Wyn LloydPavement Engineering Team

Highways Agencywyn.lloyd@highways.gsi.gov.uk

Safe roads, Reliable journeys, Informed travellers

HD 25 Pavement Foundations

- Update

IHT/Geological Society

Leamington Spa - 30th January 2007

Pavement Foundations(IAN 73/06)

� Background � Basics� Changes� How it works/Examples�Where it has worked�Where we are going

www.highways.gov.uk Doing business Technical Information

Assorted Hats

� UK Standards

� HA trunk roads

� Advice

� Congestion

Reasons:� Budget

� Less Energy� Use of materials/Sustainability

Design robustness

Change in concept:

� Use of local materials in foundations

� Use of secondary materials

� Allowance for stronger foundations

� Performance related design

FABM

SBM

SS

SFA

HRBBM

CBGM

SC

Foundation Classes

Design Stiffness

Class 1 50MPa

Class 2 100MPa

Class 3 200MPa

Class 4 400MPa

When?

Foundation Considerations

Variables:

Subgrade strength

Material Properties

Testing regime

Thickness

With/without capping

Age/Curing/Cracking Temperature/Season

Unbound/bound

Economics

Foundation Class

Availability

Drainage!

� Design

� Construction

� Maintenance

ExistingWidening

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

Proposed Changes

� Terminology

� Intermediate layer testing

� Thin layers reduced

� Clarification/Simplification

� Total thickness value (charts)

� Charts clarified

Standard designs

� Limited materials

� Limited options (Class 1 – 3 only)

� For small schemes

� Recognises greater uncertainty

Subbase or Capping only

Analytical DesignsPerformance related

Variables:

� Foundation Class

� Bound/Unbound

� Slow/fast setting

� Material Properties

� Thickness

�With/without capping

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!

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

Design Methods

• Charts

• Equations

• Layered linear elastic model (e.g. BISAR)

Possible designs!

40020010050Design Stiffness Modulus

Slow Curing 150

Slow Curing 75

Fast Curing 300

Fast Curing 150

5025

Minimum

Slow Curing 300

Slow Curing 150

Bound 100Bound 50

Fast Curing 600

Fast Curing 300

Unbound 80

Unbound 40

Characteristic

Class 4Class 3Class 2Class 1Foundation Class

Surface Modulus MPa

On site requirements

Design

Evaluate subgradeStiffness Modulus

for design

Select Foundation Class

Design Foundation

Measure subgrade in-situStiffness Modulus or CBR of Demonstration Area

Demonstration Area

Construct Demonstration Area

Check material requirements (e.g. strength and density)

Adjust Target and Minimum Stiffness Modulus values

Check In-situ Stiffness Modulus

Trafficking Trial

Check subgradein-situ Stiffness Modulus or CBR

Main Works

Check material requirements (e.g.

strength and density)

Check In-situ Stiffness

Modulus at specified ageand/or prior to being

covered

Monitor rutting; measure as required

Decide on target stiffness

Re-design

Construct main works

Test Methods

� DCP

+ � Compressive strength� Density

� Springbox

� Dynamic Plate

Specification

� Subgrade

� Foundation

� Demonstration Area

� Stiffness Modulus

� Density & Deformation

� DCP

TRL Report PPR 127

Road Foundation Design for Major UK Highways

Chaddock & Roberts

www.trl.co.uk

Examples

Standard design FC3

2.5%Class 3 Subbase CBGMA or CBMGB C8/10

Standard DesignsExample

Foundation Class 3 (200MPa) on 2.5% CBR

• 340mm of CBGMA/B C8/10

Standard designs FC2on capping

5%

Standard Designson 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

Analytical designM29 Widening

3 Foundation Classes

3 Methods

� Charts FC2 (Capping + Type 1)

� Equations FC3 (FABM1)

� Modelling FC4 CBGM C8/10

M29 - Class 2 (Charts)

Design CBR = 2 ½ %

� 6F2 Capping Layer Modulus = 75MPa� Type 1 subbase Layer Modulus = 150MPa

� Use Figure 5.6

2.5%

510mm

250mm

M29 Class 2 Design Thickness

� Total foundation thickness = 510mm

� Capping thickness = 250mm

� Subbase thickness

= 510mm - 250mm = 260mm

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

Class 3 Design Thicknesses

Class 3 Design Thicknesses

�ESB-0.480 = 0.043�ESB-0.008 = 0.949� Ln(2.5) = 0.916

� HSB = 8.44*103*0.043*(1.0-0.261*0.949*0.916)= 362.92*(1.0-0.227)

= 280mm� Add construction tolerance

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

Model Parameters

200 to 235 of subbase @ 4000MPa ( PR = 0.35)

1500 mm of subgrade @ 31MPA (PR = 0.45)

Semi-infinite layer @ 10,000 MPA (PR = 0.45)

Model Parameters

Strain Criteria

Minimum thickness

Deflection Criteria

Trial Calculations

235 mm

Summary

Class 2 : 260mm Type 1 on 250mm 6F2 Capping

Class 3: 280mm FABM1 C6/8

Class 4: 235mm CBGM B C8/10

Tolerances!!!

Summary

Class 2 : 270mm Type 1 on 250mm 6F2 Capping

Class 3: 290mm FABM1 C6/8

Class 4: 250mm CBGM B C8/10

40020010050Design Stiffness Modulus

Slow Curing 150

Slow Curing 75

Fast Curing 300

Fast Curing 150

5025

Minimum

Slow Curing 300

Slow Curing 150

Bound 100Bound 50

Fast Curing 600

Fast Curing 300

Unbound 80Unbound 40

Characteristic

Class 4Class 3Class 2Class 1Foundation Class

Surface Modulus MPa

On site requirements

Adjustment for CBR - 1Demonstration 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

Adjustment for CBR - 2

AdjustedAdjusted Table 5.1Table 5.1

459 MPa300 MPa918 MPa600 MPaClass 4

115 MPa75 MPa230 MPa150 MPaClass 3

77 MPa50 MPa122 MPa80 MPaClass 2

MinimumCharacteristic

�

M29

Class 4 Foundation

280mm HDM50

250mm + CBGMB 8/10

Design CBR = 2.5%

Main Works (untrafficked): Effect of pre-cracks

0

250

500

750

1000

1250

1500

1750

2000

2250

5100 5200 5300 5400 5500 5600 5700Site chainage (m)

Foun

dati

on s

tiffn

ess

(MPa

)

Slabs - Running mean of 6 Cracks - Running mean of 6

Average: 600MPa

Foundation Class FC4:

Quick curing target:

y = 1.0063xR2 = 0.7622

0

20

40

60

80

100

120

140

160

180

200

0 20 40 60 80 100 120 140 160 180 200

FWD stiffness results at stress 163kPa (MPa)

Rat

io a

djus

ted

PR

IMA

sti

ffne

ss r

esul

ts a

t st

ress

112

kPa

(MPa

)

PRIMA correction factor = 1.20

� IAN 73/06 – revised

� HD 25/07

Looking ahead

Thank you

Wyn LloydPavement Engineering TeamHighways Agency0123 479 6081wyn.lloyd@highways.gsi.gov.uk