SEE PAGE 6

TJ WORLDNEWS

A SELECTION OFHIGHLIGHTS

FROM THE TJWEBSITE’S DAILY

NEWS SERVICE

SEE PAGE 36

SUPPLYDEMAND TJ TALKS TO

RICHARDSCHULKINS

ABOUT HIS ROLEAS AN

INTERNATIONALSUPPLIER

SYDNEYSYSTEM

A NEW METHODFOR TRACKING

TUNNELSEGMENTSEXPLAINED

journalTunnelling

The international journal for the tunnelling industry

www.tunnellingjournal.com September 2016

SEE PAGE 50

GOING LIKE LIGHTENING IN LAOS

WHERE NEXT FOR SCL?

AT THE END OF JULY, SELI Overseaspassed the halfway mark on its 11.5kmlong low-pressure headrace tunnel for theXe-Pian Xe-Namnoy Hydroelectric Project,in southern Laos, having completed6,442m of the drive. Using a 5.74mdiameter Terratec Double Shieldmachine, the contractor also smashed itsprevious single month production record– 816m at the Kishanganga HydroProject, in India – achieving an

impressive advance of 1,005m. Having commenced TBM excavation in

March 2015, the machine has faced a numberof unique challenges while boring through the

region’s mudstones, sandstones and siltstones,which have required the contractor and TBMsupplier to collaborate closely over the courseof the design, commissioning and operation ofthe machine.

Project backgroundThe Xe-Pian Xe-Namnoy Power Company's(PNPC) US$1.02 billion Xe-Pian Xe-NamnoyHydroelectric Power Project is located in anisolated area of national park on the BolavenPlateau, in the south of the Laos People’sDemocratic Republic (PDR), approximately35km northwest of the provincial town ofAttapeu and 80km east of the larger Mekong

SITE REPORT

In July, SELI Overseas set a new double shieldexcavation record of 1,005m in a single month

at the Xe-Pian Xe-Namnoy HydroelectricProject, in the Laos People’s Democratic

Republic. Amanda Foley visited the projectduring this record-breaking production period

to find out how SELI Overseas and TBMmanufacturer Terratec worked together to

overcome challenges at this remote location

Going like lightning

IN LAOS

16 TUNNELLING JOURNAL

Top: Hexagonal segments are cast at theon-site segment factory using Fama moulds

Above: The moving tripper conveyorefficiently loads the muck wagons

River town of Pakse. Formed in October 2012, PNPC is a

consortium consisting of Korea’s SKEngineering and Construction (SK E&C), KoreaWestern Power (KOWEPO), Thailand’sRatchaburi Electricity Generating Holding(Ratch), and Lao Holding State Enterprise(LHSE). SK E&C was awarded the engineering,procurement and construction (EPC) contractfor the project, while KOWEPO was awardedthe operations and maintenance contract for aperiod of 27 years. Ratch is responsible for theconstruction supervision.

The main components of the410MW scheme include a largereservoir that is in the process ofbeing formed via the constructionof a number of dams and buriedtransfer conduits – combining therunoff from two neighbouringwatersheds (see Figure 1).

From the new reservoir, anintake will draw water into a13.7km long concrete-lined low-pressure tunnel (11.5km of whichis being driven by TBM) to avertical drop shaft and high-pressure tunnel; developing ahead of some 650m that will beharnessed by four turbines at anopen-air powerhouse at the baseof the plateau, and released via a6km long open cut tailracechannel that connects with the XeKong River (see Figure 2 on p18).

When commercial operationsbegin, currently anticipated in2019, about 90% of the powergenerated will be sold to the

Electricity Generating Authority of Thailand(EGAT) under a 27-year power purchaseagreement, signed in February 2013, with thebalance going to Electricite Du Laos (EDL).

In January 2014, SK E&C awarded Italiantunnelling specialist SELI Overseas thesubcontract to excavate the 11.5km TBMdriven section of the low-pressure headracetunnel, along with the construction andoperation of the project’s pre-cast tunnelsegment manufacturing facility. SELI Overseasin turn placed an order with Australian TBMmanufacturer Terratec for a 5.74m Hard Rock

Double Shield TBM – a first, as despite bothcompanies being very active in Asia, they havenot collaborated on a project before now.

TBM designBeing an experienced tunnel contractor, SELIOverseas had a lot of input into the TBM’sdesign and configuration. This, combined withTerratec’s expertise, has resulted in a robustmachine with some unique features. “We hada lot of requests, in terms of adapting theequipment to fit our needs and what wewanted,” says Dario Vizzino, Project Director

for SELI Overseas. “There was a lotof back and forth during the designand manufacturing phases andduring this process we developed avery positive working relationship.”

The machine’s cutterhead isdressed with 39 x 17in back loadingdisc cutters and features four largebucket openings. A 2000kWelectric VFD main drive providesmaximum speeds of 7rpm in harderrock zones, while delivering atorque of 8,000kNm to cope with anumber of fractured fault zonesanticipated along the alignment. Inorder to mitigate potentially difficultground conditions within thesefault zones, a high-power probedrill is also installed within the TBM,to conduct any drilling or groutingdeemed necessary (see Figure 3).

Having selected the use of rollingstock rather than a continuousconveyor, for spoil removal, a keyfeature of the machine is the use ofa tripper conveyor to fill the muck

TUNNELLING JOURNAL 17

SITE REPORT

L A

OS

V I

E TNA

T H A I L A N D

CAMBODIA

C H I

MYA

NMAR

Saddle Dams

Xe Pian Dam

Tailrace channel

Power waterways

Powerhouse

Xe K

ong

Figure 1: Location and configuration of the project

Muck wagons are tipped directly into a holdingarea near the edge of the plateau for removal

by main contractor SK E&C

wagons. “The TBM conveyor empties ontothe back-up conveyor, which then loads the[moving] tripper conveyor,” explains BillBrundan, Terratec’s Site Operations Manager.“So the train can come into the tunnel andpark, and the conveyor moves rather than thetrain. Actually it’s a very good system, it makesthe 60-minute process to fill the muck skipsabout 10 minutes faster, and so it just fine-tunes the production.”

The use of pea-gravel to backfill the annulusbehind the project’s hexagonal segment ringsalso prompted some interesting designfeatures, including a hydraulic lift within thepea-gravel bays on the back-up to lift andempty the gravel cars; and a double capacitypea-gravel pumping system to facilitate theanticipated advance rates of the machine.

Among many other refinements, alsoincluded were a number of designmodifications to accommodate the width ofthe segments, as well as a custom fabricatednarrow gauge MineARC refuge chamber.

Project mobilisationWhile key parts of the TBM were beingproduced in Australia and Japan, SELIOverseas mobilised on site in the summer of2014 and began clearing and landscaping anarea for the project’s segment factory, as wellas its site offices, workshops andaccommodation buildings. The actual tunnelportal area is located a further 5km on fromthe main site, very close to the 650m cliff-edge of the plateau (see photo on p22).“There was only jungle here in thebeginning,” says Vizzino. “There was the[hard packed dirt] road, which was built by SKE&C four years ago, but that was it. We hadto prepare everything you see here and wedidn’t have that long to do it.”

Considering the highly isolated nature ofthe site, and frequent monsoons during therainy season that often wash out the road,preparing the site in just under six months wasno mean feat. With the nearest major hospitallocated five hours away on the other side ofthe Thai border, safety is also a concern for theproject. There is no helicopter support

available and, in addition to the standard riskof construction and road accidents, there arealso a number of highly venomous snakespecies prevalent in this area.

After a tight assembly period at Terratec’sfacilities in China, the TBM arrived inBangkok’s seaport in the last week of January2015. “From there it took about two days totransport the machine by road to the Laosborder and then we started sending all thecomponents up to site using five trucks aday,” says Brundan. “As the cutterhead isformed of two pieces [to facilitate disassemblyat the end of the drive], the largestcomponent was the cutterhead support atabout 60 tonnes.”

