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MAIN ROADS Western Australia Document 71/04/141.1 Issue Date: 13 January 2012D11#276100

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DETERMINATION OF THE CALIFORNIA BEARING RATIOOF A SOIL: STANDARD LABORATORY METHOD FOR AREMOULDED SPECIMEN

1 SCOPE

This method sets out the procedure for thedetermination of the California Bearing Ratio (CBR) ofa soil when compacted and tested in the laboratory.The method is applicable to fine-grained and medium-grained soils, as defined in Test Method WA 105.1.

2 SAFETY

This method does not attempt to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this method to establishappropriate occupational health and safety practicesthat meet statutory regulations.

3 REFERENCED METHODS

Austral ian Standards

AS 1152 Specification for test sieves

AS 2103 Dial gauges and dial test indicators

AS 2193 Methods for calibration and grading offorce-measuring systems of testingmachines

WA Test Methods

WA 105.1 Preparation of Disturbed Soil and GranularPavement Material Samples for Testing.

WA 110.1 Soil and Granular Pavement MaterialMoisture Content: Convection OvenMethod.

WA 115.1 Particle Size Distribution: Sieving andDecantation Method

WA 115.2 Particle Size Distribution: AbbreviatedMethod for Coarse Materials

WA 132.1 Dry Density/Moisture ContentRelationship: Standard Compaction. Fineand Medium Grained Soils

WA 133.1 Dry Density/Moisture ContentRelationship: Modified Compaction. Fineand Medium Grained Soils

4 DEFINTIONS

Laboratory moisture ratio the ratio of the moisturecontent of the specimen to the optimum moisturecontent of the material as determined on materialprepared in accordance with Procedure 6.1(b),expressed as a percentage.

Laboratory density ratio the ratio of the dry densityof the specimen to the maximum dry density of thematerial as determined on material prepared inaccordance with Procedure 6.1(b), expressed as apercentage.

5 APPARATUS

(a) Steel penetration piston with a 49.6 0.1 mmdiameter over the length of penetration. The length ofthe piston will depend upon the number of surchargesand the depth of penetration required.

(b) Loadingmachineequipped with

i. A moveable head or base capable oftravelling at a uniform (not pulsating) rate of 1

0.2 mm/min for use in forcing thepenetration piston into the specimen; and

ii. A force-measuring device meeting theaccuracy and repeatability requirements ofAS 2193 Grade C testing machines for therange of forces used in the test. The force-measuring device shall be also capable ofindicating seating loads of approximately 50 Nand 250 N.

NOTE:

The indicator points of the force-measuringdevice at the seating loads of approximately, but notgreater than, 50 N (for expected CBR values equal toor less than 30) and 250 N (for expected CBR valuesgreater than 30) need not necessarily meet the GradeC requirements of AS 2193 but should be displayedas definite numbers or marks.

(c) Thermostatically controlled oven with good airventilation capable of maintaining a temperature withinthe range of 105

oC to 110

oC.

(d)Cylindrical metal mould (Figure 1) of known

volume with an internal diameter 152 1 mm, height

178 1 mm and wall thickness of at least 5 mm,provided with a metal extension collar and a perforatedmetal baseplate.

TEST METHOD WA 141.1 2012

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(e) Steel spacer disc (Figure 2) of 150 1 mm

diameter and 61 0.25 mm high, fitted with aremovable handle for lifting the disc from the mould.

(f) Compaction apparatus complying with the

requirements of WA 132.1 or WA 133.1, as applicable.

(g) Metal stem and perforated platewith a mass of

1.00 0.025 kg (Figure 3).

(h) Metal surcharges, with each surcharge having a

mass of 2.25 0.025 kg, a diameter of 150 0.5 mm

and with a centre hole of 55 1.0 mm diameter (Figure4).

NOTE: During penetration the surcharge in contactwith the soil should meet the tolerances as specified.Other surcharges may be slotted and may be outsidethe tolerances provided the total surcharge mass is

within the required tolerances and there is no contactwith the side of the mould and the penetration piston.

(i) Device for measuring swell (DMS), consisting of adial gauge or similar capable of measuring theexpected range of travel, graduated to at least 0.01mm and meeting the accuracy and repeatabilityrequirements of AS 2103 and a metal tripod (Figure 5)

(i) Setting piece, a length of bar to suit the device formeasuring swell.

