Road drainage : technical guide

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:..............................................