Ing. Remo Grandori – RETC Difficult Ground - Construction of the Turin Metro Line 1 Tunnel by No
Total Page:16
File Type:pdf, Size:1020Kb
SELI SPA – Ing. Remo Grandori – RETC Difficult Ground - Construction of the Turin Metro Line 1 Tunnel by no. 3 EPB TBMs CONSTRUCTION OF THE TURIN METRO LINE 1 TUNNEL BY N.3 EPB TBMS “INJECTION OF FINES INTO THE CUTTERHEAD CHAMBER EXTENDS THE GROUND RANGE OF APPLICATION OF EPB TBMS “ Authors: R.Grandori, President SELI spa Ing. A. Ciamei, Project Manager SELI spa Ing. A. Busillo, Project Manager SELI spa Ing. A. De Biase, Project Manager SELI spa Ing. Doct. P. Perruzza , chief Geologist SELI spa ABSTRACT The Turin metro alluvium soil is mainly made of large boulders, cobbles and gravel, few sand and almost no fines. This grain size curve is out of the range of application for EPB and Slurry TBMs. In order to bore 5 of the total 7,5 kms of Line 1 tunnel, two specially designed Lovat EPB TBMs were utilised in combination with a systematic non structural pre-grouting of a small volume rectangular slab just above the tunnel section. The same pre-grouting was not however applicable for lack of access on surface in some sections of the remaining 2,5 km of tunnel that had to be bored below important buildings/structures, with under ground water pressure up to 1,5 bar, with curves radius of 180 m only. For these more critical sections it was necessary to study and implement a new technical solution and improve the capacity of the TBM to work efficiently in EPB mode even in this unsuitable ground and overall conditions. After months of studies the selected and adopted solution has been to inject inside the cutterhead chamber, in addition to the almost standard foams & polymers additive mixes, a suspension of limestone powders. This with the scope of compensating the lack of fines of the natural ground with rock powders. The implementation of this so called “fines compensation injection” technique proved to be effective in producing an homogeneous, impervious “EPB suitable” ground mix in the cutterhead chamber. As a consequence it was possible to bore even the most critical tunnel sections without suffering instabilities, over-excavations as well to avoid ground water inflows through the screw conveyor of the TBM. 1 SELI SPA – Ing. Remo Grandori – RETC Difficult Ground - Construction of the Turin Metro Line 1 Tunnel by no. 3 EPB TBMs CHAPTER 1 – THE TURIN AUTOMATIC SUBWAY - LINE 1 The Turin Automatic Subway – Line 1 is composed by: o 7500 m of tunnels bored by n.3 EPB TBMs (from Fermi up to Porta Nuova stations) o 15 stations plus a deposit and workshop area for the Metro trains maintenance. o 18 shafts ventilation and safety purposes (14) as well for the execution grouting works (4). o A number of small tunnels to connect the main line to the shafts and to allow consolidation works constructed by conventional method. o 910 m of surface line connecting the train deposit to the first underground station of Fermi. o 80 m of tunnel line excavated by traditional methods (from Principi d’Acaja station toward XVIII December station) Figure 1- Plan view of Turin Metro Line 1 The Client is GTT S.p.A., a company owned by Turin Municipality. The works for the construction of the tunnel line and stations have been devised in n.3 lots, Lots 3-4&5, each one including almost 1/3 of the tunnel line and the relative stations. The three lots have been awarded to different Joint Ventures in 2001 Each Joint Venture was required to utilise a different TBM, for a total of n.3 TBM to be operated at the same time in the project. 2 SELI SPA – Ing. Remo Grandori – RETC Difficult Ground - Construction of the Turin Metro Line 1 Tunnel by no. 3 EPB TBMs The deadline for the completion of the three lots was linked to the necessity to put into operation the line for the winter Olympic to be held in Torino at the beginning of 2006. SELI, as TBM specialist contractor, has been in charge of the study and of the operation of the n.3 TBM sites. CHAPTER 2- PROJECT GEOLOGY AN ALIGNMENT OVERVIEW The formation interested from the tunnel line is mainly constituted by river-glacial and river- Rissian deposit (Quaternary), of gravel sand and cobbles in silty matrix. Within this formation there are 4 units identified by specific granulometry and of different cementation: • unit 1 – superficial ground • unit 2 – gravel with sand from loose to slightly cemented • unit 3 – gravel with sand from weak to medium cemented • unit 4 - gravel with sand from medium to highly cemented. The tunnel excavation of Lot 3 and 4 (from Collegno to Acaja ) interested unit 2 and 3 which were foreseen to have the following average granulometry.. Characteristic Average Cobles (%) 3.4 Gravel (%) 46.1 Sand (%) 37.4 UNIT 2 Filler (%) 13.2 WL 19.3 WP 16.3 IP 3.2 Cobles (%) 7.6 Gravel (%) 41.6 Sand (%) 37.4 UNIT 3 Filler (%) 20.0 WL 17.6 WP 11.8 IP 6.9 Figure 2 table resume the average size distribution of the soil as indicated in the project design. 