LAUSR

Abstract Driven timber displacement piles are being increasingly used to densify and reinforce soils against earthquake-induced ground deformations. However, the role of timber piles to reinforce the soils and redistribute cyclic stresses to timber piles has not been established, despite their excellent flexural properties. This study presents a series of dynamic 3D, linear-elastic, numerical simulations set with the unit cell framework to evaluate the role of the tapered timber pile and design variables such as pile length, spacing and relative density on the amplification and stress redistribution possible with this ground improvement technique. The simulations indicate that the depth-dependent shear strain and shear stress redistribution variously depend on the pile length, spacing, relative density, and input motion frequency. Further, the previously-accepted shear strain compatibility assumption developed for stone columns served to greatly overestimate the magnitude in cyclic shear stress reduction. Due to the tapered pile geometry and the depth-varying soil properties implemented, the accuracy of a recently proposed approach to estimate shear stress redistribution to account for column flexure was found to depend on the flexibility of the composite soil-pile system: longer, more flexible piles and lower relative density were predicted more accurately than shorter, stiffer timber piles with higher relative density. In general, the average shear strain ratio between the improved and unimproved soil is most sensitive to pile length, moderately sensitive to relative density, and least sensitive to pile spacing, and the average ratio of shear stress reduction coefficients is most sensitive to pile spacing, moderately sensitive to pile length, and is least sensitive to relative density.