ENS 080507 en RR AFTESrecomendationsforwaterproofinganddrainage

8/11/2019 ENS 080507 en RR AFTESrecomendationsforwaterproofinganddrainage

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AFTESGUIDELINES ON

WATERPROOFING AND DRAINAGE

OF UNDERGROUND STRUCTURES

Drafted byJ.L. MAHUET Chairman, GT9 on Waterproofing of Underground Structures

with the assistance ofP. HINGANT (SCETAUROUTE-DTTS) M. JERRAM & C.TRUFFANDIER (SNCF) J.L. REITH & B. CONSTANTIN (CETU)

J.P. BENNETON (LRPC, Lyon) Mlle BEORO (LRPC, Nancy) J.F. JABY (EOS) )MM. MERLE & MOREAU (DORKEN France) MM. MANRY & AUMOITTE (WAVIN)

MM. SAFFAR & PORTAIL (COBLOND) - M. FAYOUX (ALKOR DRAKA)M. JOLLY (PAVITEX) M. ROUGERIE (POLYFEUTRE)

M. LEBLAIS (SIMECSOL) M.ANDRE (SNCF) M. CHEZE (SIAAP)kindly helped with the final editing

Version 1 approved by Technical Committee 3 May 2000

PagesPages

1 - FIELD OF APPLICATION OF GUIDELINES . . . . . . . . . 116

2 - DEFINITIONS AND VOCABULARY . . . . . . . . . . . . . . . . 1163 - PREPARATION AND ACCEPTANCE OF BACKING

SURFACES TO RECEIVE A GEOMEMBRANE

WATERPROOFING SYSTEM IN CUT-AND-COVER

TUNNELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

3.1 - FIELD OF APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . 117

3.2 - BACKING SURFACE PREPARATION AND ACCEPTANCE 1173.2.1 - Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

3.2.2. - Acceptance of backing surfaces and corrective

measures for non-conformities . . . . . . . . . . . . . . . . . . . . . . . 118

3.2.3 - Summary table of backing surface acceptance operations . 119

4 - CHARACTERISTICS OF GEOTEXTILE AND

GEOCOMPOSITE PROTECTIVE BARRIERS . . . . . . . . . . . 119

4.1 - GENERAL CHARACTERISTICS OF PROTECTIVEBARRIERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

4.2 - CHEMICAL COMPOSITION OF GEOTEXTILE FIBRES . 119

4.3 - MINIMUM UNIT WEIGHT OF PROTECTIVE BARRIER . 119

4.4 - HYDRAULIC CHARACTERISTICS . . . . . . . . . . . . . . . . . . . 119

4.5 - PHYSICAL AND CHEMICAL PORPERTIES . . . . . . . . . . . 120

4.6 - RESISTANCE OF PROTECTIVE BARRIERS AGAINST

HEAT DAMAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

5 - GEOSPACERS AND DRAINAGE . . . . . . . . . . . . . . . . . . 121

5.1 - DRAINAGE FUNDAMENTALS . . . . . . . . . . . . . . . . . . . . . 121

5.2 - DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

5.3 - REFERENCE STANDARDS AND TESTS . . . . . . . . . . . . . . 122

6 - INTERCEPTION OF LOCALISED LEAKS . . . . . . . . . . 122

6.1 - ROOF AND SIDEWALL INTERCEPTORS . . . . . . . . . . . . . 122

6.2 - TEMPORARY INTERCEPTION AND DRAINAGE OF

INVERT IN STRUCTURES RENDERED COMPLETELYWATERTIGHT BY A GEOMEMBRANE WATERPROOFING

SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

6.2.1 - Driven tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

6.2.2 - Cut-and-cover tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

7 - DRAINAGE SYSTEM ASSOCIATED WITH A

GEOMEMBRANE WATERPROOFING SYSTEM AT

BOTTOM OF TUNNEL ROOF . . . . . . . . . . . . . . . . . . . . . 125

7.1 - PURPOSE OF DRAINAGE SYSTEM . . . . . . . . . . . . . . . . 125

7.2 - CHANGES IN DRAINAGE SYSTEM DESIGN . . . . . . . . 125

7.3 - DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

7.4 - ACCEPTATION OF DRAINAGE SYSTEM . . . . . . . . . . . . 127

8 - POROUS CONCRETE . . . . . . . . . . . . . . . . . . . . . . . . . 1278.1 - POROUS CONCRETE MIX COMPOSITION . . . . . . . . 127

8.2 - POROUS CONCRETE SPECIFICATIONS . . . . . . . . . . . 128

8.3 - POROUS CONCRETE DRAINAGE SYSTEM . . . . . . . . . 128

9 - PERMANENT DRAINAGE SYSTEM FOR

SIDEWALL AND ROOF JOINTS . . . . . . . . . . . . . . . . . . . 128

9.1 - DESCRIPTION OF CONTRACTION JOINT

DRAINAGE SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

9.1.1 - Physical and chemical characteristics of seepage . . . . . . . 128

9.1.2 - Frost protection to drainage system . . . . . . . . . . . . . . . . . 130

9.1.3 - Drain discharge and hydrostatic pressure . . . . . . . . . . . . . 130

9.2 - DRAINAGE SYSTEM DESIGN . . . . . . . . . . . . . . . . . . . . 131

10 - BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

SUMMARSUMMARYY

TUNNELS ET OUVRAGES SOUTERRAINS HORS-SERIE N 2 2005

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Guidelines on waterproofing and drainage of underground structures

1 FIELD OF APPLICATIONOF GUIDELINES

These Guidelines are applicable to thewaterproofing and drainage of under-ground structures such as machine-bored,

cut-and-cover, partially-immersed andother tunnels.

They provide additional details to beinserted into the CCTP ContractSpecifications and CCAP SpecialConditions in Fascicule 67 Titre III of the CCTGGeneral Specifications on Waterproofingof Underground Structures, which shouldbe amended accordingly, unless theGuidelines are made part of the contractdocuments.

Since the official issue in January 1992 ofTitre III of this Fascicule, the use of, forexample, geosynthetics as a waterproo-fing or drainage material in undergroundstructures has greatly expanded, leadingto the appearance on the market of inno-vative techniques and products.

The appearance of such new productssoon revealed a lack of detail in, orabsence from the specifications in Fascicule67 Titre III relevant to these new products.

While, for example, synthetic geomem-brane-type waterproofing products arethemselves generally adequately descri-

bed in the CCTGGeneral Specifications,there are gaps in the materials and proce-dures specifications regarding the prepa-ration of the backing surface to whichthey are applied, and the physical, chemi-cal and (most importantly) hydraulic pro-perties of de-bonding geotextiles.

AFTES working group GT9, aware thatthese omissions in the French regulationsmight impede the development of thesenew waterproofing and drainage tech-niques, undertook in 1997 the task ofupdating the CCTGGeneral Specifications

in the following areas: Preparation and acceptance of tunnelbacking surfaces destined to receive ageomembrane waterproofing system.The new AFTES Guidelines were publi-shed in the journal Tunnels et OuvragesSouterrains No. 150, November/ December1998. The present wording of theseGuidelines extends the field of applica-tion of Article 3 to backing surfaces of cut-and-cover tunnels whose sidewalls consistof diaphragm walls, Berlin walls, etc.

Formulation and publication of AFTESexpert opinions to add to the list ofwaterproofing products and techniquesnot currently covered by the text of or

commentary on Article 4 of Chapter III ofFascicule 67 Titre III of the CCTG GeneralSpecifications.

Updated lists of AFTES expert opinionsare published regularly in the journalTunnels et Ouvrages Souterrains.

