A grain-based model (GBM) is generally employed by many researchers to simulate the microcracking process of crystalline brittle rock by the distinct element method. In this study, a novel ...grain-based model (nGBM) in two-dimensional Particle Flow Code 5.0 (PFC2D 5.0) is proposed to emulate the brittle failure of crystalline rock. First, the nGBM scheme is introduced, in which the flat-joint model is employed to model the contacts in mineral grains and the smooth-joint model is assigned to the grain interface contacts. Then, compressive tests are performed using Alxa porphyritic granite, and the strength values are fitted with the Hoek-Brown failure criterion. Third, a nGBM was generated based on the petrographic texture of realistic rock, such as mineral constituents, grain size, and distribution. The input microscale parameters are carefully calibrated according the experimental results. Finally, this model is applied to study the microcracking process of Alxa porphyritic granite and the influence of spatial distribution of minerals. It is found that a relatively high ratio of uniaxial compressive strength to tensile strength of each mineral or synthetic samples can be reproduced by the nGBM. Moreover, the simulated results show this model can capture the nonlinear characteristic of the Hoek-Brown failure criterion. After modeling, numerous mineral grains were cut across, which is consistent with the actual experimental observation; the tensile crack is over the shear crack in the models, while the number of intra-grain shear crack increases dramatically with increasing confining pressure. In addition, the numerical results indicate that the effect of spatial distribution of minerals has limited influence on the evolution of microcracks but has great impact on microcrack distribution. In summary, the proposed nGBM in PFC2D can well reproduce the realistic failure process of granitic rocks under different loading conditions.
•We propose a novel grain-based model (nGBM) in PFC2D to emulate the brittle failure of crystalline rock;•Compressive tests are performed using Alxa porphyritic granite to calibrate the nGBM model;•The nGBM model well reproduce the failure process and microcracks distribution of granitic rocks under various conditions;•The proposed model not limited to simulate the failure process of granitic rock but the complex rock engineering.
•The Flat-Joint contact is incorporated into grain-based model to model the minerals.•Effects of mineral boundary properties on the crystalline rocks are investigated.•Mineral boundary stiffness ...controls the deformation process of crystalline rocks.•Strengthening mineral boundaries is likely to promote the generation of micro cracks.
The grain-based model (GBM) in two-dimensional Particle Flow Code (PFC2D) is widely employed to investigate the mechanical response characteristics of crystalline rocks under external load considering the realistic petrographic texture. However, due to the poor self-locking effect of the Parallel-Bond (PB) inside the minerals and unreasonable parametric assignment for the Smooth-Joint (SJ) at the mineral boundaries, the original GBM cannot reproduce the exact microcracking process of brittle rocks. To solve the problem, the novel grain-based model (nGBM) composed of the Flat-Joint (FJ) and the SJ was proposed in our previous research, which not only enhances the rotational resistance of particles, but also improves the simulation of the mineral boundaries. In this study, the nGBM was carefully established and calibrated based on the properties of Alxa porphyritic granite. A series of simulation tests of uniaxial compression, triaxial compression and direct tension under different mineral boundary parametric conditions were carried out to observe the deformation, microcracking and failure behaviors of the nGBM. Quantitative analyses of the mineral boundary properties and the mechanical behaviors of the numerical specimen revealed the extremely complicated relationships between them, which can help explain the micromechanical damage process of crystalline rocks and provide valuable reference for the model calibration.
Mineral grain size heterogeneity is one of the fundamental reasons leading to differences in rock mechanical behaviours. Several indices have been proposed to quantify grain size heterogeneity, ...however, the applicability of the existing indices is limited due to various preconditions. An improved grain size heterogeneity index He was proposed in this study. By comparing with the previous index, the improved index was proved to be more applicable for analysing rock mechanical properties. Through a series of grain-based model (GBM), the grain size heterogeneity effect, material heterogeneity effect and mineral content effect were further discussed. For a simple grain size heterogeneity effect, the crack initiation stress, damage stress, peak stress and crack initiation stress ratio of rock decreased linearly as the improved index He increased. After accounting for the material heterogeneity effect, the above characteristic stresses and elastic modulus decreased. A significant material heterogeneity effect and mineral content effect will impact the linear correlation between the rock macro-mechanical parameters and the He index. When the axial stress was low, the grain size heterogeneity had little effect on the number of microcracks, but this heterogeneity became the main factor affecting the evolution of microcracks as the axial stress increased. The number of intragrain tensile cracks increases and the number of intergrain shear cracks decreases with increasing He, when the axial stress reached the rock peak strength. Besides, the combined effects of material heterogeneity and mineral content may control the type and number of microcracks, further weakening the effect of grain size heterogeneity.
•An improved grain size heterogeneity index He was proposed which was more applicable for analysing rock problems.•The correlation between the rock macro-mechanical parameters and the He index was linear.•The effect of grain size heterogeneity on the type and number of microcracks was investigated.•The material heterogeneity and mineral content also have significant effects on the rock mechanical parameters.
