Abstract Deep geological repositories are a feasible and reliable way to dispose of spent nuclear fuel, and the mechanical and thermal properties of the host rock are key factors in their long-term safety. The mechanical properties of rock, including uniaxial compressive strength, tension strength and elastic modulus are thermally-dependent - for example, the uniaxial compressive strength of rock will decrease with increasing temperature, as a result of thermally-induced cracks between mineral particles. However, thermally-induced cracks and the micro-mechanisms of rock damage are difficult to observe by experiments. We therefore used uniaxial compressive strength test and Brazilian disk PFC models with heterogeneous thermal expansion properties to reveal the micro-mechanisms of rock damage induced by thermal heating. Based on the mineral compositions of granite, heterogeneous models contained four particle types with different thermal expansion properties (quartz, potassium feldspar, plagioclase, and biotite). A series of heating simulations (temperature increment: ΔT = 80 – 300 °C) showed that thermally-induced cracks occurred when the temperature increment exceeded 250 °C, and that the main crack type was tension crack. In homogeneous PFC models no thermally-induced cracking occurred even at ∆T = 300 °C. In simulations of thermal-mechanical coupling, the heterogeneous PFC models have the advantage of revealing differences in radius expansion of various mineral particles with increasing temperature, resulting in the additional and uneven distribution of contact force, stress concentration between different particles and bond breaking, and it lead to decreases in uniaxial compressive strength, elastic modulus and initial crack stress. 1. Introduction In the construction and operation of deep geological repositories of nuclear waste, the physical and mechanical properties of host rock are influenced by excavations and decay heat induced by the installation of nuclear waste canisters. This may result in a variety of changes in rock porosity and seepage conditions in the rock mass, the formation of excavation damage zones and the occurrence of thermally-induced rock damage, etc. Thermally-induced damage results from heterogeneous thermal properties in rock - for example, the thermal expansion coefficient of quartz (24.3 × 10 −6 /°C) is three times that of biotite (8.0 × 10 –6 /°C), leading to the differential expansion of mineral volume and macro-mechanical properties of rock with increasing temperature. In order to understand and interpret the influences of thermally-induced damage on the mechanical behavior of rock, homogeneous and heterogeneous bonded particle models were adopted to simulate a uniaxial compressive test (UCS) and Brazilian indirect tensile test in this study.

Abstract During circular process of gas injection and withdrawal, the salt cavern for gas storage experience rapid temperature changes. The thermal effect coupling with the boundary conditions generates thermal stress, which induce the micro-fractures rock salt at the wall of underground cavity. Based on DEM, the Particle Flow Code is used to simulate the rock salt with interlayers. A novel hybrid DEM model is proposed, incorporating the rheological behavior of the pure rock salt, and the brittle character of interbedded mudstone. This model is capable of representing the macro-mechanical rock properties of laboratory observations. The high temperature decreases the compressive strength, makes the behavior of rock salt become more ductile instead of being brittle. The presence of interlayer induces more complex micro-cracking path, due to the heterogeneous heat transfer. Results illustrates the significant influence of temperature on the rock salt, resulting in the attenuation of the strength, induced thermal tensile cracking, and form weak zone around the interface of interlayers. The investigation of micro-mechanical response to the temperature influence can help us to predict the evolution of the damage zone around the interbedded salt cavern gas storage. 1. Introduction Rock salt is commonly accepted as host media for natural gas storage, as well as disposal of nuclear wastes, due to its characters, such as high solubility in pure water, very low permeability (Berest and Brouard 2003), creep behavior (Guessous et al., 1987), great potentiality of self-healing after damage (Chen et al., 2013), and relatively mechanical stability (Li et al., 2014; Zhu et al., 2016). The properties of non-halite evaporates varies different from one to another. (Jackson and Hudec, 2017), the behavior also changes when response to different temperature and confining pressure. High temperature changes the crystal structure of rock salt, which results in the variation of physical properties (Soppe et al., 1994; Cuevas 1997). Underground Gas Storage (UGS) is usually exposed to different temperature environment as the depth of its location varies. Therefore, an adequately capture and characterization of salt rock under different temperatures is essential for the design, construction, and operation of UGS. As an alternative and promising simulation method, Discrete Element Method (DEM) can be applied to investigate the complexity of rock according to its discontinuum basis (i.e. the discrete element is independent to move from rock mass). DEM treats the rock material as an assembly comprising individual particles bonded at certain contacts modes, for simulating microscopic rock behavior including crack and deformation. Different from the conventional simulation methods, such as Finite Element Method (FEM), or Boundary Element Method (BEM), the cracks in PFC Modeling is the spontaneous consequence of breakage of bonds at which the bond strength is being exceeded by the motion of particles. The simulated fracture can be regarded as extensive microcracks to investigate its complex constitutive behavior. PFC modeling has advantage in study of micro-mechanical behavior of unconsolidated as well as complex non-elastic characters, according to direct application of Newton's second law (Cundall and Strack 1979; Jing and Stephansson, 2007; Martinez, 2012).

