Response of bioinspired scale arrangement in a suction caisson to penetrating into clay reflected by using interface direct shear tests

The suction caisson has been used to support the offshore wind turbine in last decade. Normally, the resistance of the traditional suction caisson (TSC) to penetrating into the seabed is overcome by suction resulting in high soil plug causing early termination in installation. Therefore, this study proposes a novel scaled suction caisson (SSC) that adopts the bionic design concept of little forward resistance and large backward resistance in scaled belly of reptiles like snakes. The bioinspired scale is set on the outer sidewall of the TSC, which is called the SSC. Scale arrangement is the key factor to reduce penetration resistance of the SSC. To simulate the penetration, the interfacial direct shear tests are carried out along the cranial direction (i.e., forward direction of the snake). The interfacial behavior of the scaled steel plate and clay is studied under different consolidation pressures and normal stresses. The results show that normal stress is the key factor compared with the consolidation pressure. There are clay-scale shear zone and clay-clay shear zone during shearing with the increase of the scale height, respectively. In addition, the theoretical formula for calculating critical shear stress is proposed, and the calculated results are in great agreement with the model test. As the scale height increases from 0.5 mm to 1.5 mm, the peak shear stress first increases and then decreases. Meanwhile, it is determined that the design of the scale height in the clay cannot exceed 108 d₅₀. Finally, the optimal geometric characteristics and scale arrangements of the SSC are determined by analyzing the peak shear stress and peak internal friction angle of various scale-clay interfaces. The results can contribute to optimizing the scales arrangement for easy penetration of the SSC in clay.