Table of Content

28 December 2023, Volume 29 Issue 6

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The effect of biochar releases and its mitigation strategies and applications

YUE Meiru , HU Jiajun , GAO Mintian , LI Jixiang, , LIU Nan

2023, 29(6):  1003-1021.  doi:10.12066/j.issn.1007-2861.2560

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Biochar has been widely used in environmental remediation due to its high specific surface area, rich surface functional groups, stable structure, low cost, and its derivation from regenerable biomass. However, most existing studies focus on the physicochemical properties and functions of biochar, with few examining biochar releases. This paper analyzes the positive and negative effects of biochar releases in detail, lists methods to reduce soluble releases of biochar, and presents existing applications of low-release biochar. It provides useful methods and ideas for the preparation, modification, and application of low-release biochar in the future.



Preparation of silver nanowires and their flexible transparent conductive films

Liu Xiaowen, Qian Fei, Zhang Bo, Wu Meiying, Li Hongbin, Zhang Baohua

2023, 29(6):  1022-1029.  doi:10.12066/j.issn.1007-2861.2304

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Silver nanowires with a diameter of approximately 40 nm and a length to diameter ratio of approximately 300 were prepared via the polyol method. Subsequently, uniform, stable, and flexible transparent conductive films of silver nanowires were prepared by the spin coating method. Polyethylene terephthalateco-1,4-cylclohexylenedimethylene terephthalate (PETG) film was used as the substrate and Chitosan or Xanthan gum as the auxiliary film forming agent. It was found that the deposition density of silver nanowires dispersion had an significant effect on the transparency and electrical conductivity of silver nanowires flexible transparent conductive films. The light transmittance and electrical conductivity of the films reached a maximum when the deposition density was 10 mg/cm2 . The bending performance test of the film indicated good flexibility.



Meso mechanism analysis of geogrid reinforced foundations under strip footing

HOU Juan, , XU Dong , ZHANG Chen

2023, 29(6):  1030-1041.  doi:10.12066/j.issn.1007-2861.2463

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The geogrid reinforced foundation is a foundation treatment method to improve the bearing capacity of the foundation by laying appropriate geogrids at a certain depth under the footing. Based on model tests, a 3D particle flow code (PFC3D) was applied to simulate the geogrid reinforced foundation under strip footing. The bearing capacity and the reinforcement mechanism of the geogrid reinforced foundation were investigated by analyzing stress distribution, sand particle displacement, sand particle contact force, geogrid deformation and geogrid-sand interaction, et al. The results demonstrated that a more uniform loading was applied on the foundation by using the geogrid reinforcement, and the effective reinforcement length was approximately 1.3~1.5 times of the footing width. The primary reinforcement involved surrounding soil materials to interlock across the geogrid plane. This interlocking enhanced passive resistance, rendering the geogrid-reinforced foundation more integral. Consequently, stress redistribution occurred, leading to an improvement in bearing capacity. In addition, the lateral restraint of the transverse ribs was the main reason for inducing a tensile force in the longitudinal ribs. The deformation of geogrid had a reverse bending point under the applied loading. An upward and downward force was applied to the sand particles at the two sides of the reverse bending point, respectively. The tension membrane mechanism of the geogrid decreased the uneven settlement in the overall geogrid reinforced foundation.



Crack damage identification in beams based on crack-induced chord deflection

OUYANG Yu, XIA Dengke, CHU Penghui

2023, 29(6):  1042-1052.  doi:10.12066/j.issn.1007-2861.2341

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Based on the constructional characteristics of the crack-induced chord deflection function, the static damage identification method for cracks in Euler-Bernoulli beams with arbitrary boundary conditions is presented. First, with the crack taken as a linear torsional spring, the general analytical solution of the static bending deflection of the cracked Euler-Bernoulli beam with arbitrary boundary conditions was obtained. Second, its crack-induced chord deflection function was proven to be a piecewise cubic polynomial function, and a deflection-based numerical method was developed to identify the crack location and its equivalent torsional spring flexibility by fitting a crack-induced chord deflection function. Finally, the applicability and reliability of the crack damage identification method presented were verified numerically, and the influences of deflection measurement error, crack location, and depth on the damage identification results were examined. The accuracy of identifying the crack location was found to be higher than that of crack equivalent torsional spring flexibility, and the number of cracks and the selection of the crack identification interval have limited influence on the crack damage identification results. The identification method has strong robustness.



Integrated optimization of isolated structures throughout their lifetime

DUAN Boyang, ZHU jiejiang

2023, 29(6):  1053-1067.  doi:10.12066/j.issn.1007-2861.2368

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The current building standards do not fully satisfy the fortification target required by the existing aseismic regulations. As building design continues to develop, more designers have adopted the performance-based seismic design approach. The costeffectiveness index is a crucial principle in this approach. In this study, an immune genetic algorithm is utilized to optimize the isolated structure based on the cost-effectiveness index by considering the characteristics of isolated structures. The seismic isolation design simultaneously considers the initial cost, cost of loss, and maintenance cost of the structure, and an integrated optimization of the isolated structure is conducted. An actual isolated building is used to obtain the optimal layout of the seismic isolation layer. The results demonstrate that isolated buildings are better equipped to ensure the security of the building and reduce economic loss throughout its lifetime.



