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PurposePermeability is one of the primary concerns in geotechnical engineering research. The permeability coefficient, the most significant parameter defining permeability, has a significant impact on the mechanical and physical properties of the soil by virtue of its value. Because soil is a bulk material and its internal seepage channels are intricate, it is challenging to accurately describe those using straightforward physical parameters. As a result, the models currently in use for calculating the coefficient of permeability of soils are mostly skewed towards empirical statistics and have issues with uneven magnitude and ambiguous physical significance. Thus, one of the key scientific issues in the field of geotechnical engineering is the development of a permeability coefficient estimate model that can characterize the seepage channel.MethodsBased on the idea of hydraulic radius in circular pipe flow, this paper establishes the calculation method of the equivalent hydraulic diameter by analyzing the microstructure of the soil body and proposes the idea of equivalent hydraulic force inside the soil body, taking into account factors such as granular gradation, dry density, and specific gravity of solid particle. Furthermore, a theoretical model based on the equivalent hydraulic diameter has been constructed for the permeability coefficient of the soil body, by introducing the coefficient of fluid dynamic viscous and the water gravity. In order to assess the accuracy and validity of the equivalent hydraulic diameter and the model of soil permeability coefficient estimation, permeability tests were designed and the results of undisturbed loess, single particle size quartz sand, and multi-grain-size quartz sand combinations were obtained. The results of the estimated model, the traditional estimated model, and the permeability coefficient of the tests were compared and analyzed.Results and conclusionsThe findings indicate a square relationship between the permeability coefficient and the equivalent hydraulic diameter and a correlation coefficient of more than 97% between the equivalent hydraulic diameter calculation results and the measured permeability coefficient results; the error analysis results demonstrate that the equivalent hydraulic diameter calculation results can meet the permeability test error range. This paper presents an estimation model for the soil permeability coefficient that is universally applicable to a wide range of particle sizes (0.002 to 2 mm). It is compared with experimental test results, Terzaghi formula, Hazen formula, and Amer formula. The results demonstrate that the model developed in this paper has a higher degree of agreement with the experimental results.

To investigate the influence of cations on the microstructural characteristics of electrochemical reinforcement in soft clay, a study was conducted using three different cationic salt solutions—NaCl, CaCl₂, and FeCl₃—for grouting treatment. Four sets of indoor experiments were performed to examine the reinforcement mechanism of the electrochemical method. The findings indicate that increasing the valence of injected cations significantly affects the electrochemical reinforcement effect and the soil’s microstructural properties. Higher-valence cations notably enhanced the soil’s electrical permeability coefficient and conductivity, leading to a substantial improvement in shear strength. Furthermore, the pore volume of the soil increased following electrochemical treatment compared to soil treated solely by electro-osmosis, due to the flocculation effect induced by cation injection. Nevertheless, the pore size distribution became more uniform, especially in the cathode region, as a result of pore redistribution. The chemical cementation reactions triggered by Ca 2+ and Fe 3+ injections mitigated the impact of flocculation on the microstructure, resulting in a more favorable pore volume and size distribution compared to Na + treatment.

This study develops a pore-scale model to analyze how particle arrangement and variable cross-sectional pore geometry on the hydraulic behavior of unsaturated soils. The particle-size distribution is partitioned into groups, within which pore systems of three, four, and five-particle arrangements were constructed. Using the pressure-difference method for connected channels and the Young–Laplace equation, a calculation framework for the unsaturated permeability coefficient and soil–water characteristic curve was established, explicitly considering soil micropore distribution. Model performance was verified with 18 soil datasets from the Unsaturated Soil Hydraulic Database and further examined through variable-head permeability tests on extremely fine sands with varying silty fine sand and fine-particle contents. Results show that the model reliably predicts the unsaturated permeability coefficient and Soil Water Characteristic Curve (SWCC) for loamy sand, sand, and sandy loam across both high and low water contents when suitable particle arrangement systems are applied. The five-particle system is more effective for high water content in permeability calculations and for coarse-grained soils in SWCC prediction, whereas the three-particle system better represents low water contents and fine-grained soils. The model requires only particle-size distribution, dry density, saturated permeability coefficient, and saturated water content, without introducing additional empirical parameters, thereby offering a concise and practical approach for characterizing unsaturated soil hydraulic properties.

