Univ Los Andes Bogota 2005

8/22/2019 Univ Los Andes Bogota 2005

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Bauhaus-Universitt Weimar / Germany

Seismic Site Investigations

for the Application in Geotechnical and

Earthquake Engineering

Dr.-Ing. Hans - Gottfried Schmidt

Bauhaus - University WeimarLaboratory of Soil Mechanics

Content:

Site investigations tasks

and goals

Site specifics in seismic

affected areas

Requirements of the design

Use of strain-dependent

parameters

Strain dependence and

Investigation methods

Use of the Seismic site

investigation methods

Seismic field tests

borehole and surfacemeasurements

Spectral analysis of surface

waves SASW

Inversion of surface wave

data

Examples


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Site investigations tasks and goals

Investigation of the variously varying soil structures

Characterization of the natural or reclaimed soildeposits with all uncertainties

+ geometryof soils strata and their spatial variability

+ groundwater conditions+ geostatic stresses and related stress histories

+ characteristics of hydraulic conductivity+ deformation and damping characteristics assessedin the strain range of interest (!)

+ drained and undrained monotonis and cyclic shearstrength for cohesionless and cohesive strata

+ liquefaction potential of the soil deposits

+ direkte Aufschlsse eingeschrnkt einsetzbar

+ ergnzende geophysikalische /seismische Messungen

mglich/notwendig (zerstrungsfrei)

Investigation of disturbances in site conditions: holes,

stones, waste deposits, parts of old buildings


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Site Investigations in seismic affected zones

Site investigations related to the Geotechnical Earthquake

Engineering (GEE) aspects

+ depth-dependent velocity- or stiffness profiles, generally for

small strains+ characteristics of the amplification and filter effects of the

sediment layers >>site dependent input motions+ statements to the dominant site frequencies

>> different during main and after shocks ?+ deformation / damping characteristics in a wide range of strains+ shear strength by various conditions+ assessment of the land slides, liquefactions

In GEE:

+ investigation of great affected areas

+ fast and effective investigations

+ use of geophysics to receive realistic soil

parameters, additionally with lab-tests

+ use of all these investigation methods with

consideration of the requirements of thedesign and the risk assessment


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Requirements of the design

Current development: Adjustment of the material parametersCurrent development: Adjustment of the material parameters

to the current strain level of the task of design (see Tatsuoka,to the current strain level of the task of design (see Tatsuoka,

Fahay, Mayne, Burland, Atkinson)Fahay, Mayne, Burland, Atkinson)

10-6 10-5 10-4 10-3 10-2 10-1

G

G0

Earthquakes

Foundations

M achines

Tunnels

Roads


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Use of the strain-dependent soil parameter in the Soil

Dynamics / Geotechnical Earthquake Engineering

Use of a visco-elasto-plastic constitutive law with a definition of one ormore yield surfaces and>> non linear - elastic computations within the yield surface

into a wide range of strains (Tatsuoka, Hamburg 1997)

large acceptance for practical computations in the Dynamics:

>> equivalent linear iteration cycles with the adjustment to thecurrent strain level

>> that means: Hypoelasticity - incremental linear

Hyperbolic law (u.a. Kondner) for the

mean curve (skeleton curve) and the

Masing-Rule for the Hysteretic slope

r

f


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Dynamics / Amplification Functions

In = Rock motion

Amplificationfunction

Out = Responseof the layer (top)

On the basis of the sufficient knowledge of theOn the basis of the sufficient knowledge of the

material parameters there is a good agreement ofmaterial parameters there is a good agreement of

the dominant site frequencies of various methods:the dominant site frequencies of various methods:

(1) amplification function(1) amplification function (matrix(matrix--reductionreduction--algorithm)algorithm)

(2) H/V(2) H/V technology (Nakamura)technology (Nakamura) (comparing of the(comparing of the

displacements at the ground surface)displacements at the ground surface)

(3) Dispersion curves of the surface waves(3) Dispersion curves of the surface waves

11

22

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Dynamics / Amplification Functions

GoodGood agreementagreement betweenbetween amplificationamplification

functionfunction (1) and H/(1) and H/VV--ratioratio (3)(3) byby usingusing

thethe samesame soilsoil parameterparameter

Change inChange in thethe frequenciesfrequencies and inand in thethe

sizesize ofofamplitudesamplitudes duedue toto thethe variationvariation ofof

thethe soilsoil stiffnessstiffness// velocitiesvelocities causedcaused byby

differentdifferent inducedinduced strainsstrains ((seesee 1 and 2)!1 and 2)!

