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The decanoic acid-palmitic acid/SiO2@TiO2 phase change microcapsule (D-P-SiO2@TiO2 PCM) not only has the temperature regulation function, also it can degrade pollutants though photocatalysis and control humidity. In order to optimize the photocatalytic-humidity performance of the D-P-SiO2@TiO2 PCM, the uniform test was designed and RBF model was used to optimize the preparation parameters. The degradation rate of gaseous formaldehyde by the optimized D-P-SiO2@TiO2 PCM was 69.57% after 6 h and the moisture content was 0.0923–0.0940 g·g− 1 at 43.16–75.29% RH. The comparison result between model optimization and the experiment sample that prepared by using the optimized parameters showed that the theoretical photocatalytic-humidity performance target value was 2.0502, and the tested target value was 2.0757. The error of the two was only 1.24%, and both were bigger than the best value of uniform experimental. Micro-structure analysis of the optimized D-P-SiO2@TiO2 PCM showed that it had uniform spherical structure, the particle size was about 200 nm, the phase transition temperature range was between 16.97 ~ 28.94 oC, within the comfort range of human body. The optimized D-P-SiO2@TiO2 PCM had high specific surface area and multiple pore structure, so it can regulate air humidity. Further analysis of the preparation mechanism of D-P-SiO2@TiO2 PCM showed that the super-water system and acidic conditions were favorable for the hydrolysis of tetraethyl silicate to generate SiO2 with 3D short chain structure, so as to effectively encapsulate the decanoic acid-palmitic acid compound phase change material. The pH controlled 2 ~ 3 was necessary for hydrolyzing of tetraethyl titanate into anatase phase TiO2. The above is the basis conditions for preparing D-P-SiO2@TiO2 PCM with photocatalytic-humidity performance.

In rock engineering, damage evolution upon loading imposes significant impacts on the stiffness of rock mass and its deformation characteristics. In order to investigate the influence of both damage and plasticity on cavity expansion, a plastic damage solution is derived for undrained spherical cavity expansion in rock medium. For the consideration of plasticity-damage, Modified Cam-Clay (MCC) model is selected as the plasticity driver, a damage evolution criterion is adopted and coupled with MCC. The coupled damage MCC model is validated against experimental data in the literature. The proposed cavity expansion solution with the consideration of plasticity damage is verified through a classic solution in literature. The role of damage in undrained spherical cavity expansion is investigated by studying the spatial variations of effective stress, pore pressure and damage for cases with different stress ratios. Distribution of cavity expansion induced plastic and damage zones for cases with different stress ratios are also reproduced and discussed. Cavity expansion results show that, the damage zone should be considered for engineering application as the plastic zone is affected due to the damage evolution. In addition, the stability (e.g., radial stress) of rock mass is overestimated in classical solution without the consideration of damage zone.

ABSTRACT: In carbon capture and storage schemes, the carbon dioxide (CO2) can be injected at high pressures and low temperatures for permanent storage in deep reservoirs. In the North Sea, the storage sites will be predominantly sandstone. Triaxial tests on sandstone were conducted until failure using representative in-situ stresses to estimate the mechanical properties of the rock. A theoretical constitutive model, using Finite Element Modelling (FEM), describing the stress-strain behavior and damage evolution of rock during triaxial testing, is presented alongside the results of the tests. The model reproduced the experimental outcomes satisfactorily and was used to estimate the critical state mechanic parameters. Lower temperature indicated higher strength on sandstone, a decrease in the Poisson’s ratio and, consequently, damage increase. 1. INTRODUCTION Potential Carbon Capture and Storage (CCS) schemes include injecting liquid carbon dioxide (CO2) from ships into subsea formations for permanent storage. CO2 on a ship is stored at a temperature close to the triple point of CO2 at around -50°C~-57°C and exposed to almost 0.6~0.7 MPa pressure in order to keep the containment of the CO2 mixture in liquid form (Reppas et al., 2021, Wetenhall et al., 2014). The difference between the injected CO2 from a ship and the temperature of the wellbore wall, which is increasing by 30°C/km, is causing temperature fluctuations and external stresses. These loadings and their mechanical effects on the wellbore wall can be described by triaxial tests. Laboratory tests were undertaken to determine how the mechanical properties of sandstone elastic modulus E, Poisson’s ratio n, the shear modulus G and bulk modulus K of rock— are influenced by the different confining pressures and temperatures. As sandstone is found in the sub-sea basins, it has high porosity and can be a likely storage medium for CCS, it was selected as the type of rock for the triaxial testing. Three different temperatures 15°C, -5°C and -10°C were experimentally examined. The three temperatures represent a different injection scenario of CO2. Confining pressures of 12.5 MPa and 24 MPa were used to represent rock conditions at 500m depth and 1000 m depth under the North Sea, respectively.

