Pavement design in the UK and future developments Andy Collop Professor of Civil Engineering Director of NTEC
Outline Standard UK pavement design Foundation Upper pavement Long Term Pavement Performance Model (LTPPM) Summary
UK pavement design HA method for Trunk Roads & Motorways Includes long-life designs (> 80 msa) 40 year design life (can be 0 years) Semi-empirical (analytical alternatives allowed) Divided into foundation design and upper pavement design
Foundation design Where does the foundation start? Upper pavement HD6 Surfacing Upper Base Lower Base Subbase Pavement foundation HD5 Capping Subgrade
Philosophy Based around the concept of a Surface Modulus (half-space)
Foundation classes Class 1 50MPa Capping Only (< 0 msa) Class 100MPa Granular Subbase (< 80 msa) Class 3 00MPa Weak Cemented Subbase (including hydraulically bound) Class 4 400MPa Strong Cemented Subbase (including hydraulically bound)
HD5 Standard Designs for Classes and 3 (+ Class 1 for non HA roads); restricted choice of materials; CONSERVATIVE Performance Designs Performance Designs for Classes 1 to 4; very wide choice of materials; much more testing specified; MORE REALISTIC
Standard Class (100MPa) Thickness (mm) 700 600 500 400 300 00 100 0 CBR (%) 3 5 8 10 1 15 0 5 Class Capping, MCHW1 Series 600 Tot al Foundat ion t hickness, Subbase Types 1,, 3 and R Tot al Foundat ion t hickness, Subbase Types CBGMA or CBGMB, C3/ 4 or C5/ 6 0 50 100 150 Subgrade Stiffness Modulus (MPa)
Performance designs Basis of Designs: Three criteria Surface deflection (relates to Surface Modulus) Subgrade Strain (relates to rutting) Practical minimum thicknesses Circular contact area, radius 151mm Subbase Capping Subgrade 40kN Surface deflection Subgrade strain 10000MPa layer assumed 1.5m below surface of subgrade
Performance Class (100MPa) Subbase Thickness (mm) 500 400 300 00 100 0 CBR (%) 3 5 8 10 1 15 0 5 Class E(subbase) = 150MPa E(subbase) = 00MPa E(subbase) = 50MPa 0 50 100 150 Subgrade Stiffness Modulus (MPa)
Performance Class 3 (00MPa) Subbase Thickness (mm) 500 400 300 00 100 0 CBR (%) 3 5 8 10 1 15 0 5 Class 3 E(subbase) = 500MPa E(subbase) = 750MPa E(subbase) = 1000MPa E(subbase) = 000MPa 0 50 100 150 Subgrade Stiffness Modulus (MPa)
Stiffness measurement CBR FWD DCP Springbox Table 3.1 Equilibrium Subgrade CBR Estimation Soil PI High Water Table (%) Heavy Clay Silty Clay Sandy Clay Plate Loading 70 60 50 40 30 0 10 Poor Construction Conditions Average Construction Conditions Good Construction Conditions Poor Construction Conditions Low Water Table Average Construction Conditions Good Construction Conditions Thin Thick Thin Thick Thin Thick Thin Thick Thin Thick Thin Thick 1.5 1.5 1.5.5.5 1.5.5 3.5 4 3.5.5 3 4 3.5 3 4 5 6.5 3.5 4.5 3.5.5.5 3 5 7 7 Chart 1.5 1.5.5 3 3.5.5 3.5 4 4 3 4 5 4.5.5 3 4 6 7 Silt* - 1 1 1 1 1 1 Sand (poorly graded) Sand (well graded) Sandy Gravel (well graded) - - - ------------------------------------------------------------0------------------------------------------------------------ ------------------------------------------------------------40------------------------------------------------------------ ------------------------------------------------------------60------------------------------------------------------------ * estimated assuming some probability of material saturating 3 4 6 6.5.5.5 3.5 6 8 >8 Triaxial
Upper pavement design (Flexible & composite)
Other layer combinations Any combination of layers possible The designer has to carry out a Multi- Layer Linear Elastic analysis to ensure that the criteria are all satisfied Surface deflection Subgrade strain Practical minimum thickness
Outline Standard UK pavement design Foundation Upper pavement Long Term Pavement Performance Model (LTPPM)
Background LTPPM developed with University of Cambridge (Cebon) Similar concept to MMOPP (Ullidtz) Flexible (asphalt) pavements Deterministic iterative procedure (profile & damage tracking) Aggregate damage type of approach
LTPPM Road model Vehicle simulation Dynamic vehicle/axle group models Primary response calculation Damage calculation Feedback mechanisms Fatigue damage fed back into primary response model Log N Environment Material properties Log ε Force Distance Time Damage Strain Influence function Strain Road response calculation Road strain at each point Time Road damage model Theoretical road damage Tyre forces static Surface rutting fed back into vehicle model Distance along road
Example Effect of road friendly suspensions classes of pavement simulated Major road (350mm asphalt) Minor road (15mm asphalt) Typical 3 layer flexible pavement structure 4 o C to 18 o C variation in MMAT
Surface profile evolution (Major road) 0.03 Surface Profile Elevation / m 0.0 0.01 0-0.01-0.0 Initial profile 36 million load passes (10 years) 7 million load passes (0 years) -0.03 0 10 0 30 40 50 60 70 80 90 100 Distance / m
Rutting evolution (Major road) Average Rut Depth / mm 16 14 1 10 8 6 4 'Critical' rut depth Steel fleet Road friendly fleet 0 0 10 0 30 40 50 60 70 80 Load Passes (Million) 0 years
Fatigue evolution (Major road) 3.5 x10-3 95th Percentile Fatigue Damage 3.5 1.5 1 0.5 Steel fleet Road friendly fleet 0 0 10 0 30 40 50 60 70 80 Load Passes (Million) 0 years
Rutting evolution (Minor road) 0 Average Rut Depth / mm 15 10 5 'Critical' rut depth Steel fleet Road friendly fleet 0 0 0. 0.4 0.6 0.8 1 1. Load Passes (Million) 0 years
Fatigue evolution (Minor road) 95th Percentile Fatigue Damage 1 0.8 0.6 0.4 0. Steel fleet Road friendly fleet 'Critical' fatigue damage 0 0 0. 0.4 0.6 0.8 1 1. 0 years Load Passes (Million)
Predictions % increase in life changing from steel to road friendly (air) suspensions Major Minor EC 4% 4% LTPPM (3.5) 3% 39% LTPPM (1) 0% 90%
Outline Standard UK pavement design Foundation Upper pavement Long Term Pavement Performance Model (LTPPM) Summary
Summary UK design Foundation design + upper pavement design 4 performance levels (surface modulus) for foundations More flexible designs (wider range of materials) Performance designs allowed
Summary LTPPM (1) Deterministic LTPPM described based on aggregate damage approach LTPPM comprises: i. Dynamic vehicle simulation ii. Pavement primary response simulation iii. Material damage simulation iv. Deterioration feedback
Summary LTPPM () Different modes of deterioration predicted for different classes of pavement Changing from steel to air increases life of major road by <3% (< 10 million) & minor road by between 40% and 90% ( 100 million - 40 million)
Pavement design in the UK and future developments Andy Collop Professor of Civil Engineering Director of NTEC