Outline of presentation

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Outline of presentation
Mitigation of groundvibration by double
sheet-pile wallsLars Andersen, Peter Frigaard
Anders Hust AugustesenDepartment of Civil
Engineering Aalborg University, Denmark

• Introduction
• A two-dimensional numerical model
• Double sheet-pile walls in original soil
• Open trench lined by sheet-pile walls
• Barrier with aircushions and concrete lid
• Conclusions

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Introduction
Introduction A two-dimensional numerical
model Double sheet-pile walls in original
soil Open trench lined by sheet-pile
walls Barrier with aircushions and concrete
lid Conclusions
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Introduction
Introduction A two-dimensional numerical
model Double sheet-pile walls in original
soil Open trench lined by sheet-pile
walls Barrier with aircushions and concrete
lid Conclusions

• Open or in-filled trench?
• Open trench is good in theory
• Sides will collapse
• Backfilled with another materialor stabilised,
  e.g. by sheet piles
• Mechanical / acoustic impedance
• Definition z ? / c
• High for concrete and steel
• Very low for air and aircushions
• Not very low for water
• The efficiency also depends on
• The barrier depth
• The barrier width
• The barrier position

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A two-dimensional numerical model
Introduction A two-dimensional numerical
model Double sheet-pile walls in original
soil Open trench lined by sheet-pile
walls Barrier with aircushions and concrete
lid Conclusions

• Coupled Finite ElementBoundary Element scheme in
  the frequency domain
• Finite elements
• (K i C - ?² M) U(?) KFE(?) U(?) F(?)
• Sheet pile walls and foundation
• Boundary elements
• H(?) U(?) G(?) P(?)
• Turned into macro finite elements
• Used for soil (open domains)
• Quadratic interpolation
• Response measured in dB
• ?1 20 log10(U1 / V0)
• ?2 20 log10(U2 / V0)
• V0 U2(10 Hz) at loading point
• Hysteretic material damping

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A two-dimensional numerical model
Introduction A two-dimensional numerical
model Double sheet-pile walls in original
soil Open trench lined by sheet-pile
walls Barrier with aircushions and concrete
lid Conclusions
Material Youngs modulus, E (MPa) Poissons ratio, ? (-) Density, ?(kg/m3) Loss factor, ? (-)
Soil 200 0.25 2000 0.05
Steel 200,000 0.30 7850 0.01
Concrete 20,000 015 2500 0.03
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Double sheet-pile walls in original soil
Introduction A two-dimensional numerical
model Double sheet-pile walls in original
soil Open trench lined by sheet-pile
walls Barrier with aircushions and concrete
lid Conclusions

• Reduction at 20 Hz
• Horizontal 1 2 dB
• Vertical 2 4 dB
• Reduction at 40 Hz
• Horizontal 2 4 dB
• Vertical 4 8 dB
• Reduction at 60 Hz
• Horizontal 5 6 dB
• Vertical 8 16 dB
• Reduction at 80 Hz
• Horizontal 6 8 dB
• Vertical 9 18 dB
• Optimal distance 4 8 m(for all frequencies)

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Open trench lined by sheet-pile walls
Introduction A two-dimensional numerical
model Double sheet-pile walls in original
soil Open trench lined by sheet-pile
walls Barrier with aircushions and concrete
lid Conclusions

• Reduction at 20 Hz
• Horizontal 10 20 dB
• Vertical 10 20 dB
• Reduction at 40 Hz
• Horizontal 10 20 dB
• Vertical 20 40 dB
• Reduction at 60 Hz
• Horizontal 15 30 dB
• Vertical 20 40 dB
• Reduction at 80 Hz
• Horizontal 15 30 dB
• Vertical 20 40 dB
• Optimal distance 4 m(for all frequencies)

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Barrier with aircushions and concrete lid
Introduction A two-dimensional numerical
model Double sheet-pile walls in original
soil Open trench lined by sheet-pile
walls Barrier with aircushions and concrete
lid Conclusions

• Reduction at 20 Hz
• Horizontal 0 10 dB
• Vertical 5 10 dB
• Reduction at 40 Hz
• Horizontal 10 15 dB
• Vertical 15 20 dB
• Reduction at 60 Hz
• Horizontal 15 20 dB
• Vertical 20 25 dB
• Reduction at 80 Hz
• Horizontal 10 15 dB
• Vertical 15 20 dB
• Optimal distance 4 12 m(frequency dependent)

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Conclusions
Introduction A two-dimensional numerical
model Double sheet-pile walls in original
soil Open trench lined by sheet-pile
walls Barrier with aircushions and concrete
lid Conclusions

• A reduction of about 10 20 dB is achieved in
  the present case 1/3 1/10 of original
  response
• A low distance between the vibration source and
  the barrier provides better mitigation
• A barrier with aircushions and a concrete lid is
• better than a double sheet-pile wall in the
  original soil
• not as good as an open trench lined with
  sheet-pile walls
• The reduction in mitigation efficiency is
• similar with regard to horizontal and vertical
  vibrations
• small within the mid-frequency range 40 60 Hz

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Thank you for your attention

• Lars Andersen la_at_civil.aau.dk