Strainburst is the most common type of rockbursts. The research of strainburst damage mechanisms is helpful to improve and optimize the rock support design in the burst-prone ground. In this study, an improved global-local modeling approach was first adopted to study strainburst damage mechanisms. The extracted stresses induced by multiple excavations from a three-dimensional (3D) global model established by fast Lagrangian analysis of continua in 3 dimensions (FLAC3D) are used as boundary conditions for a two-dimensional (2D) local model of a deep roadway built by universal distinct element code (UDEC) to simulate realistic stress loading paths and conduct a detailed analysis of rockburst damage from both micro and macro perspectives. The results suggest that the deformation and damage level of the roadway gradually increase with the growth of surrounding rock stress caused by the superposition of mining- or excavation-induced stresses of the panel and nearby roadways. The significant increase of surrounding rock stresses will result in more accumulated strain energy in two sidewalls, providing a necessary condition for the strainburst occurrence in the dynamic stage. The strainburst damage mechanism for the study site combines three types of damage: rock ejection, rock bulking, and rockfall. During the strainburst, initiation, propagation, and development of tensile cracks play a crucial role in controlling macroscopic failure of surrounding rock masses, although the shear crack always accounts for the main proportion of damage levels. The deformation and damage level of the roadway during a strainburst positively correlate with the increasing peak particle velocities (PPVs). The yielding steel arch might not dissipate kinetic energy and mitigate strainburst damage effectively due to the limited energy absorption capacity. The principles to control and mitigate strainburst damage are proposed in this paper. This study presents a systematic framework to investigate strainburst damage mechanisms using the global-local modeling approach.

Modeling unsaturated flow in fractured rocks is essential in various subsurface engineering applications, but it remains a great challenge due to the difficulties in determining the unsaturated hydraulic properties of rocks that contain various scales of fractures. It is generally accepted that the van Genuchten (VG) model can be applied to fractured rocks, provided that the hydraulic parameters could be representatively determined. In this study, scaling relationships between the VG parameters (α and n) and hydraulic conductivity (K) across 8 orders of magnitude, from 10−10 m/s to 10−2 m/s, were proposed by statistical analysis of data obtained from 1416 soil samples. The correlations were then generalized to predict the upper bounds of VG parameters for fractured rocks from the K data that could be obtained more easily under field conditions, and were validated against a limited set of data from cores, fractures and fractured rocks available in the literature. The upper bound estimates significantly narrow the ranges of VG parameters, and the representative values of α and n for fractured rocks at the field scale can then be determined with confidence by inverse modeling using groundwater observations in saturated zones. The proposed methodology was applied to saturated-unsaturated flow modeling in the right-bank slope at the Baihetan dam site with a continuum approach, showing that most of the flow behaviors in fractured rocks in this complex hydrogeological condition could be properly reproduced. The proposed method overcomes difficulties in suction measurement in fractured rocks with strong heterogeneity, and provides a feasible way for modeling of saturated-unsaturated flow in fractured rocks with acceptable engineering accuracy.

Underground rock dynamic disasters are becoming more severe due to the increasing depth of human operations underground. Underground temperature and pressure conditions contribute significantly to these disasters. Therefore, it is important to understand the coupled thermo-mechanical (TM) behaviour of rocks for the long-term safety and maintenance of underground tunnelling and mining. Moreover, investigation of the damage, strength and failure characteristics of rocks under triaxial stress conditions is important to avoid underground rock disasters. In this study, based on Weibull distribution and Lemaitre’s strain equivalent principle, a statistical coupled TM constitutive model for sandstone was established under high temperature and pressure conditions. The triaxial test results of sandstone under different temperature and pressure conditions were used to validate the model. The proposed model was in good agreement with the experimental results up to 600 °C. The total TM damage was decreased with increasing temperature, while it was increased with increasing confining pressure. The model’s parameters can be calculated using conventional laboratory test results.

