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Vertical drain assisted by vacuum and/or surcharge preloading is an effective method for improvement of soft ground with high water content. A large settlement will occur, and the water flow may deviate from the Darcy's law. The creep is also non-negligible in estimating the long-term settlement of such soft ground. To accurately predict the consolidation process, this study develops an axisymmetric finite strain consolidation model based on Barron's free-strain theory incorporating the creep, radial and vertical flows, non-Darcian flow law, and void ratio-dependent hydraulic conductivity during the consolidation process. First, to mathematically validate the model and highlight the new model's features, the existing model not considering the creep and the non-Darcy flow is also adopted as a reference for comparison based on a benchmark simulation. Then, Rowe cell tests involving non-Darcian flow are simulated by the new model to experimentally validate the predictive performance. Furthermore, the model is applied to simulate the consolidation process of a long-term monitoring embankment to examine the applicability of the model for engineering practice. All results demonstrate that the model is capable of accurately describing the consolidation of soft soils with vertical drains under combined loading with features of creep and non-Darcy flow. • An axisymmetric finite strain consolidation model is developed, incorporating the extended 1D Yin–Graham EVP model and a non-Darcy flow law. • Consolidation governing equations including the radial and vertical water flow are solved using alternating direction implicit (ADI) method. • The model performance describing non-Darcian flow and creep is verified by comparing with physical model tests and long-term field test. [ABSTRACT FROM AUTHOR]

Hydraulic conductivity tests were conducted on six bentonite-polymer (B–P) geosynthetic clay liners (GCLs) to investigate the effect of the slow cation exchange process and polymer elution on the long-term hydraulic conductivity of B–P GCLs. Tests were conducted up to 1458 days and as many as 443 pore volumes of flows (PVFs). Three B–P GCLs consist of linear polymer whereas the other three have crosslinked polymer. One sodium geosynthetic clay liner (Na–B GCL) was used as a control. Hydraulic conductivities (K 6766) of B–P GCLs (5.4 × 10−12 m/s to 3.7 × 10−11 m/s) per ASTM D6766 were approximately 2-3 orders of magnitude lower than that of Na–B GCL (2.3 × 10−9 m/s to 3.5 × 10−9 m/s). Tests were continued after hydraulic and chemical equilibrium to investigate the long-term hydraulic conductivity of GCLs. Hydraulic conductivities of GCLs had an increasing trend after hydraulic and chemical equilibrium. The ratio of K L /K 6766 for B–P GCLs was 3.5–14.7, whereas ratio of K L /K 6766 for Na–B GCLs was 1.0–1.7. Total organic carbon (TOC) tests results confirmed that polymer elution occurred during the entire permeation process. The higher ratio of K L /K 6766 for B–P GCLs was attributed to the effect of polymer elution. • Hydraulic conductivity tests were conducted up to 4 years to test long-term hydraulic conductivity of B–P GCLs. • The ratios of K L /K 6766 for B–P GCLs to synthetic CCP leachate were higher than that of Na–B GCLs (e.g., 3.5 to 14.7 vs. 1.7). • Polymer elution from B–P GCLs affects the long-term hydraulic conductivity of B–P GCLs. • The polymer elution should be measured and considered as an additional termination criterion in ASTM D6766. [ABSTRACT FROM AUTHOR]

The effect of applied stress (20, 60, and 150 kPa) on the diffusion of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) through a geosynthetic clay liner (GCL) is examined. The diffusion coefficients deduced from GCL diffusion tests for PFOA and PFOS decrease linearly with decreasing final bulk GCL void ratio (increasing applied stresses). The different components of the same GCL are also tested for PFOA and PFOS sorption. No statistically significant sorption of PFOA is observed for any of the components of the GCL. However, some sorption of PFOS onto the cover and carrier geotextiles of the GCL is observed with in an average distribution coefficient, K d ∼2.22 ml/g for the GCL. Permeants containing different PFAS compounds are tested to assess their impact on the Geomembrane (GMB) - GCL interface transmissivity in composite liners. Results show PFAS concentrations up to 20 ppm had negligible impact on the GMB-GCL interface transmissivity. Lastly, the GCL specimens extracted from the diffusion tests are tested for hydraulic conductivity. No impact of PFAS is seen on the hydraulic conductivity of GCLs subjected to high applied loads, but a small increase is seen on the GCLs subjected to relatively low applied stresses. • First diffusion test and parameters on PFAS migrating through a GCL and evaluation of a diffusion coefficient for PFOS and PFOA. • First interface transmissivity test with a PFAS-contaminated solution and assessment of the effect of PFAS on interface transmissivity and evaluation of the effect of PFAS on the hydraulic conductivity of GCL used in transmissivity tests. • Use of a diffusion test to independently verify batch test results for partitioning of PFOS and PFOA to a GCL. [ABSTRACT FROM AUTHOR]

Experiments are conducted to investigate the effect of a drainage layer in/below saturated tailings on leakage through a hole of various shapes and sizes in a 2-mm-thick HDPE geomembrane. Three cases: no drainage (Case 1), drainage layer between two layers of tailings (Case 2), and drainage layer below tailings and above the GMB (Case 3) are examined. Analytical solutions predicting leakage through a circular GMB hole overlain by tailings with an internal drainage in (Case 2) and below (Case 3) tailings are developed, and match the experimental and numerical results well. Results show that a drainage layer separated from the GMB by a thin layer of tailings (Case 2) gives leakage slightly greater than if no drainage layer is present, but 3-5 orders of magnitude lower than when the drainage is placed directly over the GMB (Case 3). In Case 3, leakage is dependent on the hydraulic conductivity k of both the drainage and subgrade, and is not affected by the tailings. Unlike Cases 1 and 2 where the subgrade has negligible effect on leakage, a low permeability subgrade with k less than 10% of k for the drainage layer is recommended in Case 3 to minimize leakage through geomembrane defects. • first investigation of the effect of an internal drainage within tailings on leakage through a GMB defect. • first evaluation of where to place the internal drainage in order to minimize leakage through a GMB defect. • first guidance on how to predict leakage through a GMB defect when a drainage is placed at different positions. [ABSTRACT FROM AUTHOR]

• Large column and water tank were used to study the properties of particle layer. • Salt-resistant bentonite showed excellent adsorption capability for heavy metals. • Particle layer showed excellent properties under different depths of seawater. • Particle layer performed well under waste loaded seawater condition. The complex seabed conditions and ocean environment pose significant challenges to the material selection and construction of bottom liners for offshore final disposal sites. To overcome the challenges, this study proposed a novel isolation particle layer for offshore final disposal sites. The isolation particle was composed by salt-resistant bentonite coating material and cement core material (D10 was 10 mm in core diameter and 2 mm in coating thickness; D20 was 20 mm and 4 mm). Upon immersion in artificial seawater, the isolation particles underwent expansion, leading to the formation of the novel isolation particle layers with low hydraulic conductivity less than 1 × 10-7 cm/s and adsorption of heavy metals in bentonite interlayers. Large column tests showed that both D10 and D20 isolation particle layers exhibited remarkable swelling capacity and low hydraulic conductivity (4.3 × 10-9 cm/s and 2.6 × 10-8 cm/s) under 3 m seawater pressure. During one year of observation, water tank test demonstrated that both isolation particle layers displayed remarkable stability and low hydraulic conductivity of 2.73 × 10-10 cm/s and 8.36 × 10-10 cm/s with load. The maximum adsorption capacities of salt-resistant bentonite were 123.55 mg/g for Pb2+, 60.29 mg/g for Cd2+ and 54.22 mg/g for Cu2+. Both isolation particle layers exhibited a high removal rate of over 95 % for heavy metals in water tank tests. The large-scale laboratory tests indicated the significant potential of the novel isolation particle layer for offshore final disposal sites. Subsequently, a testing ocean site will be selected to further investigate its practical engineering performance. [ABSTRACT FROM AUTHOR]

• Trona ash leachate (TAL) has high ionic strength among coal combustion leachates. • Hydraulic conductivity to TAL is high at low GCL mass per unit area (MPUA). • Hydraulic conductivity to TAL is low at MPUA of 5.0 kg/m2. • Bundles of fibers play an important role on hydraulic conductivity at low MPUAs. The barrier performance of geosynthetic clay liners (GCLs) to coal combustion products (CCPs) is of primary importance. One of the CCPs leachates that has a damaging effect on hydraulic conductivity is trona ash leachate (TAL). In this study, the hydraulic conductivity of sodium GCL (Na-GCL) to TAL was investigated in terms of mass per unit area (MPUA). The hydraulic conductivity of GCLs to TAL was 2.6 × 10-6 and 7.6 × 10-7 m/s when the MPUA was 3.0 kg/m2 (M b3) and 4.0 kg/m2 (M b4), respectively. Dye tests conducted on these GCLs showed that flow preferentially occurred through bundles of fibers existing in the GCLs. In contrast, increasing the MPUA to 5.0 kg/m2 (M b5) led to a decrease in the hydraulic conductivity (i.e. 4.1 × 10-11 m/s). Additional tests were performed on fiber-free GCLs to determine the role of fiber bundles. Regardless of MPUA, the fiber-free GCLs had low hydraulic conductivity (6.7 × 10-11 m/s). Prehydrating M b3 and M b4 with deionized water (DIW) before permeation with TAL also decreased the hydraulic conductivity. The hydraulic conductivities of prehydrated M b3 and M b4 were 1.6 × 10-10 and 4.8 × 10-11, respectively. Chemical analyses showed that the cation exchange reaction had a negligible influence on the hydraulic conductivity. Because TAL was a potential source of Na+ throughout the tests. [ABSTRACT FROM AUTHOR]

