Mixed Methods Move Gautrain ForwardSouth Africa's public rail transport system is undergoing an extensive revamp, and one of the most prominent projects is the Gautrain Rapid Rail Link. The fast train will travel the 80 km distance between Pretoria and Johannesburg in less than 40 minutes, at a speed of 160 km/h. Not only will the train alleviate pressure on the busy stretch of highway between Pretoria and Johannesburg by ferrying up to 120,000 passengers per year, but it has also alleviated a situation of poverty for many.The ZAR20 billion Gautrain has two major branches: one running north-south between Johannesburg and Pretoria, and one running east-west between the business district of Sandton and OR Tambo international airport (see map). The project includes 16 km of tunnel, double and single tracks, between the Marlboro and Johannesburg stations. Apart from the three main stations of Johannesburg, OR Tambo and Pretoria, there are another seven stations along the way. Three stations will be underground, four will be at ground level, and the remaining three will be elevated. Visit www.gautrain.co.zaConstruction on the Gautrain began in September 2006. Just two weeks before the FIFA World Cup, which kicks off on 11th June, 2010, a stretch of the route between OR Tambo airport and the Sandton station, including two stations in between and the Midrand operations centre, will be opened. This constitutes the first phase of the development. Construction of this phase is scheduled to last 45 months. This will be a crucial segment of the route, as the majority of football fans visiting the country will enter through OR Tambo airport and disperse to their hotels and guesthouses.However, the second phase, also under construction at the moment, will take nine months longer and is due for completion in March 2011. This section includes the route from Sandton into Johannesburg central, and the Pretoria to Midrand portion of the network.The Gautrain project is a JV between the Gauteng provincial government and Bombela concession company, which consists of Bombardier Transportation, Bouygues Travaux Publics, Murray & Roberts and Strategic Partners Group as shareholders, making it a public-private partnership (PPP). Bombela Civils Joint Venture (CJV) is responsible for the Gautrain construction. Bombela CJV consists of Bouygues TP (45%), Murray & Roberts (45%) and Strategic Partnership Group (10%). Click za/11. Visit www.bouygues-construction.com and www.murrob.com Geology and hydrogeologyThe southern end of the tunnel alignment route within Johannesburg is situated in a bedded sequence of sediments (Witwatersrand formation where the South African gold is found) comprising of a thick and inclined sequence of shale, quartzite and conglomerates. It represents 2,900 metres of the tunnel length which is 18% of the ground excavated. The groundwater level is between 10 m and 40 m above the tunnel crown level. The rest of the tunnels is driven through the granitic complex which forms a roughly circular outcrop from Johannesburg to Pretoria. Depending on the depth of the tunnel, the granite is weathered to highly or completely decomposed in the Rosebank area and moderately decomposed to fresh around Sandton and Marlboro.In the granite, the water table is between 10 and 30 m head above crown tunnel level. Locally, the hydrogeology is modified by faults and dykes, they are generally associated with high groundwater inflows like in Sandton area or like between Park and emergeny shaft E2.Mix of methodologiesMost of the tunnel excavation is done using traditional drilling and blasting, except for a 3 km stretch of soft rock and waterlogged soil being tackled by a TBM, and a 1 km segment in weathered rock using pipe roofing with canopies of steel tubes. The Rosebank north tunnel site is equipped with a tunnelling excavator ITC 312 with loading conveyor more appropriate to soft excavation in weathered granite. Visit www.itcsa.comDrill and blastThe total length of the tunnels excluding the stations and cut-and-cover sections (underground structure constructed from the surface and then back filled) stretches for 16,172 metres. The total length of the drill-and-blast tunnel is 13,295 metres, of which 5,864 metres is double track and 7,431 metres is single track.The double and single-track tunnels in the drill-and-blast section are horse shoe-shaped. The single-track tunnel is 6 m x 6 m wide with an average excavated section of 35 square metres. The tunnel holds one train track and a side walkway. The double-track tunnel is 10.8 m wide x 6.2 m high. It holds two train tracks and has a central partition wall with a walkway on either side.The tunnels are built from nine access points to achieve the tight programme so as to be ready between Sandton and the airport for the football World Cup in June 