Understanding the strength and deformation behavior of recompacted loess is essential for the stability assessment of man-made geotechnical structures in loess regions. While numerous studies have examined the macroscopic mechanical properties of unsaturated recompacted loess, the underlying particle-scale micromechanical deformation mechanisms remain inadequately explored. In this study, a series of drained triaxial tests were conducted on unsaturated recompacted loess under varying matric suctions and mean net stresses to investigate their effects on strength and deformation behavior. The experimental results indicate that higher matric suction increases deviatoric stress due to suction-induced apparent cohesion, whose influence weakens with increasing mean net stress. Moreover, all specimens exhibit continuous volumetric contraction during shearing, consistent with the strain-hardening behavior observed in the stress–strain curves. To interpret these observations from a micromechanical perspective, the original Hill contact model within the discrete element method (DEM) framework was modified by incorporating suction-dependent micromechanical parameters. The modified model was calibrated and validated against laboratory data, showing good agreement in reproducing both stress–strain and volumetric deformation behaviors. Further micromechanical analysis reveals that suction enhances capillary bonding at low net stress, but its influence diminishes as the mean net stress increases. Specifically, at low net stress, higher suction results in a greater proportion of tensile (i.e., capillary) contacts and slightly reduced particle displacements, indicating stronger interparticle bonding. As the mean net stress increases, particle displacements become slightly larger and contact stability is primarily governed by vertical contact forces rather than suction effects. These micromechanical insights are consistent with the experimental observations, thereby establishing a clear link between particle-scale interactions and macroscopic mechanical responses.

Wetting-induced collapse is a characteristic instability of loess that poses serious risks to geotechnical structures and infrastructure in arid and semi-arid regions. Previous studies have focused on loess microstructure before and after collapse, with limited attention to pore evolution and even less to particle evolution. This study addresses this gap. Malan loess (Q3) from Yan’an, China, with varying initial water contents, was subjected to oedometer tests to assess wetting-induced collapse. The collapse process was divided into four stages. Scanning electron microscopy (SEM) and deep-learning-based image segmentation (U-Net++) were employed to quantify particle and pore morphology in different stages. The results showed that increasing initial water content reduced collapsibility. Specimens with higher initial water contents underwent greater compression before wetting, whereas drier specimens retained a more open pore structure and exhibited a larger collapse response upon wetting. Microstructural analyses showed that wetting-induced collapse involved the coordinated rearrangement of solid units and reconfiguration of the pore system under wetting and external loading. Specifically, larger weakly cemented aggregates broke down into smaller solid units, whose boundaries became smoother and rounder, with an increasingly horizontal alignment. Meanwhile, macropores transformed into smaller and more regular pores, resulting in a denser and more ordered soil structure. These findings provide new insights into the microstructural mechanisms underlying wetting-induced collapse in loess.

While several models can describe the impact of void ratio changes induced by mechanical loading on the soil-water retention curve (SWRC), they often do not account for the hysteretic behavior of the SWRC. This hysteretic behavior is crucial because it directly influences the redistribution of water within the soil, affecting both seepage patterns and the potential for irrecoverable deformation. In this study, we proposed a novel SWRC hysteretic model that considers the void ratio variation induced by both mechanical and hydraulic loading. The model links the physical quantities at the micro- and macroscales. Specifically, two expressions are derived to describe the relationship between the void ratio, mean net stress, and matric suction under wetting and drying conditions, based on two independent stress-state variables. Two existing formulations from a recent study, specifically those for the liquid bridge volume and the improved expression for evolving contact angles, were incorporated into the model. The proposed model has a clear physical meaning, and its parameters are easily obtainable. The model simulation results were compared to experimental data from isotropic and K0 stress states and an experimental condition in which the void ratio remained approximately constant throughout the drying process. The findings demonstrated that the model effectively captured the main features of the evolution of the SWRCs with void ratios, including the void ratios under different stress levels and matric suctions. The model ability to account for hysteretic behavior provides a more comprehensive description of unsaturated soil behavior.

