Browse Prior Art Database

Self-penetrating Spike Pile Foundation for GBS on Shallow Permafrost

IP.com Disclosure Number: IPCOM000240214D
Publication Date: 2015-Jan-13
Document File: 4 page(s) / 374K

Publishing Venue

The IP.com Prior Art Database

Abstract

Exploration drilling of shallow offshore Arctic prospects (in water depths less than about 100m) could be greatly facilitated through use of a mobile Arctic Gravity Based Structure (GBS) that can be repeatedly redeployed from one location to another. Such a GBS must be able to develop adequate base shear to resist ice loads when installed in the wide range of soil conditions that may be encountered on the Russian Arctic Shelf, including presence of shallow permafrost. Similar needs exist for potential Production GBS’s that must attain high base shear capacity to resist forces imparted by moving sea ice. The concept involves using the very high on-bottom weight of the GBS to plastically displace soft surficial soils (if present) and drive short spike piles into underlying permafrost or much firmer soils to gain adequate base shear capacity to resist ice loads anticipated during the exploration well drilling program. In this invention, short piles would be used in lieu of the customary skirts that are often installed on the bottom of the GBS base to improve coupling to the seafloor and base sliding resistance.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 49% of the total text.

Self-penetrating Spike Pile Foundation for Arctic Gravity Based Platform Located on Shallow Permafrost

Exploration drilling of shallow offshore Arctic prospects (in water depths less than about 100m) could be greatly facilitated through use of a mobile Arctic Gravity Based Structure (GBS) that can be repeatedly redeployed from one location to another.  Such a GBS must be able to develop adequate base shear to resist ice loads when installed in the wide range of soil conditions that may be encountered on the Russian Arctic Shelf, including presence of shallow permafrost.  Similar needs exist for potential Production GBS’s that must attain high base shear capacity to resist forces imparted by moving sea ice.  Issues with developing such a GBS concept include:

  • Permafrost - many areas are known to have shallow permafrost at 3-10m depth overlain by gouged and remolded soft soils, which makes it impractical to develop adequate base shear through frictional contact between the GBS and the seabed
  • Skirts - conventional GBS skirts cannot be expected to penetrate permafrost (issues with meeting refusal or skirt bending and structural failure).  In addition, skirts leave no pathway for soft surface sediments to be extruded from beneath the base.
  • Piles - short installation and drilling seasons make it impractical to spend the time required for driving of pin piles into the permafrost to achieve base shear capacity.  In fact, in the event of no open water, ice loads might skid the GBS during the pile installation process.  Access ports for piles coupled with the necessary cranes and pile driving equipment complicate structural design, add non-drilling payload and increase costs.  There is a good chance for piles to become wedged in slots following high lateral ice loading, which would hinder moving of the GBS from one site to another.
  • Suction caissons – caissons installed through slots or pre-installed via a template and latched into the GBS could be used to develop base shear.  This would be a good solution for soft over firmer soils, but in shallow water depths where the available head of water is limited, suction caissons cannot penetrate permafrost.

Description of the Concept

The concept involves using the very high on-bottom weight of the GBS to plastically displace soft surficial soils (if present) and drive short spike piles into underlying permafrost or much firmer soils to gain adequate base shear capacity to resist ice loads anticipated during the exploration well drilling program.  In this invention, short piles would be used in lieu of the customary skirts that are often installed on the bottom of the GBS base to improve coupling to the seafloor and base sliding resistance.  A conceptual schematic of the invention is shown in Figure 1. 

The piles would be penetrated into the seafloor soils using the high bearing pressures imparted on the pile tips by the weight of the GBS as it is achieves a ballasted condition.  Weak surficial ...