2010 and eight months later for the rest of the line. The underground section includes three deep stations (Park, Rosebank and Sandton), seven emergency access shafts (between 16 and 85 m deep) and one temporary main construction shaft (Mushroom Farm Park). The cover to the tunnel crown varies from approximately 15 m to 100 m.The 13,295 m drilled and blasted tunnel is excavated from 12 faces in total. Park station 1 face single track tunnel E2 shaft 2 faces single track tunnel Rosebank north 1 face single track tunnel E5 shaft 1 face single track tunnel Sandton south 2 faces single track tunnel double track tunnel Sandton station main cavern 1 face towards north Mushroom south 2 faces single track tunnel double track tunne Mushroom north 1 face double track tunne Marlboro 1 face double track tunne Each face is equipped with its own set of machinery comprising:Single-track tunnel one Robofore fully computerised jumbo (two booms and basket able to drill 4 m holes for face drilling and rock bolting). Robodrill supplied six similar computerised two-boom jumbos on a total of 17 for the project). Visit www.robodrill-sa.com one LHD GHH 6.3 with side tipping bucket (2 cu m capacity). GHH supplied four similar LHDs to the project. Visit www.ghh-fahrzeuge.de one tunnelling excavator CAT 314 with specific short boom design for scaling and soft ground excavation equipped with bucket or breaker. CAT supplied six similar excavators. Visit www.cat.com one shotcrete robot Putzmeister PM 407. Putzmeister supplied eight similar robots. Visit www.putzmeister.com versatile dumpers Paus 10000 (20 tonnes) equipped with 10 cu m bucket or 5 cu m concrete mixer. ITC is partnering with Paus and supplied a total of 35 dumpers including 20 concrete mixer kits for all tunnel sites. Visit www.paus.de one Normet boom basket Himec 9915 with arch erector. A fleet of eight machines is used on all tunnel sites. Visit www.normet.fi Double-track tunnel one Robofore fully computerised jumbo (three booms and basket able to drill 6 m holes for face drilling) and one Pantofore (two booms and basket able to drill 4 m holes for rock bolting). Robodrill supplied two three-boom Robofore and two two-boom Pantofore. For some of the other works (shaft sinking), they also supplied seven single-boom Pantofore. one CAT loader 972, 966 or 938 side tipping bucket (on a total of 14 units) one scaling excavator CAT 323 (on a total of four units) one tunnelling excavator CAT 320 (on a total of six units) one shotcrete robot Putzmeister PM 500 (two purchased) one Normet boom basket Himec 9915 with arch erector (on a total of eight). Lifting equipment for both single and double-track sitesFour sites are fitted with 30-tonne or 40-tonne gantry cranes supplied by Morris South Africa. Three sites are equipped with 100-tonne or 130-tonne Liebherr crawler cranes. The emergency shafts are equipped with a 100-tonne mobile crane Terex AC100. Civil works and stations use 11 Liebherr tower cranes 200 ECH 10 or 200 ECH 12 or 16. Visit www.morris.co.za, www.liebherr.com and www.terex-cranes.com Rock reinforcementThe primary tunnel support will comprise shotcrete and rock bolts or arches depending on support classes with the secondary lining of shotcrete. The tunnel final support consists of both the primary support and the secondary lining acting as a single composite member. Where required, prior to excavation, ground improvement to reduce permeability is carried out. Drainage measures to suit subsequent encountered groundwater conditions are installed as part of the tunnel final support. The general construction sequence is as follows: blasting, scaling and mucking out, rock mapping and spot bolting of localised wedges/instabilities, primary shotcrete lining (in accordance with support class requirements), pattern bolting (in accordance with support class requirements), next round of excavation, grouting of the bolts, installation of drainage provision as required, and secondary lining (in accordance with support class requirements). Shotcreting at Marlboro site The rock bolts are 20 mm bar core diameter Dywidag-Systems International (DSI) DCP bolts. These are a proprietary product, constructed from special high strength steel and incorporate an expansion shell (for immediate tensioning), a HDPE sheeting, providing corrosion protection over the bolt length, and a grouting bell/nut arrangement. Head plates and shotcrete connectors (spiders) are used in conjunction with the rock bolts. Click here for more on bolting. Visit www.dywidag-systems.comIn areas of poorer ground, the primary support includes lattice arch girders and spiles as required.In soil, a canopy tube of 114 m diameter and steel arches TH-29 are used in replacement of rock bolts. The structural shotcrete is 25 MPa polypropylene fibre reinforced. The tunnel support is designed