Flexible pavement thickness design by Haryati Yaacob (fka, utm)

Transcription

1 Flexible pavement thickness design by Haryati Yaacob (fka, utm)

2 Flexible pavement thickness design Flexible Pavement Structure Factors to be Considered in Designing Flexible Pavement Thickness Thickness Design Methods

3 Pavement types

4 Type of Pavement & their Load Distribution

5 Pavement Types & How They Effect the Subgrade

6 Flexible pavement structure Elements of a flexible pavement: 1. Sub-grade upper layer of natural soil or fill, support load transmitted from overlaying layers. 2. Sub-base specified material, secondary load spreading layer, prevent infiltration of sub-grade into pavement, construction platform for construction traffic, drainage layer 3. Road base specified material, main load spreading layer, provide pavement with added stiffness and resistance to fatigue 4. Surfacing uppermost layer, provide safe & comfortable riding surface, withstand traffic stresses, protect lower layers, impermeable and flexible, may consist of BC and WC, premix layer.

7 Failure Criteria 1. Failure mechanism 2 categories: - Permanent deformation- fail if rut (accumulation of permanent strain)> 20mm - Crack (fracture under repeated or fluctuating stress)

8 Rut

9 Factors to be considered in designing pavement thickness Axle wheel configurations Vehicle speed Load repetitionsunrecoverable damage Traffic Loading Traffic distribution Tyre loads and pressure **Traffic Damaging Power CV (BTM > 1.5 ton, 3 ton for RN31), convert to SA (80 kn, 8160 kg, lb), for design life ESA/CSA e = (L/Ls) 4 - examples

10 Commercial vehicle 1

11 Commercial vehicle 2a

12 Commercial vehicle 2b

13 Commercial vehicle 3

14 Commercial vehicle 4

15 Commercial vehicle 4

16 Commercial vehicle 5

17 Factors to be considered in designing pavement thickness Rheology Temperature Expansion and contraction Sunlight Environmental Safety Moisture Rainfallunbound material Placing HMA in wet conditions

18 Pavement thickness design methods Objective to provide a structure that will be suitable in a specific environment and able to sustain the anticipated traffic loading Design methods Empirical Group Index, RN 29, RN 31, 1993 AASHTO design method Mechanistic Empirical Shell, Chevron, Kentucky, TRRL 1132, Circly

19 Design process

20 Pavement Thickness Design Methods ATJ 5/85 ATJ 5/85 (2013) RN31

21 ATJ 5/85

22 Pavement Thickness Design ATJ 5/85 Data required: 1. Design period proposed 10 years 2. JKR Hierarchy 3. Average Daily Traffic (opening year) ADT (PLH) 4. Percentage of Commercial Vehicle - Pc 5. Traffic Growth Rate - r 6. Sub-grade strength - CBR 7. Terrain

23 Design Procedure 1. Estimate Vo = ADT x (1/2) x 365 x (Pc/100) 2. Determine Vc= Vo [(1 + r) n - 1] / r 3. Convert to ESA, ESA = Vc x e (Table 3.1 or e = 2.52) 4. Check capacity (Table 3.2, 3.3, 3.4) 5. Determine Sub-grade CBR 6. Determine TA from nomograph 7. Calculate thickness for each layer (Table 3.5, 3.7, 3.8) TA = S N = a 1 D 1 + a 2 D a n D n 8. Sketch thickness obtained

24 Equivalence Factor- Table 3.1

25 ATJ 5/85 (Determine Sub-grade CBR) In case of varying CBR for 1m depth of sub-grade, mean CBR is determined as follows: CBR eff = [(h 1 CBR 1 1/3 + h 2 CBR 2 1/3 + + h n CBR n 1/3 ) / (1000)] 3 where: CBR eff CBR 1, CBR 2, CBR n h 1, h 2, h n h 1 + h h n = effective CBR = CBR of soil strata = thickness of soil strata (mm) = 1000 mm

26 Maximum Hourly capacity

27 Reduction Factor

28 Terrain Factor

29 Nomograph

30 Layer Coefficient, a

31 Standard and Construction Thickness, D

32 Minimum thickness of bituminous layer

33 ATJ 5/85- Design Example Design Example: JKR 05, carriageway width = 7.5m, shoulder = 2.0m ADT = 6600 Pc = 15 % r = 7 % Sub-grade CBR = 5 % Rolling Terrain Material: Surfacing = AC Road base = wet mix Macadam Sub-base = sand

34 ATJ 5/85 Design Method (2013 revision)

35 Data required: Type and volume of commercial vehicles Design life Sub-grade type and strength Type and properties of paving materials Environment which pavement will be exposed to

36 Criteria

37

38 Traffic Data Number of commercial vehicles during Year 1 of Design Period, which is the expected year of completion of construction. Vehicle class and axle load distribution. Directional and lane distribution factors. Traffic growth factors.

