驗(yàn)算路面結(jié)構(gòu)層厚度

1、Flexible pavement designSubstract:According to AASHTO flexible pavement design method, check the structural thickness of pavement in the feasibility study and provide one logical structural thickness to construction.Key word; pavement structural thickness, structural number (SN), performance service

2、abilityIntroductionIn this book it has been developed the structural analysis of the pavement for the Qaisar-Balamurghab Road Project contract no MPW/441/ADB. After the investigations already carried out and analysis the traffic data considering some technical economic method for pavement design.Thi

3、s flexible pavement consists of AC wearing course, AC base course, crushed stone base, granular subbase and prepared roadbed (subgrade).The flexible pavement design procedure includes the following:Determination of design variables: time constraint, traffic, reliability, environmental effectTo find

4、performance criteria and serviceability based on the project conditionDetermination of material properties: effective roadbed soil resilient modulus, pavement layer characteristics and layer coefficientCalculation of structural numbers and layer thicknessesScope of WorksDesign Section: contract leng

5、th of the project road is total 90km. The design section is selected on the basis of available data and it is from Chelgazi (Km 343+000) to Ghormach (Km317+000)Design Length: 26 km (Km 343 + 000 Km 317 + 000)Data Collection: Traffic VolumeTraffic Count SurveyAxle Load SurveyESAL Roadbed Soil Investi

6、gationLaboratory CBR testDesign CBRFigure 2.1 Location Map Proposed Qaisar-Bala Murghab RoadDesign ConsiderationsPavement Performance -Performance ServiceabilityThe serviceability of a flexible pavement is defined as its ability to serve the type of traffic which uses the facility. The primary measu

7、re of serviceability is the present serviceability index (PSI), which ranges from 0 (impossible road) to 5 (perfect road).In AASHTO road test, it is recognized that the P (initial serviceability index) is 4.2 for flexible pavement. When the serviceability index decreases to 2.5, the road condition i

8、s then stated to be unacceptable by 55% of the users.For this project, following values have been adopted:Initial serviceability index (Po):4.2Terminal serviceability index (Pt):2.5The design APSI ithus selected to be 1.7 (Refer to Appendix-H)Traffic AssessmentTraffic Assessment SurveyThis traffic c

9、ount survey was made in accordance with the guidelines cited in TRL Overseas Road Note 40 A guide to axle load surveys and traffic counts for determining traffic loading on pavement”.The survey was conducted in two locations Chelghazi and Ghormach (Km 343 + 000, Km 317 + 000) from 8 June to 15 June,

10、 2007 at two points vi z. DuAbi and Chelghazi and 12 hours daily for the period.The data forecast involved both the collection and analysis of useful data relating to the traffic and its characteristics of the project road sections. Pavement design factors to be assessed with in this data.Traffic vo

11、lume is one of the important factors to effect on determining pavement thickness. For forecast traffic volume, countrys economy recovers and growth in the future should be considered. The classified traffic volume shall be based on the forecast traffic volume. The result of traffic counts survey is

12、shown in the Appendix A.Table 3.2.1.1 Time period for traffic count surveySectionLocationDateTimeItemsKm 343+000Chelgazi8th to 11th June,20076:00 to 18:00Traffic countKm322+500Duabi8th to 11thJune,20076:00 to 18:00Traffic countAxle Load SurveyAs prescribed in the contract documents, this Axle Survey

13、 is based on the Transport Research Laboratory Overseas Road Note 40 A guide to axle load surveys and traffic counts for determining traffic loading on pavement” . The axle load survey has been carried out on existing buses, rigid trucks and articulated trucks at one selected location using a portab

14、le electronic wheel load-measuring device in order to estimate the ESAL values.The survey was conducted for the section between Chelgazi and Ghormach (Km 343 + 000 to Km 317 + 000)Duration of survey was 12 hours and for 4 consecutive days.-Date: 5th July 9th July, 2007-Hours: 6.00 18.00 (12 hours)Eq

15、uivalent single Axle Load Factor was calculated for each vehicle weighed and average ESAL values for each of the vehicle classifications on each road has been determined. The result of axle load survey is shown in the Appendix B.Table 3.2.2.1 Time period for the axle load surveyFigure 3.2.2.1 Axle,1