2 - DEFINITIONS ANDVOCABULARY

Waterproofing and drainage of under-ground structures now refers to com-plexes or systems combining severalmaterials of sometimes widely differingcompositions and functions. New termshave recently appeared, and the mea-nings of some of them have been officiallydefined at European level.

The definitions of the more importantterms in these Guidelines are as follows:

Waterproofing. Article 2.1 of CCTGGeneral Specifications in Fascicule 67 Titre III property such that a product or combi-nation of products prevents the passageof a liquid such as water:

- Waterproofing may be partial, as withumbrella waterproofing for example fora tunnel roof, in which case it is not expo-sed to hydrostatic pressure (in this case,the pressure is not total but not necessa-

rily zero).- Waterproofing may be total, meaningthat it may completely surround the struc-ture, and in this case, it is subject to thehydrostatic pressure.

Drainage. Interception at a point orover an area of water flowing into anunderground structure. This water is col-lected and disposed of by means of thestructures main drainage system.Drainage may be temporary, in order, forexample, to allow the waterproofing com-plex to be installed in the correct manner,

or permanent and contribute to thewaterproofing of the structure.

Geomembrane waterproofing sys-tem. Independent extrados waterproo-fing complex consisting of several mate-rials, each fulfilling a precise function:

- protective puncture barrier placedagainst the backing, under the waterproofgeomembrane,

- translucid synthetic waterproofing geo-membrane,

- protective mechanical barrier on top ofthe geomembrane when the permanentlining is reinforced. This barrier is alsoused in the form of strips, 1.00m to 1.50m

wide, over each concrete joint in the tun-nel roof.

Protective static puncture barrierpla-ced in contact with the backing surface,under the waterproofing geomembrane.It is sometimes called the extrados pro-

tection in connection with a geomem-brane waterproofing system to a driventunnel or cut-and-cover tunnel built withina supported trench. It consists essentiallyof a nonwoven geotextile, sometimesassociated with a PVCP or polyethylenefilm such that, in the event of a majorinflow of water, it may act as a first water-tight barrier to enable thermal seamingof the geomembrane to proceed. Thephysical and mechanical properties of theprotective barrier are specified in Article7.4.2.3 of Fascicule 67 Titre III CCTG

General Specifications and tables 1 and 2below.

Protective dynamic puncture barrier,on top of the waterproofing geomem-brane, sometimes called intrados pro-tection in connection with a geomem-brane waterproofing system to a driven(reinforced) tunnel or cut-and-cover tun-nel within a supported trench. This barriermust always consist of a membrane ofsynthetic material (PVCP or polyethylene).The physical and mechanical properties of

the protective barrier are also specified inArticle 7.4.2.3 and No. 7 of Annexe 4 ofFascicule 67 Titre III CCTG GeneralSpecifications.

Geospacers. Polymer structure consis-ting of sheets of thermo-formed materialor monofilament or any other structurewhose purpose is to impart a high voidratio promoting the free flow of waterunder either temporary or permanentconditions.

Mechanical protective geocomposite.Combination of a nonwoven geotextileand a thin sheet of generally PVCP orpolyethylene synthetics. The geotextileply is placed in contact with the backingsurface.

Supported tunnel. Structure built withinthe confines of a supporting structure(diaphragm walls, Berlin walls, etc.) whichacts as the backing for the waterproofingand drainage systems.

Unsupported tunnel. Structure builtwithout temporary support (in excavationwith sloping sides), in which case the

waterproofing and drainage systems areinstalled after building, directly on thepermanent concrete.


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Drainage geocomposite. A combina-tion of geospacer and one or more geo-textiles providing a filtering effect.Drainage geocomposites are generallyused as permanent drainage to the side-walls in cut-and-cover tunnels built inunsupported trenches.

Drainage hoop. Strip drain consistingeither of a geospacer or drainage geo-composite of variable width placed atright angles to the tunnel centrelinewhose main function is to facilitate thedischarge of water flowing in from thebacking towards the drainage system atthe bottom of the sidewall or roof.

Horizontal drainage strip.Strip drain consisting eitherof a geospacer or drainagegeocomposite of variablewidth placed parallel to the

tunnel centreline whosemain function is to facilitatethe discharge of water flo-wing in from the backingtowards the drainage sys-tem at the bottom of thesidewall or roof.

Sidewall or roof bottomdrainage. Circular drainsmade of synthetic materialor box-outs in the ban-quette to collect dischargefrom a geomembrane

waterproofing system andconvey it to the main drai-nage system.

Figure 1 illustrates the various compo-nents associated with a geomembranewaterproofing system.

3 - PREPARATION ANDACCEPTANCE OF BACKINGSURFACES TO RECEIVE AGEOMEMBRANE WATER-PROOFING SYSTEM INCUT-AND-COVER TUNNELS

AFTES Guidelines on the preparation oftunnel surfaces destined to receive a geo-

membrane waterproofing system publi-shed in the November/December issue(No. 150) of Tunnels et Ouvrages Souterrainsadd important details on tunnel water-proofing to Article 9 of Fascicule 67 Titre IIIof CCTGGeneral Specifications. However,

specifications regarding backing surfacepreparation in cut-and-cover supportedtunnels, i.e. having temporary support inthe form of diaphragm walls, Berlin walls,sheet piling and similar steel support,etc. suffer from the same omissions inArticle 9.2.4 of Fascicule 67 Titre III. Thepresent text expands the recommenda-tions applicable to tunnels to include ins-tallation of a geomembrane waterproo-fing system in cut-and-cover tunnels,especially as, unlike the umbrella typegeomembrane waterproofing systemused in some tunnels, the geomembranewaterproofing system in this case isalways exposed to hydrostatic pressureunder operational conditions.

3.1 - FIELD OF APPLICATION

These Guidelines apply to all tunnels builtin a shored trench using the followingtypes of support:

- diaphragm wall

- precast diaphragm wall

- slurry wall

- Berlin wall (steel soldiers with timber orprecast concrete lagging)

- nailed shotcrete

- sheet piling with concrete counterwall

- sheet piling with high density polysty-rene filling the troughs.

3.2 - BACKING SURFACE

PREPARATION AND

ACCEPTANCE

3.2.1 - Characteristicsa) Diaphragm wall precast diaphragm

wall concrete counterwall

Specifications in Article 9.1.2.1. of Fascicule67 Titre III are adequate.

b) Slurry wall

This type of support is not covered byFascicule 67. Working group GT9 suggestthe following specification: The slurryshall have the mechanical strength requi-red by the CCTPContract Specifications

before installing the geomembranewaterproofing system.



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Figure 1 - Illustrates the various components associated with ageomembrane waterproofing system.

Photo 1 - Mechanical protective geocomposite and hori-zontal drainage strip

Photo 2 Geospacer on steel temporary support


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Dry, loose superficial slurry shall beremoved.

Length of intermediate fastening nailsfor the geomembrane waterproofing sys-tem shall be set with reference to themechanical strength of the slurry. Steel

sections shall be flush with the slurry wallsurface to within 5cm.

c) Berlin wall and sheet piling with poly-styrene filling the troughs

- c1) Steel

The specification in Article 3.1.3. of theguidelines published in No. 150 ofTunnels et Ouvrages Souterrains shouldbe added to those in Article 9.1.2.3. ofFascicule 67 Titre II

- c2) Polystyrene

Add the following to Article 9.2.4b ofFascicule 67 Titre III: The polystyreneshall be a perfect fit in the sheet pilingtroughs and shall be class EM as descri-bed in French standard NFT 56 201 withminimum compressive strength of not lessthan 90 kPa.

d) Shotcrete

The specification in Article 3.1.1. of theguidelines published in No. 150 of Tunnelset Ouvrages Souterrains should be added tothose in Article 9.1.2.2. of Fascicule 67 Titre

III.

e) Fillet

A fillet should be formed where the verti-cal surface meets the tunnel invert (appli-cable to all surfaces mentioned above).The fillet is generally mortar radiused tomore than 5cm radius.

