us 0605a road drainage

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M a r c h 2 0 0 6

T r a n sl a t e A u gu s t 2 0 0 7

Technical guide

Road drainage


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The Technical Department for Transport, Roads and Bridges Engineering and Road Safety (Serviced'tudes techniques des routes et autoroutes - Stra) is a technical department within the Ministry ofTransport and Infrastructure. Its field of activities is the road, the transportation and the engineering

structures.

The S t ra s uppo r t s t he pub l i c ow ne r The Stra supplies State agencies and local communities (counties, large cities and urbancommunities) with informations, methodologies and tools suited to the specificities of the networks inorder to:

improve the projects quality; help with the asset management; define, apply and evaluate the public policies; guarantee the coherence of the road network and state of the art;

put forward the public interests, in particular within the framework of European standardization; bring an expertise on complex projects.

The S t ra , p roduc e r o f t he s ta te o f t he a r tWithin a very large scale, beyond the road and engineering structures, in the field of transport,intermodality, sustainable development, the Stra:

takes into account the needs of project owners and prime contractors, managers and operators; fosters the exchanges of experience; evaluates technical progress and the scientific results; develops knowledge and good practices through technical guides, softwares;

contributes to the training and information of the technical community.

The S t ra , a wo rk i n pa r tn e rs h ip The Stra associates all the players of the French road community to its action: operational services;research organizations; Scientific and Technical Network (Rseau Scientifique et Technique del'Equipement RST), in particular the Public Works Regional Engineering Offices (Centresd'tudes techniques de l'Equipement CETE), companies and professional organizations;motorway concessionary operators; other organizations such as French Rail Network Company(Rseau Ferr de France RFF) and French Waterways Network (Voies Navigables de France -VNF); Departments like the department for Ecology and Sustainable Development

The Stra regularly exchanges its experience and projects with its foreign counterparts, throughbilateral co-operations, presentations in conferences and congresses, by welcoming delegations,through missions and expertises in other countries. It takes part in the European standardizationcommissions and many authorities and international working groups. The Stra is an organization fortechnical approval, as an EOTA member (European Organization for Technical Approvals).


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This document is the translation of the work"Drainage routier" published in March 2006 underthe reference 0605.

Technical guide

Road drainage


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Road drainage Technical guide

"Tools" Collection Stra 4 septembre 2007

This Road Drainage guide has been written by a working group, including:

Marie-Odile Cavaills (Stra)

Yasmina Boussafir (CETE Normandie-Centre - LRPC Blois)

Marc Valin (CETE Nord-Picardie)

Francis Van laethem (CETE Nord-Picardie - LRPC Lille)

The team has relied heavily on the in-depth work carried out in 1997 by:

- Jean-Louis Paute (CETE de LOuest - LRPC Saint-Brieuc), with inputs from:

- Yves Arnaud (CETE de Lyon - LRPC Clermont-Ferrand),

- Jean-Louis Aussedat (Scetauroute),

- Vronique Berche (CETE Normandie-Centre - LRPC Saint-Quentin),

- Patrice Bioche (CETE de LOuest - LRPC Angers),

- Pierre-Yves Bot (DDE du Morbihan),

- Didier Giloppe (CETE Normandie-Centre),- Herv Havard (LCPC),

- Alain Quibel (CETE Normandie-Centre).

Notes on reading the guide

- Bibliographical references: the numbers in square brackets [ ] in the text relate to the documents listed inthe bibliography in Appendix 5

- The abbreviations encountered in the text are explained in Appendix 6.1

- References to the glossary: words or expressions marked by * in the text relate to terms explained inAppendix 6.2


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ContentsThe Stra supports the public owner............................................................................2The Stra, producer of the state of the art....................................................................2The Stra, a work in partnership..................................................................................2

Contents..................................................................................................................... 5

Introduction............................................................................................................ 10

Chapter 1................................................................................................................. 11

1 - General notions about drainage ...................................................................... 11

1.1 - Definition of drainage .................................................................................... 12

1.2 - Criteria to be considering during a drainage study.................................... 14

1.2.1 - When is drainage necessary? .................................................................... 14

1.2.2 - Climatic or meteorological context........................................................... 15

1.2.3 - Hydrogeological context (see Appendix 1)............................................... 17

1.2.4 - Type of subgrades and pavement courses................................................. 19

1.2.5 - Unusual pavement points .......................................................................... 19

1.3 - Effects of drainage on the environment ....................................................... 21

Chapter 2................................................................................................................. 22

2 - Drainage in a new road project ....................................................................... 22

2.1 - General dimensioning rules .......................................................................... 23

2.1.1 - Designing the drainage project.................................................................. 23

2.1.2 - Optimizing the road project layout ........................................................... 23

2.1.3 - Subsequent maintenance and repair .......................................................... 23

2.1.4 - Geometric characteristics of drainage systems ......................................... 23

2.1.5 - Rules for evacuating drainage water ......................................................... 24

2.1.6 - Environmental impacts.............................................................................. 25Impact on water..........................................................................................................25Waste management.....................................................................................................25

2.1.7 - Flow rate assessment................................................................................. 26Drainage of subgrades...............................................................................................26Pavement drainage.....................................................................................................27

2.2 - Earthworks..................................................................................................... 28

2.2.1 - Site capacity and traffic............................................................................. 28

2.2.2 - Improvement in the hydric state of soils to be re-used; ............................ 30

2.2.3 - Interception of water ingress in cut........................................................... 31Generalized water ingress and bank stabilization .....................................................31

Random water ingress................................................................................................31Unpredictable random water ingress.........................................................................31


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2.2.4 - Interception of water ingress in fill ........................................................... 33General case...............................................................................................................33Special case of natural slopes ....................................................................................33

2.3 - Pavement formation levels ............................................................................ 35

2.3.1. - Subformation (below capping level) (PST): ............................................ 35PST (Subformation (below capping level)) classification and improvement .............35Treatment of singular points in the longitudinal section............................................40

2.3.2 - Capping layer ............................................................................................ 42

2.4 - Pavement......................................................................................................... 44

2.4.1 - Drainage systems in pavement courses..................................................... 44

2.4.2 - Drainage systems at singular points.......................................................... 47Shoulder and emergency hard shoulder (BAU) .........................................................47Median........................................................................................................................47

Dividing island, directional island and obstacle island.............................................47Roundabout ................................................................................................................47

Chapter 3................................................................................................................. 48

3 - Drainage of an existing pavement ................................................................... 48

3.1 - Types of disorder encountered in pavements.............................................. 49

3.1.1 - Flexible pavements.................................................................................... 49

3.1.2 - Rigid or semi-rigid pavements.................................................................. 50

3.1.3 - Cement concrete pavements...................................................................... 50

3.1.4 - Bituminous material courses..................................................................... 50

3.1.5 - Modular material pavements (paving blocks and slabs) ........................... 50

3.1.6 - List of singular pavement points with respect to drainage........................ 50

3.2 - Analysis ........................................................................................................... 52

3.2.1 - Compiling information.............................................................................. 52

3.2.2 - Putting the analysis together ..................................................................... 54Marking systems.........................................................................................................54Table interpretation....................................................................................................54

Decision model...........................................................................................................55

3.3 - Definition of work solutions .......................................................................... 56

3.4 - Dimensioning or assessment of flow rates to be drained through the old pavement

.................................................................................................................................. 56

Chapter 4................................................................................................................. 58

4 - Characteristics of drainage systems and of materials used in them ............ 58

