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Rock masses generally contain many fissures filled with weak materials. At present, the interaction mechanisms of crack coalescence and seepage in rock with filled fissures are still poorly understood. Therefore, this study conducts systematic laboratory tests on sandstone samples with two filled fissures under hydromechanical coupling conditions. The influences of the fissures, filling, ligament length, and bridge angle on the strength, fracture pattern, and permeability are explored. The results show that the strength properties of the sandstone are weakened more significantly by fissures than by water pressure. The increase of strength properties induced by the fillings is more remarkable in the samples with either a longer ligament length or a lower bridge angle. Unlike for mud filling, for sand filling, most of the sand particles in the fissures are crushed after loading, reflecting that the bearing capacity of the sand filling is fully utilized. Thus, sand filling generally has a greater effect on the strength properties than mud filling does. Furthermore, the failure of double-fissure sandstone can be divided into five modes. With the exception of the samples with a high bridge angle, the samples undergo failure modes that change with the existence of fillings, and for samples with a long ligament length or a low bridge angle, the change is more sensitive to the filling type. The weakening effect of fillings on permeability is associated with the failure mode, and it is more remarkable in samples with the “wing cracks + indirect crack coalescence” or “wing cracks + direct crack coalescence” failure modes than in other samples.

Background Chlorophylls, green pigments in chloroplasts, are essential for photosynthesis. Reduction in chlorophyll contents may result in retarded growth, dwarfism, and sterility. In this study, a yellow-green leaf mutant of maize, indicative of abnormity in chlorophyll contents, was identified. The physiological parameters of this mutant were measured. Next, global gene expression of this mutant was determined using transcriptome analysis and compared to that of wild-type maize plants. Results The yellow-green leaf mutant of maize was found to contain lower contents of chlorophyll a , chlorophyll b and carotenoid compounds. It contained fewer active PSII centers and displayed lower values of original chlorophyll fluorescence parameters than the wild-type plants. The real-time fluorescence yield, the electron transport rate, and the net photosynthetic rate of the mutant plants showed reduction as well. In contrast, the maximum photochemical quantum yield of PSII of the mutant plants was similar to that of the wild-type plants. Comparative transcriptomic analysis of the mutant plants and wild-type plants led to the identification of differentially expressed1122 genes, of which 536 genes were up-regulated and 586 genes down-regulated in the mutant. Five genes in chlorophyll metabolism pathway, nine genes in the tricarboxylic acid cycle and seven genes related to the conversion of sucrose to starch displayed down-regulated expression. In contrast, genes encoding a photosystem II reaction center PsbP family protein and the PGR5-like protein 1A (PGRL1A) exhibited increased transcript abundance. Conclusions The yellow-green leaf mutant of maize contained fewer active PSII centers with lowered net photosynthesis rate, but have the similar value of the maximum photochemical quantum yield of PSII with that of the wild-type plants. Analysis of differentially expressed genes through transcriptome analysis revealed the down-regulated genes which may be responsible for chlorophyll deduction and changes of photosynthetic characteristics. The up-regulated genes would be helpful to maintain the active PSII centers of the yellow-green leaf mutant.

Our goal was to develop an effective research tool for tunnels with significant deformations supported by arch–bolt union system. The improved numerical simulation approach is constructed through additional development of FLAC3D. There are four parts that form the approach: a yieldable supporting arch module, a separable arch–rock interaction module, a breakable anchor bolt module, and a practicable surrounding rock module. The yield criterion of the supporting arch was proposed and embedded in the modified beam element via the FISH language programming. A separation criterion is proposed for the arch–rock interaction link, and the separable arch–rock interaction module is realized through modifying the normal-yield attachments of the built-in arch–rock links. A tensile breakage failure criterion is proposed for the anchor bolt using the ultimate elongation ratio δf of the whole anchor-free part as the criterion. Taking an actual mining roadway tunnel as the simulation object, two simulation schemes adopting the newly improved approach and the original method were carried out respectively, and comparisons of the results show that: (1) the bending moment and axial force at the yielding moment of the compression-bending element change from independent to related after modification, and the computed deviation of the arch model caused by the shortcomings of the original beam element were effectively suppressed; (2) the separable link is proved effective by the supporting forces curves and arch deformation responses; (3) the breaking property of the anchor bolt is implemented, and the response is sensitive; and (4) the surrounding rock controlling results in the modified model scheme are closer to the actual. The analysis shows that the improved numerical simulation approach is much more reliable for large deformation tunnel behavior with arch–bolt union support, especially concerning the bearing and failure behaviors of the supporting arch and anchor bolt.

