WEB NEWSROUND-UP

GOTTHARDCOMPLETE, DTL 3

TBM AWARDS,CROSSRAIL

CONTRACTS OUT

SEE PAGE 48SEE PAGE 32SEE PAGE 6

BRIGHTONRE-VISITEDTJ RETURNS TO

SITE TO COMPARETHE TWO TBM

DRIVES

SETTLEMENTDISCUSSED

SETTLEMENT ANDUPHEAVAL CAUSED

BY EPBMTUNNELLING

REVIEWED

journalTunnelling

The international journal for the tunnelling industry

www.tunnellingjournal.com April/May 2011

SINGAPORE LTA - 29 TBMS FOR DTL 3NEW LINING METHODS IN PRACTICE

HONG KONG’SWARMING UPINTERVIEW - MTR’S NEW CHIEFCIVIL CONSTRUCTION ENGINEER

TJ_0411_extra_pages.qxd:Feature 19/4/11 21:35 Page 20

journalwww.tunnellingjournal.com

north american

FULL BORE ATCALDECOTT

NATM EXCAVATIONOF THE 4TH BORE IS

NOW WELL UNDERWAY IN OAKLAND

SEE PAGE 20SEE PAGE 16

SEATTLE’SGREAT LEGACYNATJ TAKES A LOOKBACK AT THE CITY’SHISTORY OF LARGE

DIAMETER TUNNELS

RETC 2011PREVIEW

SAN FRANCISCO‘S

CONFERENCE

RUNDOWN AND

EXHIBIT PREVIEW

TunnelingApril/May 2011

DETAILS ON PAGES 26-34

SAN FRANCISCO NATM SPECIALDEFINING DETAIL AT DEVIL’S SLIDE

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NATM

LAST OCTOBER, tunnel crews and membersof the public alike celebrated as Kiewit brokethrough on the 4,100ft (1250m) long Devil’sSlide twin tube tunnels, in San Mateo County,California. Once complete, the tunnels andtwo new 1000ft (300m) long bridges willsteer California’s famous scenic Highway 1route away from a perilous section of coast-line, which is eroding due to harsh winds andthe powerful Pacific Ocean. Dubbed by thecontractor as “The Best Tunnel Job in Amer-ica” there is little doubt that the dreamlikeocean scenery of this area is hard to beat.However, when it comes to rock-falls, Devil’sSlide is more of a nightmare. On several occa-sions, landslide damage has been so severethat the road has been closed for long periodswhile extensive repairs were undertaken. Fordecades local residents fought for a perma-nent solution to the problem and ultimately, in1996, a tunnel bypass was selected.

Project overviewThe northbound and southbound Devil’s Slidetunnels, which are 4,133ft (1.26km) and4,035ft (1.23km) long, respectively, passunder the San Pedro Mountain at depths of650ft (200m). The two 30ft (9m) wide x 22ft(6.8m) high horseshoe shaped openings eachhouse a single traffic lane, plus an emergencyshoulder, and are connected every 400ft(120m) via nine 16.5ft (5m) wide x 60ft (18m)long pedestrian cross-passages. A tenth, cen-

10 NORTH AMERICAN TUNNELING JOURNAL

The detail in the

DEVIL’S SLIDELocated on one of the world’s most beautiful

coastlines, the twin tube Devil’s Slide Tunnel isCalifornia’s first NATM highway tunnel. Dan Zerga,

of NATM tunnel designer ILF Consultants, andSebastian Kumpfmueller, of CM partner Dr Sauer

Corp, discuss experiences gained during the designand construction management of the project

Clockwise (from left): Aerial view ofRoute 1 and the south portal; Top

heading face inspection; Installation ofdowels in the northbound top heading

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trally located, 20ft (6m) wide cross-passage isalso provided for access/egress of emergencyvehicles. There are two mined equipmentchambers situated between the tunnels, atthe south portal and at the center of thealignment, with a third cut & cover equipmentchamber located between the north portals.

