Seymour-Capilano encounters May 2007

Shani Wallis, Editor

Both TBMs on the Seymour-Capilano project in Vancouver are more than 1,000m into their 7,100m long drives. The 3.8m diameter Robbins machines were assembled by contractor Bilfinger Berger, at the bottom of the 180m-deep access shaft and launched on their 7,100m drives before the end of 2006. By early May 2007, TBM1 had advanced to chainage 1,765m and TBM2 was at 1,179m.

“We are moving - not as expected but as well as is likely through the rest of the drives”, said Josef Messner, Construction Manager for Bilfinger Berger who has taken over as Project Manager from Christian Genschel. “TBM2 is going better than TBM1 at the moment [when contacted in early April]. TBM1 hit water last week and the Engineer instructed us to stop and grout off the inflow.”

Water ingress through a drilled hole

It was not a lot of water at about 3 liter/sec, but in the 7.1km long downhill drives water inflow is taken seriously. Production was down for a total of five days while seven 40–45m long holes were drilled and some 3,400 liters of group was injected to reduce inflow to about 1 liter/sec. The TBM2 heading coming up behind is about 100m parallel and it is hard to say, but it is unlikely there well be a benefit for the parallel heading or if it too will run into water at the same chainage.

This is the second phase of instructed water control grouting to date. The first was in TBM2 tunnel and comprised a similar grouting program. TBM1 tunnel was already ahead and there was no noticeable affect in that parallel tunnel. Water was not encountered when TBM1 passed that particular chainage earlier and there was no grouting required.

Systematic probe drilling is a contract specification and a 40m probe and a 10m overlap is maintained. Each machine is fitted with two Atlas Copco 1838 drill rigs, one either side of the main beam.

Grouting injection pressure gauge

Chips and fines
A more persistent time losing factor is the amount of fines generated by the boring process. “The rock is a particular mix of harder and softer zones and frequent changes from hard to soft conditions”, said Messner. As a result, rather than producing well-defined chips, the TBM is grinding a lot of fines that lead to excessive sedimentation and causing various problems. It interrupts operation of the TBMs’ transfer conveyor back to the muck skips; blocks the water pumps at the TBM heading; clogs the dewatering tanks on the TBM; and creates trouble at the main water sump-pumping station in the bottom of the access shaft and at the water treatment plant on the surface.

A small feeder belt has been installed under the TBMs for clearing fines by hand onto the main belt. Pumps, dewatering tanks and sumps also need regularly cleaning which is a big job. The fines are said to settle and pack like concrete that takes some shifting. Cleaning the main shaft sump means shutting down shaft activities and TBM production to get at the sump and undertake the maintenance.

“The rock is not as consistently hard or strong as predicted in the geotechnical report and has these pockets or lenses of softer material that create a mixed face that don’t require high power and rather grind down into the fines which are a pain”, said Messner. Conditions were said to be similar to the mixed conditions encountered during excavation of the access shaft that caused problems with the drill+blast cycles and “cost us much extra time.”

Flat car of Chemgrout pre-grouting equipment

The two HP Robbins machines dressed with 26 x 19in cutters (one purchased by BB and the other on lease) are capable of boring hard rock tunnels of up to 5.2m-diameter. Power will not be an issue for the smaller 3.8m-diameter headings in Vancouver. “Achieving optimum availability from the machines is more the concern,” said Messner.

Cutter ware is also influencing by the fines phenomenon. “The biggest ware problem is a face of mixed hard rock and pockets of softer rock”, said Messner. ‘Disc ware is unusual compared to more normal chipping ware and cutter changes in the small diameter tunnel are taking longer to complete. Although only two inches bigger on diameter and 50kg heavier than 17in discs, 19in discs, at about 200kg each for face and gauge cutters and 335kg for center cutters, take special handling and you wouldn’t think it but this really does make a difference.”

All things combined, progress is usually between 17-18m/day working two 10h production shifts and a 4h maintenance shift/day. “We are running TBM1 seven days/week”, said Messner “but only have crews at present to operate TBM2 from Monday to Saturday afternoon. This will change when another 15 workers arrive from the Philippines. Permits were issued recently by the Canadian authorities and we are just waiting for clearance in the Philippines.”

Each TBM is fitted with two drill rigs

These extra workers will increase the number of expat-Philippinos on the project to 48, or about 40% of the work force, and will increase TBM2 production to 24h/7days/week. “We are still behind the original schedule”, said Messner, “and there is little chance that we will be able to make up any time lost during the shaft excavation and assembly and start up of the TBMs, but we might yet reach program advance rates of 27-28m/day - not as an average but as a regular daily rate. Our best advance to date was slightly more than 30m/day recorded by TBM1. Average progress is now being influenced by the fines situation, by grouting cycles required, by rock support installation, and by the frequency of cutter changes.”

BB’s 49.5-month contract to create the water transfer connections between the Seymour and Capilano reservoirs for the Greater Vancouver Water District (GVWD) started in January 2005 and is currently projected to finish in June 2009. Pacific Liaicon and Associates (part of the SNC Lavalin Group) is undertaking project and construction management for GVWD and Hatch Mott MacDonald is supervising construction after completing feasibility, preliminary, and final design of the design-bid-build tunnel contract. Golder Associates completed geotechnical investigations and contributed to preparation of this demanding contract’s geotechnical data and geotechnical baseline reports (GDR and GBR).

References

Facing the challenges ofSeymour-Capilano -TunnelTalk, Dec 2006
Robbins TBMs for Vancouver -TunnelTalk, Dec 2004
Three bid Vancouver tunnels -TunnelTalk, Sep 2004
Vancouver drives towards better quality drinking water -TunnelTalk, Mar 2004