16、Load SurveySectionsLocationDateTimeItemKm343+000 to + 317+000Duabi5th to 9th July,20076.00 to 18.00Axle loadThe surveyed vehicle types were 5 types of commercial vehicles.Large busHeavy truckMedium truckTrailer andTractorESAL (Equivalent Single Axle Load)The calculation procedure is according AASHTO

17、, and the detail calculation refers to Appendix D. The total traffic volume during the design life (15years) is 3,483,730 ESAL for Chelgazi to Ghormach section based on present traffic condition.And according to the feasibility study report, the total estimated traffic volume during the design life

18、(15 year) is 6,744,226 ESAL for Andkhoy to Bala Murghab section.Define Existing ground Strengths (Roadbed Soil)The definitive material property used to characterize roadbed soil for flexible pavement design in AASHTO guideline is the resilient modulus (M R). The resilient modulus is a measure of the

19、 elastic property of soil recognizing certain nonlinear characteristics. The resilient modulus can be used directly for the flexible pavements.It is recognized that many agencies have not the equipment for performing the resilient modulustest. Therefore, suitable factors are reported which can be us

20、ed to estimate MR from standard CBR,R-value, and soil index test results or values.Heukelom and Klomp have reported correlations between the Corps of Engineers CBR value, using dynamic compaction and the in situ modulus of soil. The correlation is given by the following relationship:MR(psi) = 1500 x

21、 CBRThis relationship have used extensively by design agencies and researchers and is considered reasonable for fine grained soil with a soaked CBR of 10 or less. The CBR values correspond to the expected field densities. This correlation has been used in the design.Other In-situ and Laboratory Test

22、ingIn this design, test pits exploration was conducted at the verge of the carriageway in whole section to investigate the collected roadbed material for CBR test.Laboratory CBR tests: Design parameter for AASHTO CBR Method.Existing carriage way and sub-soil profileThe laboratory CBR test to obtain

23、the basic design variable according to AASHTO was carried out for the samples taken at 41 points (test pits). Test pits were chosen according to existing ground condition. The depth of the pit was about 1m each. The total weight of a sample was about 40 kg.The summary of the test pits for CBR tests

24、is shown in the table below.Table 3.3.1 InformationoS Test PitsSectionLocationDateNo. of Test PitsChelgazi toKm343+000 to Km11 Aug.to 15 Oct., 2007 & 27Ghormach317+000Apr. to 29 Apr. 200841CBR ResultsAll details shown on appendix - CSelection of Pavement Materials for ConstructionPrepared Roadbed (s

25、ubgrade)The prepared roadbed is a layer of compacted roadbed soil or select borrow material which has been compacted to specified density.The CBR of prepared roadbed material should be more than 10% and the compacted density should be more than 95%.Subbase CourseThe subbase course is the portion of

26、the flexible pavement structure between the roadbed soil and the base course. It usually consists of a compacted layer of granular material, either treated or untreated, or of layer of soil treated with a suitable admixture.Base CourseThe base course is the portion of the pavement structure immediat

27、ely beneath the surface course. It usually consists of aggregates such as crushed stone, crushed slag, crushed gravel and sand, or combinations of the materials.Asphalt Concrete Surface CourseAsphalt Concrete Surface course consists of AC wearing course, track coat, AC base course and prime coat.Env

28、ironment EffectsThe environment can affect pavement performance in several ways. Temperature and moisture changes can be effect on the strength, durability, and load-carrying capacity of the pavement and roadbed materials. Another major environmental impact is the direct effect roadbed swelling; pav

29、ement blowups, frost heave, disintegration, etc. can have loss of riding quality and serviceability. Additional effects, such as aging, drying, and overall material deterioration due to weathering are considering in the model.ReliabilityThe reliability of a pavement design-performance process is the

30、 probability that a pavement section designed using the process will perform satisfactorily over the traffic and environmental conditions for the design period.According to AASHTO guidelines, reliability of urban area in interstate and other freeway is suggested 85%99.9% and reliability of rural is

31、suggested 80%99.9%. Future traffic situation is not easy to expect exactly especially for urban area.For the project, the design reliability is considered as 85% which is less than the average value for urban and rural area (refer to Appendix H).The standard normal deviate is -1.037 at 85% level. (R

32、efer to Appendix H)Overall Standard DeviationThe estimated overall standard deviation for future traffic is considered as 0.49 for flexible pavements.The estimated overall standard deviation for traffic with the revised pavement performance model is considered as 0.44 for flexible pavements.And the