The California Department of Transporta-tion (Caltrans) awarded construction of theproject – the state’s first highway tunnel sincethe third bore of the Caldecott Tunnel openedin 1964 – to Kiewit Infrastructure West onJanuary 3, 2007, at a bid price of $273 mil-lion. Due to the complex and highly variableground conditions along the alignment, theNew Austrian Tunneling Method (NATM) wasspecified for construction. As this was the firsttime a California highway tunnel had beendesigned using the NATM method, Americanand European tunnel engineers led a coordi-nated team design effort.

HNTB was the prime and was responsiblefor the final lining design including mechanicaland electrical systems. Subconsultant ILF Con-sultants was responsible for NATM design ofthe initial lining and ground support, geohy-drology, drainage systems and waterproofing.Kiewit employed Gall Zeidler Consultants toprovide specialist NATM construction support.While a joint venture of URS and Dr G SauerCorporation (DSC) was selected to performtunnel excavation inspection and schedulingfor Caltrans. ILF had a geotechnical engineeron site during construction to assure that thedesign was properly implemented.

Excavation of the tunnels commenced fromthe southern portals in November 2007. De-pending on encountered ground conditions,two 120-ton Voest Alpine ATM105 roadhead-ers, a twin-boom Sandvik Axera drilling jumboand a Terex TE210 excavator, were employedto mine the tunnels in a concurrent top head-ing, bench and invert sequence. Averageadvances of 32ft/week (9.8m) were achievedin the northbound tunnel with a best day of19ft (6m) and week of 75ft (23m). The south-bound tunnel had a best day of 22ft (7m),week of 75ft (22m) and averaged 31.5ft/week(9.6m). Excavation progressed ahead of finish-ing works, which include a drained water-

proofing system incorporating a 2mm thickSikaplan sheet waterproofing membraneinstalled by Wisko America, and a 13.7in(350mm) cast-in-place concrete lining withtwo layers of rebar reinforcement. This finallining is cast using custom Ceresola reinforce-ment gantries and arch forms that facilitateongoing construction traffic within the tunnel.At the time of writing, these lining workswere roughly 68% complete in the north-bound tunnel and 66% complete in thesouthbound tunnel. Installation of mechanicalinstrumentation and other operational sys-tems had also begun in areas where the finallining was already in place.

Geology Ground conditions along the Devil’s Slidealignment are divided into three distinct ge-ological zones, separated by three inactivefaults (Figure 1): The ‘South Block’ is pre-dominantly massive quartz diorite, locallygrading to granodiorite, with irregularquartz and felsic dikes; the ‘Central Block’comprises thick interbedded layers of mas-sive marine sandstone, conglomerate, andclay-siltstone; while the ‘North Block’ con-sists of thin bedded interlayered fine-grained marine sandstone andclay-siltstone, with lenses of sandy con-glomerate. The North Block is disturbed bya wide shear zone consisting of steeplysouth-dipping planar zones of fault gouge.

Fault A, in the South Block, is an internalfeature within the granitic rock and dips at ashallow angle to the north. Fault B dips mod-erately to the north near the center of thetunnel, where the overburden is greatest, andforms the boundary between the crystallinebedrock and the overlying sedimentary rocks.While the steeply dipping Fault C separatesthe Central Block from the North Block.

Aside from the portal areas, the groundwa-ter table lies above the tunnel. However, thegroundwater level disconnects by about 330ft(100m) in the vicinity of Fault B, indicating thefault acts as a groundwater drain. Majorgroundwater migration paths include frac-tured fault zones and contact surfaces be-tween different formations and different

materials within the formations. During initial investigations, a horizontal

borehole drilled from the north portal throughthe shear zone resulted in a significant in-crease of water inflow, from 0.5 to 2 gallons/sec (2 to 8 liters/sec), where the boreholeintersected Fault C; indicating this faultbehaves as a groundwater barrier.

Lining designRock mass characteristics of the geology alongthe alignment[1] were grouped based on fac-tors such as lithology, properties of intact rockand rock discontinuities. For each of the 10rock mass categories defined for the project,rock mass parameters – such as compressivestrength and deformability – were derived.The boundary conditions of the tunnel exca-vation were then evaluated to determine rockmass behavior, including potential failuremechanisms. Among the parameters consid-ered were the virgin (primary) stress field,groundwater conditions, orientation of thetunnel opening in relation to the rock massstructure and the dimensions/geometry of theexcavation opening.

