Dynamic Soil Properties

Soil Dynamics
4. Dynamic Soil Properties
Cristian Soriano Camelo1
1Federal University of Rio de Janeiro
Geotechnical Engineering
August 17ht, 2017
Cristian Soriano Camelo (UFRJ) Soil Dynamics August 17ht, 2017 1 / 44

Outline
1 Introduction
Dynamic Soil Properties
2 Measurement of Dynamic Soil Properties
Field tests, Laboratory tests
3 Stress-Strain behavior of Cyclically Loaded Soils
Equivalent linear model, Shear modulus, Damping ratio

Outline
1 Introduction

Introduction
Behavior of soils sub-
jected to dynamic loading
Governed by dy-
namic soil properties
The nature and distribution of
earthquake damage is strongly
inﬂuenced by the response
of soils to cyclic loading
Wave propagation eﬀects: low levels of strain are induced.
Stability of masses of soil: large strains are induced in the soil.

Outline
1 Introduction

Measurement of Dynamic Soil Properties
The selection of testing techniques for measurement of dynamic soil
properties requires careful consideration and understanding of the
specific problem at hand.
Low strain properties: Stiffness, Damping, Poisson ratio and
Density.
High-strain properties: Stiffness, Damping, Influence of rate and
number of cycles of loading and volume change characteristics.

Field Tests
Field tests allow the properties of the soil to be measured in situ.
Advantages: Do not require sampling, Measure the response of large
volumes of soil, Many field tests induce similar soil deformations to
those of the problem of interest.
Limitations: In many field tests, the specific soil property of interest
is not measured, but must be determined by theoretical analysis or
empirical correlation.

Low-Strain tests: operate at strain levels that are not large enough
to induce signiﬁcant nonlinear stress-strain behaviour of the soil,
typically at shear strains below about 0.001%.
Seismic geophysical tests: determination of dynamic soil properties by
the creation of stress waves (S,P) and the interpretation of their
behavior from measurements at one or more locations.

Seismic Reﬂection Test: measurement of wave propagation velocity
and thickness of superﬁcial layers.
Measuring the arrival time, wave velocity is obtained by the ratio
between the distance of travel (x) and the wave velocity (vp1):
td = x
vp1

Seismic Reflection Test: Part of that wave is reflected back toward
surface, and arrives at a time given by:
tr =
2
√
H2+(x/2)2
vp1
Therefore, the thickness of the layer (H) can be calculated as:
H = 1
2 t2
rv2
p1 − x2
Limitations:
- Seismic reflection test typically makes use of P waves (special careful must be
taken when groundwater is present due to possible overestimation of soil stiffness).
- It is rarely used for delineation of shallow soil layers.
- Seismic reflection tends to be 3-5 times more expensive than seismic refraction
(Briaud,2013).

Seismic Refraction Test: This test involves measurement of the
travel times of p- and/or s-waves from an impulse source to a linear
array of points along the ground surface at diﬀerent distances from the
source.

Seismic Refraction Test: The direct waves produce the ﬁrst wave
arrival at short source-receiver distances, but head waves (critically
refracted waves) arrive before the direct waves at distances greater
than the critical distance, xc.

Seismic Refraction Test: At any time the critically refracted wave
travels along the interface and refracts back into the upper layer.
The upper layer thickness can be calculated as:
H = xc
2
v2−v1
v2+v1

Seismic Refraction Test: A result of processing seismic refraction
data ( Grit, M. and Kanli, A., 2016 )

Seismic Cross-Hole Test: Two or more boreholes are used to
measure wave propagation velocities along horizontal paths. The test is
performed at various depths and a velocity proﬁle can be obtained.

Seismic Down-Hole Test: In the down-hole test, an impulse source
is located on the ground surface adjacent to the borehole. Within the
borehole a set of seismic receivers are deployed.

Seismic Down-Hole Test: Travel time from down-hole test in San
Francisco Bay Area (Schwarz and Musser, 1972).

High-Strain Tests: These tests are most commonly used to measure
high-strain characteristics such as soil strength, their results have also
been correlated to low-strain properties. For geotechnical earthquake
engineering problems:
Standard Penetration Test
Cone Penetration Test
Dilatometer and Pressuremeter Test

Seismic Piezocone Test: The main output of this test is shear wave
velocity and the small strain shear modulus Gmax.

Seismic Piezocone Test: Results of CPTU tests in Rio de Janeiro
soft clay- Sarapui test site ( Ortigao, 2007 )

Laboratory Tests: Usually performed on relatively small specimens
that are assumed to be representative of a larger body of soil.
Laboratory tests provide accurate measurements of soil properties
depending on the ability to replicate the initial conditions and loading
conditions of the problem of interest.
Low strain element tests: Resonant column, Bender element.
High strain element tests: Cyclic triaxial, Cyclic direct shear
Model tests:Shaking table, Centrifuge

Low strain element tests- Resonant column: Is the most
commonly used laboratory test for measuring the low-strain properties
of the soil. A cylinder of soil is subjected to cyclic torsion (controlled
harmonic or random noise loading).

Low strain element tests- Resonant column
Rotation amplitude vs. frequency of induced vibration, where, fn is the
fundamental frequency of the specimen in which occurs resonance ( Briaud, 2013 ) .

Low strain element tests- Resonant column: Example of test
results, Shear modulus vs. Shear strain, the strain that can be tested
with this test typically ranges from 10−6 to 10−3 ( Briaud, 2013 ).