4.1 - Drainage structures and systems.................................................................. 59

4.1.1 - Deep ditches .............................................................................................. 60Objective.....................................................................................................................60Standard schemes.......................................................................................................60Operating method.......................................................................................................62


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Durability and maintenance.......................................................................................62Elements required for dimensioning ..........................................................................62

4.1.2 - Cutoff drains.............................................................................................. 63Objective.....................................................................................................................63Standard schemes.......................................................................................................63

Operating method.......................................................................................................63Shallow trench............................................................................................................................63Deep trench ................................................................................................................................63


4.1.3 Grips and draining stacks ............................................................................ 68Objective.....................................................................................................................68Standard schemes.......................................................................................................68Operating method.......................................................................................................68


4.1.4 - Fin drains at pavement edge (EDRC) ....................................................... 70Objective.....................................................................................................................70Standard schemes.......................................................................................................70Operating method.......................................................................................................72


4.1.5 - Draining courses........................................................................................ 73Objectives ...................................................................................................................73Standard schemes.......................................................................................................73Operating method.......................................................................................................74


4.1.6 - Shafts (vertical drainage) .......................................................................... 75Objective.....................................................................................................................75Standard schemes.......................................................................................................75Operating method.......................................................................................................77


4.1.7 - Bank stabilization systems (shields and stacks)........................................ 78Objective.....................................................................................................................78Standard schemes.......................................................................................................78

Operating method.......................................................................................................78Durability and maintenance.......................................................................................80Elements required for dimensioning ..........................................................................80

4.2 - Stipulations on materials............................................................................... 81

4.2.1 - Draining and filtering materials ................................................................ 81Filtering power...........................................................................................................81Draining power ..........................................................................................................81Other criteria..............................................................................................................83Comment on porous concretes ...................................................................................83

4.2.2 - Geotextiles and related products ............................................................... 84

Role in the drainage structures ..................................................................................84Main characteristics to be determined.......................................................................84Filtering function........................................................................................................................84Drainage function.......................................................................................................................84Mechanical characteristics .........................................................................................................84


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Elements required for choosing the geotextile ...........................................................88

4.2.3 - Drains or drain pipes ................................................................................. 90Role and types ............................................................................................................90Pre-coating.................................................................................................................92Dimensioning: Flow rate - Diameter - Slopes ...........................................................92

Durability and maintenance.......................................................................................924.3 - Ancillary structures ....................................................................................... 94

4.3.1 - Crossings.........................................................................................................944.3.2 - Inspection chambers .......................................................................................944.3.3 - Outlets .............................................................................................................94

Chapter 5................................................................................................................. 96

5 - Execution of work, application of quality assurance, completion of drainage work,

operation and maintenance ................................................................................... 96

5.1 - Execution of drainage work.......................................................................... 975.1.1 - Execution of work..................................................................................... 97

Optimum work period.................................................................................................97Managing interfaces...................................................................................................97

5.1.2 - Special drainage applications in earthworks phase................................... 98Surface maintenance ..................................................................................................98

Evacuation of rainwater.............................................................................................98A few rules for carrying out the work.......................................................................100

5.1.3 - Checks ..................................................................................................... 100

5.2 - Application of quality assurance in the drainage work............................ 1015.2.1 - Quality Assurance Plan Organizational Scheme (SOPAQ).................... 101

5.2.2 - Site-specific Quality Assurance Plan (PAQ) .......................................... 101

5.2.3 - Quality Master Plan (SDQ) ................................................................... 103

5.3 - Completion of drainage work ..................................................................... 104

5.3.1 - Acceptance .............................................................................................. 104

5.3.2 - Handover of as-built drawing.................................................................. 104

5.4 - Drainage system operation and maintenance............................................ 104

5.4.1 - Inspection of structure with as-built drawing.......................................... 104

5.4.2 - Establishment of the zero point in the absence of an as-built drawing... 104

5.4.3 - Maintenance and repair work ................................................................ 105Monitoring................................................................................................................105

Repairs and repair frequency...................................................................................105

Appendices ............................................................................................................ 106

Appendix 1 - Special hydrogeological* studies.................................................. 107

G11 mission, preliminary feasibility study ........................................................ 107G12 standard mission, geotechnical* feasibility study ...................................... 107

G2 standard mission, geotechnical* feasibility study ........................................ 107


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Appendix 2 - Improvement in hydric conditions of materials ......................... 108

Appendix 3 - Assessment of flow rates to be drained........................................ 110

3.1 - Through subgrades..................................................................................... 110

3.2 - Through the pavement................................................................................ 1123.2.1 - Diffuse infiltrations via the surface courses..................................................1123.2.2 - Infiltration through the cracks (see Diagram 45).........................................114

Sample estimation of a drainage system dimensioning. ..........................................................115Checking the utility of draining ...............................................................................................115

Appendix 4 - Elements to establish the special technical clauses (CCTP)...... 116

1 - Description of work to be carried out ........................................................... 1161.1 - Localization of work.........................................................................................1161.2 - General description of work reserved for the contractor ................................1161.3 - Work not included in the contract....................................................................116

1.4 - References to drawings extracted from the capital investment project...... 1162 - Quality assurance .......................................................................................... 116

3 - Material, product and component specifications .......................................... 1163.1 - Required characteristics of drainage systems..................................................1163.2 - Materials for earthworks and backfill..............................................................1163.3 - Ancillary structures..........................................................................................117

4 - Work execution method (example for cutoff drains and EDRC) ................. 1174.1 - Specifications on installation and setting out of systems .................................1174.2. - Acceptance and storage of supplies and materials .........................................1174.3 - Trench execution method .................................................................................117

4.4 - Laying specifications........................................................................................1174.5 - Compacting specifications...............................................................................1174.6 - Dealing with singular points............................................................................1174.7 - Installing inspection chambers, connections to outlets....................................1174.8 - Ancillary work..................................................................................................1174.9 - Using the road during the work .......................................................................118

5 - Checks and quality ........................................................................................ 1185.1 - Compacting reference areas ............................................................................1185.2 - Checks at hold points .......................................................................................118

Appendix 5 - Bibliography .................................................................................. 118

Standards: ........................................................................................................... 118Technical documents:......................................................................................... 118

For information:.................................................................................................. 119

Appendix 6 - Abbreviations and glossary .......................................................... 120

6.1 - Abbreviations ............................................................................................. 120

6.2 - Glossary...................................................................................................... 120


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IntroductionVarying amounts of water are found in the road environment, be it in the cut and fill banks, inside thepavement itself or in the underlying soils or adjacent shoulders.

A well-drained pavement has better mechanical behavior in a subgrade whose bearing capacity is alsoimproved. The result of pavement and formation levels containing less water throughout the climatic cyclesis a considerable increase in pavement lifetime, less frequent maintenance sequences and effectiveprotection against the highly-damaging effects of freezing and thawing phenomena.

The terms "draining" and "drainage" are used to describe both the evacuation of run-off water and theelimination of subsurface water. To avoid any confusion in the purpose and design of systems, cleardistinction is made between the specific functions of internal pavement draining systems and surfacedrainage, as indicated in Chapter 1.

This guide is the first methods document on road drainage to encourage taking drainage needs in roadworks systematically in account. It suggests solutions based on the type of structure, siting, dimensioningand maintenance for new road projects, including earthworks and for existing pavements.

This document is intended for Project Engineers and Clients, managers, Design Offices and public workscontractors involved in studying, creating and maintaining road drainage.


