Shani Wallis, Editor

Four tunnel boring machines working on the Yellow River Diversion project in Shanxi Province in China are setting record rates of performance and advance.

Portal of Tunnel 5 and culvert between Tunnels 5 and 6 on the Lot II contract

Since starting in 1998/1999 the four ± 5m o. d. machines two new Robbins TBMs, a used Robbins TBM, and a new NFM-Boretec machine - have turned in averages of up to 220m/week each and a combined average of more than 3,060m/month working three 8h shifts/24h day, 6 days/week. In January 2000, one of the new Robbins TBMs recorded an advance of 1,821m of 4.92m o. d. (4.3m i. d.) lined tunnel in one month. Even the slowest of the four machines has averaged nearly 800m/month for more than a year.

While recognizing these data as world records of their class, a visit to the project presented one of those rare opportunities to examine the experiences, performances and details of a group of similar sized machines working through similar host rock material, and to understand the influences that affect project-wide progress.

The four machines are working towards completing some 88.7km of 4.2 to 4.3m i. d. reinforced precast concrete segmentally lined water tunnel for the project on Lots II and III. These two contracts were awarded in August 1997 to a JV of Impregilo (Sponsor - 48%) and CMC (42%) of Italy and with Chinese partner construction Bureau 4 of CWCHM, the China Water Conservancy and Hydropower Ministry (10%).

Yellow River Diversion project. General layout of South Line

Project overview
The Yellow River Diversion project is of enormous scale. A network of more than 300km of water tunnels and conduits, treatment plants and pumping stations, is designed to divert water from the Yellow River to meet critical water supply needs initially in the Shanxi Provincial capital Tai Yuan, and in the future to Da Tong, the Province's second city.

Work on the project started some years ago when China's project authority financed construction of the Wanjiazhai concrete dam on the Yellow River to create the diversion reservoir. The first section of tunnel, the 22km long x 6m diameter feeder tunnel, was completed in the mid-1990s by the Italian JV CMC/Seli. The JV partners, and CMC in particular, has been tunnel contracting in China since the Yindaruqin irrigation tunnel project in Gansu Province in the late 1980s. A new Robbins TBM was used on the Yindaruqin project and the JV used another new 6m diameter Robbins machine for the Yellow River feeder tunnel.

At about the same time, 1993/94, China's project owner bought a 4.8m diameter TBM from Robbins to start the tunnel drives on the main line aqueduct south towards Tai Yuan. For unknown reasons the TBM was never mobilized and remained in storage at the site location.

Meanwhile, the project authority solicited assistance from the World Bank to help fund the project and move it forward. This was offered providing that the world Bank-supported contracts would be open to and advertised among the international contracting community, and that the construction contracts be based on FIDIC terms and conditions.

An initial funding agreement of $US 400 million from the World Bank is supporting three major construction contracts: a large capacity water treatment plant (Lot 1) adjacent to the Wanjiazhai Dam at the head of the feeder tunnel, and the two Lot II and III tunnel contracts which, in addition to the near 90km of about 5m o. d. TBM tunneling, includes a further 10km of adits and cut-and-cover culverts to connect tunnel drives. Following the international pre-qualification and tendering process, the treatment plant contract was awarded to the Mayreder/Alpine (Austrai/Shanghai Tunnel Construction Company (China) JV as the lowest bidder at RMB 355.14 million (approximately $US 40.4 million). Impregilo (sponsor)/CMC/Bureau 4, trading as the Wan Long JV, won the tunnel contracts as the lowest bidder for each and, with an added 1.8%, as the lowest bidder of the two combined at RMB 1.6 billion (about $US 192 million) (Table 1).

Table 1: Table 1. Bid results, in RMB million, of the Lots I, II and III World Bank-supported contracts

Other bidders for the pump station contract included Skanska, Taisei/Maeda, Dumez GTM, and Dong Yah of Korea

Contract mobilization
To complete the 89km of TBM tunneling within the contract's 48-month period, Impregilo and its JV partners mobilized the four TBMs The two new Robbins machines and the new NFM Mitsubishi/Boretec machine were assembled in China at different factories in the Shanghai area, and the used Robbins TBM is the machine purchased new by the Prader, Deneriaz, Evequoz & Cie, Imboden, Locher & Cie, Losinger, Seli, Bouygues consortium for the 45° inclined high-power penstock tunnel for the Cleuson-Dixence hydropower station in Switzerland in the mid- 1990s.

