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 KONGSWARMING UPINTERVIEW - MTRS 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

SEATTLESGREAT LEGACYNATJ TAKES A LOOKBACK AT THE CITYSHISTORY OF LARGE

DIAMETER TUNNELS

RETC 2011PREVIEW

SAN FRANCISCOS

CONFERENCE

RUNDOWN AND

EXHIBIT PREVIEW

TunnelingApril/May 2011

DETAILS ON PAGES 26-34

SAN FRANCISCO NATM SPECIALDEFINING DETAIL AT DEVILS SLIDE

NATJ_0411_NAFNTCOVER_001_V3.qxd:cover 17/4/11 21:10 Page 1

NATM

LAST OCTOBER, tunnel crews and membersof the public alike celebrated as Kiewit brokethrough on the 4,100ft (1250m) long DevilsSlide twin tube tunnels, in San Mateo County,California. Once complete, the tunnels andtwo new 1000ft (300m) long bridges willsteer Californias 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, DevilsSlide 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 Devils 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

DEVILS SLIDELocated on one of the worlds most beautiful

coastlines, the twin tube Devils Slide Tunnel isCalifornias 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

NATJ_0411_DevilsSlide_010_014.qxd:Feature 17/4/11 22:47 Page 10

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 states 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 Devils 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 Blockcomprises 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

NATJ_0411_DevilsSlide_010_014.qxd:Feature 17/4/11 22:47 Page 11

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 devi