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Soil Mechanics - Settlement control

and realistic soil parameters

Measurement of the strains in the soils (relativsettlements)beneath a foundation (Kriegel/Wiesner 1973); Burland 1989

MeasuredSettlements invarious depth z

(e.g. withExtensiometers)

Calculation of thestrains (relative

settlements):* in wide soil regionswe have local strainsunderneath 0,1%

* max. values areabout 0,3%

Reason for differencesof the observed andcalculated settlements

> the most soil deforma-tionen are in the rangelower than 0,1%

> there is a strict nonlinearsoil behaviour over awide range of strains

Consequence:

use of the strain

dependent soil stiffness

and improved

computional algorithm


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Use of strain-dependent Soil Parameters in Routine

Designs of the Soil Mechanics

Increasing tendency: Consideration of the pronounced non-linearity

within the range of small strains (-> WCSMFE 2001)

Goal realistic computations e.g for Settlements(Atkinson 2000, Mayne 2000)>> thatmeans non-linear - elastic computations with strain-dependent

parameters analogue to the Soil Dynamics

LinearLinear

computationcomputation

NonNon--linearlinearcomputationcomputation

FoundationFoundation settlementsettlement:: ComparisonComparison PredictionPrediction (non(non--linear)linear) -- MeasurementMeasurement

S

Qfs

BE=

0,3

0 ult

Qfs

BE 1 (Q /Q )=


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Mechanics / Geotechnical Engineering

Use in routine computations in the soil mechanicse.g. Settlement calculation after Berardi (Diss. 1992)

(Janbu)

(Settlement)

(Loads)

(SPT)Modul factor KE

strain 0,1%

Here arepossibe actualcurves ofmeasurements!

GoalGoal

::

reductionreduction

ofof

thethe

oftenoften

largelarge

differencesdifferences

betweenbetween

thethe

prognosisprognosis

andand

thethe

observationobservation ofofsettlementssettlements!!


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Strain-dependent soil parameter in the Soil Mechanics /

Soil Dynamics / Geotechnical Earthquake Engineering

Degradation ofDegradation ofthethe StiffnessStiffness:: forforstaticstatic loadingsloadings

dehnungsabhdehnungsabhngigngig

beanspruchungsabhbeanspruchungsabhngigngig

Proposals of the Degradation curves for the non-linear Soil Stiffness (after Fahay)

0 r

G 1

G 1=

Degradation ofDegradation ofthethe StiffnessStiffness::

forfordynamicdynamic loadingsloadings

((e.ge.g.. seesee Kramer:Kramer:

GeotechnicalGeotechnical EarthquakeEarthquake Engineering)Engineering)

g

0

G 1 f( )G max

=


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Strain-dependent soil parameter in the Soil Mechanics /

Soil Dynamics / Geotechnical Earthquake Engineering

G0

Static degradation

Dynamic degradation

10-6 10-1

failure

MainMain tasktask forforthatthat descriptionsdescriptions::

++ realisticrealistic maximummaximum valuevalue ofofstiffnessstiffness GmaxGmax ororGG00 forforveryvery smallsmall strainsstrains

++ Adjustment of the stiffness to the current stress / strain of thAdjustment of the stiffness to the current stress / strain of the soile soil

WhatWhat areare thethe possibilitiespossibilities ofofthethe sitesite investigationinvestigation and laband lab methodsmethods??

DifferentDifferent

curvescurves

forfor

differentdifferent loadload regimesregimes !!

There is not only theThere is not only the

one characteristicone characteristic

parameter for a soil.parameter for a soil.


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Geotechnical Site Investigation Methods

How much can material parameters be derivedHow much can material parameters be derived

from a number punch?from a number punch? ((MayneMayne 2001)2001)Is this procedure rational?Is this procedure rational?

What can we begin with seismicWhat can we begin with seismic

measurements?measurements?

Indirect explanations: ProbesDirect explanations (drillings) and samplings: disturbed / undisturbed ?


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Strain Dependence and Investigation Methods

ShearShearstrainstrain

SeismicSeismic boreholeboreholemethodsmethods

SeismicSeismic surfacesurface

methodsmethods

PossibilitiesPossibilities andand limitationslimitations of differentof different investigatioionsinvestigatioions methodsmethods

Advantages of Seismicmeasurements: clear

mechanical relations to othersoil parameters- Schubmodul G0=.vs

2

- Hooke-Modul E0=2(1+)..vs2

(Steifezahl Es=.vp2

- Querdehnzahl =(vp2-2vs

2)/2(vp2-vs

2)

- GeschwindigkeitsverhltnisvR/vs(0862+1,14)/(1+).