A study was conducted to investigate the multi-scale pore structure-based mechanism controlling the hydraulic conductivity of polymer-enhanced geosynthetic clay liners (GCLs) prepared by the wet-mixed method to bauxite liquors (BLS and BLA). The multi-scale pore structures were evaluated using MIP and N 2 GA tests quantitatively. Conventional GCL permeated with BLS had a larger flow path volume than with DI water (0.194 > 0.119 cm³/g), attributed to the bentonite swelling inhibition and the montmorillonite dissolution, leading to the higher hydraulic conductivity (3.0 × 10−7 > 2.7 × 10−11 m/s). Polymer-enhanced GCLs developed more micropores and had a smaller quantity proportion and volume of flow paths since polymer formed more micropores to clog pores, contributing to a lower hydraulic conductivity than conventional GCL to BLS. The hydraulic conductivity of polymer-enhanced GCL to BLS (ionic strength: 622.5 mM) was higher than that to BLA (156.9 mM) (2.6 × 10−9 > 6.0 × 10−12 m/s), given that the coiled or contracted polymer conformation left a smaller quantity proportion (5.54% < 6.71%) and volume (0.0002 cm3/g < 0.0035 cm3/g) of micropores. [Display omitted] • This study evaluated the multi-scale pore structures of GCLs by combining MIP and N 2 GA tests. • Conventional GCL had higher hydraulic conductivity to bauxite liquors because of wider flow paths. • The polymer formed micropores to clog pores, leading to narrower flow paths and lower hydraulic conductivity. • The higher ionic strength affected micropores by changing polymer conformation, resulting in higher hydraulic conductivity. • GCLs with higher polymer loading had lower hydraulic conductivity since sufficient polymers created more micropores. [ABSTRACT FROM AUTHOR]

Measuring hydraulic conductivity by instantaneous profile method needs to detect the pore water content of soil at different positions, but most of the detecting methods will disturb the soil sample. In the study, the axial slice scanning of soil samples was carried out by using static filed gradient multi-slice Carr-Purcell-Meiboom-Gill (SFG-MSCPMG) sequence of nuclear magnetic resonance (NMR) technology, which can nondestructively determine water content and distribution at different positions of soil column. In this experiment, three clays were used to illustrate the relationship between NMR test results and oven drying results of water content. The results show that there is a good linear relationship between the NMR signal and water content. Combining mercury intrusion porosimetry (MIP) data, the transverse surface relaxivity parameters (ρ 2) of clays are obtained. With ρ 2 = 41.90 μm/s the T 2 distribution curve of pore water in the ordinary clay can be converted into the pore water distribution curve, which is in good agreement with that obtained with MIP. Nevertheless, it is found that the T 2 distribution curve of pore water in expansive clay obtained with NMR technique is more suitable for analyzing the average pore water distribution because of the fast exchange of pore water between the interlayers, intra-aggregates and inter-aggregates in expansive clay. [ABSTRACT FROM AUTHOR]

At the bottom of the geomembrane cut-off walls, pollutants may seep out through the bottom gap between the geosynthetic membrane and the low-permeability bedrock, contaminating the groundwater and the surrounding environment. Therefore, to address the occurrence of bottom gap seepage, this study adopts a mixture of attapulgite and cement in a certain proportion, mixed and stirred to form a sealing material. This sealing material is used to connect the bedrock and the geosynthetic membrane, thereby creating an efficient composite vertical barrier with special containment capacity. A series of laboratory experiments were conducted to investigate engineering properties of cement-attapulgite sealing slurry, including flow value tests, unconfined compressive strength (UCS) tests, improved flexible wall permeability tests, and bedrock and sealing slurry adhesion tests. The results show that the flow value of the slurry decreases with the increase of attapulgite content, and it increases with the increase of water-cement ratio. The UCS strength increases with the increase of attapulgite content, and it decreases with the increase of water-cement ratio, but the range of change is different. The hydraulic conductivity measured with hexavalent chromium solution as the penetrant is less than 50 % higher than that measured with water as the penetrant, and hexavalent chromium solution has little effect on the hydraulic conductivity of sealing slurry. The bonding performance between sealing slurry and bedrock is satisfactory, and the hydraulic conductivity of bedrock-sealing slurry is less than 1 × 10−7 cm/s (28d curing age), it is concluded that use of cement-attapulgite sealing slurry as bonding material between bedrock and geomembrane meets the engineering design requirements. [ABSTRACT FROM AUTHOR]

Low-cost ceramic water filters are a very effective point-of-use technology for removing bacteria and protozoa from drinking water. The filters are made from locally sourced clay and a porogen materials such as sawdust. It is recommended that the sawdust be sieved to 30-sieve (600 μm) to make reliable filters. However, the size distribution of sawdust is usually broad and can extend below 100 μm. This study divided 30-sieve sawdust into four narrower size distributions and made filter disks for measurement of hydraulic conductivity and bulk density. Additionally, the microstructure of the materials was examined in three dimensions by micro-CT. The results showed that, independent of sawdust particle size, the void volume fraction in the filter increased linearly with the weight fraction of sawdust. In contrast, the permeability coefficient increased non-linearly as the fraction of sawdust increased. The magnitude of the permeability was higher for the larger sawdust particles when the sawdust fraction was 10 wt% or higher. Three-dimensional imaging of the pore structure in the filters suggested that the non-linear increase in permeability with increasing weight fraction of sawdust may be associated with increased interaction of the cavities created by the sawdust. [ABSTRACT FROM AUTHOR]

Flow in an idealized geosynthetic clay liner (GCL) containing bentonite comprised of equisized and equispaced square granules was simulated using a hydrodynamic model to quantitatively evaluate the premise that the hydraulic conductivity of GCLs diminishes as the bentonite granules hydrate and swell into adjacent intergranular pores, creating smaller and tortuous intergranular flow paths. Predictions with the model indicate that hydraulic conductivity decreases as granules swell and intergranular pores become smaller, and that greater granule swelling during hydration is required to achieve low hydraulic conductivity when the bentonite is comprised of larger granules, or the bentonite density is lower (lower bentonite mass per unit area). Predictions made with the model indicate that intergranular pores become extremely small (<1 μm) as the hydraulic conductivity approaches 10−11 m/s. These outcomes are consistent with experimental data showing that GCLs are more permeable when hydrated and permeated with solutions that suppress swelling of the bentonite granules, and that the hydraulic conductivity of GCLs with bentonite having smaller intergranular pores (e.g., GCLs with smaller bentonite granules, more broadly graded particles, or higher bentonite density) is less sensitive to solutions that suppress swelling. • Impact of bentonite granule swelling on flow through intergranular pores and hydraulic conductivity of GCLs is demonstrated. • Effect of granule size and bentonite density on flow in intergranular pores and hydraulic conductivity is illustrated. • Bentonite granule size can be selected to to make GCLs more resilient to chemical interactions that suppress swelling. [ABSTRACT FROM AUTHOR]

The hydraulic conductivity of geosynthetic clay liners (GCLs) widely used as barrier systems considerably depends on their hydration status after the initial hydration of virgin GCLs and the rehydration of desiccated GCLs. Free hydration tests were performed on virgin and desiccated GCLs over sandy subgrades to compare their hydration level. In addition, high-resolution micro-X-ray computed tomography (CT) images of both GCLs and sandy subgrades with different gravimetric water content (i.e. 15%, 20%, and 25%) after the initial hydration were analyzed for better insights. The results show significant influences of subgrade water content on moisture content and thickness of virgin GCLs. Water loss of sandy subgrades and the time interval necessary for reaching a steady state of desiccated GCLs during rehydration was greater and longer than virgin GCLs during initial hydration. X-ray CT images verified a dense distribution of bentonite particles, macropores, and minor desiccation cracks that existed in poorly-hydrated GCLs over unsaturated sand. On the other hand, the completely saturated sandy subgrade facilitated the hydration of GCLs, leaving a lot of macropores in the sand. The relationship between water distribution and the frequency of macropore generation observed in the upper contact zone of sandy subgrades was also indicated via these X-ray CT images. • Greater water loss of sand and longer time for GCLs to reach steady water content during rehydration than initial hydration. • Dense distribution of bentonite particles, pores, and minor cracks in poorly-hydrated GCL placed over low water content sand. • Saturated sandy subgrades facilitated the GCL hydration and generated macropores in the upper zone of sandy subgrade. • X-ray CT imaging indicated the highest total pore volume in saturated sandy subgrades after initial hydration. [ABSTRACT FROM AUTHOR]

• MacCormack scheme based Numerical Model for simulating temperature profile in landfill. • Model Considers waste stratification as new and old as aerobic and anaerobic. • Includes depth Variability in density, moisture content & hydraulic conductivity. • A correlation of 0.8 and 0.73 is obtained in calibration & validation. • Landfill temperature rises at all depths and in all season. Elevated Landfill temperatures have an undesirable effect on landfill cover, stability, slope and leachate migration pattern. Thus, to predict the temperature profile in the landfill a distributed numerical model using MacCormack finite difference method is developed. The developed model considers stratification of the upper and lower layers of the waste as new and old waste by assigning different values of heat generation for aerobic and anaerobic processes. Further, as the new layers of the waste get accumulated over the older layers, the density, moisture content and hydraulic conductivity of the underlying waste layers get modified. The mathematical model utilizes a predictor–corrector approach with a Dirichlet boundary at the surface and no flow condition at the bottom. The developed model is applied to the Gazipur site located in Delhi in India. A correlation coefficient of 0.8 and 0.73 is obtained between the simulated and observed temperatures in calibration and validation respectively. The result shows that the temperature at all the depths and in all the seasons was found to be higher than the atmospheric temperature. The maximum difference of 333 °C was observed in December, and the minimum difference of 22 °Cs was observed in June. The temperature rise is higher in the upper waste layers as it undergoes aerobic degradation. The locus of the maximum temperature gets modified with moisture movement. Since the developed model shows a good agreement with the field observation, it can be used to predict the temperature variation within the landfill under different climatic conditions. [ABSTRACT FROM AUTHOR]

