Australian Research Council Centre of Excellence Geotechnical Science and Engineering

Mr Hassan Sabetamal

Qualifications

MSc

Education

  • 2007
    Master of Science in Geotechnical Engineering, Tabriz University, Tabriz, Iran

Research Interests

  • Soil – Structure Interaction
  • Finite Element Analysis
  • Physical Modelling in Geotechnics
  • In situ Soil testing and Site Investigation
  • Soil Conditioning in Mechanised Tunnelling

Supervisors

  • Dr Majidreza Nazem
  • Professor Scott Sloan
  • Professor John Carter

Research Topic

Finite Element Algorithms for Dynamic Analysis of Geotechnical Problems

A computational scheme has been developed and implemented into a FE code (SNAC) by H. Sabetamal for the analysis of coupled geotechnical problems involving finite deformation, inertia effects and changing boundary conditions.

In the numerical scheme, the mechanical behaviour of a two-phase saturated porous medium is predicted using mixture theory, which models the dynamic advection of fluids through a fully saturated porous solid matrix. High-order contact algorithms have been formulated to account for contact problems of the saturated porous medium based on a mortar segment-to-segment scheme. An Arbitrary Lagrangian–Eulerian (ALE) approach has been utilised to consider geometrical nonlinearities and avoid possible mesh distortions. Suitable absorbing boundary conditions have been adopted to absorb the outgoing bulk waves and eliminate spurious wave reflections.

The utility and robustness of the numerical scheme is shown in the following by modelling two challenging problems of offshore geomechanics, including dynamically penetrating anchors, and pipeline-seabed interaction

Simulations

Coupled analysis of Dynamically Penetrating Anchors

Dynamically penetrating anchors (DPAs) have proven to be promising systems for anchoring taut mooring lines of floating offshore oil and gas exploration and production units because of their relatively easy installation process. The kinetic energy of a DPA attained by gravity throughout free-fall through the water column provides the required dynamic penetration force, making it more practical and cost-effective than other offshore structures such as suction piles, driven piles, drilled and grouted piles, and drag embedment anchors.

Despite the increasing relevance of DPAs in offshore applications, the estimation of embedment depth, pull-out capacity and the prediction of stresses in their structure remain a challenge.

The major limitation is a lack of knowledge of the effective stress state and pore pressure around the anchor. No laboratory tests have yet been reported with measurements of excess pore pressures or effective stresses in the soil during or following the dynamic penetration of objects. This is largely because of the fast and transient nature of the problem, which requires a set of sophisticated piezometers and instrumentation techniques in low permeability materials such as clay. Therefore, the problem still remains as to how pore pressures and stresses are affected by the installation of DPAs.

The following animations show the deforming mesh and the generation of excess pore pressure throughout the installation process and set-up of a DPA.

** For high quality video please change the resolution to HD (720p) at setting**

Dynamic coupled analysis of pipeline-seabed interaction under large amplitude cyclic movement

Controlled on-bottom lateral buckling of partially embedded pipelines is a novel and cost-effective solution to relieve the developed axial compressive stresses resulting from cycles of thermal expansion and the contraction of operative pipelines.

To properly engineer lateral buckles, it is necessary to make accurate predictions of the initial as-laid pipe embedment and the subsequent soil–pipe response because of the combined loading from the thermal expansion and pipe self-weight.

The plasticity solutions for the vertical collapse load of a shallowly embedded pipeline may closely predict the deformation mechanisms during pipe penetration, but they do not allow large deformation effects, such as heave, to be incorporated. In addition, including the dynamic effects involved in the lay process is essentially difficult. Further, the steady lateral response of the soil–pipe system is governed by the growth of a soil berm, which is created as the pipe rises from the initial embedment. However, the changing geometry is not the only factor affecting the pipe–soil response. Pore-pressure dissipations may occur during lateral sweeping and for the period of start-up and shutdown events. This gives rise to the reconsolidation of the disturbed soil within the berm and can significantly increase the berm resistance. Therefore, there is a need for a numerical simulation that can address the different phenomena involved.

The following animations show the deforming mesh and the generation of excess pore pressure throughout the pipe laying process, the subsequent consolidation and the lateral movement of the pipe.

** For high quality video please change the resolution to HD (720p) at setting**

** For high quality video please change the resolution to HD (480p) at setting**

** For high quality video please change the resolution to HD (480p) at setting**