(k) Balanceof at least 15 kg capacity readable to 1 g,with a Limit of Performance (F) of not more than 5 g.

(l) Jack, lever, frameor other suitable device, whichmay be used for extruding specimens from the cylinder(optional).

(m) Sieves, 19 mm and, if required, a 4.75 mm sieve,complying with AS 1152

(n) Water tank or container capable of maintainingwater at a level above the moulds, during soaking.

(o) Other apparatus such as a mixing bowl,straightedge, filter paper and dishes.

6 PROCEDURE

6.1 PREPARATION OF THE TEST INCREMENT

(a) Using the 19 mm sieve, sieve a representativesample of the soil prepared in accordance with theprocedure described in Test Method WA 105.1.Determine the percentage of material retained on thesieve. Only the material passing the 19 mm sieve is tobe used for the test.

NOTES:

1. Where it is obvious that all material passes the19.0mm sieve (e.g. sand), testing by WA 115.1 or

WA 115.2 is not necessary. It is sufficient to recordthat the material passes the 19.0mm sieve by visualassessment.

2. The removal of small amounts of stone retained onthe 19 mm sieve will affect the CBR obtained only byamounts comparable with experimental error involvedin measuring CBR. The exclusion of a large portion ofstone coarser than 19 mm (such as is present, for

example, in a gravel of 75 mm maximum size) mayhave a major effect on CBR compared with thatobtainable with the soil as a whole, and on theoptimum moisture content. There is at present nogenerally accepted method of testing, or of calculation,for dealing with this difficulty in comparing laboratoryCBR test results with CBR values obtained in the field.

The percentage by mass of material retained on the 19mm sieve should be included in the report.

3. Material, which has been compacted previously inthe laboratory, should not be re-used, as breakdown ofthe material during compaction can lead to misleadingresults.

(b) Determine the dry density/moisture contentrelationship on a representative sample passing the 19mm sieve in accordance with Test Method WA 133.1

(c) Obtain a representative test increment from theCBR test portion. Determine the hygroscopic moisturecontent in accordance with Test Method WA110.1.

(d) Select the dry density / moisture content condition at which the test increments are to bemoulded.

(e) Calculate the dry mass of the testincrement using the equation:

100100

Where:

= dry mass of test increment in grams = wet mass of test increment in grams

= hygroscopic moisture content as apercentage(f) Calculate the mass of water to be added tobring the test increment to the desired moisturecontent using the equation:

100

Where:

= mass of water to be added to the testincrement in grams

= moisture content (%) condition at whichthe test increments are to be moulded.

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= hygroscopic moisture content (%) of thetest increment

= dry mass of test increment in grams

Thoroughly mix the test increment with a suitableamount of potable water to bring the test increment tothe required moisture content.

(g) Cure the test increment for 12 hours or moredepending upon the soil type. Record the duration ofcuring.

NOTE: It is important that the water is thoroughlymixed into and uniformly distributed through the soilsince inadequate mixing gives rise to variable results.It is desirable to keep the soil in a sealed container toallow the water to become more uniformly distributedthrough the soil before compaction. For materials oflow plasticity and high permeability prepared in a moistcondition close to optimum moisture content, little or nocuring is required, but if the soil is dry and containsheavy clay, up to 7 days curing prior to compactionmay be required. The more cohesive a soil, the moretime required for moisture to infiltrate and equilibrate.All soils should be cured for a minimum of 12 hours.

6.2 PREPARATION OF THE TEST SPECIMEN

(a) Calculate the desired wet density of the testspecimen using of the following equation:

100

100

Where:

= desired wet density of test specimen in t/m = desired dry density of test specimen in t/m = moulding moisture content of the test specimenas a percentage

(b) Calculate the desired wet mass of the testspecimen using the following equation:

Where:

= desired wet mass of the test specimen in grams = desired wet density of test specimen in t/m = volume of the mould in cm3(c) Calculate the wet mass of each layer that is to becompacted in the mould using the equation:

5

Where:

= wet mass of soil per layer in grams

= wet mass of test specimen in grams(d) Determine the mass of the mould and perforatedbaseplate ().