Abstract In this study, the geometrical effects of vertical ore passes contributing to ore pass hang-ups were simulated by 3D discrete element method (3D-DEM). DEM is a method of calculating the movement of each discrete element in an analytical region and is suitable for simulating the movement of ore in an ore pass. Here, two types of cross-sectional shapes of vertical ore passes are assumed: circular and square. These ore passes are initially filled with discrete elements, and the ores are then extracted from the bottoms of the vertical passes. In our analysis, the conditions which cause ore pass hang-ups were evaluated, and the effect of the cross-sectional shapes and the possibility of the ore pass hang-ups were discussed. Results showed that cohesion exerted a strong influence on the occurrence of hang-ups. Moreover, the conditions under which hang-ups consistently occur were determined. In addition, the results showed that the hang-up conditions of circular ore passes were more severe than those of square ore passes and that square ore passes were preferable for avoiding hang-ups. 1. Introduction More than 200 limestone mines are operative in Japan, most of which are located on mountainsides (Limestone Associate of Japan website). Therefore, vertical ore passes are commonly used to transport ore to industrial sites and shipping sites (Fig.1), meaning ore pass hang-ups are a serious problem (Hadjigeorgiou, 2007), and can cause extensive damage during mining operations. Thus, effective methods and designs to avoid from ore pass hang-ups are crucial. In general, circular cross-sections of vertical ore passes are widely used; however, other cross-sectional shapes have recently been introduced. Nevertheless, the degree to which ore pass hang-ups can be avoided remains unknown. In order to investigate the mechanism of this phenomenon, Sato and Obara (2014, 2015) conducted numerical simulations by 2-dimensional discrete element method (DEM), which is a method for calculating the movement of each discrete element in an analytical region and it is suitable for simulating the movement of ore in ore passes. In that study, the cohesion between ores and ore pass walls was revealed to be the dominant factor in causing ore pass hang-ups in vertical ore passes. However, these analyses were conducted using 2-dimensional model. Thus, the effect cross-sectional shape was not considered.