on the basis of a drained tunnel.The average rates of drill-and-blast excavation are very high (40 to 45 m/week in double-track tunnels and 30 to 35 m/week in single-track tunnels). The first tunnel breakthrough will be in late September, when the tunnels from Mushroom Farm Park and Marlboro meet. While the emphasis of the project has been placed on the Johannesburg side, the project is now in progress along the entire route and the Pretoria side is also taking shape. The building of the Gautrain stations will also begin soon. The progress achieved on 21st June, 2008 is shown below: Drive from Metres excavated Completion rate Park station to emergency shaft E1 440 m of 1,323 m 27% Emergency shaft E2 to shaft E1 0 m of 1,086 m 0% E2 to TBM 0 m 0% Rosebank TBM to E2 1,501 m 53% Rosebank north 315 m 42% E5 to E7 614 m of 2,296 m 26.7% Sandton south 64 m 6% Sandton cavern 39 m 48% Sandton small cavern 56 m 34% Mushroom to Sandton single track 449 m 100% Mushroom to Sandton double track 334 m 66.4% Sandton south to E7 0 m 0% Mushroom north to Marlboro 963 m 66% Marlboro to Mushroom 2,149 m 78.2% TOTAL 6,924 m 45% Drive from Start date Expected breakthrough date Park towards E1 (1,626 m) 15/08/2007 30/09/2009 E2 towards E1 (707 m) 09/06/2008 30/09/2009 E2 towards TBM (220 m) 10/11/2008 05/03/2009 Rosebank TBM towards E2 (2,827 m) 02/01/2008 13/12/2009 Rosebank north (745 m) 10/09/2007 28/02/2009 E5 towards E7 (2,382 m) 01/09/2007 31/08/2009 Sandton south (1,029 m) 01/02/2008 10/09/2009 Sandton cavern (82 m) 01/02/2008 31/08/2008 Sandton small cavern (167 m) 01/05/2008 31/07/2008 Mushroom to Sandton single track (449 m) 15/07/2007 01/05/2008 Mushroom to Sandton double track (503 m) 15/07/2007 31/10/2008 Sandton south towards E7 (340 m) 07/06/2008 10/05/2009 Mushroom north to Marlboro (1,470 m) 01/06/2007 10/10/2008 Marlboro to Mushroom (2,748 m) 01/04/2007 05/10/2008 TBMThe 325-tonne earth pressure balance tunnel boring machine, nicknamed Imbokodo (meaning rock in Zulu), and its 560 tonnes of 13 gantry trailers in backup equipment, was commissioned and specially built over a 12-month period by Herrenknecht, at a cost of ZAR300 million. The 160 m-long machine comprising the 12 m shield and cutter head has a diametre of 6.81 m. The cutter head features 150 drag teeth for soft rock. It also comprises 45 single disc cutters and four twin disc cutters for hard rock conditions. The TBM has a total thrust of 4,070 tonnes that is created by seven motors that pack 2,450 kW of power. The machine, which requires 3.2 MW of power to drive it, has its own electricity substation. Visit www.herrenknecht.comThe tunnel boring machine began work on the tunnel in the Rosebank section of the route, north of Johannesburg, in January 2008 and has already progressed to Park station about 1,190 metres underground as of 20th June. Geology in this area features a high water table as well as varying degrees of hard rock, sand, and soft water-clogged soil. The machine can tunnel at 80 mm/min in rock conditions, and this results in 11 metres of tunnel being excavated a day on average. The TBM will be active for some 14 months. The machine is expected to take 14 months to complete the structure. The TBM is operated and driven by a qualified engineer or pilot from within a control cabin situated within the first one of the 13 trailer gantries that are attached to the back end of the TBM. The control room is equipped with a computerised guidance monitoring system and real-time monitors that display the status of the various subsystems, such as pressure of the machine, cutter speed, and the position of the laser-guided shield. There are also closed-circuit television cameras in front of the cutter head so that crews can see what is happening with the ground at the cutter face. This provides information to the TBM pilot on a continuous basis. It also allows the pilot to steer the machine, and to continuously monitor the actual position of the TBM in relation to the theoretical centre line of the tunnel at any given location along its route. The TBM is operated 24 hours every day, with downtime of some three hours each day to facilitate maintenance of the machine.Behind the rotating cutting wheel which excavates the ground is a chamber where the excavated material accumulates, before being extracted by a screw conveyor. Marti Technik's belt conveyor Excavated soil is then transported on a Marti Technik conveyor belt back up to the Rosebank south shaft, where it is picked up by tipper trucks. The belt extends as the TBM progresses and will stretch for 3 km in total and is designed to transport 450 tonnes/hour. Visit www.martitechnik.chThe TBM can operate in two modes, namely open and closed mode. In open mode, the machine can operate as a conventional rock TBM with the disc cutters causing the rock to spall