Category WATER IN ROAD STRUCTURES

[1] Annex C contains a Glossary of terms that may be unfamiliar to some readers.

[2] The terms permeability and hydraulic conductivity are both used to mean the ease with which water travels through saturated, porous media. In this book the term permeability is used pref­erentially. In particular the ‘coefficient of hydraulic conductivity’ and the term ‘coefficient of permeability’ are identical and given the symbol K.

[3] Co-ordinating Author:

23 S. Erlingsson

Haskoli Islands/University of Iceland, Iceland & Statens vag-och transportforskningsinstitut/ Swedish National Road and Transport Institute, Sweden e-mail: sigger@hi. is

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_2, © Springer Science+Business Media B. V. 2009

[4] Co-ordinating Author:

23 S. Erlingsson

Haskoli Islands/University of Iceland, Iceland & Statens vag-och transportforskningsinstitut/ Swedish National Road and Transport Institute, Sweden e-mail: sigger@hi. is

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_3, © Springer Science+Business Media B. V. 2009

[5] Reference should be made to Chapter 10, Section 10.3, and to Eqs. 10.1-10.4 for an explanation of FWD assessment and of BCI and SCI.

[6] Co-ordinating Author:

23 A. Hermansson

Vag-och Transportforskningsinstitut / Swedish Road and Traffic Institute (VTI) e-mail: ake. hermansson@vti. se

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_4, 69

© Springer Science+Business Media B. V. 2009

[7] Co-ordinating Author:

E3 A. R. Dawson

University of Nottingham, Nottingham, UK e-mail: andrew. dawson@nottingham. ac. uk

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8.5, © Springer Science+Business Media B. V. 2009

[8] In British English, bitumen refers to the binder in an asphaltic material whereas in American En­glish the term asphalt-cement is normally used, or simply ‘asphalt’. In this book the term bitumen is used to describe the binder and the word asphalt (which in British English refers to the whole mixture) is not used alone, to avoid confusion.

[9] AAD is one of the core SHRP bitumen binders

[10] PG = Penetration Grade

[11] 0

0 10 20 30 40 50 60

Months since opening

[12] Co-ordinating Authors:

ISIL. Folkeson

Statens vag – och transportforskningsinstitut/Swedish National Road and Transport Research Institute (VTI)

e-mail: lennart. folkeson@vti. se IE3 T. B^kken

Norsk Institutt for Vannforskning/Norwegian Institute for Water Research (NIVA) e-mail: torleif. baekken@niva. no

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_6, © Springer Science+Business Media B. V. 2009

[13] The use of the word ‘particle’ here is to differentiate the type of chemical component being exchanged from protons and electrons which are much smaller. It is not used to indicate a solid and visible particle (e. g. of sand) as elsewhere in the book.

[14] See previous footnote

[15] Alphanumeric codes are as used in Fig. 6.5

* Co-ordinating Authors:

23 T. Leitao

Laboratorio Nacional de Engenharia Civil / National Laboratory for Civil Engineering (LNEC), Portugal

e-mail: tleitao@lnec. pt

[17] A. R. Dawson

University of Nottingham, Nottingham, UK e-mail: andrew. dawson@nottingham. ac. uk

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_7, © Springer Science+Business Media B. V. 2009

[18] for runoff: FHWA (1987, 1996), Hamilton et al. (1991), Hvitved-Jacobsen & Yousef (1991), and Wanielsita & Yousef (1993);

• for surface water: Ruttner (1952), Krajca (1989), Environment Agency (1998);

• for groundwater, soil water and soil: Barcelona et al. (1985), Canter et al. (1987), Nielsen (1991), Clark (1993) and Boulding (1995).

[19] extract metals of the exchangeable and acid extractable fraction (using CH3 COOH 0.11 M);

• extract metals of the reducible fraction (using NH2OH, HCl 0.1 M; pH 2);

[20] Co-ordinating Author:

R. Charlier

University of Liege, Belgium e-mail: robert. charlier@ulg. ac. be

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_8, © Springer Science+Business Media B. V. 2009

[21] water entered through the joints between the slabs;

• the water softened the supporting layers allowing the slab to deflect under traffic;

• the increased dynamic movement of the slab when trafficked caused a “pumping” action by which water was rapidly displaced from the pores in the supporting material;

[22] Co-ordinating Author:

E3 L. Laloui

Ecole Polytechnique Federal de Lausanne, Swiss Federal Institute of Technology, Switzerland email: lyesse. laloui@epfl. ch

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_9, © Springer Science+Business Media B. V. 2009

[23] An elastic (resilient) model with a modulus depending on the stress and suction level. A rigorous development should lead to a hyper-elastic model. Such a model would be sufficient for routine pavement design. It seems not to exist at present.

