Direction Leader: Distinguished Professor Shi Xiusong

Participants: Liu Kai, Xiong Hao

Soil-rock mixtures (S-RMs) are widely distributed in the mountainous areas of southwestern China and the coastal regions of southeastern China. They are extremely heterogeneous loose geomaterials composed of gravel, sand, fine-grained soil, and pores. As an important carrier of geological disasters in mountainous areas, the study of their deformation mechanisms and constitutive theories has significant theoretical value for the assessment of sudden geological disasters. The team at the Institute for Future Underground Cities, Shenzhen University, has long been dedicated to research in the field of deformation calculation of S-RMs. (1) They proposed a characterization method for the size effect of S-RMs^[1]; using a complex contact network analysis method, they defined "fine-grained bridges" and clarified their important contribution to the "coarse-grain reinforcement" effect^[2,3]; (2) they clarified the influence mechanism of multi-scale structural evolution on the strength and stiffness of S-RMs, constructed a unified structural variable to describe the coarse-grain reinforcement effect of S-RMs, and established a simplified homogenization method for deformation analysis of S-RMs^[4,5]; (3) they established a series of constitutive models for S-RMs based on the simplified homogenization method^[5,6] and applied them to the stability analysis of S-RM accumulation bodies, proposing simplified analysis methods for the bearing capacity of S-RM foundations and slope stability^[7] The research results have formed multi-scale structural characterization and deformation analysis methods for S-RMs, providing a certain theoretical basis for geological disaster analysis of complex accumulation bodies in mountainous areas.

Fig. 1 Multi-scale deformation analysis of soil-rock mixtures

Fig. 2 Photoelastic images of binary granular media under stepwise loading and

evolution of contact force chain networks

Fig. 3 Simplified calculation method for bearing capacity of soil-rock mixture foundations

Direction Leaders: Distinguished Professors Jin Yinfu & Fei Jianbo

Large-deformation disasters in geotechnical engineering, such as tunnel collapse, slope instability, water and mud inrush in foundation pits, and submarine landslides, generally exhibit complex characteristics of strong nonlinearity and multi-physics coupling. Traditional finite element methods are often limited in handling such problems due to severe mesh distortion and low computational efficiency, making it difficult to accurately capture the complete evolution process and impact range of disasters. Against this background, the team at the Institute for Future Underground Cities, Shenzhen University, has made a series of breakthrough advances addressing this challenge:

(I) The team innovatively integrated the strain smoothing method with the particle finite element method (PFEM) and proposed the stable nodal integration particle finite element method (SNS-PFEM)^[1-3] This method successfully achieves continuous and smooth simulation of geomaterials from small deformation to large deformation and even the entire failure process, not only significantly broadening the applicable boundaries of traditional mesh-based methods but also effectively improving the computational efficiency and accuracy of the particle finite element method;

(II) They originally proposed a unified theoretical framework of liquid-like soil dynamics with coupled granular rheology^[6-9], breaking through the limitations of traditional continuum theory in characterizing the particle friction-flow coupling mechanism, establishing a progressive modeling approach from "quasi-three-dimensional" (Saint-Venant-like equations) to "true three-dimensional" (extended N-S equations), pioneering the μ(J)-dilatancy simultaneous criterion with embedded dilatancy effect, establishing the Froude number criterion for saturated granular roll waves, and achieving cross-scale description of submarine landslide motion from thin-layer flow to three-dimensional mass flow;

(III) Based on the self-developed SNS-PFEM method, they constructed a computational system capable of handling complex multi-physics coupling problems, developed single-point two-phase^[4] and two-layer two-phase^[5] stable nodal integration particle finite element methods suitable for fluid-solid coupling, and successfully applied them to simulate typical engineering scenarios such as slope instability induced by water level fluctuations, large underwater landslides and the potentially disastrous surges they may trigger, verifying the engineering practicality of the proposed methods.

The above research results have greatly enhanced the capability for refined simulation and prediction of the dynamic processes of large-deformation disasters in geotechnical engineering, effectively overcoming the bottleneck problems of traditional numerical methods in extreme deformation analysis. The related technologies have been successfully applied to the analysis of multiple actual disaster cases and engineering risk assessments, providing powerful scientific tools and key technical support for improving China's disaster prevention and mitigation capabilities.