NORTH AMERICAN TUNNELING JOURNAL 11

Fig 1: Longitudinal cross section with geological conditions and core hole locations; the vertical white lines indicate where analyses were conducted for the three models used for the geohydrology study

NATM

Fig 2: Geotechnical design flowchart

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Failure mechanisms were separated intothe following failure modes: Failure of rockblocks; fracturing induced by stresses and/ordiscontinuities; progressive failure induced bystresses; failure induced ahead of tunnel face;and failure of tunnel face (face stability).Depending on the potential failure mode, keyblock theory, Finite Element (FE) and slopestability models, were then used to analyzeand define five individual support categoriesfor the tunnels (Table 1). For cases of potentialrock mass failure, initial lining deformationswere calculated for each of the relevant sup-port categories. Expected lining deformations,tolerances for initial lining deformation andconstruction tolerances were all defined.

A geotechnical monitoring program wasdevised to ensure verification of the designedsupport categories during construction. Thisincluded monitoring and observation of thebehavior of the excavation opening bysurveying predefined deformation points;measurement of the rock mass behavior viaextensometer; rock dowel performancethrough measurement devices attached tospecial dowels; and stress measurement in theshotcrete lining and/or at the interfacebetween the rock mass and the shotcrete

lining using pressure cells.The intent of NATM is to activate the

strength of the ground and combine it withthe initial support to form a ring-like structurearound the perimeter of the tunnel excava-tion. Rock loading on the initial support sys-tem results in deformation of the integratedexcavation/lining structure. Tunnel deforma-tions are continually monitored and comparedwith pre-determined warning levels, thus pro-viding continual verification of analysis resultsand the opportunity to adjust support meas-ures as required in the field.

It was assumed that the initial lining sup-port will deteriorate over time. The initial sup-port loading, as determined by analysis, wasthen directly applied to the final lining result-ing in a conservative design. The dimensionsof the final lining were mainly dictated by therock and seismic loads. However, fire, trafficand utility loads as well as loads from temper-ature changes were also considered.

Seismicity was a key factor in design sincethe project is relatively close to the San An-dreas Fault and earthquakes are quite com-mon within the region. For this reason, thereare no expansion joints in the final lining andsteel reinforcement is continuous along the

full length of the tunnels.Additional reinforcementis also installed at all inter-sections in order to trans-fer the longitudinal forcesfrom the tunnel lining intothe adjacent profiles. Twolayers of rebar reinforce-ment are required for thefull length of both tunnels.

Fiber reinforced shotcreteThe contract specifications for the Devil’s SlideTunnels called for a fiber reinforced initialshotcrete lining but left the use of steel or syn-thetic fibers to the discretion of the contractor.In this case Kiewit opted to use BarChip54structural synthetic fibers[2]. A batch plant forshotcrete production was set up on-site, nearthe south portal, which was of great benefitto the project and is highly recommended toavoid delivery and/or quality problems.

Each excavation advance received an initialflashcrete layer, which was applied to seal theexposed rock and protect miners. The first150mm (3.9in) layer of shotcrete was appliedafter the lattice girders were placed. Beforethe second and final layer was applied, threeexcavation rounds from the face, rock dowelsand other pre-support measures wereinstalled. In CAT I a single layer of shotcretewas applied on bare rock after the rockdowels were installed (Table 2).