• Hydraulic conductivity of MSW, E&PW, and their mixtures were measured. • The four main influential factors impact hydraulic conductivity were evaluated. • Hydraulic conductivity of 20%MSW + 80%E&PW mixtures decreased below 10-9 m/s. • Hydraulic conductivity of E&PW dropped when dry unit weight surpassed 14kN/m3. • Hydraulic conductivity of E&PW reduced substantially when void ratio < 0.8. This study evaluated the effects of addition of oil and gas exploration and production wastes (E&PW) on hydraulic behavior of municipal solid waste (MSW). A series of laboratory experiments were conducted to assess the impacts of vertical stress, waste composition, mixture ratio of MSW to E&PW based on total mass (e.g., 20% MSW + 80% E&PW), and mixing methods on hydraulic conductivity. Hydraulic conductivity (k) for MSW-E&PW mixtures with 20% and 40% E&PW contents reduced from 3 × 10-5 m/s to 10-7 m/s as vertical stress increased from 0 to 400 kPa. An increase in the mixture ratio above 60% resulted in an additional order-of-magnitude decrease in k to 10-8 m/s as vertical stress increased above 200 kPa. The addition of E&PW did not impact the available flow path, even though adding E&PW to MSW reduced the void spaces. This indicated that the waste matrix is capable of accepting E&PW while keeping the flow structure within the waste matrix. However, for vertical stress greater than 50 kPa, mixtures of MSW + 80% E&PW were observed to yield hydraulic conductivity < 10-9 m/s. [ABSTRACT FROM AUTHOR]

• BHET treatment formed a flocculated bentonite matrix. • The flocculated bentonite matrix entraps water in its micropores. • BHET hydrogel constrained drainage path. • The hydroxyl groups of BHET retain a high amount of water. • The carbonyl and hydroxyl groups adsorb Pb2+. Polyethene terephthalate (PET) waste poses major environmental harm which can be minimized by reusing it in clay soil stabilization. In general, various polymers are known to reduce hydraulic conductivity and increase the shear strength of clays. However, the application of the effect of a chemically depolymerized form of PET, i.e., Bis (2-Hydroxyethyl) terephthalate (BHET) has not been performed as an additive in Compacted Clay Liners (CCLs) for landfills. This research focuses on the effect of the air curing period (1 and 28 days) on the hydromechanical behavior of BHET-treated SBM (0, 1, 2, 3, and 4 % by dry weight). Results from One Dimensional Consolidation tests showed that an increase in BHET content reduced both compressibility and hydraulic conductivity of SBM due to pore clogging mechanism of swollen BHET hydrogel, however, hydraulic conductivity reduced over 28 days of curing due to loss in re-swelling availability of the hydrogel, thereby allowing less tortuous paths to flow. Results from Consolidated-Drained Direct Shear tests showed that for 1 and 28-days curing, BHET treatment to SBM increased the cohesion (c') due to strong polymer interparticle bridging, however, polymer coating over the sand grains causes a reduction in its surface roughness to decrease the frictional angle (ϕ'). SEM (Scanning Electron Microscopy) and EDX (Energy-dispersive X-ray spectroscopy) analysis on BHET-treated specimens support the flocculation of bentonite, polymer bridging of sand and clay-sand polymer links. A significant Pb2+ removal capacity was also observed with BHET-treated SBM from the batch tests. FTIR (Fourier Transform Infrared Spectroscopy) analysis on batch sorption specimens confirms the role of the carbonyl groups (C = O) and hydroxyl groups (OH) present in the BHET structure indicating the possibility to adsorb Pb2+. The findings of the study suggested that a mechanism of interaction exists between sand-bentonite and BHET polymer and it can be adopted in CCLs design. [ABSTRACT FROM AUTHOR]

• Water retention curves (WRCs) of municipal solid wastes (MSWs) • Hysteresis of WRCs of MSWs with decomposition. • Effects of decomposition and paper content on the WRCs. • Unsaturated hydraulic and gas conductivity of MSWs. This paper investigates the drying and wetting water retention curves (WRCs) of municipal solid wastes (MSWs) with different paper contents, dry unit weights and degrees of biodegradation (DOBs). Fresh synthetic samples were prepared based on the field composition of the MSWs at Mugga Lane Landfill, the Australian Capital Territory (ACT), Australia. The degraded samples were prepared in simulators with MSWs of different initial dry unit weights and decomposition periods with leachate recirculation. The water retention curves (WRCs) of the MSWs were determined using pressure plate tests, in both drying and wetting phases. The outflow from MSWs was analysed using Gardner's method to obtain the unsaturated hydraulic conductivity. The results indicate that the WRCs of the MSWs are greatly affected by the DOB, paper content and dry unit weight. When DOB < 30 %, as DOB increases, the air-entry pressure of MSWs with paper increases, and the residual moisture content decreases regardless of paper content. With DOB > 30 %, the air entry pressure and residual water content depend on the balance between organic matter and highly decomposed organic constituents. The paper content affects the WRCs of MSWs due to its water retention capacity and change in the particle size distribution with decomposition. The increase in the dry unit weight of MSWs significantly increases the air entry pressure and residual moisture content, similar to the borehole samples with combined effects of biodegradation and increase in stress level from literature. Hysteresis effects have been observed during the drying and wetting of MSWs. The hysteresis of WRCs increases with the paper content and DOB. [ABSTRACT FROM AUTHOR]

• Machine learning predicts the hydraulic conductivity of landfill liners and covers. • Physical properties, compaction, and hydration of liners and covers are considered. • 93% of the predicted hydraulic conductivity is within 10-fold of the measurements. • Only five impact factors are required for hydraulic conductivity predictions. Machine learning models (MLMs) were developed to predict saturated hydraulic conductivity of compacted soil barriers and help to identify appropriate soils for the construction of landfill liners and covers. Data from hydraulic conductivity tests on compacted soil barriers were collected from the literature and compiled into a database for MLM construction. The database contains 329 records of hydraulic conductivity tests associated with 12 selected impact factors covering physical properties, compaction efforts, and hydration and mineralogy behaviors of compacted soil barriers. Three machine learning algorithms (random forest, gradient boosting decision tree, and neural network) were used to develop MLMs, and a statistical technique (multiple linear regression) was used to compare the precision of predictions with the MLMs. Results from this study showed that the random forest model provided the best prediction of the hydraulic conductivity of compacted soil barriers, with 100% of predicted hydraulic conductivity within 100-time differences to measured hydraulic conductivity and 93% within 10-time differences. Feature importance analysis showed that void ratio after compaction, fines content, specific gravity, degree of saturation after compaction, and plasticity index of soils are the top-five factors (in descending order) that influence the hydraulic conductivity of compacted soil barriers and are recommended for a precise prediction. Three predictive MLMs were created for industries as simple tools to screen the soils prior to the construction of compacted soil barriers in landfill liners and covers. [ABSTRACT FROM AUTHOR]

• This study was conducted to evaluate the hydraulic performance of GCL overlaps. • Na-B GCLs consisting of different geotextile combinations were tested. • Test were conducted with saline solutions at 20 to 500 kPa confining stress. • The GCL overlaps permeated with saline solutions had horizontal flow. • The horizontal flow through GCL overlaps reduced at higher confining stress. Hydraulic conductivity of the overlap region of two needle-punched sodium bentonite (Na-B) geosynthetic clay liners (GCLs) permeated with CaCl 2 solutions under confining stresses of 20, 100, 250, and 500 kPa were evaluated. One of the GCLs consisted of a uniform layer of Na-B encapsulated between a nonwoven (NW) and a woven (W) geotextile, and the other one consisted of NW geotextiles on both sides. Supplemental bentonite was placed within the overlap region. Experiments were conducted with 10, 20, and 50 mM CaCl 2 solutions representing dilute and aggressive leachates. The results indicate that in most of the scenarios there is a possibility that the flow is not completely vertical (meaning flow passes through the overlap region horizontally). As the confining stress increased, the horizontal flow through the overlap region for GCLs reduced effectively when permeated with deionized water and 10 mM CaCl 2 solution, whereas the reduction of horizontal flow was limited to 20 mM and 50 mM CaCl 2 solutions. [ABSTRACT FROM AUTHOR]

[Display omitted] • High temperatures can increase the permeability of sand-clay liners in landfills. • When temperature is 62 ℃, the corresponding threshold gradient i 0 approached 0. • Temperature affected not only permeate viscosity but also intrinsic permeability. • To consider μ and K, the new equations to obtain k and i 0 with T were proposed. High leachate heads and dry cracking of clay barriers are common problems in landfills. The use of sand-clay barriers with a non-darcy percolation patterns can not only prevent leakage of large amounts of leachate but can also potentially reduce the development of dry fractures due to loss of water. Thus, it has been suggested that sand-clay materials could be used as barriers at the bottoms of landfills or as a vertical barriers. However, biochemical degradation of waste in a landfill generates much heat, and the temperature can reach 60 °C. A high-temperature field can inevitably affect the permeability of sand-clay barriers. The change in sand-clay barrier permeability under the influence of temperature has received increasing attention. Therefore, in this study, a temperature-controlled permeameter with flexible walls was used to conduct experiments on permeability of sand-clay mixtures at four temperatures. The results indicated that the hydraulic conductivity gradually increased and the threshold gradient gradually decreased with increasing temperature. The hydraulic conductivity and threshold gradient exhibited exponential relationship with the temperature, respectively. Experiments were designed to measure changes in the permeate viscosity at different temperatures. The previously established hydraulic conductivity equation (that considered only the influence of temperature on the permeate viscosity) greatly differed from the measured values. In contrast, the newly established hydraulic conductivity equation (that considered the influence of temperature on both the permeate viscosity and intrinsic permeability) agreed well with the measured values. Statistics based on a large amount of data (collected previously) showed that the intrinsic clay permeability exhibited a power law relationship, with increasing temperature to a threshold gradient at 25 °C (Eq. (9)). Above the threshold, the intrinsic permeability experimental data increasingly deviated from Eq. (9). To consider the effect of the temperature on both the intrinsic permeability and permeate viscosity, an equation for calculation of the threshold gradient was proposed, and it could be found that the calculated values suitably agreed with the measured values. The results of this study provide an important theoretical basis and data to support the development of high-performance barriers with long service life for landfills. [ABSTRACT FROM AUTHOR]

