Technical guide - Road drainage
This Road Drainage technical guide is the first methodsdocument to encourage taking drainage needs in road workssystematically in account. It suggests solutions based on thetype of structure, installation, dimensioning and maintenancefor new road projects, including earthworks and for existingpavements. This guide is intended for Project Engineers and Clients,managers, Design Offices and public works contractorsinvolved in studying, creating and maintaining road drainage.
Varying amounts of water are found in the road environment, be it in the cut and fill banks, inside the pavement itself or in the underlying soils or adjacent shoulders. A well-drained pavement has better mechanical behavior in a subgrade whose bearing capacity is also improved. The result of pavement and formation levels containing less water throughout the climatic cycles is a considerable increase in pavement lifetime, less frequent maintenance sequences and effective protection 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 the elimination of subsurface water. To avoid any confusion in the purpose and design of systems, clear distinction is made between the specific functions of internal pavement draining systems and surface drainage, as indicated in Chapter 1. This guide is the first methods document on road drainage to encourage taking drainage needs in road works systematically in account.
Contents
The Sétra supports the public owner ............................................................................ 2
The Sétra, producer of the state of the art.................................................................... 2
The Sétra, 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.............................................................................. 25 I
mpact on water.......................................................................................................... 25Waste management..................................................................................................... 25
2.1.7 - Flow rate assessment................................................................................. 26
Drainage of subgrades ............................................................................................... 26
Pavement 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 ........................................................... 31
Generalized water ingress and bank stabilization ..................................................... 31
Random water ingress ................................................................................................ 31
Unpredictable random water ingress ......................................................................... 31
2.2.4 - Interception of water ingress in fill ........................................................... 33
General case............................................................................................................... 33
Special case of natural slopes .................................................................................... 33
2.3 - Pavement formation levels ............................................................................ 35
2.3.1. - Subformation (below capping level) (PST): ............................................ 35
PST (Subformation (below capping level)) classification and improvement ............. 35
Treatment 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 .......................................................... 47
Shoulder and emergency hard shoulder (BAU) ......................................................... 47Median........................................................................................................................ 47
Dividing island, directional island and obstacle island ............................................. 47
Roundabout ................................................................................................................ 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 ............................................................ 54
Marking systems ...................................................................................................... 54
Table 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 ...................................................................................... 60 Objective..................................................................................................................... 60
Standard schemes ....................................................................................................... 60
Operating method....................................................................................................... 62
Durability and maintenance ....................................................................................... 62
Elements required for dimensioning .......................................................................... 62
4.1.2 - Cutoff drains.............................................................................................. 63 Objective..................................................................................................................... 63
Standard schemes ....................................................................................................... 63
Operating method....................................................................................................... 63
Shallow trench............................................................................................................................63
Deep trench ................................................................................................................................63
Durability and maintenance ....................................................................................... 65
Elements required for dimensioning .......................................................................... 67
4.1.3 Grips and draining stacks ............................................................................ 68 Objective..................................................................................................................... 68
Standard schemes ....................................................................................................... 68
Operating method....................................................................................................... 68
Durability and maintenance ....................................................................................... 68
Elements required for dimensioning .......................................................................... 68
4.1.4 - Fin drains at pavement edge (EDRC) ................................................ 70 Objective..................................................................................................................... 70
Standard schemes ....................................................................................................... 70
Operating method....................................................................................................... 72
Durability and maintenance ....................................................................................... 72
Elements required for dimensioning .......................................................................... 72
4.1.5 - Draining courses................................................................................. 73 Objectives ................................................................................................................... 73
Standard schemes ....................................................................................................... 73
Operating method....................................................................................................... 74
Durability and maintenance ....................................................................................... 74
Elements required for dimensioning .......................................................................... 74
4.1.6 - Shafts (vertical drainage) ................................................................... 75 Objective..................................................................................................................... 75
Standard schemes ....................................................................................................... 75
Operating method....................................................................................................... 77
Durability and maintenance ....................................................................................... 77
Elements required for dimensioning .......................................................................... 77
4.1.7 - Bank stabilization systems (shields and stacks)................................. 78 Objective..................................................................................................................... 78
