Relative Hydraulic Conductivity Research Articles

Water flow in two Cactaceae species: standardization of the method and test under different drought conditions

AbstractInvestigating water flow in the vascular system of plants is important to identify the water path and conduction capacity of different plant species, mainly in succulent species living in dry regions. This study aimed to standardize a method to track water flow in the xylem of Mammillaria bocasana and Echinocereus reichenbachii var. fitchii (Cactaceae) and test it under different drought conditions. The plants were kept under greenhouse conditions to perform the split root method, water flow tracing, and different drought treatments. The plants of each species were separated into three treatments: constant irrigation, drought with water and dye, and drought with dye. Plants were cut 24 h after staining, total and lumen diameters were taken, and the relative theoretical hydraulic conductivity was calculated. The absorption method was adequate for the tracing of water flow, and it worked in all the treatments of the drought experiment. Conducting elements, including wide-band tracheids, were stained violet and were located near the vascular cambium. In Mammillaria bocasana, half of the vascular cylinder was stained, while in Echinocereus reichenbachii var. fitchii, the entire cylinder was stained due to the cortical bundles. M. bocasana had a higher lumen diameter and relative theoretical hydraulic conductivity than E. reichenbachii var. fitchii. With the absorption staining method, the flow of water was traced, and differences in conduction under water stress conditions between the two species of cacti were detected. These results suggest that cacti species living under water stress solve the water movement in different ways.

Study on water migration and the microstructure of unsaturated expansive clays

Because of the characteristics of water swelling and drying shrinkage, the mechanical performance of expansive clays in semi-arid areas deteriorates with changes in humidity and temperature. Hence, investigating the moisture migration in expansive clays is of great significance. Herein, scanning electron microscopy and water migration tests of unsaturated soil were carried out to address the water variation law and microscopic mechanisms in unsaturated expansive clays. It was found that small- and medium-sized pores (2–10 μ m) are dominant, and these pores are conducive to an increase in the water content in the soil. Soil with a high water content exhibits a flocculent structure, characterized by a small fractal dimension and a high relative hydraulic conductivity. Conversely, soil with a low water content displays a dispersed structure, featuring a large fractal dimension and a low relative hydraulic conductivity. The water migration tests, which were carried out at constant temperatures (5, 20 and 40°C) and variable temperatures (15–25°C), show that the amount of migration at 5 and 20°C was about 25–40 and 40–60% of that at 40°C, respectively. The amount of water migration at a constant temperature was obviously lower than that recorded at variable temperatures. The research results have provided technical support for the effective control of soil change.

A modified model predicting the hydraulic properties of variably saturated soil accounting for film and capillary flow

Accurate knowledge of hydraulic properties of unsaturated soil is vital to modelling water and solute transport process and addressing soil salinisation problems. Due to the defect that the van Genuchten (VG) model cannot represent soil water characteristics (SWC) during the drying stage, we have introduced a modified model, which combines capillary flow with film flow models to describe the unsaturated hydraulic conductivity. The capillary SWC is obtained by assuming the specific water capacity function with lognormal distribution. The film SWC is modified using the logarithmic nonlinear expression by introducing a modification coefficient into the Campbell equation, and the film relative hydraulic conductivity (RHC) is obtained based on the logarithmic nonlinear relationship. The calculated modification coefficient values range from 0.99 to 2.49. Finally, the proposed model’s rationality and applicability are validated through root mean square error (RMSE) analysis with measured values and comparison with the VG model. While the calculation RMSEs of SWC in the two models are basically consistent, the RMSEs of RHC in the proposed model are around 1–10 times smaller than those of the VG model, indicating its superiority in calculating the hydraulic conductivities over the entire matric head.