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Chapter 1

1 - General notions about drainage


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1.1 - Definition of drainageRoad drainage relates to the collection and evacuation of water present in the subgrade and pavements. Itis one of three aspects of road drainage (see Technical Guide [21]), along with surface water evacuation

(surface drainage) and re-routing natural flows.Drainage is an essential component in the pavement's good mechanical behavior and thus makes asignificant contribution to the durability of road structures.

Subsurface water to be drained comes from:

infiltrations through the pavement towards the pavement layers and pavement/subgrade interfaces;

infiltrations from the shoulders towards the pavement layers and pavement/subgrade interfaces fed bythe formation level;

water ingress from the lateral surroundings towards the pavement/subgrade interfaces and the subgradeoriginating from catchment areas, cuts and discharges from water tables.

Although the various drainage systems frequently use common outlets, it is essential to distinguish

between them, for they have distinctive functions: in particular, the drainage network conveying a so-called"clean" water (not soiled) must not in any circumstances be disturbed by run-off water, which is frequentlypolluted (mud, oils, vegetation, etc.) and flows faster (to prevent loading).

Diagram 1: distinction between the various road drainage systems

Prcipitations RainfallRuissellement Run offFoss de crte Ditch on crest

Evacuation EvacuationInfiltrations dans la structure Infiltrations in the structureDEBLAI CUTInfiltrations InfiltrationsREMBLAI FILL


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Drainage chausse Pavement drainageDrainage terrassement selon contextehydrogologique

Earthworks drainage depending onhydrogeological context

Drainage commun chausse + terrain Common pavement + ground drainageEquilibre avec une nappe ventuelle Equilibrium with any water table

Remontes capillaires Capillary risesNappe ou circulation d'eau sous-jacente Water table or underlying water circulation


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1.2 - Criteria to be considering during a drainage study

1.2.1 - When is dr ainage necessary ?

The French climate imposes systematic draining of the subgrades, capping layer and pavement.

It is however possible to avoid mandatory drainage in the following cases:

favorable climate context; in the earthworks phase, the drainage must be analyzed with specificreference to the hydrogeological context (see1.2.2);

very light heavy traffic (T5) for a correctly-dimensioned pavement;

favorable hydrogeological context, subgrade and type of pavement courses in the short and long term(see1.2.3).

Diagram 2: subgrade, capping layer and pavement drainage.*Ruissellements Run offDblai CutContexte climatique Climatic contextIndice d'humidit Humidity indexIntensit du gel Frost intensityVgtation VegetationCouche de chausse Pavement courseSols support SubgradesGel FrostEquilibre avec une nappe ventuelle Equilibrium with any water tableRemblai FillNature des sols support et couches dechausses

Type of subgrades and pavement courses

Contexte hydrogologique Hydrogeological contextNappes, zones humides, sources Water tables, wetlands, springs


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1.2.2 - Cl im at ic or meteoro log i ca l cont extThe mapping is based on the siting and density of meteorological stations.

Studies have shown that the French climate is normally wet to very wet (seemap 1), with rare dry areas.However, whatever the type of climate, humidity spread throughout the seasonal cycle, with heavyconcentrations over a few months, accentuates the risk of damage to pavements from moisture.

The degree of humidity in soils and pavement materials is linked to the climate and its fluctuations. Waterreduces the mechanical characteristics of soils and materials (see 3.1).

This characteristic worsens when temperatures drop below freezing and the water freezes in the structures(seemap 2). This map takes into account the maximum frost index (exceptionally hard winter) read in 95stations during the period 1951-1991.

The designer is advised to take the least favorable criterion on the edge of a zone.

Two contexts are possible depending on the geographical location of the project:

where drainage can be avoided: dry climatic variations with moderate climatic variations;

where drainage should be systematically planned: in wet to very wet climatic zones.

Map 1: humidity distribution in France. Map based on Mto France study [16].

The value of climatic indices on a particular site may be calculated more accurately when neighboring meteorological readings

are available. However, this greater accuracy can only be illusory, as the climate at a given point undergoes major fluctuationsand is not reproduced identically every year.

Lgende Keytrs humides avec de fortes variationssaisonnires

very humid with major seasonal variations


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humide avec de fortes variations saisonnires humid with major seasonal variationssche avec de fortes variations saisonnires dry with major seasonal variationstrs humide avec variations saisonniresmodres

very humid with moderate seasonalvariations

sche avec variations saisonnires modres dry with moderate seasonal variations

trs humide sans variations saisonnires very humid with no seasonal variations


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In conclusion, drainage is necessary in the majority of cases, except for dry zones with moderateseasonal variations (southern Corsica, part of the Bouches-du-Rhne and part of Alsace (seemap 1).

1.2.3 - Hydrogeolog i ca l co ntext (see Appendix 1).This context must at least be defined in the geotechnical study. Additional studies will be performed onspecial cases.

The hydrogeological context is:

favorable when the pavement does not intercept any known hydrogeological system. This is oftenthe case of a pavement with long sections filled in or at the top of a relief.

unfavorable: when the pavement intercepts hydrogeological systems with varying degrees ofdurability or size. This scenario is frequently encountered in a succession of cut and fill or for mixed-profile pavements. This is made worse when the crossfall accentuates water concentration in somezones;

very unfavorable when the alignment definitely intercepts known hydrogeological systems. These aretypically pavements with skimming profile on the plain, pavements in cuts and mixed-profilepavements.

Note that depending on project progress, the context can become favorable by altering the geometriccriteria of the alignment: by raising the red line*, creating fills, modifying the alignment siting, etc.

Map 2: variation of atmospheric frost index*. Map based on Mto France study [16].

I 250 : regions marked by long winters with low temperatures (frost). The frost front penetrates in depth in the soil, hence

damage during the thaw. 100I 250 : regions where the temperature fluctuates around 0C. Some years the frost-

thaw cycles can affect the road foundation materials. I < 100 : regions marked by mild winters. Moderate frosts only have an


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impact on certain flexible, lightweight pavement structures.

Indice de gel Frost indexC x jours C x days


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1.2.4 - Type of su bgr ades and pavement c our sesSubgrades

The bearing capacity performance of some subgrades can be seen to fall over time due to water infiltrationor rises in water table. These are "water-sensitive" soils. This characteristic is taken into account whendimensioning the subformation (below capping level) and the thickness of the capping form.

Distinction must be made between soils of different types (seeTable 14 in Appendix 2):

favorable (porous soil): these are soils insensitive to water which require no special drainageprecautions (D, B1, B3, some C1 and C2);

unfavorable (water-sensitive soils): their hydric state can improve or remain constant under the effectof draining action, within reasonable timescales (A1, B2, B4, B5 and some B6);

very unfavorable (impermeable soils): the water content of these water-sensitive soils hardly diminishesthrough draining action if they are in wet hydric states initially, whilst remaining within reasonable deadlines(A2, A3, A4, some B5 and B6).

Water circulates in rocks through cracks or general discontinuities (stratification, fracturing, etc.).

Few rocks disaggregate under the effect of water (unlike soil), but site traffic, blasting, re-use operationsand so on can change the part involved by the earthworks. In this case, the rocky zone likely to changewill be assimilated with a soil by the geotechnical engineer and classified under the same criteria.

The following distribution is frequently accepted:

favorable: certain R1, certain R2, certain R4 and certain R6;

unfavorable: R11, R21, R22, R32, R33, R41, R42, R61 and R62;

very unfavorable: R12, R13, R23, R31, R34, R5, certain R43 and R63.

