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EQUIVALENTNUMBER&MITIGATELIQUIFACTION

Disusun Oleh:

DAMRIZAL DAMOERIN

Referensi:

. , ,, ,Co., Inc., 1984

2. Prakash, Soil Dynamics, McGraw Hill, 1981.

3. Nayak, N. V., Foundation Design Manual, Dhanpat Rai & Sons,Publishers, Delhi, 1982.

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9/38

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10/38

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11/38

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12/38

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Valera and Donovan (1977) stated that the methods of evaluation of liquefaction potential can be classified into categories:

(1). Methods where both the cyclic shear stresses induced within a soil deposit and the signifi cant number of stresses cycles and their

distribution with time are computed using simplified procedures

(2). Methods where the cyclic sresses induced within a soil deposit are computed by means of ground response analysis.

(3). Empirical methods based on field performance data.

Methods (1):

The maximum shear stress at a depth h:

max = m x a max = [( x h ) / (g)] x (amax)

max : maximum shear stress

: unit weight of soil

h : depth below ground surface

g : acceleration due to gravity

a max : maximum ground surface acceleration

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max : maximum shear stress

: unit weight of soil

h : depth below ground surfaceg : acceleration due to gravity

a max : maximum ground surface acceleration

The soil column is not a rigid body:

max(modified) = x x g x a maxCd : st ress reduction factor

( 1.0: at the ground surface; 0.5: at about 100 ft below ground surface )

It has been shown that the maximum shear stress determined from the shear stress-time history during an earthquake can be converted into an

equivalent number of significant stress cycles.

According to Seed and Idriss (191):

` av = 0.65 x max(modified) = 0.65 x Cd x [( x h ) / (g)] x (amax)

The 0.65 factor assumes that the equivalent uniform shear stresses,

av , is 65 % of the absolute maximum earthquake induced shear stress.

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2

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2

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2

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2

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2

Ug=excess pore waterpressure generatedby cyclic shear

stress

Tv=initialconsolidationpressure

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2

(a): Ns/Ni=1

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2

(b): Ns/Ni =2

: Ns/Ni =3

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2

(d): Ns/Ni =4

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2

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2

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3

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3

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3

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3

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3

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3

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3

Relative Density Dr vs. SPT N

(Holtz and Gibbs, 1957)

Relative Density and Frict ionAngle of Sand vs. SPT N

Nvalue Density D (%) (blows/ft) description

0to44to10

10to3030to50

>50

VerylooseLoose

Medium

Dense

Verydense

0to1515to3535to6565to85

85to100

41

(Terzaghi and Peck, 1967)

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3

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