A Dimension-Reduced Line-Element Method to Model Unsaturated Seepage Flow in Porous Media

Contrary to the continuum hypothesis, which averages water flow across the entire domain, including both grains and pores, the line-element model concentrates unsaturated flow in the pore space in the intermediate region of horizontal and vertical channels. The flux equivalent principle is used to deduce the equivalent unsaturated hydraulic conductivity, the flow velocity and the continuity equations. It is found that the relative hydraulic conductivities derived from the line-element model and the continuum model are identical. The continuity equations in the two models are also similar, except that the coefficient in the water content term is half that in the line-element model. Thus, the unsaturated flow problem in porous media is transformed into a one-dimensional problem. A dimension-reduced finite line-element method is proposed that includes a complementary algorithm for Signorini’s-type boundary conditions involving the seepage-face boundary and the infiltration boundary. The validity of the proposed model is then proved by good agreement with analytical, experimental and simulated results for one-dimensional infiltration in a vertical soil column, unsaturated flow in a sand flume with drainage tunnels, and transient unsaturated flow water-table recharge in a soil slab, respectively. In general, the proposed method has good computational efficiency, especially for smaller mesh sizes and short time intervals.

Assessment of bed clogging in surface water reservoirs under different hydrologic conditions

Physical clogging of porous media plays an important role in controlling their hydraulic conductivity. This study investigates how uniformly graded medium-to-coarse sand in a reservoir’s bed performs in response to the inflow of turbid water with fine suspended sediments. Different particle sizes, heads, and concentrations were simulated to cover a range of hydrologic conditions. A 1D sand column was used with three bed material sizes and three suspended particle sizes. Seven particle size ratios were tested under a constant head. Four heads and three suspended sediment concentrations are also evaluated. It was concluded that the decline in the relative hydraulic conductivity of the bed material is directly proportional to the ratio of sediments-to-bed particle sizes. Increasing the concentration of suspended sediments accelerated the rate of clogging, while bigger heads increased the depth of clogging. The study highlights how physical clogging affects the water balance in surface reservoirs and threatens the safety of dams.

Rhamnolipid-induced alleviation of bioclogging in Managed Aquifer Recharge (MAR): Interactions with bacteria and porous media

The prevention and treatment of bioclogging is of great significance to the application of Managed Aquifer Recharge (MAR). This study investigated the alleviating effect of biosurfactant rhamnolipid (RL) on bioclogging by laboratory-scale percolation experiments. The results show that the addition of RL greatly reduced bioclogging. Compared with the group without RL, the relative hydraulic conductivity (K′) of the 100 mg/L RL group increased 5 times at the end of the experiment (23 h), while the bacterial cell amount and extracellular polymeric substances (EPS) content on the sand column surface (0–2 cm) decreased by 60.8% and 85.7%, respectively. In addition, the richness and diversity of the microbial communities within the clogging matter decreased after the addition of RL. A variety of bacterial phyla were found, among which Proteobacteria were predominant in all groups. At the genus level, RL reduced the relative abundance of Acinetobacter, Bacillus, Klebsiella, and Pseudomonas. These microbes are known as strong adhesion, large size, and easy to form biofilms, therefore playing a critical role during MAR bioclogging. Moreover, RL changed the surface properties of bacteria and porous media, which results in the increase of electrostatic repulsion and decrease of hydrophobic interaction between them. Therefore, RL mediated the bacteria-porous media interaction to reduce biomass in porous media, thereby alleviating bioclogging. This study implies that RL's addition is an environmentally friendly and effective method to alleviate the bioclogging in MAR.

Water uptake, anatomical, and biochemical changes of sorghum genotypes subjected to polyethylene glycol-induced drought stress

