In situ road recycling The Ridgeway Enfield

Bob NoakesRoad Surface Treatment Association

In situ road recycling The Ridgeway Enfield

A Case Study Presented by Bob Noakes 

• The Problem for the Highway Authority  London Borough of Enfield

• Investigation into the causes and design of remedial solution 

• Undertaking the construction process 

• Conclusions  

Investigation Proposal from Norfolk Partnership Laboratory

• Core every 200m using 350mm dia cores

• On removal of the core, carry out stiffness testing of the layer directly below

• DCP from the bottom of the core, for 1m

• Remove sub-base material for trial mix testing

• Carry out stiffness testing below the sub-base material

• Hand auger for plastic and liquid limits samples from the London clay

• At trial pits in failed areas ensure the full suite of in situ testing is carried out, plus hand auger

Norfolk Partnership LaboratoryCounty Hall, Martineau Lane

NORWICH, Norfolk NR1 2SGTel: 01603 222416Fax: 01603 222457

Email: civil.laboratory@norfolk.gov.uk

Stabilised Pavements Ltd Our Project No SPAV0004FAO G Howe Our Report and sample No NPL25533-604

Your Sample Ref D001Your Project or Order No

P&T Project No.

Date Report Issued 10-Jan-12

Email: Page 1 of 1

Scheme EnfieldLocation TP3 Depth 0.5 - 1mDate sampled 23-Nov-11 Date received 23-Dec-11Date tested 10-Jan-12Sample type Small disturbed sample Sample MassIf a sample certificate was provided it is available for inspection.The accuracy of information provided by third parties cannot be guaranteed.

MaterialDescription

Supplier Ex site Source UnknownConveyance note No. Not applicable

TEST SPECIMENLocation Not applicableOrientation Vertical

PREPARATION DETAILSMethod of Division WholePreparation Method Wet Sieving Oven dried @ 40°CPassing 425µm (%) 83

Natural MC (%) 12

Liquid Limit (%) 34Plastic Limit (%) 17Plasticity Index (%) 18Modified PI *(%) 15 *BRE Digest 240:1993.

This calculation is outside the scope of UKAS accreditation.Soil Classification CL

Remarks

Version 78

Test Code = 604 David Houseago (Lead Technician)

SoilLight greyish-brown slightly gravelly SILT. Gravel is fine to medium subangular flint.

PO Box 6909 Lutterworth Leicestershire LE17 4WW

Determination of Liquid Limit to BS1377-2:1990 Clause 4.3 Cone Penetrometer Method (definitive method)and Determination Plastic Limit and Plasticity Index to BS1377-2:1990 Clause 5

0920

www.norfolk.gov.ukwww.maygurney.co.uk

Table 3.1 Construction Thickness and Mechanical Properties. Summary of Results

Core Ch’nage Remarks Asphalt thickness (mm)

Sub Base Sub Grade

Thicknes s (mm)

Stiffness Modulus (MPa)

Stiffness Modulus (MPa)

Minimum Calculated CBR (%)

1 50 350 350 255 2

2 250 400 225 38 2.5

3 355 Area of settlement 415 85 170 40 4.5

4 450 430 420 170 5

5 650 480 200 38 4.5

6 850 340 310 95 >10

7 1050 445 85 380 90 4.5

8 1080 Area of settlement 375 190 38 4.5

9 1250 350 270 34 3.5

Note 1: The cores were all 350mm diameter. Note 2: Stiffness Modulus (Sm) was determined with a Light Weight Dynamic Plate (LWD) test. With the exception of cores 3 and 7 it was not possible to measure Sm of the sub- grade because it was too deep to allow operation of the LWD. Note 3: The results of Dynamic Cone Penetrometer (DCP) tests were used to calculate values of California Bearing Ratio (CBR).Note 4: Silt and clay are water sensitive and the long term values of Sm and CBR may be lower than the quoted values.

Atterberg Limits etc.

Atterberg limits

Core No. Basic Description

Natural moisture content (%)

Plastic Limit (PL)

Liquid Limit (LL)

Plasticit y Index (PI)

Dessicated

1 Clay 36 25 83 58 No 2 Clay 42.9 24 67 43 No 3 Silt 12.1 17 34 18 Yes

4 Sand N/A N/A N/A N/A

5 Clay 24.4 20 50 30 No

6 Sand N/A N/A N/A N/A

7 Clay 38.2 24 67 43 No 8 Clay 31.3 29 72 44 Marginal

9 Sand N/A N/A N/A N/A

Pavement Design to TRL 386Asphalt 135 mm Re-Cycled, Cement Bound, Structural Layer 240 mm

Foundation Platform (mm) 85mm of bound constructionOr300mm of un bound construction.

Sub grade improvement • The thickness of the unbound platform is increased by replacement of a suitable

depth of sub grade with unbound material. Consideration could be given to placing the unbound material on a geo grid.

• Treat the cohesive sub grade with lime or lime and cement to increase its surface modulus to a minimum of 100MPa. This would be subject to testing for the presence of sulphates.

The Proposed Construction Solution 

Lime is White

Cement mixing 

Checking spread rate 

Compacting stabilised layer 

Testing

Sulphate tests 

The Recycled Road 

Reduced local disruption and CO2 

Quicker build times

Rural project example:  Outputs 2,000m2 per day

Further cost savings: Preliminaries Supervision Traffic Management

Less disruption

Days to Complete

Thanks now off to the Sunset