The present study investigates the behaviour of plug on pile load capacity and effect of plug removal. The sand used as a foundation soil is poorly graded clean sand. It was prepared at different densities using a raining technique. To simulate the pile load test in the field, a new apparatus was manufactured. A driving–pressing system for pile installation was manufactured. The soil plug is removed by a device manufactured to remove the soil column entrapped inside the pipe piles during installation by driving and pressing devices. The present study focuses on the determination of effect of soil plug on the ultimate compression capacity of single open-ended steel pipe pile, and makes a comparison with closed-ended pipe pile. A new type of pipe piles is suggested; it is closed–open-ended pipe piles driven and pressed into sandy soil of different densities (medium and dense) in which axial compression load tests were performed on model piles. The pile end will be open to a predetermined depth in order to m...

Bearing capacity of open-ended pipe piles with restricted soil plug

We investigate the effects of high solvated-methane concentration on methane-hydrate nucleation at 250 K and 500 atm. We consider solutions at four levels of methane molar fraction in the initial H2O–CH4 solution, χCH4 = 0.038, 0.044, 0.052, and 0.058, which are higher than (metastable) bulk supersaturation. χCH4 is controlled independently of the temperature and pressure thanks to the use of special simulation techniques [Phys. Chem. Chem. Phys. 2011, 13, 13177]. These conditions mimic a possible increase of local methane concentration beyond supersaturation induced, for example, by freeze concentration or thermal fluctuations. The nucleation mechanism and kinetics are investigated using the dynamical approach to nonequilibrium molecular dynamics. We demonstrate a hydrate-forming/-ordering process of solvated methane and water molecules in a manner consistent with both the “blob” hypothesis and “cage adsorption hypothesis”: the system initially forms an amorphous nucleus at high methane concentration, wh...

Mechanisms and Nucleation Rate of Methane Hydrate by Dynamical Nonequilibrium Molecular Dynamics

A comprehensive review and proposed architecture for offshore power system

First reported in the 1960s, offshore freshened groundwater (OFG) has now been documented in most continental margins around the world. In this review we compile a database documenting OFG occurrences and analyse it to establish the general characteristics and controlling factors. We also assess methods used to map and characterise OFG, identify major knowledge gaps and propose strategies to address them. OFG has a global volume of 1 million km3; it predominantly occurs within 55 km of the coast and down to a water depth of 100 m. OFG is mainly hosted within siliciclastic aquifers on passive margins and recharged by meteoric water during Pleistocene sea‐level lowstands. Key factors influencing OFG distribution are topography‐driven flow, salinisation via haline convection, permeability contrasts, and the continuity/connectivity of permeable and confining strata. Geochemical and stable isotope measurements of pore waters from boreholes have provided insights into OFG emplacement mechanisms, while recent advances in seismic reflection, electromagnetic surveys and mathematical models have improved our understanding of OFG geometry and controls. Key knowledge gaps, such as the extent and function of OFG, and the timing of their emplacement, can be addressed by the application of isotopic age tracers, joint inversion of electromagnetic and seismic reflection data, and development of three‐dimensional hydrological models. We show that such advances, combined with site‐specific modelling, are necessary to assess the potential use of OFG as an unconventional source of water and its role in sub‐seafloor geomicrobiology.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020RG000706

