Draft UTG3 - Structural Design of Urban Roads

. ........................................................................................................... SynopsidSinopsis .......................................................................................... Preface Hierdi@dokument handel oor die struktuurontwerp van stedelike geplaveide en gruis~aaie . Dit dek die keuse en ontwerpstrategieg, die skatting van ontwerpverkeer, materiale, praktiese en omgewingsoorwegings. struktuurontwerp en koste- . Structural design urban roads. paved roads. gravel roads. catalogue of designs. design traffic materials. environment, cost analysis introduction: The scope and philosophy of the report .................. 1 1.1 1.2 ......................................................... General objective ...................: . , The design process ............................................................................. 1 2 2.1 Road categoy Definition of road categories ................................................................................ ............................................................... 3 3 2.2 Importance. service level. traffic and road standard ............................ 4 3 6 3.2 ......................:.................................................... Analysis period. structuraldesign period and design strategy ............. Selection of analysis periodand structuraldesign period .................... 4 Design traffic '9 4.2 .................................................................................... Traffic classes for structural design purposes ..................................... Detailedcomputation of equivalent traffic ........................................... 10 5 Materials ...:..................................................................................... 19 5.1 General list of pavement materialsand abbreviatedstandards 19 5.3 ........... ..................................................... Descriptionof major material types Availability. experience and current unit costs ..................................... 6 Environment 6.2 6.3 Topography ........................................................................................ Climatic regions and the design of pavements .................................... 23 23 6.4 Climate andsubgrade CBR ................................................................. 23 6.5 Material depth ..................................................................................... 24 3.1 5.2 . ~ ~ iv 1 4.1 S m u r a l m g n d u b ~ mad8 n UTG3 Pretoria Souh AM j s iii Design strategy ................................................................................... 1 6 6 9 19 22 23 6.6 Delineationof subgrade areas 24 6.7 DesignCBR af subgrade ..................................................................... 24 BNOml d a g n d urban mads UTQ3.R~Sovthli(nes 1988 DesignCBR in cut .............................................................................. 26 Structural design and pavement type selection ............................ 27 General ...............................................................................................27 Behaviourof different pavement types .............................................. 27 Possiblecondition at end of structural design period .......................... 33 Selection of pavement types for different road categories. traffic classes and climatic regions .............................................................. 33 The catalogue design method .............................................................34 Gravel roads .......................................................................................37 .................................................................. 4j Drainage ............................................................................................. 41 41 Compaction ........................................................................................ Subgrade below material depth ....................... . . ........................... 42 Road levels .........................................................................................42 Practical considerations ............................................................................... 43 Pavement cross-section .................................................................. 43 Considerations for concrete pavements .......................................... 43 Kerbs and channels ......................................................................... 44 Edging ................................................................................................ 44 ... Access~b~l~ty ........................................................................................44 Service trenches ................................................................................... 46 ...............................................................................................46 Present worth ................................................................................... 47 Construction costs (C) ....................................................................... 48 Real discount rate (r) .......................................................................... 48 Future maintenance (MJ ................................................................... 48 Salvagevalue (S) ............................................................................... 51 Cost analysis General References ........................................................................................ 2 3 Glossary ............................................................................................. 53 The influence of township layout on thechoice of road category ......... 55 ..................... 4 Exampleof the structural design of aCategory UB road 56 Example of the structural design of C a t e g o ~UC and UD roads within a township ................................................................................ 65 5 The catalogueof designs .: ................................................................. . LIST OF FIGURES Structural design flow diagram (mainly for Category UA and UB 1 roads) .................................................................................................. Simplified design flow diagram for residential roads (Category UC or UD) ...................................................................................................... 67 n L 3 illustration of different road categories ............................................. 4 Illustrationof design periods and alternative design strategies ........... 7 Nomogram for determining design traffic class from the initial EBOs/lane/day. thegrowth rateand the structural design period ......... 18 Definition of material symbols used in catalogue of designs ................ 20 .................................... Macroclimaticregions of southern Africa ............................................ ~eneralized behaviour characteristics ................................ Check-list of material availability and unit cost 22 25 29 Ranges of terminal rut depth conditions for different road categorles ...................................................................................................... 34 ................................ CBR design curvesfor cover thicknessof gravel roads ....................... Design curve forthe passability of unpaved road 39 40 The degree of structural distress to be expected at the time of rehabilitationfor different structural design periods ................................... 45 pavement structure terminology ......................................................... 46 m e influence of layout on mad category ............................................. 55 Check-list of material availability and unit cost .................................... 58 possible pavement structures (SDP = 15 years).................................. 61 52 vii LIST OF TABLES 21 1 Definitionofthe four road categories ................................................. 5 22 2 23 3 ......................... Classificationof traffic for structural design purposes .......:................. 4 80 kN single-axle equivalency factors derived from Structural design periods for various road categories . F= (9)':......................................................................... 8 9 1, 5 Determmatlonof E8Os per commerc~al veh~cle.................................... 12 6 Traffic growth factor (g) for calculation of future or initial traffic from 14 present traffic .................................................................................. 7 Traffic growth factor (fy) for calculation of cumulative traffic over prediction period from initial (daily) traffic .............................................. 15 8 Design factors for the distribution of traffic and equivalent traffic among lanes and shoulders ......................................................... 16 Material depths to be used for determining the design CBR of the 26 subgrade ........................................................................................... 9 10 11 12 13 14 15 16 Subgrade CBR groups used for structural design ............................... 26 Possible condition at end of structural design period for various road categories and pavement types ..................................................... 33 Suggested pavement types for different road categories and traffic classes ...............:................................................................................ 35 Preparation of subgrade and required selected layers for the different subgrade design CBRs ............................................................... 36 Design thickness of gravel wearing course for different road categories ......................................................................................................38 Compaction requirements for the construction of pavement layers (and reinstatement of pavement layers) .............................................. 41 Typical ranges of surfacing life periods for various surfacing types for the different road categories and base types (if Me surfacings are used as 9iven in the catalogue) ...................... ............................... 