Abstract

The recent 2011 Tohoku earthquake and tsunami served as a stark reminder of the destructive capabilities of multi-hazard events. Whilst Civil Engineers must design robust protective measures, their deployment over long stretches of coastline necessitates an economical and environmentally friendly design. The dual row retaining wall concept – which features two parallel sheet pile walls with a sand infill between them and tie rods connecting the wall heads – is potentially an efficient and resilient system in the face of both earthquake and tsunami loading. This research seminar will cover the centrifuge modelling and numerical analyses that were conducted to investigate the potential of the dual row wall systems. Studying the mechanics of the walls in dry sand from the soil stresses to the system displacements revealed the complex nature of the soil structure interaction. Recognising the dynamically varying vertical effective stresses promotes a purer understanding of the earth pressures mobilised around the walls and may encourage a move away from historically used dynamic earth pressure coefficients. In a similar vein, the proposed modified Winkler method can form the basis of an efficient preliminary design tool for practice with a reduced disconnect between the wall movements and mobilised soil stresses. When founded in liquefiable soil and subjected to harmonic base motion, the dual row walls were resilient to catastrophic collapse and only accrued deformation in a ratcheting fashion. The experiments and numerical simulations highlighted the importance of relative suction between the walls, shear-induced dilation and regained strength outside the walls, and partial drainage in the co-seismic period. The use of surrogate modelling to automatically optimise parameter selection for the advanced constitutive model was successfully explored. Ultimately, focussing on the mechanics of the dual row walls has helped further the academic and practical understanding of these complex but life-saving systems.