Introduction to liquefaction

Introduction to liquefaction

Introduction to liquefaction

Introduction to liquefaction

Introduction to liquefaction

Introduction to liquefaction

http://www.youtube.com/watch?v=_pWy1e6Q8k4&list=PL0E4806678ACDD325

http://www.youtube.com/watch?v=c9bQ1O5or_Q

http://www.youtube.com/watch?v=1KqlAMWMjOE

http://www.youtube.com/watch?v=DlhIHhadTqc

http://www.youtube.com/watch?v=rn3oAvmZY8k

Introduction to liquefaction

Introduction to liquefaction

Introduction to liquefaction

from Ishihara (1985)

Cyclic behaviour of sands:

Loose sand Dense sand

Introduction to liquefaction

from Ishihara (1985)

Cyclic behaviour of sands:

Loose sand Dense sand

Introduction to liquefaction

The void ratio at which sand does not change in volume when subjected

to shear is referred to as critical void ratio.

The critical void ratio is not a constant value, but changes with confining

pressure.

Introduction to liquefaction

Introduction to liquefaction

The critical void ratio concept cannot be used as a unique criterion for a

quantitative evaluation of the liquefaction potential.

The liquefaction potential depends on:

1. Relative density;

2. Confining pressure;

3. Peak pulsating stress;

4. Number of cycles of pulsating application;

5. Overconsolidation ratio;

6. Compositional characteristics (particle shape, size and gradation);

7. Depth of GWT.

Introduction to liquefaction

Well-graded soils are less susceptible to liquefaction than poorly graded

soils.

Soils with rounded particle shapes are more susceptible to liquefaction

than angular-grained soils.

Simplified procedure for the evaluation of initiation of liquefaction (i.e.

cyclic stress approach):

The earthquake induced loading, expressed in terms of cyclic shear

stress (CSR), is compared with the liquefaction resistance of the soil,

also expressed in terms of cyclic shear stress (CRR).

At locations where the loading exceeds the resistance liquefaction is

expected to occur, i.e.:

The cyclic shear stress (CSR) is a function of the maximum shear stress

tmax induced by the earthquake at the specific depth. This can be

predicted by a detailed ground response analysis or by the use of a

simplified approach.

Introduction to liquefaction

1 L

CRRF

CSR

The uniform cyclic shear stress amplitude induced by an earthquake can

be estimated using the simplified procedure proposed by Seed and

Idriss (1971):

where the stress reduction factor rd is given, for depths smaller than

20m, by (Idriss and Boulanger, 2004):

The equivalent number of uniform stress cycles increases with

increasing earthquake magnitude.

Introduction to liquefaction

max max

0 0 0

0.65 0.65t t

cyc vd

v v v

aCSR r

g

exp 1.012 1.126sin 5.133 0.106 0.118sin 5.14211.73 11.28

d

z zr M

Introduction to liquefaction

Soil liquefaction resistance (CRR) based on laboratory tests:

Introduction to liquefaction

Soil liquefaction resistance (CRR) based on in-situ tests:

Introduction to liquefaction

Soil liquefaction resistance (CRR) based on in-situ tests:

Introduction to liquefaction

Soil liquefaction resistance (CRR) based on in-situ tests:

Introduction to liquefaction

Evaluation of initiation of liquefaction – cyclic stress approach:

Introduction to liquefaction

Evaluation of initiation of liquefaction – cyclic stress approach:

Introduction to liquefaction

Pastor-Zienkiewicz Mark III model (1990)

Effective stress-based response analysis approach:

when incorporated into non-linear ground response analyses advanced

cyclic non-linear models allow computation of the generation,

redistribution and dissipation of pore pressures. The effective stress

conditions throughout the soil deposit can be monitored during and after

the earthquake to evaluate liquefaction hazards.

Introduction to liquefaction

Effective stress-based response analysis approach: