Geopolymer is a low-carbon building material made of silico-aluminous solid waste and alkaline activator, and the appropriate initial curing temperature (ICT) can improve its macroscopic mechanical properties. This study developed blast furnace slag (BFS)-fly ash (FA)-red mud (RM) geopolymers (BFRG) through a calcium carbide residue-activated industrial solid waste technology. The methods used in this study include unconfined compressive strength testing, computer (CT) scanning, and nuclear magnetic resonance (NMR) to examine how ICT affects the compressive strength of BFRG. The results show that ICT has a threshold temperature effect on BFRG compressive strength. Medium temperature (20-40 degrees C) curing is beneficial to the development of strength in each stage. Although high-temperature (50-60 degrees C) curing improves early strength, the long-term increase decreases. Therefore, the curing effect of medium temperature (20-40 degrees C) is better than that of high temperature (50-60 degrees C). For specimens cured for 1 day, both pore number and volume increased gradually with temperature, with most pores falling within the 0-100 nm range. The morphology of hydration products changed from rod-like to network-like structures, and microcracks began to appear at 60 degrees C. As ICT increases, the potential, kinetic, and non-bonded energies, as well as the total energy of the system under the NVT ensemble, rise, though at a slow rate, indicating that the system remains stable. These findings offer a theoretical foundation for optimizing the design and supporting the sustainable development of BFRG.

To address the inefficiency of repeated grouting in conventional microbial soil reinforcement, this study investigates a novel single-grouting approach incorporating pre-hydrolysis for sandy soil stabilization via biocarbonation. By regulating the dosage of reactive magnesia cement (RMC), urea concentration, and prehydrolysis duration, the effects on sand column mechanical properties, carbonate mineral formation, and urea utilisation rate were systematically examined. Combined with multiple mineralogical characterisation techniques, the crystalline phases and morphological features of the bio-carbonation products were analysed. Experimental results indicate that when the RMC content exceeds 10 %, pre-hydrolysis enhances the mechanical properties of the specimen, carbonation degree, and urea utilization, with these improvements increasing alongside the urea concentration. However, excessively high RMC content impedes pre-hydrolysis bio-carbonation. Mineralogical and microscopic analyses revealed that the pre-hydrolysis process enhances cementation by increasing carbonate supersaturation and the degree of carbonation. This generates abundant mixed crystalline phases comprising both metastable and stable states, manifesting as micro-spherulites, rods, cubes, and other morphologies. This study validates the feasibility of urea pre-hydrolysis bio-carbonation technology for singlegrouting reinforcement of sandy soils, providing valuable reference for its practical application as a grouting reinforcement technique in engineering projects.

This study investigates the impact of blending polypropylene fibers of multi-length (3, 6, 9, and 12 mm) on the flexural properties of controllable low-strength materials. Three-point bending tests and scanning electron microscopy (SEM) were conducted on geopolymer-cemented aeolian soil (GCAS) reinforced with multi-length fiber. The geopolymer was prepared using red mud, slag, and fly ash as raw materials. The influence law of the multi-level fiber structure on the flexural strength and fracture parameters, and microscopic mechanisms of GCAS was analyzed. The results show that the contribution of short fibers (3-6 mm) is mainly reflected in the initial stage of crack initiation, the medium-length fibers (9 mm) achieve the best balance in number and length, and the long fibers (12 mm) can still effectively connect the two sides of the crack surface after crack propagation, so that the specimen shows higher residual bending strength. After the chemical reaction between geopolymers and the surface of aeolian soil particles, a thin layer is formed to cover the surface of soil particles. Geopolymers form a "locking" effect with fibers through mechanical embedding, so as to enhance the binding force between the fiber surface and geopolymers. C-H is stacked in a sheet-like structure, and C-S-H presents a short chain and amorphous structure. When the multi-level fiber composite structure mode is 6-9-12 mm, the synergistic effect of the fibers makes the GCAS exhibit stronger flexural failure resistance, and the peak flexural strength reaches 0.85 MPa. This represents a 174 % improvement over unreinforced specimens and demonstrates superior performance compared to conventional cement-based materials. Which can provide a theoretical basis for optimizing the mechanical properties of controllable low-strength materials.