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Main focuses for this concept: + determination of the maximal value Go or Eo

+ degradation curve for the non-linear stiffness

Strain Dependence and Investigation Methods

0=0,001%

Main Problem: Conventional Lab- and Field tests cannot provide soil parameters in the demanded lowstrain range (e.g. Burland, Atkinson, Fahay, Tatsuoka)

Consequently we use in the present time

-> Seismic field tests in undisturbed conditions and in a very small strain range

(see 1: < 10-5 )

characteristicalvalue

We focus: In situ - soil parameter should be measured in situ


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TheoreticalTheoretical backgroundbackground:: wavewave propagationpropagation theorytheory in ain a layeredlayered halfspacehalfspace

Seismic Field Measurements

DifferentDifferent fieldfield measurementmeasurement methodsmethods::

++ BoreholeBorehole measurementsmeasurements:: directdirect measurementmeasurement ofofthethe wavewave velocitiesvelocities

++ MeasurementMeasurement ofofthethe groundground surfacesurface wavewave fieldfield withwith manymany differentdifferentevaluationevaluation methodsmethods:: noninstrusivenoninstrusive indirectindirect measurementmeasurement ofofthethe wavewave velocitiesvelocities

-- Reflexion andReflexion and RefractionRefraction ofofseismicseismic waveswaves -- onlyonly bodybody waveswaves areare usedused

-- DispersionDispersion MethodsMethods dominantdominant surfacesurface waveswaves areare usedused

DispersionDispersion thatthat meansmeans frequencyfrequency dependentdependent wavewave velocitiesvelocities!!

-- H/VH/V techniquetechnique:: measurementmeasurement ofofthethe groundground surfacesurface displacementsdisplacements

andand determinationdetermination ofofthethe dominantdominant sitesite frequencyfrequency

-- Geotomographie: 3DGeotomographie: 3D--detection ofdetection ofnearnearsurfacesurface disturbancesdisturbances

+ Dispersion+ Dispersion MethodsMethods::-- determinationdetermination ofofthethe experimentalexperimental dispersiondispersion curvescurves byby usingusing ofof

differentdifferent mathematicalmathematical correlationcorrelation andand convolutionconvolution// transformationtransformation

techniquestechniques

-- determinationdetermination ofofthethe depthdepth--dependentdependent velocityvelocity ororstiffnessstiffness profileprofile

withwith inversioninversion methodsmethods ((comparisoncomparison ofofthethe experimental andexperimental andtheoreticaltheoretical computedcomputed dispersiondispersion curvecurve))


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Seismic Field Measurements Borehole Methods

Crosshole-, Downhole-, Uphole-Methods

relatively simple, but complex measurements

+ importantly: Contact in the borehole > > balloons+ problem: suitable borehole excitation > > S-wave

further effective developments> Probes with geophones (SCPT)> Pressiometer with geophones

> dilatometers with geophone

CH DH

(Kalinski/Stokoe 2003)

DilatometerDilatometer


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Seismic Field Measurements Borehole Methods

Plot ofPlot ofthethe registeredregistered boreholeboreholetimetime historieshistories

ExcitationExcitation byby a horizontala horizontal

polarizedpolarized shearshearwavewave -- ever twoever two

measurements with oppositemeasurements with opposite

direction of the excitationdirection of the excitation

RunningRunning time oftime ofthethe SHSH--wavewave


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Ground Surface Wave Field Measurement (1)

SYSCOM / BARTEC

MR 2002 CE-variant

Geophone

Punctual measurements of time historiesPunctual measurements of time histories

from surface wave fieldsfrom surface wave fields

a)a) due to active sources (pulsator, hammer):due to active sources (pulsator, hammer):

usually smaller, linear arraysusually smaller, linear arrays

b)b) due to passive sources (Noise): twodue to passive sources (Noise): two--

dimensional arrays with larger receiverdimensional arrays with larger receiver

distances are possibledistances are possible

The measured time histories possess theThe measured time histories possess the

information of the continuous medium! Theinformation of the continuous medium! The

analysis of these recordings can take placeanalysis of these recordings can take place

with differently strong methods!with differently strong methods!

