Nonlinear Viscoelastic-Plastic Creep Model of Rock Based on Fractional Calculus

A rock creep constitutive model is the core content of rock rheological mechanics theory and is of great significance for studying the long-term stability of engineering. Most of the creep models constructed in previous studies have complex types and many parameters. Based on fractional calculus theory, this paper explores the creep curve characteristics of the creep elements with the fractional order change, constructs a nonlinear viscoelastic-plastic creep model of rock based on fractional calculus, and deduces the creep constitutive equation. By using a user-defined function fitting tool of the Origin software and the Levenberg–Marquardt optimization algorithm, the creep test data are fitted and compared. The fitting curve is in good agreement with the experimental data, which shows the rationality and applicability of the proposed nonlinear viscoelastic-plastic creep model. Through sensitivity analysis of the fractional order β2 and viscoelastic coefficient ξ2, the influence of these creep parameters on rock creep is clarified. The research results show that the nonlinear viscoelastic-plastic creep model of rock based on fractional calculus constructed in this paper can well describe the creep characteristics of rock, and this model has certain theoretical significance and engineering application value for long-term engineering stability research.

Breakage Characteristics of Quartz Sand Based on Ring Shear Tests: Implications for the Fragmentation Processes of Rock Avalanches

To investigate the effects of internal shear fragmentation on dry granular flow, in this study a series of ring shear tests were performed on quartz sand samples under different normal stresses (100 kPa, 200 kPa, and 300 kPa), shear displacements (3 m, 5 m, 10m, 15 m, and 20 m), and shear rates (30 deg min−1, 60 deg min−1, and 90 deg min−1). Next, the grain-size distributions, fractal dimensions, and microcharacteristics of the quartz sand before and after the experiments were compared and analyzed. The study results show that grain breakage under shearing preferentially occurs at the edges of the particles and forms a bimodal distribution in frequency grain-size distribution curves, which is consistent with observations of rock avalanches. The fine particles prevent the coarse particles from breaking, in turn leading to the ultimate grain-size distribution and stable fractal dimension (2.61) of quartz sand at relatively small shear displacements compared with the travel distance of rock avalanches. The results of this study suggest that the fragmentation of rock avalanches during the shear spread stage may be far less significant than previously believed. Therefore, the fragmentation effect is not considered to be a major factor of the hypermobility in the late stage of rock avalanches.

Extended Ultimate-Pit-Limit Methodology for Optimizing Surface-to-Underground Mining Transition in Metal Mines

The transition from surface mining to underground is a critical issue for metal mines. The commonly cited procedure cored by ultimate-pit-limit (UPL) methodology is restricted to maximize the profit from both surface and underground mining, due to the absence of the integration of the profit from either of them. Under the target for such maximization, this study proposes a new optimization approach, which directly relates the design of open-pit limit and underground stopes, by equalizing the marginal profit from either surface or underground mining. The variation of the crown pillar size is involved in this approach. The proposed approach is applied to the Dagushan iron mine, and results show the total profit increased from 3.79 billion CNYs (original design by conventional UPL methodology) to 4.17 billion CNYs (optimal design by the proposed approach), by 9.91%. Moreover, the marginal profit from surface and underground mining, as well as total profit, of all possible designs of surface-to-underground mining transition in Dagushan iron mine is calculated to validate the proposed approach. When the marginal profits satisfy the criterion of the proposed approach, the maximum value of the total profit appears, and this demonstrates the proposed approach is robust to maximize the total profit in surface-to-underground mining transition. This work contributes to existing literature studies primarily from practical aspect, by providing a unified approach to optimize the transition from surface to underground mining.