Large shear deformation problems are frequently encountered in geotechnical engineering. To expose the shear failure mechanism of rock tunnels, compression-shear tests for rock models with circular tunnel were carried out, including single tunnel and adjacent double tunnels. The failure process is recorded by the external video and miniature cameras around the tunnel, accompanied by real-time acoustic emission monitoring. The experiments indicate that the shearing processes of rock tunnel can be divided into four steps: (i) cracks appeared around tunnels, (ii) shear cracks and spalling ejection developed, (iii) floor warping occurred, and (iv) shear cracks ran through the tunnel model. Besides, the roughness of the sheared fracture surface decreased with the increase in normal stress. Corresponding numerical simulation indicates that there are tensile stress concentrations and compressive stress concentrations around the tunnel during the shearing process, while the compressive stress concentration areas are under high risk of failure and the existence of adjacent tunnels will increase the degree of stress concentration.

The rationality of using strain energy storage index (Wet) for evaluating rockburst proneness was theoretically verified based on linear energy storage (LES) law in this study. The LES law is defined as the linear relationship between the elastic strain energy stored inside the solid material and the input strain energy during loading. It is used to determine the elastic strain energy and dissipated strain energy of rock specimens at various loading/unloading stress levels. The results showed that the Wet value obtained from experiments was close to the corresponding theoretical one from the LES law. Furthermore, with an increase in the loading/unloading stress level, the ratio of elastic strain energy to dissipated strain energy converged to the peak-strength strain energy storage index (Wetp). This index is stable and can better reflect the relative magnitudes of the stored energy and the dissipated energy of rocks at the whole pre-peak stage than the strain energy storage index. The peak-strength strain energy storage index can replace the conventional strain energy storage index as a new index for evaluating rockburst proneness.

Debris flows are rapid mass movements with a mixture of rock, soil and water. High-intensity rainfall events have triggered multiple debris flows around the globe, making it an important concern from the disaster management perspective. This study presents a numerical model called debris flow simulation 2D (DFS 2D) and applicability of the proposed model is investigated through the values of the model parameters used for the reproduction of an occurred debris flow at Yindongzi gully in China on 13 August 2010. The model can be used to simulate debris flows using three different rheologies and has a user-friendly interface for providing the inputs. Using DFS 2D, flow parameters can be estimated with respect to space and time. The values of the flow resistance parameters of model, dry-Coulomb and turbulent friction, were calibrated through the back analysis and the values obtained are 0.1 and 1000 m/s2, respectively. Two new methods of calibration are proposed in this study, considering the cross-sectional area of flow and topographical changes induced by the debris flow. The proposed methods of calibration provide an effective solution to the cumulative errors induced by coarse-resolution digital elevation models (DEMs) in numerical modelling of debris flows. The statistical indices such as Willmott's index of agreement, mean-absolute-error, and normalized-root-mean-square-error of the calibrated model are 0.5, 1.02 and 1.44, respectively. The comparison between simulated and observed values of topographic changes indicates that DFS 2D provides satisfactory results and can be used for dynamic modelling of debris flows.

Dynamic failure of rock masses around deep tunnels, such as fault-slip rockburst and seismic-induced collapse, can pose a significant threat to tunnel construction safety. One of the most significant factors that control the accuracy of its risk assessment is the estimation of the ground motion around a tunnel caused by seismicity events. In general, the characteristic parameters of ground motion are estimated in terms of empirical scaling laws. However, these scaling laws make it difficult to accurately estimate the near-field ground motion parameters because the roles of control factors, such as tunnel geometry, damage zone distribution, and seismic source parameters, are not considered. For this, the finite fracturing seismic source model (FFSSM) proposed in this study is used to simulate the near-field ground motion characteristics around deep tunnels. Then, the amplification effects of ground motion caused by the interaction between seismic waves and deep tunnels and corresponding control factors are studied. The control effects of four factors on the near-field ground motion amplification effect are analyzed, including the main seismic source wavelength, tunnel span, tunnel shape, and range of damage zones. An empirical formula for the maximum amplification factor (αm) of the near-field ground motion around deep tunnels is proposed, which consists of four control factors, i.e. the wavelength control factor (Fλ), tunnel span factor (FD), tunnel shape factor (Fs) and excavation damage factor (Fd). This empirical formula provides an easy approach for accurately estimating the ground motion parameters in seismicity-prone regimes and the rock support design of deep tunnels under dynamic loads.