Abstract Due to the high shale content and low permeability in shaly unconsolidated sandstone (SUS) reservoirs, the crude recovery rate can be very low. Fracturing is the key technology for developing such reservoirs. Thus, whether smooth fractures can be formed or not is important to improve production and to maximize economic benefit. In the study, a SUS model based on PFC discrete element method (DEM) is established firstly. Through the stress-strain curve fitting of the uniaxial pressure experiment, the microcosmic parameters are obtained. Meanwhile, the hydraulic fracturing PFC model of SUS is built by considering the fluid-solid coupling theory. The simulation shows that natural fractures can be connected by fracturing fluid to form branching fractures in hydraulic fracturing, but the main fracture still extends along the direction vertical to the minor principal stress. The crustal stress field can obviously affect the shape of hydraulic fractures in SUS. The smaller the stress difference is, the more fractures have the tendency to form disorderly fracture zones; with the increase of stress difference, fractures become more and more straight. It is also found that the stress chain direction is obvious after loading stress field to SUS, but the uneven distribution of stress is serious. The phenomenon leads to the shear stress emergence in the process of fractures expansion, making fractures direction more easily turn to the branches and produce fracture zones. Combining PFC microcosmic parameters and fracturing curves, it is believed that the normal and shear stiffness of sandstone particles are larger than those of shaly ones. To achieve the same stress, shaly ones need larger displacement, requiring more hold pressure time. Besides, the Poisson's ratio and strong plasticity both are related to SUS shear failure. The study results can provide a basis for optimizing the design of hydraulic fracturing in SUS reservoirs. 1. Introduction The newest round of oil & gas resources evaluation in China indicates that shaly unconsolidated sandstone (SUS) reservoirs are widely distributed and equipped with large reserves, occupying a foremost position in the whole oil & gas exploitation and production. How to develop efficiently and rationally this type of oil & gas reservoir has become one of the essential growth points is China's relevant industry, which can be of great significance to improve the output and reduce production cost.

Abstract This paper shows a modelling framework for simulation of thermal effect on the fracture behavior of a clay-rich sandstone. The framework was based on the particulate discrete element method (DEM), combined with a coupled thermal-mechanical scheme. Pure mode I and mode II, and mixed-mode (I+II) fracture toughness of the rock was measured under elevated temperatures (up to 600°C) using the ISRM-suggested semi-circular bend (SCB) specimens. The simulation results were validated against analytical predictions. 1. Introduction This study relates to thermal effect on fracture toughness of rock. Fracture toughness is a parameter of geo-materials that describes its ability to resist fracturing. This parameter is fundamentally important to rock and reservoir engineering applications, for example hydraulic fracturing for geothermal energy, oil and gas extractions (especially in the tight and low permeable formations), as well as wellbore stability assessment. Although fracture toughness is often deemed as an intrinsic property of rock, it still can with factors including geological anisotropy (e.g., Chandler, 2016), temperature and confinement (e.g., Funatsu et al., 2014), experimental setup and loading conditions (e.g., Shang et al., 2018a). Chong and Kuruppu (1987) experimentally investigated the fracture behvaiour of layered oil shale, where semi-circular bend (SCB) specimens (later suggested by ISRM) containing different proportions of organic matter were prepared. It was found that organic-rich shale specimens had a higher fracture toughness than leaner specimens. Chandler et al. (2016) reported fracture toughness measurements on Mancos shale in three principal crack orientations (i.e., arrester, divider and short-transverse) using a short-rod method, and found that fracture toughness of the divider oriented specimens was much higher (increased by a factor of 3.4) than that measured using the short-transverse oriented specimens. Temperature can be another important factor that affects fracture toughness of rock, especially in the deep underground. It is well accepted that fracture toughness of a rock material can increase under elevated temperatures until it reaches an elasto-plastic transition phase (Mahanta, 2016), after which a decrease in fracture toughness can be seen. The transition phase is rock type- and temperature-dependent, which is probably due to the variations in mineral composition leading to various thermal dilations, as well as due to mineral grain interactions at microscale. This paper reports a particulate DEM study on the thermal influence on mixed-mode fracture toughness of a clay-rich sandstone, where a fully coupled thermal-mechanical model was used. 2. Methodology In the study, a series of semi-circular bend (SCB) specimens with the ISRM-suggested dimensions were numerically manufactured using the Particle Flow Code (PFC) to measure the fracture toughness of rock under elevated temperatures (up to 600°C). Fig.1 shows a representative numerical sample used in the study, where main minerals in the Midgley Grit Sandstone (MGS, Shang, 2016) were differentiated by assigning particles with different thermal expansion coefficients (i.e. quartz, 24.3×10 −6 K −1 ; feldspar, 8.7×10 −6 K −1 ; biotite, 1.0×10 −6 K −1 ; clay, 3.6×10 −6 K −1 ) (Fei, 1995; Zhao, 2016). Thermal strains can be produced in the sample by accounting for the thermal expansion of the particles as well as the bonds which act as thermal pipes (only apply to parallel bond). Specific heat of each particle and thermal expansion per unit length were 1.0e 3 J/kg°C and 0.3°C/Wm, respectively. The DEM samples used in the study were first heated to desired temperatures up to 600°C, followed by three-point bending tests (without cooling phase) as shown in Fig. 1. It is worthwhile mentioning that a group of particles (green particles in Fig. 1) contacting the loading bar and the two supporting bars was generated and these particles were not heated (thus, no thermal expansion) so as to eliminate stress concertation which can be due to the different contact conditions arising from different expansion coefficients of the particles. Sample dimensions are shown in Fig. 1, in which sample radius R (50 mm), span length 2s (55 mm), thickness t (30 mm), and crack length a (25 mm) are constants, and the crack angle β varied from 0° to 46° to allow a complete modes of fracture toughness to be measured (Shang et al. 2018a). Table 1 shows the micro-parameters used in the study which have been calibrated by Shang et al. (2017).