The mechanical behavior of structured soils is influenced by both inter-particle bonding and fabric arrangements. Existing constitutive models primarily account for soil structure through fabric arrangements. In this study, we first present experimental investigations on intact loess samples, including isotropic compression (IC), conventional consolidation undrained (CU), and consolidation drained (CD) triaxial tests, which reveal the complex structural properties of the soil. Next, we employ the work done by strain energy to comprehensively account for soil structure, incorporating both inter-particle bonding and fabric arrangements. Subsequently, a new strain work constitutive model for structured soils is presented within the critical state framework. Specifically, a linear decreasing function between strain power and mean effective stress is introduced to capture structural degradation, and a new hardening rule is derived from the relationship between strain work and mean effective stress. Compared to traditional structured soil models, the proposed model offers clear physical meaning, and its parameters are easily obtainable. The model’s simulation results are validated against experimental data, demonstrating its ability to capture key mechanical and deformation characteristics, such as strain softening under CU conditions and strain hardening under CD conditions. Finally, we compare our model with the structured cam clay (SCC) model, and the results show that our model provides a better fit to the experimental data, further confirming its accuracy and effectiveness.

AbstractAdvancing and receding water contact angles, often denoted as the maximum and minimum apparent water contact angles, are crucial parameters reflecting a soil's water holding capacity. These parameters play an important role in establishing theoretical soil–water characteristic curves (SWCCs) for unsaturated soils. However, pre‐assuming constant advancing and receding contact angles during soil wetting and drying processes may be erroneous due to their close correlations with the water content and void ratio. To address this research gap, systematic laboratory measurements were conducted on a loess with different void ratios and water contents. Apparent water contact angles were acquired using an axisymmetric drop shape analyzer, enabling a comprehensive dataset. Analysis of variance was employed to assess the statistically significant differences between void ratios and water contents. The results reveal a significant increase in the observed water contact angle as the void ratio decreases and a decrease with increasing water content. Although both the void ratio and water content influence the water contact angle, the latter has a more pronounced effect. The relationship between the receding water contact angle and water content/void ratio is observed to be linear. The identification of this linear relationship offers insights into the fitting of the SWCC for loess across varying void ratios. This study serves to enhance theoretical methodologies, particularly in the adaptation of contact angles, thus facilitating the development of more precise SWCC models.

With the increasing demand for energy and the depletion of traditional resources, the development of alternative energy sources has become a critical issue. Shale gas, as an abundant and widely distributed resource, has great potential as a substitute for conventional natural gas. However, due to the low permeability of shale-gas reservoirs, efficient extraction poses significant challenges. The application of hydraulic fracturing technology has been proven to effectively enhance rock permeability, but the influence of environmental factors on its efficiency remains unclear. In this study, we investigate the impact of gas fracturing on shale-gas extraction efficiency under varying environmental conditions using numerical simulations. Our simulations provide a comprehensive analysis of the physical changes that occur during the fracturing process, allowing us to evaluate the effects of gas fracturing on rock mechanics and permeability. We find that gas fracturing can effectively induce internal fractures within the rock, and the magnitude of tensile stress decreases gradually during the process. The boundary pressure of the rock mass is an important factor affecting the effectiveness of gas fracturing, as it exhibits an inverse relationship with the gas content present within the rock specimen. Furthermore, the VL constant demonstrates a direct correlation with gas content, while the permeability and PL constant exhibit an inverse relationship with it. Our simulation results provide insights into the optimization of gas fracturing technology under different geological parameter conditions, offering significant guidance for its practical applications.

岩土体结构的破坏是由于施加能量超过变形能阈值所造成,基于能量的结构性参数更有利于反映结构性的本质特征.对不同含水状态,不同干密度的延安桃花山原状与压实重塑黄土进行了侧限压缩试验,发现孔隙比e与竖向压力P在ln(1+e)-lgP双对数坐标系内有良好的分段线性关系.在此基础上,基于应变能密度理论,推导提出了侧限压缩条件下的结构性参数映射能,并将该参数推广至复杂加载条件.进一步通过多个区域内,原状与重塑,不同含水率,不同干密度,不同埋深深度,不同粒度土体的侧限压缩试验结果,以及不同含水率土体的等向压缩试验结果,对提出结构性参数的合理性进行了验证.结果表明提出的结构性参数映射能物理意义明确,且能准确地定量表征不同状态,不同试验条件下土体的结构性.

