Seismic  Testing  –  Determination  of  Deformation  Parameters

K.  R.  Massarsch Geo  Risk  &  Vibration  AB,  Stockholm,  Sweden  

Overview •  Introduction •  Applications of seismic testing

o  Seismic field testing o Compaction control o Deep soil mixing monitoring

•  Small-strain shear modulus •  Static shear modulus from seismic tests

o  Strain-softening Effects

o Modulus Reduction •  Conclusions

Application  of  Seismic  Field  Testing

•  Acoustic emission monitoring (in rock and soil

•  Monitoring of construction activities which generate ground vibrations (pile driving, blasting, ground improvement, traffic etc.)

•  Control of foundation works by seismic methods (piling, ground improvement etc.)

•  Determination of dynamic and cyclic soil and rock properties

•  Determination of static soil and rock properties (modulus)

Reasons  for  Increased  Use •  Robustness of electronic systems for use at

construction sites (out of the office..) •  Sensitive and less expensive vibration sensors

(airbags, computers) •  Powerful data acquisition systems (storage

capacity, data handling) •  Data transmission from construction site

(Mobile phone, Internet) •  Powerful software for data analyses (music

industry) •  Computer programs for advanced analyses

Seismic  Field  Testing  Methods

•  Seismic refraction •  Surface waves (e.g. SASW, MASW) •  Cross-hole •  Down-hole o Seismic cone penetration testing

(SCPT) o Seismic dilatometer (SDMT)

•  Seismic tomography

Vibration  Emission  from  Vertically  Oscillating  Mass

Rayleigh  Wave

Compression  Wave

Shear  Wave

FEM  Simulation  by  Dr.  W.  Haupt,  Karlsruhe

Surface  Wave  Test

x

y

Identification  of  Particle  Motion  during  Surface  Wave  

Test x

y

Vertical

Horizontal

Vertical

Horizontal

Analyses  and  animation  by  Torben  Kirk  Wolf  

Seismic  Refraction  Test

SASW  Falling  Weight  Test

10 !

Falling  Weight  (1  ton,  1  m)

Geophone

Spectral  Analysis  of  Surface  Wave

 Seismic  Cross-­‐‑hole  Test

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Vibration  Source Vertical  or Horizontal Geophone

 Seismic  Down-­‐‑hole  Test

Evaluation  Methods

› First arrival › Peak to peak › Cross-over › Cross correlation

Testing  of  Mixed-­‐‑in  Place  Columns

Injection  of  dry  cement in  soft  clay

Mixing  tool

Determination  of  Soil  and  Column  Stiffness

Load  distribution  between  soil  and  columns depends  on  relative  stiffness

Dry  Mixed-­‐‑in-­‐‑Place  Column

Transducer

Source

Amplifier

Oscilloscope Trigger

Det går Det går

Connecting  Accelerometer

Insertion  of  Accelerometer  into  Measuring  Tube

Soft  Column

Accelerometer

Accelerometer

Seismic  Down-­‐‑hole  Test  in  Soil  Column

Seismic  Monitoring  of    Vibro-­‐‑compaction

Resonance  Compaction,  Map  Ta  Phut,  Thailand

Compaction  Control  by  Seismic  Test

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Seismic  Tomography

Seismic  Tomography

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Shear  Wave  Speed  before  and  after  Compaction

Compaction

Before  Compaction

Time,  hours

Shear  W

ave  Sp

eed,  m

/s

Determination  of  Small-­‐‑Strain  Soil  Modulus  from  

Seismic  Test

2max SG Cρ=

2max PM Cρ=

Small-Strain Shear Modulus from Shear Wave Speed

Confined Modulus from Compression Wave Speed

Modulus  ratio  for  different  values  of  Poisson’s  ratio   E = 2(1+ν )G M =

(1+ν )(1− 2ν )(1+ν )

E

Poisson’s  ratio,  ν  is  an  important  parameter  –   but  which  value  should  be  chosen?

Relationship  between    S-­‐‑wave  and  P-­‐‑wave  Speed    

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ν =cP2 − 2cS

2

2 cP2 − cS

2( )

Dry  Soils Water-­‐‑saturated  Soils

ν  is  Strain-­‐‑dependent!

28 From:  Wojciech  Sas,  Katarzyna  Gabryś,  Alojzy  Szymański  (2013)

Seismic  Testing

Poisson’s  Ratio,  ν  is  Strain-­‐‑dependent

•  At shear strain <10-3 %, Poisson’s ratio is approximately 0.15 – 0.20.

•  Do not rely on P- and S-wave speed for determination of ν.

•  Poisson’s ratio increases with increasing strain. •  When shear strain > 10-1 %, Poisson’s ratio is

approximately 0.3 – 0.5. •  Poisson’s ratio depends on drainage condition

(ν ≈ 0.5 at undrained loading).

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Shear  Modulus  Variation  with  Depth  and  Void  Ratio

Shear  Strain

Shear  S

tress

Effect  of  Strain  on  Soil  Modulus

Shear Stress

Deformation

Shear Modulus

Deformation

Shear  Modulus  Decrease  with  Shear  Strain

Clay

Sand Rm

= G

* / G

max

Shear Strain

Relativ

e  Stiffness.  G

/Gmax Modulus  Reduction  

Factor:   RM  =  G/Gmax

Effect  of  Shear  Strain  on  Shear  Modulus

Effect  of  Shear  Strain  on  Soil  Modulus

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0.50  %

Cohesive   Soils

Non-­‐‑cohesive  Soils

R M  =  G/G

max

0.1  % 0.25  %

Modulus  Reduction  Factor Mod

ulus  Red

uctio

n  Factor,  R

M

Modulus  Reduction  Factor,  RM  at  0.5  %  shear  strain

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RM = 0.0043 PI + 0.103

Effect  of  Degree  of  Saturation

RM = 0.0003 Sr + 0.1069

Effect  of  Void  Ratio RM = 0.11 e+ 0.063

DENSE VERY  DENSE COMPACT LOOSE

Effect  of  Strain  Rate •  Strain rate at seismic field test ≈ 0.0005 to

0.005 %/s. •  Strain rate at static triaxial (CU) test ≈

0.0003 %/s •  Resonant column tests (50 Hz) and

torsional shear tests (one week) give same shear modulus, Gmax

•  Strain rate at seismic tests comparable to static laboratory tests

•  Shear modulus not (strongly) affected by strain rate 40

Determination  of  Static  Modulus  from  Seismic  Test 1.  Determine Gmax from cS. 2.  Use effective (dry) density of material to

calculate Gmax?! 3.  Calculate small strain moduli, (Emax, Mmax)

using small-strain Poisson’s ratio, ν. 4.  Estimate static shear modulus, GS by

applying modulus reduction factor, RM. 5.  Calculate Emax, Mmax using large-strain

Poisson’s ratio, ν. 41

Static  Modulus  from  Seismic  Test

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GS = RM Gmax

0.5  %

Conclusions •  Seismic field and laboratory testing has

gained increasing use in geotechnical and earthquake engineering

•  Seismic field testing can reliably determine wave speed in soil and rock

•  Wave speed can be correlated to deformation modulus (rock or soil)

•  Small-strain shear modulus can be correlated to static shear modulus applying modulus degradation

•  Increasing potential for seismic methods in geotechnical and civil engineering, especially for field monitoring.

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