39 Type of Terrain Terrain factor, T Flat 1.0 Rolling 1.1 Mountainous/steep Design period 10 years for low volume and rural road. 20 years for high volume and urban road 4. Design traffic (1st year of design period) ESALY1 = ADT x 365 x PCV x LEF (3.7) x L x T ESALY1 = number of ESALs for base year (design lane) ADT = Average Daily Traffic PCV = Percentage of CV (un-laden weight > 1.5 tons) VLF = Vehicle Load Equivalent Factor (including Tire Factor) L = Lane Distribution Factor T = Terrain Factor

40 If traffic distribution by vehicle type is available: ESALY1 = [ADTcv1 x LEFcv1 + ADTcv2 x LEFcv2 + + ADTcv3 x LEFcv3] x 365 x L x T

41 5. Design Traffic (Number of ESALs) for the Design Period ESAL DES = ESAL Y1 x [(1 + r) n 1)]/r ESAL DES = design traffic for the design lane in one direction r = annual traffic growth rate factor for design period n = number of years in design period ESAL DES = ESAL Y1 x TGF OR

42 Total Growth Factor (TGF)

43 6. Decide traffic category Normal distribution with single tailed analysis, the following normal deviate values shall apply: 60% Probablility: Mean x STD 70% Probablility: Mean x STD 85% Probablility: Mean x STD statistical analysis shall be used to evaluate laboratory or field test results for use as input for pavement design (sub-grade, sub-base, road base and bituminous courses)

44 7. SG categories Min 5% CBR for T1- T3 If not, at least 0.3 meter of SG shall be replaced or stabilized to ensure the minimum value is met. Large volume traffic T4 and T5, min CBR 12%

45 8. Get T and S, choose from catalogue Mechanistic Design using Elastic Layer Programs Asphalt Institute SW-1 (based on Manuals MS-1; MS-11; MS-17; MS-23) Pavement Design: A Guide to the Structural Design of Road Pavements, STANDARDS AUSTRALIA and AUSTROADS, 2004, in conjunction with CIRCLY Version 5.0 SHELL SPDM Version 3.0 Pavement Design and Analysis by Yang H. Huang, Second Edition, 2003 in conjunction with KENLAYER Layer Elastic Theory using RUBICON TOOLBOX Version

46 3 types of pavement : Conventional flexible pavement with granular base. Deep-strength flexible (composite) pavement with bituminous surface course(s) and a base stabilized with Portland cement, bituminous emulsion, or a combination of both. Full-depth asphalt pavement with bituminous base course

47 T1 : < 1 million ESALs

48 T2 : 1-2 million ESALs

49 T3: 2-10 million ESALs

50 T4 : million ESALs

51 T5 : > 30 million ESALs

52 T5 : > 30 million ESALs ( Polymer Modified Asphalt)

53

54

55

56 Properties of Paving Materials Bituminous Wearing and Binder Courses

57 Bituminous Road base similar to binder and wearing course except a lower temperature used for this layer Crushed Aggregate and Wet Mix Road Base Performance -> shear strength, stiffness and by material breakdown that may occur during construction and heavy traffic similar composition but construction practices are different Min CBR 80%, elastic modulus 350±100 Mpa

58 Stabilized Road base In situ or Plant 2 types: STB 1. Aggregates stabilised primarily with cement or lime. 3% to 5% Portland cement. E = 1800 MPa; v = 0.40 STB 2. Aggregates stabilised primarily with a bituminous emulsion/foamed bitumen + cementitious. Bituminous emulsion or foamed bitumen and a maximum of 2% Portland cement. E= 1200 MPa; v 0.35

59 Other options for Low Volume Roads

60 Example 1 Traffic count data: ADT 2700 vehicles both directions (24 hour period) PCV: 16% ( no detailed break down by vehicle type) Terain : rolling Design life: 20 years Annual traffic growth: 4% CBR mean =18.5%, standard deviation= 4.4%, 85% probability

61 Example 2 Design a road pavement for a 4-lane freeway (concession toll-road) with an average daily traffic of 7286 vehicles, of which 20% are commercial vehicles with an un-laden weight > 1.5 tons CV 1 = 624 CV 2 = 456 CV 3 = 316 CV 4 = 102

62 Road Note 31

63 RN31 Emphasis on 5 aspects: 1. Influence of tropical climate on moisture conditions in road sub-grades 2. Severe conditions imposed on exposed bituminous surfacing by tropical climates 3. Interrelationship between design and maintenance 4. High axle load and tyre pressures 5. Influence of tropical climate on the nature of the soils and rocks used in the road building

64 RN31 Designed for tropical and sub-tropical countries to carry up to 30M CSA Heavy vehicle > 3 ton Equivalence: e = (L/Ls) 4.5 Design procedure: 1. Estimate CSA for design life >>> T (Table 3.9) 2. Assess sub-grade strength >>> S (Table 3.9, 3.10) 3. Select combination of material and thickness from structure catalogues based on T and S

65 Table 3.9, T & S determination

66 S determination

67 Material Definition

68 Granular base, surface dressing

69 Granular base, structured surface

70 Road Note 31 Design Example 1: ADT = 250/day.dir, Pc = 55 %, r = 5 %, CBR = 7 % Design Example 2: CSA = 12M, PI > 45, WT = 2m below formation

71 Example The predicted commercial vehicle of a proposed two lane urban highway is 31%. The ADT of highway in 2015 is 3500 and the highway is expected to complete and open to traffic in 208. If the traffic growth rate is estimated at 4% over the 20 year design life. Subgrade thickness and CBR value are 350mm (9%), 400mm(7%) and 250mm (4%). Determine the required thickness for the pavement layers using Road Note 31.

72 Example Design a two lane state road with the following known parameters using Road Note 31 method. Road will be opened to traffic in Clearly state all the assumptions used. -ADT 2016= Directional spilt=60/40 -Percentage of heavy vehicles (Pc)= 20% -Annual Average traffic growth rate (r)=7% -Subgrade CBR and thickness: 12% (300mm), 8% (350mm) and 5% (350mm).

73 QUESTIONS?