PROOF ROLLING

PROOF ROLLINGFUNDAMENTALS

Effect of variations in gross weight and tyre inflation prssure onground contact pressureGross Weight ( lb )7650153002250025000 ( kg )347069401020611340Tyre SizeInflationGround Contact PressurePressure(psi)psi*pli**psiplipsiplipsipli 7.50 x 155043145502505634258378 10 ply6047152542546034762382705016258258643506638580541756226468354703899058183652727135974392 7.50 x 155043153502505734359378 12 ply60471645525661347643837051170592646635168386805518462270703577239290582026627673364763971006221869289763697940211065224722937937582406 7.50 x 155047158572536334865385 14 ply605017059260673536838970521816226869358723948055192652767336575399905721068281763707840510061225712907937782408110652307529383385854171206823979301873918942313071243823189040093431 * Ground contact pressure in psi(1 psi = 6.895kPa) **Ground contact pressure in lbs per inch of tyre width(1 kPa = 0.145psi)Source : Firestone Tyre and Rubber Company.(1000 lb = 454 kg)

INTRODUCTIONDoes not provide a one size fits all solutionMany variables impact the outcome of test.Material typeSoil moisture contentSoil stiffness,Applied loadInterpretation of visible deformation as an accepted criterion

All parameters to be considered and discussed.3FundamentalsWhat are we measuring?Objective of proof rolling (one or several) :To identify zones of poor compaction (as evidence by large plastic deformation)To identify zones of high moisture content in clayey foundation soil (springing or large elastic deformation) To prove that subgrade has adequate stiffness (very small elastic deformation) to comply with pavement requirements (design subgrade CBR strength)

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What are we measuring?

FundamentalsImpact of Proof Rolling on objectives :Positive impact:Likely to improve density of poorly compacted soil (assuming suitable soil moisture conditions)Negative impact : Dry cohesive soil shows no visible deflection even though compaction/soil density is unsatisfactory.Springing action under proof rolling of high moisture soil acts as a soil pump. Continued rolling is likely to draw more moisture into the soil, thus further weakening it.Subgrade already almost 100% compacted is likely to fail/deform if overstressed.

Negative impact:Where the near surface soils are cohesive and well dry of optimum moisture content, the transient insitu soil strength is likely to be high, even when the soil density is low.Further rolling of weak cohesive soils is likely to result in progressive bearing capacity failure of the soil, and even greater deformation.6FundamentalsFactors Influencing Proof Rolling :Material Type:E.g. Non-cohesive soils (clean sand and gravels) behave differently to cohesive (clayey) soils under compaction.Soil Moisture:Stress / Load Applied

Material type : 1. Sands are usually easily compacted but localised bearing capacity failure typically occurs at the surface under wheel loads, so proof rolling is generally inappropriate unless it can be carried out after placing a thin capping layer to confine the sand.Well graded granular soils with relatively low contents of fines are readily compacted and insensitive to moisture variations and over compaction.Cohesive soils with clay content greater than 12% are sensitive to negative impacts outlined.

7Following the terminology discussed by Crovetti (2002), proof rolling and test rolling are considered similar in concept, though distinguished by the type of equipment and purpose of the test.

Proof rolling typically involves use of a smooth-wheel or pneumatic rubber-tired construction roller, to identify areas of weak subgrade, the test is intended to correct minor compaction inadequacies. Test rolling usually utilizes a vehicle with widely-spaced, narrow wheels such as a standard construction dump truck, the configuration is not intended to increase compaction, but rather identify weak areas exclusively.Proof RollingTest Rolling

PROOF ROLLING SPECIFICATION2.0 EQUIPMENT (Std. Proof Roller)Have body suitable for ballast loading (25 to 50 tons) gross roller weightMin. 2 axles with not more than 2 pneumatic tyred wheels per axle.All wheels arranged to carry approx. equal loadsMin. contact width 2.3m under working conditions Tyres capable of operating under various loads with variable air pressures up to 1030 kPa (150 psi)

PROOF ROLLING SPECIFICATIONEQUIPMENT (Std. Proof Roller)(cont.)Smooth tread tyres to impart minimum ground contact pressure of 520 kPa (75 psi)Operating load and tyre pressure shall be within manufacturers chart range.Proof roller shall be drawn by power train or self-propelled

PROOF ROLLING SPECIFICATIONALTERNATIVE EQUIPMENTWritten approval by the S.O.Subject to requirements of std. proof roller except with respect to minimum contact width, axle/tyre arrangement and tyre tread.