Sanitary landfill is a common method for the treatment of municipal solid waste. The landfill leachate contains a large amount of NH4+, which will affect the physicochemical properties of bentonite, and subsequently change the anti-seepage function of the bentonite enhanced cutoff wall. The permeability tests were carried out on bentonite-clay mixed soil infiltrated by the ammonium salt solutions using a head pressure control permeameter. The results show that saturated permeability coefficient of the bentonite-clay mixture increases with the decrease of bentonite content and with the increase of NH4+ concentration. Moreover, the reasonable mass content of bentonite is about 10% if the studied bentonite-clay mixture are used in vertical cutoff wall. The scanning electron microscope (SEM) and the nuclear magnetic resonance (NMR) measurements were conducted on the bentonite-clay mixed soil samples with different bentonite contents, and samples infiltrated by the ammonium salt solutions with different concentrations, and afterwards the variations of the micro pore structure and pore-size distribution were obtained. Connecting the Donnan osmotic pressure with saturated permeability of bentonite-clay mixed soils, the effect mechanism of bentonite content and ammonium solution concentration on the permeability of the bentonite-clay mixture was analyzed.

Soil water retention curves (SWRC) are commonly used to predict unsaturated infiltration coefficients, but the conditions studied in traditional SWRC models are mostly isochoric conditions. It is assumed that there is a coupling function linking changes in water ratio with changes in void ratio, and that the coupling function depends on soil saturation under constant suction conditions. Based on the above assumptions the void ratio is introduced into the SWRC model and a SWRC for deformed soils is established. The two parameters added to the new model can be determined by constant suction compression tests. The final model for predicting the unsaturated permeability coefficient of deformed soils was obtained based on the SWRC discretization. The unsaturated permeability coefficient prediction model has only one additional parameter compared to the SWRC model and the parameter is a constant for the same soil and can be obtained from simple saturated permeability tests. Finally, the reliability of the model for application in the compacted loess of Yan’an was verified by means of a self-designed device for water infiltration.

Anisohydric plants are thought to be more drought tolerant than isohydric plants. However, the molecular mechanism determining whether the plant water potential during the day remains constant or not regardless of the evaporative demand (isohydric vs anisohydric plant) is not known. Here, it was hypothesized that aquaporins take part in this molecular mechanism determining the plant isohydric threshold. Using computational mining a key tonoplast aquaporin, tonoplast intrinsic protein 2;2 (SlTIP2;2), was selected within the large multifunctional gene family of tomato (Solanum lycopersicum) aquaporins based on its induction in response to abiotic stresses. SlTIP2;2-transformed plants (TOM-SlTIP2;2) were compared with controls in physiological assays at cellular and whole-plant levels. Constitutive expression of SlTIP2;2 increased the osmotic water permeability of the cell and whole-plant transpiration. Under drought, these plants transpired more and for longer periods than control plants, reaching a lower relative water content, a behavior characterizing anisohydric plants. In 3-yr consecutive commercial glasshouse trials, TOM-SlTIP2;2 showed significant increases in fruit yield, harvest index and plant mass relative to the control under both normal and water-stress conditions. In conclusion, it is proposed that the regulation mechanism controlling tonoplast water permeability might have a role in determining the whole-plant ishohydric threshold, and thus its abiotic stress tolerance.

The permeability coefficient of rock mass is a critical parameter for groundwater flow analysis of underground water-sealed oil storages. Based on the site geological investigation, monitoring information, and data statistics, a method of determining representative permeability coefficients of original and grouted rock mass for underground water-sealed oil storage was proposed. Then, the proposed method was applied to the flow field analysis of an underground water-sealed oil storage under construction. The assessment of containment properties, the prediction of water inflow, and the analysis of grouting effect were carried out. For the similar kind of underground water-sealed oil storages, the geometric mean of the tested permeability coefficients was suggested to be the representative value of original rock mass. The relationship between the permeability reduction factors of grouting and the original permeability coefficients was obtained to predict the grouting zone permeability. Based on the proposed method, the representative original permeability coefficient of the storage zone is determined to be 1.96E−03 m/day, and the permeability coefficient of the grouted zone is conservatively suggested to be reduced to 10% of the original value. The predicted results of water inflow and grouting effect by flow simulation were compared with that by engineering analogy and theoretical analysis, which further verified the rationality of the proposed method and the reliability of the flow field analysis. The method of determining the representative permeability coefficients of rock mass and its application can help improve the accuracy of groundwater flow field analysis and offer guidelines for the construction of underground water-sealed oil storage.