Abstract A three-dimensional distinct lattice spring method is a numerical model in which matter is discretized into individual particles connected by springs. The connected springs include a normal spring and a shear spring for each pair of particles and their stiffnesses of the springs are calculated for a pair of fixed values of the Young's modulus and the Poisson's ratio. The very simple cubic structure of particles is introduced and three different types of spring setup to connect particles are assumed to model a linear elastic medium. The relationship between stiffness of these micro springs and the macro elastic constants must be examined to simulate not only static deformation and failure of rock materials but also dynamic fracturing problems. In this paper, a relation based on the classical elastic theory is introduced and simple two numerical examples will be presented, the first is the uniaxial compression loading of parallel-shaped cell model and the second is a cantilever model subjected to bending. The aim of the second simulation is to study more complex stress state which will be produced in the medium, tensile, compression and shear. These numerical examples are presented to show and discuss the abilities of the method in modeling elastic problems.

Abstract Grouting is a widely used method to seal and/or reduce permeability of fractured rock masses around underground structures. However, the filtration and penetration mechanism of cement-based grout have not been clarified sufficiently yet due to complicated physical and chemical processes of grouting. Therefore, the grout material and injection parameters such as injection pressure and water/cement ratio (W/C) are usually determined empirically by technical experts at the injection site. In this paper, for better understanding of the penetration and filtration mechanism of cement-based grout through rock fractures, the two-dimensional numerical model of coupled Computational Fluid Dynamics and the Distinct Element Method (CFD-DEM) was developed and the effect of particle adsorption on the filtration and penetration mechanism was numerically investigated. The simulation results clearly show that the effect of particle adsorption on the movement of cement particles and the amount of injected cement particles is significant.

Abstract The paper presents a numerical procedure based on Smoothed Particle Hydrodynamics (SPH) framework to analyze the fracture and fragmentation process of rock medium under dynamic stress wave followed by gas expansion. To analyze the dynamic fracture mechanism related to blast-induced borehole breakdown and crack propagation, a rectangular rock mass with/without rock joint containing a single centrally located source of explosive were numerically blasted in the proposed SPH framework. This paper uses modified Grady-Kipp continuum damage model to analyze dynamic fracture behavior of rock mass in tension due to blast loading. For shear failure, Drucker-Prager yield criterion with associative rule is employed in the constitutive model for plastic deformation. The damage pattern around the blasthole and the formation of tensile cracks near free surfaces were subsequently simulated using the developed numerical tool. It is found that the developed procedure has the potential to provide valuable information to understand the physical phenomena those occur in the failure process of rock mass under blast induced dynamic loads.