3.2.2. - Acceptance of backingsurfaces and corrective measuresfor non-conformities

Once special points have been dealt withas described above, the acceptance pro-cedure for the prepared backing surfacecomprises the following operations:

a) Diaphragm wall precast diaphragmwall concrete counterwall

- a1) diaphragm wall with trowelled mor-tar finish as described in Article 9.2.4c ofFascicule 67 Titre III Precast diaphragmwall with concrete counterwall: Add toArticle 9.2. of Fascicule 67 Titre III: Surfacesor panels shall be flush to within 5cm. Anyedges exceeding 5cm shall be feathered

to 45 with mortar or other type of incom-pressible material.

- a2 ) Diaphragm wall ground downwithout trowelled mortar

a2.1) Verification of general geo-metry of backing surfaces: Article 3.2.1of recommendations published in No. 150of Tunnels et Ouvrages Souterrains applies.

The verification should be performedaccording to the procedure in Appendix 1of the recommendations.

a2.2) Verification of surface rough-ness of diaphragm wall: Article 3.2.2 ofthe recommendations published in No.150 of Tunnels et Ouvrages Souterrainsapplies. The verification should be perfor-med according to the procedure inAppendix 2 of the recommendations.Characteristics of the geotextile protec-tive barrier appear below in table 2, para.

4.1.4 below.

b) Slurry walls

The general geometry should raise noproblems, and the only verification nee-ded is maximum misalignment betweenthe surface and the steel members, andsuperficial cohesion of the slurry.

c) Berlin wall and sheet piling withpolystyrene filling

Ditto para. b above, the only verification

needed is misalignment between steelmembers and plates, panels and polysty-rene blocks.

d) Shotcrete

- d.1) Verification of general geometryof shotcrete surface: Article 3.2.1 ofrecommendations published in No. 150 ofTunnels et Ouvrages Souterrains applies. The

verification should be performed accor-ding to the procedure in Appendix 1 ofthe recommendations.

- d2) Verification of backing surfaceroughness of shotcrete: Article 3.2.2 ofthe recommendations published in No.150 of Tunnels et Ouvrages Souterrainsapplies. The verification should be perfor-med according to the procedure inAppendix 2 of the recommendations.


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Photo 3 - Ground diaphragm wall support

Photo 5 - Hybrid support: Berlin wall and nailed shotcrete

Photo 4 - Sheet piling support with polystyrene filling troughs


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3.2.3 - Summary table of backingsurface acceptance operations

The sequence of surface acceptanceoperations described in Table 1,Appendix 1, of the recommendations

published in Tunnels et OuvragesSouterrains No. 150 is also applicable tothe acceptance of cut-and-cover tunnelbacking surfaces.

The only difference concerns the charac-teristics of geotextile protective barriers;the characteristics show in table 2 inpara. 4.4. apply to cut-and-cover tunnels.

4 - CHARACTERISTICS OFGEOTEXTILE AND

GEOCOMPOSITEPROTECTIVE BARRIERS

As stated in section 2 Definitions andVocabulary, geosynthetics form the firstcomponent of a geomembrane water-proofing system. Article 7.4.2.3. ofFascicule 67 Titre III of the CCTG GeneralSpecifications states that the principalfunction of these geosynthetics is to pro-vide mechanical protection against punc-turing or tearing of the waterproof geo-membrane. They are placed in contactwith the backing surface to accommodate

excessive surface roughness and providereliable, durable protection against staticpuncture due to surface defects.

This protective barrier, also called extra-dos protection on supported trench cut-and-cover structures, may consist

- either of a geotextile made exclusivelyof synthetic fibres of at least 700 g/mm2

unit weight in cut-and-cover tunnels and600 g/m2 in driven tunnels,

- or a geocomposite consisting of a thinPVCP or polyethylene geomembrane,

preferably light in colour, bonded in thefactory to a geotextile of the same natureand physical and chemical characteristicsas the geotextile described above.

4.1 - GENERAL

CHARACTERISTICS OF

PROTECTIVE BARRIERS

Articles 7.4.3.2. and 13.02.2 of Annexe 3and Article 7 of Annexe 4 of Fascicule 67Titre III of CCTG General Specificationsissued in January 1992 describe the cha-racteristics to be specified for the geotex-tiles and geocomposites associated withgeomembrane waterproofing systems.

These characteristics concern chieflymechanical strength (static puncturestrength); the draining capacity forexample of the protective barrier underboth temporary and permanent condi-tions is not considered in Fascicule 67

Titre III.The present Guidelines therefore expandthe specifications in Fascicule 67on the fol-lowing points:

- Adaptation of the mechanical characte-ristics of the protective barrier with refe-rence to the recommendations on prepa-ration and acceptance of tunnel backingsurfaces preparatory to installing a geo-membrane waterproofing system publi-shed in the November/December issue(No. 150) of Tunnels et OuvragesSouterrains. These adaptations are also

offered with reference to the recommen-dations in Article 3 and apply more speci-fically to cut-and-cover tunnels.

- Incorporation of a drainage function inthe protective barrier, more particularly inthe case of a geomembrane waterproo-fing system in tunnels.

4.2 - CHEMICAL

COMPOSITIONOF

GEOTEXTILE FIBRES

Much research has indicated a not incon-

siderable risk of hydrolysis of polyesterfibre in an alkaline environment and thismaterial must not be used in undergroundstructures where the material is usually incontact with concrete; polypropylene orsimilar materials must be used.

4.3 - MINIMUM UNIT

WEIGHT OF PROTECTIVE

BARRIER

There follows a summary of the relevantparts of the Fascicule 67 Titre III CCTG

General Specifications (as regards mini-mum permitted and not nominal unitweights).

a) Driven tunnels

Article 13.02.3. of Annexe 3 specifies aminimum unit weight of 600 g/m2. Thisminimum remains unchanged in the speci-fications to be included in a CCTPContractSpecification.

The CCTPContract Specification mayrequire a higher value, on the basis ofshotcrete roughness values (mean maxi-mum depth at sidewall and roof of shot-crete roughness) measured following thesuitability test performed on site, with

reference to acceptance conditions asdescribed in Table 1 of the recommenda-tions published in Tunnels et OuvragesSouterrainsNo. 150.

As stated elsewhere in these recommen-dations, and bearing in mind develop-

ments in tunnel support, minimum unitweights for protective barrier materialshave been introduced for the followingtypes of surface:

- 800 g/m2 for metal fibre reinforced shot-crete

- 600 g/m 2 for concrete segments(machine-bored tunnels)

- 1000 g/m2 for steel support.

b) Cut-and-cover tunnels

Article 7 of Annexe 4 specifies a minimumunit weight of 700 g/m2. This minimumvalue remains unchanged for the follo-wing types of surface:

- diaphragm walls precast diaphragmwalls concrete counterwalls slurry walls sheet piling with polystyrene filling.

The unit weight for diaphragm walls notfinished with trowelled mortar and shot-crete may be increased on the basis ofmean maximum depth of sidewall rough-ness measured during suitability tests onsite. As in the case of driven tunnels, the

increase in unit weight should refer to thedifferent acceptance situations in Table 1appended to the recommendations publi-shed in Tunnels et Ouvrages SouterrainsNo. 150.

The minimum unit weight for Berlin wallsis 1000 g/m2.