SledgeSledge

hammerhammer

-- sourcesource


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Direct wave

c

Reflexions / Refraction (only the propagation of P- and S- waves)

DetectionDetection ofofthethe diferentdiferent runningrunning

timestimes ofofthethe differentdifferent waveswaves typestypes

andand derivationderivation ofofthethe wavewavevelocitiesvelocities

Determination of HDetermination of the wave velocities

from the time distance - diagram

linearlinear arrayarray


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Rayleigh wave Dispersion Measurement (conventional)

linear array of the Geophones / different spacings /harmonic excitation with various frequencies and detectionof phase differences between e.g. 2 Geophones

PhasePhase velocityvelocity forforeacheach frequencyfrequency

c(fc(f) = Geophon) = Geophon spacingspacing/ Phase/ Phase differencedifference

ResultResult:: DispersionDispersion curvecurve :: cc--ff--curvecurve

vertical particle motion

layer 1

layer 2

half space low freq.high freq

WaveWave lengthlength andand influenceinfluence depthdepth

z

surface

(1/3 . ) RW,1 cRW(f1) or 0,92 cs

StiffnessStiffness profileprofile ofofthethe sitesite:: determineddetermined

velocities arevelocities are

arranged with thearranged with the

(0,3(0,3--0,5)0,5)-- wavelengthwavelength

over the depth!over the depth!

( )RW 1 RW,1 1 1 2 1c (f ) s/ t f s 2 f /= = =

( )RW,1 2 12 s/ =


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ExperimentalExperimental SurfaceSurface WaveWave FieldField Analysis (1)Analysis (1)

Measurement of wave field with few receivers and with a variable offset!

1. Phase1. Phase DifferenceDifference MethodMethod (linear(lineararrayarray)) -- SASWSASW

Determination ofDetermination ofthethe PhasePhase

differencesdifferences ororthethe PhasePhasevelocitiesvelocities withwith followingfollowing stepssteps

++ FourierFourier--TransformationTransformation fromfrom

thethe TD inTD in thethe FDFD

++ determinationdetermination ofofthethe CrossCross

correlationcorrelation spectrumspectrum ofoftwotwo

measuredmeasured signalssignals++ determinationdetermination of dieof die phasephase

differencedifference withwith ReRe-- andand ImIm--partpart

( ) ( )( )( )( )

ij

s 2 f

c f fa rc tan

ij f

=

Method well been suitable, if only one mode of theMethod well been suitable, if only one mode of the

surface waves, e.g. the fundamental mode issurface waves, e.g. the fundamental mode is

evaluatedevaluated -- >> an averaged dispersion curve resultsan averaged dispersion curve results

(if necessary from many branches)(if necessary from many branches)

Generally a surface wave field possesses severalGenerally a surface wave field possesses several

modes, i.e. at a measuring point several velocitiesmodes, i.e. at a measuring point several velocities

or several wave fields with different velocities existor several wave fields with different velocities exist

> >> > the detection of the higher modes isthe detection of the higher modes is

extremelyextremely importantimportant for the success offor the success ofseismic field investigations!seismic field investigations!

Fundamental modeFundamental mode

HigherHighermodesmodes

AveragedAveraged experimentalexperimental

dispersiondispersion curvecurve

In allIn all casescases:: thethe determinationdetermination ofofthethe dispersiondispersion characteristicscharacteristics ofofthethe sitesite!!

( ) ( ) ( )

( ) ( ) ( )

ij 1 2

ij 1 2

t g g t d

f G f G f

7

= +

=


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2.2. FrequencyFrequency -- WaveWave numbernumber-- Analysis (Analysis (fkfk -- Analysis)Analysis)

Transformation ofTransformation ofthethe measuredmeasured timetime historieshistories inin thethe FrequencyFrequency -- WaveWave

numbernumber DomainDomain withwith aa doubledouble FourierFourier TransformationTransformation -- techniquetechnique

The distances of the geophones affect the wave number ranges whiThe distances of the geophones affect the wave number ranges which can bech can be

detected and the spatial Aliasing effects; but the analysis is adetected and the spatial Aliasing effects; but the analysis is a durabledurable

procedure with a high resolution!procedure with a high resolution!

Improvement of the technology of evaluating of measured time historiesby consideration of the changes both over the time and the distance

DispersionDispersion analysisanalysis byby usingusing ofofseveralseveral receiversreceivers withwith discretediscrete

signalsignal samplingsampling andand processingprocessing inin thethe timetime-- andand spacespace--domaindomain

( ) ( )c / k =


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3. Wave3. Wave FieldField TransformationTransformation (Slant Stack Transformation)

( ) ( ), , ixS p P x px e d

= +

-> good method for the evaluation of the higher modes

-> slant stack - that means a linear time-shift and summing of the amplitudesover the outset axis (plane wave decomposition of a wave-field)

-> the mathematical operations: transformation of the wave field in the

p - - domain (a special mapping domain) by two independent lineartransformations: first a slant-stack or special Radon-transformationfollowed of a one-dimensional Fourier-transformation