• Improving the available models, such as the Chazallon-Hornych, the Suiker or the Mayoraz models, implies the addition of yield/potential surfaces and a de­pendency on the suction. The elastic stress space, lying inside the yield surface would be higher for high suction; wetting would reduce the elastic domain and then increases the irreversible strains that occur under each load cycle.

[24] Co-ordinating Author:

EE3 C. Cekerevac Stucky SA, Switzerland e-mail: ccekerevac@stucky. ch

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8.10, © Springer Science+Business Media B. V. 2009

[25] Co-ordinating Author:

R. Charlier

University of Liege, Belgium e-mail: robert. charlier@ulg. ac. be

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_11, © Springer Science+Business Media B. V. 2009

[26] This concerns Galerkin’s approximation. For advection dominated problems, other weighting functions have to be used.

[27] Co-ordinating Author:

IE3 M. Brencic

Geoloski zavod Slovenije/Geological Survey of Slovenia e-mail: mihael. brencic@geo-zs. si

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_12, © Springer Science+Business Media B. V. 2009

[28] Co-ordinating Author:

23 J. S. Faisca

Estradas de Portugal/Roads of Portugal, Portugal e-mail: jose. faisca@estradasdeportugal. pt

A. R. Dawson (ed.), Water in Road Structures, DOI 10.1007/978-1-4020-8562-8_13, 299

© Springer Science+Business Media B. V. 2009

[29] This can be said because, under vertical flow, there is a hydraulic gradient of1 so the Darcy flow velocity has the same numeric value as the coefficient of permeability.

[30] Typically soakaways should be able to cope with water flow from a two-year return period ‘high’ (or other agreed return period).

[31] deep GBR on side slopes – where the GBR is installed under the drainage col­lection system and covers the entire slope as well as the ditch area (Fig. 13.35);

[32] Standard terminology has been adopted for pavement layers in EN standards and these are given here. In parentheses are given the traditional terms

This section provides general designs of the final elements the water runs through before going to existing water bodies.

B.6.1 Retention Ponds/Кексіves стггукрat^ct^s

B.6.2 Soakaways/Аушуоі а^аушуі]s o^Ppiwv

The designs of fin drains vary dependant upon the flow capacity that is required. The geosynthetic has the capacity to transport a certain flow (i. e. it has a certain transmissivity) – see diagram A, above. Where this is insufficient a pipe can be added to increase the outflow capacity, diagrams B and C. The dimension of the pipe varies depending on the additional capacity that is required.

B.5.3 Core Designs for Fin Drains

Core designs other than those shown here are also used. The purpose of the core is to support the geotextile membrane without hindering the flow of water within the thickness of the geosynthetic.

The figure, above, shows a plan view of a geocomposite highway edge drain, comprising a core (3/4/5) between two geotextile sheets (1/2). Some cores have one permeable side (e. g. geotextile layer 1) and one impermeable side (e. g. in place of geotextile layer 2) where water is to be collected from one side of the fin drain and not to be drained from the other, but these are seldom employed in highway construction except where an impermeable face (e. g. part of a retaining wall) abuts the pavement. The core may be formed in a number of ways, some of which are illustrated here: 3=plastic plates with pillars to separate faces; 4=concertina waffle structure, 5=dimpled plastic sheet. Nets/grids and stiff, entangled polymeric strands may also be used to provide a permeable core.

This section provides general designs of french and fin drains used to drain the subsurface section of highways.