4.4 HYDRAULIC

CHARACTERISTICS

Working group GT9 recommends that adrainage capability should be added tothe mechanical strength originally devol-ved on protective barriers against staticpuncture by Fascicule 67 Titre III. This willmake it possible to intercept and drainsmall water flows during construction,preventing water passing through thegeotextile with the possibility of interfe-ring with thermal seaming of the strips ofsynthetic waterproofing geomembrane.Depending on seepage rates, the geotex-tile might be replaced locally by a protec-tive/draining geocomposite as describedbelow.

This draining function is even more impor-tant on completion of the works, underpermanent operating conditions, because



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it must collect water flowing in from thesurrounding ground and convey it to thedrainage system generally installed at thebottom of the sidewall or roof.

In order to ensure lasting performance ofthe draining capability of the protective

barrier, GT9 will expand this recommen-dation at a later date after examininggeotextile filtering properties, to preventfouling if for example the inflowing see-page displays incrusting properties; ano-ther factor considered will be permeabi-lity to water (NFENISO 10319).

It might be noted that protective geo-composites are commercially availablewith the following properties:

- filtration with a layer of geotextile

- drainage with a thick layer of geogrid

- watertightness with a thin synthetic layer(PVCP).

These protective geocomposites mayusefully be recommended if the seepagewater is highly incrusting or carries aheavy load of fines from the surroundingground.

This hydraulic characteristic is not requi-red for protective barriers in which thegeomembrane waterproofing systemdoes not provide permanent drainage (forexample, in cut-and-cover tunnels).

Proposed hydraulic characteristics

Following many comparative laboratorytests of hydraulic transmissivity on severaltypes of geotextile, working group GT9recommends the following minimumhydraulic values:

- minimum capacity 15 litres/metre/hour

- minimum transmissivity 4.6 x 10-6 m2/s

These values were determined from atransmissivity test performed by theprocedure described in French standardNF EN 15012958 under the conditionsdescribed in para. 5.3.

These values are proposed for water flowshabitually encountered in undergroundstructures; for higher flows, GT9 recom-mend the following modifications to thegeomembrane waterproofing system.

Underground structures displayinglocally high flows (more than 0.5 l/min): Atleakage sites, install hoops consisting ofgeospacers of variable width to conveythe water to the drainage system at thebottom of the sidewall or roof before ins-talling the geotextile protective barrier. Atplaces where inflow is more than 30 l/min,interception and drainage must be provi-ded by drains, as described in section 6 ofthese Guidelines. The drains must be

connected to the sidewall or roof drai-nage system if designed as permanentinstallations, or filled with grout if desi-gned as temporary installations.

Underground structures with large areasof support and diffuse seepage liable to

pass through the geotexti le protectivebarrier: Replace the geotextile protectivebarrier with a geocomposite consisting ofa geotextile placed against the backingsurface having a unit weight of up to 600to 1200 g/m2 (to suit mean maximumroughness depth at bottom of sidewalland roof) and a transmissivity of not lessthan 4.6 x 10-6 m2/s. On the geomembraneface, the geotextile is combined with asynthetic film of the following thickness(to suit the relevant geotextile unitweight):

- 600 g/m2

: thickness 200 microns mini-mum

- 800 g/m2: thickness 150 microns mini-mum

- 1000 g/m2: thickness 100 microns mini-mum

- 1200 g/m2: thickness 100 microns mini-mum.

The geocomposite is fastened to the bac-king surface by means of synthetic disksas described in the GT9 recommenda-tions on the use of PVC disk fasteners forgeomembrane waterproofing systemspublished in Tunnels et Ouvrages

SouterrainsNo 138.

4.5 - PHYSICAL AND

CHEMICAL PROPERTIES

Working group GT9 recommend adaptingand amending the specifications concer-ning

- tensile properties according to Frenchstandard NFP 84.501 for synthetic mem-brane protective barriers and NF EN ISO10319 for geotextiles and similar pro-ducts,

- static puncture strength according toNFP 84.507.

These new specifications are shownagainst structures and backing surfacetypes in tables 1 and 2 below.


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Table 1 - Specifications for driven tunnels

(*)Minimum not nominal specification

Table 2 - Specifications for cut-and-cover tunnels

Steel archMinimum requirement

Shotcrete Concreteand platesupport segmentssupport

w/o fibre w/fibr600 80 600 1000

0.6 0.8 0.6 7

70 70 70 70

12 12 12 12

4.6 x 10-6 4.6 x 10-6 4.6 x 10-6 4.6 x 10-6

Support shutteredBerlinor trowelled concrete, Ground

Minimum wall, sheet piling Shotcrete diaphragm wall,requirement (*) with polystyrene wall hybrid

filling

w/o fibre w/fibre

Geotextile unit weight

(g/m2) 700 700 800 800 1000

Static puncture (kN) 0.7 0.7 0.8 0.8 1

Elongation atmax force (%) 50 50 50 50 70

Tensile strength

(kN/m) 12 12 12 12 30

Unit weight (g/m2)

Static puncture 8mmdia needle (kN)

Elongation at max force (%)

Tensile strength (kN)

Transmissivity at 150 kPa (m2/s)

NFEN 963

NFP 84507

NFEN ISO10319NFEN ISO10319

NFEN ISO12958

Standard


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4.6 - RESISTANCE OF

PROTECTIVE BARRIERS

AGAINST HEAT DAMAGE

During thermal welding of special synthe-tic disks to the geomembrane with hot air

at 200-300C, it often happens that theprotective barrier, usually a geotextile, isaccidentally burned superficially or moredeeply, considerably reducing it staticpuncture strength locally. To control thistype of damage, GT9, following labora-tory and field testing, recommends thefollowing practices to suit different typesof protective barrier:

- Geotextile protective barrier: use faste-ning disks of the type described in therecommendations published in Tunnels etOuvrages SouterrainsNo. 138 having a

skirt of substantially larger diameter thanthe disk proper to provide greater protec-tion locally against accidental heatdamage.

- Protective geocomposite: partial protec-tion against heat damage is provided bythe synthetic film on the geomembraneside. Polyethylene film performs betteragainst accidental burning provided thefilm is not less that 200 microns thick.

Fire resistance of protective barrier

In the absence of any tests and French or

European standards, the fire resistance ofprotective barriers was not specificallydealt with by GT9, but in view of the sen-sitivity to fire of, in particular, geotextiles,which are frequently the source of ignitionand sustain the subsequent fire in a geo-membrane waterproofing system, theworking group realise the need to intro-duce fire resistance specifications in themedium term. Such specifications requi-ring, among other things, a minimum fireresistance of class MI or BI (DIN 4102) canbe expected in the near future, especially

as manufacturers already possess thistype of product in the laboratory; in themeantime, preference should be given toproducts of this type.

5 - GEOSPACERSAND DRAINAGEGEOCOMPOSITES

5.1 - DRAINAGE

FUNDAMENTALS

Synthetic materials basically providingdrainage performance as defined anddescribed in section 1 above are used.

These drainage materials can be used forthe following functions:

- Temporary interception of water flowinginto the driven or cut-and-cover tunnel, inwhich case, they must always be used inconjunction with a geomembrane water-

proofing system.- Permanent seepage interception anddrainage in an underground structure, inwhich case the drain material is generallyused alone without a geomembranewaterproofing system (except in a fewcases where it may for example be used incombination with a partial geomembranewaterproofing system installed only at theroof or cover decking). In this configura-tion, the drainage system provides themain seepage control system for thestructure by intercepting and discharging

seepage from the surrounding groundand preventing the build-up of hydrosta-tic pressure.

These drain materials can be installed asfollows:

a) Localised drainage

Interception and drainage of inflow withlocalised peaks in excess of 0.5 l/min. Thesystem described in section 1 above maytake the form of a hoop when installed asvertical strips of variable width or in the

form of horizontal strips 1.50m to 2.00mwide.

