Record tunnelling advances on a major water supply project in Ecuador were the subject of the British Tunnelling Society‘s informal discussion held on February 22, 2001 at the ICE. Over 80 of the Society’s members and guests heard speakers Fernando Luiz Reis, project manager and Danilo Abdanur, construction manager, both from contractor Odebrecht, describe this vast project to bring water to a part of Ecuador that has no natural water sources.
Fernando Reis started the presentation with an overview of the project called the Trasvases Manabi, inter-basin water supply and irrigation project which had been let to Odebrecht for a contract cost of US$212M. The project was to bring water to an area of the country called Manabi province and to encourage the development of agriculture in an area of the country, which contained 13,250 hectares of land and a population of 650,000, but very little natural water. Fernado Reis said that the very name Manabi meant "land with no water".
Odebrecht is a privately owned Brazilian company with operations in 15 different countries. It has a gross revenue of US$4bn of which engineering and construction account for around US$1.8bn. The company has work in progress on both the Lima and Caracas Metros and over 33,000 employees of which 19,000 are Brazilian.
The Engineering News Record has placed Odebrecht as the 26th largest contractor in the world, fifth largest in water supply and number one in hydro plants.
Manabi contract
Fernando Reis went on to describe the contract in Manabi province saying that Manabi was situated on the west Pacific Ocean coast of Ecuador just below the equator.
This massive irrigation and water supply project was conceived in three phases: La Esperanza dam, Transbasin I (tunnel) and Transbasin II and III (pumping station, pipeline, 11km and 4.4km tunnels). All three phases, at a total cost of US$360M, were procured through CRM (Centre de Rehabilitation de Manabi), a government agency responsible for development of infrastructure in the region.
The main aim of the scheme was to provide links between existing bodies of water with tunnels, pipelines and a large pumping station, in order to bring much needed drinking water to 70% of the population of the province (6% of the entire population of Ecuador) and to irrigate over 14,000 hectares of land with possible extensions (up to 10,000 hectares) at a later date.
The Spanish contractor, Dragados, completed Transbasin I, an 8.3km long tunnel, between 1996 and 1998 at a cost of US$59.62M with finance provided by Deutsche Morgan Grenfill (46%), CAF (19%) and the government of Ecuador (35%).
The third phase, Transbasin II and III, was awarded to Odebrecht in May 1999 for US$212.18M with completion due in December 2001. Finance was through BNDES (53%), CAF (32%) and the government of Ecuador (15%).
From the start
The main starting point for the contract was the establishment of two major access roads through mountainous jungle terrain, the first to the main campsite and pumping station and the second to the mid-point between the two tunnels.
The first access road was 10km long and rose over 350m in the first 4km. This road was completed in just seven months. The second access road was 15.3km long and was completed in six months.
At the main campsite, the workers’ village was a major construction undertaking in itself. It was required to accommodate 1,610 people at the peak of construction covering an area of seven hectares – some 2,550 meals were served daily on the site. There was a conference room for 50 people, four restaurants, a chapel, bank, water supply of 150m³/day and 5,000 kVA power supply.
Adjacent to the main campsite was the main pumping station, situated on the edge of the La Esperanza reservoir. This pumping station was originally designed by Japanese engineers and involved 35,000m³ of concrete and 350,000m³ of excavation, but a redesign by the contractor allowed significant savings to be made by reducing the concrete quantity to 6,400m³ and excavation to 166,000m³. Supply and installation of the six pumps and switchgear was by Alsthom/ABB.
In order to supply power to the pumps an overhead transmission line over 34km long had to be constructed over very inhospitable terrain.
From the pumping station a pipeline was constructed at 3.5m diameter for a length of 6.3km up to the tunnel portal. The pipe line was protected by a surge shaft just above the pumping station.
It was also found necessary to redesign much of the tunnel lining to create economical designs. The original Japanese design was for a horseshoe shaped tunnel with a 500mm thick concrete lining. The redesign by the contractor was for a circular segmental lining only 200mm thick with significant savings in excavation and concrete volumes.
The segmental lining used was of interlocking hexagonal segments with steel fibre reinforcement erected behind a double-shielded Robbins TBM refurbished by SELI. This TBM on the Transbasin II tunnel contract, drove downstream at a record average rate of 39.05m/day.
Significant outlet and inlet structures were constructed after redesign by shotcrete to make large savings to the contract. The outlet to the Transbasin III tunnel was designed as a shaft on the side of the Poza Honda reservoir to allow work to be completed in the dry with a short connection to the reservoir, ready to be completed after the tunnel.
At the present time the TBM is assembled at the portal to the Transbasin III tunnel ready to start in early March.
Fernando Reis said that a lot had been learnt from the first tunnel and it was anticipated that tunnelling on this 4.47km tunnel would take three months at the rates on the first drive.
The safety record on this contract was something of which Odebrecht was very proud. With over six million man hours worked, there had been no fatal accidents – only 21 reportable accidents and only 704 man days lost.
For the construction aspects of the work Fernando Reis handed over to Danilo Abdanur, construction manager for Odebrecht, who started by describing the geology.
Geology
Much was known of the geology of the area which was recognised as containing very consistent units of muddy sandstones and sandy mudstones in predominantly very uniform, horizontal sedimentary formations of the Onzole group. This was confirmed in the first tunnel and the same conditions were expected in the second.
With 400m cover to the tunnel, very little could be gained by drilling investigation holes and it was expected that there would be very consistent tunnelling conditions with little or no water, little faulting and low rock strengths.
SELI was selected to refurbish the TBM as it had considerable experience in the area having provided the TBM for the Transbasin I works. The company was also assisted by John Foster (MTS) who provided operational and TBM design expertise.
The TBM was to have the following features:
The contractual arrangement with SELI included a rental subcontract and a performance guarantee of 32m/day for the whole system. Design and fabrication took seven months with delivery and erection taking a further 2.5 months.
Ventilation was provided by a 1,200mm diameter duct, reduced to 800mm diameter in the back-up, to give 7m³/min at the face. A two stroke system of segment supply and spoil removal was adopted as the most efficient for this length of tunnel.
The segmental lining design was overseen by Chris Smith (CRS) and support to the 1.2m long by 200mm thick ring was by pea ballast injection prior to final grouting. Reinforcement was steel fibre at 30kg/m³ and the segments had no sealing gaskets.
The segments were cast on site using local labour, with steam curing to provide the required throughput of 120 segments per day, to meet the very fast production schedules. A total of 53,000 segments were produced using 51 men per shift. Demoulding strength was set as 10MPa and the final segment strength was 35N/mm².
The TBM has a daily maintenance period of around 4.5 hours with an overall utilisation (net boring time) of 37%. The overall production rate for the second drive based on this production from the first drive is expected to provide another record production of 39m/day ensuring that the contract remains five months ahead of programme.
This record production has much to do with the planned preventative maintenance, said Danilo Abdanur. He also said that the success of the TBM was due to:
He also confirmed Odebrecht’s commitment to safety matters and its excellent safety record on this contract.
Related Files
La Esperanza-Poza Honda and Poza Honda-Mancha Grande tunnels
Location and layout
Cross section through the tunnel