Room cooling load prediction model based on deep learning

LIN Yue, , LIU Tingzhang

2023, 29(6):  1068-1075.  doi:10.12066/j.issn.1007-2861.2532

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Accurate prediction value of room cooling load is the basis data for energy conservation in air conditioning operating process. Firstly, according to the room energy balance equation, with analysis of relationship among cooling load, heat extraction and heat storage, the room cooling load prediction model is put forward. The frequency domain decomposition method is employed to realize the calculation of heat storage, while the deep recurrent neural network is employed to realize the prediction of room cooling load under room air constant condition. Finally, combining the heat storage under room air temperature fluctuation condition and room cooling load under room air constant condition, the room cooling load prediction value under temperature control mode can be obtained. In order to improve the learning efficiency of deep recurrent neural networks, an adaptive switching method between Gauss-Newton method and Levenberg-Marquardt (LM) method is introduced. The building energy consumption simulation toolkits and real-test based experiments show that the proposed method can realize the prediction of hourly room cooling load quickly and efficiently. The proposed model and method realizes accurate prediction for room cooling load under temperature control mode, and can be utilized to realize the quantitative analysis for building passive thermal energy storage, as well as provide references for the direct load control in power grid demand side management.



Test of static neighbor pile shading effect model based on DIC technology

LIU Kai , LU Ye , TANG Qiaochu

2023, 29(6):  1076-1089.  doi:10.12066/j.issn.1007-2861.2472

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During the construction of a pile foundation, the initial-pressure pile pressing exerts shading effects on the post-pressure pile, and the post-pressure pile displaces and compacts the surrounding soil, causing the initial-pressure pile to float and tilt. These combined effects affect the bearing capacity and stability of the pile foundation. Therefore, it is of great engineering significance to study the shading effect of the piles during soil displacement. Model testing and digital image correlation (DIC) technology were used to investigate the effect of the initial-pressure pile on the post-pressure pile, varying parameters including pile spacing, sand and soil grain size, and pile body roughness. Through an examination of the horizontal displacement of the soil around the initial-pressure pile during the sinking of the post-pressure pile, a reduction was observed in the horizontal the shading effect with increasing pile spacing. By fitting the horizontal attenuation amplitude for various pile spacings, it was inferred that when the pile spacing reaches 6D (D=30 mm), there was basically no shading effect of the initial-pressure pile on the postpressure pile. Varying the soil grain size had no significant impact on the horizontal shading effect of neighboring piles. However, the attenuation amplitude decreased as the pile body roughness decreased, indicating that smoother pile body resulted in smaller shading effects. As the post-pressure pile exerted pressure on the initial-pressure pile, the initial-pressure pile experienced tilting and uplifting. In conclusion, the smaller the pile spacing and the rougher the pile body, the larger the horizontal displacement, tilt angle, and uplift effect on the initial-pressure pile. Moreover, the finer the grain size of the soil around the pile, the smaller the horizontal displacement and uplift effect on the initial-pressure pile, but the larger the tilt angle it experienced.



Characteristic analysis of freezing temperature field of connecting channel in saline saturated silt stratum under effect of groundwater flow

LI Fei, WANG Changhong, ZHANG Haidong, DONG Jihan

2023, 29(6):  1090-1103.  doi:10.12066/j.issn.1007-2861.2353

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Owing to the rapid development of urban underground space, the artificial freezing method has been widely used in the construction of subway-tunnel connecting channels. However, the mechanism of the freezing method as a joint result of water seepage and saline soil remains unclear. Hence, the originally planned freezing time is extended. A multifield coupling analysis under the interaction of water seepage and salt in the freezing process is proposed. The No.4 connection channel between Yongxing Avenue Station and Shennan Road Station of the Nantong Urban Rail Transit Line 1 is the research object in this study. First, based on heat transfer theory, as well as water seepage and salt migration in porous media, the physical-mathematical equation of the water-thermal-salt coupling method is established. Second, the finite element software COMSOL Multiphysics is used to simulate the freezing model test of saline soil mass, and the results of the model test are verified. Finally, the method above is applied to the construction simulation of the connecting-channel freezing method. A multiphysical field data monitoring equipment is designed, and the simulation and actual monitoring data are compared. The results show that the temperature of saline soil varies more slowly than that of non-saline soil. Additionally, a higher salt concentration in the soils implies a longer time required for their temperature to decrease to the same temperature. Moreover, the water head difference results in an asymmetrical frozen wall, and the thickness of the frozen wall upstream is smaller than that downstream. By calculating the thickness and average temperature of the frozen wall, it is discovered that the simulated freezing for 45 days does not satisfy the design requirements, and that the freezing time reaches 50 days. This study shows that safety is guaranteed when the freezing method is used in the connecting channel of Nantong Urban Rail Transit Line 1. The freezing method is a multifield coupling method that can be used under complex environmental conditions.



Experimental investigation on the impact of bedform permeability on hyporheic exchange characteristics

ZHAO Liang, , WANG Xueyong, , WANG Daifeng, , FAN Jingyu,

2023, 29(6):  1104-1114.  doi:10.12066/j.issn.1007-2861.2418

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The influence of bedform physical properties on the hyporheic exchange process was assessed by investigating the quantitative correlation and variation between the permeability of bedform elements and hyporheic exchange flux. This investigation was conducted using laboratory annular flume experiments and conceptual two-dimensional discrete bedforms. Based on the results, it was observed that bedform permeability has a significant impact on the hyporheic exchange process. Within the bounds of the experimental parameters, the presence of bedforms was found to introduce an additional pumping exchange. The contribution of this pumping exchange to the overall hyporheic exchange flux was found to be closely related to the permeability variation in the bedform elements. When the permeability of these elements was low, the pumping exchange and turbulence penetration decreased, leading to an overall reduction in the effective diffusion coefficient when compared to scenarios with a flat bed.