Absract To investigate the water uptake, anatomical and biochemical changes of sorghum, three genotypes including grain sorghum [Sorghum bicolor (L.) Moench subsp. bicolor], Sudan grass [Sorghum bicolor (L.) Moench subsp. drummondii (Steud.) de Wet ex Davidse] and Johnson grass [Sorghum halepense (L.) Pers.] were subjected to polyethylene glycol (PEG 60000)-induced drought stress (PEG 60000) at 0, −0.15, and −0.3 MPa levels, hydroponically. In all genotypes, stele diameter decreased as osmotic potential of the medium decreased and the largest stele diameter (247 µm) was observed in Johnson grass at control and declined to 196 µm under −0.3 MPa PEG. Drought affected the diameter of peripheral metaxylem (PMX) and central metaxylem (CMX), negatively. The number of PMX and CMX in Johnson grass was 36 and 200% more than in grain sorghum under −0.3 MPa PEG, respectively. In all genotypes, chlorophyll a and b declined under drought, but in Johnson grass, it only decreased 25 and 29%, respectively. Johnson grass had the highest total chlorophyll content, while carotenoid content was stable under drought stress in this genotype. Drought stress increased catalase and peroxidase activities but decreased relative water content (RWC) and hydraulic conductivity (hc). Under drought, the higher seedling dry weight and root to shoot ratio in Johnson grass might be related to higher hc, total chlorophyll content, and RWC. Moreover, Johnson grass showed less water loss and more efficiency in water uptake under induced drought stress; and it could be attributed to the larger stele diameter, number, and diameter of PMX, substantiating their roles in drought adaptation.

Fractal-based hydraulic model of unsaturated flow in deformable soils considering the evolution of pore size distribution

This paper presents a fractal-based hydraulic model for unsaturated flow, which includes the soil water retention curve (SWRC) and relative hydraulic conductivity curve (RHCC), and considers the evolution of pore size distribution (PSD) during soil deformation. In this model, soil PSD is assumed to follow the fractal scaling law, and soil deformation is characterized by a change in the fractal dimension and air entry value. By combining the intrinsic constraint between void ratio and fractal dimension, the fractal description of PSD evolution during volumetric deformation of soils is clearly defined, and the void ratio-dependent SWRC and RHCC are derived. All model parameters can be calibrated from the SWRC data of soils under two initial void ratios, and can then be used to predict the SWRC and RHCC of the soil under arbitrary deformation states. Eight experimental data sets, including SWRC and RHCC data under different initial void ratios, are used to evaluate the proposed model. Results show that: (1) the fractal-based hydraulic model can well describe the influence of volumetric deformation on the hydraulic properties of unsaturated soils, and (2) ignoring the evolution of PSD during soil compression will significantly overestimate the water retention ability and hydraulic conductivity of soils.

Analysis of soil electrical resistivity and hydraulic conductivity relationship for characterisation of lithology inducing slope instability in residual soil

Slope instability occurrences as damaging shallow-landslides in the residual soil around mountains has been widely studied with geophysical, geotechnical and hydrogeological techniques but relating soil electrical resistivity to hydraulic conductivity for characterisation of lithology inducing of these landslides is not common. In this study, we used Electrical Resistivity Tomography (ERT) data and Hydraulic Conductivity (HC) data obtained from soil samples collected within 1–4.5 m depth in the borehole to assess the characteristics of soil that can induce landslide in the study location. The HC data were derived empirically from Beyer, Kozeny-Carman and Slitcher formula which were validated with HC obtained from laboratory experiment. The Empirical Derived Hydraulic Conductivities (EDHC) were correlated with the soil resistivity. The result shows a strong correlation between soil resistivity and HC with regression values of R2 = 0.9702, R2 = 0.9153 and R2 = 0.9232 for Beyer, Kozeny-Carman and Slitcher formula, respectively. The ERT model revealed a possible sliding surface between two contrasting resistive top material and underneath conductive materials at about 4 m depth. The HC assessment result corroborated the ERT model result because high and low-HC values were obtained in the borehole soil samples within 0–4 m and > 4 m depths from EDHC, respectively. The low-HC zone below 4 m depth was responsible for the occurrences of the shallow-landslides in the study.

