C.F. Leung

Eulerian Finite-Element Technique for Analysis of Jack-Up Spudcan Penetration

The numerical analysis of an object penetrating deep into the seabed is a fundamentally challenging problem. This paper presents the application of a novel Eulerian-based finite-element technique to simulate the continuous penetration of a jack-up spudcan foundation into seabed of different soil profiles. The finite-element mesh is kept stationary throughout the analysis and the material is allowed to move independent of the element nodal points. Consequently, termination of computing execution from severe mesh distortion does not occur despite the material undergoing large deformation. The first part of the paper elucidates the mesh density requirement, the effect of penetration rates, and factors influencing the simulation time. The applicability of the Eulerian finite-element model is then validated through comparison with published experimental data for different soil profiles. In general, the Eulerian finite-element model is able to replicate the experimental observations well. With the Eulerian appr...

A constitutive model for rock interfaces and joints

A constitutive model based on limit concept is proposed to predict the behavior of rock interfaces and joints. For the limit case of an interface with thickness approaching zero, an ellipse yield function is adopted and associated flow rule is recommended. This yield function is not of proportional type, and its motion in stress space is governed by its center position and the hardening rule of yield function. The shear anisotropy is described by a shape function that incorporates the elastic shear stiffness, yield function and hardening rule. An equivalent relative displacement is obtained based on normalized plastic work and limit concept. This equivalent relative displacement yields a hardening rule from which the dilatancy is directly associated with the asperity of the interface. The validity of the proposed constitutive model is verified using data obtained from several existing experimental studies on natural and artificial rock joints.

A simplified homogenisation method for composite soils

Abstract Composite soil may consist of composite ground made up of soft soil reinforced by stiff soil columns or mixed soil made up of thoroughly mixed soft and stiff soils. In general, the behavior of composite soil is not well understood due to non-homogeneous structure of soil matrices. In this paper, a simplified homogenisation method is proposed to model the behavior of mixed soil and composite ground. It assumes that micro-stress/micro-strain is homogeneous in the matrix and the reinforcement of a composite soil and a localization tensor is developed. A microstructure knowledge-based model is proposed to distribute the micro-stress/micro-strain in each phase. This assumption largely simplifies the numerical procedure at the unit cell of composite soils. The validity of the proposed method is verified by comparing the predicted parameters with existing experimental data on mixed soils and composite grounds. Examples show that the proposed method can be applicable to well-randomly mixed soil and oriented composite ground.

Numerical Simulation of Pipeline Undergoing Cyclic Lateral Motion in Clay

In a deepwater oil and gas development, a pipeline is often laid directly on the seabed rather than being buried in a trench. In addition to the cost benefit of not having to perform expensive underwater trenching, a pipeline laid in such a manner with planned geometric imperfection accommodate the axial elongation arising from thermal expansion and contraction cycles. Under such a scheme, the change in length of the pipeline during a thermal expansion and contraction cycle manifests itself as a lateral deflection of the pipeline on the seabed and the process relieves additional axial stress that would otherwise be induced. In order to employ this scheme successfully, comprehensive understanding of both the evolution of lateral soil resistance as well as the tendency of pipeline to self-embed into the seabed is required. As an alternative to experimental investigation, numerical analysis can be performed to simulate the response of the system under a cyclic lateral displacement of the pipe. In order to circumvent the deficiencies of a Lagrangian-based finite element approach in analyzing such problems, an Eulerian based finite element technique is employed in this study.Copyright

Effects of Tunneling on Underground Infrastructures

In urban cities like Shanghai, the increasing need for urban tunnelling to serve the ever-growing population in space-constrained cities will result in part of the proposed tunnelling route running close or beneath infrastructures, such as pipelines and buildings founded on shallow or pile foundations. The ground volume losses due to the over-excavation of the tunnel result in ground, subsurface and lateral movements. These ground movements, result in additional stress and deformation on the existing infrastructures. Thus, a type of displacement control methods has been developed and widely applied to the risk assessment of the infrastructures subjected to tunneling. This paper will fully review the existing studies on the displacement control methods and their results to conclude critical responses of various infrastructures, provide effective methods of evaluating the responses for practical engineering.