Proper curing of the shotcrete and failedtoughness tests caused a number of problemsat the start of the project. However, thanks tothe onsite batch plant – which allowed imme-diate adjustment of the shotcrete mix – andthe contractor’s quality management team,who did a great job and pushed for a quicksolution, these issues were soon solved.Improving the water temperature at the batchplant and revising dosing programs on theMeyco Potenza shotcrete robot, as well asincreasing the fiber content of the shotcretemix, from 5kg/m3 to 7kg/m3, proved necessaryadaptations and guaranteed a shotcretequality throughout the project that far ex-ceeded the contract requirements. In additionto compressive strength testing, the shotcrete

NATM

12 NORTH AMERICAN TUNNELING JOURNAL

Fig 3a: Possible Hazards: Type 1 Failure of Rock Blocks

Table 1: Toolbox Items for top heading excavation

Support Typical Initial Lining Length of Spacing of Spiles and Length of Face Flash Category Advance Thickness Rock Dowels Lattice Girders Canopy Face Dowels Thickness

I 2.2m 100mm 3.6m n/a n/a n/a n/a

II 1.6m 200mm 4m 1.6m n/a n/a n/a

III 1.2m 250mm 6m & 4m 1.2m 4m n/a n/a

IV 1.0m 300mm 6m & 4m 1m 4m n/a 50mm

V 1.0m 300mm 4m 1m Canopy pipes 9m 100mm

Fig 3b: Possible Hazards: Type 2 Fracturing induced by stresses and/or discontinuities (loosening pressure)

Fig 3c: Possible Hazards: Type 3 Progressive failure induced by stresses

Fig 3d: Possible Hazards: Type 4 Progressive failure induced by stresses

ahead of the face

Table 2 : Summary of shotcrete application

Category Total Flash 1st 2nd mm mm layer layer

mm mm

I 100 0 0 100

II 200 25 150 25

III 250 50 150 50

IV 300 100 150 50

V 300 100 150 50

Right: Successful three-piece break forRound Determinate Panel (RDP) test

Opposite page top: Completing the invertin the northbound tunnel

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NORTH AMERICAN TUNNELING JOURNAL 13

was required to meet ASTM 1550 Round De-terminate Panel (RDP) test requirements[3].These tests had to be conducted for every100m3 of material used in the lining. RDP testsare being implemented on more and moreprojects to test flexural toughness of fiberreinforced concrete. One reason Kiewit chosesynthetic fibers over steel fibers was to meetthe specified requirement for RDP values inexcess of 320 Joules at 40mm deflection at anage of seven days. The RDP testing wascarried out at an on-site facility, erected closeto the portal, which included a fully air-condi-tioned curing room to provide a controlledenvironment for panel production andstorage. In order to achieve best results it alsoproved necessary to have a single individualresponsible for the panels from production totesting.

Instrumentation & monitoring Convergence arrays with optical targets, pres-sure cells and extensometers were used incombination to monitor rock behavior and de-formations during excavation[4]. While datacollection from pressure cellsmainly assisted design validationand back analysis, the convergencearrays and extensometers werevital instruments for daily excava-tion and support decisions and forverifying the stability of the struc-ture. Rod-type borehole exten-someters with hydraulic bladderanchor and vibrating wire trans-ducer were incorporated at fourmonitoring sections along thealignment of each tube. These sec-tions were adjacent to the southand center equipment chambers,at the start of the North Blockwhere the weakest ground was ex-pected and near the north portalwith the lowest overburden.

The intervals of convergence ar-rays were determined in the de-sign, based on the ground support categories,but were modified on-site if deemed neces-sary. A set number of readings were per-formed daily in the vicinity of ongoing

excavation works. Once a week, the NATMteam determined the appropriate frequencyfor the rest of the monitoring sections, whichcould be daily, weekly or monthly. As per thecontract documents, instrumentation warningand alarm levels were defined and establishedfor each ground support category. When in-strument readings exceeded warning levels,additional excavation support measures hadto be installed and the frequency of monitor-ing doubled until movements stabilized. Ifreadings exceeded alarm levels, excavationand all associated activities at that locationhad to be suspended until the contractor pro-posed measures to stop further movements.Stability of initial shotcrete lining was definedas closure measurement of <0.5mm/day for10 consecutive days.

Discussion of monitoring data was part ofthe daily meeting and incorporated in all deci-sions. Through observation of the ground, forexample, it was agreed classification of somelocations should be amended from CAT II toCAT III. Convergence results also had a majorinfluence in the elimination of the initial lining

invert in these same Category III areas. At thetime of placing the inverts, convergence read-ings indicated the structure, with all the in-stalled support measures and lining in place,was fully stable. All parties therefore agreedinvert installation was unnecessary, which re-sulted in time, cost and material savings.

