IHT/Geological Society Leamington Spa - 30 th January HD 25 Pavement Foundations - Update

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1 Safe roads, Reliable journeys, Informed travellers IHT/Geological Society Leamington Spa - 30 th January 2007 HD 25 Pavement Foundations - Update Wyn Lloyd Pavement Engineering Team Highways Agency wyn.lloyd@highways.gsi.gov.uk

2 Pavement Foundations (IAN 73/06) Background Basics Changes How it works/examples Where it has worked Where we are going Doing business Technical Information

3 Assorted Hats UK Standards HA trunk roads Advice

4 Reasons: Congestion Less Energy Budget Design robustness Use of materials/sustainability

5 Change in concept: Use of local materials in foundations Use of secondary materials Allowance for stronger foundations Performance related design

6 CBGM HRBBM SC SFA SBM FABM SS

7 Foundation Classes Design Stiffness Class 1 50MPa Class 2 100MPa Class 3 200MPa Class 4 400MPa When?

8 Foundation Considerations Foundation Class Variables: Subgrade strength Testing regime Material Properties Availability Economics With/without capping Unbound/bound Thickness Age/Curing/Cracking Temperature/Season

9 Drainage! Design Construction Maintenance

10 Existing Widening

11 IAN 73/06 (HD 25) Role of foundations Materials (CBR & Stiffness Modulus) Restricted designs Performance designs Assessment Targets Demonstration Area Flow chart Example design charts Annexes Test methods

12 Proposed Changes Terminology Intermediate layer testing Thin layers reduced Clarification/Simplification Total thickness value (charts) Charts clarified

13 Standard designs Limited materials Limited options (Class 1 3 only) For small schemes Recognises greater uncertainty

14 Subbase or Capping only

15 Analytical Designs Performance related Variables: Foundation Class Bound/Unbound Slow/fast setting Material Properties Thickness With/without capping

16 Background Based on TRL Report LR1132 Layered linear elastic model Needs realistic estimates of in-situ stiffness of pavement materials Requires proving on site to show that design assumptions have been met Not new!

17 Procedure Site testing has been formalised Measuring the Surface Modulus of the subgrade along the site Demonstration Area Uses dynamic plate testing Target values of stiffness Density and material properties tested

18 Design Methods Charts Equations Layered linear elastic model (e.g. BISAR) Possible designs!

19 On site requirements Foundation Class Design Stiffness Modulus Characteristic Minimum Class 1 50 Unbound 40 Bound Surface Modulus MPa Class Unbound 80 Bound Class Fast Curing 300 Slow Curing 150 Fast Curing 150 Slow Curing 75 Class Fast Curing 600 Slow Curing 300 Fast Curing 300 Slow Curing 150

20 Design Evaluate subgrade Stiffness Modulus for design Demonstration Area Measure subgrade in-situ Stiffness Modulus or CBR of Demonstration Area Main Works Check subgrade in-situ Stiffness Modulus or CBR Construct main works Select Foundation Class Design Foundation Decide on target stiffness Construct Demonstration Area Check material requirements (e.g. strength and density) Adjust Target and Minimum Stiffness Modulus values Check In-situ Stiffness Modulus Check material requirements (e.g. strength and density) Check In-situ Stiffness Modulus at specified age and/or prior to being covered Monitor rutting; measure as required Re-design Trafficking Trial

21 Test Methods DCP Dynamic Plate Springbox + Compressive strength Density

22 Specification Subgrade Foundation Demonstration Area Stiffness Modulus Density & Deformation DCP

23 TRL Report PPR 127 Road Foundation Design for Major UK Highways Chaddock & Roberts

24 Examples

25 Standard design FC3 2.5% Class 3 Subbase CBGMA or CBMGB C8/10

26 Standard Designs Example Foundation Class 3 (200MPa) on 2.5% CBR 340mm of CBGMA/B C8/10

27 Standard designs FC2 on capping 5%

28 Standard Designs on capping Example Foundation Class 2 (100MPa) on 5% CBR 450mm total foundation thickness 230mm of Type 1, Type 2, Type 3 or Category B over 220mm of capping material to MCHW1 Series 600