B.1 Introduction

The purpose of this document is to show some standard designs for pavements and associated drainage items and to present the names of these in several languages. The diagrams contained within each section show the general layout only. No de­tail is included regarding the specifications of the materials or specific dimensions. Many of the figures in this Appendix have been adapted and simplified from draw­ings made available courtesy of the Highways Agency (Manual of Contract Doc­uments for Highway Works, Volume 3 – Highway Construction Details, Section 1 “Carriageway and Other Details” (March 1998, updated with amendments including November 2005, May 2006 & November 2006)). Where possible translations have been given in German (de), Spanish (es), French (fr), Italian (it), Greek (gr), Polish (po), Portuguese (pt), Serbian (cs), Danish (dk) and Slovenian (si).

This section provides general details of the layout of single and dual carriageway roads. Details of the carriageway are given in Section B3, and the carriageway edge and drain arrangements in Section B4.

B.2.1 Single Carriageway

This section provides details of the general layers and sections in pavement construction.

B.3.1 Flexible Pavement (with Verge)/EvKa^-nro oSoaTpw^a

SUD (Sustainable Urban Drainage) refers to pavements that are designed to behave more like natural soils (i. e. they allow the infiltration and storage of stormwater). As the SUD pavements have the capacity to hold water and release it slowly, unlike impermeable asphalt and concrete pavements, their use reduces the risk of flash flooding downstream from their discharge points.

This Section provides general layouts of the pavement edges. More specifically it provides the general designs used for surface and subsurface drainage. In most cases drainage pipes have outlets into large piped networks collecting surface run-off and sub-surface drainage water. These in turn outlet into ditches, streams, rivers and soakaways depending on which is most accessible given the local environment.

The Danish design system deals with seasonal variations by adjusting the ex­pected bearing capacity (E-modulus) of each pavement layer. In the design software MMOPP (Mathematical Model of Pavement Performance) (Ullidtz, 1993) the user can choose an advanced design procedure, where the performance of the road is simulated over (for example) 40 years. The program is given constant E-modulus values as material parameters for each pavement layer. These moduli are then var­ied over the seasons as shown in Table A.1. The constant E-values given as input represent the summer values. In wet seasons the E-moduli of unbound layers are reduced. In frost seasons the values are increased.

A.6 Sweden

When designing pavements in Sweden the different layers are given stiffness vary­ing with the season of the year. The procedure is very similar to the one used in Denmark (see above). In Fig. A.2 the first column holds the thickness of each layer and the other six columns show how the stiffness of each layer is predicted to vary over the year.

A.7 Poland

The Catalogue of Typical Flexible and Semi Rigid Pavement’s Construction, was developed for the Polish General Directorate of Public Roads. Typical structures were designed, based on analysis of stresses and deformations in pavement, using multilayer elastic and viscoelastic half space theory. According to this Catalogue and the Roads Design Guidelines (General Directorate of Public Roads, 1995), in pavement design process following factors should be taken into account:

• climatic and ground-water conditions,

• intensity and kind of traffic structure during whole designed life period (20

years),

• values of allowable loads from vehicles (100 kN/axle),

• function of pavement.

Climatic conditions are freezing depth, average annual temperature and temperature differences.

Subgrade bearing capacity groups (G1-G4) depend on type of soil, water condi­tions and CBR value. The G1 is the best subgrade, mainly sandy soils of CBR > 10, G4 is the weakest subgrade, mainly cohesive soils of CBR < 3. Bearing capacity group has an impact on the necessity and kind of subgrade improvement. For typi­cal structures taken from the Catalogue, the bearing capacity of the subgrade to be achieved is as follows. The secondary static modulus, E2, must be greater or equal to 100 or 120 MPa and the compaction ratio, Is, must be greater or equal to 1.00 or 1.03 depending on the traffic loading.

Water conditions are evaluated depending on ground water depth (z) from the bottom of the pavement structure. If subgrade drainage is required, a capping layer made from frost non-susceptible materials with a coefficient of permeability, K > 9.3 x 10-5 m/s should be used. The capping layer (at least 15 cm thick) should be placed across the whole width of road bed. For the situation where there is unim­proved soil under the capping, a “tightness condition” is imposed for the layers:

^ < 5 (A.1)

«85

where:

D15 is the dimension of sieve, through which 15% of grains of separating layer or drainage layer will pass and d85 is the dimension of sieve, through which 85% of grains of the foundation soil will pass. In situations when the above layer tight­ness condition cannot be fulfilled, then between these layers a separating layer (of thickness at least 10 cm of suitably graded soil) should be arranged or a non-woven geosynthetic interlayer should be inserted.