49 . . 17 18 19 20 viii Typical future maintenance for cost analysis ....................................... 50 Cumulative equivalent traffic and applicable traffic class for SDP=15years .....:......................................................................... 57 ............................................................. Selected layers for the differentsubgrade areas ................................. Design CBR of the subgrade 59 59 ........ Typical salvage Values for different pavement types ........................... Present worth of costs ........................................................................ Typical maintenancemeasures forthedifferent pavement types 62 62 63 2 THE DESIGN PROCESS A flow diagram of the design process discussed in this document is shown in Figure 1.1 INTRODUCTION: THE SCOPE AND PHILOSOPHY OF THE REPORT The procedures for the structural design of road pavements presented in this document are applicable to urban roads and surfaced residential roads in southern Africa. materials available and .1 GENERAL OBJECTIVE when a road pavement reaches the end of its serviceable life. It is important to attend to layout planning and drainage design before the structural des~gnof a road is addressed. The structural design of a pavement is aimed at the protection of the subgrade through the provis~onof pavement layers. A special section on gravel roads has also been included. namely road category. The design philosophy may be summarized as follows: The aim of design is to produce a structurally balanced pavement which. 1. traffic. it is usually rehabilitated in some way to provide a further period of service. the pavement should be capable of being strengthened by means of various rehabilitation measures tocarry the traffic over the full analysis period. The procedures cover a range of pavement types and materials currently used in local practice. 1. It must be kept in mind that the proposed procedures do not necessarily exclude other design methods. Each section will be treated separately but all sections have to be wnsidered as a whole before a deslgn can be produced. subgrade soils. A comparison can be made by taking into account both the structural capacity of the initial pavement and estimates of the rehabilitation measures that will probably be necessary to maintain the pavement in a se~icablecondition over a realistic analysis period. With rehabilitation a chosen level of service has to be achieved over the analysis period as cheaply as possible. environmental conditions. will carry the traffic for the structural design period in the prevailing environment at an acceptable service level without major structural distress. design traffic. usually cost. If the designer has to make a fair comparison of proposed new pavement designs. The Row diagram has eight sections. The procedures are based on a~wmbinationof existing methods. The first five sections represent the basic inputs to pavement design. Structural design encompasses factors such as time. at minimum present workh of cost. pavement materials. experience and fundamental theory on the behaviour of structures and materials. he requires a common basis. construction details and economics. If necessary. design strategy. UB. UC and UD are considered (Figure 3). Each design has been checked by means of mechanistic pavement design techniques. lightly trafficked residential. . SUBGRADEAREAS . namely UA.UNIT X FIGURE 2 Simplified design flow diagram for residentialroads (Category UC or UD) COSTS Wter back 10 SECTION 2 . reauire a more detailed analysis by means of other methods. reiterate FIGURE 1 Structuraldesign flow diagram (Mainly for category UA and UB mads) 2 ROAD CATEGORY 2. INCLUDE PRICTICAL CONSIOERATIOHS .UNIT OF COSTS .The four road categories mentioned above cover the range from every important arterial road with a very high level of service and very high volume of traffic. However. special conditions mav . CROSS-SECTION OcHCRETE .roads and culs-de-sac with a moderate to low level of service.AVAILABILITY MATERIALS . I.. With these as inputs the design will use the catalogue of various pavement types to obtain possible pavement structures.CONSIDER The catalogue should be adequate to provide the basic design required. DRAINAGE SECTION 7 SECTION 4 .U&UC A simplified design flow diagram for the structural design of residential roads (Category UC and UD) is suggested in Figure 2. . service level..- environment.1 DEFINITIONOF ROAD CATEGORIES For the purpose of this document.PROBLEM SUBGRADES CRDSS-KCTtDN CONCRETE PAVEMENTS ANALYSIS DEFINE SECTION 5 I TOPOGRAPHY CLIMATIC REGION COSTS. Figure 3 gives a schematic illustrationof the different road categories. and eventually to compare the different pavement structures on the basis of cost. A road category is defined by a combination of parameters (fable 1) such as importance. traffic and Const~Ctedstandard. to less important.PAVEMENT TYPE SELECTION . STRUCTURAL SELECT CATEGORY S E ~ T ~( O ~ ROAD UA.CATALOGUE I I . four different road categories. to include future maintenance measures and some construction considerations. ESTIMATE BEHAVIWR . OR U D SECTION 6 I The catalogue is based on experience of pavement construction and pavement behaviour throughout southern Africa. Also industrialroads. TABLE 1 Definitionof the four roadcategories r Road Catwow . The design traffic is expressed in terms of the total number of equivalent standard axles (E80s) over the structural design period (refer to Section 4). Residential access collectors. to the generai standard of the facility and partly to the volume of trafk carried. the user will expect a better riding quality on a dualcarriageway arterial road than on a minor residential road. Moderate to low Low level of level of service.. CBD roads. Also car parks. I UA UB UC General description Primary and distributor roads Local access roads Road class 1 and 2 3 and 4 5(al and 5@) 5@lto 5(f) Detailed Trunk roads description and and prinWy function distributors (SAICE: Freeway and major alterials).05 3 x 100 .8 . EBOsllane - ~0.3 x 10D EBOsilane (b) ifmad does not carry construction 0. m i c e .2. access ways. c0. SERVICE LEVEL TRAFFIC AND ROAD STANDARD The deslgner should ascertain whether the traffic volume and other factors comply wlth Table 1 and whether they are acceptable to the controlling authority.8 . No bus routes.05 . access cwrts. access strip and culs-desac. Local access roads Imps.50 x 100 E80sAane 0.2 x 10' EBOsnane Total traffic over structural design period: FIGURE 3 ~Ilustration of dinerent road cstsgo"es UD (a) if road carries contruction traffic 0. The level of service that a user expects from a road is related to the function of the road. goods loading areas and bus routes. For example. Important Moderate level of service Less important. Also by-passes and certain mral main roads. High level of service level mice. ImpMtanoBand Very important.50 x 10D EWane 0. District and local distributors (SAICE: Minor arterials and collectors). Unimportant.2 IMPORTANCE.05x 10' EBOdane - . 1 Selection of analysis perlod The analysis period is a realistic cost period. The analysis period is a convenient planning period during which complete reconstruction of the pavement is undesirable.988 L TlME Ibl DESIGNZ REQUIRES THREE RESURFACIMS A N 0 NO STRENGTHENING DURING THE AWLISIS PERWD IF SURFACING 6 NOT W I N T A I H D AND IF WATER-SUSCEPTIBLE M A T E W S A E USED IN THE P N E K N T . The accuracy of the prediction could be improved by having a feedback system. ~tis necessary to consider how the pavement is expected to perform over the analysis period. There may be a difference between the analysis period and the total period over which a facility will be used. The actual maintenance should be determined by way of a proper maintenance procedure.2. For Category UC and UD roads. In the case of a short geometric life in a changing traffic situation. STRUCTURAL DESIGN PERIOD AND DESIGN STRATEGY The design strategy could influence the total cost of a pavement structure. a period of 30 years should be used.2 SELECTION OF ANALYSIS PERIOD AND STRUCTURAL DESIGN PERIOD 3. The analysis period will influence the salvage value referred to in Section 9. The manner in which a design strategy can be presented is demonstrated schematically in Figure 4 which shows the generalized trends of riding quality decreasing with time and traffic for two different pavement structures.I JTRUCTWAL REWBILITATION USUALLV OCWRS AT ALATER S T G FIGURE4 ll~ustrationof design periods and aiternaiive design strategies . 3.2 Selection of structural design period (a) Category UA roads For Category UA roads. 3. If the road alignment is fixed. TlME I 1.2. namely: .1 ANALYSIS PERIOD.3 DESIGN STRATEGY 3. The analysis period i s often related to the geometric life.3) OESIGN I REQUIRES TWO RESURFACINGS AND ONE STRUCTURAL REHABLITATION W I N G THE ANALISIS PERIOD It is important to note that any design procedure can only estimate the timing and nature of the maintenance measures that may be needed. the structural deslgn per~odshould be reasonably long because 6 ShWEtUd da4lgn d " 6 8 8 &I UTW. Design 1. Normally a design strategy is applicable only to Category UA and UB roads. Naturally such estimates are only approximate but they provide a valuable guide for a design strategy. which requires resurfacing to maintain the surface in a good condition. In order to fulfil the design objective of selecting the optimum pavement in terms of present worth of cost. and later some structural rehabilitation such as an overlay (Figure 4(a)). and Design 2. Rstona ~ o u m ~fnm . the design periods are fixed. The structural design period is defined as the period for which it is predicted with a high degree of confidence that no structural maintenance will be required. a short analysis period will be used. which is structurally adequate for the whole of the analysis period and requires only three resurfacings (Figure 4(b)). 0 X . This cumulative equivalent traffic can be determined in two different ways: . Long structural design periods (20 years) will be selected when circumstances are the same as for Category UA roads. very few heavy vehicles. 