Materials making up the pavement courses

The mechanical performances of these materials are normally reduced in the presence of water. Thechange varies, however, depending on the technique adopted and pathologies also appear based on the

type of pavement technique.Distinction is made between techniques:

favorable: these are structures that are hardly influenced by the presence of water when they areconstructed correctly such as material courses treated with hydrocarbon binder;

unfavorable: materials processed with hydrocarbon binders and concrete courses have specialdrainage needs relating to the appearance of cracks;

very unfavorable: this involves untreated graded aggregates, where performance depends greatly onthe water content.

1.2.5 - Unusu al pavement po in ts

Some parts of a structure require draining more than others regardless of the meteorological andhydrogeological* criteria or types of material. For example:

medians and central islands;

cut and fill transition zones;

low points in longitudinal section;

cut crossfall zones.


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Photo 1: water accumulated in the central

island exists by the lowest point and flows

onto the pavement. (Photo CETENormandie

- Centre/LRPCBlois)


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1.3 - Effects of drainage on the environmentDrainage water is so-called "clean" (not soiled by the collection system) which is evacuated into the naturalenvironment via an outlet.

The environment is modified in varying degrees by building the drainage structures. The designer must beaware of:

regulations in force [15];

State undertakings under the project in terms of the environmental protection and also with respectto local residents.

Some negative effects from drainage and earthworks:

the effect on vegetation, particularly shrubs near the structures through drying out of soils (and largeoak trees that were marked for preservation on the edge of the cut have rapidly turned into a majorhazard for users through decline and the risk of falling);

reduction of wet zones which have been dried out (not dealt with in this guide);

settling of structures built on barely compacted soils, host to a water table lowered without specialcare (not dealt with in this guide);

altered water flow directions through barriers.


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Chapter 2

2 - Drainage in a new road project


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There are three stages in a new road project:

the earthworks;

the formation levels (upper earthworks and capping layer);

the pavements.

This chapter gives the general dimensioning rules and describes the draining requirements and specificdimensioning rules for each stage.

2.1 - General dimensioning rules

2.1.1 - Desi gni ng t he drainage pro jectThe drainage must be examined at each project phase from the preliminary study until the work is carriedout. The study levels relating to the drainage project are defined in Appendix 1.

The design trend nowadays is to "stick" to the natural landscape as far as possible (objectives of roadcalming, landscape integration, etc.).

2.1.2 - Opt im iz ing t he road pr o ject layoutThe designer can adapt his project for optimum drainage by modifying the red line* and avoiding:

long upwards gradients;

slopes < 0.5%;

low points in cut zone;

cuts in water tables;

wet zones.

2.1.3 - Subs equent m aint enance and repairThe effect of drainage is taken into account in the mechanical dimensioning of the roadbed for its long-term operation; it is therefore essential to organize the verification and schedule the maintenance of thedrainage system to increase its lifetime.

2.1.4 - Geometr i c c haracter is t ic s o f dr a inage systemsThe geometric characteristics of drainage systems (height, depth, slope) depend on:

the part of the structure to be drained (road foundation, shoulder, median, cut, structure abutments, etc.),

the drainage system adopted;

restrictions in project execution;

the amounts of water to be evacuated;

taking the pavement longitudinal slope into account;

taking crossfalls into account, especially those accentuating concentrations of moisture at the lowpoints;

the choice of the location of drainage systems in the cross section;

the location of possible outlets.

A description of the various drainage structures and an indication of the orders of magnitude of thedimensions of these structures can be found in Chapter 4.

The slope - a major parameter - must reconcile the following essential requirements:

a minimum slope > 2% is necessary. Less slope (up to 0.5%) requires drains to be over-dimensioned andmore frequent maintenance. These values can vary from one structure to the next (seeChapter 4);

too pronounced a slope (more than 5 to 10%), as found in mountain areas, for example, createsexcessive water speeds, especially with respect to problems of structure erosion (ditches, banks, etc.)which dictate suitable precautions (stabilized ditches, partitioning of ditches, energy dissipationstructures and more crossings).


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2.1.5 - Rules fo r evacuat i ng d rain age waterIt is normally advantageous to avoid mixing drainage water, evacuated in priority towards the naturalenvironment, and road run-off water in order to optimize structure dimensioning. In some cases (e.g. insouthern France), drainage water added to storm water treatment basins can make them more efficient(better water oxygenation and maintaining dead storage).

in cutThe water is evacuated at the exit of the cut trench. Like the drainage systems, the collector installed atthe edge of the cut roadbed must be connected to a drain at the foot of the fill bank (ditch, trickle channel,etc.) which leads to a natural outlet. in fillThe water drained by the collector is evacuated at the foot of the fill through drainage outfalls aligned tothe longitudinal slope (the lesser the slope, the lesser the distance must be between outfalls) and to theminimum in the low points. in mixed profileWater collected in cut are directed towards the ditch at the foot of the fill through under-pavementcrossings and returned to the banks by drainage outfalls, as for fills.


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2.1.6 - Envi ro nment al impact s

Impac t on w a te r

Planned drainage activities and systems in theconstruction of road infrastructures are governed by theauthorizations and declarations provided for under ArticlesL.214.1 to L.214.6 of the Environmental Code (formerArticle 10 of Law 92-3 on water of 3 January 1992). Waterpolicing applies to all surface, groundwater, state- orprivately-owned, coastal maritime waters and wetlands.

Decree 93-743 of 29 March 1993 sets the nomenclature ofoperations thus subject to authorization (A) anddeclaration (D). The headings likely to involve drainagework more especially are as follows:

Reminder: creating a drainage network alters the water

content in the surrounding soils and diverts or interruptsunderground flows. These disturbances modify the siteecology. These headings are designed to protect andpreserve groundwater bodies which are potentially major,fragile water resources. Similarly, protecting wetlands is anational priority (environments with huge diversity andecological wealth). It is therefore important to prevent orlimit their degradation.

Overall, drainage culminates in water originating fromvarying points of the land being concentrated towards theoutlet. Water inputs are therefore greatly increased at agiven point and there is no harm in assessing this action

particularly in sensitive ground to avoid disordersappearing downstream.

Ideally, the discharge point chosen or found on the site isa natural, already-existing flow zone, with no sign ofdisorder and capable of absorbing the drained water.

It is also useful to channel the drainage water from theoutlet to the natural receiving flow for a few meters toprevent in particular problems of erosion or the effect ofnatural deposits.

In the event of accidental pollution, the manager mustmonitor the outlets and discharge points.

Waste management

This involves materials extracted during work which in anideal scenario will be re-used. Excess cuts from the sitefootprint must be evacuated in accordance with the WasteEvacuation and Management Organization SchemeSOGED (seeCCTP type earthworks).

- "1.1.0. Sounding, borehole, building of shaft or

underground structure not intended for domesticuse, created for the purposes of research ormonitoring or groundwaters or for temporary or

permanent sampling in the groundwaters,

including in the water course water tables D".

