Application of DCP in Prediction of Resilient Modulus of Subgrade Soils

Louay Mohammad, Ph.D.Louisiana Transportation Research CenterLouisiana State University

2006 Pavement Performance SeminarApril 10, 2006, Ruston, LouisianaApril 11, 2006, Alexandria, LouisianaApril 12, 2006, Baton Rouge, Louisiana

Topics• Background• Objective• Scope• Methodology• Experimental program• Results

What is Resilient Modulus?MR

Stiffness of SoilsUnder Dynamic Loading

Why Resilient Modulus was Selected?• More realistic way to characterize moving

wheel loads

Subgrade

AC

Base

D

TimeStress or load pulse

Deviator stress

Plastic R

Total

P

Resilient

StrainDeformation of soil sample

RD=RM σ

ε

σ

ε

ε

ε

Deviator stress

Where is MR Used?

• Design of New & Rehabilitated pavements• Forensic analysis of Pavement Failures • Quality Control for fill or cut sections

Where is MR Used?• Design of New & Rehabilitated pavements

– LADOTD 1993 AASHTO

( )

log . log ( )

.log

. .

.. log .

.

10 18 10

10

5 19

10

9 36 1

0 20 4 2 15

0 40 10941

2 32 8 07

W Z S SNPSI

SN

M

R o

R

= + + −

+ −⎛⎝⎜

⎞⎠⎟

++

+ −

Δ

Sensitivity Example of Mr to Flexible Pavement Thickness Design (1993)

-4-3-2-1012345

-4 -3 -2 -1 0 1 2 3 4 5 6 7 8

Change in Mr (ksi)

Cha

nge

in o

verl

ay (i

n)

Where is MR Used?• Design of New & Rehabilitated

pavements –M-E Design Guide

• Traffic• Climate• Structure• Thermal

Where is MR Used?• Design of New & Rehabilitated pavements

– M-E Design Guide

Default MREstimated

MRMeasured MRSubgrade

Default MREstimated MRMeasured MRGranular Materials

Default MREstimated MRMeasured MRStabilized Materials

Default EMEstimated EMMeasured EMPCC

Default DM

Estimated DMMeasured DMAsphalt Concrete

InputLevel 3

InputLevel 2

InputLevel 1

Material

Where is MR Used?• Forensic analysis of Pavement Failures

– Assessment of soil conditions – develop an appropriate rehabilitation

strategy

Where is MR Used?• Quality Control for fill or cut sections

– pavement section is designed based upon a targeted resilient modulus

How is Resilient Modulus Determined?• Direct Measurement

– Lab Test: AASHTO T 307– Undisturbed– Disturbed, remolded and compacted

• Reverse Engineering– in-situ

• DCP, Minincone– nondestructive test (NDT) methods

• FWD, Dynaflect

• Prediction– Soil properties

• SSV (DOTD)• other

– Unconfined compressive strength– CBR

Limitations: Direct Measurement

• Direct Measurement– triaxial type of test– Laborious and time consuming– Require advanced testing

equipment– Skilled Personnel

Limitations: MR Predictions Models• Static properties of soils

– SSV, etc: average value for each Parish – Do not represent the dynamic behavior

of traffic loadingMR=1500 + 450[(53/5)(SSV-2)] - 2.5[(53/5)(SSV-2)]2

Alternative InAlternative In--situ Techniquesitu Technique

MR Prediction Models Dynamic cone penetration (DCP)

fast, simple, and economicalGeotechnical investigation

ObjectivesDevelop MR prediction Models

– In-situ• DCP test results• Soil properties

ScopeThirty one sitesFour common cohesive soil types in Louisiana– A-4, A-6, A-7-5, and A-7-6

Field DCP testsVarious moisture-density levels

Laboratory test– Mr from RLTT– Soil physical properties

Three tests per site

EXPERIMENTAL PROGRAM• Field Activities

– Field projects• DCP• Soil Sampling

• Laboratory tests– Repeated load triaxial test– Physical properties– Compaction and strength characteristics

Field Testing Layout• Three sections of testing at each field

project– A, B, and C

• Each section contains nine points

1 2 3 4 5 6 7 8 9

DCP DCP DCP

Core Core Core

Mini-Cone

3' 3' 3' 3' 3' 3'15' 15'

Mini-Cone

Mini-Cone

Set A

-40.0

-30.0

-20.0

-10.0

0.0

10.0

20.0

30.0

0 50 100 150 200 250 300Blow Count

Cum

ulat

ive

Pene

tratio

ncm

Stone

Cement TreatedSubgrade

Compacted Embankment

Blow countD

epth

Dep

th

0

20

40

60

10

30

50

70

5 mm/blow

1 mm/blow

7 mm/blow

Dep

th(c

m)

Dynamic Cone Penetrometer Test: DCPI

Repeated Load Triaxial Test: MR

10 100Deviator stress, σd (kPa)

10

100R

esili

ent m

odul

us, M

r (M

Pa)

Sample depth=0.8 m

Confining stressσc =41.3 kPa

σc =20.7 kPa

σc =0.0 kPa

Silty clay

Relationship B/W Mr and 1/DCPI

R2 = 0.82

0

20

40

60

80

100

0 0.02 0.04 0.06 0.08 0.1 0.121/DCPI, Blows/mm

Mr,

MPa

Development of MR Prediction Models

Moisture ContentDensity

DCPI

MR = f(DCPI, physical properties)M

R

Resilient Modulus Prediction Models

⎟⎠⎞

⎜⎝⎛=

DCPIM R

14.122

Direct Model: R2=0.82

42-97Passing #200 Sieve (%)

8-86Clay (%)9-72Silt (%)22-98LL (%)8-82W (%)50-115γd (pcf)4-61PI (%)

9-85DCPI(mm/blow)

1.0-14Mr (ksi)RangeParameter

Soil Property Model: R2=0.89

⎟⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛=

wDCPIM d

Rγ42.010.221

32.1

0

40

80

120

0 40 80 120

Measured Mr (MPa)

Pred

icte

d M

r (M

Pa) Modeling

Equality line

Verification

UCL- UpperControl LimitLCL- LowerControl Limit

Measured vs. Predicted: Direct Model

⎟⎠⎞

⎜⎝⎛=

DCPIM R

14.122

Measured vs. Predicted: Soil Property Model

⎟⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛=

wDCPIM d

Rγ42.010.221

32.1

0

40

80

120

0 40 80 120

Measured Mr (MPa)

Pred

icte

d M

r (M

Pa) Modeling

Equality line

Verification

UCL- UpperControl LimitLCL- LowerControl Limit

0

3

6

9

12

15

0 3 6 9 12 15

Lab Mr (ksi)

Pari

sh M

r (k

si)

Equality Line

7.6-9.2Parish-Mr(ksi)

0.9-14Lab-Mr(ksi)

RangeMr

Measured vs. Predicted: Parish Map

Summary• MR prediction Models were developed

– DCP• Good agreement

– Measured and predicted– Improvement

• Current practice

• Tools– Design of New & Rehabilitated pavements

• Current & M-E Design Guide– Forensic analysis of Pavement Failures – Quality Control for fill or cut sections

⎟⎠⎞

⎜⎝⎛=

DCPIM R

14.122

⎟⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛=

wDCPIM d

Rγ42.010.221

32.1

Report No. 417