Finite element or different method (FEM/FDM) based analysis is an effective way for geotechnical design and disaster protection. Our objectives are to develop advanced constitutive models (e.g. elastic viscoplastic model of clay, critical state based models of sand), to implement them into available FEM/FDM codes, to develop smoothed particle finite element method (PFEM) with model implementation for large strain analysis while keeping the accuracy of small strain analysis, and to develop macroelement model inspired from constitutive modelling and beyond FEM/FDM analysis.
Related PhD Students ｜ Peng-Lin LI, Wei Cheng
1.1 Time-dependency of soft soils - ANICREEP
Natural soft clays exhibit several features: (a) significant anisotropy developed during their deposition, sedimentation, consolidation history and any subsequent straining; (b) some apparent bonding which will be progressively lost during straining; and (c) time-dependent stress-strain behaviour which has a significant influence on the shear strength and the pre-consolidation pressure. Since all these features cannot be neglected, in the modelling we considered all above features. The application of the proposed model ANICREEP requires the same experimental information as needed for the Modified Cam Clay model, which makes the model attractive for geotechnical practice.
1.2 Grading-dependency of granular soils - SIMSAND
Mechanical properties/behaviours are significantly affected by the grain size distribution of the granular soil, which is called “grading-dependency”. The grading change can be induced by grain breakage. Bigger sized grains are easier to be crushed. If the soil is gap-graded, the change of fines content can be induced by seepage force so-called suffusion/internal erosion. Currently, we focuses on how the soil grading evolves, what is mechanical consequence, and how to model the full coupling for engineering design.
1.3 Modelling thermo-mechanical behaviors of saturated clay
Modeling rate-dependent thermo-mechanical behaviors of saturated clays and solving related boundary value problems are crucial for temperature-sensitive geotechnical engineering applications. The three relevant key points are as follows: 1) Advanced constitutive models that better reflect the complex thermo-mechanical behaviors of clays. 2) Efficient stress updating algorithms based on mathematical optimization theory that are applicable to the relevant constitutive models. Unified computational frameworks that integrates model and element scales, along with high-performance optimization algorithms.
Related PhD Students ｜ Jing-Cheng TENG ｜ Min-Hao ZHANG ｜ Rui LIANG
The implementation of the advanced constitutive models into FEM/FDM codes is necessary for engineering design. We adopted some famous commercial codes for our model implementation: ABAQUS, PLAXIS and FLAC.
2.1 User-defined material – UMAT/VUMAT in ABAQUS
UMAT and VUMAT allow us to implement advanced constitutive models of soils. The former is typically for implicit calculation and small strain analysis, and the latter is typically for explicit calculation and large deformation analysis.
2.2 User-defined friction – FRIC/VFRIC in ABAQUS
FRIC and VFRIC allow us to implement advanced interface models of soil-structure. The former is for implicit calculation and the latter for explicit calculation. We implemented the recently developed exponential function based nonlinear incremental interface model.
2.3 User-defined element – UEL/VUEL in ABAQUS
UEL and VUEL allow us to develop advanced multiphysics modelling. The former is for implicit calculation and small strain analysis, and the latter is for explicit calculation and large deformation analysis.
2.4 Practice of cohesive interface element
Cohesive interface elements are useful in modelling adhesives, bonded interfaces, gaskets, and rock fracture. The constitutive response of these elements depends on the specific application and is based on certain assumptions about the deformation and stress states that are appropriate for each application area.
2.5 User-defined material – UDM in PLAXIS
UDM allows us to implement advanced models of soils in the code. Such models must be programmed in FORTRAN, then compiled as a Dynamic Link Library (DLL) and then added to the PLAXIS program directory. We implemented the ANICREEP model for geotechnical analysis relating to soft soils.
2.6 User-defined material – UDM in FLAC
UDM allows us to implement advanced models of soils in the code, similar to that in PLAXIS. We implemented some advanced soil models for geotechnical analysis.
Related PhD Students ｜ Lu-Jia YU ｜ Ze-Yu WANG ｜ Xian-Han WU
Geotechnical structures involve small deformation for the design purpose to large deformation for the failure analysis and disaster protection. Particle finite element method (PFEM) has both the accuracy of small deformation and the ability of large deformation, due to which we adopted the framework of PFEM to enhance/develop more advanced methods.
3.1 Edge-based smoothed PFEM
We developed a novel edge-based smoothed PFEM for large deformation analysis.
3.2 Implicit edge-based smoothed hydromechanical PFEM
Based on the proposed edge-based particle finite element method (ES-PFEM), we developed the hydromechanical coupling of ES-PFEM (C-ES-PFEM) with implementing ANICREEP model.
3.3 Explicit stable node-based smoothed PFEM (SNS-PFEM)
To solve the drawbacks (overly soft and temporal instability) of the node-based particle finite element method (NS-PFEM), we developed stable node-based NS-PFEM (SNS-PFEM) and applied it to large deformation analysis.
Related PhD Students ｜ Min-Hao ZHANG
Soil–structure interaction (SSI) consists of the interaction between soil (ground) and a structure built upon it, in which the foundation structures with their surrounding soils (in certain range which soil is disturbed) can be regarded as an entire system, so-called a macro-element, with global forces (or moments)-displacements (or rotations) responses. Currently, we focused on the design of caisson foundation by means of discrete element method, finite element method and mesh-free method for progressive failure analysis and failure envelope investigation, which have been later applied to establish “forces-displacements” models in structural level so-called macro-element models.
Related PhD Students ｜ Chang HE
The Pearl River Estuary and Hong Kong waters (PRE-HK) is one of the most energetic coastal areas in view of oceanic circulation. Tides from the South China Sea brings numerous energy and momentum which were dissipated around the PRE-HK when interacting with river plumes and complex coastlines. A high-resolution model (50m – 10km) was well-validated, based on the Finite Volume Community Ocean Model. Currently, we focused on the flow structure and the role of monsoon wind and tides, as well as macro-vortices generation and transport around the PRE-HK.