Localised drainage may be used in the fol-lowing situations:

- Temporary drainage in which case, it isusually conceived as preformed cellularpanels 8-20mm thick (thickness to suitdischarge required under 100-150 kPa

green concrete pressure). Hoops and hori-zontal strip drains are simply pinned tothe backing and connected up to the geo-membrane waterproofing system drai-nage system.

- Permanent drainage in which case, itgenerally consists of strips of geocompo-site with a filter layer. The strips are gene-rally pinned to the backing (in driven orsupported cut-and-cover tunnels),verti-cally across joints in the linings to driventunnels or in open trench diaphragmwalls, and horizontally in driven tunnels at

the cold joint between invert and roof.Strips of geospacer may also be used,provided they are fitted at the edges witha waterstop (precompressed type) to pre-vent ingress of cement laitance whenconcreting the permanent lining. Drainstrips must always be connected to a lon-gitudinal drain, generally placed at thebottom of the roof or sidewall.

b) Area drainage

As with localised drainage, two cases aremet with.



121

Photo 6 - Temporary localised drain using geospacer strip

Photo 7 - Vertical drainage geocomposite onsupported-trench cut-and-cover tunnel sidewalls


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- Temporary area drainage, used incombination with a geomembrane water-proofing system to drain areas in the roofdischarging high seepage flows, orinflows at the invert as mentioned in sec-tion 6.2 below. Preformed cellular panels

are generally used for this purpose. Theyare pinned to the backing with overlaps,depending on the system, of between0.10m and 0.20m per layer, and connec-ted to the temporary drainage or dewate-ring system.

- Permanent area drainage, whichincludes a waterproofing capability, isused mainly in cut-and-cover tunnels builtin supported or unsupported trenches,but never where exposed to hydrostaticpressure. It is usually the sidewalls that areso equipped, and sometimes the invert,

but this type of drain is quite rare inFrance. For a permanent drainage system,it is strongly advised to use drainage geo-composites having a filter layer to ensuredurability of the drainage system. Thedrain strips are unwound vertically with anoverlap (depending on the system) of0.10m to 0.20m. The drain strips are pin-ned to the backing at the top and, ifnecessary, due to the height of the strip,at intermediate levels. The vertical drai-nage system must connect with a poly-ethylene system with an inspection coverat most every 50m for cleaning the sys-

tem.

5.2 - DESIGN

The designer must not specify the drai-nage capacity of the material on the basisof the capacity of the longitudinal drain,but from the expected seepage flow fromthe surrounding ground. The capacity ofthe longitudinal drainage system will ulti-mately be of course set on the basis of theexpected inflow rate, but must also referto operational requirements specified bythe owner (in particular, locations anddimensions of inspection points).

a) Driven tunnels

Drainage geospacers and geocompositesare ranked in table 3 below.

The diameters in table 3 show the crosssection theoretically needed to dischargethe flows considered but do not allow forany fouling that might be expected withreference to the chemistry of the water.

For localised major inflows, extra inter-

ceptors should be provided, and thesecall for special longitudinal interceptionand drainage systems.


Inflow is usually less in cut-and-cover tun-nels than in driven tunnels. Therefore, inthe absence of precise data on the flowsto be considered in designing the drai-nage system, the first step will be to checkthat the transmissivity of the drainagematerial is compatible with the permeabi-lity of the surrounding ground.

When designing the drainage system forthe invert or cover deck, the classificationin table 3 might apply. However, the desi-gner will have to calculate the longitudinalflow rate to check the drainage capacity(under a low hydraulic gradient) of thedrain material specified and decide thespacing of pumpage points.

5.3 - REFERENCE

STANDARDS AND TESTS

Working group GT9 recommends desi-

gners including the following tests andstandards in the Specification for drainmaterials to be incorporated in under-ground structures, without losing sight ofthe fact that they must reflect the condi-tions under which the materials willactually be used.

Note that the designer might use experi-mental standard G 38.061 (Feb. 1993) onrecommendations on the use of geotex-tiles determination of hydraulic proper-ties in drain and filter systems, and mightalso begin to refer to draft European stan-dard NF EN 13252 on characteristics of

geotextiles in drainage systems.

a) Driven tunnels

The transmissivity test should be perfor-med by the procedure in NF EN ISO12958 with a gradient i = 1, although it

should be modified with the testspecimen placed between a rigidpanel and a flexible membrane.

Test pressure should be 150 kPa for6 hours (the time required forconcreting the roof).


b1) Vertical drainage for opentrench tunnel

In this case, the vertical drain material issubject to a permanent pressure whosevalue depends on the height of the back-fill. In the most common cases, it will bebetween 50 kPa and 100 kPa.

The following tests should be specified:

- Transmissivity test with gradient i = 1performed as described in para. 5.3.a)Driven Tunnels above. A post-creep trans-missivity test should also be required, bythe method described in XP ENV 1897 ondetermination of creep properties undercompression classification index(G38126) (this standard is as yet experi-mental in France).

- Long term creep test under compressivestress according to the standard in force.

B2) Horizontal drainage

A low-gradient (i = 0.02 or 0.05 or as adefault value 0.1) transmissivity testshould be specified under 50 kPa stress.

6 - INTERCEPTION OFLOCALISED LEAKS

It may be necessary to intercept localisedinflows of water, for example, beforeapplying shotcrete or installing a geo-membrane waterproofing system in order

to allow these works to proceed normally.Two types of interceptor can be conside-red:

- Localised interception, with hemispheri-cal or cylindrical drains of suitable diame-ter for the flow rates involved.

- Area interception, mainly under theinvert, using geospacers or geocompo-sites whose characteristics are chosenwith reference to table 3.

6.1 - ROOF AND SIDEWALL

INTERCEPTORS

Temporary or permanent interceptionmay be considered, both in driven andcut-and-cover tunnels, under the follo-wing circumstances:

a) Before spraying shotcrete, to inter-cept localised leaks where the watermight adversely affect the bond with thesurrounding ground or support. In thiscase, semi-cylindrical flexible pipes areused, general made of PVC, with a flowsection habitually ranging from 6 cm2 to 20cm2. The pipes are held in place at inter-

vals with pats of rapid hardening cementor metal staples. They do not usually needto be connected to the geomembranewaterproofing system except if the lea-


122

CategoryDrainage Drain dia.capacity at 2% slope

1 0.1 l/s/m 100 mm

2 0.1 0.25 l/s/m 125 mm

3 0.25 0.5 l/s/m 150 mm

Table 3 - Classification of drainage geospacersand geocomposites


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kage exceeds 1 l/m, in which case, it isadvisable to use cylindrical PVC drains fortemporary installations or cylindrical HDPEdrains for permanent systems.

When using very large diameters to per-manently drain large flows from, for

example, intermittently or permanentlyflowing karsts under hydrostatic pressure,it is recommended a drain of at least100mm diameter, again in polyethylene,with a compressive strength of not lessthan 150 kPa.

As with any large permanent drainagesystem, drains for localised inflows areusually connected directly to the cleanwater main drainage system.

The connection of this type of circulardrain with the geomembrane of a geo-membrane waterproofing system must betreated as a singular point in the contrac-tors waterproofing detail design dra-wings. The connection with the geomem-brane is effected either by a metal system(flange-to-flange type) or (the most com-monly used arrangement) by a syntheticstub collar as shown in sketch 3 on dra-wing 1 below.