Force-Deformation Study on Glass Fiber Reinforced Concrete Slab Incorporating Waste Paper

This study inspects the viability of engaging the discarded paper wastes in concrete by varying the volume proportions from 0%–20% with each 5% increment in replacement of the weight of cement. A physiomechanical study was conducted, and the results were presented. A glass fiber reinforced rectangular slab with a longer span (ly) to shorter span (lx) ratio of (ly: lx) 1.16 was cast with optimum replacement of waste-paper mass and compared the force-deformation characteristics with the conventional concrete slab without waste paper. The optimum percentage of discarded papers for the replacement of cement is 5%. Also, the results imply that the compressive strength at the age of 28 days is 30% improved for the optimum replacement. Based on the outcomes of the investigation, it can be inferred that the compressive strength gets progressively reduced if the volume of the discarded paper gets increases. The incorporation of glass fibers improves the split and flexural strength of the concrete specimens considerably. The ultimate load-carrying capacity of the glass fiber reinforced waste paper incorporated concrete slab measured 42% lower than that of the conventional slab. However, development of the new type of concrete incorporating waste papers is the new trend in ensuring the sustainability of construction materials.

Measuring Compressive Strength Characteristics of Soil-Dobak-Glue Mixtures over Curing Time

The building materials used by mankind in the past, such as stone, soil, and wood, have been environment-friendly. However, the various building materials invented over time with the development of the industrial age pose problems such as environmental hormone generation and waste generation/disposal. To overcome these problems, building materials based on soil, a traditional building material, are being developed by researchers. However, the improvement in soil’s structural characteristics is insufficient as it excessively emphasizes efficacy and function only. In this study, lime and Dobak-glue were mixed with soil to solve the structural problems and improve the strength of soil, and water content and change in strength in accordance with curing time were tested. In order to understand the change in strength, a compaction test was performed by preparing a standard specimen based on the optimum water content and maximum dry density. The lime mix required optimum water content and quantity of lime equal to 3% of soil weight, while the Dobak-glue mix was prepared by soil mixing in the same weight ratio as optimum water content. Changes in water content and compressive strength were measured over curing time of 3, 7, and 28 days. Three specimens, lime mixed specimen, Dobak-glue mixed specimen, and standard specimen, were prepared, and their water content and compressive strength values were averaged. Although the change in water content according to the curing period differed depending on the material mixed with soil, there was no significant difference between 7.12% and 2.82% after 7 days. As for the change in compressive strength, the initial compressive strength in lime mixed specimen was excellent, but the Dobak-glue mixed specimen displayed the greatest strength after 7 days. To conclude, Dobak-glue is an eco-friendly material, and it can be very useful in compensating for the structural shortcomings of soil.

Dynamic Rock-Breaking Process of TBM Disc Cutters and Response Mechanism of Rock Mass Based on Discrete Element

Rock-breaking efficiency of full-face rock tunnel boring machine (TBM) is closely related to the performance of the disc cutter and the characteristics of the rock mass. In the point of view of mesomechanics, the particle flow code (PFC) is used to establish a numerical model of the rock mass and the disc cutter, and the process of TBM disc cutter intrusion into the rock mass is analyzed. The dynamic response mechanism and crack evolution process of the rock mass under the action of the disc cutter are studied on the basis of micromechanics, and the relationship between the rock mass crack, penetration, and cutting force during the intrusion of the disc cutter is revealed. The sensitivity analysis is carried out on the confining pressure conditions and the influence parameters of the disc cutter spacing. The results show that the rock breaking by disc cutter undergoes the transformation characteristics of compaction, shearing, and tension failure modes, and the failure process of the rock mass is the joint action of tension and shear. In the whole process of rock breaking, the disc cutter has the phenomenon of repeated loading-unloading alternation and leaping rock breaking; after the penetration of the disc cutter reached 9.0 mm, penetration creaks begin to appear on the surface of the rock mass; the penetration was obviously reduced with the increase of confining pressure, and it is mainly the penetration cracks on the surface; after the disc cutter spacing reaches 100.0 mm, there is no penetration crack between the two disc cutters. The research conclusion can provide a reference for the disc cutter optimization design.