Blasting has been widely used in mining and construction industries for rock breaking. This paper presents the results of a series of field tests conducted to investigate the ground wave propagation through mixed geological media. The tests were conducted at a site in the northwestern part of Singapore composed of residual soil and granitic rock. The field test aims to provide measurement data to better understand the stress wave propagation in soil/rock and along their interface. Triaxial accelerometers were used for the free field vibration monitoring. The measured results are presented and discussed, and empirical formulae for predicting peak particle velocity (PPV) attenuation along the ground surface and in soil/rock were derived from the measured data. Also, the ground vibration attenuation across the soil-rock interface was carefully examined, and it was found that the PPV of ground vibration was decreased by 37.2% when it travels from rock to soil in the vertical direction. Keywords: Rock blasting, Field tests, Blast wave propagation, Peak particle velocity (PPV), Rock-soil interface

Clay has wide application in engineered barriers, such as buffer barriers in deep geological nuclear waste disposal, clay liners in landfill, and earthen slopes and embankments, to name a few. However, most clay soils have a high potential to crack under extreme weather induced moisture loss. From a macro-mechanical view, clay tensile strength which is a critical factor governing the cracking behavior is highly dependent on the moisture content and corresponding matric suction. In this study, a series of laboratory tests on two typical clays (kaolinite and sodium bentonite) were carried out to investigate the relationship between clay tensile strength and moisture content by using a specially designed device which can measure tensile strength directly (Stirling et al. 2014, 2015). In addition, the study also investigated the effect of silica sand additive on the tensile strength at a wide range of moisture contents. The results demonstrate that both moisture content and sand additive have a significant impact on the measured tensile strength of the clays.

An anisotropic plasticity model for the description of nonisotropic mechanical behaviors of porous media is presented. This model is developed using bounding surface plasticity theory with...

Expansive soils exhibit swell-shrink behaviour in wet-dry periods resulting in distresses on light-weight structures founded on/in them. Therefore, it is essential to investigate the climate-ground interaction when designing structures on expansive soils. Laboratory-based models are preferred to investigate the climatic-ground interaction of expansive soils due to the uncontrollability of the boundary conditions and expenses associated with field monitoring. More flexibility in analysing the climatic-induced hydraulic responses in expansive soils can be achieved by finite element modelling of data from physical model tests. However, these laboratory-based models regularly encounter the effects of boundary flaw, preferential flow paths and entrapped air that needs to be accounted for when numerically simulated. In this study, the authors aim to numerically model the hydraulic responses in an instrumented Vertosol soil column (ISC) under controlled laboratory conditions. The effects of the preferential flow paths and boundary flaws were incorporated into a modified hydraulic conductivity as a practical approach to model the hydraulic responses in ISC. Influence of the entrapped air was rectified by a suitable correction factor. These findings present a practical method for geotechnical practitioners to accurately estimate the suction and volumetric water content profiles in laboratory-based expansive soil model tests., Civil engineering; Earth sciences; Environmental science; Geotechnical engineering; Construction engineering; Soil composition; Soil hydrology; Environmental engineering; Unsaturated soil; Expansive soil; Numerical simulation; Climate-ground interaction; Mechanical properties; Sensors; Wetting

