Conference Agenda

Problems involving large deformation invite onerous computational approaches, but adequate accuracy can potentially be obtained using models built from relatively simple principles. Model efficiency is highly desirable for numerous reasons, ranging from unlocking possibilities for virtual prototyping to enabling faster than real-time (FTRT) simulation for control and path planning. This presentation discusses pathways for constructing efficient models based on approximating the shape of the boundary and/or the rule(s) for updating the boundary. The first method, referred to as the ‘sequential kinematic method,’ rests on notions from flow theory of plasticity. Key advantages of this approach are the clarity and rigor of the underlying principles, but the method is limited in its applicability, particularly with respect to restrictions on material type. The presentation describes a second class of techniques, referred to as ‘data-driven methods,’ that are more general but resort to machine learning, thus obscuring the formulation and requiring that sufficient data is available for model training. Examples covered in the presentation include indentation, granular column collapse, and orthogonal cutting. These methods and examples lend insight into the physical nature of the problems and highlight possible future modeling techniques with high potential for efficiency.

Particle-based methods have effectively simulated large deformation issues involving geotechnical hazards such as landslides, debris flows, and earth dam breaches, and have garnered widespread attention in the field of computational mechanics in recent years. Currently, commonly used particle-based methods for geotechnical large deformation simulation include Smoothed Particle Hydrodynamics (SPH), Material Point Method (MPM), and Particle Finite Element Method (PFEM). Among them, PFEM, inheriting the solid theoretical foundation of the finite element method, is increasingly receiving attention in the field of computational mechanics. In response to the shortcomings of PFEM, such as the need for continuous mapping of field variables between Gaussian points, we introduce a node integration technique based on strain smoothing into PFEM and propose an improved particle finite element method—the Smoothed Particle Finite Element Method (SPFEM). The complete computational theory framework for SPFEM is derived. This method is further extended to dynamic, coupled, and contact analysis, ultimately enabling three-dimensional GPU parallel numerical computation of large deformations in geotechnical hazards under fluid-solid interaction.

This talk introduces a novel stable node-based smoothed particle finite element method (SNS-PFEM) integrated with the dual mortar contact method, designed to address fully coupled thermo-hydro-mechanical (THM) structure-soil interaction geotechnical problems, particularly those involving large deformation. The proposed SNS-PFEM framework offers three key advancements: (1) it proposes a smoothed thermal strain, enabling elastoplastic thermo-mechanical analysis in NS-FEM and SNS-FEM; (2) it presents the SNS-PFEM framework as a viable model for fully coupled THM large deformation problems; and (3) it implements the dual mortar contact method within the THM SNS-PFEM framework to effectively model structure-soil contact. The validity of this method is demonstrated through four benchmark tests, including the thermo-mechanical (TM) coupled sliding beam, the hydro-thermal (HT) coupled moving liquid, the THM coupled thermal consolidation, and the THM coupled half space heating. Additionally, the proposed THM SNS-PFEM framework is applied to investigate the interaction behavior between submarine pipelines and seabed soil during penetration and buckling, with a specific focus on thermal effects. The results reveal the competition mechanism between thermal expansion and friction degradation, and how these factors influence soil resistance, providing a promising contribution to the understanding and modeling of complex geotechnical problems.

The process of dynamic fracture propagation within saturated porous solids is known to exhibit variability, often deviating from smooth and continuous behavior. Experimental evidence and field observations have consistently documented instances of stepwise fracture tip advancement and pressure oscillation within such media. This phenomenon arises from the complex interplay between mechanical waves and pore pressure waves, leading to a transition in fracture advancement behavior from smooth to stepwise, and ultimately to forerunning patterns. In this study, we employ a hybrid Finite Element Method (FEM) and Peridynamic (PD) model to delve into the fracture advancement process within porous media under diverse loading conditions. The Peridynamics model accurately captures the deformation of the solid skeleton and tracks crack propagation, while the FEM equations describe fluid mechanics within the porous medium. The coupling between hydrodynamics and mechanics adheres to Biot theory, and a staggered scheme is utilized to solve the coupled system. A one-dimensional dynamic consolidation problem is first addressed for validation of the presented approach. The dispersion behavior of the PD-FEM model is also analyzed. Subsequently, a cantilever beam model is simulated under various loading conditions, considering both dry and saturated porous media. The numerical simulations elucidate that forerunning fracture phenomena are prevalent in both dry and saturated porous media. This occurrence can be attributed to the influence of incident stress waves within the material domain ahead of the crack, or the intricate interaction between incident stress waves, reflected stress waves, and pore pressure waves. The phenomena presented in this study open up interesting suggestions for further research, particularly in the context of potential experimental investigations.

The multi-physical field coupling simulation of rock is a very important issue in geomechanics and petroleum engineering. The complicated coupling process among different physical fields is very difficult to simulate in the framework of conventional continuum mechanics because it involves the fracturing problem. To explore new approach to this problem, the discretized virtual internal bonds(DVIB) is extended to modelling the multi-physical field coupling process of rock. DVIB was originally proposed to simulate the dynamic fracture of solid. It considers a solid to consist of discrete bond cells. Each cell has a finite number of bonds. Each bond is characterized by a bond potential in mechanics, which intrinsically contains the fracture mechanism. In the present multi-field coupling analysis of rock, each bond simultaneously functions as the mechanical linkage, the thermal conductivity, the fluid flow and the acid reactant transport channel. By this method, the hydraulic, mechanical, thermal and chemical field are unified together on an individual bond. The coupling process is allowed to occur in a bond. The coupled governing equations of a bond are derived. By this approach, the complicated 3D multi-field coupling process is reduced to a 1D bond problem, which significantly simplifies the analysis of the coupling problem and improves the efficiency of numerical simulation. The perspective of this method should be inspiring in the simulation of reservoir stimulation.

Disposing of the waste deep underground in the geological repository is the most preferred long-term solution for nuclear waste disposal. The canister containing the high-level waste can be buried deep underground and encapsulated by engineered barrier material (EBM), which separates it from the natural rock. Bentonite clay is the most preferred EBM due to its advantageous properties, such as low cost, great long-term stability, high thermal resistance, and low permeability. However, bentonite is subjected to a complex multiphysics environment as the canister generates heat, causing bentonite to desiccate, while moisture infiltrating from the host rock causes bentonite to swell. A better-performing EBM that is less permeable and more resistant to desiccation cracking and chemical degradation is imperative. As a promising solution to the significant societal challenge, an inorganic microfiber-reinforced EBM (i.e., IMEBM) is proposed. This study investigates the effects of inorganic microfibers embedded in bentonite to develop such IMEBMs by conducting laboratory tests and integrating the tests with computational multiphysics modeling. Experimentally, two tests were developed and conducted: (1) a restrained ring shrinkage test was designed and conducted to observe the desiccation-induced deformation and cracking behavior captured by a digital image correlation (DIC) system, and (2) a 3-D soil tube test incorporating moisture (mass) transport and heat transfer, which is to identify multiphysical material characteristics of IMEBMs. Each laboratory test was computationally simulated based on a multiphysical finite element (FE) method to identify material properties that are a function of moisture and temperature. The resulting test data (DIC images of deformation, 3-D X-ray CT images of soil microstructures, measurements of temperatures and moisture over time, etc.) and multiphysical model parameters demonstrate the effects of microfibers on crack-associated desiccation behavior of bentonite subjected to complex multiphysical conditions of the engineered barrier system for geological repositories.