Effect of biofilms on the clogging mechanisms of suspended particles in porous media during artificial recharge

Artificial recharge of groundwater is an effective technology for solving the shortage of water resources. The clogging of porous media is a bottleneck that limits the application of this technology. In this study, percolation experiments in sand columns were conducted to investigate the influence of different types of biofilms on the deposition of suspended particles and clogging evolution during artificial recharge. A unique aspect of this study is the consideration of biofilms coated on porous media when the clogging mechanisms of suspended particles in porous media are explored. At the end of the recharge process, the relative hydraulic conductivity (K’) of the porous media in descending order was Pseudomonas aeruginosa experimental group (PA) > Bacillus subtilis experimental group (BS) > mixed microbial consortium experimental group (MC) > suspended particle only group (SP). The suspended particles in SP- moved more deeply into the sand column than those in BS, PA, and MC. Electron microscopy, high-throughput sequencing, and confocal laser scanning microscopy were used to identify the mechanisms governing clogging evolution under the influence of biofilm existence. The presence of a biofilm not only alters the surface charge and physical roughness of the porous media, but also affects the electrostatic interaction between the porous media and suspended particles. Biofilms combine tightly with suspended particles by binding and adhesion, which can form tight biofilm-particle aggregations. Compared with deposition of particle-only in SP, the biofilm-particle aggregations on the surface of the porous media are more firm. The biofilm coated on the surface of porous media occupied the pore vacancy and narrowed the void space compared with that in clean sand, which induced physical straining. As the thickness of biofilm coated on the sand surface increased, the more suspended particles were deposited on the sand surface in PA. These findings provide insights into clogging under the influence of biofilms and have implications for future field-based artificial recharge.

Upgraded closed‐form soil hydraulic functions from oven dryness to saturation

AbstractIn the past decades, remarkable progresses have been made in developing soil water retention (SWR) functions and relative hydraulic conductivity (kr) models for the full range of matric suction. However, such an existing SWR function and the corresponding kr model were found not to have a consistent prediction performance, that is, for a given soil, the SWR function could perform very well but the kr model might perform poorly or even fail. Given that both water retention and hydraulic conductivity need to be accurately predicted to simulate land‐atmosphere interactions, vadose‐zone soil–water dynamics, and shallow groundwater recharges, this paper proposed an upgraded SWR function and derived a new closed‐form kr model by combining the function with the well‐known Mualem model. The upgradation was done by introducing an exponential function for the pendular (i.e., dry and very dry) range of matric suction. The SWR function and kr model keep the conventional simplicity, reflect the capillary versus adsorptive soil–water mechanisms, eliminate fictitious parameters, and are continuously differentiable with closed forms. The assessment using the experimental data for 35 soils with nine different textures indicated that the upgraded SWR function and new kr model reproduced the data more accurately than the existing functions and models, as measured by visualization plots and four statistics, namely coefficient of determination, sum squared error, root mean squared error, and Nash–Sutcliffe efficiency. The contribution of this paper is to overcome the inconsistent‐performance issue mentioned above.

Applying lysozyme, alkaline protease, and sodium hypochlorite to reduce bioclogging during managed aquifer recharge: A laboratory study

Alleviating bacterial-induced clogging is of great importance to improve the efficiency of managed aquifer recharge (MAR). Enzymes (lysozyme and alkaline protease) and sodium hypochlorite (NaClO) are common biological and chemical reagents for inhibiting bacterial growth and activity. To investigate the applicability of these reagents to reduce bioclogging, percolation experiments were performed to simulate a weak alkaline recharge water infiltration through laboratory-scale sand columns, with adding 10 mg/L lysozyme, alkaline protease, and NaClO, respectively. The results showed that, with the addition of lysozyme, alkaline protease, and NaClO, the average clogging rates (the reduced percentages of relative saturated hydraulic conductivity of the sand columns per hour during the percolation experiments) were 0.53%/h, 0.32%/h and 0.06%/h, respectively, which were much lower than that in the control group (0.99%/h). This implied that bioclogging could be alleviated to some extent following the treatments. For further analyzing the mechanisms of the regents on alleviating bioclogging, the bacterial cell amount and extracellular polymeric substances (EPS) concentration were also measured to study the effects of lysozyme, alkaline protease, and NaClO on bacterial growth and EPS secretion. Lysozyme and alkaline protease could disintegrate bacterial EPS by hydrolyzing polysaccharides and proteins, respectively, while they had little effect on the bacterial cell amount. The addition of NaClO significantly decreased the bacterial cell amount (P < 0.05) and thus greatly alleviated bioclogging. Although the lowest average clogging rate was achieved in the NaClO group, it can generate disinfection by-products that are potentially harmful to the environment and human health. Therefore, the biological-based method, i.e., enzyme treatment, could be a promising option for bioclogging control. Our results provide insights for understanding the mechanisms of lysozyme, alkaline protease, and NaClO to alleviate bioclogging, which is of great importance for addressing the clogging problem during MAR activities and achieving groundwater resources sustainable utilization.