Municipal solid waste (MSW) landfill cover systems are designed to minimize the infiltration of rainwater into waste and to mitigate the biogas emissions to the atmosphere. In the present study, the efficacy of such a landfill cover system consisting of a Geosynthetic clay liner (GCL)in mitigating the hydraulic flow and gas emissions under arid climatic conditions was investigated critically. For this purpose, the water retention curve (WRC), hydraulic conductivity function, and gas flow characteristics of the chosen GCL were studied through experimental methods in the laboratory. The unsaturated transient state seepage analysis utilizing coupled hydraulic and gas flow mechanisms was performed in the study to assess the performance of the cover system. The results obtained from the experiments were used as input parameters. The effect of drying/desiccation and the self-healing nature of GCL due to climatic changes were also analyzed by exposing the GCL directly to the climatic boundary for one year. It was observed that the GCL present in the chosen cover system effectively functions as a hydraulic barrier in arid climatic conditions. However, during the summer and winter seasons, an increase in gas flow from 0.02 g/h/m2 to 24.7 g/h/m2 was observed, probably due to the drying anddesiccation of GCL. Interestingly, due to the self-healing nature of the GCL, gas flow through the cover system was substantially reduced to 0.02 g/h/m2 during the rainy season. The effect of drying was more pronounced when the GCL was exposed to the climatic condition, leading to an early gas breakthrough and an increase in gas flow from 0.02 g/h/m2 to 957 g/h/m2. The percolation through the cover system remains considerably low throughout the year, mostly due to the unsaturation and low hydraulic conductivity in GCL. A cumulative percolation close to 0.1 m3 was observed at the end of one year in arid climatic conditions. • Numerical investigation of landfill cover system with GCL in mitigating hydraulic flow and gas emissions. • Water retention curve, hydraulic conductivity function, and gas flow characteristics of GCL were established. • Assessment of desiccation and self-healing nature of GCL due to climatic boundary conditions. • Temporal variation of suction, volumetric water content, gas mass flux, and net percolation of the cover system was monitored. • Effect of desiccation is pronounced when GCL was exposed to climatic conditions, leading to an early gas breakthrough. [ABSTRACT FROM AUTHOR]

In geotextile filtration, the soil fines are either accumulated near the interface, clogged, or washed out, which primarily depends on the grain size distribution (GSD) of soil and the constriction size distribution (CSD) of geotextile. Also, the movement of fines significantly affects the flow capacity of geotextile. Currently, the retention requirement is satisfied based on representative grain and opening sizes, whereas the hydraulic conductivity and clogging requirements are satisfied considering the properties of virgin geotextile. This paper presents a probabilistic retention criterion considering the grain and constriction sizes as random variables. The influence of geotextile thickness is incorporated into the criterion by considering the number of geotextile constrictions in a filtration path. A theoretical approach to predict CSD is presented if the measured data is unavailable. For hydraulic conductivity and clogging requirements, a criterion is presented considering the expected partial clogging of geotextile, which is predicted based on the semi-analytical approach. The limit states for the developed criteria are evaluated based on the wide range of experimental data from the current study and published literature. The developed design criteria are applicable to internally stable and unstable soils, which offers an improvement in design compared to the existing criteria in practice. • Gradient ratio tests were performed on a wide range of soils and commercially available geotextiles. • A probabilistic retention criterion is developed by considering the grain and constriction sizes as random variables. • A hydraulic conductivity criterion is developed by considering the expected partial clogging of geotextile. • A procedure for geotextile design is proposed based on the developed criteria and limit states of failures. [ABSTRACT FROM AUTHOR]

Plant domestication may lead to the suppression of attributes that enable survival in adverse environments. In this context, considering the scarcity of information on water transport in Jatropha curcas L., an experiment was conducted to compare the anatomical variables and hydraulic parameters of roots, stems, and leaves as well as the contribution of aquaporins in water transport of roots between wild and domesticated genotypes. Under irrigation, it was observed 10.2% larger xylem vessel diameters in roots but 7.9% and 11.3% smaller xylem vessel diameters in stems and leaves, respectively, of domesticated genotypes as compared to their wild counterparts. Overall, domestication resulted in 57.5% lower hydraulic resistivity in roots, 87.2% higher hydraulic resistivity in leaves, 22.4% higher vein length per leaf area, 10.5% lower net photosynthetic rate, 36.7% and 42.6% lower theoretical leaf area-specific hydraulic conductivity in roots and stems, respectively. Conversely, in domesticated genotypes, theoretical mass-specific hydraulic conductivity was respectively 58.4% and 57.7% higher in roots and stems. Furthermore, in these genotypes, the root volume was 13% smaller and the contribution of aquaporins to the hydraulic conductivity of roots was greater. In conclusion, domestication has driven the selection of genotypes with roots that are more efficient in conducting water through effects on the anatomy of xylem vessels and activity of aquaporins. However, leaves of such genotypes are more conservative in anatomical and photosynthetic terms. [Display omitted] • Domestication of J. curcas resulte in water transport efficient genotypes. • Such efficiency resulted from aquaporin activity and from changes on xylem anatomy. • Domestication improved leaf water distribution, without changes on photosynthesis. [ABSTRACT FROM AUTHOR]

A laboratory investigation on the hydration behavior of GCLs from lateritic soils was conducted under isothermal and thermal conditions (tropical climate), varying subsoil moisture contents, GCLs bentonite particle size and mineralogy. GCL hydration levels from lateritic subsoils under isothermal conditions (55%) were similar to literature findings. A slight decrease in water content of some GCLs after long periods of contact with the lateritic soils indicates that equilibrium can demand long time in these soils. GCL with granular bentonites were less efficient to hydrate from lateritic subsoils. GCLs with activated-calcium bentonites maintained hydration levels in long-term. Nonwoven geotextile facing down favored capillary effects. Thermal cycles significantly influenced GCLs hydration from subsoils. Capillary connections developed during hydration under isothermal conditions due to suction gradient reductions. Post-hydration tests under isothermal conditions showed more alterations in GCLs swelling and cation exchange properties than thermal cycles test. An increase in the saturated hydraulic conductivity of GCLs was observed in both lateritic soils, mainly for isothermal condition, although continued attending hydraulic conductivity requirements for barrier applications. • GCLs with activated-calcium bentonites maintained hydration levels in long-term. • GCL with granular bentonites were less efficient to hydrate from lateritic subsoils. • Nonwoven geotextile facing down favored capillary effects. • Thermal cycles significantly influenced GCLs hydration from subsoils. • Isothermal conditions showed more alterations in GCLs properties than thermal conditions. [ABSTRACT FROM AUTHOR]

• The geotechnical properties of municipal wastes based on field characterization. • Effects of leachate exposure on municipal solid wastes. • Effects of initial compositions on the geotechnical properties of municipal solid wastes. This paper investigates the geotechnical properties of a type of synthetic municipal solid waste (MSW). The tests were conducted on five groups of synthetic MSW compositions, based on the field characterization of fresh MSW samples collected from Mugga Lane landfill site, ACT, Australia. Compaction, hydraulic conductivity, compression, drained and undrained shear properties of the MSWs with water and leachate addition to the field moisture content were studied. The study shows that adding leachate could increase the maximum dry density of the MSWs under given moisture contents and compaction energies. The hydraulic conductivity of the MSWs could decrease by 100-fold when the confining pressure increases from 15 kPa to 240 kPa. The shear behaviours of the MSW samples follow the strain hardening behaviours of loose sand. The cohesion of the MSWs decreases but the friction angle of the MSWs increases with leachate addition due to the change in the surface tension and viscosity of the pore liquids and the loss of cementitious components. The addition of leachate increases the compression ratios of the MSWs by around 10% to 30% due to the change in the pH of the pore liquids. The most significant components affecting the shear and compression behaviours of the MSW were paper and wood. The effects of leachate exposure on the geotechnical properties of the MSWs is not very significant. It is important to consider the variation of MSW properties to the leachate properties (viscosity, pH and surface tension) in the large body of MSWs in the landfills. [ABSTRACT FROM AUTHOR]

[Display omitted] • A soil column test is conducted to explore CBC's performance under continuous rainfall. • A design criterion for CBC considering the unsaturated infiltration process is proposed. • The proposed design criterion is verified to be robust against multi-climate regions. The service performance of capillary barrier cover (CBC) under continuous rainfall is unclear, leading to a lack of the design criterion for CBC in humid regions. This study proposed a design criterion for CBC in multi-climate regions. First, the influence of fine layer thickness, initial water content and rainfall intensity on the performance of CBC under continuous rainfall was clarified through a soil column test. Subsequently, calculation models of effective water storage capacity and breakthrough time were derived based on test results. Finally, a design criterion for CBC in multi-climatic regions was proposed and verified. The main findings were as follows: (1) As expected, increasing the fine layer thickness and decreasing the initial water content enhanced the water storage capacity. Within the test range, the breakthrough time has a linearly positive, linearly negative, and negative power function relationship with the fine layer thickness, initial water content, and rainfall intensity, respectively. (2) The infiltration rate of CBC is controlled by saturated hydraulic conductivity under extremely continuous rainfall, and can be described by the equivalent infiltration rate. (3) The calculation results of the proposed water storage capacity and breakthrough time models are consistent with the test results, and the proposed design criterion is robust against various climates from drought to humidity. The research results can provide a reference for the design of CBC in multi-climate regions. [ABSTRACT FROM AUTHOR]

