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As an effective energy-absorbing cable, constant resistance large deformation (CRLD) cables have been widely applied in rock engineering projects; however, to the best of our knowledge, its interaction mechanism with the surrounding rock has never been studied. According to previous practical projects, the CRLD cable–rock interaction differs from that of conventional cables because of the tubular expansion during the CRLD process, and it influences the performance of the cable reinforcement system. Therefore, an attempt was made to investigate the characteristics of the CRLD cable–rock interaction under static pull-out loading by using a coupled numerical method. The structure of the CRLD cable was modelled via the finite-difference method, and the surrounding rock was modelled via the discrete-element method. The micro-parameters of the surrounding rock were carefully calibrated, and the macro-parameters of the CRLD cable were verified by comparing them with a corresponding experimental test in the laboratory. The numerical results were carefully analysed. The constant resistance forces of a single CRLD cable and a CRLD cable reinforcement system were compared. The distribution of the normal and shearing stresses on the cable–rock interface was obtained, and the evolution mode of the pull-out strength was examined. In addition, the failure mode of the grouting material and surrounding rock was studied on a micro-scale. The findings describe the interaction of the CRLD cable against the surrounding rock, reveal its special anchorage mechanism, and can be used to predict and improve the performance of the CRLD cable reinforcement system.

Montmorillonite is an important layered phyllosilicate material with many useful physicochemical and mechanical properties, which is widely used in medicine, environmental protection, construction industry, and other fields. In order to a get better understanding of the behavior of montmorillonite under high pressure, we studied its atomic structure, electronic and mechanical properties using density functional theory (DFT), including dispersion corrections, as function of the interlayer Na and Mg cations. At ideal condition, the calculations of lattice constants, bond length, band structure, and elastic modulus of Na- and Mg-montmorillonite are in good agreement with the experimental values. Under high pressure, the lattice constants and major bond lengths decreased with increasing pressure. The calculated electronic properties and band structure show only a slight change under 20 GPa, indicating that the effect of pressure on the electronic properties of Na- and Mg-montmorillonite is weak. The bulk modulus, shear modulus, Young’s modulus, shear wave velocity and compression wave velocity of Na- and Mg-montmorillonite are positively correlated with the external pressure, and the other mechanical parameters have a little change. The calculated studies will be useful to explore experiments in the future from a purely scientific point of view.

Flow-type landslides are an important hazard that can cause great destruction due to the rapid flow velocity and large disaster area. This paper presents a catastrophic flowslide that recently occurred at a landfill in Shenzhen, China. This disaster involved an area about 1100 m in length and 630 m in maximum width, and caused the death of 77 people and the destruction of 33 buildings. The precise reason for the landfill’s failure is still unknown, and therefore we try to contribute an increased understanding of the event for future prevention. In this study, the failure mechanism of the studied slope was analyzed and described under partially saturated condition. The solid–fluid transition during the flowslide occurrence was described using a unified constitutive model. The model was used to perform the hydro-elasto-plastic modeling in the pre-failure stage, the viscous modeling in the post-failure stage, and the second-order work criterion was introduced in between to model the solid–fluid transition. The consistent evolution of the flowslide, including initiation, propagation, and deposit stages, was simulated and analyzed using the finite element method with Lagrangian integration points after careful calibration of the viscous parameters. The numerical results were compared with the real case and used to explain the failure mechanism.

This paper investigated mechanical behaviors and monotonic plasticity of a new type of high strength and high ductility meta steel with negative Poisson’s ratio effect (termed as NPR steel in this study). NPR steel can postpone necking initiation, so it has a high uniform elongation of 55.3% and a high elongation till fracture of 61.7% in this study. Classical plasticity theory postulates that metals have a constant Poisson’s ratio of 0.5 under plastic straining, but Poisson’s ratio of NPR steel decreases from around 0.5 to 0.44 at the plastic stage. In this paper, experimental and numerical studies on the new material were conducted, and four types of conventional engineering steels were also investigated for comparison. For each type of steel, coupons of three different gauge lengths were tested to examine the size effect. Full-range true stress – true strain relationships of the five types of steels under monotonic tension were obtained by a unified post-necking modification method newly proposed in this study, and numerical results compared well with the corresponding experimental ones. Finally, a unified plasticity model and ductile fracture parameters were presented for the steels.