Threshold Recognition of Water Turbidity for Clogging Prevention during Groundwater Recharge Using Secondary Effluent from Wastewater Treatment Plant

The recharge efficiency during artificial groundwater recharge (AGR) is reduced primarily by clogging that is triggered by suspended particles. However, there are loopholes in the current standards of recharge-water quality for clogging control during AGR, and the threshold values of turbidity to prevent clogging have not been reasonably determined. In this study, secondary effluents from wastewater treatment plants (WWTPs) were injected into saturated sand columns to simulate the process of AGR. Batch experiments under different turbidity conditions were conducted, and the numerical modeling of particle transport and deposition was performed to assess the clogging processes. Theories of single-collector contact and interfacial interaction energy were applied to elucidate possible microcosmic mechanisms. The results showed that the diluted secondary effluent (SE) with turbidities of 0.540 ± 0.050, 1.09 ± 0.050, and 1.84 ± 0.060 NTU caused considerable clogging in the porous media, which decreased the relative hydraulic conductivities (K/K0) by 13.2%, 17.6%, and 83.6%, respectively. The filtered SE with a turbidity of 0.160 NTU did not cause clogging, and K/K0 was reduced by only 1.70%. The clogging was attributed to the deposition of suspended particles in the sand matrix because they have a high collision efficiency (0.007–1.98) and attachment efficiency (0.029–0.589 kBT). Finally, this paper recommends that the turbidity of the recharge water should not exceed 0.500 NTU during AGR practices.

Epoxy lining influence on recycled water quality during pipeline transit for potable reuse.

An epoxy treatment was applied to a pipeline used to convey advanced treated recycled water from a purification facility to a recharge site. The epoxy treatment was applied to prevent further deterioration (corrosion) of the interior cement mortar lining (CML). A soil column study was conducted to evaluate the effect of the epoxy liner on the clogging potential of water before and after conveyance. The clogging potential was represented by differences in the column's relative hydraulic conductivity and water quality, between the treatment plant and injection site, before and after epoxy lining. Hydraulic conductivity of columns at the injection well site declined rapidly before epoxy and improved considerably after epoxy application. Total suspended solids (TSS) and cellular adenosine triphosphate (cATP) median concentrations improved significantly. Before epoxy, TSS increased with pipeline transit from 0.005 to 0.053 (mg/L) compared with 0.009 mg/L after epoxy. Before epoxy, cATP increased from 0.14 to 1.6pg/ml across pipeline transit compared with 0.37 pg/ml after epoxy. Aluminum and nitrate followed similar trends. Results indicate that epoxy liner reduced the clogging potential of high purity recycled water, likely due to a decrease in particle and biomass load (clogging constituents) accumulated during pipeline transit. PRACTITIONER POINTS: Clogging potential of advanced treated recycled water increases with pipeline transit. Epoxy lining the pipeline used for conveyance reduces the particulate and microbial loading of the highly purified water. Applying epoxy to pipelines used to convey advanced treated recycled water has the dual benefit of infrastructure protection and improving water quality. Reducing particle and microbial load in the advanced treated recycled water can reduce maintenance frequencies and elongate production periods for MAR applications.