In the case of frost susceptible subgrade soils, it is necessary to check if the total thickness of all layers (taken from the Catalogue) and any improved subgrade layer is sufficient to achieve frost resistance. In situations when this condition cannot be fulfilled, then the lowest layer of improved soil should be thickened.

In Croatia, the design of pavement structures primarily considers the traffic load. However, if the subgrade soil is frost susceptible and if the hydraulic conditions are unfavourable, the originally designedpavement structure shouldbe additionally tested to determine the impact of freezing. If there is a risk of freezing, certain technical measures have to be planned within the pavement structure or under it in order to avoid the risk of freezing or to significantly lower the impact of freezing. In Croatia the pavement testing concerning freezing is carried out in the following manner.

Based on the soil mechanics characteristics, the pavement materials and sub­grades are grouped into one of the following four groups according to their freezing susceptibility (in compliance with the national standard HRN U. E1. 012):

G1 – lightly susceptible (gravel) containing 3-10% of particles smaller than 0.02 mm.

G2 – lightly to moderately susceptible (gravel, sand) containing 10-20% of small particles.

G3 – moderately susceptible (gravel, sand, clay with PI higher than 12) con­taining over 20%, i. e. over 15% of particles smaller than 0.02 mm.

G4 – highly susceptible (dust, very fine dusty sand, clayey dust) containing over 15% of particles smaller than 0.02 mm.

According to the national standard HRN U. C4.016, it is established whether the hydrological circumstances are favourable or not.

400-500

300-400

Fig. A.1 Contour map with air freezing index (FI) for the territory of Croatia (Srsen et al. 2004). Reproduced by permission of the Croatian Association of Civil Engineers

Then the freezing depth is determined according to the national standard HRN U. B9. 012. It is required to determine the Freezing Index (FI) for that purpose. The FI value is taken from the freezing index contour map shown in Fig. A.1. That map is derived from an IGH study on Freezing Index determination for national roads in 2003, elaborated in cooperation with the Metrological and Hydrological Service. The study is based on the data on the highest and lowest air temperatures noted in 39 meteorological stations in Croatia in a period of 25 years (1976-2000) (Srsen et al. 2004).

The freezing depth under the pavement surface is read from a diagram based on FI and from the data on pavement thickness (designed or completed), its spatial mass and humidity and from data on the soil type under the pavement.

Fatigue design is made using either methods based on Odemark’s formula or on analytical calculation methods (e. g. a multi-layer linear elastic design program). In both, the seasonal variation can only be considered by choosing the material proper­ties for each (especially the unbound) layer so as to represent weighted mean values for the whole year. The “worst” thawing and moist period of the year (the so-called spring bearing capacity period) has a very large influence on the mean value us­ing this weighting approach. Calculations are also made using a single temperature (+20 °C).

A.2.3 Rutting

The obligatory use of winter tyres (most of them studded) during four to five months each winter causes most of the rutting in Finnish medium and high volume roads. The design against rutting is based on empirical information between rutting speed and amount of traffic, asphalt type, binder and aggregate properties. No seasonal variation is considered, but it is well known that moist/wet conditions at the road surface will increase the rate of rutting.

At the moment only discussions about the possibility of using several, varying – length, time periods (each associated with individual material parameters – depend­ing on moisture, temperature and density) have been carried out. During the analyses mentioned above the vertical deformation (the elastic recoverable strain) is also checked to to ensure that it remains less than the maximum allowable limit for each layer material.

As a brief summary it can be said that seasonal variation is only taken in to account by choosing parameter values based on the most dominating period, the spring thaw period.

A.3 USA

The new AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG) (AASHTO, 1998 & 2004) integrates climatic factors, materials properties, and traf­fic loadings to predict pavement performance. The Enhanced Integrated Climatic Model (EICM) that is used in the new AASHTO MEPDG integrates three models:

• The two-dimensional drainage infiltration model (ID Model), developed at Texas A&M University, that evaluates the destination of the rainfall on the pavement.

• The Climatic-Materials-Structure Model (CMS Model) developed at the Univer­sity of Illinois. A one dimensional finite difference engine is used to calculate coupled heat-moisture flows in pavement structures and predict pavement tem­perature.