While experimental designs developed in recent decades have contributed to research on dynamic nonequilibrium effects in transient two-phase flow in porous media, this problem has been seldom investigated using direct numerical simulation (DNS). Only a few studies have sought to numerically solve Navier–Stokes equations with level-set (LS) or volume-of-fluid (VoF) methods, each of which has constraints in terms of meniscus dynamics for various flow velocities in the control volume (CV) domain. The Shan–Chen multiphase multicomponent lattice Boltzmann method (SC-LBM) has a fundamental mechanism to separate immiscible fluid phases in the density domain without these limitations. Therefore, this study applied it to explore two-phase displacement in a single representative elementary volume (REV) of two-dimensional (2D) porous media. As a continuation of a previous investigation into one-step inflow/outflow in 2D porous media, this work seeks to identify dynamic nonequilibrium effects on capillary pressure–saturation relationship (Pc–S) for quasi-steady-state flow and multistep inflow/outflow under various pressure boundary conditions. The simulation outcomes show that Pc, S and specific interfacial area (anw) had multistep-wise dynamic effects corresponding to the multistep-wise pressure boundary conditions. With finer adjustments to the increase in pressure over more steps, dynamic nonequilibrium effects were significantly alleviated and even finally disappeared to achieve quasi-steady-state inflow/outflow conditions. Furthermore, triangular wave-formed pressure boundary conditions were applied in different periods to investigate dynamic nonequilibrium effects for hysteretical Pc–S. The results showed overshoot and undershoot of Pc to S in loops of the nonequilibrium hysteresis. In addition, the flow regimes of multistep-wise dynamic effects were analyzed in terms of Reynolds and capillary numbers (Re and Ca). The analysis of REV-scale flow regimes showed higher Re (1 < Re < 10) for more significant dynamic nonequilibrium effects. This indicates that inertia is critical for transient two-phase flow in porous media under dynamic nonequilibrium conditions.

Pore pressure is an essential parameter for establishing reservoir conditions, geological interpretation and drilling programs. Pore pressure prediction depends on information from various geophysical logs, seismic, and direct down-hole pressure measurements. However, a level of uncertainty accompanies the prediction of pore pressure because insufficient information is usually recorded in many wells. Applying machine learning (ML) algorithms can decrease the level of uncertainty of pore pressure prediction uncertainty in cases where available information is limited. In this research, several ML techniques are applied to predict pore pressure through the over-pressured Eocene reservoir section penetrated by four wells in the Mangahewa gas field, New Zealand. Their predictions substantially outperform, in terms of prediction performance, those generated using a multiple linear regression (MLR) model. The geophysical logs used as input variables are sonic, temperature and density logs, and some direct pore pressure measurements were available at the reservoir level to calibrate the predictions. A total of 25,935 data records involving six well-log input variables were evaluated across the four wells. All ML methods achieved credible levels of pore pressure prediction performance. The most accurate models for predicting pore pressure in individual wells on a supervised basis are decision tree (DT), adaboost (ADA), random forest (RF) and transparent open box (TOB). The DT achieved root mean square error (RMSE) ranging from 0.25 psi to 14.71 psi for the four wells. The trained models were less accurate when deployed on a semi-supervised basis to predict pore pressure in the other wellbores. For two wells (Mangahewa-03 and Mangahewa-06), semi-supervised prediction achieved acceptable prediction performance of RMSE of 130–140 psi; while for the other wells, semi-supervised prediction performance was reduced to RMSE > 300 psi. The results suggest that these models can be used to predict pore pressure in nearby locations, i.e. similar geology at corresponding depths within a field, but they become less reliable as the step-out distance increases and geological conditions change significantly. In comparison to other approaches to predict pore pressures, this study has identified that application of several ML algorithms involving a large number of data records can lead to more accurate prediction results.