Opening holes in rock including their size and distribution can affect the performance of rock-related structures. A good understanding on this will contribute to, for example, rock cavern design, and construction, tunnelling, and mining engineering. To improve the understanding, a comprehensive investigation of the opening hole effect on the rock mechanical behaviour under biaxial loading condition is carried out by virtue of a hybrid continuum-discrete element method. Laboratory specimens with both single hole and multi-hole of various radii are investigated and compared with the cases subjected to uniaxial compression. It is demonstrated that the confining pressure can increase both the stiffness and strength due to delaying the crack initiation and propagation. The increase due to the confining pressure is more evident for the compressive strength. For single hole specimens with 0.75 mm radius hole, the increase ratio of the compressive strength is a linear increasing function with width and the increase ratio ranges from 2.15 for the specimen with 3.5 mm width to 2.45 for 10 mm width. For the single hole specimen with 10 mm width, the increase ratio starts at 2.13 for the specimen with 0.75 mm radius hole, ascending to the peak of 2.37 for the specimen with 1 mm radius hole, followed by a decline to 2.2 for the specimen with 1.25 mm radius hole. However, for the multi-hole specimens, the increase ratio varies from 1.66 to 3.13. In addition, to verify the influence of confining pressure magnitude on the performance of the rock specimens, totalling 10 confining pressure levels are applied and modelled. The simulation results show that even though there are opening holes in the specimens, the simulated compressive strength generally follows the generalised Hoek-Brown model. Keywords: Rock with opening, Simulation, Biaxial loading, Strength, Stiffness

Drilling and blasting is one of the most widely-used methods for large-scale excavation in rocks and soils. However, rock blasting can induce many adverse effects, and the typical influence of rock blasting on the surrounding environment is illustrated in Fig. 1. Explosion induces ground and structures vibration1., 2. and annoying noise. When the explosive is detonated, an extremely high-pressure pulse is generated, which is transmitted into rock mass adjacent to the blast hole, producing a dilatational wave that propagates away from the charge. Stress waves due to blasts may cause damage to the surrounding rock and, furthermore, when the wave reaches a free face or open fissure (non-transmission), it will be reflected and converted into a tensile wave, which may produce tensile cracking and spalling if the tensile strength of the rock is exceeded by the tensile wave.3., 4. Also, due to the fact that some rock blasting projects are close to the inhabitant area, the surrounding buildings may be damaged due to blasting-induced ground vibration if large stress wave propagates in the soil foundation and shock wave propagating through the air.5 Disruption of some business activities, possible structural damage and emotional-traumatized residents are the problems that need to be addressed.2., 6. Therefore, the influence of ground vibrations on surrounding buildings, sensitive devices and people in urban environments is a significant consideration in obtaining project approvals.

A double porosity finite element model (FEM) is used to analyse the stability of a wellbore during carbon dioxide (CO2) injection in a carbon capture and storage (CCS) scheme. Elastoplastic deformation and continuous damage effects were considered. Attention was given to the pore and fissure pressures of the rock sur-rounding the wellbore as these can create stresses which can lead to potential fracturing. The size of the wellbore was also discussed as well as the studied depth and the different injection pressures of CO2.

Openings including their size, shape and distribution in rock play a significant role in the performance of rock related structures. The well-established knowledge in this area can contribute to the engineering practices, for example, underground space design, planning and optimisation in Civil and Mining Engineering and wellbore stability in Drilling Engineering, among others. Thus, understanding the failure mechanism of rock with openings is theoretically and practically meaningful. Laboratory testing on rock or rock-like materials with openings have been studied extensively in the literature, which, however, primarily focuses on the cracks/fractures. In this paper, a comprehensive numerical study on the effect of non-banded openings, i.e., circular, rectangular, and triangular opening, on the rock mechanical behaviour is performed using a hybrid continuum-discrete element method. It is revealed that the proposed simulation method can reproduce reasonably the crack initiation and propagation, and predict well the change of the mechanical behaviour due to the openings. In addition, the influence of the opening shape and opening ratio (=area of opening/specimen area) on the mechanical behaviour is also investigated.

We examine a new continuum micromechanical approach to predicting the macroscopic mechanical responses of Haubourdin chalk under various load conditions. The approach is based on a simple breakage model that accounts for an evolving microstructural degradation through coccosphere crushing with only five physically meaningful parameters and one grading index. The model correlates the intrinsic failure mechanisms including the coccosphere crushing, pore collapse and plastic shearing that are identified by corresponding internal variables within thermodynamic framework. On this basis, numerical predictions of the stresses and strains are examined against their experimental counterparts as well as the results from an existing continuum model. Parametric studies are further conducted to investigate the effect of the model parameters. The favourable agreements in various conventional and complex compression tests indicate a satisfactory performance of the breakage model, highlighting the importance of capturing the microscopic degradation mechanisms when building a constitutive model.