Low strain element tests- Bender Element Test: Measurement
of shear wave velocity on laboratory specimens. A ceramic nickel ﬁlm
generates motion when driven by an oscillating electrical signal. The
bender element can act as source and receiver.

Low strain element tests- Bender Element Test: Orientation of
BE for S- and P- Wave velocity measurement

Low strain element tests- Bender Element Test: Example of BE
input and output signals, tip-to-tip distance between BE source and
receiver d=144.44 mm ( Kim, T .et al., 2015 ).

High-Strain-Element tests: Cyclic Triaxial Test: Measurement
of dynamic soil properties at high strain levels. The load is applied in
the radial and axial direction, therefore, the principal stresses are
always vertical and horizontal.

High-Strain-Element tests - Cyclic Triaxial Test: The cyclic
triaxial test can be performed under isotropically consolidated or
anisotropically consolidated conditions.

High-Strain-Element tests - Cyclic Direct Simple Shear Test:
A short cylindrical specimen is restrained against lateral expansion by
a rigid boundary and is applied a cyclic horizontal stress at the bottom
of the specimen.

High-Strain-Element tests - Cyclic Direct Simple Shear Test:
Conventional simple shear tests are limited to their inability to impose initial shear
stresses other than those corresponding to K0 conditions. Cyclic direct shear tests
on Trakya Sand under various normal stresses ( Cabalar, A .et al., 2013 )

High-Strain-Element tests - Cyclic Torsional Test: allows
isotropic or anisotropic initial stress conditions and can impose shear
stresses on horizontal planes with continuous rotation of principal
stress axes.

High-Strain-Element tests - Cyclic Torsional Test: Measurement
of stiﬀness and damping over a wide range of strain levels.
Comparison between Resonant Column (RC) and Cyclic Torsional Shear test (CTS)
results performed on medium and low plasticity silty-clayey soils
( Fedrizzi, P .et al., 2015 )

Model Tests - Shaking Table: Most shaking tables utilize a single
horizontal translation degree of freedom. Shaking tables of many sizes
have been used for geotechnical earthquake engineering.

Outline
1 Introduction

Stress-Strain behavior of Cyclically Loaded Soils
Equivalent Linear Model: Because some of the most used methods
of ground response analysis are based on the use of equivalent linear
properties, considerable attention has been given to the
characterization of Gsec(secant shear modulus) and ε (damping ratio).

Equivalent Linear Model
The inclination of the loop depends on the stiﬀness of the soil and the
tangent modulus (Gtan) varies during the loading process, therefore an
average value can be approximated by the secant shear modulus:
Gsec = τc
γc
, where τc and γc are the shear stress and shear strain
amplitudes.
The breadth of the hysteresis loop is related to the area, which as a
measure of energy dissipation and can be described by the damping
ratio:
ε = WD
4πWs
=
Aloop
2πGsecγ2
c
, where WD is the dissipated energy, WS the
maximum strain energy and Aloop is the area of the hysteresis loop.

Shear Modulus: The secant shear modulus varies with cyclic shear
strain amplitude. At low strain amplitudes, the secant modulus is high,
but it decreases as the strain increases.
The stress-shear strain tip points corresponding to diﬀerent hysteresis
loops conform the backbone curve.

Shear Modulus: The variation of the modulus ratio (G/Gmax) is
described by the modulus reduction curve.

Shear Modulus: Normalised modulus reduction curve at diﬀerent
ranges of shear strain ( modiﬁed after Atkinson and Salfors, 1991 ).

Maximum Shear Modulus, Gmax: The use of shear wave velocities
is the most reliable means of evaluating the in situ value of Gmax.
- Seismic geophysical tests are commonly used to evaluate Gmax:
Seismic Reﬂection, Seismic Refraction, Cross-Hole, Down-Hole, Seismic
Cone.
-Gmax can also be estimated from in situ test (SPT, DMT, CPT,
PMT) parameters by means of empirical correlations. However its use
should be limited to preliminary estimates of Gmax. Gmax is a small
strain parameter and in situ tests imply larger strains.

Damping Ratio: Experimental evidence shows that some energy is
dissipated even at very low strain levels, so the damping ratio is never
zero.
Schematic ﬁgure showing
the dynamic deformation
characteristics test and
data processing
( Kiku and Yoshida, 2000 ).

Damping Ratio: Damping behavior is inﬂuenced by plasticity
characteristics. Damping ratios of highly plastic soils are lower than
those of low plasticity soils at the same cyclic strain amplitude.
Variation of damping ratio of ﬁne grained soil with cyclic shear strain amplitude and
plasticity index (After Vucetic and Dobry, 1991).

For Further Reading I
Steven L. Kramer.
Geotechnical Earthquake Engineering.
Prentice Hall, 1996.
Briaud, J.L.
Geotechnical Engineering: Unsaturated and Saturated Soils.
WILEY, 2013.
Kiku H and Yoshida N (2000), Dynamic Deformation Property Tests at Large
Strains, 12th World Conference on Earthquake Engineering, Auckland, New
Zealand.
Ortigao A.R (2007), Wave propagation and microstrain behaviour of soils.
Research Report, Terratek, Rio de Janeiro - Brazil.
◮ SOIL DYNAMICS AND SEISMIC GEOTECHNICAL ENGINEERING. Prof.
George Gazetas. URL: http://www.issmge.org/media/recorded-webinars/soil-
dynamics-and-seismic-geotechnical-engineering
Link to ISSMGE Website

Dynamic Soil Properties

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