By mid-March the TBM was assembled onthe edge of the plateau and ready tocommence excavation. Originally, the machinewas to be advanced through a 500m long drilland blast adit to the launch chamber on a500m radius curve. However, a last minuterealignment reduced that radius to 300m.“We had to keep a specific distance from thedrop shaft, so SK E&C had to change theangle of the entry point,” explains Vizzino.“But the TBM was already in production whenthat decision was made.”

Rather than redesign the backup, it wasagreed that SELI Overseas and Terratec would

find a way to make the machine fit aroundthe curve somehow. “And we did it,” saysBrundan, “but it did cause some problems,particularly in terms of the TBM conveyors.”

Another issue at the beginning of the drivewas the challenge posed by fluctuations in thepower supply to the TBM, which was having asignificant impact on the machine’s progress.“It was initially suggested that the TBM’stransformers were the issue, but we had goodsupport from our component suppliers andwe were sure that wasn’t the case,” saysBruce Matheson, Terratec’s Sales andMarketing Director.

SELI Overseas and Terratec therefore spent alot of time working together to find a solutionto the issue and Electricité du Laos (EDL)offered a window of time that provided theleast amount of draw on the electrical grid,between 1am and 5am, when they couldprovide the best power supply possible. “It stillwasn’t good,” says Brundan. “We were goingup to specification on the voltage drops, and itwasn’t really resolved.”

“By this stage we were pretty sure theproblem was coming from the main powergrid,” says Matheson. “So we brought insome pretty high-tech datalogging equipmentto monitor the supply coming in and all itsqualities.” Terratec eventually proved its case

Cutter Headassembly

TBM

Backuptow point

Probedrill

Probe drillcarriage

Segmentfeeder

TBMconveyor

Bridge gantryassembly

ErectorAuxiliary thrustcylinder

Main thrust cylinder

Articulation cylinder

Figure 2: Configuration of the 5.74m diameter Hard Rock Terratec Double-Shield TBM

18 TUNNELLING JOURNAL

SITE REPORT

Section - I Section - II Section - III

Transfer Conduit(L=8.05km)

Low Pressure Tunnel(D=3.6~4.4m, L=1,565m)

DBM (2.1km,‘13.12.15~’18.05.31)SELI (11.8km,‘14.01.06~’17.09.07)

Reservoir Capacity(1,043mil.m3)

Vertical Shaft(D=4.4m, L=458m)

High Pressure Tunnel(D=3.6~4.4m, L=1,565m)

Turbine & Generator(410MW)

TL230kV (110km) 500kV (60km)

Tailrace Channel(L=6.33km)

Delivery point

Xe KongRiver

Xe-Pian Dam(H=48m, L=1,307m)

Xe-Namnoy Dam(H=73.7m, L=1,600m)

Power House &Penstock Civil WorkHSS (D=3.6, L=810m)

Surge Shaft(D=8m, 14m, L=217m)

Lao PDR Thailand

Figure 3: Main components of the Xe-Pian Xe-Namnoy Hydroelectric Project

and an order was placed for five Cummins800kv generators, which arrived on site in July2015. “Things immediately got much betterwith the more constant power supply and westarted to get some good production rates,”says Vizzino. “The generators have workedreally very well for us ever since then.”

As a result of the delays caused by thepower issues, SELI Overseas made the decisionto add an extra shift and now works threeeight-hour shifts during the week, with two12-hour shifts at the weekends. “So when wefinally started getting good production, wefound we were suddenly getting very goodproduction,” says Vizzino. “In the last threemonths alone we have done 2.5km. Recentlywe have been averaging about 33m per dayand we hope to reach 1,000m of productionthis month. Our best day so far is 50m with abest shift of 21m.” (See Figure 4)

With a scheduled completion date of June2017, the team is currently running aboutthree months ahead of schedule. “At themoment production is very high. I don’t wantto assume we will carry on doing 900m or1000m per month, but as we only have 5kmleft to go, it’s safe to assume that 600m or700m per month will be fairly easy toachieve,” says Vizzino.