All the machines are telescopic double-shielded gripper machines capable of excavating the stroke and erecting the precast concrete tunnel lining concurrently. They are all dressed with backloading 17 inch disc cutters, and the three new machines have electric, variable speed cutterhead drives, while the used Robbins TBM has a two speed drive (Table 2).

Mucking out from behind the machines is by trains of rota-dump skips supplied by valente of Italy and pulled by 35ft Schoma locomotives. Each machine is required to complete between 17 and 26km each and California switches are inserted into the long single-track drives at about 6km intervals. The Seli-designed back-ups on all four machines are double-tracked to accommodate two trains and are equipped with floor chain movers to shunt the muck skips as they fill.

There are various inspection adits on the tunnel drives but these, for the most part, will not be used for ventilation during excavation. Ventilation is generated at a rate of a minimum 5.4m3/s by high-powered fans manufactured by GIA of Sweden. These are situated at the tunnel portals and fresh air is delivered to the faces via 1.4m diameter flexible ducting also supplied by GIA.

Lining design
The aqueduct is concrete lined throughout and with precast concrete segments in the TBM drives. The segmental TBM tunnel lining is specified as the hexagonal design. Known also as the "honeycomb", "mosaic" or "volleyball" concept, the four segments in each 1.4m wide ring of hexagonal lining are identical with rail plinths cast into the invert segments and are erected half a ring at a time the invert and crown segments on the first 700mm 11alf stroke, and the two side wall segments with the next half stroke, The hexagonal system is a single segment sized, non-bolted lining using dowels to assist placement accuracy, and packers to negotiate curves and manage alignment corrections. The annulus is backfilled with pea gravel which is subsequently consolidated with a thin backfill grout.

Table 2: Technical specifications of the four Lot II and Lot III TBMs

The hexagonal lining system was first introduced in Switzerland about 30 years ago and has been used as a concurrent lining system on several rock TBM tunnel drives. Seli in particular has used the design as the lining system of choice on many of its TBM projects around the world including the earlier Yindaruqin project and the feeder tunnel on the current project. The major difference on the Lot II and III contracts is that for the first time, a sealing gasket has been added to the hexagonal lining design.

In this dry north-west corner of China where the Gobi Desert is making an alarming advance into the country, and where the karst phenomenon of the geology drains the little water available, water is precious, water loss from the long Supply conduit must be minimized. Water flow in the tunnels is gravity fed but not pressurized. The seal on the joints of the segmental lining is specified in efforts to prevent water losses and render the conduit as watertight as possible. There is no gasket on the hexagonal segmental lining in the 6m diameter feeder tunnel.

Assembly of rebar reinforcement cages

The gasketed lining for Lots II and III is designed for the project by D2 consult of Austria Various Chinese design bureaus are involved in the design, construction management, and supervision of the project and Canada China Power Inc, comprising Acres, AGRA Monenco and SNCLavalin of Canada, is engaged as the design checker. The Binnie Black & Veatch/Mott MacDonald JV is appointed as technical advisers to the Lot II and III Engineer and its on-site supervision team.

The approximate 253,500 segments needed to line the near 89km of tunnel on Lots II and III are cast at the central on-site casting factory. The facility has four steam-curing carousels and is equipped with 32 moulds/carousel designed by CIFA of Italy and manufactured in China. The four TBMs are all slightly different in outer diameter and linings specific to each are required. In addition the lining is reinforced to various degrees to suit four different geological classifications. The reinforcing cages for the segments are also fabricated at the on-site casting facility and production from this hive of activity has averaged 150 segments/day/carousel and has peaked at a maximum 654 segments/day.

Segment factory fitted with CIFA moulds

Tunneling programme
The first machine on site was the used Robbins machine from Switzerland and the three new machines arrived from Shanghai during late 1998. Each machine was then launched from its respective portal or adit between December 1998 and February 1999. When TunnelTalk visited the project in early June 2000, the four TBMs were more than 50% through the total length of tunnel and are now 70% of completing TBM tunnel excavation.

In addition to the outstanding 1,821m achieved by the new Robbins TBM in one month, the technical specifications of the machines provides each with the capability of achieving exceptional advance rates in the prevailing geology.

Shanxi Province lies on the famous Loess Steppes of China, and while little of the excavation is in this soft compacted material, the tunnel alignment lies within the underlying, largely homogeneous strata of sandstone, mudstone and limestone. Rock strengths range between 120 to 220 MPa and there is little ground water.