During the process of sand cementation using the traditional biocementation technology EICP/MICP (Enzyme/Microbially induced carbonate precipitation), the significant release of ammonium ions and ammonia gas poses environmental concerns. This study proposes an eco-friendly approach: Soybean urease induced calcium phosphate compounds precipitation (SICCP). This method employs bone meal, soybean, and urea as raw materials to stabilize sand. The effectiveness of SICCP-stabilized sand was assessed using a variety of analytical methods, including unconfined compressive strength test, precipitation content analysis, three-dimensional reconstruction of CT images, microstructural observation, and mineral composition analysis. Results indicate that optimal sand column strength, reaching up to 625 kPa, was achieved with an initial cementation solution pH of 3 and a soybean urease solution ratio of 0.2. Increasing the initial pH of the cementation solution and the soybean urease solution ratio led to decreased uniformity of calcium phosphate compounds (CPCs) and a corresponding reduction in strength. Compared to EICP/MICP technology, the cost of SICCP is lower, and the amount of ammonia gas and ammonium ions released into the environment can be reduced by approximately 96 % and 57 %. The findings of this study provide novel insights and a theoretical foundation for advancing biocementation technologies toward a more environmentally sustainable direction.

Soil salinization is a significant challenge to land use in NW China, and the continuous dry and wet cycles in the region also have long-term effects on the engineering properties of saline soils. In this study, dry and wet cycles tests were conducted on artificially prepared salinized loess to analyze the hydraulic properties of saline soils under alternating dry and wet conditions. The saturated infiltration coefficient and soil–water characteristic curves of the soil specimens were measured after dry and wet cycling. Numerical simulation models were employed to quantitatively analyze the effects of dry–wet cycles and salt content on soil permeability properties. The study found that salt content had a significant effect on the saturated permeability coefficient of saline loess, and that the permeability coefficient of the soil decreased and eventually stabilized with an increase in the number of dry and wet cycles. The experimental results were used to establish a saturated permeability coefficient model and a soil–water characteristic curve fitting model, which take into account the number of dry and wet cycles and soil salt content effects, and the models were then used to predict and analyze the unsaturated permeability coefficient of the soil.

Dispersive soil is highly susceptible to water erosion, leading to significant engineering challenges, such as slope instability and canal damage. Common modifiers such as lime are effective but cause environmental pollution. Therefore, it is important to explore eco-friendly modifiers. This study investigates the effects of sticky rice and calcium chloride (SRC) on dispersive soil. Dispersivity tests identified an optimal ratio of sticky rice to calcium chloride of 3:1. To analyze the effects of different SRC contents and curing times on the soil properties, tests of dispersivity, hydraulic, mechanical, chemical, and microscopic mechanisms were conducted based on this optimal ratio. The results indicated that 1.5% SRC effectively eliminated soil dispersivity even without curing, and its effectiveness improved with an extended curing time. After 28 days of curing, the water stability increased significantly, permeability decreased by an order of magnitude, and cohesion improved by approximately 85.97%. SRC reduced soil dispersivity through three primary mechanisms: lowering the pH, promoting ion exchange between Ca2+ and Na+, and the cementing effect of the sticky rice paste. Additionally, Ca2+ acted as a bridge between organic colloids and clay particles, further strengthening the structural stability of microaggregates. Overall, SRC proved to be an effective eco-friendly modifier for improving physicochemically dispersive soil.

Seepage causes the soil structure changing that would influence the safety and stability of geotechnical infrastructures significantly. However, the effect of grain size distribution on seepage behaviors subject to suffusion of sand remains unclear to date. A series of suffusion tests on different grading considering the fines content and grading parameter was carried out to explore the seepage behaviors of gap-graded sand. The results showed that the suffusion evolution process of the gap-graded sand can be divided into three stages: stabilization, development, and failure stage. Fines content and grading parameter have a significant influence on the hydraulic conductivity of gap-graded sand. The critical hydraulic gradient, including initiation and failure hydraulic gradient, of different grading gap-graded sand can be obtained. The final fines loss rate decreases with an increase in fines content, and increases with an increase in grading parameter. The variation of global and local hydraulic conductivity of gap-graded sand can be described as a “tree structure”, which can be distinguished into two stages: “tree trunk” and “dendrites”. The local hydraulic conductivity of the upper parts is smaller than that of the lower parts of the sample. A three-dimensional surface describing the correlation among the fines eroded ratio, the suffusion time, and the initiation hydraulic gradient is proposed and verified by the tested data of sand and sandy gravel samples.

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Dispersive soil is a common problematic soil that segregates in water, resulting in instability of slopes and posing significant threats to the safety of earth structures. However, there is a limited amount of research on the hydraulic erosion of dispersive soil. Splash erosion is the initial stage of hydraulic erosion. A clear understanding of splash erosion is crucial for investigating dispersive soil hydraulic erosion. This study explored the influence of soil dispersity and rainfall intensity on the characteristics of splash erosion by conducting consecutive single-drop rainfall tests on artificially prepared non-dispersive and dispersive soil samples with varying sodium carbonate content. High-speed cameras and single-lens reflex (SLR) cameras were used to capture the variations of the splash crown, splash pan, and splash crater. Results showed that the content of sodium carbonate significantly affected splash erosion. High soil dispersity resulted in smaller masses of splashed soil material and infiltration water, but a larger mass of splashed water. It also led to a smaller volume and depth of the splash crater. The critical value of the content of sodium carbonate for soil dispersity discrimination was 0.15 %, the same as the threshold for the splash process to stop significant changes. The shape of the splash crown also helped analyze the process of splash erosion and was relevant to the splash crater shape. Increasing soil dispersity diminished the impact of rainfall intensity on splash erosion. These findings provide new comprehension of the mechanism of splash erosion of dispersive soil and lay a foundation for the systematic study of hydraulic erosion of dispersive soil in engineering slopes.

Purpose The purpose of this paper is to develop an appropriate machine learning model for predicting soil compaction degree while also examining the contribution rates of three influential factors: moisture content, electrical conductivity and temperature, towards the prediction of soil compaction degree. Design/methodology/approach Taking fine-grained soil A and B as the research object, this paper utilized the laboratory test data, including compaction parameter (moisture content), electrical parameter (electrical conductivity) and temperature, to predict soil degree of compaction based on five types of commonly used machine learning models (19 models in total). According to the prediction results, these models were preliminarily compared and further evaluated. Findings The Gaussian process regression model has a good effect on the prediction of degree of compaction of the two kinds of soils: the error rates of the prediction of degree of compaction for fine-grained soil A and B are within 6 and 8%, respectively. As per the order, the contribution rates manifest as: moisture content > electrical conductivity >> temperature. Originality/value By using moisture content, electrical conductivity, temperature to predict the compaction degree directly, the predicted value of the compaction degree can be obtained with higher accuracy and the detection efficiency of the compaction degree can be improved.

Dispersive soil is a widely distributed problematic soil in arid or semiarid areas of the world and can cause pipe erosion, gully damage and other seepage failures. This study analyzed the effect of environmentally friendly enzyme-induced carbonate precipitation (EICP) on the dispersivity of dispersive soils. This methodology was tested for the stabilization of three dispersive soil types (two high-sodium soils, two low-clay-content soils, and two soils with both high sodium and low clay contents) to examine the impact on dispersivity based on the results of pinhole tests and mud ball tests. Physical, chemical, mechanical, and microscopic tests were also conducted to investigate the effects of the components in the EICP reaction solution on dispersive soil modification. The experiments showed that the concentration of the reaction solution and the curing time required to limit the dispersivity decreased with increasing clay content in the soil. Ca2+ limited the dispersivities of dispersive soils via four distinct mechanisms. The first mechanism was ion exchange; Ca2+ decreased the percentage of exchangeable sodium ions to less than 7

The compaction degree is an important parameter for evaluating the quality of soil compaction in many engineering constructions such as roads, housing construction, and water conservancy project, and it correlates with moisture content and electrical conductivity. Frequency domain reflectometry (FDR) can rapidly measure soil moisture content and electrical conductivity. Firstly, in this research, FDR was adopted to rapidly measure the values of soil moisture content and electrical conductivity regarding lateritic soil, expansive soil, and loess at varying compaction degrees. Secondly, the measured values of moisture content were calibrated in laboratory, and the calibration curves of the three soils were obtained accordingly. Thirdly, empirical relationships between compaction degree, moisture content and conductivity of the three soils were established using the partial least squares regression (PLSR) analysis method, and compared with the measured value. Fourthly, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests revealed its mechanism from microscopic aspect. Finally, the predicted value of the compaction degree obtained by the fitting equation was verified, and an error evaluation system was established. The results show that such fitting equations based on the relationship between compaction degree, moisture content, and electrical conductivity have a high prediction accuracy. Therefore, the results in this work can provide a good reference for the rapid detection of soil compaction in roads, housing construction, water conservancy and other projects.

木钙与玄武岩纤维均可作为土壤改良剂,玄武岩纤维可有效提高土体黏聚力和抗剪强度,木钙可有效提高土体的水稳性和持水性,为探讨二者复合使用的效果,通过土工试验和人工降雨冲刷试验,研究了在黄土中单独掺加木钙、玄武岩纤维及二者复合掺加对黄土边坡力学性能及抗蚀性的影响.结果表明:玄武岩纤维和木钙复合使用可显著改善黄土的力学指标,木钙掺量为 1.5%+玄武岩纤维掺量为 0.4%是二者复合使用的最优配比,按此配比改良的黄土的黏聚力、内摩擦角与单掺 1.5%木钙相比分别增大67.2%、17.8%,与单掺 0.4%玄武岩纤维相比分别增大 14.4%、9.8%,且崩解速率较素土显著降低;改良黄土边坡抗渗能力显著提高、渗透系数减小、雨水入渗减缓、抗蚀性显著增强,在雨强为 50 mm/h、降雨时长3h的情况下累计冲刷量比素土边坡累计冲刷量减少99.8%.

