UTEC’s Jim Edmunds explains how the company’s geoROV tool can assist with geotechnical surveys.
Geotechnical surveys are a prerequisite for establishing engineering soil parameters to enable robust and efficient seabed interaction design solutions – foundation design, on-bottom stability, excavation assessment, geohazard evaluation, etc. There are a number of methods in common use for acquiring the soils data including in situ test methods, such as cone penetration testing (CPT) and T-bar testing, as well as recovery of physical soil samples for subsequent logging and laboratory testing. Historically geotechnical surveys have been conducted using standalone seabed samplers and in situ test machines deployed on lift wires or using a geotechnical drilling system.
In 2010, UTEC Geomarine introduced a new ROV-deployed geotechnical survey tool, the geoROV CPT and Sampler. The geoROV system is a plug-and-play addition to a work-class ROV spread comprising a linear drive unit with control and real-time data acquisition. The system can be flown to the required location and works in water depths to 3000m, where it can be precisely positioned and in situ test data or soil samples acquired. Multiple in situ tests can be completed on a single dive; in excess of 50 tests have been completed in a single 12hr shift.The geoROV linear drive unit is capable of delivering around 15kN of thrust force, but in order to use this force without jacking the conveyance vehicle off the seabed, sufficient reaction force must be available. Some vehicles (such as trenching machines) are sufficiently heavy to provide the full reaction, but a free-flying ROV can typically only deliver up to 0.4kN reaction force using a combination of negative buoyancy and vectored down-thrust. An ROV-delivered 0.4kN is sufficient to penetrate up to 3m in loose sands or low to intermediate strength clays, but for deeper penetration in stronger soils, more reaction force is necessary.
In 2013, the geoREACT tool skid was introduced to increase the capabilities of the free-flying ROV deployment. The tool skid utilizes two suction cans to provide additional reaction force in suitable seabeds (i.e., most seabeds, except gravel or strong clay). The geoROV drive unit is mounted above the pair of suction cans and the chassis is attached to the underside of the ROV using a standard, four-point tool-skid connection.
The system is useful where conventional deployment may be technically challenging, hazardous, expensive, or impossible to undertake, and it is also gaining a reputation for efficient operation compared with conventional methods. Additionally, it is often convenient for a contractor to have the ability to recover high quality geotechnical data during their offshore campaign without dedicating the entire spread to the sole purpose of acquiring geotechnical data. The geoROV system can be installed and removed from an ROV in less than an hour, allowing for flexible mission planning in response to events and evolving requirements.
Since inception, the geoROV systems have been used in a wide and interesting range of projects including:
- Investigating thickness of sand cover above soft clay along a planned pipeline route (for design of the pipeline against down-heave buckling).
- Obtaining geotechnical parameters for foundation design in an area of gravel dump adjacent to existing subsea infrastructure – the test location could be positioned in between individual gravel pieces to ensure reliable data; several locations were adjacent to or beneath a live platform and all were adjacent to subsea structures in an area of gravel dump.
- Cable and pipeline route investigations mounted in a standalone frame.
- Mounted on a variety of jet trenching machines to benchmark trencher performance, to quantify unexpected trenching behaviour, or to enable real-time route and trenching programme development.
- ROV-deployed acquisition of data for design of foundations for subsea manifolds offshore Vietnam. ••ROV-deployed seabed investigation for a planned large gravity base platform on Australia’s northwest shelf; about 200 CPTs were conducted on tight grid spacing to verify the absence of localized pockets of soft material.
- As part of a multi-task campaign gathering data for the decommissioning of a large platform in the Central North Sea, geoROV CPT was used to conduct a series of 50 tests on the drill cuttings mound beneath a live platform. Due to operational constraints, the work had to be completed in a single 12hr window.
- As part of a multi-task ROV campaign in the Gulf of Mexico, geoROV was used to investigate newly appeared seabed anomalies and obtain engineering data (pipe-soil friction factors) for pipeline design.
- The first use of geoREACT was for a major development project West of Shetland in 2013; geoROV CPT and Sampler were used together with geoREACT to acquire around 200 CPTs, cyclic T-Bars, and push samples; an intensive program of advanced laboratory testing followed, enabling optimized design using cutting edge techniques of flowlines and subsea structures.
Further advances and innovations in the geoROV tool suite are planned in 2014, including a heavier duty linear drive unit, electric drive version, and ultra-deep water (6000m) capability.
Jim Edmunds has spent 20 years in the offshore geotechnical industry, four with UTEC Geomarine as technology director. Edmonds has also been heavily involved in developing new technological solutions for seabed investigations starting with miniature CPT equipment in the 1990’s, progressing to a deep water heave compensated drilling spread, and more recently ROV-deployed geotechnical drilling, sampling, and in situ testing systems. In 2010, Jim joined UTEC Geomarine to head up the development of new and innovative subsea technology and to build the integrated consulting and contracting business. He holds a B.Eng (Hons) Civil Engineering from Manchester University.