05.31: Experiments and fem‐simulations of local buckling of sand‐filled tubular piles

ABSTRACTThin‐walled large‐diameter tubular piles loaded in bending are susceptible to local buckling. Depending on the bending moment distribution over the length of the pile, this local buckling failure may occur in the part of the pile that is embedded in the soil. In large‐diameter piles, soil is also present at the inside of the pile. The soil mass inside and outside of the pile may influence the bending behaviour and local buckling behaviour of the piles.In case the internal soil plug consists of granular material and is sufficiently stiff and resistant, the soil influences the buckling shape and the critical stress and strain at which local buckling occurs.Experiments that were performed in 2012 on empty and fully sand‐filled tubes loaded in pure bending showed a significant effect of the sand‐fill. The experiments were verified with finite element analyses to better understand the occurring failure mechanisms in tube and soil and the effects of parameter variations.In 2014, new experiments were carried out in the port of Rotterdam on 914 mm diameter piles installed in the harbour bed. After installation, the embedded part the piles remained predominantly filled with soil, whereas the upper part was empty. Eight piles were installed and were loaded with a lateral force up to excessive yielding and local buckling failure. These experiments were analysed with FEM calculations. These analyses included effects of the soil plug and the soil around the pile.The outcomes of the FEM model calculations confirm the experimental findings of a change in buckling shape as a result of the presence of sand inside the pile. The experiments and finite element analyses show that there is an evident contribution of the inside sand with certain properties to the resistance to local buckling. For the piles that are not completely filled with sand but have a plug at a certain level, design rules for the effect of the sand plug were derived.