Table 7.24.

Nearshore jack-up barge with in situ testing, sampling and coring

Offshore site investigationMethodApplicationsLimitations
Graphic
  • Cable percussion, vibrocore, sonic-core, direct-push CPT or rotary open-hole drilling or coring systems from multi-legged jack-up barge (JUB);

  • Range of barge sizes to deal with sea state and water depths;

  • Towed into place by tug, some barges navigable under own power;

  • Barge will raise legs to jack-up to create static working platform above sea level.

  • Nearshore sites, typically <25 m water depth;

  • Supports a range of drilling techniques allowing a high degree of adaptability for sampling and testing glacial deposits;

  • High-quality sample recovery and preparation for testing in onshore laboratories;

  • ‘Walking’ JUBs offer beach zone access;

  • Allows downhole geophysical logging of boreholes.

  • Limited to nearshore water depths;

  • Small- to medium-sized barges do not provide crew facilities, requiring regular crew changes and ‘weathered down’ risk;

  • Drilling rates typical of onshore investigations in glacial deposits, with associated risks;

  • Additional time for movement between locations and for jacking up. May be delayed by weather, sea state and tide.

Cost factor: high in relation to typical onshore costs. Cost will depend on access requirements, wave/tidal conditions and the size of vessel required to deal with these.
Relevance to glacial/periglacial depositsThis is the principal option for main/detailed phase investigations in the nearshore environment with initial phases or seabed surface sampling sometimes undertaken from small inshore craft. The stability of the JUB may sometimes offer preferable rotary coring capabilities over drill-ships within the shared zones of operation dictated by water depth. Capability for cable percussion drilling allows potential for better recover in some glacial deposits that rotary coring alone cannot deliver. Capability of direct-push CPT likely to allow significantly greater penetration over seabed CPT systems in glacial deposits.