The soil-water characteristic curve (SWCC) describes the relationship between water content (or saturation) and matric suction (or soil-water potential) in unsaturated soils. It is worth noting that the amount of water stored in soils during the drying process caused by evaporation or gravity drainage is more than that during the wetting process caused by infiltration and capillary rise under the same matric suction level. This phenomenon is described by the hysteretic behavior of the SWCCs. Based on existing knowledge, the contact angle and the ink-bottle effect caused by the grain-size distribution (or pore-size distribution) are the two main factors that affect the hysteretic behaviors of the SWCCs. First, the behaviors of a liquid drop sitting on an inclined surface are investigated by the numerical method, and a relationship between the contact angle and the water content during the wetting and drying processes is proposed based on the principle of the minimum potential energy. Second, the expression for the volume of the liquid bridge is modified to make the Young-Laplace equation keep valid in calculating the matric suction in the boundary affected zone, transition zone and the part of the residual zone on the w-lns plane. Finally, an analytical model for analyzing the hysteretic behaviors of SWCCs is proposed after introducing the Roshin-Rammler grain-size distribution function. The model has a clear physical meaning, and the parameters can be obtained easily. Moreover, the model can describe the hysteretic behaviors of the SWCCs. Taking the SWCC of recompacted loess in a foundation pit in Qujiang, Xi'an as an example, the model is verified. The results show that the proposed model can well reflect the nonlinear relationship between the matric suction and the water content. The model can also be used for studying the shear strength and the constitutive model for unsaturated soils.

Domestication and cultivation of edible and medicinal mushrooms are ongoing similar to 1,400-year-old evolutionary experiments. There are roughly 55 commercially cultivated mushrooms worldwide; however, genomes for many species are lacking, as is our understanding of mushroom domestication. In this work, 22 high-quality reference genomes, along with 63 transcriptome and 381 re-sequencing data, were reported for the first time. Combined with public genome resources, an integrated omics database (MushDB, http://mushroomomics.com) were constructed including 50 reference genomes, 265 transcriptome and 621 whole-genome re-sequencing data, covering similar to 90% of the worldwide commercially cultivated mushroom species. Using multi-omics data in MushDB, whole-genome variations of the representative wild and cultivated populations were used for selective sweep analysis to identify putative functional genes contributing to the mushroom domestication. Key genes in the starch and sucrose metabolism and mitogen-activated protein kinase signaling pathway, such as chb1, cdc24 and hog1, were putatively selected in Auricularia cornea, Lentinula edodes, Pleurotus eryngii and Pleurotus tuoliensis, indicating those genes might play important roles during mushroom domestications. The function of hog1 in the low temperature stimulation adaptation and short growth period in cultivation environment, which could facilitate the successful domestication, was validated using CRISPR/Cas9 system. Our work offers valuable and abundant omics open resource for wide research communities and lays solid foundations for multi-purposes in mushroom evolution, genetics, and breeding studies.

通过对胡麻岭隧道红层软岩进行侧限与三轴压缩试验,系统地分析该类软岩的压缩特性、脆性及延性区的强度参数、扩容特性以及能量转化特征.在此基础上,引入帽子屈服面模型,探究脆?延转化压力PT与名义先期固结压力P～C的关系.研究结果表明:正常沉积岩的名义先期固结压力均大于岩石历史最大竖向有效应力;当脆、延性区试样处于峰值应力点时,对应的黏聚力均大于其处于残余应力点时对应的黏聚力,而处于峰值应力点时,试样的内摩擦角均比残余应力点时试样的内摩擦角小;当脆性区试样处于峰值与残余应力点时,对应的黏聚力均比延性区试样的小,但内摩擦角均比延性区试样的大;在不同围压下,试样均先发生压缩而后扩容,扩容起始点均发生在峰值应力点前;扩容起始点所对应的体积应变、试样吸收的单元总应变能U与单元耗散能Ud均随围压增大而增大;总应变能?轴应变关系曲线在残余应力点出现明显的转折,单元耗散能?轴应变关系曲线在峰值应力点与残余应力点处均出现明显的转折,且转折趋势会随围压的增加而逐渐淡化;在施加围压时,延性区试样已经进入弹塑性变形阶段,初始屈服面为闭合的帽子模型;PT与P～C的关系与地质历史沉积环境、强度参数相关.