A smoothed particle hydrodynamics (SPH) numerical modeling method implemented for the forward simulation of propagation and deposition of flow-type landslides was combined with different empirical ...geomorphological index approaches for the assessment of the formation of landslide dams and their possible evolution for a local case study in southwestern China. The SPH model was calibrated with a previously occurred landslide that formed a stable dam impounding the main river, and it enabled the simulation of final landslide volumes, and the spatial distribution of the resulting landslide deposits. At four different sites on the endangered slope, landslides of three different volumes were simulated, respectively. All landslides deposited in the main river, bearing the potential for either stable impoundment of the river and upstream flooding scenarios, or sudden breach of incompletely formed or unstable landslide dams and possible outburst floods downstream. With the empirical indices, none of the cases could be identified as stable formed landslide dam when considering thresholds reported in the literature, showing up the limitations of these indices for particular case studies of small or intermediate landslide volumes and the necessity to adapt thresholds accordingly for particular regions or sites. Using the occurred benchmark landslide as a reference, two cases could be identified where a complete blockage occurs that is more stable than the reference case. The other cases where a complete blockage was simulated can be considered as potential dam-breach scenarios.
Background and Purpose
Transient receptor potential vanilloid type 4 (TRPV4) channels are expressed in brain endothelial cells, but their role in regulating cerebrovascular tone under physiological ...and pathological conditions is still largely unknown.
Experimental Approach
Wild‐type (WT) mice and mice that overexpress a mutated form of the human amyloid precursor protein (APP mice, model of increased amyloid β), a constitutively active form of TGF‐β1 (TGF mice, model of cerebrovascular fibrosis) or both (APP/TGF mice) were used. Dilations to the selective TRPV4 channel opener GSK1016790A (GSK) or to ACh were measured in posterior cerebral artery segments.
Key Results
Both GSK‐ and ACh‐induced dilations virtually disappeared following endothelium denudation in WT mice. These responses were impaired in vessels from APP, TGF and APP/TGF mice compared with WT. Pre‐incubation of WT vessels with the selective TRPV4 channel blocker HC‐067047, or with small‐conductance (SK channel, apamin) and/or intermediate‐conductance (IK channel, charybdotoxin, ChTx) Ca2+‐sensitive K+ channel blocker abolished GSK‐induced dilations and massively decreased those induced by ACh. These treatments had no or limited effects on ACh‐induced dilation in vessels from APP, TGF or APP/TGF mice, and IK and SK channel function was preserved in transgenic mice. Antioxidant superoxide dismutase or catalase normalized GSK‐ and ACh‐mediated dilations only in APP brain arteries.
Conclusion and Implications
We conclude that endothelial TRPV4 channels mediate ACh‐induced dilation in cerebral arteries, that they are impaired in models of cerebrovascular pathology and that they are sensitive, albeit in the reversible manner, to amyloid β‐induced oxidative stress.
The design of core-shell structure is considered as a facile approach to obtain polymer composites with excellent dielectric properties and high breakdown strength (Eb). In this work, ...thiol-terminated poly(vinylidene fluoride) (PVDF-SH) and polystyrene (PS-SH) are synthesized by a two-step process. The as-prepared polymers are applied to modify BaTiO3 (BT) nanoparticles. The subsequent morphologies, dielectric properties, and Eb of PVDF-based composites are investigated systematically. PVDF encapsulated BT (PVDF@BT) fillers carries more desirable compatibility with matrix compared with PS encapsulated BT (PS@BT) and raw BT. For instance, the Eb of the 30 vol% PVDF@BT composites slightly decreased from 150.6 to 117 kV/mm for PVDF matrix, as compared to the raw and PS@BT composites, for those the values intensively reduced to 58.5 kV/mm and 107 kV/mm, respectively. It is also observed that PVDF polymer shells play a significant role in the improvement of composites dielectric constant (εr). Moreover, the design of the polymer shell also contributes to the suppression of dielectric loss. The results are of great importance for understanding the effect of polymer shells and fluorinated filler on composite properties. This study provides a strategy for preparing composites with high εr while maintaining high Eb for the next generation of dielectric capacitors.
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•Ferroelectric polymer poly(vinylidene fluoride) is used simultaneously as a matrix and BaTiO3 modifier.•The breakdown strength of PVDF@BT/PVDF is 100% larger than that of BT/PVDF at 30 vol% filler loading.•15% increase in dielectric constant is observed in PVDF@BT/PVDF as compared to PS@BT/PVDF at 30% filler loading.
Residual pesticides in soil may be taken in by plants and thus have a risk for plant growth and food safety. In this study, uptake of triadimefon and its subsequent translocation and accumulation ...were investigated with wheat as model plants. The results from hydroponics indicated that triadimefon was absorbed by wheat roots mainly through apoplastic pathway and predominantly distributed into the water soluble fractions (66.7−76.0%). After being uptaken by roots, triadimefon was easily translocated upward to wheat shoots and leaves. Interestingly, triadimefon in leaves was mainly distributed in the soluble fraction by 52.5% at the beginning, and gradually transferred into the cell wall by 47.2% at equilibrium. The uptake of triadimefon from soils by wheat plants was similar to that in hydroponics. Its accumulation were mainly governed by adsorption of the fungicide onto soils, and positively correlated with its concentration in in situ pore water (CIPW). Thus, CIPW can be suitable for predicting the uptake of triadimefon by wheat from soils. Accordingly, uptake of triadimefon by wheat was predicted well by using the partition-limited model. Our study provides valuable information for guiding the practical application and safety evaluation of triadimefon.