Large-scale discontinuities can significantly affect the mechanical properties of rock masses. However, the tensile behavior of rock discontinuities is often less investigated. To study the statistical characteristics of failure strength and fracture characteristics of rock discontinuities, Brazilian disc tests were conducted on limestone specimens with a single natural discontinuity at different load-discontinuity angles (β). In this study, β=0° and β=90° correspond to the discontinuity parallel and perpendicular to loading direction, respectively. The results show that Brazilian failure strength (BFS) can reasonably represent the tensile strength of rock with discontinuities, by comparing the BFS and tensile stress in the disc center at peak force. The two-parameter Weibull distribution can capture the statistical BFS characteristics of rock discontinuities parallel to loading direction (β=0°) and at different load-discontinuity angles (β≠0°). All specimens with discontinuity at different load-discontinuity angles show more plastic deformational behaviour than intact rock specimen. With increasing β, the mean BFS of limestone with discontinuity increases before reaching a plateau at β=45°. The single plane of weakness theory best explains the BFS of fractured limestone with β. Only a specific segment of pre-existing rock discontinuity could affect the fracture process. When β=0°, interfacial cracks and alternative cracks formed. When β≠0°, mixed failure mode with shear and tensile failure occurred, particularly when β=30° and β=60°. The findings can contribute to better understanding the failure and fracture characteristics of rock with discontinuities, particularly the interaction of pre-existing discontinuities with stress-induced fracturing.

This paper attempts to study dolomite failure using small-scale blast tests. The experimental setup consisted of a cylindrical specimen with a central borehole fitted with a detonation cord inside a copper pipe. The specimen was confined using lead material. During the test, acceleration histories were recorded using sensors placed on the lead confinement. The results showed that heterogeneity and initial cracks significantly influenced the observed failure and cracking patterns. The tests were numerically represented using the previously validated Johnson-Holmquist II (JH-2) constitutive model. The properties of the detonation cord were first determined and verified in a special test with a lead specimen to compare the deformation in the test with that of numerical simulation. Then, the small-scale blast test was simulated, and the failure of the dolomite was compared with the test observations. Comparisons of acceleration histories, scabbing failure, and number of radial cracks and crack density confirmed the overall repeatability of the actual testing data. It is likely that the proposed model can be further used for numerical studies of blasting of dolomite rock.

An analysis of tunnel face stability generally assumes a single homogeneous rock mass. However, most rock tunnel projects are excavated in stratified rock masses. This paper presents a two-dimensional (2D) analytical model for estimating the face stability of a rock tunnel in the presence of rock mass stratification. The model uses the kinematical limit analysis approach combined with the block calculation technique. A virtual support force is applied to the tunnel face, and then solved using an optimization method based on the upper limit theorem of limit analysis and the nonlinear Hoek–Brown yield criterion. Several design charts are provided to analyze the effects of rock layer thickness on tunnel face stability, tunnel diameter, the arrangement sequence of weak and strong rock layers, and the variation in rock layer parameters at different positions. The results indicate that the thickness of the rock layer, tunnel diameter, and arrangement sequence of weak and strong rock layers significantly affect the tunnel face stability. Variations in the parameters of the lower layer of the tunnel face have a greater effect on tunnel stability than those of the upper layer.

This work aims to investigate the mechanical behaviour of medium-grained sandstones under cyclic loading with different loading/unloading rates. This type of cyclic loading is called differential cyclic loading (DCL) and is considered for testing rock behaviour. In the experiments, constant amplitude and multi-level cyclic loadings were performed. Three loading modes were designed to consider different relationships between loading and unloading rates. Axial strain evolution and energy dissipation were analysed for different loading/unloading rates and maximum cyclic load level. The correlations between P-wave velocities and strengths of rocks deduced from this research are compared with existing published data. The relationships between final strength and axial strain at failure under different loading patterns were also discussed and a rough assessment of the remaining fatigue life is introduced using the predicted value by fitting the axial peak strain.

