Increasingly, hydrocarbon discoveries in the North Sea are remote fields with limited reserves at high temperature and pressure. Reserves from these fields are often transported, in an untreated state, through highly insulated, small diameter, steel pipelines to existing infrastructure in the area.The installation and operation of such pipelines raises a number of issues which must be addressed at the design stage. Small diameter, insulated pipelines are usually very light, which can cause problems during installation and are often susceptible to rapid upheaval buckling on start-up or cyclic ratchetting during extended operation.A number of incidents of pipeline floatation and upheaval buckling have occurred in recent years in the North Sea 1,2 . The majority of incidents can be attributed to a lack of understanding of geotechnical conditions during installation and operation. The cost of remedial measures can be very significant.Coflexip Stena Offshore have sponsored a number of geotechnical research programmes since 1995 in an attempt to mitigate risk during pipeline installation and operation.Several breakthroughs have been made including the practical demonstration of pipeline flotation during backfilling; the validation of a mechanism for cyclic ratchetting in a full-scale laboratory experiment; confirmation that soft clay backfill can be effectively modeled as a frictional material when considering uplift resistance; and derivation of applicable axial friction factors for coated pipelines in sand.

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A buried pipeline can buckle upwards if there is not enough resistance to movement. Both the uplift resistance (the maximum force per unit length) and the mobilisaion distance (the distance the pipeline has move before the maximum force is reached) are important in design. Tests on pipes in several soils were carried out at 1 g at full scale and in a centrifuge at 10 g and 1/10 scale. A comparison shows that the measured uplift resistances are consistent with the conventional understanding of centrifuge tests, but that the measured mobilisation distances are not consistent with that understanding. Unscaled mobilisation distance in the centrifuge is roughly the same as at full scale. Mobilisation distance does not scale with particle size. This discrepancy is related to the formation of shear zones, and to theory and observations in other areas of the mechanics of brittle materials, among them ice, concrete and heavily overconsolidated clays. An idealised analytical model displays the same behaviour.

Cables and pipelines are buried in deepwater to provide thermal insulation, on-bottom stability and physical protection. In the soft soils associated with deepwater regions cable ploughs and ROV based jet trenchers are the tools of choice.The Offshore Engineering Division of the Coflexip Stena Offshore (CSO) Group and Perry Slingsby Systems have contributed significantly to the development of deepwater cable and pipeline burial systems. Significant resources continue to be allocated to geotechnical research programmes to support product developments. This paper discusses the key technical issues with respect to deepwater cable and pipeline burial. The state-of-the-art of geotechnical engineering and research, and it's application to new burial product developments, is also presented.

The Loma Prieta earthquake (ML=7.1) produced only minor damage to solid waste landfills located near the epicenter. Site personnel were interviewed using a questionnaire to determine Modified Mercalli Intensity customized for landfills. Questionnaire results showed maximum intensities of VII near the epicenter and VI on bay muds. Estimated Peak Horizontal Accelerations for these sites ranged from 0.10 to 0.45g. Earthquake acceleration and duration appear to be the most important factors for predicting the seismic behavior of solid waste landfills.