Production and Evaluation of Porous Photocatalyst Concrete Filter (deNOx PCF) for NOx Reduction

A porous photocatalyst concrete filter (deNOx PCF) is successfully manufactured to reduce NOx by mixing TiO2 photocatalyst with lightweight aerated concrete. From the results, 4% infusion rate of each foaming agent provided the smallest change of the height, and the optimal quality of the air bubbles can be produced by using foaming agent B with 4% of infusion rate. When 3% of TiO2 photocatalyst was mixed, less irregular and relatively homogeneous pores were formed on the surface with white color due to the proper amount of photocatalyst applied. For 3% of photocatalyst mixed with deNOx PCF, 1.03 μmol/hr of NO was reduced equivalent to 10.99% of NO reduction, suggesting that the TiO2 photocatalyst dispersed in the continuous and well-developed pores inside the specimen successfully performed the removal of NO flowing through deNOx PCF using synergistic effects of adsorption and photodegradation reaction. Finally, the specimen of porous deNOx PCF for reducing NOx developed in this study can be applied to various construction sites and the air quality can be solved by reducing NOx contributing to the formation of fine particles.

Study on Strengthening Mechanism of Epoxy Resin/Rubber Concrete Interface by Molecular Dynamics Simulation

Rubber concrete has high environmental and economic benefits. However, the difference in the physical and chemical properties of the interface causes a weak interface between rubber and concrete, which limits the use of rubber concrete to a certain extent. Based on the macroexperiment of epoxy resin (EP) modified rubber concrete, from the nanoscale level, three interface models of Rh (natural rubber)/C-S-H, EP/C-S-H, and Rh/EP/C-S-H were constructed by molecular dynamics simulation to explore the interaction between epoxy resin and rubber cement-based interface and reveal its microreinforcement mechanism. The results of interaction energy, radial distribution function, and mean square displacement show that the addition of EP not only improves the interface interaction energy between Rh and C-S-H but also provides a large number of hydrogen bond donors and receptors, promotes the diffusion of Ca, and increases the adhesion between Rh and cement matrix. The results of the analysis of mechanical properties show that the elastic modulus of the rubber concrete interface model is improved and the interface properties are improved after adding EP.

Effect of Ball Milling Time on the Performance of Phosphorous Building Gypsum

The use of phosphogypsum to prepare phosphorus building gypsum (PBG) is of great value to the resource utilization of phosphogypsum. In this study, PBG was ball-milled to obtain phosphorus building gypsum with good performance, which can meet the requirements of the Chinese standards for first-class building gypsum. Meanwhile, the changes of net slurry physical properties, mechanical properties, and particle size parameters of PBG under different treatment times were analyzed. With the increase of ball milling time, the particle size of PBG decreased rapidly and then stabilized, and the specific surface area gradually increased and then started to rise back. Ball milling can significantly reduce the standard consistency water requirement of phosphogypsum, resulting in a shorter setting time and higher strength of phosphogypsum. In the fixed water consumption test, the effect of ball milling time on the performance of phosphogypsum was small. Compared with sieving, washing, aging, and other means of PBG treatment, ball milling has the advantages of simplicity, environmental protection, and low cost, and it has some practical significance in production.

Evaporative Cracking Characteristics of the Embankment Soil Affected by the Saline Concentration

Embankment soil affected by saline can not only cause roadbed settlement, frosting, and road cracks but also cause corrosion and cracking of roadbed pipelines, which seriously affects the stability of the road. Water evaporation and dry cracking of the saline soil mainly cause soil swelling, poor water stability, and corrosive characteristics of the embankment soil. In this study, the evaporative cracking characteristics of soil with different saline concentrations were investigated. The results showed that the moisture content decreased linearly with the drying time in the early evaporation process, subsequently decreased slow down in the mid-term evaporation, and finally become got and remain a residual moisture content, which are 46.39%, 44.05%, 42.70%, and 40.27% with the increase of the saline concentration. The evaporation process with different saline concentrations in the soil can be divided into three stages: uniform evaporation stage, slow down evaporation stage, and equilibrium evaporation stage, which was consistent with the moisture content change. With the development of the drying time, the cracks gradually appeared on the soil surface, gradually deepened in the soil, and expanded the crack network. The development of cracks can be divided into three stages: the cracking preparation stage, the crack development stage, and the crack stable stage. The cracking began at high evaporation rate under high saline concentration, and the fractal dimension remained stable under similar saline concentration. The fractal dimension was gradually increased with the decrease of the moisture content and the increase of the saline concentration, respectively. The soil began to crack with larger moisture under high saline concentration. The drying cracks in the nature were consistent with the configuration of the cracks formed in the experimental results.