29 Analytical design M29 Widening 3 Foundation Classes 3 Methods Charts FC2 (Capping + Type 1) Equations FC3 (FABM1) Modelling FC4 CBGM C8/10

30 M29 - Class 2 (Charts) Design CBR = 2 ½ % 6F2 Capping Type 1 subbase Layer Modulus = 75MPa Layer Modulus = 150MPa Use Figure 5.6

31 510mm 250mm 2.5%

32 M29 Class 2 Design Thickness Total foundation thickness = 510mm Capping thickness = 250mm Subbase thickness = 510mm - 250mm = 260mm

33 M29 Class 3 (Equations) Foundation Class 3 (Design Modulus = 200 MPa) Laboratory testing of FABM1 C6/8 gives an Element Modulus of 7000MPa Para 3.30 IAN73 requires 10% of laboratory or Element Modulus to be used for design Permitted Layer Modulus = 700MPa Equations

34 Class 3 Design Thicknesses

35 Class 3 Design Thicknesses E SB = E SB = Ln(2.5) = H SB = 8.44*103*0.043*( *0.949*0.916) = *( ) = 280mm Add construction tolerance

36 M29 Class 4 (Modelling) Determine estimates of Layer Moduli Laboratory testing of CBGMB C8/10 gives an Element Modulus of 20,000MPa Para 3.30 IAN73 requires 20% of laboratory or Element Modulus to be used for design Permitted Layer Modulus = 4000MPa Estimate subgrade modulus E = 17.6(CBR) 0.64 E = 32 MPa Use Modelling method

37 Model Parameters

38 Model Parameters 200 to 235 of 4000MPa ( PR = 0.35) 1500 mm of 31MPA (PR = 0.45) Semi-infinite 10,000 MPA (PR = 0.45)

39 Strain Criteria Deflection Criteria Trial Calculations Minimum thickness 235 mm

40 Summary Class 2 : 260mm Type 1 on 250mm 6F2 Capping Class 3: 280mm FABM1 C6/8 Class 4: 235mm CBGM B C8/10 Tolerances!!!

41 Summary Class 2 : 270mm Type 1 on 250mm 6F2 Capping Class 3: 290mm FABM1 C6/8 Class 4: 250mm CBGM B C8/10

42 On site requirements Foundation Class Design Stiffness Modulus Characteristic Minimum Class 1 50 Unbound 40 Bound Surface Modulus MPa Class Unbound 80 Bound Class Fast Curing 300 Slow Curing 150 Fast Curing 150 Slow Curing 75 Class Fast Curing 600 Slow Curing 300 Fast Curing 300 Slow Curing 150

43 Adjustment for CBR - 1 Demonstration Area SBC Ltd get onto site and find that actual CBR is even higher than the estimated 9% Target & Minimum stiffnesses need to be adjusted for Demonstration Area Factor = 1.28 x Log (Actual CBR / Design CBR) = 1.28 x Log 9/3.5 = 1.28 x 0.25 = 1.53

44 Adjustment for CBR - 2 Characteristic Minimum Table 5.1 Adjusted Table 5.1 Adjusted Class 2 80 MPa 122 MPa 50 MPa 77 MPa Class MPa 230 MPa 75 MPa 115 MPa Class MPa 918 MPa 300 MPa 459 MPa

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47 M29 Class 4 Foundation 280mm HDM50 250mm + CBGMB 8/10 Design CBR = 2.5%

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49 Foundation stiffness (MPa) Main Works (untrafficked): Effect of pre-cracks Foundation Class FC4: Quick curing target: Average: 600MPa Site chainage (m) Slabs - Running mean of 6 Cracks - Running mean of 6

50 Ratio adjusted PRIMA stiffness results at stress 112kPa (MPa) PRIMA correction factor = 1.20 y = x R 2 = FWD stiffness results at stress 163kPa (MPa)

51 Looking ahead IAN 73/06 revised HD 25/07

52 Thank you Wyn Lloyd Pavement Engineering Team Highways Agency