Hemmed in on three sides by the sea and the deltas of two major rivers east and west, rapid expansion of Guayaquil in Ecuador has been north, beyond a set of hills that separate the old historic city centre from the new northern suburbs.

Existing carriageways pass around the hills into the city centre but these are now heavily congested. With no room for expansion or construction of new surface highways, the adopted solution is to excavate two three-lane tunnels through the hills and direct traffic into and out of the city on a new high capacity one-way system.

Sixty firms in eleven consortia qualified for the project when it was advertised internationally in 1998. Of these, five groups submitted bids – two groups sponsored from Brazil, two from Spain and one from Mexico. The joint venture of local construction company Semaica, one of the oldest construction companies in Ecuador with major tunnelling experience, and OHL of Spain (a merger of the Spanish companies Obrascon, Huarte and Lain) won the contract with the lowest bid of $US60M.

In addition to the tunnels, the contract includes all the m&e installation, longitudinal ventilation plant and finishes. There is also extensive cut-and-cover work at the four portals and drainage culverts to prevent flooding during heavy rain. 1.3km of viaducts and other complex surface works will integrate the new highway with the existing roads at either end. Cut-and-cover work at the north end of the tunnels rises to 25m, with the concrete structure including two rooms above the road surface to house equipment and the tunnel operating stations. While cut-and-cover at the south end of the east tube includes reconstruction of a concrete water supply reservoir and reconstruction of an amphitheatre.

Notice to proceed on the awarded 28-month contract was granted in May 2000 after the contract’s financial arrangements were adjusted to accommodate "dollarisation" of the Ecuadorian currency. In January 2000, Ecuador adopted the US dollar as its official currency, replacing the Sucre.

The volume of money in circulation in Ecuador, as well as other crucial monetary criteria, is now under the direct control of the US treasury. This is seen as a positive factor in controlling inflation and speculation on the national currency, and in promoting economic stability and growth.

Geological conditions

The mined section of each three-lane tunnel is 264m long and 585m for a total tunnel length, including the cut-and-cover sections at each portal, of 541m and 745m, respectively. The hills through which the tunnels pass are formed by intrusive rock known locally as Lutita and covered by subsequent layers of colluvium. These rise to a maximum of 89m above sea level and from a tunnel overburden of 78m.

Under the particular climate conditions of coastal Ecuador the geology of the hills is highly weathered. On the Bieniawski (RMR) system of rock classification, conditions range from Type V at the portals to more competent Types III and II through the central core. The friable weathered colluvium at the portals and towards the more competent core has little cohesion and is highly permeable. Although dry and friable in the dry season, the material becomes sticky and claggey, and susceptible to swelling when under the influence of excessive water percolation during the heavy wet weather season.

In efforts to complete tunnelling as soon as possible and open the new highway by the September 2002 due date, excavation will advance from the two north portals, and the south portal of the longer of the tunnels, on a 24h-day, seven day week schedule. Continuous excavation is also required to quickly limit and arrest anticipated ground movement. There are a series of sensitive telecommunication towers on the summit of the hills, a local access road crossing the tunnel alignment and, although established without official planning permission, there are several houses on the slopes of the hills, all of which would be adversely affected by excessive ground movement. All major structures, and the tunnel excavation itself, are monitored by comprehensive arrays of geotechnical instrumentation and the tunnel design includes several measures to improve ground stability and prevent excessive movement. Spiling, face nailing, short rounds of excavation, and the potential to divide the faces into smaller, more easily controlled drifts, are all measures to control these challenging conditions.

Principal designer for the project for the Municipality of Guayaquil is STIPE of Italy with the professional assistance of Professor Sergio Olivero, and TYPSA of Spain is the client’s construction supervisor. The project is financed 25% by Guayaquil Municipality and 75% by CAF, (Corporacion Andina Fomento), the funding agency established by five South American countries – Ecuador, Venezuela, Peru, Colombia and Bolivia. This is to help finance infrastructure projects in these Andean countries, particularly projects capable of paying for themselves over time. The CAF loan to the Guayaquil project is to be repaid over 20 years starting three years after opening.

When T&TI visited the site in November 2000, Semaica/OHL was diverting services and preparing the portal zones to start excavating by early this year. "We have about five times more services than expected to move," said Mauricio Martinez, the project’s technical manager and a director of Semaica. "This includes moving a water supply main from directly in the tunnel face at the northern portals. Its existence was not indicated on any of the site investigation drawings and while we will get paid for diverting all these extra services, it is eating at our limited contract period."

Excavation sequence

Two ITC–Schaeff machines are being used to excavate the tunnels on their top heading, bench and invert sequence. "We already owned an ITC-Schaeff 112 E4 mucking machine that we bought for a project in 1994, and the JV has bought a second new and bigger ITC 312 H6 machine for this project," said Martinez. The new 30 tonne 312 machine is a combined tunnelling and loading machine and is equipped with a patented hammer-shovel combination. The hydraulic hammer will loosen the inter-bedded soft and hard rock strata, while a grab and loading shovel transfers the excavated material to a chain conveyor. The boom of the machine is fitted with a tilting and swiveling control unit to allow the operator to reach every point of the cross-section and excavate the profile with precision.