If a PVC drain provides the temporary leakinterception function, it must always befilled with quick setting cement or poly-mer resins after the permanent tunnellining has been concreted. If polymers are

used, it is recommended using two-partwater-reactive polyurethanes which aremuch less pervious than single-compo-nent polyurethanes. Whatever material isused, the method of filling the drain (typeof filling material, grouting pressure,

length of filled portion) must be the sub-ject of a specific operat ing proceduresubmitted to the Engineer for approval.

b) After spraying shotcrete on verti-

cal surfaces: in this case, inflow is inter-cepted and disposed of in the followingmanner:

- The same PVC or polyurethane pipes aregenerally used as before spraying shot-crete. In cut-and-cover tunnels, it is betterto use strips of geospacer of the cellulardrainage panel type as shown in sketch 1on drawing 1, because a 0.30m to 0.50mwidth is more efficient in intercepting lea-kage through a diaphragm wall joint.

The connection to the temporary or per-manent longitudinal drainage system ofthe geomembrane waterproofing systemcan be made as follows:

- either directly into the horizontal stripdrain of the geomembrane waterproofingsystem, for semi-cylindrical pipes andgeospacer strips,

- or directly (depending on drain diameterand flow rate) into the permanent drai-

nage system of the geomembrane water-proofing system or the clean water maindrainage system.

6.2 - TEMPORARY

INTERCEPTION ANDDRAINAGE OF INVERT IN

STRUCTURES RENDERED

COMPLETELY WATERTIGHT

BY A GEOMEMBRANE

WATERPROOFING SYSTEM

6.2.1. Driven tunnels

Generally, waterproofing is done in twostages:

- Stage 1: waterproof invert and bottoms

of sidewalls

- Stage 2: waterproof roof.

The invert is usually concreted before ins-talling the roof waterproofing system.

Temporary drainage problems very oftenonly concern intercepting and drainingwater flowing between the blindingconcrete and floor geomembrane water-proofing system during the variousconstruction phases.

Invert drainage can be provided in the fol-lowing ways, to suit construction method:



123

Drawing 1

TEMPORARY SIDEWALL

AND ROOF INTERCEPTION

Figure 1 - Drain panel strip drainage

Figure 2 - Half-round drain

Figure 3 - Connection between drain intercepting localisedleakage and geomenbrane waterproofing system


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a) Top to bottom method

Geomembrane waterproofing system ins-tallation and invert concreting proceedfrom the highest point on the longitudinaltunnel profile to the lowest.

There is a choice of three possibilitiesfrom the arrangements shown in drawing2 Invert drainage during construction.

Sketch 1: Cellular panel between blin-ding concrete and geomembrane water-proofing system. The width of the panel isgoverned by the drainage capacity requi-red. For example, a panel 20mm deep hasa capacity of 1.3 l/s per metre width. Thesketch shows the most commonly usedsystem because, apart from its goodhydraulic capacity, it has the advantage ofnot interfering with the installation of the

waterproofing system and fixing steelreinforcement.

Sketch 2: Flat gully drain at the lowestpoint of the invert between the blindingconcrete and geomembrane waterproo-fing system. Capacity is governed by theflow to be discharged (see table 3).Compared to the alternative in sketch 1,this arrangement is mostly used wherehigh inflows are encountered. Its disad-vantage is that it collects only part of theflow from the invert and hampers thework of installing the geomembrane

waterproofing system (at the transverseseaming locations) and steel fixing.

Sketch 3: Cylindrical drain in drainagetrench. This arrangement appears themost suitable for heavy inflows, firstlybecause of the discharge capacity offered

by the 150mm circular drain commonlyused, and more importantly, because itavoids all interference with geomembranewaterproofing system installation andsteel fixing.

b) Bottom to top methodGeomembrane waterproofing sys-tem installation and invert concre-ting proceed from the lowest pointon the longitudinal tunnel profile tothe highest.

The three arrangements alreadymentioned apply, although gene-rally, preference is given to

- sketch 1 for low inflows rates

- sketch 3 for high inflow rates withthe risk of pockets of water lifting

the geomembrane waterproofingsystem when pouring the invertconcrete.

6.2.2. Cut-and-cover tunnels

Temporary drainage problems onlyarise with supported-trench tunnels,where the sidewall support mayallow water to seep into the trench.There are two possible situations:

a) Tunnel above water table

This is the simplest case because noparticular drainage system is neededexcept perhaps for providing a man-hole or sump at low points to pumpout rainwater.

b) Tunnel below water table

This is the commonest situation, withinflow coming from the side supportand excavation bottom. After provi-ding the localised drainage arrange-ments described in para. 5.1. or

grouting the ground if inflows are tooheavy, the water collected isconveyed by a pair of lateral headers,as shown in sketch 4, drawing 2.

Circular drain diameter is chosenwith reference to drainage capacityshown in table 3.

The headers discharge into a sumpor manhole at the lowest point.

To avoid water pockets formingunder the geomembrane waterproo-fing system, it is important to pro-vide for permanent or intermittent

pumping, as dictated by the rate atwhich water collects in the sump ormanhole.

Where pump sumps are present, theconnection to the geomembrane water-proofing system must be made as shownin sketch 5, drawing 2.

The steel cover to the pump sump mustbe watertight all the time the tunnel is

exposed to hydrostatic pressure.


124

Photo 8 - TGV HST tunnel, Marseille.Temporary interception and drainage at invert

under geomembrane waterproofing system

Sketch 5 - Junction between geomembrane waterproofingsystem and temporary pump sump

Sketch 4 - Longitudinal drains in blinding concretein cut-and-cover tunnel

Sketch 3 - Drain embedded in blinding concreteor invert base concrete

Sketch 2 - Flat gully drain

Sketch 1 - Cellular drain pannel

Drawing 2

TEMPORARY INVERT DRAINAGE

DURING CONSTRUCTION


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7 - DRAINAGE SYSTEMASSOCIATED WITH AGEOMEMBRANE WATER-PROOFING SYSTEM ATBOTTOM OF TUNNEL ROOF

7.1. PURPOSE OF

DRAINAGE SYSTEM

These arrangements at the bottom ofeach roof arch collect seepage water flo-wing in from the surrounding ground, col-lected by the geomembrane waterproo-fing system on the extrados of thepermanent tunnel lining.

The water is then conveyed either by acombined or separate drainage system toa natural discharge point.

7.2 - CHANGES IN

DRAINAGE SYSTEM DESIGN

The appearance of these seepage collec-tion systems coincides with the use of thefirst synthetic geomembranes employedfor providing a tunnel with umbrella typeseepage control.

The design of these systems subsequentlyevolved over time to reflect the practicesand experience of engineers and respondto emerging concerns of owners regar-

ding their maintenance.This process was marked by the followingthree stages, which have led to profoundchanges in the design and function ofthese drainage systems.

a) Use of agricultural-type circulardrains

These 80mm dia. circular drains (with orwithout an outer covering of geotextile)around which a waterproofing geomem-brane is wrapped, were very widely used

in the nineteen-eighties.The drainage system was simply suspen-ded from the support, before concretingthe banquette, by means of PVC stripspinned to the support.

