Subgrade Modulus -Ppp

7/24/2019 Subgrade Modulus -Ppp

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SUBGRADE MODULUS


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Content

1. Intoduction 2. Scope 3.Method of determination 4. Factor eecting k References


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Introduction

It is dened as the !contact" #earing pressure ofthe foundation against the soi$ that %i$$ produce aunit de&ection of the foundation.

Modu$us of su#grade reaction is the reaction

pressure sustained #' the soi$ samp$e under a rigidp$ate of standard diameter per unit sett$ementmeasured at a specied pressure or sett$ement

(he use of the parameter imp$ies a $inear e$astic

response) and therefore in design the pressuregenerated #' the su#grade modu$us is a$%a's$imited #' the a$$o%a#$e #earing pressure of thesoi$.


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In practice) the parameter is oftenrecommended #' the *eotechnica$+ngineer and used #' the Structura$

+ngineer for ana$'sis of the structure. (hestructura$ ana$'sis is not on$' used togain insight into the sett$ement of thestructure) #ut a$so pro,ides consideration

of sett$ement-induced stresses %ithin thestructure.


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IR species that the / ,a$ue #e measured at1.20 mm sett$ement.

(o ca$cu$ate the Modu$us of Su#grade Reaction)

Plate Bearing Test is conducted. In this a compressi,e stress is app$ied to the

soi$ pa,ement $a'er through rigid p$ates ofre$ati,e$' $arge sie and the de&ections are

measured for ,arious stress ,a$ues. (he eact $oad de&ection #eha,ior of the soi$

or the pa,ement $a'er in-situ for static $oads iso#tained #' the p$ate #earing test.


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Plate Bearing Test(IS 92141979)

Apparatus Bearing Plates: onsist of mi$d stee$ 0 cm

in diameter and .0 to 2.0 cm thickness and

fe% other p$ates of sma$$er diameters !usua$$' 5)

40) 3 and 22.0 cm" used as stieners. Loading Equipent: onsists of a reaction

frame and a h'drau$ic 6ack. (he reactionframe

ma' suita#$' #e $oaded to gi,e the needed

. reaction $oad on the

p$ate


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Settleent Measureent:(hree orfour

dia$ gauges ed on the peripher' of the

#earing p$ate. (he datum frame shou$d#e

supp$ied far from the $oading area.


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Procedure 7repare the test site and remo,e the $oose

materia$ so that 0 cm diameter p$ate restshorionta$$' in fu$$ contact %ith the soi$ su#-grade.

7$ace the p$ate accurate$' and then app$' aseating

$oad e8ui,a$ent to a pressure of . kg9cm2and

re$ease it after fe% seconds. (he sett$ement dia$ readings are ad6usted to ero

for ero $oad.


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Procedure !Contd"# : $oad is app$ied #' means of the 6ack) su;cient to

cause an a,erage sett$ement of a#out .20 mm.


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(he $oad is increased ti$$ the a,erage

sett$ement increased to a further amountof

a#out .20 mm and the $oad and thea,erage

sett$ement readings are noted as #efore.

(he procedure is repeated unti$ thesett$ement is a#out 1.0 mm.


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$actor e%ecting &'(

In this stud') eecti,e parameters onmodu$us of su#grade reaction in c$a'e'soi$s. (he studied parameters inc$ude=

1. Sie eect of foundation 2. +ect of foundation>s shape

3. +ect of depth of foundation

4. +ect of rigidit' of foundation


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(he Su#grade Modu$us is not a soi$ propert' #ut It isa function of the fo$$o%ing= 1. Soi$ e$astic properties= Modu$us of +$asticit') + )

and 7oissons Ratio) ? . 2. Foundation p$an dimensions= @ength) @) and


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Si)e e%ect o* *oundation on +s

(he (eraghi>s e8uation for estimatingthe modu$us of su#grade reaction %ithp$ate $oad test resu$ts is=

/s is su#grade reaction modu$us for

protot'pe foundation) /s1 is su#gradereaction modu$us #ased on p$ate $oadtest resu$ts and A is the side dimension offoundation.


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Decreasing o* +s-it. side

diension o* *oundation


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Consistenc/ e%ect o* cla/e/ soilon +s0alues


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Modi1cation coe2cient


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E%ect o* *oundations( s.ape on+s


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(eraghis e8uation) for estimating themodu$us of su#grade reaction ofrectangu$ar foundation #ased on p$ate

$oad test resu$ts) is=

m is the side dimensions ratio of rectang$efoundation !A9@".


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E3edent dept. e%ect o**oundation on +s

the #est t for corre$ation #et%eenmodu$us of su#grade reaction in surface!/s" and in depth !/sd"

%here) 8is $oad intensit' in surface !k

m-2") D is depth in meter and G is the unit%eight of the soi$ in !k m-3".


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Rigidit/ e%ect o* *oundation on+s


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RE$ERE4CE

IS code H214- 1HH Su#grade Modu$us Re,isited

Dec, 2014 By George Aristorenas, Ph.D.,

P.E. and Jess Ge!, P.E., D.GE "nArticles, #tr$ct$ral Design.

Subgrade Modulus -Ppp

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