In deep ground engineering, the use of high-strength and high-toughness steels for rock bolt can significantly improve its energy absorption capacity. However, the mechanisms and effects of rock loading conditions on this kind of high energy-absorbing steel for rock bolt remain immature. In this study, taking Muzhailing highway tunnel as the background, physically based crystal plasticity simulations were performed to understand the effect of rock loading rate and pretension on the deformation behaviors of twinning induced plasticity (TWIP) steel used for rock bolt. The material physical connecting to the underlying microscopic mechanisms of dislocation glide and deformation twinning were incorporated in numerical modeling. The rock loading conditions were mimicked by the real-time field monitoring data of the NPR bolt/cable equipment installed on the tunnel surrounding rock surface. The results indicate that the bolt rod exhibits pronounced deformation-softening behavior with decrease of the loading rate. There is also a sound deformation-relaxation phenomenon induced by the dramatic decrease of loading rate after pre-tensioning. The high pretension (>600 MPa or 224 kN) can help bolt rod steel resist deformation-softening behavior, especially at low loading rate (<10−1 MPa/s or 10−2 kN/s). The loading rate was found to be a significant factor affecting deformation-softening behavior while the pretension was found to be the major parameter accounting for the deformation-relaxation scenario. The results provide the theoretical basis and technical support for practical applications.

The use of explosives is restricted on some important holidays, and the handling of unexploded charge is very dangerous. Therefore, an innovative non-explosive technology called instantaneous expansion (IE) was developed for tunneling. IE, whose components are derived from solid wastes such as coal gangue and straw conduces to realizing the reuse of waste. Moreover, its cost is lower than explosives. Blind guns of IE are easy to treat with water. The IE tunneling method is classified into two categories, i.e. IE with a single fracture (IESF) and IE with multiple fractures (IEMF), which are used to form the tunnel cross-section directionally cross-section and to fragment the rocks inside the cross-section, respectively. In this study, the principle of IE tunneling was elaborated first. Then, tunneling experiments and numerical simulations were performed on IE, conventional blasting (CB) and shaped charge blasting (SCB) in comparison. The experimental and numerical results show that IE achieved the best performance of directional rock breaking and corresponded to the most minor excavation-induced damage zone of the surrounding rock. Besides, the tunnel cross-section created by IE was flat and smooth. Comparing IE with CB and SCB, the over/under-excavation area decreased by 64% and 17%, and the excavation-induced damage zone fell by 26% and 11%, respectively. The range of the loose circle is reduced, which is conducive to improving the long-term stability of the roadway. The research provides a safe and economical tunneling method with excellent application prospects.

Tamusu mudstone, located in Bayin Gobi Basin in Inner Mongolia of China, has been selected as a potential host rock for high-level radioactive waste (HLW) disposal in China. A series of tests has been carried out, including X-ray diffraction (XRD) tests, scanning electron microscopy (SEM) tests, disintegration tests, permeability tests and triaxial compression tests, to estimate the physico-mechanical properties of Tamusu mudstone in this work. The mineral composition of Tamusu mudstone was analyzed and it was considered as a stable rock due to its low disintegration rate, i.e. approximately 0.11% after several wet/dry cycles. Based on the results of permeability test, it was found that Tamusu mudstone has a low permeability, with the magnitude of about 10–20 m2. The low permeability makes the mudstone well prevent nuclide migration and diffusion, and might be influenced by temperature. The triaxial tests show that Tamusu mudstone is a stiff mudstone with high compressive strength, which means that the excavation disturbed zone would be smaller compared to other types of mudstone due to construction and operation of HLW repositories. Finally, the properties of Tamusu mudstone were compared with those of Opalinus clay, Callovo-Oxfordian (COx) argillite, and Boom clay to further discuss the possibility of using Tamusu mudstone as a potential nuclear waste disposal medium.

