The soil can be considered as a collection of grains or aggregates with microstructures, aggregates are composed of particles with interparticle voids, and grains or particles are made of minerals with atomic structures. Thus, the origin of mechanical behaviours/properties of the soil can be investigated by downscaling, and the mechanical modelling of the soil can be conducted by upscaling.

Topic 1: Practice of molecular dynamics method in geomechanics

Related PhD Students | Wang-Qi XU

We adopted the molecular dynamics method to simulate mechanical behaviours/properties of clay minerals (montmorillonites, kaolinite, illite) at nano scale. We have also utilized the molecular dynamics method as an effective tool to provide new insight concerning the mineral-mineral interface and the mineral-epoxy interface under dry and lubricated conditions at nano scale.

  • Zhang LL, Zheng YY, Wei PC, Diao QF, Yin Z-Y (2021). Nanoscale mechanical behavior of kaolinite under uniaxial strain conditions. Appl. Clay Sci., 201:105961.
  • Wei PC, Zhang LL, Zheng YY, Diao QF, Zhuang DY, Yin Z-Y(2021). Nanoscale friction characteristics of hydrated montmorillonites using molecular dynamics, Appl. Clay Sci., 210:106155.


Topic 2: Practice of discrete element method in geotechnics

Related PhD Students | Shun-Xiang SONG

2.1 Development of DEM codes

We developed several DEM codes for realistic modeling of granular particles with arbitrarily irregular shapes. Compared with the simplified shape models such as disk-clump, the proposed method can consider more realistic contact mechanics between irregular shape particles. The capability and efficiency of the developed program will pave a viable pathway for the researchers to conduct more quantitative and credible studies on how the realistic particle shapes would affect the macro- and micromechanical properties of granular materials.

  • Wang, X., Yin, Z. Y., Su, D., Xiong, H., & Feng, Y. T. (2021). A novel Arcs-based discrete element modeling of arbitrary convex and concave 2D particles. Computer Methods in Applied Mechanics and Engineering, 386, 114071.
  • Wang, X., Yin, Z. Y., Xiong, H., Su, D., & Feng, Y. T. (2021). A spherical‐harmonic‐based approach to discrete element modeling of 3D irregular particles. International Journal for Numerical Methods in Engineering, 122(20), 5626-5655.

We proposed several efficient methods for generation of realistic granular particle specimen with different particle sizes and shapes in DEM.

  • Wang, X., Yin, Z. Y., Su, D., Wu, X., & Zhao, J. (2021). A novel approach of random packing generation of complex-shaped 3D particles with controllable sizes and shapes. Acta Geotechnica, 1-22.
  • Wang, X., Yin, Z. Y., Zhang, J. Q., Xiong, H., & Su, D. (2021). Three-dimensional reconstruction of realistic stone-based materials with controllable stone inclusion geometries. Construction and Building Materials, 305, 124240.

We proposed several efficient methods for modeling of realistic biaxial/triaxial tests in DEM considering flexible membrane boundary and realistic particle shapes. The presented works lay a foundation for further studies on revealing the mechanisms of the conventional triaxial test, e.g., the effect of end restraint and rubber membrane. Moreover, the proposed systematic framework can be applied to precisely capture the real mechanical properties of various types of granular materials in DEM simulations.

  • Zhang J, Wang X, Yin Z-Y, Liang Z (2020). DEM modeling of large-scale triaxial test of rock clasts considering realistic particle shapes and flexible membrane boundary. Eng. Geol., 279: 105871.
  • Zhu H, Yin Z-Y (2019). Grain Rotation-based Analysis Method for Shear Band. J. Eng. Mech. ASCE, 145(10): 04019073.
  • Jiang MJ, Yin Z-Y, Shen ZF (2016). Shear band formation in lunar regolith by discrete element analyses. Granul. matter, 18:32.
  • Liu Y, Li G, Yin Z-Y, Dano C, Hicher PY, Xia XH, Wang JH (2014). Influence of grading on undrained behavior of granular materials. CR Mecanique, 342: 85-95.

For granular materials, samples with different grain sizes exhibit different deformability and strength. We have focused on investigating the size effect of granular materials in two aspects: under mechanical loading with significant grain crushing, the sample with bigger grain size has more deformability and less strength, whilst under mechanical loading with few or no grain crushing but significant shear band, the sample with bigger grain size has bigger strength. Our work includes experimental study, discrete element modelling and continuum mechanics modelling up to the engineering application.