33、range of S O values provided in AASHTO Part II (section 2.1.3 ) are based on the values identified above:0.300.40 Rigid Pavement0.400.50 Flexible PavementFor this project, the average value SO 0.45 for flexible pavement is adopted.MATERIALS PROPERTIES FOR STRUCTURAL DESIGN (Pavement Layer Coefficien

34、t and Drainage Coefficient)Help Screen for the Layer CoefficientMaterialTypical UaluesAsphalt Cenent Concrete Asphalt Treated Agg. Base Bit Lin. Treated Agg. Base Cenent Treated Agg. Base Cenent/Fly Ash Agg. Base Graded Stone Base Crushed Stone Base Granular Subbase4 804 3 3 2 2 111-M- -M- -M- -K-St

35、ructural Layer Coefficient, a op Asphalt Cenent Surface Coiirse 0.5 E0100200300400 500Elast ic Mo du Ills , Eac , ofAsphalt Concrete Layer NLimber：Layer Coefficient:.054.1 Asphalt Concrete Surface CourseIn AASHTO Guideline, Figure 2.5 provide a chart to estimate the structural layer coefficient of a

36、 dense-graded asphalt concrete surface course based on its elastic modulus (EAC) at 68 F.For this project, the AC layer coefficient is considered as a1 = 0.32 (EAC= 240,000psi).導(dǎo)匚口如 J - wnljaj1 一匕上-/- u1XH-J-_1Q.lft.O1W?DMFlnlrC McmJi.iIuei. lp?il. uf cl.Aihall Ciiikrrrtrn IM 6日年)ITiliur J-S, Cbi代 W

37、SEKl如甬Il)T n#nM-GT&ded Asphalt Cunrwi1!他r傾KJ蛔詔(P細(xì)路眥隔血1呻Crushed Stone Base CourseIn AASHTO guideline, Figure 2.6 provides a chart that may be used to estimate a structural layercoefficient, a2, from one of four difference laboratory test result on a granular base material, including base resilient mo

38、dulus, EBS.UMU ISn格U. HJ. 12t.in0 QA0皿V 口ri 02e7Df50-4D-=K-既 - J -J I12.0-JI# r- - . - - -JQ-= 25-旺FL1&-I I I段宙己 d 3 ivoritginQ nrrL.lcii in nF obiQirinrl Ir-nrTi h Imni.12 |DWPWij g jiucrOQing cormiH inn? cih:nini：rl 1Cnliirniii. NewLird131 S村同-如5日 By S晶i 珂in口 Lri I lie- Aauali “時(shí);。凱Fwni瓦 Pieyf May

39、lu3 and WyiwriGId I Swl略 ciFrikisid k(?n rsiiibdli!?伯 uKdumF irrn:-ijMiij朝 Oil KICHRP prrijr：rr yjj.Figure 2.1. Mnrh&!iun in GraiiRil&r Subhiuicwith、敏禰m Subbust *明山Ihuanicttrs CJ|From the chart, we considered the layer coefficient is following in the project:a3 = 0.11 m3 = 1.0 (Ref. AASHTO Table 2.4

40、)Esb = 15,000CBR = 30 (approximate)Ibbl牛 W.4r 只*可叩“姑以1成e ni| 楠hi敗 for Mu曲俱 SlruriLinil tuflkknitf uf Unircttd Eltive ind Siihb MWeWbLi in KleKibb ftivennU；Ftercenl 密 Tjmr PiLmirni Sth UCthirt 坷 liSplXTJtrt Lii MgIsciji LctHs ApprviKtiijig 如叫WIjudliiy 4I DratnugtTlwn.1%L-眺5-1豌(If 心虹 ThAD 15L.45J.W5-

41、SN1D * SN 2 - SN;2 a mSN* + SN* SND SN3 - (SN; + SN*)3a mFigure 6.3.1 Procedures for Determining Thicknesses of Layersa, D, m and SN are as defined in the text and are minimum required values.An asterisk with D or SN indicates that it represents the value actually used, which must be equal to or gre

42、ater that the required values.In accordance with AASHTO guideline, asphalt layer and macadam base layer thicknesses are considered that when ESAL value is between 2,000,000 and 7,000,000, the minimum thicknesses of asphalt and aggregate base are recommended as 8.89cm and 15.24cm. (Refer to AASHTO 3.

