Application of top-down track construction technology
We have achieved significant successes at several Hungarian city rail construction tenders. As a result, we have gained experience in performing complex tasks that require excellent organizational skills as well.
Our company has played a prominent role in the renovation and construction works of the Budapest Metro lines. Within the framework of the Budapest East-West Metro 2 line reconstruction, the tunnel track construction project management was carried out by Tóth T.D. Ltd. Besides large scale international ventures, the contract-based construction tender for the recently built first section of the Budapest Metro line 4, namely the construction of the Co 08 Tunnel and Surface (Depot) Tracks was won by the 100 percent Hungarian owned SME, Tóth T.D. Ltd. Concurrently with other assignments, we successfully accomplished a contract project worth approximatively 15 billion to the satisfaction of our principal and the passengers of Budapest. We concluded a contract based on the FIDIC (International Federation of Consulting Engineers) Yellow Book with the Budapest Transport Plc., our principal. This project incorporated, among other things, the preparation of the construction plans with the involvement of highly skilled expert consultants. We had to coordinate our construction commitments with 12 designated contractors, who only had contractual relationships with the principal, but not with us. Though this scheme of cooperation imposed significant obligations as we had to act in a multi-way interface role, we were able to meet them all while maintaining a good partnership.
After carrying out preparatory earthworks and utility developments on the extremely small-sized Depot (see Figure 1), its length just over 500 metres, nearly 5000 metres of traditional crushed rock track network was constructed. We integrated altogether 34 turn-out groups, using the most sophisticated, state-of-the-art structure available today.
However, the real challenge was the tunnel track construction. The 5.2 m diameter hollow, tubbing structure reinforced concrete tunnel was taken over by our company from the contractor performing the drilling work.
This was the first time in the history of the Budapest Metro that the design and construction liabilities had to be assumed by a single company, namely by Tóth T.D. Ltd. Therefore, during the process of designing the tunnel tracks and turnouts we tried to take full account of:
- technical requirements.
- decades of management experience (e.g. development of rail fixing, water drainage.
- the applicable standards (e.g. Design Guidelines for Subway Construction, P1 Standards.
- the principal contractor’s requirements.
However, we had to deal with some constraints, for instance:
- The layout of the subway line did not entirely conform to our preferences (e.g. short transition curves).
- The tunnel and station constructions that had already been made.
As the first step, following the assessment and planning stages, a 70 to 75 cm thick concrete fill was made. Preparing a mixture that could be pumped to as far as 800 metres was a serious task related to concrete technology.
In order to provide the best technical performance, we were the first in Hungary to apply a top-down technology in track construction. According to our calculations, this proved to be the most economical procedure. In short, first of all the railway is completed on the filling concrete using portal structures, under extremely strict geodetic control (see Figure 2).
Relying on the experience gained from the technical literature and previous professional visits abroad we configured portal structures which allow for simple track installation and whole scale parameter adjustment. We also investigated the question of economic efficiency, so we tried to (repeatedly) reuse the largest possible number of structural elements. Our efforts proved to be highly successful, as we have managed to recover and reuse all elements except for the protective conduits (corrugated pipes) protecting the small-sized steel shoes and screw shafts. Special attention was paid to the systematic preparation of the turnout system (see Figure 3).
The track adjustment carried out with the technology described above had been checked by the principal as well, and subsequently we received permission for laying the concrete elements. The technology chosen has also shown its advantages. The anchor bolts of the engrossing structures were screwed down with 100 percent precision, with the base plate guaranteed to be evenly and accurately mounted on the track plate. One of our key priorities was the metro line’s noise and vibration dampening, as the line stretches in its entire length beneath the densely built downtown. Basically, the engrossing structure, and within that, the choice of flexible intermediate filling pads (Vossloh 336) also contributed to meet the requirements. In addition, in several sections we had to apply flexible beddings as weight bearing springs, which work together with the concrete fill (see Figure 4).
Our enterprise, Tóth T.D. Ltd., was also in charge for building every other structure in the tunnel, including the construction of the third contact rail/power-rail, the escape sidewalk, and the whole cable support structure.
Altogether just over 15 kms of tunnel tracks have been constructed and 12 rail-sidings have been concreted with this technology. Where the other conditions were met, a performance of even 120m/day could be reached, including track construction and concreting work, too.
In recent years, Tóth T.D. Ltd. has had the opportunity to take part in other major urban tramway works. In 2010 and 2011 we cooperated in the construction works covering close to a total of 20-km-long tram track in Szeged, and subsequently in Debrecen (see Figure 5).
We have developed good relationships with companies involved in national and international tramway transport, including investors, contractors, and suppliers.•