Numerical modelling of a field soil desiccation test is performed using a hybrid continuum-discrete element method with a mix-mode cohesive fracture model and Voronoi tessellation grain assemblages. The fracture model considers material strength and contact stiffness degradation in both normal and tangential directions of an interface. It is found that the model can reasonably reproduce the special features of the field soil desiccation, such as curling and sub-horizontal crack. In addition, three significant factors controlling field desiccation cracking, fracture energy, grain heterogeneity and grain size are identified.

As the free field geological condition is usually complex, the conventional wave attenuation law established for the homogeneous open field may not be applicable for actual field situations. Thus, to understand the impact of the attenuation law and the geological features on the blast wave propagation, a field rock blasting test is conducted and the ground vibration is carefully monitored. To better understand the phenomenon, a numerical model considering the field geological features is established using the finite difference method. The field test results are then used to calibrate the numerical model. From the calibration, the parameters involved in the general form of peak particle velocity have been determined. It is demonstrated that the blast wave propagation in the free field is significantly governed by the field geological conditions, especially the interface between rock and soil layers. Published version

The soil-concrete interface shear strength, although has been extensively studied, is still difficult to predict as a result of the dependence on many factors such as normal stresses, surface roughness, particle sizes, moisture contents, dilation angles of soils, etc. In this study, a well-known rigorous statistical learning approach, namely the least squares support vector machine (LS-SVM) realized in a ubiquitous spreadsheet platform is firstly used in estimating the soil-structure interface shear strength. Instead of studying the complicated mechanism, LS-SVM enables to explore the possible link between the fundamental factors and the interface shear strengths, via a sophisticated statistic approach. As a preliminary investigation, the authors study the expansive soils that are found extensively in most countries. To reduce the complexity, three major influential factors, e.g., initial moisture contents, initial dry densities and normal stresses of soils are taken into account in developing the LS-SVM models for the soil-concrete interface shear strengths. The predicted results by LS-SVM show reasonably good agreement with experimental data from direct shear tests.

In this research, a series of triaxial compression experiments and X-ray observations were conducted to explore the strength, deformability and internal damage mechanism of deeply buried marble. The results show that an increase in confining pressure results in obvious brittle–ductile transition characteristics of deeply buried marble. The Young’s modulus of the marble increased nonlinearly with increasing confining pressure. The peak and residual strength of the marble exhibit a clear linear relationship with the confining pressure, which can be described by the linear Mohr–Coulomb criterion. The sensitivity of the residual strength on the confining pressure was clearly higher than that of the peak strength. After uniaxial and triaxial compression failure, marble specimens were analyzed using a three-dimensional X-ray micro-CT scanning system. Based on horizontal and vertical cross-sections, the marble specimen is mainly dominated by axial splitting tensile cracks under uniaxial compression, but under confining pressure, the marble specimen is mainly dominated by a single shear crack. To quantitatively evaluate the internal damage of the marble material, the crack area and aperture extent for each horizontal cross-section were calculated by analyzing the binarized pictures. The system of crack planes under uniaxial compression is more complicated than that under triaxial compression, which is also supported by the evolution of the crack area and aperture extent. Finally, the brittle–ductile transition mechanism of the marble is discussed and interpreted according to the proposed conceptual models.

A comprehensive investigation of grain effect (size and distribution) in discrete element modelling of intact rock is carefully conducted through simulating Brazilian disc and uniaxial compressive tests on an intact rock using Universal Distinct Element Code. All the investigations are performed based on the same group of material parameters. Six sizes of Voronoi tessellation grains ranging from 1 to 6 mm are investigated. To investigate the influence of grain assemblage distribution, five different polygonal grain assemblages are created and tested for uniaxial compression and Brazilian disc tests. The simulation results demonstrate that grain size and assemblage distribution play a significant role in the numerical modelling of intact rock using discrete element method. It is found that larger particle size produces higher stiffness and strength. It is also observed that a more homogeneous model can produce higher strength (compressive strength, tensile strength). The modelled Young's modulus and Poisson's ratio have been demonstrated to be dependent on the grain effect.