(e) Insert the spacer disc, clamp the mould (with theextension collar attached) to the baseplate and place afilter paper on top of the spacer disc.

(f) Immediately prior to compaction thoroughly mix thecured soil and determine the moisture content () of arepresentative fraction of the test portion in accordancewith Test Method WA 110.1.

(g) Compact the specimen uniformly into the mould,using a modified compaction hammer, to the specifiedlaboratory density ratio in five layers so that thecompacted height of the soil in the mould is 21 mm to26 mm in the first layer, 45 mm to 50 mm in the secondlayer, 67 mm to 72 mm in the third layer, 92 mm to 97mm in the fourth layer and 117 mm to 122 mm in thefifth layer.

The minimum number of blows per layer, using themodified compaction hammer, shall be sixteen (16)blows. If 16 blows of a modified compaction hammerresults in the specimen not satisfying the target layerrequirements described above, a standard compactionhammer shall be used. If the standard compactionhammer is used the minimum number of blows perlayer shall be nine (9) blows.

NOTE: A suitable pattern of blows is eight (8) blowsaround the perimeter of the specimen (with minimal

overlap) and one (1) blow in the centre of the layer.

Discard specimens that do not meet the aboverequirements.

The laboratory moisture ratio shall be within 5.0percent of the specified moisture ratio and laboratorydensity ratio shall be within 1.0 percent of the specifieddensity ratio.

(h) Free the material from around the inside of thecollar and carefully remove the collar.

(i) While the base plate is still attached trim the surface

of the compacted specimen level with the top of themould by means of a straightedge. Use fines to patchany holes developed in the surface during trimming.

(j) Carefully remove the mould with compacted soilfrom the baseplate so as to not disturb the compactedsoil. Place a filter paper on the baseplate and carefullyinvert the mould with compacted soil and replace ontothe baseplate. Securely re-fasten the mould to thebaseplate.

(k) Remove the spacer disc from the mould anddetermine the mass of the mould plus compacted soil().(l) If soaking is not required, perform the penetrationtest (Procedure 6.4).

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6.3 SOAKING THE TEST SPECIMEN

(a) Determine the mass of the baseplate plus mouldplus specimen ().

(b) Place a filter paper and the stem and perforatedplate on the compacted soil specimen in the mould.Apply a surcharge in accordance with Figure 7; theminimum shall be 4.5 kg.

NOTE: Surcharges may be applied to simulate theconfining effects of the overlying material layer (seeFigure 7).

(c) Obtain and record an initial reading () using thedevice for measuring swell (DMS) and the settingpiece.

(d) Place the DMS onto the top of the mould and markthe position so that it can be replaced in the originalposition.

(e) Obtain and record the initial reading before soaking() and remove the DMS.(f) Place the specimen in the water tank and allow thewater to have free access to the top and the bottom ofthe specimen. Soak for 4 days or other specifiedsoaking period. Maintain the water level above themould during this period.

NOTE: A shorter soaking period is permissible for soilsthat take up moisture readily provided tests haveshown that the shorter period do not affect the results.

Some specimens may require longer soaking periodsto account for expected in service conditions.

(g) After soaking is completed obtain and record a finalreading () using the DMS and the setting piece. If reset the DMS so that (h) Place the DMS on the points of contact marked inProcedure 6.3(d) and record the reading after soaking().(i) Remove the specimen from the water and tilt thespecimen to remove the surface water. Return themould to the vertical position and allow the specimen

to drain downward for approximately 15 minutes. Donot disturb the surface of the specimen during theremoval of water.

(j) Remove the surcharges, stem and perforated plateand determine the mass of the baseplate plus mouldplus specimen ().(k) Perform the penetration test (Procedure 6.4) assoon as practicable.

6.4 PENETRATION TEST

(a) Place the 2.25 kg annular surcharge on thespecimen and then place the mould plus specimenplus baseplate in the loading machine. Seat the

penetration piston with the smallest possible load, notexceeding 50 N for expected CBR values 30 and 250N for expected CBR values > 30. Apply surcharges asrequired. Unless otherwise specified the surchargemass shall be 4.5 kg. If the specimen was soaked,apply surcharges equivalent in mass to those appliedduring soaking.

