Effective Hydraulic Conductivity Research Articles

Bailout test, HYDRUS‐2D, and analytical modeling for estimating permeability of ephemeral stream bed

AbstractAccurate estimation of effective saturated hydraulic conductivity (Ksat) of a vadose zone with an underlying shallow perched aquifer is challenging. Standard pumping tests and double‐ring infiltrometers are unsuitable for this purpose. Therefore, a bailout test (BOT) was conducted in nine soil pits to evaluate the hydraulic properties of the vadose zone and the subjacent shallow‐perched aquifer in a porous bed of a wadi in Oman. The analytical (Kirkham's type) and numerical (HYDRUS‐2D) models were also used. Upon instantaneous emptying, the water level rises in a pit, owing to seepage from the ambient shallow aquifer. The draw up was monitored and compared with modeling, which assumes a homogeneous or layered van Genuchten's soil. The soils of the excavated pits were characterized as sandy‐textured, gleyed, and containing calcareous and clay‐enriched layers. A good match between HYDRUS‐analytical results for layered soils and an idealized homogeneous one illustrates that BOT is a robust and quick technique for the estimating Ksat = 2–3 cm/h in the coarse‐textured wadi bed vadose zone overlaying a transient water table. BOT is better than classical auger hole tests because they test a larger soil volume through induced seepage. BOT is also more suitable for drainage trenches and other excavations, allowing for easier observation, soil sampling from the banks, and rapid dewatering.

Relationship between fault transmissivity, flow dimensions and effective hydraulic conductivity in siliceous mudstone of the Wakkanai Formation around the Horonobe Underground Research Laboratory in Japan

Effective hydraulic conductivity is typically used to evaluate groundwater flow in faulted/fractured media. Estimating effective hydraulic conductivity relies on modelling the transmissivity and hydraulic connectivity of faults/fractures using a large dataset. As an alternative to evaluating hydraulic connectivity, flow dimension is an easily available and quantitative indicator of fault/fracture hydraulic connectivity. However, the flow dimension has not been used as much quantitatively to evaluate the effective hydraulic conductivity. This study demonstrates how flow dimensions in poorly self-sealed faults directly relate to effective hydraulic conductivities. Effective hydraulic conductivities of massive siliceous mudstone of the Wakkanai Formation around the Horonobe Underground Research Laboratory (URL) in Japan were analysed by simulation with long-term (>10 years) data of hydraulic pressure and inflow during the construction and operation of the URL. The estimated effective hydraulic conductivities varied from c . 10 −8 to c . 10 −11 m s −1 with an increase in depth from c . 250 to c . 600 m. The fault local transmissivities and flow dimensions from packer tests varied from c . 10 −6 to c . 10 −10 m 2 s −1 and from c . 2.0 or more to c . 1.0 with increasing depth, respectively. When applying the Landau–Lifshitz–Matheron formula to calculate the fault effective transmissivities, these variations correlate well and the estimated effective hydraulic conductivities are sound.

Insights to the water balance of a Boreal watershed using a SWAT model

The hydrological characteristics of a watershed play a crucial role in shaping ecosystems within the Boreal zone and have a significant impact on regional environments. Knowing these characteristics, such as the distinctive topography, vegetation, soil composition, and climatic conditions in the Canadian Boreal ecozone, is essential for implementing sustainable water management. This study focuses on assessing the hydrological dynamics of the Upper Humber River Watershed (UHRW) in western Newfoundland, Canada, using the Soil and Water Assessment Tool (SWAT) model. The UHRW includes sub-basins and hydrological response units (HRUs), with diverse land uses, soil types, and slope characteristics. Key parameters influencing streamflow simulation were identified through sensitivity analysis, including the runoff curve number, the effective hydraulic conductivity, the temperature lapse rate, the soil evaporation compensation factor, and the available water capacity of the soil layer. The SWAT model, using data from the Reidville hydrometric station, shows favorable performance metrics, with R2 values of 0.79 and 0.83 during the calibration and evaluation periods, respectively. The model effectively captures seasonal and monthly flow patterns, displaying right-skewed distributions and seasonal variations. The analyzed hydrological parameters, such as precipitation, evaporation, transpiration, surface runoff, and groundwater flow, reveal their significant contributions to the water balance. The flow duration curve analysis indicates the model’s capability to estimate peak and low flows, with slight under-prediction during the recession phase. Seasonal analysis further supports the model’s performance, with positive Nash-Sutcliffe Efficiency (NSE) values ranging from 0.65 to 0.91. The study concludes that the SWAT model is suitable for simulating the hydrological processes in the studied watershed providing valuable insights for sustainable water resource management and decision-making in the UHRW. The results can be useful for other Boreal ecozone watersheds.

Application of SWAT Model for Hydrological Simulation of Rapti River Basin

This study aimed at application of SWAT model for hydrological simulations of Rapti River Basin (RRB) water systems. The Rapti River originates from Nepal and then it comes in India. SWAT (Soil and Water Assessment Tool) model was used for hydrological simulation of the RRB surface and sub surface water systems. SWAT is a comprehensive, semi-distributed river basin model that requires a large number of input parameters, which complicates model parameterization and calibration. The RRB was discretised into 4 sub-basins and 630 hydrological response units (HRUs) and calibration and validation was carried out at Bagasoti using monthly flow data of 11 years, respectively. We first calibrated the model in SWAT-CUP which is a decision-making framework that incorporates a semi-automated approach (SUFI2) using manual calibration and incorporating sensitivity and uncertainty analysis. Parameter sensitivity analysis helps focus the calibration and uncertainty analysis and is used to provide statistics for goodness-of-fit. In this study Calibration has been done between simulated and observed discharge data (1974-1985) for 50 simulations with 6 parameters that is Curve number (CN2 = 0.945), Groundwater delay (GW_DELAY = 50), Baseflow alpha factor (ALPHA_BF = 0.58), Manning's "n" value for the main channel (CH_N2 = 0.15), Effective hydraulic conductivity in main channel alluvium (CH_K2 = 10.20) and Available water capacity of the soil layer (SOL_AWC = 0.28). The results were analysed and compared with the observational data. The model performance evaluation showed acceptable ranges of values (i.e., Nash Sutcliff was 0.75 and R2 was 0.71). After model calibration, in order to predict water balance, the model was validated by using the best parameter.