Offshore freshened groundwater in continental margins

Seafloor massive sulfides (SMSs) are formed as precipitation products from hot hydrothermal fluids as a result of mixing with cold seawater and are mostly found at depths between 1500 and 3600 m. These deposits are formed in tectonically active zones of oceans (midocean ridges and “back-arc” spreading systems) and are the result of the global heat transfer from the mantle in the oceanic crust. As these fluids mix with the cold surrounding seawater, metal sulfides in the water are precipitated on or in the nearby seabed. The appearance of the solid mineral occurs as cylindrical chimney structures: the so-called black and white smoker (caused mainly by the presence of iron, copper, zinc, and sulphur). Larger sulfide occurrences are mostly originated in several generations of hydrothermal cycles, and they form deposits that can range from several thousands to about million tons. SMS contains pyrite (iron), galena (lead), sphalerite (zinc), and chalcopyrite (copper). Deep-sea mining is concentrating now to exploit such deposits. So far, the only known commercial project is the one developed by Nautilus Minerals, which is based on a horizontal system. This paper describes a preliminary design of a novel cutting tool developed for a vertical mining approach. The vertical mining method is preferred when rough terrain is expected and the device is easy to relocate. Using an atmospheric and hyperbaric cutting model, the cutting energy for two selected SMS deposits has been estimated and validated with real onshore excavation sites performed with a cutting tool normally used for diaphragm wall installation (i.e., the trench cutter technology). Preliminary results suggest that the estimated cutting energy ${\bf E}_{\bf SP}$ is 2.9 times higher with respect to the measured one in atmospheric conditions. This could be because the model considers the worst case scenario, i.e., higher energy due to the maximum cutting forces assumed. This factor has been used to design a cutting tool which is able to work up 2000-m water depth to mine SMS deposits.

Preliminary Design of a Trench Cutter System for Deep-Sea Mining Applications Under Hyperbaric Conditions

Design of a novel drilled-and-grouted pile in sand for offshore oil&gas structures

This paper presents some recent technological developments in deep mixing for the offshore sector. Deep mixing methods comprise in-situ soil treatment technologies where binding materials are added and blended with the original soils in order to improve their mechanical properties. The MIxed Drilled Offshore Steel (MIDOS) pile is introduced in this paper, which takes advantage of such deep mixing technologies. The comparison between the API approach and CPT-based methods for the prediction of the pile capacity are provided to validate the capability of the MIDOS pile as a foundational element for oil&gas structures in different geological conditions. The theoretical calculations are intended for initial estimation of pile sizing only and are not intended as a detailed design method.Copyright © 2014 by ASME

Latest Technological Developments in Offshore Deep Mixing for Piled Oil and Gas Platforms

As of 30th June 2013, according to the European Wind Energy Association, there are 1,939 offshore wind turbines, with a combined capacity of 6,040 MW. They are fully grid connected in European waters in 58 wind farms across 10 countries. About 70 % of the foundations used for wind energy are monopiles with a diameter up to 6 m. The monopiles are installed by using hammers. However, there are situations where the piles cannot be installed without the “driving and drilling technique”, above all in the glacial areas, where glacial tills, boulders or cobbles can be encountered. A new technology for supporting the installation of monopiles is the monopile-trench cutter. The following paper describes four onshore trench cutter case histories in hard geology. Based on several projects, a correlation between net cut performance and uniaxial compressive strength (UCS) values of the in situ rock is briefly described. The variation of the cut performance decreases logarithmically with increasing UCS values. However, the data showed are only based on projects already performed, and it is not possible to extrapolate the data for future projects in similar geological conditions. The findings of this paper want to show how the trench cutter technology might be a suitable technology for supporting monopile installation in difficult sea beds. Besides, the information contained in this manuscript wants to be an aid for contractors involved in offshore pile installation.

Trench Cutter Case Histories and Their Possible Application for Offshore Piles as Relieve Drilling

A boring device for producing a bore with a casing tube has a linkage, a boring tool, which can be fixed to the lower end of the linkage, a mounting frame for mounting on the casing tube, a drive and a connecting device, which is used for producing a rotary connection between the casing tube and the mounting frame. The linkage is hollow and has a first and a second flushing line. In the vicinity of the upper end of the link-age are provided a first connection for the supply of a fluid to the first flushing line and a second connection for removing the borings via the second flushing line. A boring method introduced the casing tube into the soil prior to an excavation.

Leonhard Weixler

Papers

Preliminary Design of a Trench Cutter System for Deep-Sea Mining Applications Under Hyperbaric Conditions

Design of a novel drilled-and-grouted pile in sand for offshore oil&gas structures

Latest Technological Developments in Offshore Deep Mixing for Piled Oil and Gas Platforms

Trench Cutter Case Histories and Their Possible Application for Offshore Piles as Relieve Drilling

Boring device and boring method