The local scour around offshore pile foundations often seriously affects the normal operation of offshore wind power. The most widely used numerical simulation method in the study of local scour is the Euler two-fluid model (TFM). However, the contact effect between sediment particles is neglected in this model. Thus, the momentum and energy transfer between sediment particles and the fluid is not realistically reflected, which limits its significance in revealing the mesoscopic mechanism of local scour. Therefore, the computational fluid dynamics-discrete element method (CFD-DEM) numerical model was applied in this study, which fully considers the contact between solid particles and momentum transfer between two phases. The model was first verified by experimental data of a local scour test under clear water scour. Then, the mechanism of local scour was further discussed from macro and micro perspectives. The results showed that CFD-DEM could be effectively used to study the local scour around a pile foundation. The local scour was comprehensively affected by flow velocity, gravity, fluid force, drag force, and interaction between particles, etc. Although the maximum average drag force happened in the area about 90° from the direction of incoming flow, the maximum scour depth always occurred at about 45°. Corresponding findings and conclusions can be used for future reference when designing and protecting the offshore wind power pile.

A complete and accurate method for determining the stresses and displacements of a lined arbitrary shaped tunnel excavated in orthogonal anisotropic rock mass is proposed. The method is based on an analytical method, the complex variable method, and the power series method. The basic equations can be obtained according to the stress boundary conditions along the inner boundary of the lining and the stress and displacement continuity conditions along the lining–rock interface. Based on the method, the tangential stresses along the excavation boundary, the inner and outer boundaries of the lining, and the normal and shear stresses along the lining–rock interface are given. Results show that, when the number of terms of the series is large enough, solutions with high accuracy can be obtained. The positions of the tangential stress concentration, the effect of the displacement release coefficient, and the angle of the rock layers on the tangential stresses along the excavation boundary and both boundaries of the lining are discussed.

The basic friction angle is a basic parameter for estimating the shear strength of rock discontinuities. The value of the basic friction angle can be determined using the tilt test. There are still no standard methods for such a test. Thus, the values from different researchers usually differ significantly for the same rock type. In this work, a number of tilt tests were conducted on core-based samples under different conditions. In this study, 33 different rock types and 53 groups of samples were collected, and more than 6,600 valid tilt tests were conducted. Based on the test results, some issues that may affect the value of the basic friction angle are discussed. This work may contribute to the present studies on the basic friction angle by tilt test.