Abstract This study proposes a biconcave-shaped bonding model for distinct element method (DEM) to simulate cementation efficacy between two circular particles in geo-materials such as intact sedimentary rock. Instead of original parallel bonding model between particles, the proposed model adopts the more realistic shape of cementation and considers the elastic response of cementation under external loading. The stress field and force-displacement relationship of biconcave-shaped bonding is based on the Dvorkin's theory, a modification superposition method was applied to improve the correctness and symmetry of the stress field. This method also replaces the tangential movement to normal and rotation in particle's motion, in this way the corresponding total displacements in cementation can be obtained and updated easily. To assess the validity of modified Dvorkin's theory, we compared its elastic mechanical behaviors with the numerical elasticity analysis in finite element method. After verifying the proposed model, a series of sensitivity analysis was performed to discover the effect of bonding shape and to explore the difference with previous studies. Furthermore, the proposed model has been implemented in DEM software PFC2D to certify its applicability in geotechnical practice. The results show it works well with different bonding shape and it can represent the mechanical behavior of biconcave-shaped cementation. The stress field calculated by modified Dvorkin's theory is more similar with FEM result and able to solving the reaction when two particles are both moving. In addition, the required parameters can be acquired from real bonding material instead of back calculation from laboratory experiments. This model provides an innovative way to simulate the behavior of cemented granular material.

Abstract We investigated spatial and temporal the distribution of trace metals and sedimentary particles in order to identify the relationship between benthic foraminifera and trace metals pollution within Gunnamatta Bay, Port Hacking Estuary, NSW, Australia. Risk assessments of surface sediments were conducted using hierarchical cluster analysis (HCA).A total of 59 surface sediment samples and seven subsurface sediment samples were collected in order to determine the spatial and temporal distribution of trace metals in the bay. Further, six surface sediment samples were examined for existing foraminiferal assemblages. These included muddy samples which had high and low concentrations of trace metals and sandy samples. The trace metals distribution showed that chromium, nickel, copper, zinc, arsenic, lead, rubidium and bromine had similar distributions in surface sediments. The results of trace metal concentrations were also compared with the deleterious biological effect values in marine sediments. The means of most concentrations of trace metals for the Bay were below the Effect Range Median (ERM) or the Effect Range Low(ERL), except for copper. The highest concentrations of these metals were found to be in the north east of the bay, close to discharge points and a boat yard at GU55, with concentrations of 107, 14, 398, 413, 8, 203, 27 and 182ppm respectively. Also, this trace metal pollution was found to be concentrated in the inner part of the bay, which is deep and has organic matter and clay minerals. The benthic foraminiferal assemblages had lower species diversity in the muddy samples than in the fine sandy particle samples.Furthermore, the muddy particles that had high levels of trace metals were dominated by pollution-tolerant species such as Ammonia beccarii, Brizalina spathulata and Elphidium excavatum, which have had more opportunity to flourish. In addition, the levels of trace metals dramatically declined with increasing depth. This indicates that the potential source of trace metal pollution has been from human activity, such as boating and emission of gasoline fumes, since early European settlement in this area.

Abstract Grouting is a widely used method for sealing fractured rock masses around underground structures to reduce or stop groundwater inflow. One important aspect is the grout penetrability. However, the clogging and penetration mechanism of cement-based grout have not been clarified sufficiently yet due to complicated physical and chemical processes of grout, such as pressure-dehydration, consolidation, bleeding, clogging, absorption, sedimentation and condensation etc. Therefore, design and construction of grout injection depends on the experience of field technicians. Based on this situation, authors had developed a 2D numerical model of coupled Computational Fluid Dynamics and the Distinct Element Method (CFD-DEM), and simulate a laboratory scale grout injectionexperiment to better understand the penetration and clogging mechanism of cement-based grout. However, the results have raised some problems in this 2D approach. The flow of fluid and particles in the depth direction can not be represented in the two-dimensional simulation. Then, the simulated grout injection completely stopped instantaneously when particles formed an arch structure and clogging occurs. In actual grout injection test, the amount of cement that flows out from the outlet is reduced gradually and clogging occurs as a result. 3D simulations are essential in order to accurately reproduce the above experimental results. This paper presents 3D CFD-DEM simulations for the laboratory grout injection test (called "short slot" experiment) performed in Royal Institute of Technology (KTH) in Sweden. The simulation results agree qualitatively well with the actual experimental results, and the clogging process during the injection of cement-based grout was successfully reproduced by the 3D CFD-DEM code. The presented numerical model in this paper gives a better understanding for clogging and penetration mechanism of cement-based grout.