NOTES:

1. This initial load is required to ensure satisfactoryseating of the piston and is considered as the zeroload when plotting the load-penetration curve.

2. Refer to Note in Procedure 6.3(b)

(b) Read, or set to zero, the force-measuring deviceand the displacement measuring device used tomeasure penetration. The penetration measured shallbe that of the piston relative to the mould.

NOTE: The dial gauge should be mounted such thatno other displacements in the equipment influence theactual measured penetration.

(c) Apply the load with a constant rate of penetration of

1 0.2 mm/min. Record load readings at penetrationsof 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 7.5, 10.0 and12.5 mm.

NOTE: With manually operated loading devices, it maybe necessary to take load readings at closer intervalsto control the rate of penetration.

(d) The test may be terminated after 7.5 mmpenetration if the penetration is proceeding without anyincrease in the load or the limits of the equipment arereached.

(e) Remove the soil from the mould and determine themoisture content of the top 30 mm layer andthat of the remaining specimen (wr) in accordance withTest Method WA 110.1.

7 CALCULATONS

Calculate the following:

(a) Plot the load-penetration curve (see Figure 6).When the load-penetration curve is concave upwardinitially (because of surface irregularities or othercauses) adjust the zero point as shown in Figure 6,curve 3. If the correction is greater than 2 mm theload-penetration curve shall be presented in the testreport.

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(b) Read from the load-penetration curve, corrected ifrequired, the force value in kN at penetrations of 2.5mm and 5.0 mm and calculate the bearing ratio foreach by dividing by 13.2 kN and 19.8 kN, respectively,and multiplying by 100.

Record the greater of the calculated values as theCBR of the material.

(c) Calculate the mass of dry soil in the specimen ()from the following equation:

1 100

Where:

= mass of dry soil in the specimen, in grams

= mass of mould plus compacted soil, in grams = mass of mould, in grams = moisture content of the soil immediately prior to

compaction, in percent

(d) Calculate the dry density of the specimen beforesoaking () from the following equation:

1

Where:

= dry density of the specimen, in grams per cubiccentimetre

= mass of dry soil in the specimen = volume of the specimen in cubic centimetres(volume of the mould less the volume occupied by thedisc)

(e) Calculate the laboratory density ratio (LDR) of thespecimen from the following equation:

100

Where:

= laboratory density ratio, in percent = dry density of the specimen, in grams per cubiccentimetre

= maximum dry density of the soil, in gramsper cubic centimetre.

(f) Calculate the laboratory moisture ratio (LMR) of thespecimen from the following equation:

100

Where:

LMR= laboratory moisture ratio, in percent

= moisture content of the soil immediately prior tocompaction, in percent

OMC= optimum moisture content of the soil, in percent

(g) If the specimen has been soaked, calculate thepercent swell () from the following equation:

117 100

Where:

S = the swell of the specimen, in percent

h2 = the reading after soaking, in millimetres

h1 = the reading before soaking, in millimetres

(h) If the specimen has been soaked calculate themoisture content of the specimen after soaking ()from the following equation:

100

Where:

ww= moisture content of the specimen after soaking,in percent

= moisture content of the soil immediately prior tocompaction, in percent

= mass of baseplate plus mould plus specimenafter soaking in grams

= mass of baseplate plus mould plus specimenbefore soaking, in grams= mass of dry soil in the specimen, in grams(i) If the specimen has been soaked calculate thevolume of the specimen after soaking () from thefollowing equation:

100100

Where:

= the volume of the specimen after soaking, in

cubic centimetres

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= the volume of the specimen before soaking, incubic centimetres

S = the swell of the specimen, in percent

(k) If the specimen has been soaked calculate thespecimen dry density after soaking () from thefollowing equation:

Where:

= dry density of the specimen after soaking, ingrams per cubic centimetre

= mass of dry soil in the specimen, in grams

= the volume of the specimen after soaking, in

cubic centimetres

(l) If the specimen has been soaked, calculate thelaboratory density ratio after soaking ( as apercentage of maximum dry density.

100

Where:

= laboratory density ratio after soaking

= dry density of the specimen after soaking, ingrams per cubic centimetre = maximum dry density of the soil, in gramsper cubic centimetre.