( )P x,t inputdata

t px;linearmoveout;coordinate transformation

=

1.1. StepStep:: SlantSlant stackstack

p ray-parameter as a inverse of the horizontal phase velocity c

( ) ( )x

P x, px Summationin the p domainS p, + =

SlantSlant stackstack summationsummation

2.2. StepStep: 1D: 1D FourierFourierTransformation ofTransformation ofthethe SlantSlant StackStack SummationSummation

SlownessSlowness spectrumspectrum SS

n R n nc (f )/ f =


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4.4. ExampleExample forforanan evaluatedevaluated measurementmeasurement

Deposit of an old mining industry:Deposit of an old mining industry:

height 25height 25 -- 30 m30 m

dispersion analysis of the measureddispersion analysis of the measuredwave fieldwave field

(a) time history(a) time history

(b)(b) fkfk -- transformtransform

(c ) slant(c ) slant -- stackstack -- transformtransform

aa

bb

cc


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Theoretical Wave Field Analysis Matrix Methods

1) Thomson-Haskell-Algorithm

relative simple mathematical-physical model

simple numerical realisation

2) Method of the generalized Reflex ion-and Transmission coefficients

numerical stable

7

( ) ( ){ }

( ) ( )

1 1

,

,

z z z zjd

z z z zju

j j j j

j j jj

diag e e

diag e e

=

=

2 2pk k =

2 2sk k =

k c

=

0 0 0

0 0 0

0 0 0

0 0 0

z

z

z

z

e

e

e

e

=


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Inversion of Surface Wave Data

Basis ofBasis ofthethe InversionInversion MethodMethod -- thethe experimentalexperimental dispersiondispersion

curvescurves ofofthethe surfacesurface waveswaves inin thethe FDFD

InversionInversion TechniqueTechnique representsrepresents aa newnew qualityquality ofofthethe

Dispersion Analysis >> Inversion ofDispersion Analysis >> Inversion ofthethe measuredmeasured fieldfield datadata

Goal: Investigation ofGoal: Investigation ofdepthdepth--dependentdependent soilsoil stiffnessstiffness profilesprofiles

M

i ij j

j 1

f (d, m) d Gm 0

d G m=

= =

=

Nonlinear connection between the measuredNonlinear connection between the measured

discrete data d and the material properties mdiscrete data d and the material properties m

with the function Gwith the function G

Solution of the nonSolution of the non--linear Inversion problemlinear Inversion problem

e.g. Use of thee.g. Use of the gradient methodgradient method on basis of theon basis of the linearizationlinearization of aof a nonnon--linearlinear

problemproblem (Taylor(TaylorSeriesSeries expansionexpansion))

d,d,mm difference vectorsdifference vectorsThe number of the iterative cycles depends on the nonThe number of the iterative cycles depends on the non--linearity of the problem andlinearity of the problem and

on the quality of the Input stiffness profile of the siteon the quality of the Input stiffness profile of the site (obtimization problem)

Numerical stabilization of the inversion steps with the use of the weightedMarquardt-Levenberg-Algorithmus

DiscreteDiscrete inversioninversion problemproblem iterativeiterativegoodgood adjustmentadjustment ofofthethe modelmodel vectorvectormm

toto thethe datadata vectorvectordd

T 1 Tm (G WG I) G W d = +


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Overview of the Inversion ProcedureOverview of the Inversion Procedure

Theory

Iteration

InversionSite condition

(layers, soil parameters)

j

d

11j

du

j

ud

j

d

j

d

1j

du

j

u

j

du

j

du

T)R~

R(IT~

T~

R~

TRR~

+

=

+=

( ) 0R~R~Idet 1du0ud =( ) (0)EER

~ 1u

1

22

11

21

0

ud

=

N

du

N

du

N

d

N

d

RR~

TT~

=

=

Reflection and Transmission matrixmethod (Chen,Luco)

Experi-

ment


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Site investigationSite investigation -- Determination of a soil stiffness Profile (example)Determination of a soil stiffness Profile (example)

Deposit of an old mining industryDeposit of an old mining industry: height 25: height 25 -- 30 m30 m

Inversion of the surface wave dataInversion of the surface wave data Dispersion characteristicsDispersion characteristics

(a) Slant stack dispersion of the site together with theoretical(a) Slant stack dispersion of the site together with theoretical dispersiondispersion

curves of the determined soil profilecurves of the determined soil profile

(b) depth(b) depth--dependent velocity profile (shear wave velocity)dependent velocity profile (shear wave velocity)

aa bb

Documents

Univ Los Andes Bogota 2005