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Abstract Subway stations are important components of subway system planning and urban rail transit where passengers can board, alight, transfer, or wait. With an increase in urban passenger flow, subway stations must meet greater transfer‐space demands commensurate with growing station structure sizes. In this study, the field‐monitoring and analysis method was adopted to investigate the Huaxing Street Station of the Chengdu Metro Line 19 project and explore the temperature‐variation rule in the process of mass‐concrete pouring in the station floor. Based on an ABAQUS large‐finite‐element calculation programme and secondary development of damage and failure research methods, a mechanical model of mass‐concrete pouring in subway‐station floor construction was established. The pouring temperature effect, damage, and failure mechanism of mass‐concrete pouring in subway stations were comprehensively studied. The main results were as follows: (1) the maximum temperature difference between the upper and middle layers of the floor was dominant and reached a peak within 1–3 d after the completion of pouring, and the temperature difference gradually decreased with a decrease in the hydration‐heat reaction. (2) At 0–10 d, the damage ratio of the floor increased by 1.8%, predominantly in the form of longitudinal damage. Within 10–30 d, the damage and failure ratio of the floor increased by 1.86%, primarily in the form of transverse damage and failure. Within 30–40 d, the temperature of the floor stabilized and gradually approached the ambient temperature. The damage and failure ratio of the floor increased by 0.32% at this time. (3) The lower the ambient temperature, the greater was the damage sustained by the floor at different ages, and the ambient temperature had a significant influence on floor damage.

The laminae of varying lithologies are characteristic of shale oil reservoirs, with their pronounced heterogeneity and fluid–solid coupling significantly impacting oil productivity. To this end, this study initially quantified the permeability and mechanical heterogeneity in lamina-developed shale through permeability tests and quasi triaxial mechanical experiments on shale cores from different orientations in the Jiyang Depression. These tests revealed marked brittleness in horizontally oriented cores and elasticity in vertically oriented cores. Subsequently, the strong fluid–solid coupling in lamina-developed shale formations was hereby investigated by permeability stress sensitivity experiments and CT scanning, which presented the dynamic opening and closing of laminae and strong fluid–solid coupling in horizontal direction during the fracturing shut-in and production (FSP). Based on online nuclear magnetic resonance (NMR), fluid migration in pores of different scales and laminae during the FSP was discovered. To detail the fluid seepage mode in lamina-developed shale oil reservoirs during FSP, an oil–water two-phase flow model coupling shale matrix, laminae, and hydraulic fractures was further simulated, based on the permeability heterogeneous and stress sensitivity, to delve into the variation in saturation, pressure, relative permeability, and streamlines of water in lamina-developed shale cores. The results showed that during the hydraulic fracturing, the horizontal brittleness, and vertical elasticity created a seepage channel composed of shale matrix, horizontal seams, and vertical hydraulic fractures. During the shut-in period, the expanded seepage area resulting from the opening of the laminae, combined with the extremely high pressure gradient from the seam to the matrix, facilitated the invasion of fracturing fluid into the matrix, displacing shale oil and gradually balancing the pressure among the three seepage media. During production, the extremely high pressure gradient shifted from the matrix to seams and hydraulic fractures, and oil and water were simultaneously extracted. However, due to stress sensitivity and variations in relative permeability, fracturing fluid remained trapped in the shale formation. [ABSTRACT FROM AUTHOR]

The concrete used in the main structures of subway stations has a high degree of constraint. Consequently, temperature changes and shrinkage during construction frequently lead to significant constraint stress, which can result in structural cracking. Therefore, cement with low hydration heat is commonly used in engineering to reduce the temperature of concrete during its age. Aiming at the problem of hydration and heat release caused by concrete construction, based on the principles of concrete hydration heat release and a numerical analysis method, an optimized semi-adiabatic temperature rise test method has been introduced to investigate concrete temperature rise characteristics with different mineral admixtures. The following conclusions were obtained: The effect of reducing the heat of hydration is related to the content and material properties of different mineral admixtures, but not the type of mineral admixture to be incorporated. The temperature rise performance of four common mineral admixtures is as follows: ① total cooling capacity: limestone powder > slag, fly ash > metakaolin; ② early heat generation rate: metakaolin > slag > fly ash > limestone powder; ③ heat reduction rate in the middle and late periods: metakaolin > limestone powder > fly ash > slag. [ABSTRACT FROM AUTHOR]