At present, the state has introduced the policy of forest Chinese herbal medicine planting planning, strictly prohibiting the planting of Chinese herbal medicine in basic farmland, coupled with the fact that the continuous cropping obstacles of Panax notoginseng have not yet been solved, which makes the area of arable land suitable for planting become less and less. However, the effect of soil moisture regulation on the growth of Panax notoginseng cultivated on sloping arable land has not been reported. Thus, the aim of this study was to investigate the impact of various irrigation levels and slopes on Panax notoginseng agronomic traits, physiological characteristics, disease attributes, biomass, and quality characteristics. During 2018–2020, a field experiment was conducted in the Panax notoginseng growing seasons with three irrigation levels (I1: 70–75% θ FC , I2: 75–80% θ FC , I3: 80–85% θ FC) and three slopes (S1: 2.43°, S2: 6.38°, S3: 16.38°). The results evidenced that the photosynthetic characteristics, root hydraulic conductivity characteristics, biomass and PNS of Panax notoginseng reached the maximum value in the I2S2 treatment, and at the same time, the incidence rate of Panax notoginseng root rot was the lowest. Therefore, based on the results of this study, irrigation volume I2S2 should be regarded as the optimal slope and irrigation management strategies for reducing Panax notoginseng diseases and realizing stable yield and quality improvement of Panax notoginseng. A multi-objective optimization model was established through binary quadratic regression analysis. The findings evidenced that when the irrigation interval was 187–203 mm and the slope interval was 5–10.7°, Panax notoginseng had the lowest incidengce rate, and the root biomass and saponin content reached > 95% of the maximum values at the same time. [Display omitted] • Moisture and slope coupling reduces root rot in Panax notoginseng • Panax notoginseng had the worst hydraulic conductivity under I1S3 treatment • The most suitable slope for planting Panax notoginseng is 5–10.7° • Irrigation 152–193 mm balanced the relationship between morbidity, yield, and PNS [ABSTRACT FROM AUTHOR]

Biopolymers are gaining popularity as ecofriendly soil stabilizers owing to their numerous advantages, including increased ground strength, erosion resistance, enhanced water retention and vegetation. However, the underlying engineering properties and mechanisms of the effects of curing and soil type on thermo-gelation biopolymer (TGBP)-treated soils are not well understood. To address this gap, we performed an engineering characteristic analysis considering TGBP type and concentration, curing conditions, and soil type. Increased unconfined compressive strength and decreased hydraulic conductivity were observed for higher TGBP content. The enhancement depends on the type and concentration of TGBP, which are attributed to the material characteristics of the biopolymer. The performance of TGBP-treated soils is governed by sol–gel transition and the drying process, with fine-grained soil potentially benefiting from electrostatic interactions. Notably, TGBP treatment reduces permeability by pore clogging via sol–gel transition. This implies that the material characteristics of the biopolymer can influence the determination of engineering application strategies. Furthermore, we established significant correlations among engineering properties, polymer content, curing conditions, and soil type. These findings can aid in the assessment of the effectiveness and potential benefits of TGBP-treated soils in this field. • Soil type and curing significantly affect thermo-gelation biopolymer soils. • Thermo-gelation biopolymers enhance soil strength and permeability through sol-gel transitions. • Mechanisms of soil strengthening with thermo-gelation biopolymers are analyzed. • Correlations among polymer content, soil type, and engineering properties of soils are investigated. [ABSTRACT FROM AUTHOR]

Although the effects of fertilization practices and environmental factors on tea yield and NO 3 −–N leaching have been acknowledged, the interactive effects of these influencing factors remain unknown. These effects were investigated in this study using the denitrification–decomposition (DNDC) model, which was validated using field data collected from a typical tea garden hillslope in the Tianmu Lake Basin, China. Environmental factors such as temperature, precipitation intensity, slope, saturated hydraulic conductivity (K sat), and fertilization practices (fertilizer amount and type) were combined to construct 1080 scenarios. The results revealed that DNDC achieved acceptable performance in simulating NO 3 −–N leaching under the application of a compound fertilizer (CF) and a slow-release fertilizer (SF). During the calibration period, the Nash–Sutcliffe efficiency (NSE) values were 0.48 and 0.24. During the validation period, the NSE values were 0.71 and 0.67. Scenario analysis indicated that precipitation intensity (p < 0.001), saturated soil hydraulic conductivity (K sat) (p < 0.001), fertilizer amount (p < 0.001), and fertilizer type (p < 0.001) significantly influenced the leaching flux of NO 3 −–N and tea yield. The interactive effects of different factors also varied across the different types of fertilizers. The amount of fertilizer had the most significant impact on NO 3 −–N leaching, with relative contribution rates of 70% and 53% for compound and SFs, respectively. As CF application increased, there was a significant increase (93%) in the average flux, whereas SF application resulted in an increase of only 76%. The highest contribution rate in terms of tea yield was observed for the amount of fertilizer under CF application at 44%. However, the highest contribution rate under SF application was attributed to K sat at 51%. The application of SFs resulted in a higher yield improvement rate than that of CFs as the fertilizer amount increased, with respective rates of 15% and 8%. Additionally, environmental factors, excluding temperature, exerted opposite effects on tea production and NO 3 −–N leaching flux. These findings contribute to optimizing fertilization management in tea plantations by integrating multiple environmental factors to control nonpoint nitrogen loss. Future research should conduct long-term monitoring of tea garden yield and nitrogen loss to accurately assess the impact of SF application on the ecological and economic benefits of tea gardens. • The fertilizer amount served as the dominant factor for the NO 3 --N leaching flux. • The yield was predominantly influenced by the saturated soil hydraulic conductivity (K sat) when slow-release fertilizer was applied. • Tea garden using slow-release fertilizer exhibited lower leaching flux/yield values. [ABSTRACT FROM AUTHOR]

Bentonites are considered as a suitable buffer material for the high-level radioactive waste disposal. The long-term stability of the hydromechanical properties of the bentonite barrier at high temperature is one of the key conditions for the proper functioning of the bentonite barrier. This paper presents an experimental study of the swelling pressure evolution of compacted samples of BCV bentonite exposed to high temperatures. The samples at constant volume were fully saturated at room temperature from the as-compacted state and then rapidly heated to constant temperatures of 50–150 °C. Temperatures were then held constant and the swelling pressure evolution was measured for the next 30 days. In the next stage, temperatures were decreased back to laboratory conditions and the equilibration of the swelling pressures was monitored. Finally, hydraulic conductivity of the selected samples was determined at room temperature. An additional test was performed to investigate the effect of saturation after heating on swelling pressure development. The results showed a significant decrease in the swelling pressure with time at elevated temperatures in all the samples (denoted as thermal relaxation). This decrease was more significant at higher temperatures and at temperatures above 100 °C the swelling pressure did not reach a steady state value until the end of the high temperature stage. The rate of swelling pressure decrease was quantified by the coefficient of relaxation C rel. A permanent decrease in swelling pressure due to thermal relaxation was identified after cooling. The swelling pressures decreased to 90–41% of the original swelling pressures determined before heating. The magnitude of the swelling pressure reduction increased with the applied temperature. Similar behaviour was observed for samples of different dry densities. The same effect of thermal relaxation was observed for samples saturated before and after heating. Thermal relaxation did not affect the hydraulic conductivity of the bentonite after temperature cycle, which was similar to that of thermally untreated BCV samples. • Significant thermal relaxation (swelling pressure decrease with time) of BCV bentonite was observed. • Decrease in swelling pressure accelerates with applied temperature. • Thermal relaxation resulted in permanent reduction of swelling pressure. • No effect of temperature cycle on hydraulic conductivity was observed. [ABSTRACT FROM AUTHOR]

In-situ ground improvement techniques, namely, deep soil mixing, jet grouting, cutter soil mixing, and mass stabilisation are often utilized to improve the strength of soft grounds, and construct seepage barriers. Due to economic and environmental concerns, there is a global shift towards using industrial wastes such as fly ash (FA) from conventional binders such as ordinary Portland cement and lime. There is a plethora of literature on unconfined compressive strength (UCS) of cement-treated clays, and clays treated with fly ash-cement mixes with alkali activator (FCAA) binders. However, much remains unclear about the hydraulic conductivity of the FCAA-treated clays as low permeable hydraulic barrier systems. In this paper, the hydraulic conductivities of cement-treated and FCAA-treated clays are studied both quantitatively and qualitatively for different binder-content, FA:cement ratios, curing periods, and effective confining stress. The hydraulic conductivity of treated clay is measured by performing a series of accelerated permeability tests using a custom-fabricated triaxial system. The trends obtained from the measured hydraulic conductivity values are explained from the observations of X-ray diffraction analysis and scanning electron microscopy analysis. Results showed that the values of hydraulic conductivity for cement-treated clay were mostly higher than those of untreated clay. On the contrary, the hydraulic conductivities for the FCAA clay mixes were comparable to, or even lower than those for the untreated clay. The hydraulic conductivity reduced with the increase in effective confining stress; the influence of effective confining stress, however, became less substantial for 28 days curing period and higher cement-content (40 and 50 %). The relationships between the hydraulic conductivity, UCS, and water-binder (w/b) ratios were also determined for both cement-treated and FCAA-treated clays. The exponential function was found suitable to express the relationship between hydraulic conductivity and UCS of treated clays. In contrast, a strong logarithmic relationship was obtained for measured values of hydraulic conductivity and adopted w/b ratios. The results shall serve as a guide to adopting suitable binder-content or target UCS for achieving design hydraulic conductivity in ground improvement projects that involve cement and/or FCAA-treatment of clays. [Display omitted] • Hydraulic conductivity values compared for cement- and FCAA-treated clays. • Effect of confining stress studied on hydraulic conductivity. • Effect of binder-content, FA:cement ratios and curing periods also studied. • Values for FCAA-treated clays are lower than cement-treated clay and untreated clays. • Proposed relationships between UCS, hydraulic conductivity and water-binder ratios. [ABSTRACT FROM AUTHOR]

