long, as well as access roads. And the work forms part of the much larger project to construct the 4km Variante Vespucio-El Salto-Kennedy connection, for which the new Kennedy tunnel is the latest component. Once the Variante Vespucio-El Salto-Kennedy route is finally completed it will connect Providencia and Las Condes on the eastern side of Santiago with Huechuraba and Recoleta on the northern side.
The twin tube San Cristóbal tunnels run underneath the San Cristóbal hill but were driven using very different techniques to the Kennedy tunnel being built presently. The San Cristóbal tubes were bored using conventional drill and blast techniques to remove some 549,000m3 of rock in all, with 70,000 truck loads needed to carry away the blasted material.
Three sophisticated Sandvik rigs were used for the drilling work, with steel arches and shotcreting to depths of 30-50mm used to provide for the tunnels.
The full opening of the link was delayed until December 2008 due to technical problems with the traffic monitoring system as well as to ensure the drives all met with the necessary specification however. But with the completion of the San Cristóbal tunnels, drivers were able to benefit from a link to the Vespucio Norte Express stretch of the tolled highway running around Santiago. The San Cristóbal tunnels cost around $100 million to build with construction starting in May 2006. The tunnels were partially opened with the south-to-north section in 2008. The traffic volume of the San Cristóbal tunnels recorded soon after they opened reveals the need for the construction of this link. The tunnels carried some 23,000 vehicles/day from when the link opened in 2008. And with Santiago’s expected growth in population and vehicle numbers, as well as the completion of other sections of the Variante Vespucio-El Salto-Kennedy connection, the traffic levels through the tunnels are expected to climb to some 60,000 vehicles/day by 2020.
The San Cristóbal tunnel project was awarded in early 2005 as a 33-year concession package to the Sociedad Concesionaria Túnel San Cristóbal consortium, a partnership between Hochtief and ACS Dragados. The two companies carried out the planning and construction work, as well as sourcing the necessary financing. Meanwhile the necessary IT and traffic control technology for the tunnels was provided by Indra, which won an $8.7 million deal for this portion of the project.