Generally the water drained towards theintrados of the lining was dischargeddirectly onto the footpath through plastictees at approximately ten metre intervals.This type of drainage system quickly cameup against problems, such as the fact ofhaving to follow the often tortuous confi-guration of the supports and the very

many places where head losses resultedfrom the changes of direction of the drain.In addition to this hydraulics problem,

there was the poor crushing strength ofthe drain, especially when concreting thetunnel lining when pressures of 100-150kPa from the green concrete are common.This frequently crushed the drain, sub-stantially reducing discharge capacity of

the drain.The first development of this type of drai-nage system, shown in sketch 1 on dra-wing 3 was to place the drain on top ofthe banquette; this kept it straight andthe waterproof geomembrane was laidover it before it was fixed in place on thebanquette. A shotcrete shell sprayed justbefore concreting the roof providedstrength for the drain during this phase ofthe works.

b) Generalisation of rigid straight

circular drainsThese 100mm dia. circular drains are pla-ced directly in a chase provided in the topof the banquette. Laying the drainstraight improved flow efficiency for thedrained water and reduced the risk of fou-ling (depending on water chemistry). Asshown in sketch 2, drawing 3, the water-proof geomembrane passes over thedrain to a point in the banquette where itis joined to a steel angleembedded in the concrete ora flat pinned to the concrete;

the steel angle and flat areboth co-rolled (galvanisedsteel + PVC on top face).

Only the top half of the drainhas slots spaced 120 apart,the lower half carrying awaythe water; flow is improved byplacing a horizontal strip ofgeospacer just above thedrainage system.

In this technique, the straightdrain connects every 40-50metres to a header, generally

placed under the tunnel road-way. This technique paved theway for the first CCTV inspec-tion and cleaning arrange-ments, usually comprising abay in the sidewall of variabledimensions, connected to thedrain by pipes inclined at anangle of 45.

Despite the undeniableimprovement from this typeof drainage system, it doeshave disadvantages, such as

with the branch pipes connec-ting to the under-road hea-der, since they are in danger

of being distorted by the concretingwork.

c) Circular drains replaced bygullies with rigid covers

In the nineteen-nineties, the trend in drai-nage system design was to place thewhole system inside the banquette.

This new technique consists of boxing-outthe shape of the future gully in the top ofthe banquette (so no drain pipe is nee-ded) covered with rigid material whichallows water to pass. The gully has theadvantage of allowing the flow section tobe easily increased by increasing gullydepth, with no impact on the width of thebanquette.

In tunnels where this technique is nowused, the covering materials may bemetal, concrete, or even a synthetic mate-rial capable of successfully withstandingloads applied by the green concrete,without any danger of crushing reducingthe flow section. The geomembranewaterproofing system runs on top of thegully cover and, as shown in sketch 3 ofdrawing 3, the geomembrane is anchoredeither on a co-rolled flat pinned to thebanquette, or (this was the case in some



125

Photo 9 - Puymorens tunnelRigid cover to drainage system using "metal tiles" withdrain strip


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of the A43 motorway tunnels in France) iswelded directly to synthetic grid materialforming the rigid gully cover. This type ofcover has the advantage of saving a fewcentimetres in width at the lift surface bet-ween the banquette and roof sidewall

concrete.

In nearly all road tunnels built or beingbuilt over the last five years, drainage ins-pection and maintenance bays are housedin the lining at drain level, as illustrated insketch 4, drawing 3.

These inspection bays provide for mainte-nance during operation of the structure.They are spaced 25m to 200m apart, on

the basis of the following criteria:

- flow rate of water intercepted

- physical and chemical characteristics of

the water (see design section below)

- means available and frequency of drain

system cleaning during the operational

life of the structure.


126

Sketch 1 - Agricultural drain on banquette

Sketch 2 - Straight drain in banquette concrete

Sketch 3Gully with rigid cover

Sketch 4 - Inspection & cleaning bayfor geomembrane waterproofing

Drawing 3

DRAINS ASSOCIATED

WITH GEOMEMBRANE

WATERPROOFING SYSTEM

AT BOTTOM OF ROOF


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14/19


Cement content will not usually be lessthan 350kg cement per m3 concrete.

Since porous concrete is intended to beexposed to a permanent flow of water, itis strongly recommended not to use evenC3A-poor ordinary (French designationCPA) or slag (CPJ) cement, in order toavoid any risk of the pores being partiallyor completely blocked by calcium carbo-nate precipitate.

Working group GT9 recommends avoi-ding any risk of clogging or loss ofstrength over time by preferably usingFrench designations CHF.CEMIII/B.ES orCLK.CEM.III/C.ES cement.

If supplies are not readily available, othercement types can be substituted by refer-ring to French standard P 18.011.Depending on the aggressivity of theenvironment as determined from thewater analyses, it might also be possibleto use either CLC.CEM.V/B cement,whose CaCO content is less than 50%, orCPJ.CEM.II/B containing less than 80%clinker.

c) Aggregate cementcompatibility

The cement and aggregate must not pro-duce disorders such as alkali aggregate

reaction liable to adversely affectconcrete integrity (French standard NFP18.541). In view of the permanent flow ofwater in porous concrete, such concretemust be classified as 'prevention class C'according to the 'Recommendations forthe prevention of distress due to alkaliaggregate reaction' issued by LCPC.

For this reason, aggregate for porousconcrete must qualify as 'non-reactive'(NR).

In the event of unavailability, 'potentially

reactive' (PR) or 'worst case potentiallyreactive' (PRP) aggregate may be used,subject to thorough investigation basedon experimental data acceptable to theEngineer. These tests are referred to inthe LCPC recommendations mentionedabove.

8.2 - POROUS CONCRETE

SPECIFICATIONS

Because of their high void ratios, porousconcretes are relatively low-strength. It is

therefore necessary to find a compromisebetween concrete strength and permea-bility.

a) Compressive strength

Twenty-eight day characteristic strengthfc 28 is measured on 16 x 32cm cylinders.

It is recommended specifying

fc 28 8 MPa

b) Permeability

Permeability is determined by measuringthe flow of water passing through a 16 x32cm cylinder.

The permeability coefficient is measuredwith the Darcy formula

V = KJ = K dhds

in which

K is the permeability coefficient

J = dh is the hydraulic gradientds

V is the flow velocity or flow per unit area.

It is recommended specifying

V 0.02 m/s, or V 0.20 l/dm2/s

8.3 - POROUS CONCRETE

DRAINAGE SYSTEM

The porous concrete must be accompa-nied by a drainage system to be able tomonitor, and if necessary, ensure the dura-bility of its performance. The design anddensity of this drainage system will ofcourse depend on the flow to be dischar-ged to the main tunnel clear water drai-nage system and the physical and chemi-cal characteristics of the interceptedwater. The tests mentioned in para. 7.3.above should be performed when desi-gning the drainage system.

The minimum requirements are as follows:

- drains, preferably polyethylene, to be

100mm minimum diameter with provisionfor CCTV inspection

- drainage system inspection chambersevery 25-50 metres at most (the actualspacing is determined on the basis of thechemical analyses mentioned above).

9 - PERMANENT DRAINAGESYSTEM FOR SIDEWALLAND ROOF JOINTS

These drainage systems are mainly inten-ded to intercept localised leaks throughthe contraction joints in undergroundstructures. They are generally used in

structures not waterproofed by means ofa geomembrane waterproofing system onthe extrados or waterproofing systembonded to the intrados.

They are most often employed to inter-cept and discharge the seepage which

usually occurs through joints in the side-walls of cut-and-cover tunnels in whichcast-in-place or prefabricated diaphragmwalls provide the permanent structuralsupport. Seepage is intercepted by thesesystems, generally installed vertically,discharging into open gullies at the side-wall toe which themselves discharge intothe main tunnel drainage system.

These drainage systems are also used,especially at tunnel roofs and cover dec-king, to repair defective intrados and

extrados waterproofing systems. This sub-ject will be dealt with at length in forthco-ming guidelines on treatment of leaks intounderground structures to be issued byworking group GT9 in 2001.

9.1 - DESCRIPTION OF

CONTRACTION JOINT

DRAINAGE SYSTEMS

Drawing 4 shows sketches of the varioustypes of drainage systems currently usedin underground structures.