  • Yin Z-Y, Hicher PY, Dano C, Jin YF (2017). Modeling the mechanical behavior of very coarse granular materials. J. Eng. Mech. ASCE, 143(1): C401600.
  • Jiang-Xin LIU (10/2014-03/2018), PhD topic: Numerical study of strain localization in geotechnical structures under the framework of micro-polar theory. (Nantes) Supervisor: Zhen-Yu YIN, Pierre-Yves HICHER
  • Wang P, Yin Z-Y, Wang Z (2022). Micromechanical investigation of particle size effect of granular materials in biaxial test with the role of particle breakage. J. Eng. Mech. ASCE, 148(1): 04021133.

We conducted a series of coupled DEM/FEM simulations to investigate the complex micromechanical behaviours of rigid soft particle mixtures.

2.2 Practice of DEM in BVPs

We investigated micro mechanism of failure and deformation of caisson foundation by means of DEM, considering effects of particle crushing and particle shape.

  • Yin Z-Y, Wang P (2021). Micro-mechanical analysis of caisson foundation in sand using DEM: particle shape effect. Appl. Ocean Res., 111: 102630.
  • Wang P, Yin Z-Y (2020). Micro-mechanical analysis of caisson foundation in sand using DEM. Ocean Eng., 203: 107240.
  • Wang P, Yin Z-Y (2020). Micro-mechanical analysis of caisson foundation in sand using DEM: particle breakage effect. Ocean Eng., 215: 107921.

The mechanical behavior at soil–structure interface (SSI) has a crucial influence on the safety and stability of geotechnical structures. We simulated a series of interface shear tests with discrete element method to investigate the frictional characteristics of SSI and the associated displacement localization under constant normal stiffness condition at both macro- and microscales. In addition, a quantitative analysis of the effect of particle crushability on the behavior of the soil-structure interface is performed.

  • Wang P, Yin Z-Y, Zhou WH, Chen WB (2021). Micro-mechanical analysis of soil-structure interface behavior under constant normal stiffness condition with DEM. Acta Geotech., DOI: 10.1007/s11440-021-01374-8.
  • Zhou WH, Jing XY, Yin Z-Y, Geng X (2019). Effects of particle sphericity and initial fabric on the shearing behavior of soil–rough structural interface. Acta Geotech., 14: 1699–1716.
  • Zhu HX, Zhou WH, Yin Z-Y (2018). Deformation mechanism of strain localization in 2D numerical interface tests. Acta Geotech., 13(3): 557-573.

The face stability of a tunnel is extremely important during the excavation. We analyzed the progressive face failure of a shield tunnel in sand is with coupled discrete element method (DEM) and the finite difference method (FDM) in three-dimension. Soils at the tunnel face, where large deformation occurs and continuum mechanics description does not apply, are modeled with DEM. And the FDM is used for the rest areas where deformation and displacement are relatively small. The soil movement, ground surface movement, supporting force of the tunnel face, and the distribution of microscopic contacts are analyzed during the progressive failure of the tunnel face, which demonstrate a significant effect of particle shape.

  • Yin Z-Y, Wang P, Zhang F (2020). Effect of particle shape on the progressive failure of shield tunnel face in granular soils by coupled FDM-DEM method. Tunn. Undergr. Sp. Tech., 100: 103394.

2.3 Practice of CFD-DEM in geotechnics

Considering the discrete properities and the complexity of soil-fluid interactions, we introduced the DEM coupled with CFD (computational fluid dynamics) to investigate the internal erosion in sandy soils from macro and micro perspectives. Both the influence factors and its consequences on the mechanical behavior were investigated.

  • Qian J G, Zhou C, Yin Z Y, et al. Investigating the effect of particle angularity on suffusion of gap-graded soil using coupled CFD-DEM[J]. Computers and Geotechnics, 2021, 139: 104383.
  • Qian J G, Li W Y, Yin Z Y, et al. Influences of buried depth and grain size distribution on seepage erosion in granular soils around tunnel by coupled CFD-DEM approach[J]. Transportation Geotechnics, 2021, 29: 100574.
  • Liu Y, Yin Z Y, Wang L, et al. A coupled CFD–DEM investigation of internal erosion considering suspension flow[J]. Canadian Geotechnical Journal, 2021, 58(9): 1411-1425.
  • Xiong H, Yin Z Y, Zhao J, et al. Investigating the effect of flow direction on suffusion and its impacts on gap-graded granular soils[J]. Acta Geotechnica, 2021, 16(2): 399-419.
  • Zhang D M, Gao C P, Yin Z Y. CFD-DEM modeling of seepage erosion around shield tunnels[J]. Tunnelling and Underground Space Technology, 2019, 83: 60-72.