课程组是高校基层教学组织的主要形式之一,近年来课程组在高校的功效发挥和建设发展并不理想.文章提出课程组建设主要分为制度建设和教师发展两方面的思考与探讨.从课程质量标准、教学计划、教改项目、课程建设、教材建设、教研活动制度化、指导学生7 个方面论述课程组相关的制度建设;从团队建设、新进教师准入、青年教师培养、激励与考核4个方面论述如何进行课程组教师培养与发展.

This paper investigates the damage of loess slopes under the influence of short-term extreme rainfall. The experiment took the loess soil of Yan’an City, Shaanxi Province, as the research object, and the backfill loess slopes were prepared with different slope gradient (45°, 60°, and 75°). Artificial rainfall model experiments with a rainfall intensity of 120 mm/h and a rainfall duration of 4 h were carried out on three slopes. The experiments monitored the wet front migration pattern, rainfall infiltration characteristics, water content variation, pore water pressure variation and slope damage pattern. The experimental results show that the infiltration characteristics of rainwater are similar for slopes with different gradients. As the depth of the infiltration increases, the velocity of infiltration will decrease. In the early stages of rainfall, the degree of intrusion can reach 70–80

Sodium persulfate,lime,fly ash,and carbide slag were used as solidification/stabilization agent materials to investigate the influence of different materials content ratios on the unconfined compression strength,toxic leaching concentration,and acid neutralization capacity of petroleum-contaminated soil,which based on the orthogonal test included four influenced factors and four levels.The optimization ratio of solidified/stabilized materials was selected under fuzzy optimization theory frame.The changeable rules of p H value,temperature,S 2 O 8 2– content and total petroleum hydrocarbon content were analyzed to explain the solidified/stabilized mechanism of petroleum-contaminated soil.The X-ray diffraction test （XRD） and scanning electron microscope（SEM） test were also conducted to illustrate the microscopic mechanism in solidification/stabilization of petroleum-contaminated soil further.The experimental results showed that the sodium persulfate content had the greatest influence on the unconfined compression strength and toxic leaching concentration of petroleum-contaminated soil based on the extremum difference analysis.And the lime content had the greatest influence on acid neutralization capacity of petroleum-contaminated soil.It also showed that the content of sodium persulfate,lime,fly ash,and carbide slag were 0.6%、8.0%、10.0%、6.0%,respectively,can be selected as the optimal ratio to solidify/stabilize the petroleum-contaminated soil according to the fuzzy optimization indexes of unconfined compression strength,toxic leaching concentration,acid neutralization capacity and handing cost.The unconfined compression strength was 630.40kPa.The toxic leaching concentration was 4.44mg/L.The acid neutralization capacity was 385.71cmol/kg.And the handing cost was136.46yuan/t.The solidified/stabilized petroleum-contaminated soil achieved the requirement of the strength of refuse reclamation and environmental safety.The toxic leaching concentration reduction,and the strength and acid neutralization capacity improved of the solidified/stabilizes petroleum-contaminated soil.The reasons can be explained by the fact that some petroleum can be removed from the contaminated soil because of oxidated reaction between sodium persulfate and petroleum.And the cemented substance was generated to cement the soil particles due to the hydration reaction of lime,fly ash and calcium carbide slag.

针对干湿循环作用下盐渍化黄土侧限变形问题,系统开展了侧限压缩试验及溶陷试验,研究了氯盐盐渍化黄土在不同干湿循环路径、不同干湿循环次数及不同初始干密度下的一维固结压缩特性和溶陷变形特性.结果表明:压实盐渍化黄土的压缩变形随初始干密度的降低而增大,随干湿循环次数和增湿饱和度的增加而增大;土样e-lgp(e为孔隙比,p垂直压力)曲线变化幅度及压缩系数随初始干密度的减小和干湿循环次数的增多而增大;不同干湿循环路径下土样的e-lgp曲线在干湿循环次数低于5次时差异较大,在干湿循环次数达到10次时趋于一致;盐渍化黄土溶陷特性对各类条件的敏感程度依次为增湿饱和度、干湿循环次数、初始干密度.针对不同条件下盐渍化黄土溶陷系数曲线的不同表现形式,建立简易3参数模型,并与试验数据对比,表明该模型能够表征初始干密度及干湿循环次数对溶陷系数的影响规律.研究成果可为盐渍化黄土的干湿循环效应认知提供参考.