Abstract According to the gravitational deformation of slate slope in the field, this study explored the influencing factors, including the slope angle, the foliation angle, and the material deterioration on the deformation characteristics. To simulate these phenomena, a series of physical model experiments with simplified environmental conditions were performed in the laboratory. Then, the discrete element software, PFC 3D was used for simulations to further our understanding of deformation behavior in slate slopes under the long-term influence of gravity and material deterioration. According to the physical model tests and numerical simulations the results possesses the following characteristics: Based on the model tests, two kinds of gravitational deformation of slate slope are identified, the first one is overturning destruction, it appears in the obsequent slope with high angle foliation. The other one is fold extrusion near the slope toe, it exhibits in the consequent slope with low angle foliations. It is not only influenced by gravitation but also by wet deterioration. The results of physical model test provide the basic case for the verification of discrete element simulation. The simulated deformed patterns agree well with the actual deformation under different slope angles. Therefore, the model of discrete element method and associated parameters are verified, and they could be used for the subsequent analysis in the future.

ABSTRACT Cement is a basic material for dam foundation grouting. Cement particles have nonspherical and irregular shapes. Based on the findings in Particle Engineering, spherical particles can be effectively injected into cracks than nonspherical particles. If the cement particles are spherical or have smooth surfaces, dam foundation grouting will be more effective, so we carried out laboratory grouting tests and investigated the effects of cement particles with smoothened surfaces on injection of cement based grouts. In this paper, we used ultrafine cement as grout materials and the surfaces of ultrafine cement particles were smoothened by dry impact blending method. We evaluated the shape of cement particles by electron-microscope and image analysis. We conducted laboratory grouting tests using 50μm crack width model and we found that ultrafine cement grout with smoothened surfaces could be injected well in the low injection pressure condition.

ABSTRACT Cement grouting has been used as an effective method to reduce the permeability of the fractures in rocks. This study discusses the mechanism how cement grout controlled water permeation through the fractures in rocks, and focuses on the effectiveness of the clogging of cement particles for closing water paths. Quantitative investigation is made through laboratory tests and numerical simulation implementing a finite difference method (FDM) and a moving particle semi-implicit (MPS) method. As a result, a model is proposed of grouting mechanism using cement particles, and the validity of the proposed model is verified by numerical simulation.

ABSTRACT This study focuses on a series of CFD (computational fluid dynamics) simulations that enable the optimization of drill bit design by assessing internal rock particle and air flow paths. We used the Star-CCM+ code to simulate the multi-phase flow (i.e., rock particle discharge by flushing air during drilling) with input parameters obtained from the in situ drilling tests. Three design factors were determined, with a Taguchi experimental design method utilized to evaluate optimum values for each factor.

ABSTRACT The large deposits of freshwater snail fossils aging around 12–13 million years has been discovered at Mae Moh lignite mine in the northern part of Thailand. The preserved area of snail fossils with layers of up to 12 meters deep in the mining area has been set aside; however, there is a concern about the influence of mining activities in the vicinity area as well as excavations at a deeper depth. Therefore, detailed studies of the strength characteristics of snail fossils become necessary. The present study reported part of an investigation program in which direct shear strength properties of snail fossils were focused through the direct shear test with constant vertical stress under wet and dry conditions. The intact and disturbed samples were collected from a subsurface of a location deposited outside the preservation area. The effects of vertical effective stress, water, overconsolidation, and multi-reversal shearing on the shear strength properties of snail fossils were examined. The results show that the stress ratio decreases with increasing the vertical effective stress and the number of shearing. The presence of water appeared to have an impact on strength properties to some degrees. In addition, there is a rise in the stress ratio as the overconsolidation ratio increases.