4. and through detailed computation from initial and mean daily traffic. Factors that encourage the selection of short structural design periods are: a short geometric life for a facility in a changing traffic situation. the structural design period adopted in this document is 20 years. and a lack of confidence in design assumptions.O x 10' Medtum volume of traffic. The estimation of the cumulative equivalent traffic over the structural design period from tabulated values is recommended. bus routes and arterial roads. a lack of short-term funds.05 X 1OB) Residential roads.1 TRAFFIC CLASSES FOR STRUCTURAL DESIGN PURPOSES The road alignment is normally fixed. 12-50 (d) Category UD roads The traffic volume is so limited that no structural des~gn period is applicable.3. Major arterial routes.0. J It is usually not politically acceptable for road authorities to carry out heavy rehabilitation on recently constructed pavements. For structural design. The traffic classes TABLE 3 (c) Category UC roads For Category UC roads (residential roads) a fixed structural design period of 20 years is recommended Fable 2). The class of traffic is a major factor in the selection of the actual pavement structure from the catalogue of designs. . EBOs/lane (C0.2 x 10' Lightly traffickedcollector roads. manly cars and llght delivery vehicles. varying from ER for residential roads to E4 for very heavily trafficked roads. Description X 10' High volume of traffc andlor many heavy vehicles. especially the design traffic. m e cumulative equivalent traffic (total'~80sover the design period) is grouped into six traffic classes. an estimate of the cumulative equivalent traffic over the structural design period is required. for Category UA roads. Very high volume of traffic andlor a hlgh proportton of fully laden heavy veh~cles.. The cumulative damaging effect of all individual axle loads is expressed as the number of equivalent 80 kN single-axle loads (€80~).2 . (b) Category UB roads For Category UB roads. Malor arterlal routes.12 x 10' 'The analpls per~od for Category UA and UB mads is 30 years. Structural design periods may range from 10 to 25 years. the structural design period may vary depending on the ctrcumstances. 0. As shown in Table 2. 0.0. unless more specific information is available. Normally a period of 20 years will be used (Table 2). by estimation from tabulated traffic classes.05 . TABLE 2 Structuraldesign periods for various road categories Road category UA UB UC r Structural des~gnperlod' (years) Range Recommended 15-25 10-25 10-30 20 20 20 Classificationof traffic for structural design purposes Traffic class Cumulative equivalent traffic.8 10' Collector roads and lightly trafficked bus routes. 0.8 .This is the number of 80 kN single-axle loads that would cause the same damage to the pavement as the actual spectrum of axle loads. 4 DESIGN TRAFFIC Road user costs are high and the cost of the disruption of traffic will probably cancel out any pavement cost savings resulting from the choice of short structural design periods. 3. growth rates and lane distribution factors. A~essaaaul o u Allew~ouale 3!44eJt 40 suo!wndwoa 'speor an pue 3n ho6ale3 ~ o' (j ~ 01 3 ~3 ad 03 ueql Jaq6!q aq o l punoq s! sserJ ~ E J Iu6!sap aql uaqm Aluo a(qw!fdde aq plnom 3!&e11 lua!eA!nba an!le[r. peoJ Jam01e sase3 asaql ul spaads ap!qan Jam01paledp!)ue 40 a s n m q pa~ap!suo3 aq hew {anal aa!Nas aql u! a6uetp e speo~paw!#e~lA1146!1 u!eua3 ~ o j '0301 !j3 u o sa6ueq3 ~ ~ ssep 3 ! p ~ l u6!sap aq: 1eq1 moqs 01 h e s s m u aq A e u uo!teln3ler.-.S t w-SE PC-SZ PZ-Sl s L u e u ssai - - . e '=!ye~zuo!pnJlsuo= h e 3 speol le!tuap!saJ 4! 'JanamoH .S9 P9 SS PS .000'0s 000'6E OOO'ZE 000'9Z 000'02 O0Oa9L OOO'ZL OOP'6 OOO'L OOL'S 009% 009'2 009' 1 000' 1 06S'O OZE'O OSL'O 290'0 610'0 POOO ' 000'0 PLL-SOL WL-56 P6 S8 98 -Sf PL .n aql $0 uo!mnduoo pa(!etap v 'E alqel u! pau!jap ale .an6olelee3 aql u! su6!sap aqi 6 u ! 6 ~ 4 3uew Jaqw papalas aq plnoqs hoSa)er. i)x where ... The values in Table 5 could change in the future.Ol. Table 5 also gives an indication of the number of E80s per commercial vehicle on various types of (b) Dynamic weighing procedures The traffic data logger VDL) can be used to determine the dynamic load of moving axles... the equivalent traffic can be calculated as described in 4.. in increments of 2 000 kg.... More than One growth rate may apply over the design period. 4..........3 (a) Projectionto initial design Year ~h~ present average daily equivalent traffic (daily E8W can be projected to the initial design year by multiplying by a growth factor determined fromthe Number of E8Od commercial vehicle Mostly unladen (Category UC.............1.. ~fan equivalency factor is then atmuted to each load group..i)/(l + 0........i) > 70 % laden (Category UA or UB... Retoria.. Greater emphasis should therefore be placed on period over which the visual estimation was done............. The TDL sensor installed in the traffic lane determines the load of every axle moving over it. arterial roads and bus routes) .... 4. medaily equivalent traffic in the initial year is given by: Einitial = E.................. other more detailed visual estimation procedures can be used5.....2...... where fy = cumulative growth factor......... (b) Computation of cumulative equivalent traffic mostly fully laden. especially if the legal axle load limit changes.......... S u f i AtnFa IQBB ma....2..3 g = growth factor i = growth rate = time between determination of axle load data and opening of m e traffic growth factor (g) is given in Table 6...01.... residential and collector roads) traffic (total Ems) over the structural design period may be calculated from the equivabnt traffic in the initial design year the growth rate for the design period.....4........ fy 50 % laden.............1//(O. main arterials or major industrial routes) - (y = structural design period see Section 3) m e cumulative growth factor (fy) is given in Table 7.5 ....... Where possibk the growh rate should be based on specific information.4 mecumulative equivalent t r a k may be calculated from: Ne = Einitial....01 .. the number of ~ 8 0 sper commercial vehicle has increased at a rate of about 6 % per annum... The methods are based on information gained from countrywide mostly unladen: gx= (1 + 0.............Ol........................ (c) Estimation procedures based on visual observations These procedures are used when coStly traffic determinations are not justified or when the characteristics of the road make dynamic weighing difficult.......................... struoural d w n d umsn maas UTW....... based on fy = 365 (1 + 0......Sovlh~hiulaas stmnural dergn d urban mads Pmtona... me cumulative equivalent TABLE 5 Determinationof E8Os per commercialvehicle Loading of commercial vehicles (or type of road) projection of the traffic data over the structural design period 4.......... In using these more attention is given to the actual loading conditions of the commercial vehicles on the specific route. ' of all equivalent traffic is due to laden commercial veGcles More than 90 % (ie Inore than 60 % full).... over the last 10 years... The load of the axle is then classified into one of 11 load groups......This gives an estimate of the number of repetitions of a given axle load...................... These rates will normally vary between 2 O/J and 10 % and a value of 6 % is recommended..i)Y.. 50 % unladen (Category UA or UB.... There may also be a difference between the rates for total and equivalent traffic..... 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It is applicable only to traffic classes E l to E4.W 1..50 .2...........50 0..... 4.30 0. As far as possible.. Be or B Surfaced slow shoulder Lane 1' (a) Equivalent traffic (E80s) Factor Be 2 1.... " ~ Lane 1 1s the outer or slow lane For dual-carriageway roads evu = equivalerrt vehicle unit: one commercial vehicle - 0. which would result in no further growth in traffic for that particular lane. Note that the distribution of total traffic and equivalent traffic will not be the same.. The distribution will also change along a length of road.....25 0..70 6 0....... Fi gx Y' = equivalent daily traffic at time of survey = growth factor to initial year (x = period from traffic survey to initial design year) = cumulative growth factor over structural design period (y = structural design period) = lane distribution factor for equivalent traffic Be m e designer should now go back to Table 3 to determine the design traffic E4).... TABLE 8 Design factors for the distribution of traffic and equivalent traffic amono lanes -andshoulders - Total number of traffic lanes Design distribution factor....... fy . When projecting traffic over the structural design period.. Fj) ..40 0. Be . the designer should take into account the possibility of capacity2 conditions being reached..25 - - 0.... the traffic will be distributed among the lanes.... ...oo 1. The factors should be regarded as maxima and decreases may be justified.... gx .4 Estimating the lane distribution of traffic On rnulti-lane carriageways.40 - E Surfaced fast shoulder" 3 evu 4...95 0............95 6 0.....30 0...4...70 0... .... - In order to check the geometric capacity of the road..... Suggested design factors for total traffic (€3) and equivalent traffic (Be) are given in Table 8... 4....30 0..60 (b) Trafflc (total axles or evu".....oo 4 0... Simple interpolation techniques are available (described in class (ER Section 7) if the pavement structure is to be designed to greater accuracy with regard to traffic..7 where Zt..2.....70 Lane 2 Lane 3 - - 0.50 4 0... the growth rate and the structural design period....) Factor B 2 1......00 0..8 with gx as previously defined..... Figure 5 gives a nomogram for determining the design traffic class from the initial E80s per lane per day........30 0.. the total daily traffic towards the end of the structural design period can be calculated from: n = (initial total daily traffic) ..... depending on geometric factors such as climbing lanes or interchange ramps.... gx ..5 The design cumulative equivalent traffic The design cumulatwe equivalent traffic may be calculated by multiplying the equivalent traffic by a lane distribution factor (Bd: Ne = (rti ... these factors incorporate the change in lane distribution over the geometric life of a facility.... 