Influence of pH on bioclogging in porous media during managed aquifer recharge (MAR): Effectiveness and mechanism

To investigate the effect of pH on bioclogging process during managed aquifer recharge, three laboratory-scale column experiments were conducted and the relative hydraulic conductivity, bacterial cell number and the concentrations of polysaccharide, protein and EPS were measured under pH 5, 7, and 9, respectively. High-throughput sequencing was also used to determine the characteristics of bacterial community under different pH conditions. The development of bioclogging was rather different for the case of pH 5. 7, and 9; i.e., the growth process and number of bacteria differed with pH. The shortest growth period and lowest number of bacteria were observed at pH 5. In addition, the difference in bacterial EPS concentration was mainly associated with the polysaccharides. The variation in pH led to different bacterial community composition and diversity. The acid-resistant Elizabethkingia and Bacillus were abundant at pH 5, while Chryseobacterium and Klebsiella had relatively high abundances at pH 7. In contrast, the basophilic Exiguobacterium accounted for >80% of the total bacterial abundance at pH 9. This work is of great significance to explore bioclogging mechanism during MAR process, and provides insights and guidances for field-based managed aquifer recharge.

Comparative Ecophysiology of Hybrid Wood Fern Species

Premise of research. Polyploidy and hybridization are prevalent and widespread phenomena in plants. The genetic consequences of genome duplication are numerous, but we understand very little about the comparative ecology of polyploids. In particular, the ways in which hybrid and polyploid offspring differ in ecology relative to their parents and relatives are poorly known. Among angiosperms, the triploid bridge is hypothesized to accrue some marginal fitness benefit to parent species from mostly sterile hybrid offspring. Because of the complexities of the fern life cycle, involving two free-living life stages, the ability to backcross via a triploid bridge should be more limited. If the triploid sporophyte offspring provide no fitness benefit to parents via subsequent generations, this raises the question about whether triploids further compete with parents by occupying similar ecological niches. We investigated comparative ecophysiology across light and wetness gradients of five members of the hybrid wood fern complex, Dryopteris. Methodology. We selected two related triads. Each triad consisted of a triploid and its diploid and tetraploid progenitor species: the D. × triploidea (3n) triad, with the parents D. carthusiana (4n) and D. intermedia (2n), and the D. × bootii (3n) triad, with the parents D. cristata (4n) and D. intermedia (2n). We sampled the temperature and relative humidity, population abundance and relative frequency, photosynthetic parameters, and hydraulic conductivity of populations to examine the extent of shared ecological niche space. Pivotal results. We found that triploids varied in habitat space relative to their parents. In the case of the triploid D. × bootii, this taxon occupied habitats similar to those of its parents at similar abundances and frequencies. In the case of D. × triploidea, the hybrid occurred across a more diverse range of habitats, which was more similar to its diploid parent. In both triads, the triploid’s photosynthetic rate was intermediate between those of its parents, and the majority of the photosynthetic parameters were similar to those of the parents. There were some differences in hydraulic conductivity: xylem-specific hydraulic conductivity of the triploid D. × bootii was significantly higher than that of its diploid parent. Conclusions. Our results show that related triploids, diploids, and tetraploids substantially overlap in morphological and physiological niche space. The high relative frequency of triploids in habitats and the lack of clear niche partitioning within triads suggest that in addition to not contributing to parental reproductive fitness, the triploids could also negatively impact their progenitors by potentially competing for space and light resources in similar ways.

