The purpose of this paper is to present a new algorithm for coupling discrete-element and finite-difference methods for three-dimensional problems. The finite-difference method (FDM) and the discrete-element method (DEM) are commonly used in geotechnical engineering. However, the continuous characteristics and the computational cost are the main obstacles to accurate and efficient simulation of practical problems for these individual methods. Coupling is thought to be an effective and promising way to combine the advantages and overcome the inability of these two methods. In this paper, an algorithm for coupling of DEM and FDM is presented. A two-stage searching method—namely, global domain searching and local domain searching—is proposed for detecting contact on the interface. A calculation method for force transmitting is presented. Conventional soil element tests were simulated to verify the validity of the proposed coupled algorithm by checking the constitutive behaviors, deformation compatibility, and transmission of normal and shear contact force.

Pile foundations supporting offshore structures, such as jacket platforms and wind turbines, are subjected to cyclic lateral loading. The capacity and deformation of these pile foundations under cyclic lateral loading are important and challenging design aspects. This paper presents the results of a series of four lateral load pile tests in an overconsolidated clay at the Haga site and their back-analysis using a $p\text{-}y$ framework based on fundamental soil behavior measured in the laboratory at the element level. This framework can account for site-specific cyclic soil properties, summarized in classic contour diagrams, and site-specific cyclic loading characteristics in design. The paper first provides a summary of the framework and outlines the important assumptions and calculation procedures. It then presents a detailed description of the test setup and soil conditions. The pile load test results and the back-analysis are subsequently presented. Generally, a good match between the test results and the model predictions was observed, demonstrating the model’s capability to capture the essential behavior of pile foundations under monotonic and cyclic lateral loading.