A cracked rock mass can be idealized using a three-set model of orthogonal cracks. By varying the number of cracks per set, the structural anisotropy caused by the cracks is represented, and by rotating the principal axes of the structural anisotropy a more realistic model is constructed following field observations. A constitutive law for closing a crack aperture is formulated based on the results of the extensive laboratory tests previously reported. Parameter H , which controls stress-dependent hydraulic behaviors of cracked rock masses, can be determined by a laboratory test, and its mechanical significance is explained as an index of the pseudo-elastic modulus related to crack closing. The value of H experimentally determined highly depends on the number of loading cycles and whether it is loading or unloading. Information regarding the stress history is required to estimate H for cracks in the field. The depth-dependent hydraulic conductivity tensor for a cracked rock mass is formulated in a closed form, in which the effects of structural anisotropy, non-hydrostatic stress, and rotation of crack system are considered. If the stress field is hydrostatic, the hydraulic conductivity tensor exhibits unique depth dependence, despite its structural anisotropy and rotation of its principal axes. Non-hydrostatic stress exerts a significant influence on the hydraulic conductivity tensor. Hydraulic anisotropy is determined by interference among the following three factors: (a) structural anisotropy caused by cracks, (b) non-hydrostatic stress, and (c) discordance between the principal axes of the structure and stress. The importance of the second and third factors is that hydraulic anisotropy cannot be discussed solely in terms of structural anisotropy. The depth-dependent mean hydraulic conductivity obtained by the current theory corresponds well with field measurements at two sites. [ABSTRACT FROM AUTHOR]

Rice is a plant species sensitive to cold stress, which renders seriously its cultivation. Responses to cold stress (5°C, 24 hours) in whole plants, or targeted to rice leaves or roots were followed at the hormonome, transcriptome, proteome, and sugar levels, to find organ-specific responses and processes affected by cold acclimation. Targeted stresses caused proteomic changes mainly in the unexposed organs. An increase in abscisic acid (ABA) was accompanied by a decrease in jasmonic acid (JA) (in roots and non-stressed leaves) and vice versa (JA increased in stressed leaves). Both hormones promote the cold tolerance of plants. In this way, JA could indirectly reduce negative effects of cold on photosynthesis in leaves, while ABA dominates in roots (stimulation of protective substances, especially dehydrins, control of water regime). The decrease in cytokinins trans- zeatin and dihydrozeatin in crowns correlated with stress-induced growth suppression. Leaf-targeted cold stress impaired photosynthesis and decreased sugar levels, diminishing their transport, which correlated with an increase in salicylic acid, which is a signal for sugar unloading from phloem into roots. Root-targeted stress suppressed cytokinin biosynthesis and upward transport, and promoted sugar accumulation in leaves. Acclimation per se activated the transcriptome and proteome response to cold – ABA, JA and ethylene were upregulated, moderately suppressing plant growth. Pre-acclimated plants showed less profound hormonal changes than directly stressed plants, positively affecting levels of growth-related phytohormones in the unexposed organs (cytokinins in roots of leaf-stressed plants; auxins in leaves of root-stressed plants). • Targeted stresses affected proteins predominantly in the non-exposed organs. • Abscisic acid in roots after all cold treatments regulated hydraulic conductivity. • Jasmonates in stressed leaves might diminish stress effects on photosynthesis. • Salicylic acid probably enhanced sugar unloading from phloem in roots under stress. • Pre-acclimation enhanced stress tolerance, and speeded up recovery. [ABSTRACT FROM AUTHOR]

The issue of pressurized tunnels has been sufficiently investigated in the literature; nevertheless, the long-term behavior of the problem, which is the case in very squeezing conditions, remains unexplored. From a practical standpoint, the development of a damaged zone around the tunnel, due to the poor quality of blasting for excavation, imposes an additional challenge in predicting tunnel responses. This paper introduces an analytical approach addressing both water seepage and the excavation damaged zone (EDZ) concerning the long-term behavior of lined circular pressurized tunnels. To achieve this goal, the rheological behaviors of the initial rock mass and damaged zone are modeled using the Burgers model, along with considering the time-dependent variation in the rock mass hydraulic conductivity. After the validation of the model, the conducted parametric studies reveal that rock mass and lining hydraulic conductivities, EDZ radius, and the Burger shear modulus are the most influential parameters. [ABSTRACT FROM AUTHOR]

• A new percolation-based model for unsaturated hydraulic conductivity is developed. • Weibull distribution is used in combination with critical path analysis and percolation theory. • Model validation using measured and simulated data confirms good performance. • Capillary pressure curve slightly outperforms pore-throat size in estimating K (S w). Accurate estimation of unsaturated hydraulic conductivity, K (S w), is crucial for modeling water and solute transport in variably-saturated soils. In this study, a new model for the estimation of K (S w) based on percolation theory and critical path analysis is presented, in which the pore-throat size distribution is described by the three-parameter Weibull probability density function. To evaluate the performance of the proposed K (S w) model, two datasets including more than three hundred samples are analyzed. The first dataset includes 240 pore-network simulations, while the second dataset consists of 101 soil samples from the UNSODA database. For the pore-network simulations, for which both pore-throat size distributions and capillary pressure curves are available, we estimate K (S w) from the capillary pressure curve with RMSLE = 0.54 slightly better than the estimations obtained from the pore-throat size distribution with RMSLE = 0.6. For the soil samples, since only the capillary pressure curve is measured, we estimate K (S w) from the capillary pressure curve and evaluate three previously proposed approaches for determining the exponent, α, in Poiseuille's law. We find that RMSLE = 0.98 for α = 3, RMSLE = 0.87 for α = 2(4 − D) − (3 − D)/(2 D − 3), and RMSLE = 1.06 for α = 4 − 0.74 D , in which D is the fractal dimension characterizing the pore space. Comparing the results with previous studies in which the power-law probability density function was used to characterize capillary pressure curve and pore sizes shows that the proposed three-parameter Weibull distribution, in conjunction with the CPA analysis, may more accurately estimate K (S w) for a wide variety of soils ranging from very fine to very coarse textures. [ABSTRACT FROM AUTHOR]

• We calculate watershed-scale hydraulic conductivity on substrates of different age. • Hydraulic conductivity decreases with weathering due to increasing age. • Decreasing hydraulic conductivy changes runoff-to-groundwater partitioning. • Runoff-to-groundwater partitioning changes as a function of weathering in Hawai'i. We investigated how runoff-to-groundwater partitioning changes as a function of substrate age and degree of regolith development in the Island of Hawai'i, by modeling watershed-scale hydrodynamic properties for a series of volcanic catchments of different substrate age developed under different climates. In the younger catchments, rainfall infiltrates directly into the groundwater system and surface runoff is minimal, consisting of ephemeral streams flowing on the scale of hours to days. The older catchments show increasing surface runoff, with deeper incision and perennial discharge. We hypothesize that watershed-scale hydrodynamic properties change as a function of their weathering history—the convolution of time and climate: as surfaces age and become increasingly weathered, hydraulic conductivity is reduced, leading to increased runoff-to-recharge ratios. To test this relationship, we calculated both saturated hydraulic conductivity (k) and aquifer thickness (D) using recession flow analysis. We show that the average k in the younger catchments can be between 3 to 6 orders of magnitude larger than in older catchments, whereas modeled D increases with age. Ephemeral streams with zero baseflow at daily timescales cannot be evaluated using the same method. Instead, we calculated the recession constant for two contiguous catchments developed on young ash or lava deposits of different ages. Increasing bedrock age results in slower recession response in these ephemeral streams, which is consistent with decreasing hydraulic conductivity. Our results highlight the role of the weathering history in determining the evolution of watershed-scale hydrologic properties in volcanic catchments. [ABSTRACT FROM AUTHOR]

Freezing and thawing affect the pore-space structure in agricultural soils with implications for soil hydraulic properties and water flow. Previous studies have focused on the upper few centimeters of the tilled topsoil, where most freeze-thaw (FT) cycles occur, even though deeper soil layers are also subject to freezing and thawing in cold climates. Thus, little is known about how freezing and thawing affect untilled soil layers, which often show high bulk densities that restrict vertical water movement. Furthermore, it remains unclear how shifts in FT patterns with climate change may change the pore-space structure and water flow through these soil layers. Here we investigated the effects of freezing and thawing on X-ray imaged pore-space characteristics, water retention and near-saturated hydraulic conductivity (K) in untilled soil directly below plough depth. Intact cores were sampled at two sites in central Sweden under the same long-term reduced tillage management. The two soils, a silt loam and a silty clay loam, were subjected to three FT scenarios in a laboratory environment intended to represent FT patterns that are considered likely under current and future winter conditions for this region. The latter scenario was characterised by more FT cycles and a lower freezing temperature. Freezing and thawing increased K in the near-saturated range in both soils, which we attribute to observed small (<0.01 mm3 mm−3) increases in the volume of pores of diameters close to the X-ray resolution limit. Concomitant increases in pore network connectivity and critical pore diameter, especially in the denser silty clay loam soil, probably contributed to this increase in K. The water retention data suggested that changes in pore-space characteristics below X-ray resolution also occurred in both soils. Furthermore, our results indicate that both soils may show higher drainage rates due to shifts in FT patterns in the future, although longer-term changes in pore-space structure with an increasing number of FT cycles would mostly be limited to soils with relatively high clay contents. These soils are often more compacted below plough depth and, thus, benefits from improvements in soil structure such as improved root growth and plant water supply are also expected to be larger. • Freezing and thawing affects the soil pore structure of compacted soil layers. • Changes in freeze-thaw patterns may increase drainage rates of compacted soils. • Potential benefits are expected to be largest for clay-rich soils.. [ABSTRACT FROM AUTHOR]