A numerical model of fully grouted bolts is proposed in this study by implementing the tri-linear bond–slip relationship of bolts into the numerical framework presented by Hyett et al. (1996). The bond–slip relationship of bolt–rock interface is simplified and represented by the tri-linear model. The proposed numerical model is characterized by (1) its ability in modeling decoupling mechanism of bolt–rock interface, i.e. the degradation of the interfacial shear bond stress along bolts; (2) its easy implementation in a numerical code. The proposed numerical model is verified with the pullout tests, and good agreements with the experimental results can be observed in terms of axial stress distributions in the bolt, shear stress distributions along the bolt and load–displacement relationship. The proposed model also gives a reasonable prediction on the behavior of bolts installed in the field.

This paper presents the application of the hybrid continuum-discrete element method, i.e. Universal Distinct Element Code (UDEC), to simulate soil desiccation shrinkage and cracking. Herein, soil is modelled using a mix-mode cohesive fracture model that combines tension, compression and shear material behaviour. The fracture model considers both elastic and inelastic (decomposed to fracture and plastic) displacement, with the norm of the effective inelastic displacement being used to control the fracture behaviour. The applicability and capability of the proposed approach is demonstrated through numerical simulations of laboratory linearly-constrained desiccation test. Good agreements with the laboratory observations have been obtained. The dominant influencing factors on soil desiccation cracking have been assessed, several factors including shear strength and tensile strength of soil-base, and soil sample thickness were identified to have a significant controlling influence on desiccation cracking.

A cohesive fracture model that combines tension, compression and shear material behaviour is implemented into the hybrid continuum-discrete element method, i.e. Universal Distinct Element Code (UDEC), to simulate fracturing process in rock dynamic tests. The fracture model considers both elastic and inelastic (decomposed to fracture and plastic) displacements, with the norm of the effective inelastic displacement used to control the fracture behaviour. Two numerical examples, including notched semi-circular bending and Brazilian disc tests, are conducted to verify the applicability of the model in simulating the dynamic failure of rocks. Results show that the proposed approach is capable of realistically simulating the load rate effects on the mechanical behaviour of rock materials subjected to dynamic loads.

Salt expansion deformation is the main engineering hazard of saline soil, which restricts the application of coarse-grained sulfate or sulfite soil as roadbed filling. The main factors affecting salt expansion deformation are change of salt, water and temperature. The principal research objectives of this paper is to offer a basic data reference for the structural design of coarse-grained sulfate saline soil roadbed. To investigate the deformation properties of coarse-grained sulfate saline soil under the freeze-thaw-precipitation cycles, the large-scale sample experiments under the freeze-thaw-precipitation cycles and the freeze-thaw cycles were carried out with self-designed experiment equipment. The results showed that under the same freeze-thaw-precipitation cycles experiment conditions, the minimum temperatures of these samples with 1.5% and 3.0% soluble salt contents at a depth of 20 cm were 3.32 °C and 3.56 °C, respectively. In addition, it took less time for the lower salt content (1.5%) sample to reach the same low temperature compared to the higher salt content sample (3.0%). However, after seven freeze-thaw-precipitation cycles, it was shown that deformation of the sample with 1.5% soluble salt content was 32% higher than that with 3.0% soluble salt content. The maximum deformation amount of the coarse-grained sulfate saline soil after repeated freeze-thaw-precipitation cycles experiment was approximately 1.9–9.4 times larger than that after repeated freeze-thaw cycles experiment, which indicated that precipitation had a serious impact on the deformation of the sample. However, there was almost no difference between the lower salt content and higher salt content samples in the residual deformation caused by the cumulative effect of salt expansion in each cycle. Furthermore, the results showed that under the influence of precipitation, a high-level soluble salt content did not necessarily promote expansion deformation of coarse-grained sulfate soil. Water, salt, and temperature have complex coupling effects.

Shrinkage induced crack pattern is a universal phenomenon, soil cracking due to drying shrinkage is not an exception. In geotechnical engineering, desiccation shrinkage induced cracking has a profound effect on the engineering properties of soils as it can considerably increase the hydraulic conductivity and decreases the shear strength of a soil. Thus, it poses a significant threat to the hydraulic and structural integrity of earthworks. This paper presents the application of the hybrid continuum-discrete element method to simulate soil desiccation shrinkage and cracking with a mix-mode cohesive fracture model. The applicability of the proposed approach is demonstrated through numerical simulation of laboratory and field desiccation tests. The simulation results have shown good agreements with the laboratory and field observations.