During excavations, convergence read-ings were generally less than predicted.Only one section, in the northbound bore be-tween TM 500 and 600, were warning andalarm levels exceeded. The contractor haltedexcavation works and had the owner evaluatethe situation before continuing. Luckily, theconvergence only resulted in high deforma-tions and cracks in the initial shotcrete lining,rather than failure or collapse. Following backanalyses and additional support measures, theground was stabilized and excavation contin-ued. A major shear between two ground for-mations running parallel between the bores is

the most likely reason for the unexpectedevent.

Notable changes NATM meetings (attended by owner, contrac-tor, construction management and designer)included the review of geologic parametersand monitoring data on a round by roundbasis. During the course of excavation, theowner agreed to several notable changes inorder to avoid additional costs and/or delays.One such change came about due to the highinflows of water encountered during initialgeologic probe drilling. A dewatering systemwas requested for the North Block, compris-ing three horizontal dewatering drain holesdrilled into the fault from the north portalarea. One hole drained by gravity, while theother two were slightly inclined and equippedwith pumps. In total, more than 10 milliongallons of water was drained in order to keepboth tunnel headings dry during excavationthrough the difficult shear zone.

Another change was in relation to cross-passage #8. While nine of the cross-passages

are designed for pedestrian use,cross-passage #6 at TM 700 iswider to allow access/egress ofemergency vehicles once the tun-nels are operational. During exca-vation the contractor utilized thiscross-passage to move construc-tion equipment between the twobores, which allowed concurrentoperations such as final lining or in-vert arch construction, while main-taining excavation activities thatrequired mucking out. When exca-vation expectedly slowed in theNorth Block’s poorer rock condi-tions, subsequent final lining opera-tions were expected to catch upand would have come to a halt atcross-passage #6, which had tostay accessible for excavation traf-fic. Instead, it was decided cross-

passage #8 at TM 950 should be expanded topermit the contractor to continue moving ve-hicles between tunnels. This cross-passage willbe backfilled later and restored to its originalsize.

Another change related to the North Equip-ment Chamber. The excavation and supportof the northbound tunnel in the North Blockwas designed on the assumption that totalbackfill of the portal cut & cover structurewould be completed. This backfill was to pro-vide support of the vertical wall where theNorth Equipment Chamber is located, whichextends about 165ft (50m) back from the endof the northbound tunnel. However, the topheading excavations in both bores reachedthe North Block before backfill was in placeand potential delays became a concern.

In order to progress the excavation, Caltransrequested that ILF and DSC provide alterna-tives for continuation of the northbound bore

NATM

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NATM

14 NORTH AMERICAN TUNNELING JOURNAL

without the backfill support of the cut wall.Several analyses were performed to determinewhat additional support measures would berequired. The pillar between the tunnel andthe wall was about 10ft (3m) wide, in theworst ground conditions (CAT V), thereforelonger rock dowels and canopy pipe umbrel-las were adopted. Soil nails, providing wallsupport, had to be cut as excavation ad-vanced and sequence modifications were alsomade. In addition, the monitoring program in-side and outside the tunnel was intensified.Due to these changes, breakthrough wasachieved without complication or delay.

The excavation sequence for North Blockbench and invert excavation was also

amended. Prior to starting bench and invertexcavation of the 600ft (180m) long NorthBlock section, Kiewit requested a change ofexcavation sequence to improve work effi-ciency. This included bench excavation overthe entire length of the North Block withoutinvert installation following behind. The invertwould then be installed from the north portalgoing south after the bench was completed.Original contract drawings called for invert in-stallation at 30ft (10m) in CAT III and 20ft(6m) in CAT IV & V behind the bench face andplacement of a protective material over thenewly installed invert to enable the next roundof bench excavation.