• Leaf mass-based photosynthetic rate was more enhanced in evergreen trees with eCO2. • Branch hydraulic efficiency was more enhanced in deciduous trees with eCO2. • eCO2 strengthens the coordination of stem hydraulics with leaf gas exchange. Elevated CO 2 concentration (eCO 2) in the atmosphere is expected to impact plant water relations and growth in several ecosystems across the globe. However, we still know little about such impact on tree species in subtropical regions. The present study investigated the impact of eCO 2 on leaf gas exchange, nitrogen and phosphorus concentrations, leaf and stem hydraulic conductivity, and growth of seedlings of four evergreen and four deciduous tree species from a subtropical forest in Southwest China. We found that both evergreen and deciduous tree species at eCO 2 had higher leaf area-based photosynthetic rates and lower leaf stomatal conductance. Further, leaf mass-based photosynthetic rate was more enhanced in evergreen than in deciduous trees at eCO 2. Biomass of evergreen and deciduous species was significantly higher at eCO 2 , with large species-specific variation among the evergreen species. Leaf-specific hydraulic conductivity was more enhanced in deciduous tree species than that of evergreen tree species with eCO 2 , which was mainly driven by the increase of biomass at eCO 2. Interestingly, eCO 2 significantly strengthened the coordination of stem hydraulic conductivity with leaf-gas exchange, leaf phosphorus concentration, and plant biomass across evergreen and deciduous species. These results highlighted greater enhancement of photosynthesis and greater species-specific variation in biomass at eCO 2 for evergreen species compared to deciduous species, and stronger hydraulic-photosynthesis correlations at eCO 2 than at aCO 2 for tree species from subtropical forests. The present study provides important insights on the potential impacts of eCO 2 on plant eco-physiology, growth and forest succession in a subtropical forest under global climate change. [ABSTRACT FROM AUTHOR]

• Recurrent fire leads to degraded rainforest (DRf) and herbaceous-shrubby (HS). • Ksat and 6 years of rainfall-soil suction interactions are analyzed. • HS provide shallow soil saturation even during long dry periods. • Fire decreases Ksat in topsoil and it increases soil suction in depth at HS. • Post-fire soil changes tend to favor rapid suction loss in the unsatured zone. The role of fire in vegetation-soil–water interactions and its implications for soil stability and slope failures is poorly documented in humid tropical regions. This paper focuses on the relationships between vegetation change through recurrent fire and its effects on hydraulic conductivity and soil suction. Two monitoring sites were chosen on steep slopes in the mountainous domain of the Atlantic rainforest: the first is representative of degraded secondary rainforest (DRf) 25–30 years after slash and burn agriculture; the other represents herbaceous-shrubby vegetation (HS) resulting from wildfires in short-time intervals (<5 years). Two fires had previously occurred on the HS slope, one in December 2014 and the other in September 2019. Continuous records of rainfall and soil suction at depths of 10, 20, 50, 100, 150, and 220 cm provided a 6-year data collection from January 2015 to December 2020. Hydraulic conductivity (Ksat) field tests were conducted around the two monitoring sites before and after the September 2019 fire. The main results include: a) soil suction in the topsoil of both vegetation covers follow the rainfall inputs with high values of Ksat (DRf = 195 mm/h; HS = 203 mm/h); b) while quick rainfall-suction responses prevail within the DRf soil profile, soil suction at HS maintains a mean suction value around -27 kPa below 100 cm deep; c) field observations attest to the occurrence of hydrophobicity after the 2019 fire; d) Ksat tests just after this fire indicated a decreasing mean value from 203 mm/h to 46 mm/h; and e) by the end of the dry season after fire, there is a delayed increase in soil suction reaching -143 kPa at a depth of 100 cm and in smaller proportions at 220 cm deep. These results indicate that post-fire soil changes tend to favor the sudden loss of soil stability and slope failure during extreme rainfall events. [ABSTRACT FROM AUTHOR]

Although grass waterways are an effective conservation practice to reduce soil erosion, less is known about their subsurface hydrogeology. New research is highlighting the potential for NO 3 -N load reductions in waterways, but studies have not been done to characterize regional patterns. In this study, we used field investigation and numerical modeling to evaluate subsurface hydrogeological conditions beneath grass waterways found in major landform regions of Iowa. Our goal was to identify waterways that could be best utilized in a new conservation practice aimed at reducing tile NO 3 -N export from cropped fields. Waterway stratigraphy consisted of a layer of fine-textured, nutrient-rich sediment overlying glacial or post-glacial parent material. The mean hydraulic conductivity (K) of the alluvial sediments reflected a dominantly silty matrix and it was highest in northeast Iowa where sand contents were higher. Groundwater was largely anaerobic in lowland waterway areas, where high water tables contributed to low dissolved oxygen and NO 3 -N concentrations in shallow groundwater. Numerical modeling parameterized using the field data showed that in terms of annual water balance, more water is exported from grass waterways in surface runoff compared to subsurface tile and groundwater flow. In terms of subsurface flow, tile water yields were higher in smaller and steeper catchments and when the K of the waterway alluvium was higher. Based on regional patterns of sedimentology and landscape topography, smaller and steeper catchments within a landform region found in NE Iowa may be most appropriate to test a new conservation practice aimed to capture and remediate tile NO 3 -N export from grass waterways. • Grass waterway stratigraphy in Iowa consist of fine-textured, nutrient-rich sediment overlying glacial parent material. • Waterways have high water table and hydraulic conductivity consistent with silt-dominated matrix. • Groundwater quality is anaerobic with low dissolved oxygen and nitrate concentrations. • Numerical modeling shows that more subsurface water flow occurs in smaller and steeper catchments with higher alluvial K. [ABSTRACT FROM AUTHOR]

This study aims to evaluate interlayer and surface characteristics of carboxymethylcellulose (CMC) and tetramethylammonium (TMA) modified bentonite, named as TCMB, as a potential material in contamination containment systems. The study employed a variety of experimental methods, including zeta-potential, scanning electron microscopy, X-ray diffraction (XRD), transmission electron microscopy, and Fourier transform infrared spectroscopy (FTIR), along with molecular dynamics (MD) simulations. Zeta potential results revealed increased electronegativity in TCMB compared to the conventional bentonite. By forming three-dimensional hydrogel networks capable of filling inter clusters pore spaces, CMC effectively maintained the low hydraulic conductivity of TCMB. XRD results confirmed the presence of TMA in the interlayer of montmorillonite. MD simulations and FTIR analyses validated the successful adsorption of CMC and TMA, which can be jointly attributed to hydrogen bonds between hydroxyl groups in CMC and the surface oxygen of montmorillonite, and electrostatic attraction between TMA and montmorillonite. The comparatively weak bonding between CMC and montmorillonite may facilitate CMC elution in the TCMB exposed to aggressive permeants. Furthermore, the electrical double layer thickness of TCMB and CB was estimated as 31.54 Å and 18.76 Å, respectively. Overall, the CMC and TMA treatments effectively enhance the suitability of bentonite for contamination containment applications. [Display omitted] • Interlayer and surface characteristics of the modified bentonite were determined. • CMC formed three-dimensional networks, effectively filling inter-aggregate pores. • TMA intercalated in a monolayer configuration in montmorillonite interlayer. • Modified bentonite possessed thicker electric double layer. [ABSTRACT FROM AUTHOR]

• Hydrogeological model using Equivalent Porous Media and Conduit Network approaches. • Discrete features tool application to represent karst conduits with turbulent flow. • Using tracer test results to calibrate the flow rate of karst springs. The current study consisted of the development of a hydrogeological numerical model in the Lagoa Santa Karst Environmental Protection region, in order to represent the conduit-flow karst springs in the most well-studied karst system in Brazil. Once carbonate aquifers are characterized by a complex 3D pattern with a combination of a double porosity of matrix and conduits, two different modelling approaches were used: Equivalent Porous Medium (EPM), based on Darcy's law, to represent laminar flow in the fractured massif and Conduit Network (CN), using Manning-Stricker Law and the discrete feature tool, to represent the karst conduits with turbulent flow. Modeling was calibrated in a steady-state and simulations of groundwater flow and an evaluation of water exchanges between the karstic aquifer and the other hydrogeological units, were conducted. The model was developed based on data available for many studies carried out in the area, including tracer-derived route data. The calibration results for spring discharges, water levels and mass balance were satisfactory and aligned with modeling good practices. In turn, the hydraulic conductivities and recharge rates obtained by back-analysis were in agreement with literature references. The regional groundwater flow was well represented and indicated how external water entrances can be relevant to explain the higher discharge rates observed in some karstic springs. In addition, the representation of conduits allowed for the simulation of tracer pathways, enabling the inference of potential flow rates to the karstic springs from the particle simulations. [ABSTRACT FROM AUTHOR]

• Analytical solutions for defining the riparian lens extent and saltwater discharge in stratified aquifers are developed. • The applicability of the proposed analytical solution is validated through numerical simulations and sand-tank experiments. • The impact of aquifer stratification on riparian lenses depends on inland boundary conditions. Analytical solutions for defining stable freshwater lenses within saline riparian aquifers ("riparian lenses") are largely limited to homogenous aquifers. However, real-world riparian aquifers typically consist of a surficial layer of low-permeability soils or deposits, the impact of which on the occurrence of riparian lenses has not been investigated. This study develops steady-state, sharp-interface analytical solutions for riparian lens shape and saltwater discharge in a two-layered riparian aquifer. The developed analytical solutions are verified by sand tank experiments and numerical simulations, showing good agreement. The sensitivity analysis based on the proposed analytical solutions suggests that aquifer stratification (i.e., considering a low-permeability layer overlying a high-permeability layer) leads to larger lenses in head-controlled systems (i.e., with the inland constant-head boundary) but smaller lenses in flux-controlled systems (i.e., with the inland constant-flux boundary), compared to the scenario of a homogenous aquifer. The surficial layer with hydraulic conductivity only an order of magnitude lower than the underlying high-permeability layer would have a pronounced effect on lens extent and volume. Importantly, the results suggest that the presence of the surficial low-permeability layer may lead to the outcropping of the groundwater table, favoring the occurrence of saline groundwater seepage near the edge of the river valley (i.e., a phenomenon reported by the field survey of the Murray River floodplains in South Australia). The analytical solution presented in this study can be used to provide a preliminary assessment of riparian lenses in saline stratified aquifers, expanding the applicability of analytical methods to more realistic riparian settings. [ABSTRACT FROM AUTHOR]