Openings in rock play a significant role in the performance of rock related structures. The well-established knowledge in this area can contribute to the engineering practices, for example, underground space design, planning and optimisation in Civil and Mining Engineering and wellbore stability in Drilling Engineering, among others (Gui et al. 2017). In this paper, a numerical study on the effect of non-banded openings, i.e., circular opening, on the rock mechanical behaviour is performed using UDEC. It is revealed that the proposed simulation method can reproduce reasonably the crack initiation and propagation, and predict well the change of the mechanical behaviour due to the openings.

A series of field tests using controlled blasting was conducted at a location in the North Western part of Singapore to assess the behaviour of pile foundations subjected to ground excitation. The field tests involved three piles with different pile head fixity conditions. The piles were instrumented with strain gauges to evaluate the bending moments and axial force along the piles. For the fixed-head piles, the maximum bending moment occurred at the pile head level. For free-head pile exhibited higher bending moments close to the mid-height of the pile and zero bending moment at the pile head due to the absence of restraints at the top. For all cases, the axial force was maximum at the pile head.

The anisotropic direct tensile behaviour of laminated and transversely isotropic Midgley Grit sandstone (MGS) was investigated in this paper using a particle-based discrete element method (DEM) with consideration of the incipiency of bedding planes. Laboratory experiments were conducted to quantify the direct tensile strength of the incipient bedding planes, and the results were used to calibrate the numerical model. The effects of bedding planes with different relative positions and spacing were discussed. A comparison between the simulated results of this study and the predicted results from failure criteria was completed, and a good agreement was observed.

Rockbolts have been used to minimize the deformation of underground excavations where the surrounding rock masses contain weak planes such as fractures, joints or faults. Rockbolts installed across rock joints are able to resist the opening and shearing movements of rock joints. One of the rockbolt failure modes encountered in the field is caused by the excessive shear loads. A simple analytical model based on the Beam on Elastic Foundation (BEM) method is proposed in this study to predict the shear responses of a bolt installed perpendicularly to rock joint. The shear load-displacement curve of a double shear test can be divided into three stages: the elastic stage, the elasto-plastic stage and the plastic stage. The foundation stiffness for each respective stage are varied with the curvature influencing zone Lc. The pretension effects are taken into account in the proposed analytical model. The model agrees well with the experimental shear tests, suggesting that the analytical model has the capability to predict the shear load-displacement curve of bolts crossing rock joints.

Fracture toughness of anisotropic rocks can vary with many factors such as geological anisotropy, geometrical properties of specimens used in the laboratory (e.g., pre-existing crack properties), and loading conditions. This fact has been widely acknowledged. Yet the variation in fracture toughness remains enigmatic, as there is still lack of a comprehensive study on how those influential factors affect fracture toughness behavior of anisotropic rocks. The present paper shows a broad-spectrum mixed-mode fracture toughness of an anisotropic sandstone from a numerical scheme, which is based on the Discrete Element Method (DEM). In this study, a total of 340 semi-circular bend (SCB) specimens with various geological and geometrical conditions were numerically prepared by systemically varying the orientations of planar anisotropy (i.e. incipient bedding plane), as well as the magnitudes of the ISRM-suggested geometrical parameters of the SCB specimens (i.e. crack length, crack angle, and span length). The numerical model used in the study was calibrated against a series of laboratory experiments to select proper micro-parameters to reproduce the mechanical characteristics of anisotropic Midgley Grit sandstone (MGS). Additionally, four different fracture criteria, which are based on stress and strain analysis, and the analysis of energy density, were used to predict the mixed-mode fracture behaviour of MGS. Numerical findings from this study were compared with experimental observations (qualitatively) and theoretical predictions (quantitatively). A broad agreement was observed in the comparison study.

