Sediment penetration performance of a portable underwater robot for core sampling

As described in this paper, we investigate the sediment penetration performance of a portable underwater robot with a helical screw pipe using marine thrusters with limited force. First, we derive a mathematical model based on an empirical and simple method using the undrained shear strength of cohesive soil to provide a rough estimate of maximum penetration depths. Then, we perform numerical analysis for estimating the maximum depth of sediment penetration and for designing a sampling pipe. Additionally, we use experimentation to investigate the relation between the penetration depth of the helical screw pipe and the force of marine thrusters mounted on the portable underwater robot. After testing the penetration performance in a water tank, we conduct a field experiment at Lake Biwa and obtain results of the penetration depths. The maximum penetration into the lake sediment is at least 0.30 m. The results demonstrated the possibility of using the derived mathematical model to make a rough estimation of the maximum penetration depth for clay sediments. Additionally, we can use non-powerful thrusters equipped with small autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) for sediment sampling. The proposed method is also applicable for the installation of underwater sensors using small AUVs and ROVs.