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•Triadimefon could be easily translocated upward to wheat leaves.•The subcellular distribution of triadimefon affected its translocation capacity.•Apoplastic pathways contributed to the uptake of triadimefon by wheat roots.•Concentration of triadimefon in in situ pore water can predict its uptake by wheat.
The relationship between landslides and rock mass strength is fundamental for assessing landslide hazards. Some researchers have proposed that there is an inverse relationship between the number of ...landslides and rock mass strength. However, in some tectonically active mountain ranges, higher rates of landsliding appear to be associated with greater rock mass strength. We investigated the relation between landslides and rock mass strength in the Langxian (LX), Lulang (LL), and Tongmai (TM) regions in southeastern Tibet by identifying and mapping 294 large bedrock landslides using 10-m resolution lidar bare-earth imagery. An inverse relationship between topographic relief and the slope angle of historical landslides demonstrates that rock mass strength is an important factor controlling relief in the study area. Applying Culmann's method, we back-calculated rock mass strengths ranging from 60 to 770 kPa at the landscape scale. Our data show that, at the landscape scale, more landslides have occurred on the hillslopes with greater rock mass strength than on those with lower rock mass strength. We conclude that the stability of slopes in our study areas is controlled by rock mass strength, but the dominant drivers of failure are rock uplift and river incision, rather than a reduction in rock strength as has been proposed in some tectonically passive regions.
•We back calculate rock mass strengths ranging from 60 to 770 kPa in the study area.•More landslides occurred on the hillslopes with greater rock mass strength.•The dominant drivers of slope failure are rock uplift, river incision and earthquakes.
Hydraulic fracturing is a useful tool for enhancing rock mass permeability for shale gas development, enhanced geothermal systems, and geological carbon sequestration by the high-pressure injection ...of a fracturing fluid into tight reservoir rocks. Although significant advances have been made in hydraulic fracturing theory, experiments, and numerical modeling, when it comes to the complexity of geological conditions knowledge is still limited. Mechanisms of fluid injection-induced fracture initiation and propagation should be better understood to take full advantage of hydraulic fracturing. This paper presents the development and application of discrete particle modeling based on two-dimensional particle flow code (PFC2D). Firstly, it is shown that the modeled value of the breakdown pressure for the hydraulic fracturing process is approximately equal to analytically calculated values under varied in situ stress conditions. Furthermore, a series of simulations for hydraulic fracturing in competent rock was performed to examine the influence of the in situ stress ratio, fluid injection rate, and fluid viscosity on the borehole pressure history, the geometry of hydraulic fractures, and the pore-pressure field, respectively. It was found that the hydraulic fractures in an isotropic medium always propagate parallel to the orientation of the maximum principal stress. When a high fluid injection rate is used, higher breakdown pressure is needed for fracture propagation and complex geometries of fractures can develop. When a low viscosity fluid is used, fluid can more easily penetrate from the borehole into the surrounding rock, which causes a reduction of the effective stress and leads to a lower breakdown pressure. Moreover, the geometry of the fractures is not particularly sensitive to the fluid viscosity in the approximate isotropic model.
The stiffness coefficient is a key parameter of rock fractures that controls the properties and behavior of a rock mass. According to the displacement discontinuity theory, the dynamic stiffness of ...rock fractures can be back analyzed using stress wave propagation. This study aims to measure the dynamic stiffness of rock fractures then develop an empirical ratio to describe the relationship between dynamic and static stiffness. Propped artificially fractured shale and granitic rock samples are employed. Mechanical and ultrasonic tests are conducted on two artificial rock fractures during uniaxial loading and unloading. As normal stress changes from 1 MPa to 50 MPa, the average dynamic normal stiffness of shale and granitic rock fractures changes from 330 GPa/m to 1960 GPa/m and from 90 GPa/m to 2320 GPa/m, respectively. For both artificial fractures, the dynamic stiffness is higher than the static stiffness but approaches the static stiffness with increasing normal stress. The ratio of dynamic to static normal stiffness is approximately 2.0 at a normal stress of 15 MPa; this ratio approaches 1.0 with increasing normal stress and varies widely under low normal stress. This study provides a method for evaluating the static or dynamic stiffness of rock fractures, which has important applications for seismic surveys or acoustic logs in the field of geological engineering.
•Uniaxial stress tests are conducted on propped fractures in shale and granite.•Displacement discontinuity theory is used to back analyze the dynamic stiffness.•The relationship between dynamic and static stiffness is empirically determined.•Rock joint stiffness can be better evaluated during deep geo-engineering projects.
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