standard penetration test method.pdf

8/14/2019 Standard Penetration Test Method.pdf

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STANDARDPENETRATIO

NTEST


2/29

OUTLINE

Int

roduction

Ge

neralEquip

mentandProcedures

Fa

ctorsAffectingMeasuredN-values

Ad

vantagesan

dDisadvantages

Co

rrelationsBetweenSPT

andSoil

Properties


3/29

SIG

NIFICANT

PUBLICA

TIONS

Arman,A.,Samtani,N.,Castelli,R.,andMunfakh,

G.(1997).

GeotechnicalandFoundationEngineeringModule1!

Subsurfa

ceInvestigations,FHWA-HI-97-021,305pp.

CarterM.and

Bentley,S.P.(19

91).Correlationso

fSoilProperties.

London,

PentechPressPublishers,London,130pp.

McGregor,J.

A.andDuncan,J.

M.(1998).Perform

anceandUseof

theStandardPenetrationTestinGeotechnicalEngineering

Practice.

CenterforGeotec

hnicalPracticeand

Research,Virginia

Tech.

NavalFacilitiesEngineeringCommand(1982).SoilMechanicsDesign

Manual7

.1.DM-7.1.


4/29

Sampler

Head

Ven

t

Ball

Ch

eck

Valve

Split

Barrel

Sampling

Tube

Driving

Shoe

G

ENERALEQUIPMENTANDP

ROCEDUR

ES

Split-SpoonSam

pler

NHI-FHWA


5/29

G

ENERALEQUIPMENTANDP

ROCEDUR

ES

1.0-2.0in

1

6o-23o

0.1in

Open

Shoe

1.375in

1.50in

2.0in

Ball

Vent

Rollpin

Head

18.0-30.0in

S

plit-SpoonSa

mpler


6/29

NHI-FHW

A

Safety

McG

regorandDuncan(1998)

Do

nut

NHI-FHWA

Automatic

HAM

MERS


7/29

McGregor

andDuncan(1998)

DonutHammer

Common

lyusedinRhode

Island

Opensystem

Delivers

approximately

45%ofthemaximumfree-

fallenerg

y

Highlyva

riableenergy

transfer

HAM

MERS


8/29

HAM

MERS

SafetyHammer

Common

lyusedinRhode

Island

Closeds

ystem

Delivers

approximately

60%ofthemaximumfree-

fallenerg

y

Highlyva

riableenergy

transfer

NHI-FHWA


9/29

HAM

MERS

AutomaticHammer

RarelyusedinRhodeIsland

Safestsystem

Delivers

approximately95-

100%of

themaximumfree-

fallenerg

y

Consiste

ntandeffective

energytransfer

Increase

dproduction

NHI-FHWA


10/29

ROTAT

IONOFROPE

AROUNDA

CATHEAD (

AST

MD1586)

N

HI-FHWA


11/29

STANDA

RDPENETRATION

TEST(SPT)


12/29

63.5-kg(140lb.)

Hammerdropping

0.76m(30!

)

Anvil

Split-Barrel

Drivesampler

DrillRod

SeatingSpoon150mm(

6!

)

SecondIncrem

ent150mm(

6!)

SPT

Resistan

ce

(N-value)is

totalnum

berof

blowsto

drive

sampler

the2nd

and3rd1

50mm

incremen

ts

ThirdIncrement150mm(

6!)

STANDA

RDPENETRATION

TEST(SPT)

NHI-

FHWA


13/29

Thewashboringmethodorrotarydrillingwithatriconebitshouldbe

usedtominimizesoildisturban

ce.

Waterordrillingmudintheboreholeshouldbeus

edtominimizethe

reductionin

verticaleffectivestresswithinthesoilatthesampling

location.Wateranddrillingmu

dmustbemaintainedatorabovethe

groundwatertable.

Thebottom

oftheboringshouldbebetween2.5a

nd6in.indiamete

r,

althougham

aximumdiameter

of4in.ispreferred

.

Casingshou

ldnotextendbelowthebottomofthe

boringbeforethe

SPT

isperformed

.

Themeasur

edN-valueshould

betakenfromthepenetrationbetwee

n6

and18inches.Thefirst6in.b

elowthebottomof

theboringis

consideredtobedisturbedmaterial.

ADDITIONALRECOMMENDATIONS

(S

kempton1986)


14/29

SPTN-valuesshouldbecorrectedfor60%ofthe

maximumfree-fall

energy(140

lbweightdropped

adistanceof30in

)tothedrillstem.