PROOF ROLLING SPECIFICATION4.0 Construction Methods4.2 Operating speeds (4 8 km/h)4.3 Coverage ( single pass of proof roller tyres)4.4 Where to proof rollAreas where required CBR and density has been achievedEmbankments more than 1.8m in depth below subgradeNot within 4.6m of any bridge abutment or retaining wall

PROOF ROLLING SPECIFICATION4.0 Construction Methods (cont.)4.5 When to proof rollImmediately after subgrade compaction operation, when moisture content of subgrade soil is near optimumNot for unstable areas and requiring undercutting.Before or after subsoil drains are installed.

This minimises the subgrade becoming too wet or too dry for an effective proof rolling evaluation.Subgrade too wet material will displace and rut. If subgrade too dry a dry hard surface crust (or layer) and undesireable soft wet underlying material not detected.For areas where subgrade appears to be stable without undercutting, proof rolling shall be done after the top 300mm of the subgrade meet s the compaction requirements and the subgrade has been brought to shape within the specified tolerances.

13PROOF ROLLING SPECIFICATION4.0 Construction Methods (cont.)4.6 Proof Roller Weight and Tyre PressureWeight set at gross 50 tonnesTyre pressure 1030 kPa (150 psi)(Ground contact pressure rquired = 75 psi)Tyre ground contact pressure chart

50 tonnes / 4 tyres = 12.5 tonnes/tyre (27500 lbs)Spec requirement for ground conctact pressure = 75 psiFrom table: 7.50x15 14ply inflated to 130 psi and gross weight of 25000 lbs (11.54tons) gives a ground contact pressure of 93psi.Refer to figure 10-9 for ground contact pressure at varying wheel loads and air pressures.14PROOF ROLLING SPECIFICATIONWhy specify ground contact pressure?Because contact area between tyre and the ground surface over which it passes varies with air pressure in the tyre,Specifying the total weight or the weight per wheel is not a satisfactory method of indicating the compacting ability of pneumatic rollersParameters to determine compacting ability of pneumatic tyre rollers: Wheel load, tyre size, tyre ply and inflation pressure.

15PROOF ROLLING SPECIFICATION6.0 Failure CriteriaAcceptable limits of elastic and plastic vertical deformation shall first be established.Compaction trial area of representative soil subgrade already tested and approved to min. CBR of 7% when compacted to 95% of dry densityFailure Deformation Limit (FDL) shall be approved by S.O.

CBR under 4 days soaked condition.Deformation measured using 1.5m long straight supported on 150mm standsMinimum of 5 measurements shall be taken within each compaction trial.16PROOF ROLLING SPECIFICATIONFailure Criteria (cont.)Subgrade for new road construction shall be considered to fail when;Permanent rutting is in excess of the FDL.Elastic (rebound) movement or rutting is in excess of FDL with substantial cracking or substantial lateral movement.

Elastic movement is always associated with excess water in subgrade.17PROOF ROLLING SPECIFICATION7.0 Variation in the proof rolling resultsWhere there are occasional or nominal deflections in excess of the failure criteria, the density shall be checked.If investigation shows that good soil extends throughout the top 1.0m of the subgrade, then the subgrade may to the discretion of the S.O. be accepted

PROOF ROLLING SPECIFICATION8.0 Remedial measures for soft or failed subgrade.Method for correction of failure to be submitted by the Contractor and approved by the S.O.Where soft or failed spots are found, CBR tests shall be done to determine the top 300mm meets specifications.Contractor shall correct any deficiency found and CBR test checked for compliance.