2. crushed-stone material compacted to 86-88 96 of apparent density.60) to lowerquality materials used in selected layers (CBR 3-15). If the fine aggregate is obtained from a swrce other than the parent rock. 62 and G3 may be a blend of crushed stone and other fine aggregate to adjust the grading.2 DESCRIPTIONOF MAJOR MATERIAL TYPES This subsection describes the materials in Figure 6 and their major characteristics.1 GENERAL LIST OF PAVEMENT MATERIALS AND ABBREVIATED STANDARDS The selection of materiak for pavement design is based on a combination of availability.1 Granular materials and soils (01 to 010) These materials show stress-dependent behaviour.22 Bituminous materials (BC t o TS) Bituminous materials are visco-slastic and under repeated stresses they may either crack or deform or both.a GROWTH RATE I I I 1%) G9 : 2 I \ . 5. The material codes listed in this table are used extensively in the catalogue of designs.2. 5. Waste materials (eg blast-furnace slags) and pedogenic materials have not been clas$ified because of their valying quality. These factors have to be evaluated during the design in order to select the materials best suited to the conditions. The behaviour of different pavement types consisting of combinations of these materials is described in Subsection 6. The materials are classified into various categories according to their fundamental behaviour and into different classes according to their strength characteristics. . its use must be approved by the purchaser and the supplier must furnish the purchaser with full particulars regarding the exact amount and nature of such fine aggregate. If these materials are used they should be classified according to the appropriate material codeslo.5 MATERIALS 5. 5. and under repeated stresses deformation can occur through shear andtor densification.- s l--. The classification of the materials is given in Figure 6. economic factors and previous experience. unweathered. Only abbreviated specifications are given and TR~1410should be consulted for more details. A faulty grading may be adjusted only by means of the addition of crusher sand or other stone fractions obtained from the crushing of the parent rock. DESIGN TRAFFIC CLASS FIGURE 51 A G I is a dense-graded. In gravel roads natural gravel materials of quality G4 to GI0 are used for the wearing course. 6 4 to GI0 materials cover the range from high-quality gravels used in pavement layers (CBR 25 . Normally a BC continuously graded bitumen hot . CUMULATIVE E 8 0 I / L A N E OVER STRUCTUR4L DESIGN PERIOD I I The design procedure generally uses the standard material specification defined in TRH14 Guidelines for mad construction materialslo. 4 Cemented materials (C1 t o C4) As concrete. S1 t o S8) The surfaclngs cover the range from high-quality asphalt surfacings to surface treatments and surface maintenance measures such as rejuvenators and d~luted emulsion treatments. Tar hot mixes (lC.2. especially in wet regions. C3 and C4 materials can be used as replacements for granular layers in bases and subbases.5 Surfacings (AG t o AO. Because of the excessive shrinkage cracking of C1 materials.mix wdl have a higher stability and lower fatigue life than a semi-gapgraded BS material. 5. In this document only one concrete strength is considered.2. By the application of an upper limit to the strength specification. 5. They can be either cement-treated or lime-treated. specific knowledge of construction techniques is required.7 Paving blocks (S-A. . Blocks with good interlocking shapes should be used. However.2. they are not generally used. 5. These materials also crack because of shrinkage and drying. brittle material possessing tensile strength and it may crack under excessive repeated flexure. Usually the stab~l~ty of a tar mix is the same as or h!gher than that of the equivalent bitumen mix. depending on the properties of the natural materials. possess tensile strength and may crack under repeated flexure. wide shrinkage cracks can be avoided. - - FIGURE 6 Definitionof materialsymbols usadin catalogue of deabns The use of clay bricks as paving blocks (S B)should be limited to Categoly UC and UD roads.2. pavement materials which can be used in the place of G1 to G4 materials. The performance of clay bricks is expected to be poorer than that of concrete paving blocks.6 Macadams WM to PM) These are traditional. cemented materials are elastic. A C2 material will be used when a non-pumping erosion-resistant layer is required (as for a concrete pavement).TS) will normally have lower fatigue llves than the equivalent bltumen hot mlxes. These materials are less water-susceptible than the usual granular materials and using them should be considered. 5.3 Portland cement concrete (PCC) Concrete is an elastic. high-quality. S-6) m e use of interlocking concrete paving blocks (S A) is limited to low-speed (<SO kmh) mads or terminal areas. but also labour-intensive. 52. . . Subgrade CBR (%) 7 to 15 15 to 25 > 25" Special treatment required Use The *Orrnai ements with paving blocks. a granular or cemented subbase and a soilsor gravels. but at some stage the subbase will crack under cracking may propagate until the layer eventually exhibits ProPenies those of a natural granular material. a base of of gravel or crushed stone. 6. This is illustrated in Figure 9(a). TRHg9 be consulted when a material with a CBR of less than 3 isused inthe fill. to be tittle rutting or longitudinal the subbase has cracked extensively.if the ation until the exhibits large shrinkage or thermal cracks. pavements with cemented subbases. Untreated granular-base pavements comprises a thin bituminous Surfacing.9 DESIGN CBR IN CUT The design CBR Of the subgrade in a cut should be the lowest CBR encounteredwithin the material depth. When the CBR ON FILL is On the designer must avail himself of the best information ava'lable On the localmaterials that are likely to be used. A brief description of the 150mm as subbaseor base material.5) and may atso influence the selection of the pavement type. The mode of distress in a pavement with an grade of subbase is usually deformation arising from shear or densification in untreated materials.Material depths to be used for determining the design CBR of the subgrade Road category Material depth (mml TABLE 10 Subgrade CBR groups used for structuraldesign STRUCTURAL DESIGN AND PAVEMENT TYPE may use a number of design procedures. compactedto the correct standardlo. The deformation may manifest itself as rutting or as ngitudinal roughness. It is unlikely that cracking will to the ~ ~ randf there ~ ~is likely ~ . H~wever. such as the mechanistic pavement costs are discussed in Section 8. the subbase improves the load of the pavement. The material should be at leastthe material depth. The behaviour of these different pavement types determine the type of maintenance normally required (Subsection 9. they may reflect ~ & work ~ t has shown that the post-cracked phase of a cement-treated subbase under granular and bituminous bases adds substantially to the useful '?:: . TRH14 requirements shouldbe met. namely either an 28 Smrtural W W. but the resilient deflection and radius of cu change. The design accommodates the chang subbase.2 Bituminous-base pavements These pavements have a bituminous base layer of more than 80 mm thick. namely bitumen.3000 to 5000 MPa as shown in Figure 9(c). This change in modulus does not normally increase in deformation. Many of these lower-cl materials have. Granular materials are often susceptible to and excessive deformation may occur when water ingresses through the su cracks. there may be pum from the subbase. This change is shown diagramma Figure 9(c). This relatively rigid subbase generally fatigues under traffic.rign Of "M" "rw. I GRANULAR BASE ( b 1 BITUMINOUS BASE CEMENTED-SUBBASE MODULUS BEHAV~OUR The surfacing may also crack owing to ageing of the binder or to associated fatigue cracking. In some cases the layer may behave like a go m e r i a l with a modulus of 200 to 500 MPa. Two types Of subbase are recommended. the cementing agent. and assumes a lower effective mo 1000 M W . and although the safety factor in the baqe will be red well within acceptable limits.and tar-ba pavements. proved to be adequate for lower classes of traffic. - In the mechanistic design6 these phases have been termed post-cracked phases. whereas in other cases the will be between 50 and 200 MPa.'the PI the fines. that will eventually deteriorate to a very low modulus. Deflection measurements at various Pavement have indicated that the initial effective modulus o f t . the absolute density achieved and the degre ingress of moisture can affect the modulus in the po significantly. ( .2. heavily trafficked pavements it is necessary to avoid mate. as shown in Figure 9(d).life of the Pavement. The result is that the modulus of the cemented subbase assumes very values and this causes fatigue and high shear stresses in t surface cracking will occur. however. and with the ingress of water. ( t i CEMENTED BASE (a) Bitumen-base pavements In bitumen-base Pavements both deformation and fatigue cracking are Possible. 1 The eventual modulus of the cemented subbases will depend on the qu the material originally stabilized. The water-susceptibility depends on factors such as grading. and density. Waterbound rnacadams are less susceptible to wat than crushed-stone bases and are therefore preferred in wet regions. or in even under construction traffic. 7. Relala '988 . Th can be subdivided into two major groups. For high-quality. n ofurnan mad sMM Afvim 1988 d - d. the effectiveness mixing Process. The popularity of these cks is increasing due to a number of factors: 2.2. . bituminous or granular overlays will be used. most of the traffic loading and little stress is transferred to the subgrade. this is caused mechanism of drying shrinkage and by thermal stresses in the cemented Traffic-induced cracking will cause the blocks to break up into smaller These cracks propagate through the Surface. See Figure 9(e). The procedures for the ents are presented in UTG2 ts in southem Africa13 and are are manufactured with vertically square side faces. Th a uniformfoundation and limits pumping of'subbase Through the use of tied shoulders.4 Cemented-base pavements In these pavements. 