竖向卸荷状态下黄土的强度与变形特性对挖方区边坡失稳研究有重要的理论意义,从工程应用角度出发基于伯努利方程改进了室内直剪仪,即利用水箱代替砝码进行加、卸载,研究了非线性连续卸荷路径下黄土的强度与变形特性.研究发现:非线性连续卸荷路径下土体剪应力—位移曲线与未卸荷状态不同,具体表现在非线性连续卸荷过程中剪应力不仅与剪切位移有关也与卸荷比(R)有关;剪应力(τ)—剪切位移(δ)空间中,同一初始固结压力下,试样在卸荷比(R)较小时剪应力—剪切位移曲线与未卸荷时基本重合,当卸荷比(R)增大到一定值后,剪应力—剪切位移曲线出现软化现象,且卸荷速率越大,软化越明显;同时非线性连续卸荷工况下,抗剪强度与初始固结压力有关,随着初始固结压力的增加,卸荷引起的超固结效应明显增强;基于Mohr-Coulumb强度准则,采用指数衰减的数学模型可以较好描述非线性连续卸荷过程中强度参数的演化规律.

The soil‐water characteristic curve (SWCC) plays an essential role in the analysis of the shear strength, deformation, hydraulic conductivity, and aqueous diffusion of unsaturated soils. A review of methods proposed for fitting the main SWCCs is presented. The methods can be categorized into three groups, namely, (i) empirical methods, (ii) domain methods, and (iii) theoretical methods. A hysteretic model considering the contact angle hysteresis is proposed for fitting the main SWCCs based on a theoretical method. The model links the physical quantities at the micro‐and macro‐scale. Specifically, a modified expression describing the relationship between the volume of the liquid bridge and the water content is derived, and the contact angle hysteresis behavior is modeled based on the study of total thermodynamic potential energy. The model has a clear physical meaning, and the parameters can be obtained easily. Comparisons of the model simulation and experimental data show that the proposed model accurately captures the main features of the SWCC and describes the nonlinear relationship between the matric suction and the water content during wetting and drying processes.

In this study, we investigated the preconsolidation pressure (PC) of sedimentary soft rock and its relationship with brittle-ductile transition (BDT) pressure. We proposed a generalized preconsolidation pressure (PG) suitable for both soil and sedimentary soft rock, which is defined in terms of the yield stress of the initial sediment structure under confined lateral compression. We then explored the digenetic effect on PG using 24 sediment types. Next, PG and BDT pressure were verified using confined compression and conventional triaxial tests, respectively, on red-bed soft rock in the Dingxi region of China. Finally, we discussed the BDT mechanism and analyzed the relationship between the two characteristic pressures for a given initial yield surface considered structural strength. We found that the relationship was dependent on the strength parameters, the initial structural strength, and the coefficient of earth pressure at rest. The findings of this study will have a significant impact on the determination of BDT pressure of sedimentary rock in future studies.

In order to study the influences of meso-parameters on the macro-mechanical behavior of unsaturated soils under triaxial stress, based on the PFC3Dprogram, the numerical triaxial tests on unsaturated soils under equal confining pressure and suction based on the Hill contact model, which can exert matrix suction, are conducted.The relationships between the deviator stress and the axial strain under different meso-parameters are obtained.The numerical simulation results show that the Young's modulus and the friction coefficient have the greatest influences on the unsaturated soils, while the Poisson's ratio and the damping constant have a minor effect on deviator stress axial strain curve.The initial elastic modulus of the samples increases with the increase of the Young's modulus and the phenomenon of strain softening appears as well.The relationship between the friction coefficient and the peak strength shows obviously positive correlation when other parameters keep the same.This study has a certain guiding significance for the parameter calibration of the meso-contact model for unsaturated soils.