Topic 3: Micromechanics-based stress-strain model for geomaterials

Related PhD Students | Hai-Lin WANG

Granular materials can be considered as a collection of grains, and the stress-strain relationship for the assembly can be determined by integrating the behaviour of inter-grain contacts in all directions. This micromechanical approach has advantages compared to the conventional modelling approach, i.e. the inherent or initial anisotropy of soils can be characterized by an orientation-dependence, which has a clear physical meaning and can be modelled in a direct way; adhesive forces, cementation can be considered at contact level; and so on.

  • Zhao C-F, Yin Z-Y, Hicher P-Y (2018). A multiscale approach for investigating the effect of microstructural instability on global failure in granular materials. Int. J. Numer. Anal. Methods Geomech., 42(17): 2065-2094.
  • Zhao C-F, Yin Z-Y, and Hicher P-Y (2018). Integrating a micromechanical model for multiscale analyses. Int. J. Numer. Meth. Eng., 114(2): 105-127.
  • Zhao C-F, Yin Z-Y, Misra A, and Hicher P-Y (2018). Thermomechanical formulation for micromechanical elasto-plasticity in granular materials. Int. J. Solids Struct., 138(1): 64-75.
  • Yin Z-Y, Zhao J, Hicher PY (2014). A micromechanics-based model for sand-silt mixtures. Int. J. Solids Struct., 51(6): 1350–1363.
  • Yin Z-Y, Chang CS (2013). Stress-dilatancy behavior for sand under loading and unloading conditions. Int. J. Numer. Anal. Methods Geomech.. 37(8): 855-870.
  • Yin Z-Y, Chang CS, Hicher PY (2010). Micromechanical modelling for effect of inherent anisotropy on cyclic behaviour of sand. Int. J. Solids Struct., 47(14-15): 1933-1951.

By observing the microscopic characteristics of clay and its evolution law in different scales (such as the scales of particles and aggregates), assuming the aggregates as basic mechanical unit to replace the grains of granular materials, the micromechanics-based model of granular materials is extended to clay. Several important features of clay have been studies using this approach: such as inherent and induced anisotropy, the microscopic mechanism of rotation hardening of macro yield surface, the additional strength and damage mechanism for structured soil (sensitive clay, hard clay, cemented soil, etc.).

  • Yin Z-Y, Xu Q, Chang CS (2013). Modeling cyclic behavior of clay by micromechanical approach. ASCE J. Eng. Mech., 139(9), 1305–1309.
  • Yin Z-Y, Chang CS, Hicher PY, Karstunen M (2009). Micromechanical analysis of kinematic hardening in natural clay. Int. J. Plasticity, 25(8): 1413-1435.
  • Yin Z-Y, Chang CS (2009). Microstructural modelling of stress-dependent behaviour of clay. Int. J. Solids Struct., 46(6): 1373-1388.

This work is extended from 2D H-model of Prof. F. Nicot and collaborate with him. We developed 3D H-model considering mesoscopic scale, implemented the model into finite element code (ABAQUS/Explicit) with validation for different behaviors from RVE to BVP scales.

  • Xiong H, Yin Z-Y, Nicot F, Wautier A, Miot M, Darve F, Veylon G, Philippe P (2021). A novel multi-scale large deformation approach for modelling of granular collapse. Acta Geotech., DOI: 10.1007/s11440-020-01113-5.
  • Xiong H, Yin Z-Y, Nicot F (2020). Programming the micro-mechanical model of granular materials in Julia. Adv. Eng. Softw., 145: 102816.
  • Xiong H, Yin Z-Y, Nicot F(2019). A multiscale second-order work analysis approach for geotechnical structures. Int. J. Numer. Anal. Methods Geomech., 43(6): 1230-1250.
  • Xiong H, Nicot F, Yin Z-Y (2019). From microscale to boundary value problem: using a micromechanically-based model. Acta Geotech., 14(5): 1307–1323.
  • Xiong H, Nicot F, Yin Z-Y (2017). A three-dimensional micromechanically-based model. Int. J. Numer. Anal. Methods Geomech., 41(17): 1669–1686.