- "1.1.1. Permanent or temporary samplestaken from a borehole, shaft or underground

structure in an aquifer system excluding watercourse water tables by pumping, draining,diversion or any other process: 1. Total,maximum capacity of sampling facilities greater

than or equal to 80 m3/hourA

2. Total, maximum capacity of samplingfacilities greater than 8 m

3/hour but less than 80

m3/h. D

- 4.1.0. Drying, priming, surface sealing, fillingof wetlands and marshes, the dried or primed

zone being:

1. Greater than or equal to 1 ha A

2. Greater than 0.1 ha but less than 1 ha D"

- 4.2.0*. Creation of drainage networks to draina surface area of:

1. Greater than or equal to 100 ha A

2. Greater than 20 ha but less than 100 ha D

- 4.3.0. Structures, installations, works allowing full water sampling in a zone where constantquantitative distribution measurements, in

particular under Article 8-2 of the Law of 3 January 1992 on water, have provided for the

lowering of thresholds:

1. Capacity greater than or equal to 8 m3/hourA

2. In other cases D"


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2.1.7 - Flo w r ate ass essment

Dra inage o f s ubg rades

The diagrams grouped in Appendix 3.1, with just one presented below (see Diagram 3), indicate the

orders of magnitude of the drainage flow rates (in liters per hour and for a length of 100 m) for a cutoffdrain capturing from a single side in miscellaneous contexts. These are distinguished by the permeabilityof the medium, the depth of the water table and of the drawdown (seeDiagram 4).

The diagrams show that for the majority of soils, regardless of the geometry of the water table or thedrawdown system, current drains 100-150 in diameter mm are theoretically largely over-dimensioned. Inpractice, other phenomena have to be considered:

the reduction in the useful diameter of the drain by out-of-roundness, crushing or obstruction(accumulation of settled sediments, in particular for counterslopes, or the presence of roots, animals,etc.);

ingress of unwanted or unforeseen water: for example, if the drainage network is installed in theearthworks phase, it is frequently not just the only outlet for the groundwaters but also for the storm

water during this period. In this case, the drain diameter is too small and the risk of obstruction frommud is very real;

difficulties in assessing soil permeability.

For all these reasons, we suggest:

using drains 100 or 150 mm in diameter for all common scenarios (interior drawdown at 2 m and soilswith permeability less than or equal to 1.10

-5m/s);

determining the necessary diameter after a specific hydrogeological study for all other scenarios. Thisstudy will determine in particular the overdimensioning to be considered for the drain diameter (withmultiplication coefficient for flow rates to 3).

Diagram 3: water table flow rates according to soil permeability

for a trench side and a length of 100 m

Diagram 4: flow rates according to the permeability of the

medium, the depth of the water table and the drawdown.Diagram 3 Diagram 3

Dbits en l'heure pour 100 ml Flow rates in one hour for 100 mlEpaisseur de la nappe Water table thicknessDiamtre drain Drain diameterrabattement drawdownPermabilit des sols en m/s Soil permeability in m/sDiagram 4 Diagram 4

Dbits Flow ratesRabattement DrawdownAquifre AquiferEpaisseur de la nappe Water table thicknessImpermable Impermeable


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Pav emen t d ra i nage

(seeAppendix 3.2 Assessment of flow rates to be drained through the pavement).

FT : transverse crack

PL : longitudinal crack

P : rainfall

FT : transverse crack

PL : longitudinal crack

P : rainfall

Diagram 5: schematic diagram of the various types of flow rates under pavements and shoulder. Qe, through the surface course; Qft, via the transverse cracks and Qfl via the longitudinal cracks; Qr, at the pavement-shoulder interface; Qa, corresponding to inputs from the shoulder and the lateral catchment area; Qi flow rates transiting at the interfaces; Qs flow rates feeding the subgrade.

The estimation by excess of the infiltration water flow rate is given by the sum:

Q = Qe + Qfl + Qft + Qr + Qa

New or repaired pavement

DesignationMinimum

assessed flow

rate

Maximum

assessed flow

rate

Theoretical

maximum flow

rate(1)

QeFlow rate resulting from the permeabilityof the asphalt (changing with age and 0.0125 l/h 3.75 l/h

125 l/h(porous

QflFlow rate proportional to the number oftransverse cracks and their opening

1.25 l/h 25 l/h 250 l/h

QflFlow rate proportional to the number oflongitudinal cracks (including Qr axis andedge) and their opening

1.00 l/h 15 l/h 150 l/h

QaFlow rate proportional to the permeabilityof the shoulder materials

1.80 l/h 18 l/h 18 l/h

QTotal flow rate evacuated by thepavement per linear meter

4.06 l/h 61.75 l/h 543 l/h

Total flow rate evacuated by thepavement per 100 linear meters

406 l/h 6,175 l/h 54,300 l/h

Table 1: assessment of infiltration water flow rates.(1) this scenario assumes that all the water from falling rain infiltrates a half-pavement of 3.50 m

The flow rate assessment culminates in a range of 400 to 6,000 l/h for 100 linear meters; for new andrepaired pavements the use of drains or drainage systems equivalent to 100 to 150 mm should suffice.


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2.2 - EarthworksIn the earthworks phase, the difficulties (machine progress, compacting, roadbed and bank stability) moreoften than not relate to excessive water. It is therefore obviously a distinct advantage to carry out this

phase in dry periods.Drainage in this phase can in part remedy the difficulties encountered, but when this need for drainageappears during the work phase and has not been scheduled in the project it is frequently too late to takeeffective action: the improvement actions will have a bearing on costs and timescales.

Drainage hypotheses should therefore be defined accurately during project design in conjunction withmeteorological and hydrogeological forecasts for the site (see chapter 1-2 Criteria to be consideredduring a drainage study and Diagram 6).

The following objectives are pursued with drainage techniques during this work phase:

1 - Site bearing capacity and traffic;

2 - Improvement in the hydric state of materials to be extracted;

3 - Interception of water ingress in cut;4 - Interception of water ingress in fill (stabilization of cutting banks and sometimes natural slopes).

2.2.1 - Si te capacit y and t raf f i cThe bearing capacity varies according to the water content, above all for compressible soils that aredifficult to drain.

A variety of solutions may be suggested depending on the type of soil, the position of the water table andthe meteorological conditions.

1st drainage by ditches or lateral trenches for porous soils; the efficiency of this system will alsodepend on the state of the surface, hence the importance of shaping the surface (cross slope).

there are two possibilities when the drainage is insufficient to improve the bearing capacity: introducing non-water-sensitive materials into the road for construction traffic:- sufficiently dimensioned, this road could be re-used in the capping layer;- frequently built using draining gravelly materials (water trap), the road should be designed for rapidevacuation of infiltrated waters (accentuated rooftop profile and side ditches, even subsoil drains on thebase); processing soils according to needs and possibilities.

Remember that good practices impose maintaining outlets and ditches and repairing surfaces (shaping,smoothing and compacting) seeCCTG Travaux [8].

The special case of compressible zones must be dealt with separately: although the problem of bearingcapacity can be solved by building thick roads as work progresses (possibly after cleaning), the problems

raised by the amplitude and length of settling under excess load frequently forces the use of specialdrainage techniques; these are designed to purge the water from the subgrade more rapidly via verticaldrains or more highly-specialized techniques. These special methods are not dealt with in this guide [14].


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Diagram 6: the three main causes of a need for drainage in the earthworks phase

Mtorologie dfavorable Unfavourable meteorologyCirculation d'eau libre (zones humides, nappephratique) en surface ou dans un dblai

Free water circulation (wetlands, water table)on the surface or in a cut

BESOIN DE DRAINAGE NEED FOR DRAINAGEMatriaux en tats hydriques humides Materials in humid hydric states


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2.2.2 - Impro vement in th e hydr i c s t a te o f so i l s to be re-used;Improvement is only possible within materials conducive to drainage and on condition that there issufficient drainage time before the material is extracted (see Appendix 2). This requires installing thedrainage system well before the earthworks themselves.