Although Concrete-filled Steel Tubular (CFST) arch support technology for transportation tunnels and mining roadways is developing rapidly, research regarding the determination of the bearing capacity of the CFST arch support is still limited. Based on a literature analysis, the definition and expression form of the bearing capacity of CFST supporting arch Qu was clarified, and determination approaches via laboratory testing and theoretical calculation methods were recommended. Full-size mechanical tests of CFST arches were performed by adhering to the suggested loading pattern that uses a number of hydraulic cylinders along the arch profile to simulate the surrounding rock pressure. The failure mode of the arches was determined as elastic-plastic instability with an extreme point. The critical criterion of global instability for the tested arch was proposed as the critical CFST section reaching the compression-bending limit. Based on the above criterion, a specific process for determining the Qu by theoretical calculation was proposed. Calculation examples show that the calculation results deviations were less than 4% compared with the tests results, and the reliability and accuracy of the new theoretical approach were thus verified. Finally, the limitations of the calculation method were noted.

The beam element in FLAC3D can be used to simulate the supporting arch in a tunnel. However, this approach has the shortcoming of its constitutive model, and the bearing capacity and surrounding rock supporting effect of the arch model will be significantly exaggerated. To simulate the supporting arch in tunnel engineering well, a new approach is proposed by improving the beam element. The yield criterion of the beam element subjected to compression-bending loads is established based on the now-available bearing capacity formulas of some typical compression-bending sections. In addition, the yield criterion is embedded in the FLAC3D main program by using the FISH language, and the modification of the beam model and the yielding failure simulation of the supporting arch are finally implemented. Compression-bending tests and roadway tunnel arch support example analysis were performed. The results are as follows: (1) the modified model showed the dependence of the bending moment and axial force on the yielding action of the beam element under compression-bending loads; (2) the implementation program is effective and sensitive; (3) the computing deviation caused by the shortcomings of the original beam element model was effectively suppressed, the mechanical behavior and surrounding rock supporting laws exhibited by the arch model were much closer to reality, and the calculation accuracy and design reliability were improved by the new simulation approach.

Cut blasting is the key of single-face blasting in underground rock engineering, which determines the success or failure of the blasting process. Traditional cut blasting is not suitable for deep-hole blasting engineering because of the difficulty of throwing rock fragments and the accumulation at the bottom. In this paper, an advanced concept of cavity cutting and fragment throwing (CCFT) for cut blasting is proposed, which is divided into the following two blasting processes: cut hole breaking and fragment-throwing hole throwing. By establishing a mechanical model of CCFT, cut cavity efficiency is introduced as an evaluation index of the cutting effect, and the advantages of CCFT cut blasting are analyzed theoretically. Based on the smoothed particle hydrodynamics-finite element method (SPH-FEM), a CCFT cut blasting model and a traditional cut blasting model are established and compared. The results show that the detonation of the central fragment-throwing hole in CCFT cut blasting plays a key role in the throwing of rock fragments, improving the cut cavity efficiency by approximately 20%. Additionally, 9 sets of numerical models are established to study the effects of various parameters on the cut cavity formation, and optimization suggestions are given for the parameters. The findings show that as the hole depth increases, more blasting energy is needed for the throwing of rock fragments, which can be effectively achieved by increasing the ratio of the charge weight δ. The hole spacing needs to be properly designed to ensure that the rock between the holes is penetrated and broken. The large-diameter fragment-throwing hole guides the development of blasting cracks and promotes rock fragmentation. Finally, two engineering cases, namely, one-step shaft excavation and deep-hole drilling and blasting in a rock tunnel, illustrate the application of CCFT cut blasting. The good application results provide references for similar engineering projects.

It is difficult to establish a constitutive model of damage for rock materials due to the complex meso-mechanism of the rock deterioration process. In this paper, by analysis of the damage mechanism, the reason for the existence of a rock damage threshold is explained and we conclude that damaged rock elements of micro scale can still bear stress. The correlation between damaged and undamaged elements is examined in relation to stress distribution. Rocks under different initial conditions can be defined as undamaged materials with different properties, to avoid the issue of the solution of the undamaged condition and to simplify the damage model. On the basis of the Mohr-Coulomb criterion and theories of continuum damage and statistical mechanics, a constitutive model of rock materials affected by the load-bearing capacity of damaged elements under triaxial compression is established. Compared with previous experimental data and theoretical results, we show that this model can reflect the stress-strain relationship of the whole process of rock failure. In particular, the description of the strain softening stage after peak strength is proved to be more reasonable. Programming of the constitutive model applied to stability analysis of the Qingdao subway station is achieved by secondary development of FLAC3D. The computing results compare very well with field monitoring data, indicating that the constitutive model of damaged rock can reflect the deterioration effect of weathered rock at the site. This constitutive model of rock damage may provide a useful reference for practical application.

Consumption online has been developed rapidly in recent years. At the same time, security issue is emerging with the development of consumption online. The process of consumption online can be divided into choosing goods, payment and settlement as well as logistics, and it includes user identity security, financial security and cargo security respectively. This paper will make a preliminary study from these three aspects. The paper summed up the safety precautions in consumption online in three aspects. The process of consumption online can be safeguarded successfully by using these safety precautions.