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 1 Mitigation of groundvibration by double sheet-pile walls Lars Andersen, Peter Frigaard & Anders Hust Augustesen Department of Civil Engineering Aalborg University, Denmark

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen Introduction 2 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

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen Introduction 3  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 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

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) = K FE (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:  Δ 1 = 20 log 10 (U 1 / V 0 )  Δ 2 = 20 log 10 (U 2 / V 0 )  V 0 = U 2 (10 Hz) at loading point  Hysteretic material damping 4 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

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen A two-dimensional numerical model 5 MaterialYoung’s modulus, E (MPa) Poisson’s ratio, ν (-) Density, ρ (kg/m 3 ) Loss factor, η (-) Soil Steel200, Concrete20, 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

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) 6 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

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) 7 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

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) 8 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

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 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

ACE2008 ▪ Famagusta ▪ North Cyprus ▪ 15–17 September 2008 ▪ L. Andersen, P. Frigaard & A.H. Augustesen Thank you for your attention Lars Andersen: 10