Do not however expect a miracle: the timescales are too long and the suction too high in the majority ofcompressible soils, with the result that it is impossible to achieve sufficient drop in water content for re-useas is (even if the drainage provides a genuine improvement).

Complementary solutions consist of encouraging evaporation (swelling - installation in compressible andextended layers), mixing with drier materials, treating with hydraulic binder (usually quicklime) or ofapplying the material too wet in suitable conditions (average or low compacting but in return limitedthicknesses to avoid too much settling). These techniques are expanded in the guide Creating fills andcapping layers [9].

The most common systems for improving the hydric state of cut materials, fill subgrades and soils used fora construction traffic road are:

deep ditches;

fin or cutoff drains in the bank (which can sometimes be installed before earthworks, even without agravity outlet, by pumping or negative pressure - vacuum pump);

vertical drainage (seeTable 2).

Drainage system Conditions for use Disadvantages

Deep ditch

System suitable for pre-earthworks to improvehydric conditions of soils with average to lowpermeability lending themselves to drainage(Table 14, Appendix 2).May be created using traditional methods, for

operating depths

5 meters (possible 6 or 7methods depending on the shovels).Suitable for slopes in the order of 2.5% or less.

Generates cut materials forevacuation or storage.Site safety organization (restrictedaccess, signaling, suitable bankslope, etc.)

Reduction in overall volume of re-usable cut.Not suitable for easily-erodedmaterials.

Trench or fin drain

Preferred system when long-term cutting bankstabilization or reduced interstitial pressure isalso an issue.Suitable for stabilizing homogeneous materialsand lowering a water level.Design for common structures up to 6 or 7meters deep and up to 20 meters with specialequipment (cutting machine).Suitable for all longitudinal section slopes.

Generates little cut and integrates discreetlywith the project.Can operate temporarily without gravity outlet(vacuum pump).

Needs specific equipment andmaterial resources which must beplanned in advance.Needs as-built drawings andscheduled maintenance.

Vertical drainage bypumping

Suitable for drawdown of water table located inalternating permeable and barely permeablelayers.Above all suitable for very permeable soilswhere flow rates are high.

Needs specific equipment andmaterial resources which must beplanned in advance.Site restrictions.

Vertical drainage by

wellpoint

Suitable for water table drawdown in sandymaterials and may show bubbling* phenomena.

Needs specific equipmentresources which must be planned

in advance. Site restrictions.

Table 2: systems for improving hydric states of soils (the most commonly used)


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2.2.3 - In tercept io n of water ingr ess in c ut

Genera l i z ed wa te r i ng res s and bank s tab i l i z a t i on

This is the traditional scenario where the "red line" intercepts the "blue line", i.e. when the earthworks

descend below the level of the water table. Earthwork conditions could be improved partly if:

the longitudinal section is extended to its maximum taking into account the landscape integrationobjectives;

the drainage network is installed early enough (see previous );

the earthworks are scheduled for low water periods1.

A special hydrogeological study is essential in all cases of this type (see Appendix 1). It will specify inparticular the flow rates and bank stability conditions and will suggest suitable counter-measures (watertable drawdown, drainage shield, etc.).

The solutions as the same as for the previous scenario 2.2.2 (ditches, trenches, shafts, etc.). The basicdifference lies in the slope stabilization: although the previous solutions can cut the water ingress, theycannot necessarily guarantee bank stability (particularly for the ditches).

Cutoff drains, lateral ditches and the installation of such systems as shields and draining stacks canprovide this stability (note that it can sometimes be possible to apply these systems to one side only whenthe flow directions are clear and cut across the cut).

Remember also that the "damproof course" solution can sometimes be an interesting variant (particularly ifthe course can also act as retaining structure - sheet piling, diaphragm walls) (seeDiagram 7).

Random w a te r i ng res s

The draining stack is the most frequent solution applied in the most common random water inflows(springs, fault zone, etc.). The water is evacuated towards a draining collector at the foot of the bank linkedto an outlet.

When faced with certain rocky materials where flows take preferential paths, for example limestones andtheir karstic networks, these special cases call on specific solutions (ditches, collectors, shafts) which arenot dealt with in this guide.

Unpred i c tab le random wa te r i ng res s

The geotechnical study does not always localize all the random water ingress. In the simplest scenarios,the drainage structures could be installed and dimensioned definitively during the earthworks. The contractwould provide for an estimated quantity, with greater detail provided as work progresses by contradictoryobservations.

In addition, when potential disorders are free from danger for both the structure and users and the wateringress are not visible when work takes place, one pragmatic solution is also to carry out the minimum

work, namely simple shaping, on the banks and let one winter go by.This can localize the water ingress accurately (frozen water, higher flow rates, appearance of firstdisorders) before carrying out drainage work.

Photo 2: ditch, used during the earthworks phase and part of

Diagram 7: interception of the water table, lateral damproofing

and stabilization of cutting banks by damproof course or

damproof retaining structure


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the final project, intercepting water ingress circulating at the

interface between sands and a clay substrate (A85 -

Romorantin Theillay)

(1) The water tables vary the most frequently with the seasons; the "high waters" occur most often in winter-spring and the "low waters" in summer and

early autumn.

Diagram 7 Diagram 7Ecran non arm au coulis argile-ciment Non-reinforced fin with clay-cement slurryNiveau d'eau Water levelDrainage des eaux rsiduelles Drainage of residual waterNiveau impermable Impermeable levelEcran rigide (parois arme, palplanches) Rigid fin (reinforced wall, sheet piling)Fiche Sheet


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2.2.4 - In tercept io n of water ingr ess in f i l l

Genera l case

Interception by drainage of water ingress in fill scenarios takes place in the following circumstances (seeDiagram 8 and Table 3):

Spec ia l c as e o f na tu r a l s l opes

Surface or deep drainage is one of the most efficient and most frequently used techniques to stabilizeunstable natural slopes (seeguide Stabilization of landslides [17]). It is however useful to know that themajority of these disorders are simply reactivating old disorders and they can therefore more often than notbe detected by a comprehensive geotechnical* and hydrogeological* study before the work (seeAppendix1).

Casea by the pavement or miscellaneous networks

Caseb by the cut and fill transition zone

Casec by resurgences on the slope flank underneath the fill

Cased by capillary rises

Casee via low points in the longitudinal section

Casefby stopping on an obstacle (structure pier*)

Diagram 8: identification of potential water supply routes to the fill

DEBLAI CUTZone altre Altered zoneChausse ou rseau divers Pavement or miscellaneous networksOuvrage Structure

Nappe Water tableREMBLAI FILL

Case Drainage requirementsSuggested systems

(no dimensioning)

2

Cut and fill transitionThe transition zone made up of altered,frequently permeable materials encourageswater infiltration and the formation of watertraps.

This zone can be replaced by draining materialscombined with drains at the bottom of the cavitylinked to an outlet.

3

Surface resurgences

The geotechnical study must list waterappearances or resurgences on the slopeflank. These zones found underneath the fillare the cause of slow, continuous infiltrationswhich can "undermine" the fill base.

These zones are drained via a draining courseand a drain linked to an outlet.


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4

Outcropping water table zoneFill in compressible materials like silts or fly ashcan encourage capillary water rises in the bodyof the fill when the fill subgrade is in acompressible zone or outcropping water table.This phenomenon is all the more apparent

when the material used is made up ofcompressible soils in a dry state.