Segment productionAs the TBM progresses it installs hexagonallining rings that consist of four 250mm thickand 1.5m wide steel reinforced segments withconcave and converse longitudinal joints that,along with the tunnel, were designed by Italy’sIngegneria Geotecnica (IG). These areproduced at the onsite segment factorylocated next to SELI Overseas’ main sitecomplex. Following the six-month sitemobilisation period, the first ring cast for theproject was in December 2014, “but we

didn’t go into full production until February2015.” says Vizzino. “Now we are producing24 rings per day.”

The segments are steam cured for fourhours, using four sets of moulds supplied by

Italian tunnel precast lining and gasketspecialist Fama, with two hours of prep timebefore curing. All materials are provided by SKE&C, including the cement, additives, andsteel rebar, which is welded into cages at thefactory. By the time TJ visited the site, this July,SELI Overseas had produced 7,500m worth ofsegments to date, with 1,000m of segmentskept in stock. In addition to storage at thefactory, there are also two different segmentareas at the portal site, one close to the portalfor loading onto the trains and one behind theportal area. This means SELI Overseas iscontinually moving the segments.

“Initially, we were worried about all thistransportation and movement, from theproduction to the stock areas, but thesegment quality is very good and we aren’tseeing any fractures or cracks at all,” saysVizzino. “The portal area is 5km away, so we

have to truck them down asteep slope, which is about5-7% grade. The segmentsare big, with each ringweighing 15 tonnes, andwe have had some issues,especially during the rainyseason when the road canget pretty bad. But wehave enough trucks, andplenty of storage, so nowwe keep to one ring pertruck for safety.”

Tunnel constructionFor such a long tunnel, it may be surprising tosome that SELI Overseas decided to use rollingstock rather than a continuous conveyor toremove muck from the heading on this drive.However, as Vizzino explains, there arebenefits to both approaches: “It depends onthe situation. It’s true that the investment costis lower for rolling stock, but the delivery andassembly time is also much faster. In this casewe did a comparison between the two and

SITE REPORT

TUNNELLING JOURNAL 21

Above: Thebackup duringTBM assemblyon the plateauwith the pea-gravel pumpson the lefthand side

Left: Segmentinstallationwithin the rearof the TBM

1,200

1000

800

600

400

200

0

Mon

thly

Pro

gres

s (m

)

M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13 M14 M15

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

Cum

ulat

ive

Prog

ress

(m)

44 59119

332

452385

434

109

290

819

463

744 769824

1,005Monthly Advance (m)Average: 428mBest: 1005mRemarks: Monthly Advance (m)During M1 to M3, power supply to operate the TBMavailable only 6 hours per day (00:00h to 06:00h)During M8 and M9 there was a stop to installthe switch and to make maintenanceDuring M11 there was 9 days stop at jobsitedue to Lao New Year

Figure 4: Monthly progress rates ending with July’s record-breaking 1,005m

SITE REPORT

22 TUNNELLING JOURNAL

the result was much the same, so we wentwith trains.” The other benefit is that you endup with quite a flexible solution, as you canalways add another train to increase capacity.“With a conveyor system, when that conveyoris going as fast as possible, you can’t changethat. So if the TBM is flying, you’re still limitedby your maximum conveyor speed, but thereis some flexibility with the rolling stock.”

At the time of TJ’s visit, SELI Overseas wasusing three sets of Schöma locos, each pullinga heavy train consisting of 18 cars – one carfor personnel, two pea gravel cars, four carsthat carry two rings of segments (weighing 30tonnes), and 11 muck wagons. The rollingstock is primarily manufactured by Palmieri,with design input from SELITechnologies, but alsoincludes the custom-madepea gravel cars, which werefabricated by Italianmanufacturer ELEA.

An innovative set-up at theportal area sees the muckcars unloaded with ahydraulic tipper directly into amuck bin. “Our scope ofwork ends when we unloadthe cars, it’s in the contractthat SK E&C takes away anddisposes the muck,” saysVizzino. “Initially, they used thematerial to extend the portalarea. But now it’s only used tomaintain the access roads,which is good for us, because the roads needa lot of upkeep, especially during the rainyseason.”