ABSTRACT This paper presents a review of a systematic research program for understanding scale and stress effects on transport behaviours of fractured crystalline rocks, using a hybrid discrete element and particle tracking approach. The motivation is the importance of understanding stress effects on behaviours of contaminant transport in fractured crystalline rocks, an important issue of rock mechanics for environmental safety assessments of many rock engineering projects. The study is divided into three steps. The first step is a basic study that established the mathematical platform for deriving the conditions, criteria, basic approaches and test case results for investigating stress and scale effects on hydraulic behavior of the fractured rock concerned. At the second step, based on outstanding issues drawn from the first step, the study was extended to consider effects of the correlation between the fracture aperture and size (represented by trace length) on the permeability of the fractured rock, and uncertainties in deriving equivalent continuum properties of fractured rocks. The third step added the particle/solute transport processes to the mathematical platform, including different retardation mechanisms, so that impact of stress on safety can be directly evaluated, even it can only be done conceptually. The obtained results show that stress, scale and inter-parameter correlations of the fracture system geometry are dominant issues for understanding and characterization of coupled hydro-mechanical processes of fractured rocks and play a significant role for understanding the mass transport behaviour in them, with direct impact on geo-environmental safety.

ABSTRACT The Distinct Lattice Spring Model (DLSM) is a newly developed numerical model for rock dynamics problems, i.e., dynamic failure and wave propagation. The current constitutive law for bond spring used in DLSM is the simplest brittle linear one, which is not enough to describe the complex mechanical behavior of rock material. An advanced micro constitutive law of bond springs is developed and implemented into DLSM. Using the damage variable principle, a tri-linear constitutive law and nonlinear micro constitutive law has been developed, which can fully represent the linear stage, the hardening stage and the softening stage of the bond spring. Two failure modes, tensile failure of the normal spring and shear failure of the shear spring, are considered. A preliminary study on failure behavior of DLSM model with the developed constitutive model is performed. Uniaxial tensile and compressive tests were performed to find influences of micro constitutive law on the macro mechanical response of DLSM. It is found that the ratio of compressive strength to tensile strength for DLSM is much lower than that for rock materials (typically around 10–12), e.g. it is around seven for the regular lattice model and three for the random lattice model. Therefore, further development of the constitutive model in DLSM is required.

ABSTRACT A new DEM code corresponding to unconsolidated sand was developed. The flow-coupled DEM simulations for the hydraulic fracturing in unconsolidated sand were performed to reveal the factor that significantly affects the peculiar hydraulic fracturing behavior. Especially, this research focused on the effect viscosity of fracturing fluid. As a result, the two different fracture growth patterns observed in the hydraulic fracturing experiment were successfully represented with different viscosity of fracturing fluid. When the viscosity of the fracturing fluid is 100 mPas or more, the fracture growth pattern of the Linear Fracture was observed. On the other hand, when the viscosity of the fracturing fluid is lower than 100 mPas, the fracture growth pattern became the Branched Fracture. These results indicate that the viscosity of the fracturing fluid have a large influence on the fracture growth process in unconsolidated sand. Moreover, these results suggest that the DEM model may be more appropriate for the analysis of fracturing of unconsolidated materials than the other numerical analysis techniques.

ABSTRACT Because the detonation of the explosive blasting powder creates the gas of vast quantity with strong wave at extreme short time, distinguishing the detonation and gas pressure is very difficult. But we must study two kinds pressure together for the approach to be reality. Although many scholars are proposing a various experimental and numerical blasting model method to distnguish the detonation and gas pressure each other, we can not distinguish it completely up to now. In this study, we developed the algorithm to consider the detonation and gas pressure simultaneously using a discrete element code PFC2D.