The coalbed methane (CBM) productivity is directly determined by the fracture permeability during hydraulic fracturing, which is regulated by the distribution of proppants. The proppant may be unevenly distributed in the fracture because of variables like the architecture of the fracture and the characteristics of the sand‐carrying fluid. This study used two types of random functions to produce different ununiform distributions of proppant clusters in large‐scale fractures, with the aim of investigating the effect of these distributions on the overall permeability of the fracture. A model of fluid‐structure coupling is proposed. The closure of large‐scale fractures under in‐situ stress is analyzed using solid mechanics and the penalty function; the CBM flowing in proppant clusters and the high‐speed channel between them is simulated using Darcy's law and the Navier–Stokes equation, respectively; and the overall permeability of fractures is computed using the fluid pressure drop throughout the fracture and the fluid flowing velocity in the fracture's outlet. Since most CBM flows along high‐speed channels between the proppant clusters, the simulated findings show that the overall permeability of fractures with an uneven distribution of proppant clusters is significantly higher than that of the proppant cluster itself. As CBM becomes more discretely distributed, the proportion of CBM flowing within the proppant cluster continuously drops. As the permeability of the proppant cluster increases, the volume ratio of proppant clusters decreases, and the distribution of proppant clusters becomes more discrete, the overall permeability of the fracture continuously increases. [ABSTRACT FROM AUTHOR]

The concrete of the main structure of subway stations is highly constrained, so the temperature effect and shrinkage effect generated during the construction process often cause large restraint stress, thus causing the problem of structural cracking. Therefore, low-heat-of-hydration cements are usually used in such construction work to reduce the temperature during the aging of concrete. Therefore, based on the hydration heat release subprogram of concrete, an effective numerical simulation was carried out, and compared with the semi-adiabatic temperature rise test, a method of numerical calculation and parameter fitting to solve the influence coefficient of the hydration heat model was proposed, and the sensitivity of the hydration heat release model and the influence coefficient for several concrete mixtures with additives was studied. The main conclusions are as follows: (1) Combined with the measured temperature curves of several types of mineral-admixed concrete, the composite exponential exothermic model of several types of mineral-admixed concrete can be obtained by adjusting the parameter fitting to solve the influence coefficient of the exothermic hydration model proposed in this paper. (2) One can adjust the influencing coefficient a to control the maximum temperature of concrete. Similarly, the temperature curve of concrete can be adjusted by modifying the influencing coefficient b. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing is an effective way to exploit hydrocarbons in tight oil reservoir. The success of this technique lies on the creation of high conductivity channels for the oil and gas. Quantitative analysis of factors influencing the conductivity of propped fractures is significant for the design of the operation schedule. According to the definition of sphericity, cylindrical and planar proppants of different sphericity and sizes were presented. And disordered packs of nonspherical proppants in fractures of different widths were established by the discrete element method. The change of the proppant embedment and fracture width under different closure pressures were analyzed by the solid mechanics. During the fracture deformation, the pressure and velocity of the fluid flowing in fractures were simulated by Lattice‐Boltzmann method. Based on that, the effect of the proppant size, sphericity, and the fracture width on the permeability and conductivity of hydraulic fractures were investigated. The accuracy of the model was verified by the experimental data. The simulation results show that the fracture permeability and conductivity decrease with the decrease in the rock's Young's modulus, proppant size, and sphericity, and their stress sensitivity increases with the decrease in the rock's Young's modulus and the increase in the proppant size. Increasing fracture width can improve fracture conductivity more significantly than increasing fracture permeability. The permeability and conductivity of the fractures filled cylindrical proppants are higher than that of the fractures filled with planar proppants. [ABSTRACT FROM AUTHOR]

Abstract: The chromatographic separation of several isomeric anilines is a challenging issue. Herein, a simple method for the simultaneous determination of four groups of isomeric primary aromatic amines, including chloroanilines, methylanilines, methoxylanilines, and dimethylanilines, was presented. In this method, all of the 15 primary aromatic amines were easily transformed into the corresponding imine derivative by treatment with benzaldehyde under mild conditions. The formed isomeric imine derivatives were completely separated on a commercial capillary gas chromatography column. The effects of several derivatization parameters were investigated and optimized. Linearity in the optimized method ranged from 0.050 to 50 μg/mL with the squared correlation coefficients (R2) between 0.9981 and 0.9999. Reasonable reproducibility was obtained, with the intraday relative standard deviation (N = 5) ranging from 0.89 to 4.57% and interday relative standard deviation ranging from 2.26 to 7.69% at the concentration of 5.0 μg/mL. The developed method has been successfully applied to determine these isomeric aromatic amines in real samples. [ABSTRACT FROM AUTHOR]