The three most unpredictable features of the geology are possible karst voids in the limestone; bands and deposits of soft clay (some of which have been identified, including the 533m hand-excavated clay section at Liminpu); and zones of shale with coal seams and the associated threat of methane gas. The project area in Shanxi Province is close to some of the largest coal deposits and highest output open-cast coal mining operations in the world.

While TBM advance on regular occasions has been outstanding, certain circumstances have interrupted progress consistency.

Hexagonal segments fitted with sealing gaskets

Geological delays
Ring building perhaps the most significant retarding factor on TBM advance has been construction of the segmental lining. Building the non-bolted gasketed segmental lining to within the contract's specified tolerance of 5mm in joint gaps and 4mm on steps, while at the same time achieving and maintaining compression of the sealing gaskets has and remains problematic. It is difficult to prevent movement of the erected segments when the holding rams are released to erect the next units. Maintaining compression of the seals is particularly difficult at the three-star joint of the zig-zag cross joint in the hexagonal lining and also when negotiating curves or adjusting alignment.

The segments are erected within a full tail shield (there is no slot in the shield to allow placement of the invert segment directly on the rock) and pea gravel is injected immediately as the ring segments leave the tail shield. The TBMs have wire brush seals between the shield and the segments and a steel plate seal between the shield and the rock. Together with the Short dowels on the longitudinal joints, rod dowels in the zig-zag joints behave as positioning keys. The non-pressurized back-filling grout, to ensure the integrity and stability of the lining, is injected in the invert section at the grouting station on the first back-up trailer about 5 rings from the ring erector, and grouting of the crown and sides is injected at the end of the back-up system about 300m further back.

Ring building in the tail skin

Pea gravel backfilling of the annulus

Various types of gaskets with different compressibility qualities - including composites of HDPE and hydrophilic materials - have been specified by the project designers but ring build has remained problematic. Suggestions from various sources to remove the gaskets were not adopted. The joints are also being pointed with mortar from stations on the backup. Consolidation grouting is not a billed item in the contract. Any consolidation grouting will be instructed by the Engineer. In the meantime, the issue of the lining system and its impact on tunnel advance has been referred to the contract's Dispute Review Board, another contract facility required by the World Bank.

Geological delays
The two headings most affected by adverse geological conditions are TBMs 2 and 3. After starting in Feb 1999, the new Robbins machine working from the Little Doggy adit (TBM 3) was stopped for three months in a zone of very difficult ground and had to be dug out by hand. Crews removed segments to break-out of the tunnel behind the tail shield, worked out over the top of the machine to hand dig the tunnel through the adverse zone. Advance then picked up quickly when into competent mudstone but during the visit, the machine was once again slowed by cutting through coal seams and seams of weak and faulted shale. The machine has since passed through this zone and is working toward an in-tunnel junction with the NFM/Boretec machine working from the opposite outlet portal.

The used Robbins machine working in the opposite direction from Wenling (TBM 2) has been fighting zones of soft clay since it started. At several points within the drive, steel channels have had to be bolted longitudinally to the lining at about tunnel axis to hold the non-bolted lining together. Regular sessions to dig out the cutterhead of clogged clay also retarded advance rates significantly. In the latter part of the tunnel drive, in more competent material, progress has improved and the TBM achieved its breakthrough into the Muguagou culvert section on 13 August 2000. It achieved a best advance of 75m/24h day over the last stretch of the 14,387m long drive and after an overhaul, the machine was scheduled to be relaunched in October 2000 to complete its section of Tunnel 5 (Table 3).

Maintenance crew replacing backloading discs

Speed racer
The record-holding machine is one of the new Robbins TBMs working from the upstream start of the contract. The record of 1,821m completed in one month was achieved in January 2000 when the machine had just started its second Tunnel 5 drive and was assisted by the short distance into the tunnel drive. The TBM had also been fitted with a new cutterhead after completing its first 6.9km long Tunnel 4 drive in nine months.

The new cutterhead was ordered when cracks developed in the original unit. Cracks also appeared in the cutterhead of the other new Robbins machine but these were not as severe and repair welds have held effectively. The original cutterheads for the new Robbins machines were manufactured in China while the replacement cutterhead was manufactured by Robbins in the United States.