In the present study, we tried to understand the spatially distributed damage in sandstone samples under the coupled stress-freeze-thaw (SFT) conditions. Firstly, uniaxial compressive stresses (i.e. 0 MPa, 10 MPa, 20 MPa, and 25 MPa) were applied to the samples, and then freeze-thaw (FT) cycles (0, 8, 16, and 24) were performed on the uniaxially stressed samples to realize the SFT coupling. Next, real-time CT scanning was conducted to observe the induced damage. The total porosity was introduced to quantitatively evaluate the damage degree. The local porosity variation, with the distance from the center of the sandstone sample, was analyzed to understand the spatial distribution of damage. Finally, the coupling effects of SFT on the damage gradient were discussed. The results indicate that the porosity rises with FT cycles, and the applied stresses can accelerate the increase in porosity. The damage increases exponentially with the distance from the center of the sample. The damage presents a spatial gradient distribution, not the commonly used uniform distribution in various studies. The damage gradient increases with FT cycles, and the increasing rate in damage gradient decreases at uniaxial stress of 0 MPa and 10 MPa first, but the increasing rate in damage gradient increases with FT cycles then at stress increasing to 20 MPa.

Tamusu mudstone formation, located in the Alxa area in western Inner Mongolia, is considered a potential host formation for high-level radioactive waste (HLW) underground disposal in China. In this study, complementary analyses with X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), mercury intrusion porosimetry (MIP), and N2 physisorption isotherm were conducted on the Tamusu mudstone to characterize its physical characteristics and microstructural features, such as mineral compositions and pore structure. Several minerals, including carbonates, feldspar, clays and analcime, were identified in Tamusu mudstone by XRD. Images from FE-SEM show that pores in the Tamusu mudstone were dominantly on nanometer scale and generally located within their mineral matrix or at the interface with non-porous minerals. The combination of the MIP and N2 physisorption curves indicated that the Tamusu mudstone has diverse pore sizes, a porosity varying from 2.34% to 2.84%, and a total pore volume in the range of 0.0065–0.0222 cm3/g with the average pore diameter ranging from 9.6 nm to 19.23 nm. The specific surface area measured by MIP (2.572–5.861 m2/g) was generally higher than that by N2 physisorption (1.29–3.04 m2/g), due to the pore network effect, pore shape (e.g. ink-bottle shape), or technique limits. The results related to pore information can be applied as an input in the future to model single- or multi-phase fluid flow and the transport of radionuclides in porous geomedium by migration and diffusion.

Seismic forward-prospecting in tunnels is an important step to ensure excavation safety. Nowadays, most advanced imaging techniques in seismic exploration involve calculating the solution of elastic wave equation in a certain coordinate system. However, considering the cylindrical geometry of common tunnel body, Cartesian coordinate system seemingly has limited applicability in tunnel seismic forward-prospecting. To accurately simulate the seismic signal received in tunnels, previous imaging method using decoupled non-conversion elastic wave equation is extended from Cartesian coordinates to cylindrical coordinates. The proposed method preserves the general finite-difference time-domain (FDTD) scheme in Cartesian coordinates, except for a novel wavefield calculation strategy addressing the singularity issue inherited at the cylindrical axis. Moreover, the procedure of cylindrical elastic reverse time migration (CERTM) in tunnels is introduced based on the decoupled non-conversion elastic wavefield. Its imaging effect is further validated via numerical experiments on typical tunnel models. As indicated in the synthetic examples, both the PP- and SS-images could clearly show the geological structure in front of the tunnel face without obvious crosstalk artifacts. Migration imaging using PP-waves can present satisfactory results with higher resolution information supplemented by the SS-images. The potential of applying the proposed method in real-world cases is demonstrated in a water diversion tunnel. In the end, we share our insights regarding the singularity treatment and further improvement of the proposed method.

Determining osmotic suction from the electrical conductivity (EC) of soil pore water was widely reported in the literature. However, while dealing with unsaturated soils, they do not have enough soil pore water to be extracted for a reliable measurement of EC. In this paper, the chilled-mirror dew-point hygrometer and contact filter paper method were used to determine the total and matric suctions for low-plasticity soils with different salinities (0.05‰, 2.1‰, and 6.76‰). A new piecewise function was proposed to calculate the osmotic suction, with the piecewise point corresponding to the first occurrence of precipitated salt in mixed salt solutions (synthetic seawater). EC, ion and salt concentrations used for osmotic suction calculation were transformed from the established relationships of mixed salt solution instead of experimental measurement. The calculated osmotic suction by the proposed equation and the equations in the literature was compared with the indirectly measured one (the difference between the measured total and matric suctions). Results showed that the calculated osmotic suction, especially the one calculated using the proposed function, was in fair agreement with the indirectly measured data (especially for specimens with higher salinity of 6.76‰), suggesting that the transformation of EC and concentrations from the established relationship is a good alternative to direct measurement for low-plasticity soil. In particular, the proposed method could be applied to unsaturated low-plasticity soils which do not have enough soil pore water for a proper EC measurement.