A nanostructured surface layer was fabricated on commercial pure tungsten using the method of surface mechanical attrition treatment (SMAT). The microstructure evolution of the surface layer was characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and its formation mechanism was discussed as well. Both refinement and elongation of the brittle W grains were confirmed. The elongated SMATed W was heavily strained, the maximum value of the strain at the grain boundaries reaches as high as 3–5%. Dislocation density in the SMATed W nanograins was found to be 5 × 1012 cm−2. The formation of the nanograins in the top surface layer of the W was ascribed to the extremely high strain and strain rate, as well as the multidirectional repetitive loading. Bending strength of commercial W could be improved from 825 MPa to 1850 MPa by SMAT process. Microhardness results indicated the strain range in SMATed W can reach up to 220 μm beneath the top surface. The notched Charpy testing results demonstrated that SMATed W possess higher ductility than that of commercial W. The top surface of the W plates with and without SMATe processing possesses residual compressive stress of about −881 MPa and −234 MPa in y direction, and −872 MPa and −879 MPa in x direction respectively. The improvement of toughness (DBTT shift) of SMATed W may be the synergistic effect of residual compressive stress, dislocation density improvement and microstructure refinement induced by SMAT processing. SMAT processing could be a complementary method to further decrease the DBTT value of tungsten based materials.

Coal mass is a typical sedimentary rock mass with three approximately orthogonal discontinuity sets: bedding planes, face cleats and butt cleats. The mechanical anisotropy of coal masses is dependent on this fabric to a large extent. In this paper, a framework incorporating X-ray computed tomography (CT) scanning, statistical analysis, the fracture tensor based methodology and a numerical stress analysis technique is proposed to detect, construct, quantify and simulate the fracture networks in coal blocks. The CT scanning was first used to obtain the geometric information of the fractures in cubic coal blocks. Then a statistical numerical procedure was proposed to estimate and construct the locations, orientations and sizes of the fractures. An overall assessment of the constructed fracture networks was next made using the fracture tensor based methodology to incorporate all the important features: number of joint sets, joint density, joint orientation and joint size. The fracture networks in cubic blocks were then numerically simulated through a proposed modified fictitious joint procedure to accommodate a large quantity of non-persistent joints with an acceptable numerical stress analysis effort. The framework was validated at different stages to evaluate the reliability. Finally, the implementation of this framework is shown by a numerical investigation of the influence of the fracture networks and confining stresses on the jointed coal mass strength. The proposed framework provides a systematic and innovative method to tackle the fracture network induced mechanical anisotropy of the fractured rock masses.

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Study of intact rock failure criteria is an important topic in rock mechanics. In this study, applicability of nine different intact rock failure criteria is investigated for intact coal strength data. PFC3D modeling was used to simulate the laboratory polyaxial tests for cubic intact coal blocks of side dimension 110 mm under different confining stress combinations. A modified grid search procedure is proposed and used to find the best-fitting parameter values and to calculate the coefficient of determination (R 2) values for each criterion. Detailed comparisons of the nine criteria are made using the following aspects: R 2 values, σ 1 − σ 2 plots for different σ 3, shapes on the deviatoric plane, linearity or nonlinearity on the meridian planes. Through the comparisons of R 2 values, σ 1 − σ 2 plots and meridian lines, the modified Wiebols–Cook and modified Lade criteria were found to fit the intact coal strength data best. The nine failure criteria are categorized into three types based on the appearances on the deviatoric plane.

A nanostructured laminar W-La2O3 alloy (WL10) with improved ductility was prepared using a surface mechanical attrition treatment (SMAT). φ1.5 mm ZrO2 WL10 balls subjected to SMAT (called φ1.5 mm ZrO2 ball SMATed WL10) samples possess the best surface profile and excellent integrated mechanical properties (the ductile-brittle transition temperature (DBTT) value decreases by approximately 200 °C, and the bending strength decreases by 100 Mpa). A highly dense group of laminates was detected near the surface of the φ1.5 mm ZrO2 ball SMATed WL10 sample. The SMATed WL10 laminates were composed of a micro-grain layer, an ultrafine-grain layer and a nanosized-grain layer. The nanostructured laminar surface layer of the φ1.5 mm ZrO2 ball SMATed WL10 sample is approximately 1–2 μm. The top surface of the WL10 plates with and without the SMAT process possesses residual compressive stress of approximately −883 MPa and −241 MPa, respectively, in the y direction and −859 MPa and −854 MPa, respectively, in the x direction. The SMAT process could be a complementary method to further improve the toughness of tungsten-based materials.

In this study, laboratory tests were conducted to obtain the geomechanical properties for the coal matrix and coal discontinuities. Computed tomography (CT) scanning technology was then used to detect the pre-existing fracture networks of the cubic coal blocks. Fracture tensor–based methodology was used to quantify the fracture geometry network that exists inside the cubic coal blocks. The same cubic coal blocks were subjected to the true triaxial tests to obtain the jointed coal mass strength (JCMS) values under different confining stresses. The fracture network constructed from the CT scanning was incorporated into the numerical model of jointed coal block to simulate the laboratory true triaxial tests, and to first calibrate the parameter values of the numerical model and then validate them. More numerical true triaxial tests were performed on some jointed coal blocks with selected fracture networks and five additional artificial fracture networks under different confining stress combinations t...