Horizontal drains have been widely installed along expansive soil slopes to maintain slope stability. However, these drains typically get clogged with clay particles after several years of operation and must be maintained and replaced regularly. This paper proposes a new type of horizontal drain with a replaceable tubular filter element (RTFE) to overcome the time-consuming nature and laborious replacement procedure of existing horizontal drains. Tests were conducted to compare its drainage performance with that of a conventional horizontal drain. The effects of horizontal drain clogging on the pore water pressure and slope stability were analyzed using the equivalent permeability coefficient of the expansive soil considering the adverse effects of cracks that are randomly distributed in the soil when the matrix suction exceeds the air-entry value. This coefficient was then used as one of the input parameters in the finite element analysis (FEA) for a hydro-mechanical coupling simulation. A replacement standard for the tubular filter element was established according to the numerical results, and the replacement method was explained. The study results showed that the RTFE-equipped horizontal drain was evidently superior to the conventional horizontal drain owing to the advantage of quick replacement. It can also effectively preserve the soil and prevent infiltration deformation caused by the loss of skeleton particles, implying a more economical, effective, and controllable means for the dewatering of expansive soil slopes. This study provides references for the construction and management of engineering projects involving horizontal drainage systems.

Water rich tunnels are often subject to lining seepage and water leakage. The water pressure behind lining is the main factor that causes the tunnel diseases. To calculate the water pressure of tunnel lining, axisymmetric analysis, mirror image method, and conformal transformation method are commonly used. However, axisymmetric analysis and mirror image method are only applicable to the tunnels in high water level. The conformal transformation method can be applied to both high and low water level tunnels, but cannot consider the effects of grouting rings and lining. This paper simplified the seepage of groundwater into a fan-shaped vertical shaft seepage problem, and derived the analytical formula of lining water pressure considering the shape of tunnel. A semi-analytical method of lining water pressure considering the influence of waterproof and drainage systems was proposed. The results show that the water pressure is related to the height of the initial water head, permeability coefficient of materials and geometric sizes of lining. According to the reduction degree of water pressure, it can be divided into three areas, namely, uniform reduction area of arch, discharge area of longitudinal drainage pipe and uniform reduction area of invert. With the increase of water head of the tunnel vault, the water pressure difference between vault and invert increases gradually, and the invert is easy to be damaged. The research results can provide guidance for the structural design and optimization of water rich tunnel.

Nuclear waste repositories have extremely stringent requirements for geological environment. However, natural fractures in rock mass can be potential channels for nuclide migration, therefore, the influence of fractures on the permeability of rock mass must be assessed. In this paper, a well research was conducted on well-exposed granite outcrops in the Xinchang site (the Chinese high-level radioactive waste repository). The high-precision three-dimensional model of a typical outcrop is built to obtain fracture information combined with field measurement, and then the three-dimensional fracture network model is generated using the relevant parameters by Monte Carlo method. To obtain more comprehensive fracture connectivity while avoiding the traditional method of searching the connectivity path in the complicated 3D fracture model taking up a lot of storage space and costing a lot of time, this paper presents an approach using MATLAB cell array instead of traditional adjacency matrix to search and store fracture network connectivity paths. In DFN model, the fracture disc with certain thickness is equivalent to three-dimensional pipe network model (EPNM) with variable diameter, and the equivalent path permeability coefficient (EPC) is proposed to objectively study the permeability characteristics of the seepage path in fractured rock mass based on that. Especially noteworthy is that some fractures in a certain strike range belong to open type, while those in another range belong to cemented closed fractures, when fresh fractures were exposed by cutting off the surface rock to a certain depth. The calculation of EPC under different conditions shows that the order of magnitude of EPC mean value is 1e−7m/s and 1e−3m/s, respectively, when fractures are cemented and not partly. On this basis, the size of the representative elementary volume (REV) of the fractured rock mass in the study area is determined to be about 25 m. By rotating the matrix in model, the spatial permeability tensor of the region (including permeability principal value and main direction) is obtained, which is within the range of borehole data. The predicted results may provide some reference for the related projects in the future.