The evolution of shear bands and cracks plays an important role in landslides. However, there is no systematic method for classification of the cracks, which can be used to analyze the evolution of cracks in shear bands. In this study, X-ray computed tomography (CT) is used to observe the behavior of granite residual soil during a triaxial shear process. Based on the digital volume correlation (DVC) method, a crack classification method is established according to the connectivity characteristics of cracks before and after loading. Cracks are then divided into six classes: obsolete, brand-new, isolated, split, combined, and compound. With evolution of the shear bands, a large number of brand-new cracks accelerate the damages of materials at the mesoscale, resulting in a sharp decrease in strength. The volume of brand-new cracks increases rapidly with increasing axial strain, and their volume is greater than 50% when the strain reaches 12%, while the volume of compound cracks decreases from 54% to 21%. As cracks are the weakest areas in a material, brand-new cracks accelerate the development of shear bands. Finally, the coupling effect of shear bands and cracks destroys the soil strength.

Reasonable assessment of slope deformation under cyclic loading is of great significance for securing the safety of slopes. The observations of centrifuge model tests are analyzed on the slope deformation behavior under cyclic loading conditions. The potential slip surface is the key for slope failure and follows two rules: (i) the relative horizontal displacement along the potential slip surface is invariable at an elevation, and (ii) the soil along the slip surface exhibits the same degradation pattern. These rules are effective regardless of the location of the potential slip surface throughout the entire deformation process of a homogeneous slope, ranging from the initial deformation stage to the failure process and to the post-failure stage. A new, simplified method is proposed by deriving the displacement compatibility equation and unified degradation equation according to the fundamental rules. The method has few parameters that can be determined through traditional element tests. The predictions from the proposed method agree with the centrifuge test results with vertical loading and shaking table loading. This result confirms that the proposed method is effective in predicting the full deformation process of slopes under different cyclic loading conditions.

Dredged soil and phosphogypsum are frequently regarded as wasted materials, which require further treatment to control their environmental impact. Hence, phosphogypsum is proposed as a binder to stabilize dredged soil, aiming at efficiently reducing and reusing these waste materials. In this study, the engineering properties of cement-phosphogypsum stabilized dredged soils were investigated through a series of unconfined compression tests, and the effects of plasticity index of original soils on the strength improvement were identified. Then, the microstructure test and mineralogical test were performed to understand the mechanism of physical role of original soils in strength improvement. The results revealed that the unconfined compressive strength significantly decreased with the increase in plasticity index at the same binder content. The essential factor for strength improvement was found to be the formation of cementitious materials identified as calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH), and ettringite (Aft). The normalized integrated intensity of cementitious materials (CSH + CAH + Aft) by pore volume decreased with the increase in plasticity index. Consequently, the density of cementitious materials filling the soil pores controlled the effectiveness of strength improvement. More cementitious materials per pore volume were observed for the original soils with lower values of plasticity index. That is, the higher strength of stabilized soils with lower values of plasticity index was attributed to a packed structure forming by integrated fabric through denser cementitious components. It can be anticipated from the above findings that the effectiveness of stabilization treatment will significantly reduce with the increase in plasticity of origin soil.

