dynamic soil properties - cdn-edunex.itb.ac.id

SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Dedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Dedi Apriadi, Ph.D.

Faculty of Civil and Environmental Engineering

Institut Teknologi Bandung

Introduction of Soil Dynamics & Earthquake Engineering

Dynamic Soil Properties

Dynamic Soil Properties

• Shear Modulus, Gs or Vs and Damping

Ratio, D

• The properties depend on:

– Soil Type

– Confining Stress

– Void Ratio

– Strain Level


Linear Elasticity

• Linear (approximation): if the stiffness or

modulus is constant along increasing of stress


stiffness k

Non-linear Elasticity

• Non-Linear: if the stiffness or modulus is not

constant along increasing of stress (but function

of strain)

Nonlinearity


f

y

• Elastic: if the state of stress is a function of the

current state of deformation only (no permanent

strain is allowed)

Linear & Non Linear Elasticity

• Mechanical behavior is completely reversible

• Unloading follows the loading curve


Isotropic & Anisotropic Material

• Isotropic:

- If its mechanical properties are the

same in all geometric directions.

- Constitutive relationships for these

isotropic materials should be invariant

to transformations of the coordinate

system.


• Anisotropic:

If its mechanical properties are not the same in all

geometric directions.

Inherent or cross-anisotropic: due to depositional process of materials


Isotropic & Anisotropic Material


Linear Soil Stiffness

Linear Soil StiffnessDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Linear Soil Stiffness

Parameters relationships


Linear Soil StiffnessDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Non-Linear Soil StiffnessDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Non-Linear Soil Stiffness

Stiffness changes with increasing of shear stress

Gt


Monotonic loading


Stiffness changes with increasing of shear stress

Gs


Monotonic loading


Stiffness changes with

increasing of shear stress

Gs


Cyclic loading


Stiffness degradation curves

F’ =G/Gmax


Field testDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

• Allows the properties of the soil is measured

in their existing state condition such as stress,

chemical, thermal and structural conditions.

• Do not require sampling

• Some specific properties are not measured

directly but by theoretical analysis or

empirical correlations.

Field testDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

1. Low strain tests (shear strain below

0.001%): seismic geophysical surveys such

as seismic reflection or refraction, SASW,

seismic cross-hole, seismic down (up)-hole

2. High strain tests: SPT, CPT, Pressuremeter

test, S-CPT

Vs Field test


Vs => G

Crosshole TestingOscilloscope

PVC-cased Borehole

PVC-cased

Borehole

Downhole

Hammer

(Source) Velocity

Transducer

(Geophone

Receiver)

t

x

Shear Wave Velocity:

Vs = x/t

Test

Depth

ASTM D 4428

Pump

packer

Note: Verticality of casing

must be established by

slope inclinometers to correct

distances x with depth.

Slope

InclinometerSlopeInclinometer


Crosshole Testing


Crosshole TestingDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Vs Field TestDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Laboratory testsDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

1. Low strain tests (shear strain below

0.001%): Resonant Column Test, Bender

element test

2. High strain tests: Cyclic Triaxial Test, Cyclic

Simple Shear Test etc

3. Model tests: Shaking table, Centrifuge test

Resonant Column Test


Resonant Column TestDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Gmax or Vs Correlations: N-SPTDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Gmax or Vs Correlations: CPTDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa

Gmax or Vs Correlations: Other TestsDedi Apriadi – SI 4121 Pengantar Dinamika Tanah dan Rekayasa Gempa


Gmax or Vs Correlations: Other Tests

Factors Influencing G


Factors Influencing Damping Ratio



TUGAS 4

Suatu profil tanah

Rigid Rock

Soft NC Clay

= 22 kN/m3

Vs = 780 m/det

= 15 kN/m3

Su = 5 kN/m2

PI = 45

Vs = 110 m/det

Tentukan:

1. Nilai initial modulus geser Gmax atau G0 dan damping ratio 0 untuk setiap lapisan dengan

menggunakan

- Data Su

- Vs hasil pengukuran dengan SDH tes

Kurva variasi G/Gmax dan damping ratio untuk lapisan batuan dalam gambar di atas.

2. Frekuensi natural dari lapisan soft clay

0

0.2

0.4

0.6

0.8

1

1.2

0.0001 0.001 0.01 0.1 1

G/G

MA

X

STRAIN (%)

G/Gmax

0

1

2

3

4

5

0.0001 0.001 0.01 0.1 1

DA

MP

ING

(%

)

STRAIN (%)

Damping Ratio (%)30 m

References

Dedi Apriadi – SI 6121 Dinamika Tanah dan Rekayasa Gempa

1. Kramer, S.L., Geotechnical Earthquake Engineering, Prentice Hall, 1996,

Chapter 9.

2. Das, B.M., Principles of Soil Dynamics, CENGAGE Learning, 2011.

3. Stewart, J., Geotechnical Earthquake Engineering, UCLA, 2007.

4. Bozorgnia, Y., and Bertero, V.V., Earthquake Engineering, from

Seismology to Performance Based Engineering, CRC Press, 2007.

Thank you


dynamic soil properties - cdn-edunex.itb.ac.id

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