30 e initial cracks may be rehabiliated by sealing. Those that e shaped so as to allow them to fit ''jigsaw" fashion into a paved They can be made of pressed concrete. evident. cra grinding. fobwed by fatigue cracking of the tar base. Maintenance consists of patching. Only weakly cemented subbases are used. or recycling of the base when further overlays are no longer adequate. This is illustrated in Figure 9(b). The current recommended minimum strength for structural use is given wet compressive strength of not less than 25 MPa. Th surface cracks may cause the blocks to rock pumping of fines from the lower layers. Or the may be recycled. 7. The use of segmental block avements is a recent phenomenon in South Africa. rehabilitation involves either the reprocessing oP e base or the application of a substantial bituminous or granular overlay. the pavement will be less ensitive to overloading and moisture. 7. - avements consisting'-! cemented bases on granular subbeses are very ensitive to overloadingland to ingress of moisture through the cracks. untreated granular subbase or a weakly stabilized Rutting may originate in either the bituminous or the untreated layers. (b) Tar-base pavements ~h~ fatigue life of a tar premix is well below that of most bituminous materials. most of the distress stemming from the of the pavement Can be eliminated and the slab thickness can also be red Distress of the pavement usually appears first as spalli may then progress to cracking in the wheel paths. Once traffic-load-associated acking has become extensive. or in both. See Figure 9(d). deterioration is usually rapid. they are aesthetically acceptable in a wide range of applications. fired-clay brick or any other id. and ' 0 they are versatile as they have some of the advantages of both flexible and concrete pavements. The main distress appears to be cracking of the cemented subbase. The selection of the right type of sand for these purposes is on-plastic material serves best as bedding while some quired to fill the joints.5 he blacks are manufacturedfrom local materials.3 Concrete pavements ln concrete pavements. In heavily loaded areas interlocking shapes have r8l d W n o( urban roads Pretoria. they can either ~rovidea labour-intensive operation or can be manufactured and laid by machine. The latter type of pavement is generally wnted subbase. It is likely that SO evident very early in the life of cemented bases. When 0th the base and the subbase are cemented. especially if the bituminous layer is less than 150 mm thick or if the subbase is excessively stabilized. Maintenance usually consists of a surface treatment to provide better skid resistance and to seal small cracks. Lateral movements are induced fficking and these movements cause breaks in the jointing sand. joint repair. This is a requirement for terlocking and non-interlocking shapes. 81 . Paving blocks es of interlocking and non-interlocking segmental blocks are used in a iety of applications which range from footpaths and driveways to heavily industrial stacking and servicing yards.2. an asphalt overlay in cases where riding quality needs to be restored and when it is necessary to prolong the fatigue life of the base. If the subbase is cemented there is a probability that shrinkage or thermal cracking will reflect to the surfacing. most of the traffic stresses are a layers and a littlg by the subgrade. rly laid block pavements are adequately waterproof and ingress of large tities of water into the foundations does not occur. Maintenance for tar bases is the same as for bituminous bases. - In current practice a small Plate vibrator is used to bed the blocks into a sand bedding of approximately 20 mm and to compact jointing sand between 'ndividual 'blocks. hl thick concrete. South Ahim ism . Rutting or roughness will low up to this stage but is likely to accelerate as increases. or thin concrete or bituminous overlays. The ociated opening-up of the block pavement makes it more susceptible to the ess of surface water. k Pavements require the paved area to be "contained either by kerbs or by means Of stopping lateral spread of the block.. In such cases the pattern of the blocks is an important cons Experience has shown that a herringbone pattern is best for use gradients and for industrial paving. this re-use of the biocks h disadvantages. levelling the sub compacting the subbase (often with hand hammers) and replacing the blo ~~ Length Of road on which stated types of cracking occur (%) 10 15 25 40 . spall~ngat joints. Figure 10 demonstrates that the rut depth values in Table 11 actually represent ranges of failure conditions. as shown in the previous paragraph. surface loss. especially .- 20 20 10 15 . . However. . Table 11 shows acceptable terminal conditions of rut depth and cracking for the various road categories and pavement types. there improving the total strength of the block pavement. The correction of levels is done by removing the area of blocks affected. which would result in the opening of joints and I of bond between the blocks. since the blocks are small an can easily be cut and placed to suit the geometry of the pavement. One per cent falls (minimu to the surface of block pavements allow water to drain across the paveme reducing ingress by absorption through the joints. . Cambered cross-sections are also satisfactory. > Little maintenance work is normally required with segmental block Maintenance involves the treatment of weeds and the correcting of 1 surfacing if the initial construction had been poor. .restraint is required along the edges of a block pavement to prevent outward migration of blocks. Edge. cures and junctions do not present problems in practice. action are involved. Variable road widths. . certain kinds of distress can be expected in certain pavement types and account must be taken of such distress. rocking blocks. The joints between the blocks seal better with time due the action of weathering and the addition of road detritus to the joints. pumping of fines ~. . Gadvantage of the blocks is that they '?an be re-used. They can be lift repairs have to be carried out to failed areas of subbase or if services have installed and can be relaid afterwards. pumplng Concrete pavement Slab cracking. For wid areas of industrial paving. Experience has shown that joints should be 2 to 5 mm wide. special care should be taken to ensure that the cross fall of the surface is adequate. In practic the minimum cross-fall for block pavements should be one per cent.3 POSSlBl -'~!ONDITION AT END OF STRUCTJRAL DESIGN PERloo -There is no design method available to predict the exact condition of a length of road 10 to 20 years in the future. Geometric design should follow practices for other pavements. ~ Secimental ~avinaDrovideS an exciting addition to the ~avementconstruction' ~ TABLE 11 Possible condition at end of structural design period Rut depth (mm) Length of road exceeding stated rut depth (%)(refer to Figure 10) Type of cracking: Granular base Bituminous base Road category UA UB UC UD 2n -- m . pumping of fines Crocodile cracking.non-interlocking shapes.- 7* -- 40 Crocodile cracking.?hides with a Slew' . Edge restraint can be provided by means conventional kerbing.< advantages over. and eliminate pon joints between the blocks on steep gradients may form the drainage rainwater.-.. As far as the structural desi segmental block pavements is concerned. Pumping of fines Cemented base Block cracking. 7. The required selected subgrade layers will vary pavement structures in the catalogue are wnsidered adequate to carry the I design traffic according to the upper value of the traffic classes defined in 3 w i n ol urban mads .. On top of this prepared layer. whereas the more flexible pavements generally deteriorate mo slowly. other methods should then be used. tmexpensive E4: Uncertain behaviour.71TABLE12 -.~ a m i aSouth . ER tm expsnsivs Extra thickness required to prevent fatigue cracking. but the catal 34 mete Cemsnted Smrtural dasign Df mG3. one or two layers will be added. unless special provision is drainage. pumping and rocking blocks \/ \/ V \/ Shrinkagecracks Recommended =Not recommended Not recommendedfor wet regions without special provisionfor drainage Only for steep gradients still act as a guide.5. - 7. Table 12 shows . Pavement structures consisting of water-susceptible material undesirable for Wet climatic regions.X $1 X low. S r u t h m 1 cted to a depth of 150 mm. The catalogue does not necessarily exclude other sible pavement structures. all the factors noted in Sections 2 to 6 shouki special conditions arise. RetoM. EO. Reasons why certain pavement types a not recommended are also stated briefly. Signs of distress are often more visible on rigid pavements. assumes that all subgrades are brought to equal support THE CATALOGUE DESIGN METHOD 7.1 Introduction to the catalogue Before the catalpgue is used. Suggestedpavementty&'for different road categories and trafic classes RANOES OF FAIWRE WNDlTlONS ROAD CATEGORY P b3 R 10 - LENGTH OF ROAD EXCEEDING + WCAL REPAIRS ONLY STATED RUT OEPTH (%I FIGURE 10 Rsngesaf terminal rut depth conditions for different road categwies Figure 9 indicates that the more rigid siwctures deteriorate rapidly once distres is shown. A1988 35 .recommended pavement types (base and subbase) for differe road categories and traffic classes. pumping and fauting TW ~xpallsive. IW difficult \/ \/ V \/ to trench Fatigue cracking.5 Cemented % \/ \/ \/ \/ X X X X Granular X X X X Cemented \i \/ Granular X X X Csmented X X \/ X X X X X 11 X X \rY \rY X . temperature and ultraviolet radiation). (a) The gravel road may be regarded as a long-term facility. 7. The total design traffic may be predicted with accuracy than is implied by the traffic classes.Ratau.4 Surfacings Urban and residential roads cany both traffic and stormwater run-off. at subgrade level.SwthAhica 1888 .6. In these cases a high-quality surfacing is required.1 General These unpaved roads may still be used under certain conditions. A gravel road may be regarded as a long-term facility or as an inteim step towards a paved road. road category. In these cases the designer may use linear interpolation. there is no distinction between paved and unpaved roads. Section 4 Vabie 3).2. although there may be special cases where they can be regarded as Category UB roads.5. " Compacted to the appropriate density (refer to Table 10). Therefore. the material should comply with the subbase standards applicable to the future pavement. availability.6.3 The standards for gravel wearing courses are laid down in ~ ~ ~ 1 4The 1 0quality . Normally. . material availability and traffic). GRAVEL ROADS 7. design traffic class: environment (eg moisture. If the wearing course is to be removed later. The t often consists of either large volumes of lightly loaded vehicles (eg on roads) or virtually no trafficking (eg on residential roads and culs-de-sac).6 Not applicable to Category UD roads: for these use only one selected layer required.TABLE 13 . . suuam W n d wean m d s LIW. braking movements. On more heavily trafficked roads. 7. should such a subbase be necessary later. Selected layers for gravel roads 7. Design of gravel wearing course 7. The controlling authority should Select a surfacing from the catalogue that will give satisfactory performance. The factors influencing the choice of surfacing are: 0 local experience.2 The selected layers should be designed according to 7. This follows from fundamental strength requirements and it will also simplify possible later changes from gravel to paved roads. in which case the most suitable wearing course will be selected for the prevailing conditions (climate. In such a case the designer use a simple linear interpolation technique. pavement type: . but allows a choice of surfacings for the lower categories of road. If the gravel wearing course is going to be overlaid later. interpolation is theninadequate and the designer will have to use other des methods6-12. . and gradients. Such a surfacing is al necessary becaude the road acts as a water channel.5. 0 turning movements. H there is often a change in material quality as well as in thickness. unpaved roads could be considered for use as Category UC or UD roads. This will influence the level of the surface with regard to stormwater facilities. and thickness of the wearing course may also depend on the design approach. (b) The gravel wearing course may be regarded as an interim riding surface which will be overlaid or removed when Me mad is paved. ~ The catalogue specifies the sirfacing type. In many designs the only differ between the structures for the various classes of traffic is a change in t thickness.6. intersections. consideration should be given to the inclusion of a proper subbase during construction. On urban access or residential roads it would constitute the future basecourse. If a waterbound macadam is used in the base in the place of a G1 to G4 . the gravel wearing course should be used as a future subbase. A brief description of design factors will follow. The thic requirement for the gravel wearing course can be determined from em models.(c) The gravel wearing course may be regarded as the base layer of the paved road. These values have be selected to provide an adequate pavement. M o n a . irnposrable d u n W wet season st~ctumldeslsndu h m t d s . material availability and the design approach. Designtrafficclass >El. When a gravel wearing course has to be provided the existing subgrade support the traffic loads adequately under all climatic gravel wearing course serves as protection to the subgrade. In Table 14 the thickn requirement is also given in general relation to the road category. . the thickness of gr should be the minimum cover thickness plus provision for gravel loss until road has been regravelled (usually for a six-year life).ma.1488 ' . considering that some form surface maintenance is usually applied and ruts as large as 75 mm ar not tolerated in practice. Souh A m l98B . Rood i s lrofficablc during wet season Road becornel TABLE 14 Design thickness of gravel wearing course for different road categories FIGURE 11 ~~~i~~ curve for thepassabil~of unpavedroads ' '^ The quality of the wearing course may change depending on the climate. SOU~A. Figure 12 shows a model which gives the minimum cover thickne adequate protection of the subgradeld. When gravelling. It is best determined soaked laboratory CBR of the surfacing gravel material. A distinctio made in each of these functional classes between a interim facility involving upgrading possibilities.. This will normally be possible only for some Category UD roads. LIT=.ucluraI deign d "h roads UTW. Sf. The thickness of the gravel wearing course will depend on the road and on the design approach chosen. Passability duri best criterion to use in the design of a gravel road. but then special restrictions should be placed on the plas index of the fines. Figure 11 proposed limit related to the A D T ~ ~ . TABLE15 * Compaction requirements for the construction ofpavement layers' (and reinstatement of pavement layers) 'avement layer Surfacing . Base (upper and lower) Compacted density Bituminous Crushed stone 95 % 75-blow Marshall ~il00%t0102% Mod: AASHTO Crushed stone G3 and gravel G4 Bituminous Cemented Subbase (upper and iower) Selected subgrade Subgrade (within 200 mm of selected subgrade) (within matenai d e ~ t h l ('JWSS3NM31H1 U3A03 FIGURE 12 CBR design cuwes for cover thickness of gravel roads rw (coh&3nle~ sand) ~ Refer toTRH141° 98 % Mod AASHTO 95 % 75-blow Marshall 92 %theoretical max 97 % Mod AASHTO 95 % Mod AASHTO 93 % ~ o AASHTO d 90 % Mod AASHTO 8s % Mod AASHTO 90 % Mod AASHTO (I 00 % Mod AASHTO) . erosion-resistant. rehabilitation in the form of an overlay may cause a pr particularly with respect to the level of kerbs and channels. but then provision for discharge must be made. (b) The subbase should be stabilised to a high quality to provide a nonpumping. circumstances. blistering or loss of bond of the disintegration of cemented bases and loss of density of untreated bas the excessive deflection and rebound of highly resilient soils during the Passage of a load. the pavement structure may be varied over the cross-~ectionof the that this is economical and practical. eg in expansive soils and soils with collapsib e flaws in structural support. In these cases strong consideration should bottom-heavy designs. micaceous and diatomaceous soils. rvice trenches can also be the focal points of drainage problems. This is as a result of er inadequate compaction or saturation of the backfill material. mecross-section can be varied by means of steps in the layer thickness. m road levels become a rather more important factor in urban areas tha in rural or interurban road design. eg in climbing lanes. The design of embankments should be done in accord ~ ~ ~ 1 0 9 . dwe ComwCial establishments is the primary function of an urban road. but it become much more n natural materials are used.3 SUBGRADE BELOW MATERIAL DEPTHa* Special subgrade problems may arise that require individual design procedure assumes that these have been taken into act The main problems that have to be considered are: the extreme changes in volume that occur in some soils moisture changes. In some cases. giving rise to standing water and possibly to cracking of the surface. where there are significant differences in the traffic carried by individual lanes. the non-uniform support that results from wide variations in states. eg in ash. However.7 CONSIDERATIONS FOR CONCRETE PAVEMENTS ~onstructiondetails11 are beyond the scope of this document. under favourabie conditions. Urban roads are frequently used as drainage channels for surface water This is in sharp Contrast with interurban and rural roads which are usual1 to shed the water to side table drains some distance from the road shoulde SERVICE TRENCHES hes excavated in the pavement to provide essential services (electricity. eg sinkholes. particularly in the case of excavated dealing with clay subgrades il is recommended that if it is feasible. Fractured Water. Under these carriageway. with no change in layer thickness across the road. These densities are d whengranular materials are used. . ie designs with a cemented subbase and possib cemented base. Note that below base level th independent of the type of material used. Settlement the trench. which would mainly require the same maintenance as surfacings and iiple structural maintenance during the analysis period. Sewerage or stormwater pipes lead to saturation in the subgrade and possibly in the vement layers as well. a moderate-quality granular material be used as a trench ackfill in preference to the excavated Clay. will permit the ingress of moisture. The techniques available for terrain evaluation and soil mapping are TRH28. 8. In roads of Categoty UB and higher is preferable to stabilize all the backfill material and in lower categories the provision of a stabilized "cap" over the backfill may be considered to eliminate settlement as far as possible. .6 PAVEMENT CROSS-SECTION Generally it is preferable to keep the design of the whole caniagewaY the same. camber an overhead clearances. the actual traffic predicted for each lane should be Used in determining the design traffic. 8. paction must achieve at least the minimum densities specified in the ogue of designs and material standards (Table 15). mining subsidence an instability. homogeneous pavement support. Under no circumstances should the steps be located in such a way that water can be trapped in them. . A typical pavement cross-saction for a paved urban road is shown in Figure 14. the Presence of soluble salts which. 8. However. Urban road levels place some re rehabilitation and create special moistureldrainage conditions. telephone.