Heavy metal pollution is currently of great concern because it has been recognized as a potential threat to air, water, and soil. Adsorption was one of the most popular methods for the removal of heavy metal. The adsorption of heavy metal Cd, Cu, Hg, and Ni(II) atoms on the hydroxylated (0 0 1) surface of kaolinite was investigated using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics were systematically studied for a wide range of coverage Θ [from 0.11 to 1.0 monolayers (ML)] and adsorption sites. The most stable among all possible adsorption sites for Cd(II) atom was the two-fold bridge site followed by the one-fold top site, and the top site was the most favorite adsorption site for Cu and Ni(II) atoms, while the three-fold hollow site was the most stable adsorption site for Hg(II) atom followed by the two-fold bridge site. The adsorption energy increases with the coverage for Cd, Cu, and Hg(II) atoms, thus indicating the higher stability of surface adsorption and a tendency to the formation of adsorbate islands (clusters) with increasing the coverage. However, the adsorption energy of Ni(II) atoms decreases when increasing the coverage. The adsorption capabilities of the kaolinite clay for the heavy metal atoms were in the order of Ni > Cu > Cd > Hg(II). The other properties of the Cd, Cu, Hg, and Ni(II)/kaolinite(0 0 1) system including the different charge distribution, the lattice relaxation, and the electronic density of states were also studied and discussed in detail.

The capture and storage of carbon dioxide (CO2) have considerable potential for mitigating climate change. Adsorption is one of the most popular methods for the storage of CO2. The adsorption of CO2 molecules on the hydroxylated (001) surface of kaolinite was investigated using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics was studied systematically for a wide range of coverage, Θ [from 0.11 to 1.0 monolayers (ML)], and adsorption sites. The CO2 was adsorbed on the two-fold bridge-x (see the text for a definition) and the one-fold top-x sites in the bent, recumbent configuration, and on the three-fold hollow-z, two-fold bridge-z site, and the one-fold top-z sites in the vertical configuration. The surface-adsorbed binding site of CO2 was strongest at the bridge-x site and weakest at the top-z site. The adsorption energy increased with coverage, thus indicating the greater stability of surface adsorption and a tendency to form CO2 islands (clusters) with increasing coverage. The other properties of the CO2/kaolinite (001) system, including the different charge distribution, the lattice relaxation, and the electronic density of states, were also studied and are discussed in detail.

The adsorption and diffusion of Pb(II) atom on the hydroxylated (001) surface of kaolinite were investigated using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics was systematically studied for a wide range of coverage Θ [from 0.11 to 1.0 monolayers (ML)] and adsorption sites. The most stable among all possible adsorption sites was the two-fold bridge site followed by the one-fold top site, and the adsorption energy increased with the coverage, thus indicating the higher stability of surface adsorption and a tendency to the formation of Pb(II) islands (clusters) with increasing coverage. Moreover, the energy barrier for diffusion of Pb(II) atom between the one-fold top and the two-fold bridge adsorption sites on kaolinite(001) surface was 0.23 (0.31) eV, implying that the Pb(II) atom is prone to diffusing on kaolinite(001) surface. The other properties of the Pb(II)/kaolinite(001) system including the different charge distribution, the lattice relaxation, and the electronic density of states were also studied and discussed in detail.

Kaolinite is often a cause of deformation in soft-rock tunnel engineering, leading to safety problems. The mechanism of the deformation is closely related to the interaction between kaolinite and water molecules. Because kaolinite has multiple defects, the effects of Mg, Ca, and Fe(II) doping on the atomic structure of the kaolinite (001) surface, and the subsequent adsorption and penetration of H2O into the interlayer, were studied systematically using density-functional theory. The results showed that for the Mg-, Ca-, and Fe(II)-doped kaolinites (001), the surface relaxation around the doping layer changed from contraction to expansion, due to the redistribution of electrons. The adsorption energies of the H2O monomer on Mg-, Ca-, and Fe(II)-doped kaolinites (001) were less than on undoped kaolinite (001). The results further revealed that the H2O molecule can also adsorb on the hollow site on the second-layer O surface of the Mg-, Ca-, and Fe(II)-doped kaolinites (001). For the undoped kaolinite, however, the H2O molecule adsorbs on the surface only. The energetic barriers for penetration of H2O from the adsorption site on the surface to the adsorption site on the O surface of Mg-, Ca-, and Fe(II)-doped kaolinites were also calculated: 1.18 eV, 1.07 eV, and 1.41 eV, respectively. The results imply that the influences of Mg, Ca, and Fe(II) doping on kaolinite allow the adsorbed water molecules to penetrate from the on-surface adsorption site to the O-surface site.