This

corresponds

totheenergydeliveredbythesafety

hammer.

Drillingmud

shouldbeusedto

preventliquefactio

nofloosesands

(sometimes

called"runningsands#)belowthewatertable.

Thesplitspoonsamplershould

haveauniforminsidediameterof13/8#.

Adrillingbit

shouldbeusedthatproducesanupw

arddeflectionofth

e

drillingmud.

ADDITIONALRECOMMENDATIONS

(See

detal.1984)


15/29

FACTORSAFFE

CTINGN-VALUES

N-valuesareincreasedinsandsandreducedincohesiv

esoils.

Dr

ivingofthesamplespoon

ab

ovethebottomofthe

ca

sing

SPTisonlypartiallymadeinoriginalsoil.Sludgemayb

e

trappedinthe

samplerandcompre

ssedasthesampler

is

driven,increasingtheblowcount(Thismayevenprevent

samplerecovery.)

Inadequatecleaningof

the

bo

rehole

Comments

Factors

Thewatertab

leintheboreholemu

stbeatleastequaltothe

piezometricle

velinthesand,otherwisethesandatthe

bottom

oftheboreholemaybetransformedintoaloosestateth

ereby

decreasingtheblowcounts

Fa

iluretomaintainsufficient

hy

drostaticheadinboring

IncorrectN-va

luesobtained.

No

tseatingthesampler

sp

oononundisturbed

material

NAV

FACDM7.1(1982)


16/29

FACTORSAFFE

CTINGN-VALUES

Higherblowc

ountsresultwhengra

velplugsthesample

r,

resistanceofloosesandcouldbehighlyoverestimated.

Sa

mplerpluggedbygra

vel

Blowcountsforthesamesoilusingthesamerigcanva

ry,

dependingon

whoisoperatingthe

rig,andperhapsthe

mood

ofoperatoran

dtimeofdrilling.

Attitudeofoperators

Comments

Factors

HighN-values

mayberecordedforloosesandwhensa

mpling

belowgroundwatertable.Hydrostaticpressurecancau

sesand

torisewithinthecasing.

Pluggedcasing

Higherblowc

ountsusuallyresultfromanoverdrivensampler.

Ov

erdrivesampler

NAV

FACDM7.1(1982)


17/29

FACTORSAFFE

CTINGN-VALUES

Usingmoreth

an1-1/2turnsofropearoundthedruman

dor

usingwirecablewillrestrictthefallofthedriveweight.

Freefallofthedrivewe

ight

isnotattained

Lowblowcou

ntmayresultfordensesandsinceoverwa

shing

loosenssand.

Ov

erwashingaheadof

ca

sing

Comments

Factors

Drillerfrequen

tlysuppliesdriveham

merswithweightsv

arying

fromthestandardbyasmuchas1

0lbs.

No

tusingcorrectweigh

t

Drillingtechnique(e.g.,casedholesvs.mudstabilizedh

oles)

mayresultindifferentN-valuesfor

thesamesoil.

Dr

illingmethod

NAV

FACDM7.1(1982)


18/29

FACTORSAFFE

CTINGN-VALUES

Ifthetipisdamagedandreducest

heopeningorincreasesthe

endareatheN-valuecanbeincrea

sed.

No

tusingagoodtipon

the

sa

mplingspoon

Impactenergyisreduced,increasingN-values.

Weightdoesnotstrikethe

drivecapconcentrically

Comments

Factors

Withheavierrodsmoreenergyisa

bsorbedbytherods

causing

anincreasein

theblowcount.

Us

eofdrillrodsheavier

thanstandard

IncorrectN-va

lueobtained.

No

tusingaguiderod

NAV

FACDM7.1(1982)


19/29

S

IGNIFICA

NTFACTO

RS

Hammerdropsystem

Anvilsize

Seatingo

fthesampler

Borehole

Cleaning

Insufficien

thydrostatichead

KulhawyandTrautmann

(1996)


20/29

C

ORRECTIONSTOM

EASURE

DN-VALU

ES

N1(60)=Nm

CNCECBCRCSCA

CBFCC

N1(60

)=measuredblowcountcorrectedto60%

ofthetheoretical

free-fallhamme

renergy,1tsfeffectiveoverburden

pressure,ando

therfactors;

Nm=

measuredblowcoun

tinthefield;

CN=

overburdencorrectio

nfactor;

CE=

energycorrectionfac

tor;

CB=

boreholediameterco

rrectionfactor;

CR=

rodlengthcorrection

factor;

CS=

samplingmethod(lin

er)correctionfactor;

CA=

anvilcorrection

CBF=

blowcountfrequencycorrectionfactor;a

nd

CC=

hammercushioncorrectionfactor


21/29

Manyof

thesefactorsare

notroutinelyapp

liedgeotechnical

siteinvestigationsinRhodeIsland.Asurv

eyofgeotechnical

engineer

ingfirmsintheareafoundthatco

rrectionsareapp

lied

mostlyfo

rtheanalysisof

liquefactionpotential.Inthesecases

N-values

arecorrectedforoverburdenstre

ssandhammer

energy.