43、14) So, proposed thickness for asphalt is 9cm and for macadam base is 20cm.Table -6.3.1 determination of structural NumberLayer No.DescriptionLayer coefficientDrainage coefficientLayer thickness inchProduct1Asphalt Wearing course0.321.01.570.502Asphalt Base course0.321.01.970.633Macadam base0.141.07

44、.871.104Granular subbase0.111.08.660.955Sub-grade0.081.07.870.63Total:3.82Asphalt WearingAsphalt BaseMacadam BaseGranular SubbaseSubgradeFigure 6.3 Propos用9瞄62尿0巧小 layer thicknessPavement Design Based on Contract Document ESALDesign ParametersSectionChelgazi to GhormachFrom K343+000 to Km 317+000Des

45、ign life15 yearsRefer to Contract document(Section 6 P29Design CBR6.5%Refer to Appendix CMr9,750 psi1,500 x 6.5ESAL6,744,226Refer to contract documentReliability85%Refer Appendix HA PSI1.7Refer Appendix HSo0.45Refer Appendix H7.2 Determination of Structure NumbersFollowing equation mentioned in AASH

46、TO Guideline Part 1-14 is used for determining required structural number, SN.r ,迪 SILgJ)Log (W ) = Z x S + 9.36Lg (SN +1) -0.2+ 4.W + 2.32xLog (M ) -8.071018 R O10109410 R0.40+(SN +1)5.19From the above equation, we can obtain the required structure number SN = 4.00. (Refer to Appendix E)Assessment

47、of the Pavement Layers ThicknessThe following equation provides the basis for converting SN into actual thickness of wearing, macadam and subbase. When selecting appropriate values for the layer thickness, it is necessary to consider their cost effectiveness along with the construction and maintenan

48、ce constraints in order to avoid the possibility of producing an impractical design. From a cost effective view, the thickness of every layer are selected as minimum thickness mentioned as AASHTO Guideline.SN = a D + a.D m + a Dm + a D m 1 12 2 23 3 34 4 4a1 : 0.32 (Layer coefficient for AC wearing

49、and base)a2 : 0.14 (Layer coefficient for macadam base)m2 :1.00 (Drainage coefficient for macadam base) a3 : 0.11 (Layer coefficient for gravel subbase) m3 :1.00 (Drainage coefficient for gravel subbase) a4 : 0.08 (Layer coefficient for gravel subgrade) m4 :1.00 (Drainage coefficient for gravel subg

50、rade)According to the AASHTO Standard, the pavement should be designed in accordance with the principles show in Fig 7.3 First; the structural number required over the roadbed soil should be computed. In the same way, the structural number required over the sub base layer and the base layer should a

51、lso be computed, using the applicable strength values for each. By working with differences between the computed structural numbers required over each layer, the maximum allowable thickness of any given layer can be computed. The thicknesses for the respective layers may then be determined as indica

52、ted of Fig 7.3.(ref. AASHTO Guide for Design of pavement Structures, 1993, part -1, page I -35). As per the procedure mentioned above, pavement thicknesses are proposed as follows.-SN-D * i1 aiSN* = ai D* SND * SN 2 - SN*2 a mSN* + SN* SND SN3 - (SN; + SN*)3a mFigure 7.3.1 Procedures for Determining

53、 Thicknesses of Layersa, D, m and SN are as defined in the text and are minimum required values.a) An asterisk with D or SN indicates that it represents the value actually used, which must be equal to or greater than the required values.In accordance with AASHTO guideline, asphalt layer and macadam

54、base layer thicknesses are decided. When ESAL value is between 2,000,000 and 7,000,000, the minimum thicknesses of asphalt and aggregate base are recommended as 8.89cm and 15.24cm. (Refer to AASHTO 3.14) So, proposed thickness for asphalt is 9cm and for macadam base is 20cm.Table -7.3.1 determination of structural NumberLayer No.DescriptionsLayer CoefficientDrainage CoefficientLayer Thickness, inchProduct1Asphalt Wearing course0.321.01.570.502Asphalt Base course0.321.01.970.633Macadam base0.141.07.871.104Granular subbase0.111.09.841.085Sub-grade0.081.011.810.94Tot