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Outline of presentation. Mitigation of groundvibration by double sheet-pile walls Lars Andersen , Peter Frigaard & Anders Hust Augustesen Department of Civil Engineering Aalborg University, Denmark. Introduction A two-dimensional numerical model Double sheet-pile walls in original soil
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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
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 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 Introduction • 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 = 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
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 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
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 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 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)
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 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)
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 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)
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 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
Thank you for your attention Lars Andersen: la@civil.aau.dk
