Helical piles are commonly used onshore as foundation elements for several structures such as bridges, building and towers. The following research considers the use of helical piles as a novel foundation system for the offshore piled facilities. For the design of offshore structures (e.g. renewable energy or oil and gas platforms), the tension on a footing becomes the critical design condition. Among the advantages of helical piles, the high tension bearing capacity is one of the important ones. To investigate the optimum helix-to shaft ratio, the Blessington sand from Ireland has been used for these laboratory tests. CPT tests were performed to determine the consistency of the density for each filling of the sand box. The results suggest that the optimum pile design has a helix-to-shaft diameter (defined as wing ratio) between 1.5 and 2.0.@en

Sulfidic polymetallic ore deposits, known as seafloor massive sulfides (SMS) occur on the seabed as precipitation products from hot hydrothermal solutions as a result of mixing with cold seawater and are usually found at depths between 1,500 and 4,100 m. These deposits are formed basically in tectonically active spreading zones of oceans (mid-ocean ridges and "back-arc" spreading systems) and are the result of the global heat transfer from the mantle above the oceanic crust into the water column. In these SMS deposits, metals such as copper (Cu), zinc (Zn) and lead (Pb) as well as trace elements of silver (Ag), gold (Au) and rare antimony (Sb), cadmium (Cd), gallium (Ga), germanium (Ge), and indium (In) are present. This paper describes a novel technology for mining SMS deposits based on the vertical cutting approach developed by a joint research between BAUER Maschinen GmbH and Technip. A hyperbaric mathematical cutting model has been used to calculate the forces needed to excavate SMS deposits in water depth up to 2,000m. The model shows that in hyperbaric conditions, what influences the cutting energy is the water column rather than the geomechanical properties of the rock. Based on the mathematical model a preliminary cutting tool design is shown.@en

Driven piles are used to support the majority of offshore oil and gas structures with jacket structures supported by axially loaded piles still remaining the most common form of fixed offshore platform. Piles for conventional platforms are normally driven open-ended steel piles. This paper presents general considerations regarding the use of helical (or screw) piles as a novel foundation system for offshore structures. This type of pile has many advantages over driven piles, these include; ease of installation, the ability to remove using a reverse torque technique and cost savings due to much smaller installation vessel requirements. Other uses of helical piles are as support system for anchoring systems used for floating structures (e.g. tension leg platforms, SPARS, semi-submersible production platforms). To investigate their potential a joint research project was performed between BAUER Maschinen GmbH and University College Dublin (UCD). This project to date has involved small-scale laboratory tests, full-scale field tests and finite element modelling. This paper reports the results from finite element (FE) analyses that investigated the effects of the pile geometry, soil stiffness and soil friction angle on the compression and tension capacity of a helical pile in sand. In total, 48 models were created using Plaxis 3D. Axial tension and compression load tests were performed for piles with an embedment depth of 6m. In addition to the FE analyses, a series of laboratory model tests were performed in a large sample of sand at UCD. The primary purpose of these tests was to study the effect of installation method on the capacity of a helical pile. Wished-In-Place (WIP) piles (formed by placing the pile in the testing chamber prior to sample preparation), with helical helix-to-shaft ratios of 1.2 and 2.5 were load tested and their capacity was compared to the piles installed using the torque method. The results of the lab tests suggest that torque installation results in compaction of the sand around the pile. As a result the uplift capacity of the pile of the torque installed pile was much higher than the WIP pile. The wall thickness depending on the maximum applied torque and the permissible torsion stress of the steel is also briefly discussed.

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Whilst small diameter helical (or screw) piles are used extensively for near-shore and onshore projects, the potential to use these foundations in the offshore environment is receiving increasing attention. Potential advantages of helical piles over conventional foundation systems include their high capacity, ease of installation (avoiding pile driving), ease of removal and lowcost for mass deployment. In situ testswere performed in Germany with a drill rig Bauer BG42. A series of field tests, finite element analyses and laboratory tests on helical piles are being conducted as part of a joint research project between BAUER Maschinen GmbH and University College Dublin (UCD). This paper shows the in situ tests conducted under real conditions. Besides, the results of small scale 1 g laboratory tests on 1/10th scale piles which were performed in a large sand box at UCD are extensively described. A series of experiments were performed which investigated the effect of the ratio of helix (or helical plates) to shaft diameter, and helix diameter on the pull-out capacity of helical piles. The results suggest that the optimum pile design has a helix-to-shaft diameter (defined as wing ratio) between 1.5 and 2.0. Larger helical plates were significantly harder to install, whereas smaller helical plates provided little resistance to vertical loads.

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