-Table 15 gives the minimum compaction standards required layers of the Pavement structure. the following are some basic practical recommendations: (a) The subgrade should be prepared to provide a uniform support. etc) are frequently a source of weakness. ma upwards and cause cracking. subsurface drain.4 ROAD LEVELS The fact that the provision of vehicular access to adjoining roads. Consideration should be given to thetype and method of co when deciding on a layer thickness for the base. and the gutter face is 160 mrn. A degree of saving may be possible by utilizing grass verges where longitudinal gradients are slight and storrnw low. This restraint is b achievement of specified density and strength. attention shou the detail of the spacing. ?g if the design calls for a 30 mm AG underlain by a 12 G4. ~t is common practice to construct 'kerbs upon the (upper) subb provide edge restraint for a granular base.8 KERBS AND CHANNELS Kerbs and channels are important to prevent edge erosi stormwater to the road surface. type of joint and joint sealing of 8. The shoulder should be sh to the correct level and the edge may be sealed by a prime coat. Access to dwelling units should be provided in such a way as to adequate sight distances and a smooth entry. edging could be used for certain low-traffic roads w shoulder or sidewalk soil is of adequate stability. but the access ways shoul same time keep stormwater on the road from running into adiacent prope At pedestrian crossings special sloped openings in the kerbs should provision for to accommodate the handicapped and hand-pushed carts 0 5 10 15 20 25 30 LENGTH OF STRUCTURAL DESIGN PERIOD (YEARS) FIGURE 13 degree of struciuraldisfressto be expscred st the tmm of rehabdation for drffferenr structural design penods . 8.(c) When jointed concrete pavements are used.9 EDGING Instead of kerbs. a san slurry seal or a premix. In the case of kerbing with as-fixed size Fe precast kerbing or kwbin shutters cast in situ) it may be advantageous to determine the base from the kerb size. use a 130 mm G4. .. If the difference in present worth of costs between two designs is 10 % or less. the present worth of costs (PWOC) approach has been adopted. The method of cost analysis put forward in this document should only be used to compare pavement structures in the same road category. within the analysis period z = analysis period S'= salvage value of pavement at the end of the analysis period expressed in terms of the present value. The salvage value of the pavement at the end of the analysis period can make a contribution towards the next pavement. The effect these differences have on road user costs is not taken into account directly.. only a comparison of the construction costs will normally suffice. The present worth of costs can be calculated as follows: PWOC = C + M i (1 + r)-xl + . A computer program can be designed to facilitate the calculation of the present worth of costs. The choice of analysis period and structural design period will influence the cost of a road. geometric factors such as minor improvements to the vertical and horizontal alignment and possible relocation of drainage facilities make the estimation of the salvage value very difficult.... it is assumed to be insignificant.. The construction cost should be estimated from current contract rates for similar projects.1 + where PWOC = present worth of costs C = present cost of initial construction Mi = cost of the jth maintenance measure expressed in terms of current costs r = real discount rate xi = number of years from the present to the jth maintenance measure.... The total cost can be expressed in a number of different ways but for the purpose of this document. minus the saivage value. This is because roads in different categories are constructed to different standards and are expected to perform differently with different terminal levels. For Category UC and UD'ioads. However. 9..2 PRESENTWORTH The total cost of a project over its Life is the construction cost plus maintenance costs. Mj(1 r)-xj+ S(l + r)-2 . 9. A complete cost an$-? should be done for Category UA and UB roads... and the present worth of costs of the two designs is taken to be the same. but in Section 3 it was shown that the final decision is not necessarily based purely on economics. Maintenance costs should include the cost of maintaining adequate surfacing integrity (eg through resealing) and the cost of structural maintenance (eg the cost of an asphalt overlay)..... It should be noted that since the c the present worth. the precise selection of the maintenan important. . pavement types and this is ref!ected in Table 17. Table 16 gives guidelines regarding the typical surfacing lives that can be expected of various su values may be used for a more detailed analysis of future m Typical maintenance measures that can be used for the pu are given in Tabk 77. Some maintensnce measures are used more commonly on. However. it has been shown in Section 7 that t between the type of pavement and the maintenance that might be future. Figures 4 and 9 show that the life of the surfacing plays an importa behaviour of some pavements. When different pavement types are compared on the basis of future maintenance costs should be included in the analysis to ensu sound comparison is made.5 Surfacing type iranular Slurry seal PVC-tar single surfacetreatment Bitumen single surface treatment Bitumen double surface treatment Cape seal Open-gradedasphalt' Thin conl~nuouslygraded asphaw Thln gap-graded asphan jilumlnous Slurry Seal WC-tar stngle Surface treatment Bitumen single surface treatment Bitumen double surface treatment Cape seal Open-graded asphalt' Thm cont~nuouslygraded asphalt Thin gap-graded asphalt Semenled Slurry seal PVC-tar single surface treatment Bitumen single surface treatment Bnumen double surface treatment Cape seaf Open-graded asphalt' Thin continuously graded asphak Thin gap-graded asphan " FUTURE MAINTENANCE (Mi) Maintenance management or maintenance design is be document. planned m surfacing is very important to ensure that these pavements satisfactorily. For this reason..on Road category and trafic A suriace type not normally used. A TABLE 18 Typical ranges of surfacing life periods for various surfacing types for the fferent road categories and base types (if the surfacmgs are used as given in the catalogue) Typical range of surfacing life (years) 9. . top of a continuously graded or gapgraded aspban. There are two t maintenance measure: ~ measures to improve the condition of the surfacing. and 0 ase type structural maintenance measures applied at the end of the struc period. The lives of the various types of surfacing will depend on t and the type of base used. Bituminous Concrete Cemented Paving blocks SALVAGE VALUE (S) 51 (8-13yrs) S1 (16-24yn) Sl(23-30yn) S l ( 8-13 yn) S l 116-24yn) St 123-30yrsl No maintenance measures (a) Where the existing pavement is left In position and an overlay ts constructed. the existing pavement layers may have a salvage value. which depend on the maintenance measures applied and the traffic situation on the roads. TABLE 17 ad user delay costs should also be considered. but if the road is to be abandoned at the end of the period under consideration. the salvage value could be small or zero. Table 17 makes provision for both moderate and severe distress. . In the absence of better information. vehicle maintenance and depreciation) which depend mostly on the road alignment. If structural maintenance is do soon after the end of the structural design period. (This is a difficult factor to assess as it may include aspects such as the provision of detours. Rotooa. the salvage value of the pavement would be the difference between the cost of constructing an overlay and the cost of constructing a new pavement to a standard equal to that of the existing pavement wlth the overlay. but also on riding quality (PSI). South~tnca1988 a5 3 . Therefore typical structural maintenance WI average only be necessary at a later stage.i: > . tyres.) Granular 9. Structura(m g n of urban m d a UTG3. The salvage values of individual layers of the pavement may differ considerably. and delay costs. This salvage value is termed the recycling value. If the road is to remain in the same location.. although no proper guideline eadily available. Rebuild ba Relevellingof blocks S1 (10 yrs (d) In some cases the procedure followed could be a combination of (a) and (b) above and the salvage value would have to be calculated accordingly. the salvage value of the recycled layers would be the difference between the cost of furnishing new materlals and the cost of tak~ngup and recycling the old materlals. Base type accident costs. The salvage value of the whole pavement would be the sum of the salvage values of the individual layers. typical maintenance measures given in Table 17 should be replaced by e accurate values if specific knowledge about typical conditions is available. a salvage value of 30 % of initial construction cost 1s recommended. depending on the method employed to rehabilitate or reconstruct the pavement. When structural maintenance is done much later the distress will generally be more severe. The structural design period (SDP) has been defined (Section 3) as the pe ' which it is predicted with a high degree o f confidence that no str maintenance will be required. .6 The salvage value of the pavement at the end of the period under consideration is difficult to assess. Fullher surface treatments (b) Where the material in the existing pavement is taken up and recycled for use in the construction of a new pavement. from estimates as high as 75 % to possibly as low as 10 %. The assessment of the salvage value can be approached in a number-of ways. whereas that of concrete pavements can be high or low depending on the condition of the pavement and the method of rehabilitation. Figure 13 gives guidelines regarding the degree of distress to be expected at the time of rehabilitation for different structural design periods. The factors that determine the road user costs are: running costs (fuel. The residual salvage value of gravel and asphalt layers is generally high. This is termed the restdual structural value. the distress encountered will only be moderate. which depend on road alignment and riding quality. . disintegration and permeab~litywithout necessarily Increasingthe structural strength of the pavement.the general extent to which road users experien either smooth and comfortable or bumpy and thus unpleasa dangerous.the pavement layer of concrete which