from the face. The fragmented rock is then picked up by buckets built into the rotating cutter head and then dropped onto the conveyor belt. The machine can be switched to closed mode, as weathered ground and soft materials are approached during the tunnel boring process.In the closed mode, the TBM is able to operate in either one of two submodes, that is, earth pressure-balanced mode, or in compressed-air mode. The difference between the two is that, whereas in the EPB mode, the cutter head chamber remains full of spoil with a positive pressure counteracting the ground pressure at the face, in the compressed air mode, the head remains only partially full of soft material with positive balancing pressure against groundwater being provided by an air bubble in the crown. In very wet ground conditions, it is needed to apply compressed air to the front of the TBM at the cutter head to make sure that the groundwater table is not drawn down. The compressed air pressure keeps water out of the tunnel and also keeps the tunnel from collapsing. The TBM during its naming ceremony, ready and waiting to drill at the Rosebank station The inner tunnel diameter is 5.860 m and the outer diameter 6.460 m, giving a thickness of 300 mm to the tunnel segmental lining. The permanent tunnel lining is formed simultaneously as the TBM bores through the ground, through a sophisticated segment erector housed inside the TBM shield. The erector places the precast segments of concrete to form a complete ring within the tail of the shield as the machine progresses. A total of 17,400 concrete segments will be used to construct the tunnel lining. The concrete segment consists of six 1.5 m-wide individual segments, five of which each weighs 4.1 tonnes (three being standard segments, two counter-key segments), with a final 2-tonne key segment, locking the concrete segment to form a single ring unit of the concrete tunnel lining. Once the concrete segments are installed, they are bolted to secure the ring. The key segment also locks the ring. The precast segments are manufactured by Southern Pipeline Contractors (SPC) at a factory located approximately 25 km east of Johannesburg. A super-plasticiser provided by concrete admixture producer Chryso is used by SPC in the production of the segments for the Gautrain project. SPC, part of France's Vinci group, received the year-long contract to construct the segments for the construction of the underground tunnel by the Bombela consortium. Chryso carried out extensive laboratory tests to assist in the formulation of the optimum mix and products. The super-plasticiser, which is called Premia 100 New Generation, is one of the main components of the concrete mix, which also contains fly ash, slagment and Ordinary Portland cement. Premia 100 plays an important part in reducing the water content of the mix, thereby facilitating increasing strength. A concrete strength of 55 MPa (major principle stress) has been specified for the segments. The concrete mix was designed by Bombela in tandem with SPC, for the production of the precast segments to be used for the underground tunnel lining. Visit www.spc.co.za and www.chryso.comTo ensure a watertight tunnel lining, a compressive gasket is installed around the whole perimeter of each segment, in a specially formed rebate. Read more here about the TBM-built section of the Gautrain.Challenges encounteredThe size of the project and the very tight programme to open the line between OR Tambo and Sandton stations, just 45 months after commencement of construction for the first phase and 54 months for the second phase, is the main challenge of the project.Bombela's civil joint venture has decided to increase its capacity, has bought extra equipment and has been working additional shifts. Despite being slightly behind schedule, the Gautrain is expected to be completed according to schedule.The challenges delaying the project have included the difficulties associated with managing 43 active construction sites and the fact that Bombela has hit a large underground river near the Park station tunnel. Further, South Africa does not have a homogeneous geology and the varied geology has proved to be challenging for tunnelling activities. The tunnel is constructed from a great number of sites to achieve the programme (nine access points and 12 tunnel faces).Another challenge was the difficulty of finding skilled constructed personnel in South Africa. An intensive training initiative has been put in place to develop skills and build capacity for the project. More than 90% of employees are locals who have been employed to fulfil the project commitments and to sustain the socioeconomic development of the Gauteng province. External challenges, such as the current power crisis and the future of power availability, are additional concerns.The