ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen Outline of presentation Introduction A two-dimensional.

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen

Outline of presentation 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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Mitigation of groundvibration by double sheet-pile walls

Lars Andersen, Peter Frigaard & Anders Hust Augustesen

Department of Civil EngineeringAalborg University, Denmark

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen

Introduction

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IntroductionA two-dimensional numerical modelDouble sheet-pile walls in original soilOpen trench lined by sheet-pile wallsBarrier with aircushions and concrete lidConclusions

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen

Introduction

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Open or in-filled trench? Open trench is good in theory Sides will collapse Backfilled with another material

or stabilised, e.g. by sheet piles Mechanical / acoustic impedance

Definition: z = ρ / 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

IntroductionA two-dimensional numerical modelDouble sheet-pile walls in original soilOpen trench lined by sheet-pile wallsBarrier with aircushions and concrete lidConclusions

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen

A two-dimensional numerical model Coupled Finite Element–Boundary Element scheme in the frequency domain

Finite elements– (K + i C - ω² M) U(ω) = KFE(ω) U(ω) = F(ω)

– Sheet pile walls and foundation Boundary elements– H(ω) U(ω) = G(ω) P(ω)– Turned into macro finite elements– Used for soil (open domains)

Quadratic interpolation Response measured in dB:

Δ1 = 20 log10(U1 / V0)

Δ2 = 20 log10(U2 / V0)

V0 = U2(10 Hz) at loading point

Hysteretic material damping

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IntroductionA two-dimensional numerical modelDouble sheet-pile walls in original soilOpen trench lined by sheet-pile wallsBarrier with aircushions and concrete lidConclusions

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen

A two-dimensional numerical model

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IntroductionA two-dimensional numerical modelDouble sheet-pile walls in original soilOpen trench lined by sheet-pile wallsBarrier with aircushions and concrete lidConclusions

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen

Double sheet-pile walls in original soil 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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IntroductionA two-dimensional numerical modelDouble sheet-pile walls in original soilOpen trench lined by sheet-pile wallsBarrier with aircushions and concrete lidConclusions

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen

Open trench lined by sheet-pile walls 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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IntroductionA two-dimensional numerical modelDouble sheet-pile walls in original soilOpen trench lined by sheet-pile wallsBarrier with aircushions and concrete lidConclusions

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen

Barrier with aircushions and concrete lid 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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IntroductionA two-dimensional numerical modelDouble sheet-pile walls in original soilOpen trench lined by sheet-pile wallsBarrier with aircushions and concrete lidConclusions

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen 9

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

IntroductionA two-dimensional numerical modelDouble sheet-pile walls in original soilOpen trench lined by sheet-pile wallsBarrier with aircushions and concrete lidConclusions

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen

Thank you for your attention

Lars Andersen: [email protected]

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