Assessment and application of an alternative formula to describe the hydraulic conductivity over the full moisture range

AbstractMotivated by a versatile three‐parameter water retention curve (WRC) formula of Fredlund and Xing, we proposed an alternative expression to describe the relative hydraulic conductivity (RHC) for soils that can capture oven‐dry to water‐saturated conditions (full moisture range) with a single, closed‐form equation (without having to explicitly partitioning the capillary and film flow components). This RHC expression was tested using an existing data set that includes a wide range of soil textures, and shown to be more accurate than the other two RHC expressions. Subsequently, the new RHC expression was combined with the WRC formula of Fredlund and Xing, generating an alternative model (hereafter called the FL model) applicable to describe soil hydraulic properties over the full moisture range. The FL model requires both the known WRC and RHC data since three additional fitting parameters are involved in the present RHC expression. Furthermore, the FL model was employed in a HYDRUS‐1D numerical model for simulating the soil moisture redistribution within a lysimeter. The numerical simulation with using the FL model can accurately predict the moisture redistribution, in turn confirming the validity of the FL model despite without partitioning the capillary and film flow components.

Suffusion of sand–clay mixture by three-staged change of ionic strength

The suffusion of particles classified as coarse-grained soils in the Unified Soil Classification System has been relatively well investigated in previous studies, whereas suffusion of clay particles has not been thoroughly explored. For clay particles, the surface interaction energy between clay and sand can be a critical factor in conjunction with hydraulic gradient. Therefore, this paper presented a series of designed soil-column experiments for assessing the reduction of ionic strength on suffusion of clay particles in the sand–clay mixture. The three most typical clay particles (kaolinite, illite, and montmorillonite) were selected and the ionic strength was decreased during the injection. The results indicate that the sequence of decreasing ionic strength induced substantial suffusion of clay particles, mainly attributed to the decreased attraction between sand grains and clay particles. In addition, among three types of clay particles, the high swelling potential of montmorillonite particles led to the most substantial increase in relative hydraulic conductivity caused by suffusion.

Effect of hydraulic conductivity and impeded drainage on the liquefaction potential of gravelly soils

Investigating the role of sand and fines content and in situ drainage conditions in governing the hydraulic conductivity of gravelly deposits is highly important to characterize the liquefaction potential of gravelly soil. In this study, a variation of hydraulic conductivity with sand content has been empirically obtained based on the existing gravel liquefaction case histories. It is found that the hydraulic conductivity of a soil matrix having more than about 20%–30% sand content by mass is low enough to cause liquefaction without the presence of any impervious confining layer. In addition, a numerical study has been performed using the commercial software FEQDrain to study pore pressure generation in gravelly soil at a variety of relative densities and hydraulic conductivities with and without an impermeable cap layer when subjected to a variety of earthquake loadings. For both unconfined and confined condition, excess pore pressure ratios consistently increase with a decrease in hydraulic conductivity ( k) and relative density ( Dr). Excess pore pressure ratio is correlated with hydraulic conductivity, soil compressibility, and cyclic stress ratio (CSR). For the confined condition, pore pressure in the gravel layer is primarily governed by the overlying cap layer and even a sandy cap layer instead of highly impervious clay layer can cause liquefaction.

Comparison of Seven Weibull Distribution Models for Predicting Relative Hydraulic Conductivity

AbstractModeling water flow in unsaturated soils requires accurate characterization of relative hydraulic conductivity (RHC) and water retention curve (WRC). The overall objective of this study is to investigate the performances of seven Weibull distribution models for predicting RHC using the Assouline et al. (1998), https://doi.org/10.1029/97WR03039 WRC. Specifically, a new RHC model was proposed via the approach of Assouline (2001), https://doi.org/10.1029/2000WR900254 with the assumptions of Burdine (1953), https://doi.org/10.2118/225-G and Kosugi (1999), https://doi.org/10.2136/sssaj1999.03615995006300020003x. The proposed model, together with the other six models, was then compared with data from 40 soils to explore their predictive performances for RHC. The results showed that the proposed model provides the best agreement with measured data and yields a 16.1% improvement in RHC prediction compared to the widely used Assouline et al. (1998), https://doi.org/10.1029/97WR03039‐Mualem (1976), https://doi.org/10.1029/WR012i003p00513 model. The proposed model can be used as RHC parameterization for water flow modeling in the unsaturated zone.