Geotechnical Engineering

Site Optimisation

Calcareous sediments are renowned for their variability.  Within any proposed development site there can be a wide diversity of surficial sediments.  These can range from hard cemented relict reefs to thick layers of liquefiable uncemented muds.  AG has the experience required to optimise a platform location with an appreciation of foundation options, and corresponding design drivers.

Carbonate Soils

Over the years, AG has specialised in the understanding of calcareous sediments, which are arguably the most variable marine sediments encountered in modern offshore developments, and are notorious for presenting geotechnical challenges.  To mitigate the risks that these challenges pose, AG has the best-informed personnel with the longest track-record available to offer advice on the engineering of carbonate soils.

Shallow Foundations

AG has performed the final design of numerous shallow foundations, from the simplest of shallow skirted mudmats to the most complex deep-skirted caisson foundations.  Central to optimal design is the understanding of the time-dependency of sediment strength gain under and around the foundation, as well as the behaviour under extreme cyclic loads.  Understanding how the foundation will be installed, and the impact of this on design, is also a crucial aspect.  AG has developed in-house software, which can efficiently analyse any shallow foundation, and has a proven track record of establishing complex numerical models, especially where soil-structure is important.

Piled Foundations

The early use of driven piled foundations around Australia presented severe challenges to the oil and gas industry that required innovative solutions.  Drilled and grouted piles are generally the preferred solution in cemented sediments, with or without driven primary piles.  However, drilled and grouted foundations are often vulnerable to fatigue under cyclic loading, becoming weaker with exposure to cyclic loads.  As the nature of the foundations has become better understood, AG has developed a suite of approaches and analytical tools to allow their design to be optimised.

Anchors

An increasing number of floating production platforms are being used around Australia as developments move into deeper water.  During drag-anchor preloading activities it has become apparent that standard design approaches can require large in-service drags, which are potentially unsafe.  AG has developed a data-set whereby in-house approaches have been calibrated.  AG also possesses a number of programs for analysis of other anchors, such as suction anchors, for which the well-known program AGSPANC was specifically developed.  For a number of years, AG has been at the forefront of innovative solutions for challenging sites, which have included the use of grillage and berm anchors.

Pipeline-Soil Interaction

There is a growing awareness of the issues of lateral buckling and axial expansion/walking of infield flowlines and on-bottom instability of export pipelines. Many of the major new developments around Australia require the use of a network of flowlines and long export pipelines. AG has developed state-of-the-art methods for assessing the pipe-soil interaction under various design conditions and these are rapidly being incorporated into pipeline designs.

Seismic Liquefaction Assessment

Earthquakes can pose severe threats to developments, as this can cause seabed sediments to liquefy and weaken.  This hazard is peculiar in many carbonate soils which are particularly prone to liquefaction under cyclic loading.  This can result in failures of slopes along pipeline routes, floatation of buried pipelines and general subsidence of foundations. AG has the technology to develop site specific predictions of the response of the seabed during earthquakes and has a unique understanding of the soil properties that are applicable to the assessment of seismic response in carbonate soils.

Geographic Information Systems (GIS)

GIS has become an essential tool at AG for the creation, management, analysis and visualisation of geotechnical information. GIS integrates multiple data types (site investigation logs/PCTs/interpretations, DEMS/bathymetry, CAD pipelines and infrastructure, Excel or tabular data, aerial photography, digitised alignment sheets, etc) from multiple disciplines (geotechnical, geohazard, geology, geophysics and engineering) into a 3D project model.  The results are integrated with existing client data to produce maps, sections, alignment sheets and 3D models, that can be used throughout the project life cycle.

AG uses the latest ESRI™ and Google™ 2D, 3D and 4D technologies to provide specialised data capture, data management, modelling, spatial analysis and visualisation solutions for our clients.

Case studies include:

QGC-Curtis Island Narrows Crossing

Chevron: Wheatstone Shore Crossing

INPEX: Ichthys Field Geotechnical Model