5.

0

'

va

N

P

C

forCN

1.7

forCN>1.7,useCN=1.7

60

ER

CE

ER=en

ergyratio(typically60

forsafetyhammer,45fordonut

hammer,100forautomatic

hammer)


22/29

STAN

DARDPE

NETRATIO

NTEST

Relativelyquick

andsimpletoperform

Oneprocedure

Equipmentandexpertiseforthetest

iswidelyavailablein

theUnitedStates.

Providesarepre

sentativesoilsample

.

Providesusefulindexofrelativestren

gthandcompressibilityofthesoil.

Abletopenetrat

edenselayers,grave

l,andfill

Numerouscase

historiesofsoilliquefactionduringpastea

rthquakesareavailable

withSPTN-valu

es.Themethodbasedonthishistorycan

reflectactualsoil

behaviorduring

earthquakes,whichc

annotbesimulatedinthelaboratory.

TheSPTisaninsitutestthatreflects

soildensity,soilfabric,stressandstrain

historyeffects,a

ndhorizontaleffectiv

estress,allofwhich

areknowntoinfluence

theliquefactionresistancebutaredifficulttoobtainwithun

disturbedsamples.

Advantages


23/29

STAN

DARDPE

NETRATIO

NTEST

TheSPTdoesn

ottypicallyprovidecontinuousdata(e.g.5

ft.intervals),therefo

re

importantdatas

uchasweakseamsmaybemissed.

Limitedapplicab

ilitytocohesivesoils,gravels,cobblesbouldersEquipmentand

expertiseforthe

testiswidelyavailab

leintheUnitedState

s.

Somewhatslowerthanothersample

methodsduetosampleretrieval.

Inadditiontoov

erburdenpressurean

drelativedensitythe

SPTN-valueisalso

a

functionofsoiltype,particlesize,and

ageandstresshisto

ryofthedeposit

Duetoconsiderabledifferencesinap

paratusandprocedu

re,significantvariability

ofmeasuredpenetrationresistancec

anoccur.Thebasic

problemstoconsiderare

changeineffect

ivestressatthebotto

moftheborehole,dynamicenergyreaching

thesampler,samplerdesign,intervalofimpact,penetratio

nresistancecount.

SamplesthatareobtainedfromtheS

PTaredisturbed.

Disadvantag

es


24/29

CORR

ELATION

SBETWE

ENSPT

A

NDSOILPROPERT

IES

Relativ

eDensity

EffectiveStressFrictionAngle

UndrainedS

hearStrength

Some

correlationsre

quiretheraw

N-values

whereas

othersuseth

ecorrectedN1(60)values


25/29

45

20

0

50

80

VeryLoose

Loose

Compact

Dense

VeryDense

Degrees

Tsfor

kgf/c

m2

Blows/ft

Percent

Angleof

Internal

Friction

()

StaticC

one

Resistance

(qc)

Standard

Pen

etration

Res

istance

(N)

Relative

Density

Stateof

Packing

Meyerhoff(1956)

CORRE

LATIONS


26/29

Vertical

Effective

Stress

(ksf)

0

10

20

1 2 3 4 5 60

30

40

50

60

70

80

StandardPenetrationR

esistance,Nbl/ft

15

40

50

60

70

80

90

85

100

RelativeDensity

RelativeDen

sity

(NA

VFACDM7.21982)


27/29

10

203

040

50

60

70

80 4 0

28

303

2

34

36

38

40

42

44

46

Veryloose

Loose

Mediumdense

Dense

Verydense

Relativedensity

Angleofshearingresistance,

$

SPTN-value

EffectiveStre

ssFrictionAn

gle

CarterandBentley(1991)


28/29

>200

>4000

>30

Hard

100!200

2000!4000

15!30

VeryStiff

50!100

1000!2000

8!15

Stiff

25!50

500!1000

4-8

Medium

12!25

250!500

2!4

Soft

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