• The CRREL frost heave and thaw settlement model developed at the United States Army Cold Region Research and Engineering Laboratory (US Army CR – REL) which computes temperature and moisture flow at different temperatures and predicts the depth of frost and thaw penetration.

The EICM is based on the Integrated Climatic Model, developed for the Federal Highway Administration in 1989, containing several improvements. It replaced the Gardner equation for the soil-water characteristic curve (SWCC) with the equations proposed by Fredlund and Xing (1994). It also provides better estimates of the sat­urated permeability and specific gravity of soils, given known soil index properties such as grain-size distribution (percent passing sieve no. 200 sieve (75 ^m) and effective grain size with 60% passing by weight) and Plasticity Index (PI). The unsaturated permeability prediction based on the SWCC and proposed by Fredlund et al. is also incorporated in the model (Fredlund et al., 1994).

The model uses actual climatic data (hourly or monthly) and predicts the follow­ing parameters throughout the entire pavement/subgrade profile:

• Temperature

• Resilient modulus adjustment factors

• Pore water pressure

• Water content

• Frost and thaw depths

• Frost heave and

• Drainage performance.

The model evaluates the expected changes in moisture condition from the initial or reference condition (generally, near optimum moisture condition and maximum dry density) as the subgrade and unbound materials reach equilibrium moisture con­dition. The model also evaluates the seasonal changes in moisture condition, and consequently the changes in resilient modulus, Mr. In addition the model calculates the effect of freezing, and thawing and recovery of Mr and uses these Mr values for calculation of critical pavement response parameters and damage at various points within the pavement system.

A.1 Introduction

The primary objective of this annex is to present examples of how moisture condi­tion is taken into account in pavement design and analysis.

The pavement design regarding the influence of water has significantly different objectives in different European countries. While in central and northern Europe the most important question is how to protect the pavement structure from frost action, in southern European countries it is more critical to control excessive water that suddenly penetrates the pavement after heavy rainfall. At the same time identical processes play significantly different roles in different climates. For example, the suction, that has negative effect in locations of freezing and thawing, has positive effect in southern countries by increasing the stiffness, and this influences the de­cision of which type of material is used in unbound base and sub-base. In northern countries the percentage of fines is limited typically to 5-8%, while the Mediter­ranean countries allow up to 15% fines.

In many parts of Europe freeze/thaw effects play a crucial role in pavement de­sign. How these effects are taken into account in pavement design varies in complex­ity from using the frost index, or Stefan or modified Berggren equations (Aldrich & Paynter, 1956) to calculate frost depth to coupled heat/moisture flow models. Most of the European pavement design methods take into account phenomena related to freezing and thawing by using the frost index. This indicator is supposed to account for the “quantity of frost” to which a pavement was subjected for a given period. The frost depth is then calculated based on some empirical equation as a function of frost index. Some pavement design methods also consider the influence of sunshine on this phenomenon.

Many design methods take into account the loss of bearing capacity during thaw­ing. This is typically done by adjusting the modulus of each of the unbound mate­rials by a reduction factor that depends on the frost susceptibility of the material (COST 337, 2002).

The European project AMADEUS (Amadeus, 2000) identified the need for further research of deterioration mechanisms related to freezing and thawing and development of a long-term predictive model for freeze/thaw related deterioration.

The project also identified the need for more information on how the bearing capac­ity of different types of soils is affected by the drainage conditions.

The World Bank’s Highway Development and Management Model HDM-4 (ND Lea International, 1995) models the seasonal performance variation using a simple two season model (“wet” and “dry” seasons). The program uses the follow­ing parameters:

• mean monthly precipitation,

• drainage effectiveness,

• surface cracking,

• potholed area,

to calculate the ratio between “wet” and “dry” pavement adjusted structural num­bers. Loizos et al. (2002) modified this approach in the Road Infrastructure Man­agement System (RIMS) developed for the Greek government, to enable multiple season analysis, more suitable to a European context, by introducing the environ­mental function.

In the following, examples of how seasonal variations are handled in design sys­tems are given.