Once the subgrade condition has been approved to the required CBRvalue, as per specs further proof rolling shall be done and they shall only be paid upon acceptance of the test.19PROOF ROLLING SPECIFICATION9.0 Test PitsWhere required and as instructed by the S.O., test pits shall be conducted .Test pits dug across width of subgrade in locations with highest deflections.Soil, moisture conditions, density and CBR shall be tested in the test pits.

Test pits by excavating 0.6 to 1.5m into the sugrade using Contractors equipment.Test pits to evaluate the most severe locations.Trench sidewalls and the bottom of the cut shall be inspected and documented including soil type, layer thickness, soil condition, and soil strength by using hand penetrometer. Digital pictures shall also be recorded.All test pits shall be properly filled and compacted to the specified density prior to further proof rolling tests.20Other Specifications173.03 TEST ROLLING(a) GeneralThe test rolling procedure submitted by the Contractor shall include details of when test rolling will be undertaken, the method of preparing an area for test rolling and the extent of test rolling.Plant which is nominated for use in test rolling procedures shall comply with the followingrequirements:(i) Static smooth steel wheeled rollers shall have a mass of not less than 12 tonnes and aload intensity under either the front or rear wheels of not less than 6 tonnes per metrewidth of wheel.(ii) Pneumatic tyred plant shall have a ground contact pressure under either the front or rearwheels of not less than 450 kPa per tyre. The area over which this ground contactpressure shall be applied shall not be less than 0.035 m per tyre.(b) ComplianceCompliance with the test rolling requirements shall be when an area withstands test rollingwithout visible deformation or springing.VicRoads Australia

Unified Soil Classification SystemSymbol chartMajor divisionsGroup symbolGroup nameCoarse grained soilsgravelclean gravel 50% of coarse fraction retained on GPpoorly graded gravelon No.4 (4.75mm) sievegravel with >12% finesGMsilty gravelGCclayey gravelsandclean sandSWwell graded sand, fine to coarse sand 50% of coarse fraction passes No.4 sieveSPpoorly-graded sandsand with >12% finesSMsilty sandSCclayey sandFine grained soilssilt and clayinorganicMLsiltmore than 50% passes No.200 sieveliquid limit < 50CLclayorganicOLorganic silt, organic claysilt and clayinorganicMHsilt of high plasticity, elastic siltliquid limit 50CHclay of high plasticity, fat clayorganicOHorganic clay, organic siltHighly organic soilsPtpeatFirst and/or second lettersSecond letterLetterDefinitionLetterDefinitionGgravelPpoorly graded (uniform particle sizes)SsandWwell graded (diversified particle sizes)MsiltHhigh plasticityCclayLlow plasticityOorganic

British Soil Classification SystemVery coarseBOULDERS> 200 mmsoilsCOBBLES60 - 200 mmGcoarse20 - 60 mmGRAVELmedium6 - 20 mmCoarsefine2 - 6 mmsoilsScoarse0.6 - 2.0 mmSANDmedium0.2 - 0.6 mmfine0.06 - 0.2 mmFineMcoarse0.02 - 0.06 mmsoilsSILTmedium0.006 - 0.02 mmfine0.002 - 0.006 mmC CLAY< 0.002 mm

Ballast compartmentPneumatic tyresBallast Filled Pneumatic Tyre Roller

Proof Roller or Test Roller?

Can This Be A Proof Roller?

CP271Dynapac s Pneumatic Tyred Rollers are especially designed for the compaction of bases, sub-bases and mainly for asphalt mixes on any kind of jobs . The machines have seven or nine wheels: three or five steered oscillating front wheels and four traction rear wheels.Operating mass = 12400 kg Operating mass, ballasted = 27000 kgWorking width = 2350 mm

Pneumatic Tyre Tech Data

CONCLUSIONWhat equipment can we or shall we use?Is the loading requirement too much?Can we rethink about the purpose?

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