As far as excavation goes, the rockencountered so far has primarily beenlimestone, mudstone, siltstones andsandstones with an average UnconfinedCompressive Strength (UCS) of somewherebetween 70MPa and 130MPa; and, despitean area of hard limestone (200MPa) at thebeginning of the drive, cutter wear has beengood and much less than expected. “Themost recent data says we are excavating about480m3 of rock per cutter,” says Vizzino. “Atthe beginning [in the limestone] there was aperiod where we broke a lot of cutters, butnow the rate is very consistent.”

Mining through the fault zones has alsogone better than anticipated. “Of course, therock has been weak, Class 4 and sometimesClass 5, and we have had some water. Butthat hasn’t been an issue for the TBM,” saysVizzino. “The only real problem we had waslarge boulders in the fractured ground. Wehad to slightly modify the openings of thecutterhead by welding in some grizzly bars toprevent the boulders falling down onto thefront conveyor and breaking the belt.” Despitethis, progress remained high, with 800machieved this June whilst passing through thelargest of the anticipated fault zones.

Following segment erection, SELI Overseas

backfills the annulus with pea-gravel and ultimately grouts this with mortar.“Originally, we were going to grout behindthe backup,” says Vizzino. “But we decided itwas better to separate out the activities in theend. However, at the moment we are still onlyat the first kilometer and it’s taking a lot oftime, due to the people. It’s difficult tomanage the locals in this activity, so movingforward we need to increase the number ofexpatriates we have working on this.”

There were also some quality issues with thebackfilling at the beginning of the drive. Atpresent, pea-gravel is pumped into theannulus at 10 and 3 o’clock, and if required –depending on the ground conditions – toppedup at the invert and sometimes the crown.From the outset, SELI Overseas specified ahigh-capacity pumping system for the backfill– including twin sets of Aliva compressed airpumps and compressors – knowing fromexperience that the doubled system would berequired if progress rates were high.

However, crushed aggregate was beingsupplied to SELI Overseas as the backfillmaterial rather than smooth river gravel. “Wehad problems with the pumps, problems withthe pipes. It wasn’t washed, so the fines wereclogging everything, and it just wasn’tworking,” explains Vizzino.

So the switch was eventually made to rivergravel. “Using real pea-gravel is so muchbetter. You pay a lot when you buy it, but it

also saves a lot of time. The cost of theclogged pipes is one thing, but it’s thetime that you waste changing the pipethat is terrible.”

Completing the driveLooking forward to the remainder ofthe drive, logistics will likely be themain challenge ahead. SELI Overseasalready has another Schöma locoand rolling stock set on order, whichis due to arrive in October, to copewith the ever-increasing travel timesto the heading. In July, the journey

was approximately 30 minutes, but this willmore than double towards the end of thedrive. “We will also need a new switch. Wealready have a mobile California switch behindthe backup, but within the next kilometre wewill need to put in a fixed switch about 6kmin,” says Vizzino. Train speeds are also limitedas there are now a number of activity stationsthroughout the tunnel. ”We have thegrouting activity, and then there is alsoanother station where we are manuallyworking on the invert sealing, as we don’thave space within the backup for that.”

At present, Vizzino estimates the drive willlikely be complete in March 2017. “That isvery possible, if you consider 600m permonth. The Terratec TBM is very powerful andit is performing very well. I think it is proof ofthe quality of the TBM, the team, and also allthe systems that we chose for this project. Ofcourse, you can always improve production, soI think we can even do more than 1,000m in amonth, I think we could reach 1,200m if rockconditions continue this way, it’s possible.”

The tunnel drive is due to finish under theplateau, 2km short of the new reservoirintake, in a TBM disassembly chamber thathas already been excavated by SK E&C’s Thaidrill and blast subcontractor. Followingbreakthrough, the machine will be dismantledthere and the components will be brought allthe way back through the tunnel. “Logistically,it will not be easy and we will have to plan itvery carefully,” says Vizzino.

TBM assembly at the portalarea, close to the edge of the

Bolaven Plateau