It suffices to intercept the rising water with adraining course of a thickness greater than theestimated settling and of at least 1 meter.Wetlands can also be drained to evacuate thewater from the subgrade and improve thebearing capacity by trenches/fin drains or deepditches.

5

Low points in longitudinal sectionThe low points in longitudinal section aredrained in traditional fashion to prevent wateraccumulating in water-sensitive materials.

Creation of draining stacks linked to an outlet.

6

Obstacles and friction points such asengineering and retaining structures must bedrained to prevent water accumulating incontact with the fill, on the uphill side of theslope.

If the material making up the technical fill isinsensitive to water, the drainage will be bygravity; otherwise, solutions using ageocomposite could be envisaged.

Table 3: drainage solutions for the various interception cases for water ingress in fill


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2.3 - Pavement formation levelsThey comprise two entities:

the capping layer;

the upper earthworks, the surface of which makes up the subformation level.These entities and their classification are addressed in the guide "Creating fills and capping layers [9] seeDiagram 9.

2.3.1. - Subformation (below capping level) (PST):Two problems are answered by defining the drainage needs for the subformation (below capping level)(PST):

the PST classification under the guide [9] and any improvements to it: all soils, except thoseinsensitive to water (naturally or after treatment) have mechanical properties which alter when thewater content increases. Draining operations are therefore essential when the PST is located in anunfavorable hydric context and moreover formed of material sensitive to water and frost;

the treatment of singular points in the longitudinal section: some singular points in the longitudinal sectionor cross section are potential accumulation zones for infiltration water and thus require a specific drainagesystem. Non-exhaustive examples: cut and fill transition zones, low points in fill, pronounced slopes andlow points in crossfalls.

PST (Sub fo r ma t i on (be low c app in g l ev e l ) ) c l as s i f i c a t i on and im p rov emen t

The upper earthworks, the surface of which makes up the subformation level, may be made up of:

the existing soil (depth considered around 1 m);

a lesser depth of existing soil treated with hydraulic binders;

a variable depth of substitution or input material.

The possible scenarios are defined in the guide to Creating fills and capping levels [9]. This documentclaims to distinguish between seven PST cases (PST0 to PST6) depending on the type of medium(existing soil or fill), its sensitivity to water and its hydric state. The PST quality (bearing capacity)differentiates four subformation level categories (AR1 to AR4).

To provide for PST drainage requirements and possible systems, the subgrades (particularly their drainagecapability), extreme water table levels (piezometry) and random water ingress zones need to beunderstood and identified. The geotechnical engineer will specify in particular whether specific studies arenecessary to detail the initial information. It may be important in some cases to carry out a hydrogeologicalstudy over at least on year.

Knowledge of materials and hydrogeological conditions influences earthworks strategies.

The drainage project adopted will be the result of economic comparison of the various subformation

improvement techniques (drainage, treatment or substitution) in terms of feasibility and effectiveness andtechniques (especially depths) adopted when dimensioning the pavement structure.

Distinction can be made between three scenarios in terms of drainage:

in cut or skimming profile: it will be advantageous in most cases to provide for a useful structure inthe earthworks phase which could be taken over as the final structure. The safety aspect must betaken into account at the project design stage (see guides [18] and [20]). Table 4 gives the PST-ARre-dimensioning thanks to the drainage systems;

Diagram 9: definition of various terms

plates-formes roadbeds


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Plate-forme support de chausse Formation levelAccotement ShoulderChausse roulement, base, fondation Surface course, base, foundationArase terrassement Subformation levelpartie suprieure des terrassements subformation (below capping level)

1 m en dblai ou remblai 1 m in cut or fill


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Type of soilWater

table

Initial

bearing

capacity

Long-term

bearing

capacity

Initial

PST-ARDrainage structures

Final PST-

AR

Natural soilsensitive to waterstate th

Washedby thewatertable

zero Very lowPST0-AR0

Drawdown by deepditches, trenches, etc.

PST1-AR1

Natural soilsensitive to waterstate h

Very low Very low PST1 Drainage pointless

Natural soilsensitive to waterstate m

Intermittentwater table

Good Low PST2-AR1Drawdown by deepditches, trenches, etc.

PST3-AR1

Natural soilsensitive to waterstate m

No watertable orwatertablelowered

Good Low (raininfiltration)

PST3-AR1

Drainage of pavementand capping layer (1)

PST3-AR2

Natural soil

improved bytreatment


VariableGood tovery good

PST4-AR2

Lowering by deep ditches,trenches, etc.

PST4-AR2(2)

Soil not sensitiveto water


Good GoodPST 5and 6

Drawdown by deepditches, trenches, etc.

PST 5 and6 AR 2,3,4(2)


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Table 4: PST - AR redimensioning thanks to drainage systems

Chausse et couche de forme Pavement and capping layerMaxi Max.Maxi en hiver Max. in winter

(1) see2.3.2: as the aim is to avoid humidification of the pavement subgrade, this will be the preferential domain for edge of pavement fin drains

(EDRC). Note that the drainage systems at the base of the capping layer (for capping layers comprising very permeable materials) such as drains and

draining courses, although essential cannot guarantee no infiltration.

(2) drainage remains necessary to reduce the structure's sensitivity to frost and improve earthworks conditions.


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in fill: no PST drainage (except for specialcases);

when drainage is necessary for the PST andcapping layer, it could be wise to plan a joint

structure independently of the surface drainagesystem, as shown in schematic Diagram 10.

If appropriate, attention should be paid to installingsupport anchoring (see 4.1.2) in relation to thedrainage network to avoid perforations.

The structures are miscellaneous, longitudinaldrains, trenches, EDRC, draining courses, drainingstacks, etc. (seeChapter 4).

If necessary the drainage system may besupplemented by:

transverse drains in the subformation (below

capping level) (seeDiagram 11); drains slanting from the axis ("fishbone"), so thatthey flow into longitudinal drains an axiallongitudinal drain (seeDiagram 12).

The distance between two drains and the drain depthmust be dimensioned according to thehydrogeological and geotechnical characteristics ofthe site and the project.

Diagram 10: cutoff drain installed at the foot of the cutting bank

to drain the PST

Diagram 11: sample complex draining system (slope -

subformation level)

Diagram 12: Distribution of drains or additional grips

Diagram 10 Diagram 10Cunette Trickle channelRegard de visite Inspection chamberAccotement ou bande d'arrt d'urgence Shoulder or emergency hard shoulderChausse PavementCouche de forme Capping layerDiagram 11 Diagram 11Talus BankAxe chausse Pavement axisCollecteur principal Main collectortranches latrales - tranche axiale - tranchtransversale

lateral trenches - axial trench - transversetrench

Diagram 12 Diagram 12DRAINS LATERAL, AXIAL,

TRANSVERSAL

LATERAL, AXIAL AND TRANSVERSE

DRAINSVUE EN PLAN PLAN VIEWDRAINS LATERAL, AXIAL, OBLIQUE LATERAL, AXIAL AND OBLIQUE

DRAINSAXE CHAUSSEE PAVEMENT AXIS


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T r ea t m en t o f s i n g u l a r p o i n t s i n t h el o n g i t u d i n a l s e c t i o n

The earthworks subformation level or the PST must

be drained in the following cases from thelongitudinal section: low points, cut and filltransition zones and major slopes.