Pile foundations are commonly used as foundation systems for high-rise buildings and bridges. This paper uses a fully coupled three dimensional numerical modelling procedure to study the performance of pile foundations subjected to ground shocks induced by surface explosions. The comprehensive numerical model includes the pile, surrounding soil, air and the explosive. Appropriate material models are incorporated and dynamic non-linear analysis is carried out using finite element techniques. The soil in which the pile is buried could influence the blast performance of the pile. A parametric study is hence carried out to evaluate the effects of soil properties of density, friction angle, cohesion and Poisson’s ratio on the blast performance of the pile. It is found that density and cohesion of soil have significant effects on the deflection of the pile under blast loading. Poisson’s ratio has some effect, but effect of the soil friction angle is not very significant. The findings of this study will serve as a benchmark reference for future analysis and design of pile foundations to blast loading. Published version

The distinct lattice spring model (DLSM) is extended to modelling soil desiccation cracking by introducing a two-phase bond model. The bond, which comprises a spring bond and water bond, is developed to consider the interaction of the pore pressure with deformation of the soil matrix. A parameter representing soil heterogeneity is introduced to consider the uneven drying during desiccation. The capability of the model is demonstrated through a number of numerical examples, which are in good agreement with the experimental observations. Three significant factors controlling desiccation cracking, which are soil particle size, heterogeneity and boundary conditions, are identified.

A cohesive fracture model considering tension, compression and shear material behaviour is implemented into the hybrid continuum–discrete element method, i.e. Universal Distinct Element Code (UDEC), to simulate possible multiple fracture in soft rocks. The fracture model considers both elastic and inelastic (decomposed to fracture and plastic) displacements. The norm of the effective inelastic displacement is used to control the fracture behaviour. Three numerical examples, including Mode-I, Mode-II and Mixed-mode tests, are conducted to verify the model and its implementation in UDEC. The model is subsequently applied to simulate uniaxial compression and Brazilian disc tests on soft rocks and the results are compared with experimental results. The results indicate that the cohesive fracture model is capable of realistically simulating the combined tensile, shear and mixed-mode failure behaviour applicable to geomaterials.

The mechanical damage characteristics of sandstone subjected to cyclic loading is very significant to evaluate the stability and safety of deep excavation damage zones. However to date, there are very few triaxial experimental studies of sandstone under cyclic loading. Moreover, few X-ray micro-computed tomography (micro-CT) observations have been adopted to reveal the damage mechanism of sandstone under triaxial cyclic loading. Therefore, in this research, a series of triaxial cyclic loading tests and X-ray micro-CT observations were conducted to analyse the mechanical damage characteristics of sandstone with respect to different confining pressures. The results indicated that at lower confining pressures, the triaxial strength of sandstone specimens under cyclic loading is higher than that under monotonic loading; whereas at confining pressures above 20 MPa, the triaxial strength of sandstone under cyclic loading is approximately equal to that under monotonic loading. With the increase of cycle number, the crack damage threshold of sandstone first increases, and then significantly decreases and finally remains constant. Based on the damage evolution of irreversible deformation, it appears that the axial damage value of sandstone is all higher than the radial damage value before the peak strength; whereas the radial damage value is higher than the axial damage value after the peak strength. The evolution of Young's modulus and Poisson's ratio of sandstone can be characterized as having four stages: (i) Stage I: material strengthening; (ii) Stage II: material degradation; (iii) Stage III: material failure and (iv) Stage IV: structure slippage. X-ray micro-CT observations demonstrated that the CT scanning surface images of sandstone specimens are consistent with actual surface crack photographs. The analysis of the cross-sections of sandstone supports that the system of crack planes under triaxial cyclic loading is much more complicated than that under triaxial monotonic loading. More axial and lateral tensile cracks were observed in the specimens under cyclic loading than under monotonic loading.

The stability evaluation of earth slopes is a common practice in geotechnical designs. To account for uncertain characteristics of soil properties, probabilistic evaluation that requires repeated calculations of factor of safety (FoS) is inevitably encountered. Because FoS for most slopes in practice is computed numerically due to the lack of analytical solutions, various surrogate models are usually developed to ease the probabilistic evaluation. This paper investigates the probability of slope system failure with surrogate models based on the least-squares support vector machine (LS-SVM) regression. First, some limitations in the current application of LS-SVM to complex slopes with multiple failure modes are pointed out. In the context of Monte Carlo simulations (MCS) for probabilistic slope stability evaluation, the authors first discuss the importance of space filling of training data to the success of the LS-SVM and then propose an efficient routine for generating the training data by which the global prediction of FoS is reasonably guaranteed. The application of the LS-SVM is illustrated through two well-documented slope examples. Comparative studies are conducted to identify the effect of training data size and hyperparameters on the model performance. It is observed from this study that the LS-SVM model can reasonably capture the global characteristics of complex slopes only when all the relevant soil layers are treated probabilistically; otherwise, some local inconsistency could be encountered. Focusing on the probability of failure prediction defined by different FoS thresholds, it is shown that the LS-SVM is robust and a promising method for the evaluation of complex slopes.