is placed over a pre and that acts as base and surfacing combined. quantified by a seNiceability/age fun E INFLUENCE OF TOWNSHIP LAYOUT ON THE CHOICE F ROAD CATEGORY - Present worth of wsts sum of the costs of the initial con Pavement.the completed earthworks within the road prism prior t construction of the pavement. This comprises the in situ material o roadbed and any fill material. Subgrade . quantified by factors of riding quality and Slab . and these therefore have to be Category Riding quality.the chosen minimum period for which the is designed to carty the traffic in the prevailing environment with a degree of confidence that structural maintenance will not be require . environ subg!ade support. Structural design period . especially as regards the roads within the township. partial reconstruction (of say base and surfacing). - Surfacrng the uppermost pavement layer which provides the ndmg surface for vehicles. etc). In structural design only the subgrade material depthjs considered.measures that will strengthen. correct a stmct Structural distress pavement. ownship layout has a strong influence on the choice of ioad category. the later maintenance costs and the salvage val present monetaty value.the layer($ beneath the base or concrete slab and on t selected layer. - Structural design the design of the pavement layers for adequate strength under the design conditions of traffic loading. FIGURE 15 a me influence of layout on mad category . either in situ or imporled (Classification codes GT-GI - Sewiceability the measure of satisfaction given by the pavement user at a certain time. However. or improve the riding quality of an existing pavement.. Subgrade desrgn unrt . Performance . Selected layer . Figure 15 illustrates this principle. - Surfacing marntenance a measures that matntaln the integrity of the surface in respect of skid resistance. but also on well-defined roads. Subbase . This implies that all other roads within the township will be either Categoty UC or UD roads. (eg smoothing course and surface treatment.. A well-designed layout will provide for bus routes (Category UB) within acceptable distances from all dwellings.the measure of satisfaction given by the pavem user over a period of time.a sectlon of subgrade with uniform properties and/or load-beanng capactty. in. a less-defined layout may imply that a number of roads could act as bus routes.the lowest of the pavement layers comp material.distress pertaining to the load-bearing capaci Structural maintenance . so that they all have to be designed to carry buses. 10. 16 Subgrade Area 4: CBR = 10. The current equivalent traffic may be projectedto the initial year using the growth factor (ge) from Table 6. 6. 6.2 Bv visual inspection of the given CBR values.8: 11. It will be a fou following informationis available: / (a) Centre line subgrade CBR values: 3. 6. 8. 20. 14. Design pavement structures of different base types and compare structures on the basis of costs before making a final selection.~ 1 e lane distribution factor (Be) from Table 8 is 0. 9. The unit prices listed are 1983 prices. I i I 1 (C) Road will be opened to traffic within three years. 10.2 Select structural design period (Table 2) A period of 15 years is selected. 7 growth rate. 3. 10.5. The fast lane will be designed for the same traffic as the slow lane.11. @) Current traffic (from a transportation study): Equivalent traffic = 200/day/direction. Delineatiw of subgrade areas and design CBR of subgrade 6.20. The cumulative equivalent traffic over the structural design period can be determined by multiplying the initial equivalent traffic by the cumulative OBJECTIVE A district distributor road linking a township to the existin "system of Johannesburg has to be designed. Structura desogn ofurnan mads UTG3. UTG3. 3. Saum Africa 1988 .3: 12. Expected growth rate = between 2 and 8 %.1 Road category (Table 1) This can be regarded as a Category UB road.Pretoria. 10. 6. 3 j i ~ ROAD CATEGORY DESIGN STRATEGY for x = 3 years for y = 15 years MATERIALS The table in Figure 16 may be filled in by using the check-list in Figure 7. 14 Subgrade Area 3: CBR = 20. a period of 15 years is more suitable. ThereforeAP = 30 years. 8.05and 10' and 3 x 10' structural design period.7. consisting mostly of buses (70 % laden) and light 'as well as medium heavy com vehicles. 5: 4.4.95 for the slow lane. A moderate level of service (in terms of riding quality) expected.1 ENVIRONMENT Climatic region According to Figure 8. APPENDIX 3 EXAMPLE OF THE STRUCTURAL DESIGN OF A UB ROAD 1 DESIGN TRAFFIC . 6.15: 16 10. 5: 3.6. 6: 3 SubgradeArea2:CBR = 12. 7 . 8. the design traffic class is E2. 18.5:5. 7 8. SDP = 15 years.20. 15. the road lies within the moderate climatic region. The cumulative traffic should therefore be between 0. 5. 5. I 1 1 I ' 2 " 2.South Ahica 1988 .19. 7. 5. A longer period could have been selected. !: 56 I! Str~cfvrald w g n of urban maa. 8.2 . 19. five subgrade areas can be 3.1 Analysis period (Table 2) The new alignment will probably not change again and th 30 years is selectbd.P~tnia. . 12. b as there is some uncertainty about the growth in traffic and in the area. 7 Subgrade Area 5: CBR = 4. 9:8.. 23.18. Subgrade Area 1: CBR = 3. 4. . The distress will therefore only be shows estimated maintenance measures for the TAR PREMIX 9. I FIGURE 17 .' CEMENTED ~ 3 0 ~ 4 I l.. the const the subbase. CONCRETE PAVEMENT 9.Thi regional office and one can expect timely maint 15 x SDP)...ova toot. he m special care should be given to the cross profile. class E2 traffic).3 Possible pavement structures Figure 17 shows possible pavement structures according (Category UB road..111. base and surfacing need to be considered.2 Future maintenance The structural design period is 15 years and the analysis period i iuture maintenance can be estimated from Tables 16 and 17.7. Because the catalogue of designs is updated from time to time. (A sensitivity analysis discount rates of 8. E2 .4 Salvage value The salvage value will probably vary with the type of pavement.:. PRACTICAL CONSIDERATIONS 8 The designer should consider the conseq considerations outlines in Section 8 for the p example.. . if local materials are very sensitive to water.1 Construction c3st For the comparison of different pavement types.. 9. 10 and 12 % showed that there is little difference betw and 12 %). The catalogue reflects the latest designs that have been accepted by the Highway Materials Commlnee. I.3 Discount rate A discount rate of 10 % is normally selected.OU . 9 COST ANALYSIS 9. directly from the unit costs given in Figure 14. the designs m th~s example may differ. . r. Table 22 show typical salvage values for the different pavement types. ..75 3....58 9....1 Table 23 shows the present ~ 0 1 t hof costs for each pavement type. ......qr ~(~ +p ... this Value would not be lower due to the If extra initial costs.... L S l ( l 0 years) S1 (16 Years) Sl(22 Yeam) 150 GI (25 WB) 35 AG (25 yeas) was designed for 20 years (say E3).... Cost 30 AG (12 years) 40AG (23 Years) *halt surfacing Sranular base M e n t e d subbase uphalt surfacing Bitumen premix base Granular subbase TABLE 22 Typical salvage values for different pavement types Asphail surfacing Bilumen premix base Cemented subbase Asphalt surfacing Tar premix base CBmented subbase Bituminous : Granular Surface treatment Cemented base Cemented subbase 16.. 9...........68 4.. .90 3.....68 3.iranular subbase 3...15 10...20 Discounted salvage value Wm' Present worth of costs Rlmz ..TABLE 23 Present worth of costs gvement structure lnlhsl msls Wm' D~scounted maintenanm wsts Wm2 Measure kphalt surfaang iranular base ..5 Present worth ofcosts The present worth of costs can be calculated from: P W O C = C + Z ~ M +tj-xi-..... 20 x 10' €805). ' CAMERON. the design traffic clas or EO (0. 1981. Constructi important factor influencingthe decision about t factors such as car ownership and use' could influence the decision the design traffic class.30 years is not required. R F. P l e t 0 ~ . Traffic movements in residential environments: Six olse studies in Pretoria N m R Technicd Repon RTl35181. 4 DESIGN TRAFFIC For Category UC roads. (Note: These roads will n of these roads act as a tempwary Category development. J W M and DEL MISTRO. CSIR. 6 ENVIRONMENT As before. Smmmlda~n lno urban me WG3.05 to 0. Rncw S m h A W 1 9 8 8 65' . appropriate traffic studies should be 5 MATERIALS As before. exclude some designs. THE USE OF THE CATALOGUE AND SPECIAL CONDITIONS ' The catalogue should not be used without considering the behaviour of the obtained if the catalogue is used together catalogue does not necessarily exclud pavement structures. but i ~ d ~ " o t " m " m a m UTW. The catalogue does not include practical considerations such as drainage. compaction or pavement cross-section.Rat~SoumAhkateaa . PRACTICAL CONS~DERATIONS DESCRIPTION OF THE CATALOGUE e catalogue deals with most of the factors that have to beconsidered by the COST ANALYSIS although the availability and cost of materials and also experience regarding the materials have to be considered (Section 5). The subgrade has been treated separately (Section 6) and the catalogue assumes that all subgrades are brought to equal support standards (Section 7). guide or fist approximation. . These aspects should still be consideredand are covered in Section 8. 7.5 .2.3 AND ST12NCE OR REDUCTION OF WATER SPRAYING. AC OR i FOR SELECTED LAYERS REFER TO A 0 PERMITTED AS A SURFACING h SYMBOL S OEN LRAGRAPH 7.SURE FOR SKI0 R OR 5 4 ES 5 2 UTURE MAINTENANCE TO PARAGRAPHS 7.1: FOI .I DESIGN TRAFFIC CLASS E 8 0 s / LANE DVER STRUCTURAL DESIGN PERIOD ROAD CATEGORY i S Y M B O L A DENOTES AG. 9. . 7.TAR HOT-MIX BASES DESIGN TRAFFIC CLASS EBOs / L A N E OVER STRUCTURAL DESIGN PERIOD ROAD CATEGORY .5 . ROAD CATEGORY I SYMBOL A DE FOR SELECTEI A 0 PERMITTEC I I TES AG. / LANE OVER STRUCTURAL DESIGN PERIOD . AC OR AS. DESIGNTRAFFIC CLASS €80.AYERS REFER TO PARAGRAPH 7.5: FOR FUTURE MAINTENANCE TO PARAORAPHS 7.. AND 9.2.3 i S A SURFACING MEASURE FOR SKID RESISTANCE OR REDUCTION OF WATER SPRAYING. SYMBOL S DENOTES 5 2 OR 5 4 . I CATEGORY DESIGN T R A F F I C CLASS EB C0.2 X lo6 . 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