仿岩溶碳酸氢钙(CFPK)改良碳酸盐渍土具有一定效果,但是存在碳酸氢钙分解速率慢、分解不完全等问题,导致改性效果不理想.为提高CFPK的利用率,以人工配制的碳酸盐渍土作为研究对象,采用土体中预掺入碳酸钙作为CFPK反应的晶核剂,通过物理、化学、力学、微观结构等试验方法,研究碳酸钙晶核剂对CFPK改良碳酸盐渍土效果的影响.试验结果表明,随着碳酸钙晶核剂掺量的增加,CFPK分解的速率越快,分解越彻底.碳酸钙晶核剂和CFPK联合改良后,土体易溶盐含量降低,抗湿化崩解性、无侧限抗压强度、抗剪强度大大提高.综合考虑碳酸钙晶核剂最优掺量为5％.碳酸钙晶核剂诱导CFPK分解,所形成的碳酸钙晶核剂和具有胶结作用的碳酸钙的整体,对土体有填充与固化的作用,同时可吸附土中的盐分,达到提高碳酸盐渍土工程性质的效果.

The crumb tests, the pinhole tests, the double-hydrometer tests, the pore water soluble cation tests and the exchangeable sodium ion percentage tests are the common methods for identifying the dispersivity of the fine-grained soils,which are complex and time-consuming. Based on the dispersive mechanisms of the fine-grained soils, the soil samples with different clay contents and sodium carbonate mass fractions are prepared artificially to analyze the suitability of the conventional discrimination methods for dispersivity and to propose a rapid and accurate discrimination method. The results show that the dispersive soils can be divided into physical dispersive soils which can be called low cohesive soils, chemical dispersive soils and physical-chemical composite dispersive soils. It also can be found that 10% of the clay content is the upper limit of physical dispersivity of the fine-grained soils. The mud ball tests, the pore water soluble cation tests and the exchangeable sodium ion percentage tests can be applied to all fine-grained soils, and the pinhole tests and the double-hydrometer tests are suitable for the fine-grained soils with a clay content no lower than 10%. The results of the mud ball tests should be used as the discrimination criterion for dispersivity if the clay content is lower than 10%, otherwise the discrimination criterion for dispersivity should be the strongest dispersivity results of the mud ball tests and the pinhole tests.The double-hydrometer tests, the pore water soluble cation tests, the exchangeable sodium ion percentage tests, and the pH tests are used as the explanatory tests for the dispersive mechanisms of the fine-grained soils, which have no influences on the comprehensive discrimination.

【Objective】 The influence mechanism of chemical interaction between trichloroacetic acid（TCA） and loess on its permeability was studied to provide reference for preventing groundwater pollution by TCA seepage.【Method】 The changes of pore distribution, porosity and average pore size of loess from Yangling contaminated by different TCA solutions（0%（pure water）,2% and 8%） were measured by MIP test.Soil column infiltration test was used to determine the effects of TCA solution with different mass fractions on loess permeability and water transport.Through turbidity test, X-ray diffraction test and SEM observation, the permeability of TCA in loess was analyzed from the perspectives of turbidity evolution of overburden solution, corrosion degree of loess cementation and structural morphology of surface particles.【Result】 When the mass fraction of TCA increased from 0% to 8%,the distribution density of pores with pore size between 0.1-1.0 μm decreased, the porosity increased from 25.2% to 40.4%,and the average pore size increased from 0.28 μm to 0.34 μm.TCA showed both agglomeration and corrosivity to loess.The 2% TCA solution was beneficial to the agglomeration of loess surface particles, indirectly expanded the seepage path, and enabled the overlying solution to penetrate quickly.The seepage time of the 2% TCA solution in the soil column was 70% of the pure water, which effectively increased the permeability of loess.The 8% TCA solution destroyed the cementation of loess structure and dispersed the loess surface particle dispersion to suspended particles.The settlement of suspended particles and turbidity current infiltration blocked the seepage path, and soil impervious layer with thickness of 1-3 cm was formed in the surface layer. Soil particles generated between needle and flake chloride crystallization further clogged pores and reduced the infiltration rate of solution.The seepage time in soil column was 3.6 times of that of pure water, indicating that the permeability of loess was significantly reduced.【Conclusion】 TCA solutions with mass fractions of 2% and 8% had different effects on loess permeability.The prevention and treatment of TCA pollution should consider the effects of TCA agglomeration and corrosion on loess permeability.