The inventory also includes two Aliva Duplo 285 wet-dry shotcrete machines bought by the joint venture for a previous job. For the road tunnels they will work with a specified wet mix that also carries 40kg/cm³ of Trefil Arbed Bissen 30/.70mm steel fibre reinforcement, supplied by Trade Arbed of Germany.

The nozzles of the shotcrete machines are hand-operated rather than on robot booms. "Although the final cross section is very large at 140m², each heading is smaller at about 80 m², 40m² and 20m² for the full top heading, bench and invert phases, respectively. Rounds are as short as 750mm. The volume of shotcrete/cycle will be about 8m³ and applied at about 3-4m³/h with operators working the nozzle for 20 minutes at most," said Martinez. "Volumes of 15-20m³/cycle or more would require high capacity concrete piston pumps and robot nozzle booms."

In the weathered friable material and across the wide three-lane cross section of 15m width and 10m height, ground movement around the tunnel is anticipated to be extremely high at up to 300mm of convergence in total.

"This we must control, manage and minimise," said Martinez, "and the strategy starts with a tight canopy of 12m long spiles at 750mm centres around the top heading profile. All except perhaps the central more competent core of material of the tunnels will be pre-supported with the spiles across the top heading and with a 3m overlap between rounds. There is also the facility of dividing the 80m² top heading into two smaller drifts separated with a temporary side wall, but we will try to avoid this as it will increase the excavation cycle time."

"The top heading faces will be further stabilised with glass-fibre face nails of up to 15m long and injected with high pressure grout. In addition, the faces will be sealed and supported with shotcrete between spiling operations and whenever necessary during intermediate excavation rounds."

The extensive spiling and face nailing operations are let as a specialist sub-contract to Geocisa of Spain.

Concurrent sequence

Excavation on the top heading, bench and invert sequence will progress concurrently with the top heading some 50m ahead of the bench. The invert is excavated in simultaneous with invert concreting. Rounds in the top heading in the poorest Type V ground, are as short as 750mm and all exposed faces are sealed immediately with a 50mm layer of steel-fibre reinforced wet mix shotcrete. This is followed by steel arches on 750mm centres and covered by a 100mm layer of fibre reinforced shotcrete.

In Type V conditions, a total of 180mm of shotcrete is built up in three rounds during the same shotcreting cycle: a 2m³ x 50mm thick layer of immediate shotcrete in the current 750mm round; a 4m³ x 100mm thick layer of shotcrete to cover the steel arch of the previous 750mm round; and a 2m³ x 30mm thick layer of unreinforced shotcrete in the 750mm round before that. The latter is to provide the smooth finish against which the tunnels’ plastic membrane waterproofing system will be attached.

Both Sika and MBT additives are being tested to meet the design specifications. Superplasticiser is mixed in at the batching plant, as is the steel fibre reinforcement. The liquid accelerator is injected into the stream of shotcrete about 2m from the nozzle during application. The mix further incorporates 430kg/m³ of cement, and a 5% content of silica fume. Shotcrete test panels and core samples from the tunnel are required to meet an early strength of 10N/mm² at 24h, a medium strength of 24N/mm² at seven days and a minimum 28-day strength of 43N/mm². Tests to date have regularly met early strengths of up to 12N/mm² and 28-day strengths of more than 48N/mm².

Rockbolts of up to 6m long and steel fibre reinforced shotcrete will support the better quality intrusive rock in the central section of the tunnels, which might also require some drill and blast excavation. After erecting the waterproofing membrane the tunnels are finished with an 800mm thick final lining of reinforced in situ concrete. Two large concrete forms, each 6m long to negotiate the tight curves in the tunnels, are on order from CIFA of Italy for casting the final in situ lining across the wide vault of the three-lane tunnels. These will be 11.6m wide at the road deck once completed.

If needed, concrete lining of the invert is being cast as soon as possible after excavation to avoid any possible heave of the reactive friable colluvium from the start of each tunnel portal. However the concrete lining of the vault cannot be cast until any registered ground movement is retarded to less than 2mm.

Progress to date

"Since your visit last November, we have started the top heading and bench excavation from the two north portals," said Martinez. "and we will start excavation from the south portal of the longest tunnel in May. The shorter tunnel will be excavated from the north portal only. The spile driving operation, prior to starting excavation, and using a Paccioso drill rig, has been very difficult in the fractured rock. Ground movement across the top heading has been high, as expected, and particularly so since we are now in the middle of the three-month wet season (March 2001). The highly permeable friable material at the start of each tunnel portal is much wetter than in the seven-month dry season of each year.

"We are still in the learning curve of the 24h-day, seven day week schedule and each 750mm round of excavation, shotcrete support and steel arch installation in the top heading is taking about 9h. We are programming to improve this rate to about 5h/750mm round and that should be possible within the next weeks. We are currently about one week behind schedule but this too we are hoping to make up over the coming months and stay on track to meet the September 2002 opening date for the new highway and its three lane tunnels. We stay positive and in control of the difficult geological conditions."

Related Files
Longitudinal section of one of the tunnel tubes
Plan of Guayaquil’s new one-way traffic flow system
Longitudinal section