Fig. 1 Stable nodal integration particle finite element method and simulation cases

Fig. 2 "Quasi-three-dimensional" and "true three-dimensional" models used to simulate granular collapse-sliding and

the catastrophic processes of the Erman Mountain and Wenjia Gully landslides and the induced impact airwaves

Fig. 3 Two-layer two-phase stable nodal integration particle finite element method

Fig. 4 Material point method based on second-order cone programming

Direction Leader: Distinguished Professor Yang Jie

Participant: Xiong Hao

Suffusion, a typical multi-physics coupling phenomenon in geotechnical engineering, mainly manifests as the detachment and migration of fine particles from the soil skeleton under seepage action, causing changes in pore structure and deterioration of mechanical properties. Because the suffusion process is hidden deep within the soil and its evolution path is invisible, it can easily lead to sudden disasters such as slope instability, tunnel water inrush, and ground collapse. Traditional methods have shown obvious limitations in simulating the entire process of suffusion disasters and analyzing multi-field coupling mechanisms. To address this challenge, the research team focused on the seepage-suffusion-deformation coupling mechanism and achieved dual breakthroughs in basic theory and macro-micro simulation methods:

(I) They constructed a multi-field coupled suffusion theoretical system. They proposed a quantitative criterion for particle migration-clogging behavior under hydraulic driving, revealed the intrinsic relationship among pore skeleton structure, fine particle migration paths, and local clogging evolution, and proposed a contact network anisotropy index^[1-3] By revealing the dynamic correlation mechanism between the seepage field and particle migration, they established a soil strength degradation model considering dynamic evolution of porosity, overcoming the difficulty of characterizing the correlation between microstructural variation and macroscopic mechanical response during suffusion^[4-6]。

(II) They innovatively established a CFD-DEM numerical model simultaneously considering hydraulic gradient, particle size, and real morphological characteristics^[7-8] achieving quantitative visualization of the entire process of particle structure evolution and mechanical response from the meso- to macro-scale, revealing the soil failure mechanism under seepage-induced suffusion, and realizing full-process simulation from water-soil interaction to water-soil-structure synergistic evolution^[9-10] The research results solved the problems of strong concealment, high variability, and difficulty in prediction of internal soil strength degradation, and have been successfully applied to refined analysis of key issues such as seepage instability prediction of geotechnical structures, shield tunnel excavation, grouting, water seepage, and crossing existing structures, providing important scientific basis and technical support for underground space development.

Fig. 1 Geotechnical disaster mechanisms under multi-physics environments

and prediction methods and simulation cases

Fig. 2 Coupling mechanism between the suffusion process and soil mechanical properties

[1]Xiong H, Xiao JH, Jin YF*, et al. Numerical investigation of scour development around offshore tensioners under steady current[J]. Ocean Engineering, 2024, 313: 119373.

[2]Xiong H, Sun JF, Chen F*, et al. Suffusion behavior of crushed calcareous sand under reversed cyclic hydraulic conditions[J]. Construction and Building Materials, 2023.

[3]Xiong H, Yin ZY*, Zhao J, et al. Investigating the effect of flow direction on suffusion and its impacts on gap-graded granular soils[J]. Acta Geotechnica, 2020, 16(2): 399-419.

[4]Jie YANG; Zhen-Yu YIN; Farid AOUAFA; Pierre-Yves HICHER; Modeling coupled erosion and infiltration of fine particles in granular media, Acta Geotechnica, DOI: 10.1007/s11440-019-and filtration of fine particles in granular, 2019, 14(6):1615-1627

[5]Jie YANG; Zhen-Yu YIN; Farid AOUAFA, Pierre-Yves HICHER; Analysis of suffusion in cohesionless soils with randomly distributed porosity and fines content. Computers and Geotechnics, 2019, 111: 157-171

[6]Jie YANG; Zhen-Yu YIN; Farid AOUAFA, Pierre-Yves HICHER; Hydromechanical modeling of granular soils considering internal erosion. Canadian Geotechnical Journal, 2020, 57(2): 157-172

[7]Xiong H, Zhang ZM, Yin ZY*, et al. Microscopic origins of shape effects on migration and clogging of fines in porous media using coupled CFD-iDEM[J]. Acta Geotechnica, 2024: 1-29.

[8]Xiong H, Zhang ZM, Yang J*, et al. Role of inherent anisotropy in infiltration mechanism of suffusion with irregular granular skeletons[J]. Computers and Geotechnics, 2023, 105692.

[9]Jie YANG; Zhen-Yu YIN; Farid AOUAFA, Pierre-Yves HICHER; Three-dimensional hydromechanical modeling of internal erosion in dike-on-foundation, International Journal forhanics, 2020, 44(8): 1200-1218

[10]Jie YANG; Zhen-Yu YIN; Soil-structure interface modelling with the nonlinear incremental approach, International Journal for Numerical and Analytical Methods in Geomechanics, 2021, 45(10):1381-1404

Anchor scour

Mooring dynamics simulation under following waves