Laboratory tests were conducted to investigate the properties of a bentonite slurry enhanced by the biomass derived from wheat straw. The bentonite concentration of the basic slurry varied from 40 kg/m3 to 60 kg/m3. The biomass contents of the enhanced slurry were between 37.5 kg/m3 and 87.5 kg/m3. Compared to the pure bentonite slurry, the viscosity of the biomass-enhanced bentonite slurry did not show significant increase. Moreover, the density of the biomass-enhanced bentonite slurry did not significantly increase. It appeared that the stability of suspended particles was slightly weakened by the added biomass. The minimal content of biomass needed for filter cake formation in the coarse sand decreases with the bentonite concentration. With a proper biomass content, the slurry pressure could be fully transferred to the effective support pressure within 120 s. Generally, the hydraulic conductivity value of the filter cake was less than 10-7 m/s, meeting the requirement for safe construction. Furthermore, as the biomass was gained from wheat straw, the enhanced slurry showed a high possible application in slurry-shield tunnelling. [ABSTRACT FROM AUTHOR]

[Display omitted] • Root penetration into soils result in increased gas permeability. • Biochar addition alters pore-filling and increases soil capillarity. • Gas permeability function is dependent on root length density. Biochar amendment have been explored recently for improving hydro-mechanical properties of landfill cover system and enhancing the vegetation for the ecological restoration of post closure landfills. Existing studies have predominantly focused on the hydro-mechanical properties of biochar-amended rooted soils and yet few studies have comprehensively investigated their gas permeability functions in response to unsaturated conditions. The objective of this study is to experimentally and theoretically investigate the coupled effects of biochar and root intensity on CO 2 gas permeability in unsaturated soil. Biochar-amended rooted soil was prepared by growing Chrysopogon zizanioides on granite residual soils with biochar at a mas ratio of 5 %. Gas permeability and unsaturated soil properties (i.e., suction and degree of saturation) were monitored simultaneously. Due to the presence of roots, the maximum gas permeability, hydraulic conductivity, and suction increased by 200 %, 600 %, and 50 %, respectively, compared with bare soil. This was attributed to preferential flow, micropore increasement and negative pressure induced by root growth. However, biochar addition decreased the maximum gas permeability and hydraulic conductivity by 21 % and 33 %, respectively. This was attributed to the pore filling function of biochar, increased capillarity due to intrapore of biochar, and presence of surface functional groups in biochar promoting CO 2 adsorption. A newly developed model was proposed to predict gas permeability with respected to unsaturated soil properties. It was revealed that the gas permeability function of rooted soils showed a strong dependence on the measured root length density. This study highlights the significance of adopting biochar in mitigation of gas emissions in vegetated landfill cover system. [ABSTRACT FROM AUTHOR]

The incorporation of hard data in geostatistical modeling is crucial for enhancing the accuracy of interpolating or stochastically estimating subsurface spatial features. The hard data at specified points in the model domain serve as a guide in optimizing the unknown parameters to follow the patterns of the hard data. Recently, a novel approach to solving hydrogeologic/reservoir modeling problems has emerged by using deep generative models, specifically generative adversarial networks (GANs), to generate realistic and diverse images of channelized aquifers. This subsequently can be coupled with inverse models to solve parameter estimation problems. This study focused on using an improved GAN, called a progressive growing generative adversarial network (PGGAN), conditioned with hard data to perform parameter estimation of complex facies models by coupling an ensemble smoother with multiple data assimilation (ES-MDA). First, the PGGAN was trained to an image with 128 × 128 resolution. The trained PGGAN was used to generate hydraulic conductivity fields when fed an ensemble of latent variables and hard data. The ES-MDA then was used to update the latent variable with the help of hydraulic head data obtained from the groundwater model. The approach was tested on synthetic hydraulic conductivity data. Results show that this approach was able to perform efficient estimation of an unknown facies model domain. Additionally, the proposed method was applied to a different test case of a facies model exhibiting different statistical characteristics. The results were satisfactory, demonstrating that the method is not constrained to the particular hydraulic conductivity fields introduced in the generator's training. • Coupling deep learning with data assimilation for groundwater modeling. • Both hard data and soft data are conditioned. • Synthetic examples are used to demonstrate the effectiveness. [ABSTRACT FROM AUTHOR]

• Hydrogeological parameters are main uncertainty source of physical methods • Lag effect of the thick vadose zone limits WTF and dating-based methods • Ignoring the mixing and dispersion may overestimate recharge by 36–48 % for CFC • Aquifer heterogeneity reduces the potential of 14C for recharge estimation • CMB is recommended as the optimal method for GR estimation in the loess area Groundwater recharge (GR) can be estimated with physical, tracer techniques and numerical modelling; however, the uncertainties in these methods have not been fully interpreted. This study selected six methods for actual GR estimation in the saturated zones with different data requirements and method assumptions, including two physical methods (i.e., water table fluctuation WTF and Darcy's law DL) and four tracer techniques (i.e., chloride mass balance CMB, tritium renewal rate TRR, chlorofluorocarbons CFC and 14C dating method CBD). Taking the loess tablelands of China as an example study area, we first analyzed the uncertainties in these methods and then recommended the appropriate methods for GR estimation in regions with thick vadose zones. Overall, the recharge rates from WTF, CMB and CFC (88 ± 24, 98 ± 33 and 53 ± 9 mm/year) were much greater than those from DL, TRR and CBD (10 ± 3, 14 ± 3 and 7 ± 5 mm/year). The differences in estimated GR are closely related to the method parameters, assumptions and temporal scales. Specifically, the model parameters (e.g., specific yield, hydraulic conductivity) exhibit large ranges due to spatiotemporal heterogeneity, and the physical methods are more sensitive to hydrogeological parameters compared with the tracer techniques. The uncertainties related to model assumptions originate from the simplified water/solute movement processes. The lag effect of the thick vadose zone largely limits WTF and TRR, but contributes to CMB. Ignoring the mixing and dispersion effect may overestimate recharge by 36–48 % for CFC, and the heterogeneity of the aquifer reduces the potential of CBD for recharge estimation. Overall, CMB is considered as the most optimal method for estimating GR in the thick loess deposits. This study deepens the understanding of the uncertainties in GR assessment methods in regions with thick vadose zones. [ABSTRACT FROM AUTHOR]

• The recession curves of all features followed the triple permeability model. • The percentages of water capacity in the three aquifer media were calculated. • The average values of EC in fissure, fracture and conduit water were calculated. • A hydrogeological conceptual model was constructed for each karst feature. Understanding of the hydrological behaviors in different karst features is crucial for evaluating the hydrological storage and transfer functions of a karst system. In this study, the Maocun karst underground river system, characterized by typical karst features, was selected as the research area in the southwest region of China. The main objectives of this research are to analyze the hydrogeological structure characteristics of each karst feature and assess water storage capacity in different aquifer media. Frequency distribution curve (FDC) of electrical conductivity (EC) values revealed that recharge sources in the five karst features differed and varied according to the amount of precipitation. All hydrographs of water levels in five karst features were divided into three periods due to the presence of triple aquifer media in the basin. The spatial structure of each feature was interpreted by analyzing the variation characteristics of recession exponential coefficients (λ). Additionally, the ratios of fissure water, fracture water, and conduit water sources were calculated based on the recession curves of water levels. Results showed that fast water flow had the highest proportion in the relatively open subsystem located upstream, while fracture water flow had the lowest proportion. The slow water flow was the main pattern of water storage in the basin. Values of EC in water decreased with a well-connected spatial structure and high hydraulic conductivity. There were significant differences in the values of EC among conduit water, fracture water, and matrix water. These values were calculated using mathematical relationships between EC and water level hydrographs. The results indicated that the EC values in matrix water exceeded 200 μS/cm, while EC values in conduit water/channel water were below 100 μS/cm. Finally, hydrogeological conceptual models were constructed for five karst features based on the depletion characteristics of the aquifer media during each recession period. These characteristics were interpreted using variation curves of EC and hydrographs of water levels. These findings not only elucidated the characteristics of hydrogeological structures in multiple karst features, but also had significant implications for the assessment of karst water sources. [ABSTRACT FROM AUTHOR]

• Conductivity is employed in flow models upon averaged Monte Carlo fields. • A Monte Carlo volume of 10 % of that required for full numerical stability. • A 10 % volume returns stable outputs, i.e. heads and residuals at wells' locations. The knowledge of aquifer systems, their geological setting, their structure, and subsequent modeling is highly uncertain and is usually faced through Monte Carlo-based methods in hydrogeology. One of the most important uncertainty sources for groundwater models is represented by input hydraulic conductivities, related to the aquifer's structure. There are no specific rules when simulating hydraulic conductivity fields within Monte Carlo frameworks to instruct numerical models, and information about employed conductivity fields and their numerical convergence is often not given. This technical work aims to fill this gap by investigating the impact of employing conductivity information upon different volumes of Monte Carlo simulations applied to a real case study. Thus, this work estimates the minimum volumes of Monte Carlo hydraulic conductivity fields to be employed in groundwater flow models for achieving numerically stable (i) boundary conditions, (ii) global model performances, and (iii) local ones such as simulated hydraulic heads. The present results aim to be indicative of similar hydrogeological settings and will serve as a basis for more complex ones and for investigating transport problems. [ABSTRACT FROM AUTHOR]