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Bored tunnels are some o the

most demanding and challenging

projects a waterprooer will ever

work on.Unlike tunnels close to the surace,

which are usually constructed using

cut-and-cover techniques, bored or

mined tunnels are constructed deep

below grade, where sometimes just

getting to the worksite is a major ordeal.

Additionally, the pressures, depths, and

lack o repair options inherent in this

type o work make doing the job right

even more critical than usual.

Because o these challenges, boredtunnels are usually economical only

when other construction methodssuch

as cut-and-covercant be used, usually

because the jobsite is too deep. Its not

unusual or bored tunnels to reach 160

eet below the surace. At those depths,

the tunnel is almost always carved

through solid bedrock. In other cases,

bored tunnels are preerred because the

surace cannot be disturbed.

Basic tunneling methods are airly

standard. First, the tunnel is excavated

using heavy equipment, drill-and-blast

mining techniques, gigantic tunnelboring machines (BMs) or some

combination o the above. I needed, soil

nails and rock bolts are then installed

to strengthen and stabilize the newly

exposed ace. Also, nearly every bored

tunnel receives a layer o shotcrete that

serves the same purpose.

Most o the popular waterproong

methods take advantage o this shotcrete

layer to simpliy the waterproong

process. Once this is in place, workerscan install any drainage and/or

waterproong membranes. Finally, a

grid o reinorcing steel is set up, and a

nal tunnel lining is cast. Tis lining is

usually either another layer o shotcrete

or a traditional concrete mix thats cast-

in-place using sliporms.

While each jobsite is unique and

each project requires a customized

waterproong system, these systems can

be categorized into just a ew basic types.

Crystalline Systems

Perhaps the least complex methodis to incorporate a crystalline admixture

into the shotcrete so that the concrete

itsel becomes waterproo and sel

sealing. In past decades, the product

was usually applied as a powder or a

liquid aer-the-act. Recently though,

a better method has been developed.

(For more on crystalline admixtures, see

Understanding Integral Waterproofng in

the Spring 2010 issue.)

Ann Martucci, a marketing executive

Waterproofng Techniques

For Bored Tunnels

PhotoCourtesyICSPenetron

Bored tunnels, suchas this Pacifc Coast

Highway tunnel nearDevils Slide, Caliornia,

can be a challengeor waterprooers.

Typically, the stakes arehigh, the jobsite remote,

and project size isenormous.

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on the Devils Slide tunnel, construction

ollowed the typical pattern. Workers

installed a double mat o rebar to match

the areas seismic requirements. A rail-

mounted slip-orm was used to cast the

nal tunnel lining.

CECO has recently developed a

series o PVC membranes specically

or bored tunnels. Te CoreFlex 60

integrates a 60-mil thermoplastic

membrane with DuPont's Elvaloy-

KEE (Keytone Ethylene Ester) to seal

any leaks that develop. Its reportedly

the only thermoplastic membrane

composite with this reactive, sel-sealing

perormance eature.

Te company also makes 80- 100-

and 120-mil membranes without the sel

sealing liners.

Te tunneling industry really

preers these durable PVC membranesbecause o the longer service lie, reports

Stacy Byrd, National Products Manager

at CECO.

Drainage and WaterstopsMany tunnel designsespecially

deep tunnel designsallow or a certain

amount o leakage.

Designers typically shy away rom

speciying drain sheets, as pressures

deep within the earth are extreme, andthey dont want anything compressible

in the design. Still, some sort o drainage

is needed to reduce hydrostatic pressure

on the waterproong system. Engineers

typically turn to a system o waterstops,

drain pipes, and sump pumps.

Te goal is to direct the fow o water

to the drain lines or discharge as quickly

as possible.

I a PVC membrane is used,

thermoplastic waterstops are standard,

as they can be welded to the membrane.

PVC waterstopsfexible, impermeable

barriersare installed vertically at

regular intervals to limit the distance

water can migrate behind the membrane.

Byrd reports that theyre typically

installed every 30 eet or so, dividing

the tunnel into drainage sections o

no more than a thousand square eet.

Tese waterstops are dierent rom the

conventional cold-joint waterstops used

in regular concrete work. Tey have

a dierent prole, and are so sti that

they cant easily be rolled. Tey typically

arrive at the jobsite in long straight

sections with separate actory-abricated

connections.

Te preerred solution or drain

lines is surprisingly mundane: the

standard perorated-pipe-in-gravelevery waterproong contractor is

amiliar with. On the 25-mile Channel

unnel connecting England to France,

the perorated pipe was laid in the gravel

ballast under the rails.

I possible, the pipes are run to

daylight and drained by gravity. On the

Channel unnel and other deep tunnels,

a standard sump pump setup is used.

Polyurethane GroutSystemsLike every type o project, bored

tunnels have an Achilles Heel. Cold

joints, expansion joints, and connections

to other tunnelssuch as ventilation

shas or cross passagesare prone to

leakage and require extra care.

One popular method or secondary

waterproong or remedial repair is

polyurethane grout. Teyre especially

useul when access shas or other

penetrations create geometric shapes

that are too awkward or sheet goods to

seal adequately. Tis grout is usually

injected as a liquid resin that reacts with

water to orm a watertight, permanent

seal.

Grace Construction Products

markets a sheet membrane that comes

with a grid o polyurethane grout

injection ports pre-installed. Aer the

nal tunnel lining is installed, the grout

can be injected at any location to ensure

a watertight bond.

CECOs line o thermoplastic

membranes can also be installed with

integral grout tubes.

Additional ConsiderationsWaterproong is critical in deep

tunnel applications because the stakesare so high. Maintenance or repair

work typically would cause a serious

interruption in service, so the job has to

be done right. A ailed waterproong

job, though, is not only inconvenient,

but dangerous. In a mountain highway

tunnel, or instance, any water or ice

buildup is a serious saety hazard.

Peter DAntonio, who oversees

tunnel sales or Sika Sarnal, notes,

Proper waterproong o tunnels isone o the most cost-eective ways to

increase the useul lie o these structures

and enhance saety. Water seeping into

a structure endangers the building

materials through the reeze-thaw

cycle, with water reezing inside cracks

and causing them to enlarge. Further,

preventing water rom reezing on road

suraces increases saety. n

P h o

t o C o u r t e s y X y p e x

The 25-mile-long Channel Tunnel, connecting England and France,used more than 500 tons o joint waterproofng.

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