Kaolinite is often a cause of deformation in soft-rock tunnel engineering, leading to safety problems. In order to gain a better predictive understanding of the governing principles associated with this phenomenon, the physical and chemical properties of kaolinite were investigated using an efficient, firstprinciples scheme for studying isomorphic substitution of Al ions in kaolinite by two kinds of other elements (namely, the dual defect). Elements that are relatively common in natural kaolinite were chosen from groups II (Be, Mg, Ca, and Sr) and III (Fe and Sc) of the Periodic Table as dual-defect ions to substitute for Al ions in kaolinite. By systematically calculating the impurity-formation energies (which characterize the difference in the total crystal energy before and after the defect arises) and transitionenergy levels, which characterize the energy cost for the transformation between two different charge states, the (Be + Sc)Al (i.e. the replacement of two specific Al ions in kaolinite by external Be and Sc ions), (Ca + Sc)Al, (Mg + Sc)Al, and (Sr + Sc)Al ion pairs were determined to have low formation energies, suggesting that these combinations of ions can easily substitute for Al ions in kaolinite. The (Be + Fe)Al, (Ca + Fe)Al, (Mg + Fe)Al, and (Sr + Fe)Al ion pairs have relatively high formation energies which make isomorphic substitution (or doping) in kaolinite difficult. Moreover, these combinations of elements from groups II and III were found to have relatively low transition-energy levels compared with other element pairs. Among them, (Sr + Sc)Al have the lowest transition-energy level at 0.06 eV above the valence band maximum. When compared with single external substitutional defects in kaolinite, remarkably, the dual defects have relatively low formation energies and transition-energy levels. The results are helpful in understanding the chemical and physical properties of natural kaolinite.

It is a key step of finite element method analysis to generate engineering structure mesh. The continuous conceptual model of discontinuous substance is studied. How to select similar-continuous micro-particle size is researched. The continuous conceptual model of soil body and the continuous conceptual method of geotechnical engineering are approached based on the deep mixing pile composite foundation. The results show that finite element method mesh generation based on material-continuous-nature need to more consider, and the minimum of the element size is those of similar-continuous micro-particle and the maximum is limited by the scope of geotechnical engineering project. While the material continuous nature is considered, the continuum theory would be satisfied to simulate engineering structure with finite element method.

Using the first-principles methods, we study the formation energetics and charge doping properties of the extrinsic substitutional defects in montmorillonite. Especially, we choose Be , Mg , Ca , Fe , Cr , Mn , Cu , Zn as extrinsic defects to substitute for Al atoms. By systematically calculating the impurity formation energies and transition energy levels, we find that all Group II defects introduce the relative shallow transition energy levels in montmorillonite. Among them, Mg Al has the shallowest transition energy level at 0.10 eV above the valence band maximum. The transition-elemental defects Fe Al , Cr Al , and Mn Al are found to have relatively low formation energies, suggesting their easy formation in montmorillonite under natural surrounding conditions. Our calculations show that the defects Cu Al and Zn Al have high formation energies, which exclude the possibility of their formation in montmorillonite.

This paper presents a new inverse analysis approach for identifying material properties and unknown geometries for multi-region problems using the Boundary Element Method (BEM). In this approach, the material properties and coordinates of an unknown region boundary are taken as the optimization variables, and the sensitivity coefficients are computed by the Complex-Variable-Differentiation Method (CVDM). Due to the use of CVDM, the sensitivity coefficients can be accurately determined in a way that is as simple to use as the Finite Difference Method (FDM) and an inverse analysis for a complex composite structure can be easily performed through a similar procedure to the direct computation. Although basic integral equations are presented for heat conduction problems, the application of the proposed algorithm to other problems, such as elastic problems, is straightforward. Two numerical examples are given to demonstrate the potential of the proposed approach.

Density functional theory is used to investigate the adsorption, diffusion, and dissociation of H2O on kaolinite(001) surface. It is found that the preferred adsorption sites on the kaolinite(001) surface for H2O are the threefold hollow sites with the adsorption energies ranging from 1.06 to 1.15 eV. H2O does not adsorb on the six-fold hollow site of the aluminium(001) face of the third layer of kaolinite, implying that it is difficult for water molecules to penetrate the ideal kaolinite(001) surface. In addition, we calculate the energetic barriers for the diffusion of H2O between the most stable and next most stable adsorption sites, which range from 0.073 to 0.129eV. The results also show that H2O molecules are easy to diffuse on kaolinite(001) surface. Finally, our study indicates that no dissociation state exists for the H2O on kaolinite(001) surface.