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This paper presents a summary of the results of a detailed multidisciplinary study of the near surface geology of the Dogger Bank in the southern central North Sea, forming part of a site investigation for a major windfarm development undertaken by the Forewind consortium. It has revealed that the Dogger Bank is internally complex rather than comprising a simple "layer cake" of the Quaternary sediments as previously thought. Regional and high-resolution seismic surveys have enabled a revised stratigraphic framework to be established for the upper part of this sequence which comprises the Eem (oldest), Dogger Bank, Bolders Bank formations, Volans Member and Botney Cut Formation (youngest), overlain by a typically thin Holocene sequence. Detailed mapping of key horizons identified on the high-resolution seismic profiles has led to the recognition of a series of buried palaeo-landsystems which are characterised by a range of features including; glacial, glacifluvial and fluvial channels, a large-scale glacitectonic thrust-moraine complex with intervening ice-marginal basins, a lacustrine basin and marine ravinement surfaces. Interpretation of these buried landscapes has enabled the development of an environmental change model to explain the evolution of the Dogger Bank. This evolution was driven by the complex interplay between climate change, ice sheet dynamics and sea level change associated with the growth and subsequent demise of the British and Irish and Fennoscandian ice sheets during the Weichselian glaciation. Following the decay of these ice sheets the Dogger Bank entered a period of significant climatic and environmental 2 flux which saw a terrestrial landscape being progressively inundated as sea levels rose during the Holocene. Keywords-Dogger Bank; North Sea; stratigraphy; 2D seismic data; glacial and marine environmental change Highlights • Detailed multidisciplinary study of the Quaternary of the Dogger Bank, North Sea • A revised stratigraphic framework of the Dogger Bank has been established • A number of buried, terrestrial palaeo-landscapes have been identified • A model involving ice sheet dynamics, climate and sea level change is proposed

The successful installation of the Europipe 16/llE Riser jacket in July 1994 and the coming installation of Sleipner T jachzt in spring 1996 proves that suction installed skirted plate foundations (buckets), may not only be a competitive alternative to piles, but also a complementaryfoundation solution both for noncohesive and hesive soils. This paper presents the background for the d.exign analyses of the Europipe 16/llE and Sleipner T foundations in terms of the performed field and model tests, as welt as the theoretical models and practical analysis tools utilized for design. INTRODUCTION This paper is a joint presentation made by the designers of the Europipe 16/1lE jacket, Aker Engineering, and thedesigners of the Sleipner T jacket, Kvaerner Ed and wright. The active development of bucket foundations for steel jackets was initiated by Statoil's chief foundation engineer Tor Inge Tjelta and lead structural engineer Morten Baxheirn at the end of 1989. The successfid installations of the Veslefrikk jacket, the deep skirted concrete platform Gullfaks C and the suction installed tether References included at end of Part 1 and Part 2 anchors at Snorre played a vital part in this development. However, soil conditions for the two jackets in question are dominated by dense to very dense sands, while the previous skirted foundations were installed in soft to from clays. Two novel and important issues were identified as critical with respect to the design of the bucket foundation namely.Penetration of the skirts through the very dense sandTension capacity, particularly under cyclic loading To assist in the development of practical design tools, Statoil initiated field testing comp-rising penetration and capacity tests at the actual offshore sites in late 1992. These tests formed the basis for the Europipe platform bucket design which was completed in late 1993. At the end of 1993, a comprehensive model test program was initiated aimed specifically at improving the knowledge and understanding of tension load capacity and clic loading effects for inclusion in the Sleipner T bucket design. Also included in this program were a number of penetration tests for verification of the penetration analyses performed for the Europipe buckets. These tests have been filly utilized during detailed design of the Sleipner T platform. The design is now complete, and fabrication of the jacket is under way. In the following, the background and design of the Europipe 16/1lE and Sleipner T bucket foundations are presented separately. Key elements from field and model testing arc described and mechanisms of behaviour are presented. This experience is coupled with theoretical models and transformed into design tools for the prototype foundations designed for the Europipe 16/1lE and Sleipner T platforms. PART 1- EUROPIPE 16/llE Key design data Europipe 16/1lE is a riser platform for the Europipe transport system, situated in Block 16/11 in the Norwegian sector of the North Sea. Key parameters for the site and structure are water depth 71 m, topside weight 5000 and dry support structure weight 3800 t. A 3D view of the structure is presented in Fig. 1.1.

The integration of geophysical and geotechnical datasets acquired during a site survey for the Dogger Bank wind farm has enabled a new litho‐ and seismo‐stratigraphy to be established. Although previously believed to be a relatively simple “layer‐cake”, the data reveal that the sedimentary sequence within the foundation zone includes a complex series of buried landscapes with implications for both foundation siting and design. The most significant is a Weichselian glacially derived landscape dominated by a large thrust‐block moraine complex buried beneath a thin Holocene sequence. This glacial landscape profoundly affects the structure and physical properties of sediments within the foundation zone due to locally intense glaciotectonic deformation and the occurrence of sub‐aerially desiccated horizons recording fluctuating palaeo‐climatic conditions. Understanding these landscapes, coupled with the geophysical and geotechnical data, enables the development of a predictive “geo‐model” that may be used to target areas of uncertainty, reducing the requirement for boreholes (over Cone Penetration Tests) at every potential foundation location.

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