In this paper, an anisotropic critical state model for saturated soils was extended to unsaturated conditions by introducing suction into its yield function. Combining this model with soil-water characteristic curves related to porosity ratio was employed to characterize the coupled hydromechanical behavior of unsaturated anisotropic soil. Based on the plane stress condition, the problem of the cylindrical cavity expansion in unsaturated anisotropic soils was transformed into first-order differential equations using the Lagrangian description. The equations were solved as an initial value problem using the Runge-Kutta algorithm, which can reflect the soil-water retention behavior during cavity expansion. Parametric analyses were conducted to investigate the influences of overconsolidation ratio (OCR), suction, and degree of saturation on the expansion responses of a cylindrical cavity in unsaturated anisotropic soil under plane stress condition. The results show that the above factors have obvious influences on the cavity responses, and the plane strain solution tends to overestimate expansion pressure and degree of saturation but underestimates suction around the cavity compared to the proposed plane stress solution. The theoretical model proposed in this paper provides a reasonable and effective method for simulating pile installation and soil pressure gauge tests near the ground surface of the unsaturated soils.

Geological storage of acid gas has been identified as a promising approach to reduce atmospheric carbon dioxide (CO2), hydrogen sulfide (H2S) and alleviate public concern resulting from the sour gas production. A good understanding of the relative permeability and capillary pressure characteristics is crucial to predict the process of acid gas injection and migration. The prediction of injection and redistribution of acid gas is important to determine storage capacity, formation pressure, plume extent, shape, and leakage potential. Herein, the existing experimental data and theoretical models were reviewed to gain a better understanding of the issue how the H2S content affects gas density, gas viscosity, interfacial tension, wettability, relative permeability and capillary pressure characteristics of acid gas/brine/rock systems. The densities and viscosities of the acid gas with different H2S mole fractions are both temperature- and pressure-dependent, which vary among the gas, liquid and supercritical phases. Water/acid gas interfacial tension decreases strongly with increasing H2S content. For mica and clean quartz, water contact angle increases with increasing H2S mole fraction. In particular, wettability reversal of mica to a H2S -wet behavior occurs in the presence of dense H2S. The capillary pressure increases with decreasing contact angle. At a given saturation, the relative permeability of a fluid is higher when the fluid is nonwetting. The capillary pressure decreases with decreasing interfacial tension at a given saturation. However, the existing datasets do not show a consistent link between capillary number and relative permeability. The capillary pressure decreases with increasing H2S mole fraction. However, there is no consensus on the effect of the H2S content on the relative permeability curves. This may be due to the limited availability of the relative permeability and capillary pressure data for acid gas/brine/rock systems; thus, more experimental measurements are required.

The mechanical characteristics and failure behavior of rocks containing flaws or discontinuities have received wide attention in the field of rock mechanics. When external loads are applied to rock materials, stress-induced cracks would initiate and propagate from the flaws, ultimately leading to the irreversible failure of rocks. To investigate the cracking behavior and the effect of flaw geometries on the mechanical properties of rock materials, a series of samples containing one, two and multiple flaws have been widely investigated in the laboratory. In this paper, the experimental results for pre-cracked rocks under quasi-static compression were systematically reviewed. The progressive failure process of intact rocks is briefly described to reveal the background for experiments on samples with flaws. Then, the nondestructive measurement techniques utilized in experiments, such as acoustic emission (AE), X-ray computed tomography (CT), and digital image correlation (DIC), are summarized. The mechanical characteristics of rocks with different flaw geometries and under different loading conditions, including the geometry of pre-existing flaws, flaw filling condition and confining pressure, are discussed. Furthermore, the cracking process is evaluated from the perspective of crack initiation, coalescence, and failure patterns.

Numerical back analysis is a valuable tool available to rock mechanics researchers and practitioners. Recent studies related to back analysis methods focused primarily on applications of increasingly sophisticated optimization algorithms (primarily machine learning algorithms) to rock mechanics problems. These methods have typically been applied to relatively simple problems; however, more complex back analyses continue to be conducted primarily through ad hoc manual trial-and-error processes. This paper provides a review of the basic concepts and recent developments in the field of numerical back analysis for rock mechanics, as well as some discussion of the relationship between back analysis and more broadly established frameworks for numerical modelling. The challenges of flexible constraints, non-uniqueness, material model limitations, and disparate data sources are considered, and representative case studies are presented to illustrate their impacts on back analyses. The role of back analysis (or “model calibration”) in bonded particle modelling (BPM), bonded block modelling (BBM), and synthetic rock mass (SRM) modelling is also considered, and suggestions are made for further studies on this topic.