Low points: they will be systematically drainedby a draining stack system;

cut and fill transition zone: it is treatedspecifically and virtually systematically. The aimis to purge the surface materials and drain anywater inflows from the cut (see Diagrams 13 and14);

zones with pronounced slope ( 5%) and

moreover in a major linear (

500 meters)encouraging water collection and their possibleloading at courses in aggregate material (PST orcapping layer). The solution to prevent thisscenario is regular water capture by drainingstacks. (seeDiagram 15).

Diagram 13: sample use of a draining course at the cut and fill

interface, used to improve the altered zone - cross-sectional

view

Diagram 14: sample use of drains in cut and fill transition zone -

plan view

Diagram 15: schematic diagram of positioning transverse drains

every section or every two sections at the earthworks

subformation level - cross-sectional view

Diagram 13 Diagram 13Arase de terrassement Subformation levelDEBLAI CUTREMBLAI FILLCouche drainante Draining courseCaptages ventuels sur la pente Any inflows on the slopezone de transition transition zonedistance dfinir en fonction de laprofondeur de la zone altre

distance to be defined based on the depth ofthe altered zone

Matriau drainant Draining materialDrain reli un exutoire Drain connected to an outlet

Diagram 14 Diagram 14foss de pied ditch at footfoss de crte ditch on crestREMBLAI FILLPOSITION DU DRAIN EN EPI POSITION OF DRAIN IN STACK


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DEBLAI CUTSens de la pente Direction of slopeRegard dans la berne Inspection chamber in soft vergeDiagram 15 Diagram 15

DEBLAI CUT

Zone de transition dblai - remblai Cut and fill transition zone:Epi drainant Draining stackArase de terrassement Subformation levelREMBLAI FILL


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2.3.2 - Capp in g l ayerThe capping layer dimensioning is provided for in the guide Creating fills and capping layers [9]:

where a capping layer is made up of the existing soils: the drainage is only necessary underneaththe water table level, to prevent the table rising into the capping layer or the project becoming

waterlogged. The most frequent solution is lateral trenches;

for a capping layer treated with hydraulic binders: the treated material could be considered as neutral(indifferent to the drainage), but drainage is however necessary underneath the water table level toprevent water rising through cracking. The most frequent solution is lateral trenches which may becombined with PST drainage;

for a brought-in capping layer of material insensitive to water: drainage is essential when there isdanger of creating a real water trap which could be fed by storm water as soon as it is installed, beforebeing covered by the pavements. Side trenches are more often than not used for the drainage, eitherby side longitudinal drains arranged at the bases of the capping layer combined, if necessary, withPST drainage (seeDiagrams 16, 17, 18 and 19).

In all circumstances, if the discharge is towards a ditch, the designer will take care to adjust the outlets

above the maximum water level in the ditches. (seeDiagram 20).

Diagram 16: in cut or skimming profile in zone outside water

table

Diagram 17: in cut or skimming profile in zone under drained

water table

Diagram 18: in fill

Diagram 19: installation of drain on edge of capping layer.

Diagram 20: adjustment of outlets

Diagram 16 Diagram 16

PST peu permable PST with low permeabilityCouche de forme Capping layerDiagram 17 Diagram 17


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Couche de forme Capping layerTranche axiale complmentaire si ncessaire Additional axial trench if necessaryTranche drainante latrale Lateral cutoff draincontinuit hydraulique hydraulic continuityDiagram 18 Diagram 18

Couche de forme Capping layerdrain dispos sur le fond de la couche deforme

drain laid on the bottom of the capping layer

drain dispos en encoche au fond de lacouche de forme ( privilgier)

drain laid in slot at the bottom of the cappinglayer (preferred)

Diagram 19 Diagram 19

Gotextile GeotextileEncoche SlotSillon GrooveSur arase ( viter) On subformation level (to be avoided)Diagram 20 Diagram 20

CAS A EVITER TO BE AVOIDED


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2.4 - PavementThe mechanical characteristics and performances of a pavement structure can diminish very clearly overtime in the presence of water which is frequently the cause of normally irreversible pathologies:

appearance of depressions*, edge subsidence, crazing, rising mud and slab rocking. Methods of drainingthe pavement itself are therefore also sought.

Diagram 21: required functions and possible emplacements of drainage systems

Drainer les interfaces de chausses dans leTPC

Drain the pavement interfaces in the median

Drainer le TPC Drain the medianDrainer les interfaces de chausses en rive Drain the pavement interfaces at the edgeexutoire outletpente slopeCouches d'assise Road foundationsDrainer sous la chausse Drain underneath the pavementSens de circulation de l'eau Water circulation directionInfiltration de l'eau Water infiltration

The pavement structure drainage needs are closely linked to the type of materials and singular points

(median and emergency hard shoulder).

Refer to Chapter 3 for a description of disorders encountered in pavements if there is no drainage and fora list of singular points in the pavement in terms of drainage.

2.4.1 - Drainage sys tems i n pavement co ur sesTable 5 summarizes the main drainage requirements, by providing inputs for response in terms of possibledrainage system.


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Pavement

courseDrainage requirements Possible drainage systems

Bituminous

materials

No drainage requirement inthe strict sense (except for

porous asphalts), butprotective role for underlyingcourses through: pavement maintenanceand repair, damp-proofing,etc.; checks on joint compactingand course bonding.

Material

treated with

hydraulic

binders

evacuation of waterinfiltrating in the cracks.

maintenance and repair: damp-proofing of surface pavement; prevention: pre-cracking of courses treated with hydraulicbinders:solution 1: lateral drainage in the height of the course at thepavement edge shoulder or median side (depending on cross-section

slope), by trenches or fin drainssolution 2: lateral drainage by the shoulders or the median(depending on the cross-section slope), made up of draining materialand evacuation of water through drains towards an outlet.

Concrete evacuation of waterinfiltrating in the cracks.

prevention: damproofing of cracks with seals made fromimpermeable products (shut-off joint, construction joint,longitudinal and transverse joints, contacts between the slab andthe median, the emergency hard shoulder or the shoulder); creation of a draining course under the concrete structure; for reinforced concrete structures, lateral drainage via:- solution 1: longitudinal structures such as trench or fin drain;- solution 2: shoulders in draining material and evacuation of water

through drains to an outlet.

Untreated

graded

aggregates

evacuation of free water,reduction in interstitialpressures; elimination of accumulated

water in the low points.

prevention and maintenance and repair: damp-proofing ofsurface pavement; choice of a porous untreated graded aggregate:- solution 1: lateral drainage in the height of the course at the

pavement edge shoulder or median side (depending on cross-section slope), by trenches or fin drains;- solution 2: lateral drainage by the shoulders or the median(depending on the cross-section slope), made up of drainingmaterial with greater permeability than untreated gradedaggregates and evacuation of water through drains towards anoutlet; transverse drainage of low points by draining stacks.

Table 5: drainage systems according to drainage requirements

dalle bton paisse thick concrete slabtanchification des fissures et des joints sealing of cracks and jointsGNT GNT


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couche drainante draining coursebton arm continu continuously reinforced concretebton maigre lean concretematriau drainant draining materialtranches ou crans drainants cutoff or fin drains


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2.4.2 - Dra inage systems at s ing ular p o in t s

Shou lde r and emergenc y ha rd s h ou lde r (BAU)

The infiltrated water under the shoulder or emergency hard shoulder (BAU) must be evacuating by drain at

the low point of the cross section or by a deep lateral ditch when the structure continues under the BAU tothe ditch.

Median

It must be possible to offset the d

us 0605a road drainage

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