The appropriate drainage system is cho-sen with reference to the following para-meters:

- physical and chemical characteristics ofthe water, which must be checked andassessed by the procedure described insection 7.3

- possible frost protection to drainage sys-tem

- seepage flow rate and pressure.

9.1.1 - Physical and chemical cha-

racteristics of seepage

If required by the results of the physicaland chemical analyses of the water fromthe surrounding ground, especially itscalco-carbonic aggressivity and total sus-pended solids, the permanent drainagesystem will have provision for inspectionand cleaning, or even removal and repla-cement.

This requirement also applies to integra-ted structure tunnels (e.g. diaphragmwalls with inner lining concealing the drai-

nage system). In such cases, it is recom-mended providing manholes, for inspec-ting and maintaining the drainage system.


128


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with leakage rates of less than 0.5 0.6litre-minute.

The strip is fastened to the backing withstainless steel screws and wall plugs,generally spaced 0.25m to 0.30m apart,and 80 x 8mm E26 galvanised mild steel

clamping strips.

9.1.2 - Frost protection to drainagesystem

In some situations, the drainage systemmay be exposed to sub-zero tempera-tures in winter months with consequenceswhich may have a disastrous effect onoperation of the structure.

This problem is influenced by the durationof freezing weather and the length of thetunnel. It may be confined to the portals

or cut-and-cover sections, or affect thewhole length of the tunnel.

Apart from their frost protection function,the drainage systems must have provisionfor dismantling or cleaning, depending onthe physical and chemical characteristicsof the seepage water mentioned above.

The following drainage systems may bespecified, depending on the intensity ofthe cold and seepage rates:

Temperature between 0 and 3C fornot more than 5 days, leakage less than0.5 litre/minute

- Manufactured strip with internal frostprotection layer and bolted flanges

Generally speaking, the arrangementshown in sketch 5 is adopted with, bet-ween the backing and the synthetic geo-membrane strip, another strip of thermalinsulation, commonly consisting of a 15-20mm thickness of closed-pore polyethy-lene foam weighing more than 30 kg/m3,whose thermal conductivity at 0C is lessthan 0.045 W/m/C.

The maintenance capability of this arran-

gement comes from the fact that theflange-type fixing system can be unmade.

- Prefabricated elastomer hollow strip(sketch 8)

This type of drainage system is made asfollows:

- Cut a chase with double-blade saw,usually 80mm deep and 100mm wide.

- Drill drain holes in bottom of chase, spa-ced approximately 2.00m c/c to suit lea-kage rates observed.

- Force-fit an EPDM or equivalent hollowformed strip into the chase, usually 3mmnarrower than the strip.

In order to prevent the strip being forcedout of the chase by accidental hydrostaticpressure from the ground or sucked outby the slipstream from lorries in road andmotorway tunnels, it is advisable to hold itin place with 5cm wide stainless steel

tabs, usually spaced 0.33m apart at side-walls and 0.25m apart at roof.

The hollow strip can be removed for drainmaintenance after removing these tabs.

Temperature between 3C and 15Cfor not more than 5 days, leakage bet-ween 0.5 and 1 litre/minute

- Drainage with chase and rigid thermalinsulant (sketch 9)

This type of drainage arrangementrequires prior study of thermal conditionsin order to determine the dimensions ofthe chase and shape of the polystyrene orpolyethylene foam strip acting as bothdrain and thermal insulant.

This high thermal capacity drain is gene-rally formed as follows:

- Cut a chase with a three-blade saw,usually 200mm deep and 150mm wide.

- Drill drain holes in bottom of chase, 30-50mm diameter, 1.00m to 1.50m long,spaced approximately 2.00m c/c.

- Possibly, finish chase sides with polymerresin-based mortar.

- Insert factory-formed closed-pore poly-ethylene or polystyrene foam strips, gluedin place with adhesive. Strip specificationsare as follows:

*Polystyrene foam to be class EM asdescribed in French standard NFT 56.201,minimum compressive strength not lessthan 90 kPa, thermal conductivity at 0Cless than 0.05 W/m/C.

*Wet-process cross-linked polyethy-

lene compressive strength to be not lessthan 90 kPa, thermal conductivity at 0Cto be less than 0.035 W/m/C.

To provide mechanical protection to thedrain strip in urban tunnels and prevent itbeing forced out of the slot by accidentalhydrostatic pressure, a 0.6mm stainlesssteel cover strip is recommended.

This type of drainage system usually hasan opening at the top for periodically flu-shing out the drain with low or mediumpressure water.

9.1.3 Drain discharge andhydrostatic pressure

If seepage water drain discharge andpressures are high, reference should bemade to the engineering arrangementsrecommended in section 6.1 of theseGuidelines.

The drainage arrangements illustrated infigure 7. are routinely used for this type ofleakage intercepted or draining to thedam drain system. The dimensions of thepolyethylene half-round gutter and chase

should be commensurate with the flowrate to be controlled.

The possibility of reinforcing with steelmesh the mortar or shotcrete backfill maybe considered with reference to (i) thedimensions of the chase and (ii) the maxi-mum pressure if the drain might acciden-tally run full.

If the water is very 'incrusting' or carries ahigh solid load, it is expressly recommen-ded to fit this type of drain with an orificefor periodically flushing it out with low ormedium pressure water.


130

Photo 14 Strasbourg Drain strips with rigidpolystyrene foam thermal insulant

Photo 13 Frejus ventilation shaft Drainage with cellularplate geospacers and polyethylene foam frost protection


17/19

9.2 - DRAINAGE SYSTEM

DESIGN

Dimensions and capacities of the perma-

nent drainage systems are based on the

following parameters:

- leakage rates to be intercepted and

discharged

- stresses which may or may not occur,due to the amplitude of joint movements(generally related to thermal gradient)

- physical and chemical characteristics ofthe leakage water, determined as descri-bed in section 7.3. above. For example,

with highly 'incrusting' or heavily loadedwater, it is recommended that the freedrain section should not be less than 120

cm2, and must always be accessible at the

top to monitor and periodically clean the

drain.

- thermal insulation which may or may not

be necessary, as dictated by a thermal

study lasting not less than 5 consecutivedays to determine the lowest tempera-

tures recorded at the site.



131

Drawing 4

PERMANENT SIDEWALL

AND ROOF DRAINAGE SYSTEMS

Sketch 1 - Drain strip with

sprayed concrete or mortar over

Sketch 2 - Manufactured stripdrain heat-welded to co-rolledsteel anchorage

Sketch 3 - Manufacture strip drainwith polymer adhesive


18/19



132

Drawing 4

PERMANENT SIDEWALL

AND ROOF DRAINAGE SYSTEMS

Sketch 4 - Internal drain with thin film cover bonded tobacking

Sketch 5 - Manufactured strip drain bolted along edges

Sketch 6 - Pre-formed drain pinned to backing

Sketch 7 - Half-round drain in chase

Sketch 8 - Formed hollow elastomer strip in chase

Sketch 9 - Drainage with chase and frost protection


19/19


BIBLIOGRAPHIEBIBLIOGRAPHIE

Fascicule 67 - Titre III du C.C.T.G. "Etanchit des ouvrages souterrains"

Recommandations de l'AFTES :

T.O.S. n 35 : Recommandations relatives aux joints d'tanchit dans les ouvrages souterrains T.O.S.n 82 : Recommandation sur les rparations d'tanchit en souterrains T.O.S.n 121 : Essais de poinonnement dynamique sur un D.E.G.

T.O.S.n 138 : Recommandations pour l'emploi de rondelles PVC pour les fixations d'un D.E.G.

T.O.S.n 150 : Recommandations pour la prparation des supports de tunnels recevant un dispositif d'tanchit par gomembrane.

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