为研究含水状态对脆延转化特性的影响,针对工程性质特殊的胡麻岭隧道红层软岩展开了系列试验,探究了干燥与天然含水状态试样脆延性区的强度变形规律.首先对干湿组红层软岩分别进行不同围压下的常规三轴压缩试验,进一步引入脆性指标对岩样脆性程度进行定量表征,并基于Mohr-Coulomb强度准则以及考虑结构强度的初始屈服面模型对各特征应力进行了分析.在此基础上通过试验,从宏细观尺度上探究了红层软岩脆延转化机理.研究表明:岩样干燥后,峰值强度增加了93.39％～145.35％,残余强度增加了77.83％～133.72％,脆延转化压力增加近40％,峰值应变降低了24.13％～88.92％;延性区的干湿试样的黏聚力近似为脆性区的1.8倍,但内摩擦角均小于脆性区,为脆性区的50.4％～90.5％;同时发现延性区试样在施加围压时已经进入了弹塑性变形阶段,且脆延转化压力等于等向固结压力.该研究内容可进一步丰富红层软岩的工程特性,并为穿越红层软岩地下工程的开挖支护提供理论依据.

UNSODA, a free international soil database, is very popular and has been used in many fields. However, missing soil property data have limited the utility of this dataset, especially for data-driven models. Here, three machine learning-based methods, i.e., random forest (RF) regression, support vector (SVR) regression, and artificial neural network (ANN) regression, and two statistics-based methods, i.e., mean and multiple imputation (MI), were used to impute the missing soil property data, including pH, saturated hydraulic conductivity (SHC), organic matter content (OMC), porosity (PO), and particle density (PD). The missing upper depths (DU) and lower depths (DL) for the sampling locations were also imputed. Before imputing the missing values in UNSODA, a missing value simulation was performed and evaluated quantitatively. Next, nonparametric tests and multiple linear regression were performed to qualitatively evaluate the reliability of these five imputation methods. Results showed that RMSEs and MAEs of all features fluctuated within acceptable ranges. RF imputation and MI presented the lowest RMSEs and MAEs; both methods are good at explaining the variability of data. The standard error, coefficient of variance, and standard deviation decreased significantly after imputation, and there were no significant differences before and after imputation. Together, DU, pH, SHC, OMC, PO, and PD explained 91.0%, 63.9%, 88.5%, 59.4%, and 90.2% of the variation in BD using RF, SVR, ANN, mean, and MI, respectively; and this value was 99.8% when missing values were discarded. This study suggests that the RF and MI methods may be better for imputing the missing data in UNSODA.

The strength and deformation characteristics of loess under vertical unloading path is important for the study of slope instability in excavation area. From the perspective of engineering application, direct shear test is carried out. Moreover, a discrete element method model is established to study micro-mechanism of multi-stage unloading. It is found that the shear displacement-shear stress curve of the soil under the multi-stage unloading path is different from those under the loading state. The soil sample is prone to shear failure during small deformation under multi-stage unloading. The shear strength is related to the initial consolidation pressure and unloading ratio. During the multi-staged unloading process, the number of contacts between particles does not change significantly, while the contact forces between particles decrease obviously.

Apparent preconsolidation pressure is an important parameter for soft rock. In this paper, investigated red bed soft rock was taken from Dingxi region, Gansu province, China. In order to obtain the apparent preconsolidation pressure of the soft rock, firstly, a new YS-1 high pressure oedometer was redesigned and used in the step loading confined compression experiments. Due to the soft rock’s low compressibility, the compressive curve was flat. Numerical mapping method was proposed considering curvature variation of the curve was not obvious. Secondly, the actual boundary condition which is the void ratio should monotonically decrease with the vertical pressure in the given domain was introduced. The existing 7 mathematical models were compared using the new defined conditions. The results showed that the Harris model was in good agreement with the compressive experimental results. Finally, the apparent preconsolidation pressure of the soft rock was calculated using the equations established in this research.

针对螺旋钻开采薄煤层保护层的条件,采用相似模拟实验,模拟薄煤层钻采后上覆岩层运动破断规律,确定了岩层破坏形式与裂隙发育特征.在近距离煤层群开采时,采用钻采方式开采保护层能够在不破坏被保护层整体结构的同时,起到有效卸压作用.钻采工作面覆岩运动规律与顶板位移与长壁工作面存在差异.

为指导高河煤矿W1309高瓦斯超长综采工作面安全高效开采,工作面布置双尾巷回采巷道,有效降低瓦斯浓度,防止瓦斯积聚并采用UDEC、PFC2D数值模拟的方法对超长综采工作面顶板破断特征以及不同放煤步距下顶煤的采出率进行了研究.