A.2 Finland

In Finland the design and analysis of pavement structures is done by separate con­sideration of different criteria:

• Frost resistance (structure and subgrade)

• Traffic loading/Resistance to fatigue

• Resistance to settlement (deformation in structural layers and subgrade)

• Rutting due to studded tyres

A.2.1 Frost Design

Design of public roads in Finland still, commonly, uses a semi-empirical method based on acceptable calculated frost heave, which depends on

• road class;

• structural durability;

• how homogenous the subgrade is;

• the freezing index, F10, of the geographical location (583-1416 °C. days); and on

• an empirical factor of frost heave of the subgrade, which depends on the pro­portion of soil passing the 63 ^m and 2 mm sieves and whether it is a wet/dry location.

On homogenous clay soil, the measured frost heave values can also be used.

According to the results of the “Road Structures Research Programme” the con­trol of frost behaviour of the road is divided into two parts: control of frost heave and control of the effects of thaw weakening. The frost heave of a road is estimated using the segregation potential (SP) concept, in which SP is the parameter that describes the frost susceptibility of the subgrade. The total thickness of the road structure is designed on the basis of frost susceptibility of the natural subgrade, and on the thermal conductivity of the used materials. If necessary, the structure is protected using insulation against frost, so that the permitted frost heave, set as the design criterion, is not exceeded. The procedure can be applied in designing new roads and improving old roads in all road classes. The program also calculates settlement pro­files based on the investigations and identification of variations in the water content of soil layers along the road line.

The observation of climate changes, as a consequence of global warming, reveals the aggravation of extreme situations, including alternating torrential rain periods with drought situations. Therefore, it’s important to ensure that road drainage systems are calculated for extraordinary phenomenon (both precipitation and flow) associated with a predetermined return period, which includes an allowance for the worsening of weather conditions. Designing to historic weather patterns is likely to mean that there will be an increase in the frequency when elements of the drainage system will not have adequate capacity, with inevitable consequences for the safety of users and, eventually, for the survival of the infrastructure itself.

Today’s road drainage elements should be monitored to allow measurement of the return period for which they are designed, adopting in latter life of the drainage system a solution for increasing the capacity in face of the reality found on site. One should also ensure that inside this observation phase (which could take some years), efficient cleaning and maintenance plans are implemented with adequate frequency, so that the drainage elements are in perfect functioning order. For example, after drought seasons the tendency to become clogged with sand is higher.

Future infrastructures should be dimensioned by adopting the revised values and parameters collected through information recovered in rainfall and/or water flow monitoring stations placed near the locations of the particular road scheme.

13.5 Conclusion

A safe and comfortable road requires a great investment in scheme planning, careful design, quality construction and ongoing maintenance. At each stage of the road’s life, the hydraulic, geotechnical and pavement performance must be considered alongside the environmental response of the road and its “corridor”.

Drainage standards exist to aid design, performance and maintenance, but they are not to be followed as laws, but as a reference and recommendation for a project. As important as the standards are for many facets of a highway’s design (includ­ing the safety aspects), it is the engineer’s experience and good sense that must determine the road scheme planning and its detailed execution at a project level. Greater rigor by consultants and owners concerning the choice of drainage solutions is important, yet they should be given greater flexibility in the project’s execution schedule and in construction of the work’s drainage system. It is also the consultant and owner who are best placed to determine the appropriate safety implementation.

The wide variety of solutions available to ease the road through the hydraulic en­vironment will necessitate careful study and selection in order that the most econom­ically, socially and environmentally beneficial solution is found. A similar attention will need to be paid to the selection of materials and components. This is partly because of the wide range of geosynthetic materials and composites with proper­ties specifically “tuned” to drainage applications that are now readily available and partly because of the ever-increasing pressure to use marginal, waste and by-product construction materials in place of the conventional aggregates with which designers may be more familiar.

This chapter has, albeit briefly, sought to indicate something of the breadth of solutions and the considerations. It will be apparent that much more could be written and much more detailed design advice and sample calculations could have been pre­sented. However this chapter is already the longest in the book and the book longer than intended! It will suffice for now to advise readers of the wealth of information available in the references listed below and at the end of the previous chapters.

Water is often considered the chief enemy of the pavement engineer. It is one of the materials to which the environmental expert gives prime attention. It is the very basis of the hydrogeologist who seeks to protect it so as to ensure continued pure water supplies. It is right, therefore to make it the subject of this book which, one hopes, will help to ensure that it is treated appropriately by everyone who has a role to play in providing and maintaining roads in our precious environment.