Constructing metro systems is never easy, but in the Greek coastal city of Thessaloniki contractors have faced a range of challenges that have not only delayed work, but caused redesigns and major cost increases. The 9.6km twin tunnel, which runs at a 20-25m depth below the city, is deep enough to avoid harming the historic artefacts. However the station boxes, which are constructed top down from the surface to the base encountered a raft of ancient treasures from the Roman, Byzantine and Ottoman eras which must be preserved.
TBM and station excavation work rates are usually measured in meters per day. These statistics are compared to the forecasts, the actual ground conditions, the machine wear rates and of course the overall programme. Contractors and their clients are of course seeking to maximise progress and set up their machines and site processes to ensure that the schedule is met.
Archaeologists take a very different approach. “The archeological research works were proceeding in parallel with the normal excavation,” explains Rainer Dell’Onze, project engineer for contractor Salini Impregilo which is responsible for around 42.50 per cent of the civil works on the project. Excavations would always commence under the supervision of an archeologist and as soon any findings were discovered, the archeological services would take over the continuation of the excavation with the support of the contractor. The rate of archeological excavation was of about 300mm per month.
“As soon we reached the depth where protective measures were foreseen to be installed, the archeological research works were suspended and the findings temporary covered to allow the access of equipment for the installation of shotcrete, anchors, pre-stressed anchors, struts, etc. Only after the protective measures were completed the archeological research works could be resumed,” says Dell’Onze.
Removing the findings once discovered was also very time consuming. So, it is not surprising then that the project timescale has slipped a rather long way. Commencing in May 2006, the new metro line was originally scheduled for completion by the end of 2012. The forecast budget at this time was EUR 798M (USD 930.8M) with an additional EUR 15M (USD 17.5M) for archeological excavation and research works.
But this turned out to be quite an underestimate. As of May, the actual budget was EUR 1.3bn (USD 1.52bn) with EUR 115M (USD 134.24M) for archaeological and research works and the final completion date is 2020 except for two stations where significant archaeological excavation is currently in progress. These two stations are Venizelou and Aghia Sofia which sit at the western end of the first phase of the metro project (see map, page 29).
The stations are two of 13 which fall under the scope of the first phase of the works, which also includes the excavation shafts, the 9.6km twin tunnel railway lines, one forestation, two underground crossovers for future extensions, one depot covering a surface of approximately 540,000sqf (approximately 50,000 square meters) with the operation control centre and the administration building, as well as all the electromechanical and railway systems including rolling stock formed of 18 ultraautomatic and state-of-the-art, fully air-conditioned trains.
The new line will be completely automated with a transport capacity of 18,000 passengers per hour in each direction and a frequency of 90 seconds at peak times.
Construction is being undertaken by the AIASA joint venture consisting of Greek firms Aegek/Aktor (28.78 per cent), Italy’s Salini Impregilo (26.71 per cent), Italy’s Seli (7.19 per cent), Italy’s Ansaldo STS (25.84 per cent) and Hitachi Rail Italy (11.49 per cent, formerly Ansaldo Breda). Works have been separated into two packages.
Group A which is Aegek-Aktor, Salini Impregilo and Seli is undertaking the civil works, track works and auxiliary electromechanical works. Group B consisting of the remaining partners is responsible for design and detailed design, supply, testing and commissioning, training, operation and maintenance organisation of the main electrical and mechanical systems and rolling stock.
PRESERVATION STATION
The ongoing construction of Venizelou station highlights the challenging nature of this project. Here as the team worked down through the layers of ground, they moved through almost two thousand years of Greek history.
In the first couple of metres were the remains of the city’s commercial centre, which had been buried following the great Thessaloniki fire in 1917. “As soon as the first 2m were excavated, we started to find the remains from the 19th century. This was the commercial centre of the Jewish population at this time.
“Then digging further down, we start to find relics from the Ottoman period,” explains Dell’Onze.
Under the Ottoman Empire which took control of Thessaloniki in 1430, the city had a central role as main harbour of the Balkans, building on its heritage as the Co-Capital of the Byzantine Empire when it was considered to be second only to Constantinople.
Not only did the team find Byzantine relics but it also found the Roman remains that preceded this.
Roman planners made their towns rectangular with two through roads, the Decumanus Maximus running east to west, and the Cardo Maximus running north to south.
“At Venizelou we found exactly these two roads and the same thing at Aghia Sofia. We also found the drainage system, the water supply system in this period.” So well preserved are the remains that wheel tracks are visible in the marble that constituted the Byzantine roads. The question now is how to build the station as the usual top down method, where soil is excavated above the new roof slab, would no longer be acceptable.
“Last week we received the final decision of the archaeological council for the municipality of culture who took the decision to maintain the findings so now we are trying to find a technical solution that enables us to keep the archaeological findings in situ and enable the excavation of the station,” explains Christos Panou project manager of Salini-Impregilo. The most likely methodology will see completion of the archeological research works followed by careful construction of a wall around the findings that then enables the station roof slab to be cast above. The eastern and western ventilation shafts will then be excavated and from here (the shaft bottom) the team will be able to excavate the 80m x 20m station box in many phases.
For temporary support of the shafts, 300mm diameter concrete micropiles will be concreted (or constructed) into place and metal struts will be placed to support the micropiles. Pipe jacking will then be used to create the tunnels (many phases). This process is expected to take around three years.
MOVING FORWARD
Today 80 per cent of the civil works for the project are finished, but much remains to be done with over half of the total project work still to be completed. “The TBM tunnel excavation is complete,” says Dell’Onze, “as well as the excavation works on 11 of the stations. Remaining excavation work is underway in the two stations in parallel with the archeological research works.”
“Concrete works are completed in all the excavated stations and finishing works such as masonry, plastering and painting works escalators and doors installation have started already in these stations as well as in the depot,” explains Dell’Onze.
Ground conditions along the route have been as expected in soil comprised of formations of red clay, sandstone–marl and quaternary deposits with sensible variation in the soil permeability.
The original time schedule had planned that the 6m diameter Herrenknecht EPB machines passed through five stations before their excavation was completed, and eight already excavated stations. Instead, due to delay in the expropriation of the area of some stations, some changes in design and delay in the works due to the unexpected huge amount of archeological excavation, the TBMs only broke though into two completed stations during their journey.
The archaeological findings have not been the only challenge for the project. Some station sites were handed over late due to issues around expropriation of land.
“We had two major problems. One was the Archeological findings which were beyond all the provisions of the time and the second was the expropriation of the areas which was not on time from the client.
“For these reasons the project was stopped for a long period to find a new solution and to cover the expenses,” explains Panou.
Work was put on hold following an arbitration process between the contractor consortium and its client Attiko Metro which ran from 2014 and 2015. Once resolved the project restarted again on 1 January 2016.
“The positive decision of the arbitration allowed us to cover most of expenses we were suffering,” explains Panou. The revised budget will now see the first phase of the project through to partial opening in 2020 with the outstanding work at Venizelou and Aghia Sofia following on 2022.