3 SELI SPA – Ing. Remo Grandori – RETC Difficult Ground - Construction of the Turin Metro Line 1 Tunnel by no. 3 EPB TBMs The permeability of the soil of unit 2 and 3 was foreseen to range from 10-3 to 10-8 m/sec. Furthermore local pockets of pure un-cemented sand were foreseen locally along the drives Especially in the area interested by Lot 3 tunnel it was furthermore foreseen the random presence of large and very hard boulders. Figure 3 represent the tunnel profile along the line below the city The ground water level is below the tunnel invert in Lot 3 and 4 tunnel sections while in Lot 5 for 90% of the length the water level is above the tunnel invert with a maximum pressure of 1.5 bars in the most critical sections. As far as the tunnel alignment the following are the main aspects to be considered: A first section of the tunnel in Lot 3 is interested by a shallow cover ranging from 6,00 to 12,00 m For the remaining stretch the overburden range from 11.5 m.to 13 m except for two sections in lot 5 were the tunnel underpass buildings and railways where the cover has been increased by the design up to 24,5 m In these sections at deeper elevation the ground water table has the maximum pressure above the tunnel To follow the vertical and horizontal alignment of the tunnel the vertical gradient is ranging from 0,5 .to 5,96% and the minimum tunnel radius is 180 m CHAPTERS 3- THE PRESENCE OF THE CITY AND OD CITY SERVICES In every tunnel project in urban area the presence of the city, with its buildings, foundations, services, shafts and other old/unknown objects that might be encountered by the tunnel or around the tunnel shall be carefully considered. 4 SELI SPA – Ing. Remo Grandori – RETC Difficult Ground - Construction of the Turin Metro Line 1 Tunnel by no. 3 EPB TBMs In this regard a city like Torino, with ancient buildings and man made tunnelling systems excavated since centuries, can present several surprises when bored at shallow cover. For this reason the design located the tunnel at deeper level than most city services and possible surprises,. with the exception of an initial shallow cover section in Lot 3 and a section in Lot 5 that underpasses building foundations as well in an area interested by an old tunnelling network (Pietro Micca Tunnels) CHAPTER 4- THE SELECTED TUNNELING METHODS AND TBMS The project design was indicating two tunnelling methods as suitable for the construction without indicating any specific preference. The two methods were: a) EPB TBM technique b) Slurry Shield TBM technique All Joint Venture contractors, after having received the advise of expert consultants and on the base of other specific considerations, decided since the tender stage to select the EPB TBM technique. While knowing that the tunnelling conditions would have been in any case at the critical limits also for the EPB technology, this method was preferred to the Slurry Shield TBM method for the following reasons: - The good recent experience in utilisation of EPB technique in similar critical ground conditions - The too high permeability for Slurry application - The presence of large boulders that would have required a crusher in the Slurry shield excavation chamber with all consequent problems - The presence of tunnels and other cavities underground surrounding the tunnel that could induce the sudden loss of the Slurry mud 5 SELI SPA – Ing. Remo Grandori – RETC Difficult Ground - Construction of the Turin Metro Line 1 Tunnel by no. 3 EPB TBMs Figure 4 confirm by comparison that the foreseen ground of Torino was within the range of the latest successful application of the technology in similar ground. Nevertheless, in consideration of the criticalities and peculiarities of the expected ground conditions, the n.2 TBMs ordered to Lovat for the utilisation in lot 3 and 4 were designed and equipped with several special features; and in particular: Cutterhead design Since the presence of the boulders and the unknown behaviour of the Torino ground when bored by a TBM the cutterhead was designed for the maximum flexibility in order to be able to adapt its configuration to the actual circumstances as they may vary along the tunnel drive. - The Cutterhead was therefore fitted with double cutter housings to be able to have two cuts in every grow and achieve a better penetration for revolution without destroying the cutting parure - The housing were able to accept either picks, single disc cutters and twin disc cutters, for the maximum flexibility.