From the start of the new drive, the replaced TBM 1 cutterhead has performed up to speed and after achieving the record in January the machine has maintained a consistent daily average of + 50m. But with high speed, also comes a heightened awareness of safety and an increased need for attention to quality control. Maintaining a consistent average is the preferred method of achieving programme although it is accepted that a TBM must reach peaks of double the average to maintain overall programme. After a heady period of outstanding advance, the Tunnel 5 team is progressing towards the higher clay content geology in the Uminpu area where advance rates will slow up.

View of the completed Tunnel 4 drive with its pointed and gasketed hexagonal segmental lining

Bring up the rear
The fourth machine working from the downstream outlet is the 4.88m diameter NFM/Boretec machine. Having been launched in December 1998, and following the learning curve, the machine has made consistent average progress of about 32m/day which matches its time-line estimate. But the machine could have performed better. After a positive assembly and launch, the machine's operating capacity was reduced to about 40% due in part to gear box troubles. The source of the problems remain the subject of on-going investigations but as a result, the machine will stop earlier than planned. The NFM machine in Tunnel 7 was programmed to complete the longest section of tunnel, and the longest single drive on the contract at about 25km. The JV will now terminate the drive in about December 2000 when the machine reaches Adit 17 and the Robbins machine from Little Doggy will complete the North drive. The total single-heading drive for the Little Doggy machine to Adit 17 will be about 21km.

Life in China
While the work of excavating the tunnels has settled into a routine for the tunneling crews, life for the expatriates, some with their young families, is a challenge in the remote north-west corner of China. The climate is extreme, the area is remote, distances are great, and the Chinese culture and language is foreign. Italian cuisine is served in the base camp canteens and this, together with reasonable telephone and computer modem services, and a reliable postal and shipping delivery service, are the main tangible links with home.

In the work place too, cultural differences have a significant influence. The Italian contract management relies heavily on the management personnel of its Chinese partner to work with the Chinese construction crews, as well as communicate with the owner and its design engineers. Impregilo as leader of the Wan Long JV, has worked in China for more than 10 years starting with the Ertan and the Xiaolangdi dam projects during the 1990s. Both were financed by the World Bank and while the company's experience in China is deepening with each new project, the cultural differences, as well as the different management styles of different owner organizations in China, make each new project a new learning experience in contract management and contractual diplomacy.

But the potential for working in China for the moment remains positive for foreign contractors and suppliers, particularly on World Bank supported projects and large projects which require sophisticated modern technology.

On the current Wanjiazhai project for example, the south main branch to Tai Yuan requires a further 47km of waterway while the north main branch to Da Tong involves a another 100km of tunnel or more.

Advance of the four contract TBMs when set against the excavation programme

On the south main branch and from the outlet of Tunnel 7 on Wan Long's contract, water will join the flow of the Fenhe, the mother river of Shanxi Province, for a distance of several kilometres until it is diverted once again into a buried pipeline aqueduct (Lot IV) and into the tunnel of Lot V before arriving at the main distribution reservoir and pumping station in Tai Yuan city. Early in 2000 CMC won the Lot V contract as the lowest bidder at $US 31 million. To excavate the 13.5km of tunnel CMC will use the old unused TBM bought by the owner in the early 1990s. In early June during the visit, the components of the unused TBM, still in their slipping crates after about seven years, were being moved down to the Lot V tunnel working site within the limits of Tai Yuan city and technicians from the Robbins' Kent office in the USA were providing assistance for the machine's assembly and commission.

Impregilo meanwhile has submitted the lowest responsive bid for the 47km long buried pipeline on the Lot IV contract.

For the four Lot I and III there is a high probability of continued service in China and perhaps on the north main branch of the current project. To date eight Robbins TBMs have worked in China starting in 1984 with sale of two rebuilt 10.8m diameter ex-Chicago TARP machines used on a hydropower project (Table 3). But while the potential for further work in China is undoubted, the method of doing business in China for foreign companies will have to evolve and be based perhaps more on establishing Chinese-managed subsidiary companies. In the meantime, aspects of trading and working with China will be influenced by the recent agreement by the United States to support China's membership of the global World Trade Organization. Greater experience of construction contracting practices will greatly assist more favourable working relations between Chinese owners and experienced foreign contractors.

References

D J Gunaratnam, Technology for tunnel construction with special applications for the Wanjiazhai Water Transfer Project; Conference proceedings - Tunneling Trends Tunnel Boring Machines. Trends in Design & Construction of Mechanized Tunneling. Hagenberg, Austria. Dec 1995; A A Balkema/Rotterdam/Brookfteld/1996

Single TBM heading record on current Pinglu tunnel drive - TunnelTalk, Aug 2009