Mitigation of ground vibration from pile driving by circular arrays of rigid blocks placed on the ground surface

Ground vibration associated with pile driving causes annoyance to inhabitants of the neighbouring environment and may possibly lead to damage on existing structures in the proximity of a construction site. Vibration mitigation near the source can reduce the problem. The paper investigates the effect of circular arrays of blocks, placed on the ground surface around the position at which the pile is driven. A semi-analytical model of a layered soil has been used for the analysis, and the blocks have been modelled as monolithic structures, accounting for the full structure-soil-structure interaction. Two different sites have been studied: a layered soil with three metres of soft sand over a half-space of till, and a five metres deep layer of soft clay overlying a half-space of lime. The block arrays consist of one to three concentric rings with radii 4, 8, and 12 m, respectively. The rings contain 6, 12, and 24 blocks, respectively, and the size of the blocks have been scaled such that each ring has the same total mass. The pile has not been modelled explicitly; instead vertical excitation has been applied in different depts over a circular area corresponding to the cross section of a pile. For the considered cases it has been found that an array of blocks, shaped as a "Stonehenge ", may provide significant mitigation of the ground vibration level in a receiver zone placed 20-40 m from the pile. When a load is applied within the soft tops oil layer, the array provides an insertion loss in the order of 5-20 dB, depending on the size of the blocks and the configuration of the arrays. For loads applied deeper in the soil, within the stiffer half-space, the insertion loss is small and may in some situations be negative. However, this must be seen in the context that the transfer mobility in the reference state without the blocks, i.e. the greenfield, is low when the load is applied within the stiff half-space.