(m) If the specimen has been soaked calculate thelaboratory moisture ratio after soaking () of thespecimen from the following equation:

100

Where:

= laboratory moisture ratio, in percent = moisture content of the specimen aftersoaking, in percent

OMC = optimum moisture content of the soil, inpercent

(n) Calculate the laboratory moisture ratio of the top 30mm of the specimen after penetration () of thespecimen from the following equation:

100

Where:

= laboratory moisture ratio of the top 30 mm, inpercent

= moisture content of the top 30 mm thespecimen.


(o) Calculate the laboratory moisture ratio of theremainder (i.e. excluding the top 30mm) of the

specimen after penetration () of the specimenfrom the following equation:

100

Where:

= laboratory moisture ratio of the remainder,in percent.

= moisture content of the remainder of thespecimen.


8 REPORTING

Report the following:

(a) CBR of the specimen according to Table 1:

Table 1

CBR%

Report valueto the nearest

< 5 0.55 to 20 1

>20 to 50 5> 50 10

(b) The penetration at which the CBR was determined,in millimetres.

(c) The laboratory moisture content ( and themoisture ratio at which the specimen wascompacted, to the nearest 0.1 and 0.5 percentrespectively.

(d) The laboratory dry density and dry densityratio (LDR), at which the specimen was compacted, tothe nearest 0.01 t/m and 0.5 percent respectively.

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(e) The moisture content ) and moisture ratio ofthe top 30 mm of the specimen after penetration, to thenearest 0.1 and 0.5 percent respectively.

(f) The moisture content ) and moisture ratio of the remainder of the specimen after penetration, tothe nearest 0.1 and 0.5 percent respectively.

(g) If the specimen was soaked;

The swell of the specimen after soaking tothe nearest 0.5 percent.

The dry density ratio ) of the specimenafter soaking, to the nearest 0.5percent.

The moisture content) and moisture ratioof the entire specimen after soaking, tothe nearest 0.1 and 0.5 percent respectively.

(h) The percentage by mass of the material retained onthe 19 mm sieve.

(i) The mass of surcharges applied.

(j) The compactive effort used to compact thespecimen in terms of the number of layers, the numberof blows per layer and the mass of the rammer.

(k) The period of soaking.

(l) Identification and description of sample.

(m) The load-penetration curve, if the correction to thetest curve is greater than 2 mm.

(n) The number of this i.e. Test Method WA 141.1.

(o) The maximum dry density to the nearest 0.01 t/mand the optimum moisture content of the specimen tothe nearest 0.5%.

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9 FIGURES AND DRAWINGS

150 1

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10 ISSUING AUTHORITY

Document Owner

Manager Materials Engineering

Delegated Custodian

Pavements Manager

Pavement Layer Thickness (mm)

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11 REVISION STATUS RECORD

Page No. SectionRevision

Description / Reference

All All Format Revision and Re-issue of Test Method

Reporting accuracy for moisture content , moisture ratio and OMCchanged

Reporting accuracy for laboratory dry density, dry density ratio and MDDchanged

2 6.1 (a) Note 2The following text has been removed from this note.

If it is specified that the same percentage of coarsematerial (passing the 53 mm and retained on the4.75 mm sieves) in the test sample as in the original

field sample is to be maintained, the material retainedon the 19 mm sieve may be replaced by an equalportion by mass of the materials passing the 19 mmsieve and retained on the 4.75 mm sieve.

It is important that the maximum dry density andoptimum moisture content used to determine thelaboratory density ratio and laboratory moisture ratiobe determined on the material passing the 19 mmsieve which is the same as that used to determine theCBR value. If material retained on the 19 mm sieve isreplaced by an equal portion by mass of materialspassing the 19 mm sieve, the values determined onmaterial without the replacement are not applicable.

and whether it was excluded or replaced

7 8 (h)The following test has been removed from the reportingrequirements

and whether it was excluded from thetest or replaced with material that passes the 19 mmsieve and is retained on the 4.75 mm sieve.

2 5 (e) 150 0.5 mm changed to 150 1 mm.

8 Figure 2 150 0.5 mm changed to 150 1 mm.

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