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For offshore wind development in Southern China, typhoon represents the extreme environmental loading condition to be considered in the design of the turbine structures. For the geotechnical design of the foundations, it is specified by the design code that the effect of cyclic loading on the soil strength and stiffness must be considered. This necessitates the complete time history of loads on the foundation experienced during a design typhoon. Idealised storm profiles with staged mean wind speeds and significant wave heights are commonly used as input to time-domain simulations to generate the foundation load history. However, no such design typhoon profile is provided in the Chinese design standard which creates considerable difficulty and uncertainty in the design process. In this paper, the methodology and the rationale that were applied to derive the design typhoon profiles for an offshore wind project in Guangdong province are presented. The wind and wave characteristics generated by typhoon are described in detail and the implications for the foundation design are discussed. To demonstrate application of the proposed typhoon profile, a case study for the ULS design of a suction bucket jacket is presented. • Design typhoon profiles are developed for an offshore wind farm in Southern China. • The typhoon wind and wave characteristics are described and implications for geotechnical foundation design are discussed. • The methodology and the rationale for developing the design typhoon profiles are presented. [ABSTRACT FROM AUTHOR]

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-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. [ABSTRACT FROM AUTHOR]

Abstract Large diameter monopiles are typical foundation solutions for offshore wind turbines. In design of the monopile foundations in sand, it is necessary to understand the drainage conditions of the foundation soil under the design loading conditions as the soil performance (strength and stiffness) is highly dependent on the drainage conditions. This paper presents a numerical investigation into this issue, with a purpose to develop a simple design criterion for assessing the soil drainage conditions around a monopile in sand. It is found that for typical monopile foundations in sand, the drainage condition during a single load cycle is generally expected to be undrained. However, the current state-of-practice uses p-y springs derived for drained soil responses for monopile design. The impact of this discrepancy on monopile foundation design was evaluated and found to be insignificant due to the relatively low level of loading as compared to the capacity of the soil. [ABSTRACT FROM AUTHOR]

The offshore wind industry in China has seen a rapid development in recent years and is projected to account for half of global yearly installed capacity in the years to come. Monopiles are a popular foundation solution for supporting offshore wind turbines. However, due to challenging seabed soil conditions, which often feature thick normally consolidated soft clays and harsh environmental loading (i.e. frequent occurrence of typhoons), extremely long monopiles are often designed. The large monopiles are costly to fabricate and install and sometimes kills the viability of the concept in cases where the bedrock is relatively shallow and expensive piling in rock is otherwise required. However, the state-of-practice for designing these monopiles in clays is typically by using the API p-y springs, which are widely known to underestimate soil-pile interaction stiffness and capacity for large diameter monopiles. Improvement to the design method can therefore have significant economic implications to the industry. The paper presents an effort toward this direction. A multi-spring beam-column model suitable for monopile design in soil conditions in China is proposed. The model features three soil spring components, namely the lateral p - y spring, the pile tip base shear s - y spring and rotational m - θ springs along the pile shaft. The validity of the model is verified by a comprehensive suite finite element parametric analyses. Guidance for incorporating the cyclic loading effect into design is also provided. The model proposed in this paper has large potentials for application in design practice. • Multi-spring beam-column model for monopile analysis in soft clays. • Captures lateral p-y, base shear s-y and side shear M-θ resistances. • All springs are fundamentally linked to stress-strain response of the soil. • Model demonstrates a clear improvement over the current design method. [ABSTRACT FROM AUTHOR]

Pile foundations supporting offshore structures, such as jacket platforms, are subjected to cyclic lateral loading. The capacity and deformation of these pile foundations under cyclic lateral loading are important and challenging design aspects. The purpose of this paper is to present verification of a framework for analysing the lateral pile response under cyclic loading in clay, based on fundamental soil behaviour measured in the laboratory at the element level. This framework can account for site-specific cyclic soil properties, summarized in classic contour diagrams, and the site-specific cyclic loading characteristics in design. This is a step-change improvement from current codes and standards recommendations which are based on a series of tests on a single pile at a single site (i.e. the Sabine River tests, Matlock 1962, 1970). The paper first provides a brief summary of the framework and outlines the important assumptions and calculation procedures. The paper then presents a comprehensive validation exercise of the framework through back-analyses of three sets of 1-g and centrifuge tests, covering different soil conditions (strength profile, OCR and plasticity) and loading sequences. This hindcast demonstrates the model's capabilities to capture the essential behaviours of pile foundations under cyclic lateral loading and its added value as a design tool, when compared with current practice. [ABSTRACT FROM AUTHOR]