Back analyses of top heading parametersand convergence readings indicated thechange in sequence would not result in exces-sive deformations or loadings of the lining andthat the tunnel would be stable without im-mediate application of the invert. However, ifthe newly defined settlement warning levelwas triggered, it was agreed that Kiewitwould immediately revert to placement of theinitial invert, as per original drawings. All in all,both contractor and owner benefited, as thenew sequence did not require the invert pro-tection layer and time saved on schedule.

Production ratesProduction rates within the baseline schedulewere for a seven-day week with concurrentbenching behind the top heading excavation.During the course of the project Kiewitchanged this construction sequence, advanc-ing the top heading without simultaneousbench excavation on a five- to six-day week

schedule. Actual production rates shown inTable 4 do not include downtimes, which in-cluded but were not limited to equipmentbreakdown and maintenance, shutdowns dueto ventilation moves and non-working days.

ConclusionsDuring design and prior to excavation ILFand DSC held numerous workshops andtraining sessions to further enhance teammembers’ knowledge of NATM excavationand support principles, as well as inspectionand documentation procedures. Maintainingdetailed and continuous documentation, in-cluding daily meeting minutes and excava-tion/support progress sheets, as well asgeological mapping of the face, has been avital tool during the project; and has played asignificant role during negotiations, discus-sions and the decision-making processes forexcavation and lining operations. This docu-mentation will also remain valuable in resolv-ing payment issues or claim negotiations.

As the first NATM highway tunnel to bebuilt in California, the Devil’s Slide Tunnel chal-lenged all parties involved. European NATMexperience had to be modified in order toconform to US conditions and standards; andCaltrans’ staff and Kiewit’s crews had to over-come numerous on-site difficulties – includingexhaustive evaluations, complex decisions andchallenging ground conditions. Nevertheless,all parties involved rose to the challenge, pro-ducing a high quality end result.

Last year, the project received the 2010“Outstanding Environmental & EngineeringProject Award” from the Association of Envi-ronmental & Engineering Geologists. Whenopen to traffic, in 2012, the Devil’s Slide tun-nels will greatly improve this problematicstretch of Route 1 to the benefit of locals,commuters and visitors alike.

1. Geotechnical Baseline Report. Devil’s SlideTunnel Project for California Department ofTransportation, prepared by: HNTB Corp, ILFConsultants & Earth Mechanics. October 14,2005.2. PH Madsen, JB Decker, K Zeidler, V Gall & TMO’Brien, 2009. “Experience with synthetic fiberreinforced initial shotcrete lining at the Devil’sSlide Tunnel Project.” Spritzbeton-Tagung 2009.3. JB Decker, PH Madsen & V Gall, 2010.“Examination of Shotcrete Liner at Devil’s SlideTunnel utilizing ASTM 1550 field test results andback analysis.” 44th US Rock MechanicsSymposium & 5th US-Canada Rock MechanicsSymposium, Salt Lake City.4. JB Decker& PH Madsen, 2009. “UtilizingConvergence Reading to Determine Stability andSupport Category in NATM Tunneling at theDevil’s Slide Tunnel.” 43th US Rock MechanicsSymposium & 4th US-Canada Rock MechanicsSymposium, Asheville.

REFERENCES

Table 3: Equipment use per category

Northbound tunnel equipment use Southbound tunnel equipment use

D&B Roadheader Excavator D&B Roadheader Excavator

CAT I 79% 21% CAT I 89% 11%(273.5m) (237.3m)

CAT II 99% 1% CAT I 7% 90% 3%(597.5m) (237.3m)

CAT III 48% 52% CAT III 20% 80%(249.5m) (245.3m)

CAT IV 30% 70% CAT IV 100%(86.5m) (43.9m)

CAT V 100% CAT V 10% 90%(55.0m) (28.6.0m)

Table 4: Average top teading production rates

Northbound Tunnel Southbound Tunnel

Baseline [m/day] Actual [m/day] Baseline [m/day] Actual [m/day]

CAT I 3.57 1.62 3.56 2.43

CAT II 2.86 1.90 2.83 2.37

CAT III 1.99 1.38 1.40 1.40

CAT IV 0.91 1.58 0.91 1.33

CAT V 0.69 1.13 0.69 1.20

Installation of dowels in the northboundtop heading

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