Clay has wide application in engineered barriers. However, it is prone to crack if moisture content decreases at most circumstances. This research aimed to microscopically study drying shrinkage and associated cracking of two different clays: kaolin and sodium-based bentonite, using optical microscope-Leica DM2700 M, under controlled condition. The samples used were cylindrical with 20mm in diameter and 1mm in depth. During the observation, microscopic images were captured and saved. These images were used to analyse the cracking behaviour due to drying. The testing results showed that cracks initially occur in the middle of the sample and then propagate to the sample boundary. The length and width of the crack was increased as moisture decreased.

Blasting has been widely used in mining and construction industries for rock breaking. Ground vibration induced by blasting is an inevitable side effect that may cause damage to nearby structures, if not properly controlled. In this study, response and possible damage of rock-socketed pile near soil-rock interface subjected to ground shock excitations are investigated and quantified with coupled SPH-FEM method. Results indicate that the base of the pile is relatively vulnerable and that the soil properties significantly influence on response of pile subjected to a specific blast load. Furthermore, based on the numerical results, ground vibration attenuation equation is proposed. NRF (Natl Research Foundation, S’pore) Accepted version

In order to determine the slip plane of slope directly by the calculation results of strength reduction method, and analyze the influential factors of slope stability, a numerical model was established in plane strain mode by FLAC3D for homogeneous soil slope, whose parameters were reduced until the slope reached the critical state. Then FISH program was used to get the location data of slip plane from displacement contour lines. Furthermore, the method to determine multiple slip planes was also proposed by setting different heights of elastic areas. The influential factors for the stability were analyzed, including cohesion, internal friction angle, and tensile strength. The calculation results show that with the increase of cohesion, failure mode of slope changes from shallow slipping to the deep slipping, while inclination of slip plane becomes slower and slipping volume becomes larger; with the increase of friction angle, failure mode of slope changes from deep slipping to shallow slipping, while slip plane becomes steeper and upper border of slip plane comes closer to the vertex of slope; the safety factor increases little and slip plane goes far away from vertex of slope with the increase of tensile strength.

Environmentally controlled desiccation tests are performed on clayey soils: bentonite and kaolin, including unconstrained and constrained drying tests. The evolution of radial strain, moisture content with time and the relation between moisture content and strain are identified. Geometric and statistic parameters of linear desiccation cracks and 2D crack patterns are obtained by image processing. It was found that the desiccation speed of constrained desiccation was much higher than that of unconstrained desiccation due to the produced crack face. Also, from linear constrained desiccation test, it was obvious that the bentonite has higher potential to be cracked due to desiccation.

This paper reports a series of triaxial compression experiments and X-ray observations carried out to explore the mechanical behavior and internal damage mechanism of sandstone material. The results show that the Young’s modulus of sandstone increased nonlinearly with increasing confining pressure, but the Poisson’s ratio remained unaffected. The nonlinear Hoek–Brown criterion can better reflect the peak strength properties than the linear Mohr–Coulomb criterion. However, the residual strength of sandstone exhibits a clear linear relationship with the confining pressure, which can be best described by the linear Mohr–Coulomb criterion. The sensitivity of the crack damage threshold on the confining pressure was clearly lower than that for the peak strength. After unaxial and triaxial compression failure, the sandstone specimens were analyzed using a 3D X-ray micro CT scanning system. Based on the horizontal and vertical cross-sections of sandstone specimens, we found that under uniaxial compression and lower confining pressure, the sandstone specimen is dominated mainly by axial splitting tensile cracks; however, under higher confining pressure, the sandstone specimen is mainly dominated by a single shear crack. To quantitatively evaluate the internal damage of sandstone material, crack area and aperture extent for each horizontal cross-section were calculated by analyzing the binarized pictures. The system of crack planes under uniaxial compression is much more complicated than that under triaxial compression, which is also testified by the evolution behavior of crack area and aperture extent. Finally, the fracture mechanism of sandstone during uniaxial and triaxial compression is discussed in detail and simplified models are proposed.