Standard schemes ....................................................................................................... 78
Operating method....................................................................................................... 78
Durability and maintenance ....................................................................................... 80
Elements required for dimensioning .......................................................................... 80
4.2 - Stipulations on materials ...................................................................... 81
4.2.1 - Draining and filtering materials ........................................................ 81
Filtering power........................................................................................................... 81
Draining power .......................................................................................................... 81
Other criteria.............................................................................................................. 83
Comment on porous concretes ................................................................................... 83
4.2.2 - Geotextiles and related products ....................................................... 84
Role in the drainage structures .................................................................................. 84
Main characteristics to be determined ....................................................................... 84
Filtering function........................................................................................................................84
Drainage function.......................................................................................................................84
Mechanical characteristics .........................................................................................................84
Elements required for choosing the geotextile ........................................................... 88
4.2.3 - Drains or drain pipes ................................................................................. 90
Role and types ............................................................................................................ 90
Pre-coating................................................................................................................. 92
Dimensioning: Flow rate - Diameter - Slopes ........................................................... 92
Durability and maintenance ....................................................................................... 92
4.3 - Ancillary structures ....................................................................................... 94
4.3.1 - Crossings......................................................................................................... 94
4.3.2 - Inspection chambers ....................................................................................... 94
4.3.3 - 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 .......................................................................... 97
5.1.1 - Execution of work ..................................................................................... 97
Optimum work period................................................................................................. 97
Managing interfaces................................................................................................... 97
5.1.2 - Special drainage applications in earthworks phase ................................... 98
Surface maintenance .................................................................................................. 98
Evacuation of rainwater ............................................................................................. 98
A few rules for carrying out the work....................................................................... 100
5.1.3 - Checks ..................................................................................................... 100
5.2 - Application of quality assurance in the drainage work............................ 101
5.2.1 - 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 ................................................................ 105 Monitoring................................................................................................................ 105
Repairs and repair frequency................................................................................... 105
Appendices ............................................................................................................ 106
Appendix 1 - Special hydrogeological* studies.................................................. 107
G11 mission, preliminary feasibility study ........................................................ 107
G12 standard mission, geotechnical* feasibility study ...................................... 107
G2 standard mission, geotechnical* feasibility study ........................................ 107
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................................................................................ 112
3.2.1 - Diffuse infiltrations via the surface courses.................................................. 112
3.2.2 - Infiltration through the cracks (see Diagram 45) ......................................... 114
Sample estimation of a drainage system dimensioning. ..........................................................115
Checking the utility of draining ...............................................................................................115
Appendix 4 - Elements to establish the special technical clauses (CCTP) ...... 116
1 - Description of work to be carried out ........................................................... 116
1.1 - Localization of work......................................................................................... 116
1.2 - General description of work reserved for the contractor ................................ 116
1.3 - Work not included in the contract .................................................................... 116
1.4 - References to drawings extracted from the capital investment project...... 116
2 - Quality assurance .......................................................................................... 116
3 - Material, product and component specifications .......................................... 116
3.1 - Required characteristics of drainage systems.................................................. 116
3.2 - Materials for earthworks and backfill.............................................................. 116
3.3 - Ancillary structures.......................................................................................... 117
4 - Work execution method (example for cutoff drains and EDRC) ................. 117
4.1 - Specifications on installation and setting out of systems ................................. 117
4.2. - Acceptance and storage of supplies and materials ......................................... 117
4.3 - Trench execution method ................................................................................. 117
4.4 - Laying specifications........................................................................................ 117
4.5 - Compacting specifications ............................................................................... 117
4.6 - Dealing with singular points............................................................................ 117
4.7 - Installing inspection chambers, connections to outlets.................................... 117
4.8 - Ancillary work.................................................................................................. 117
4.9 - Using the road during the work ....................................................................... 118
5 - Checks and quality ........................................................................................ 118
5.1 - Compacting reference areas ............................................................................ 118
5.2 - Checks at hold points ....................................................................................... 118
Appendix 5 - Bibliography .................................................................................. 118Standards: ........................................................................................................... 118
Technical documents: ......................................................................................... 118
For information:.................................................................................................. 119
Appendix 6 - Abbreviations and glossary .......................................................... 120
6.1 - Abbreviations ............................................................................................. 120
6.2 - Glossary...................................................................................................... 120