construction of the tunnel below Johannesburg requires to minimise discomfort and inconvenience to the public (noise enclosures around sites) and to minimise the impact of traffic disruptions. Blast vibrations and settlements around the buildings and construction sites are monitored on a 24-hour basis.The diversity of techniques used to excavate the tunnel (drilling and blasting, soft ground excavation with canopy tubes and TBM) is a major challenge as each method entails its peculiarities and requires specialist staff. The size of the single-track tunnel is too small to accommodate standard size of tunnelling equipment available on the market. The equipment is all less than two metres in width and is mostly site specific.Difficult ground conditions are also an issue. The tunnel is driven with very low covering in completely decomposed granite under the water table in Rosebank north. Major dykes have been encountered in the proximity of Sandton station which has poor ground conditions and water inflow or very hard massive (up to 400 MPa).The ground is highly fractured and a big water inflow has been encountered between Park station and Shaft E2. Ground subsided on 9th July on Oxford road in Rosebank, north of Johannesburg. The subsidence occurred as a result of ground loss above the TBM, which is currently 12 metres below ground level. No injuries were sustained and no damage occurred to either the TBM or the completed tunnel. The collapse will not have any significant impact on the project's schedule. The area affected by subsidence is not required for completion for the 2010 football World Cup and the completion date of March 2011 remains unaffected. Underground stationsThe two underground stations Park and Rosebank are constructed following the same construction principle. They are cut-and-cover structures made of diaphragm walls at Park and pile walls at Rosebank. Two train tracks and passenger platforms are located at base slab level. Plant rooms, passenger access and ticketing are located on the concourse level. The roof slab at the third level closes the station box and will be backfilled with 2 to 5 metres to re-establish roads and ground levels as was prior to construction.The sizes of the two stations are 165 m x 20 m. They are both connected to the tunnel via cut-and-cover sections: Park north by 70 metres of 10 x 20 m cut and cover, Rosebank south by 72 metres of 6 x 10 m of cut and cover, and Rosebank north by 193 metres of 6 x 6 m of cut and cover. A car park of eight levels at Park and three levels at Rosebank will be built adjacent to each station.The Sandton station is an underground station comprising of three train tracks and three passenger platforms. It is built from two main shafts: the south shaft, which is 22 x 20m x 55 m deep, and the north shaft, which is 60 x 22 m x 50m deep. Both shafts are connected by an underground staggered main cavern of 10 x 10 m x 85 m including two tracks offset by 5 m in height. Another 8 x 8 m single-track cavern is connected to the main cavern by means of five cross passages. The north shaft will be used for passenger access and the south shaft for plant rooms. A car park with underground basements will be constructed adjacent to the station. ShaftsFor safety purposes, the tunnel is connected to the surface at every kilometre on the single-track section by means of emergency shafts (E1 to E7): the southern shaft E1 is a 5.25 m finished diameter, 80 m-deep blind sunk shaft using drill-and-blast methods through shale and quartzite. Shaft E2 has been enlarged to 9 m diameter to allow for the tunnelling operation. It is 50 m deep, blind sunk with steel arch and steel plates in upper soft section and drilled and blasted in lower quartzite section. Shafts E3 and E4 are connected to the TBM tunnel. They are 9.5 m in diameter, 21 and 16 m deep respectively. They are excavated in completely decomposed granite, and below the water table for E3. A dewatering scheme has been implemented for the construction of E3. Shaft E5, like E2, was enlarged to a diameter of 9 m for tunnelling operations. It is 60 m deep and excavated with drill-and-blast methods in granite. Shaft E6 is a 6 m-diameter, 73 m-deep raise bore shaft through granite. Shaft E7, like E2 and E5, is enlarged to 9 m (for tunnelling) and is 66 m deep. Drill-and-blast excavation is used through granite. Mushroom is a temporary rectangular construction shaft (12.60 m x 22 m x38 m deep) for tunnelling towards Sandton and Marlboro and will be backfilled at the end of the job. View photos here.The portal at Marlboro is connected to 78 m a cut-and-cover section and is built in an open cut excavation. It will include plant rooms and ventilation. 29/08. Tunnelbuilder thanks Nareen Poonjala and Stéphane Polycarpe for their contribution to this article and the pictures.