Investigation of petrophysical and hydrogeological parameters of the transboundary Nubian Aquifer system using geophysical methods

The recent research aims to investigate the petrophysical and hydrogeological parameters of the Nubian aquifer system (NAS) in Northern Khartoum State, Sudan, using integrated geophysical methods, including surface electrical resistivity and geophysical well-logging. The Nubian aquifer is a transboundary regional aquifer that covers vast areas in Sudan, Egypt, Libya and Chad. The well-logs, including self-potential (SP), natural gamma ray (GR), and long normal resistivity (RS), are integrated with Vertical Electrical Sounding (VES) measurements to delineate the hydrostratigraphical units. As a result, two aquifers are detected. An upper aquifer comprises coarse sand with an average thickness of 50 m and a lower aquifer of sandstone with more than 200 m thickness. For a thorough evaluation of the aquifers, in the first stage, the petrophysical and hydrogeological parameters, including formation factor, total and effective porosity, shale volume, hydraulic conductivity, and transmissivity, are measured solely from geophysical well-logs. In the second step, the results of geophysical well logs are combined with VES and pumping test data to detect the spatial variation of the measured parameters over the study area. As a result, the hydraulic conductivity of the Nubian aquifers ranged from 1.9 to 7.8 m/day, while the transmissivity varied between 120 and 733 m2/day. These results indicated that the potentiality of the Nubian formation is high; however, in some regions, due to the sediment heterogeneity, the aquifers have intermediate to high potential. According to the obtained results, it can be concluded that the Nubian Aquifer in Khartoum state is ideal for groundwater development. This research discovered that geophysical approaches can be used to characterize moderately heterogeneous groundwater systems by comparing the Nubian aquifer with similar aquifer systems that have similar hydrogeological settings. This study emphasized the application of universal principles in extrapolating hydraulic parameters in hydrogeophysical surveys. This approach aims to reduce the costs and efforts associated with traditional hydrogeological approaches.

Estimating Effective Hydraulic Conductivity (Ke) for the Rangeland Hydrology and Erosion Model (RHEM)

Highlights Effective hydraulic conductivity (Ke ) predictive equations in all RHEM versions have satisfactory performance. New Ke predictive equations were developed for RHEM applications over broader rangeland conditions. Ke values on most rangelands can be estimated through readily measurable ground cover and soil texture data. Abstract. Effective hydraulic conductivity (Ke) is an important parameter for the prediction of infiltration and runoff by the Rangeland Hydrology and Erosion Model (RHEM). Three sets of equations to predict Ke have previously been used in RHEM. These equations are mainly based on rainfall simulation data representing undisturbed sites and have not undergone comprehensive evaluation for various rangeland conditions, particularly after disturbances. The goal of this research was to evaluate these equations using independent data obtained from rainfall simulations conducted at multiple rangeland sites. Additionally, we developed and evaluated a new set of Ke predictive equations applying readily measurable cover and soils data spanning a wide range of vegetation, soil textures, and disturbance conditions. The results show that all previous Ke equations in RHEM have a “satisfactory” performance with index of agreement (d) > 0.75 and R2 > 0.4. The new Ke approach resulted in “very good” performance with d > 0.9 and R2 > 0.5. The new set of equations enhances RHEM for applications over broader rangeland conditions, including sparse vegetation cover following disturbances or community transitions. Keywords: Disturbed Rangelands, Hillslope Runoff, Infiltration.

Compressive Stress Dewaterability Limit in Fluid Fine Tailings

Reclamation of fluid fine tailing (FFT) storage facilities to their pre-disturbance equivalent landforms is hampered because micrometer size fines, whose surface-area-to-volume ratio is remarkably high, are occupied with siloxane and hydroxy groups, which bind water strongly. The purpose of this study is to differentiate the forms of water physically distributions in FFT and determine their propensities for dewaterability under compressive stresses. Two thermal and two mechanical methods were used to analyze water distributions in FFT. Dynamic and isothermal thermogravimetric analyses of FFT gave a transition from predominately bulk water to coevolution with water of higher enthalpy of vaporization at 81% (w/w) solids. Differential scanning calorimeter studies were used to determine the non-freezable water amount, with the premise that water that does not freeze by −30 °C is also unlikely to be removable by compressive stresses encountered in tailing treatment processes. The solid weight percent of FFTs with the non-freezable water was 79.6%. A 1D finite-strain model simulation using the constitutive relations of void ratio and effective stress, void ratio, and hydraulic conductivity show that deep-pits filled with such clayey-silt FFT will consolidate to a maximum solids content of 74% (w/w). For separation by centrifugation, the solids content plateaued to a mean of 74% (w/w) for total centrifugal force of ≥30 mega Newtons. These solid contents represent upper thresholds and demonstrate dewatering limit property of an FFT under compressive stresses.

SWAT model calibration for hydrological modeling using concurrent methods, a case of the Nile Nyabarongo River basin in Rwanda

The Nile Nyabarongo, which is Rwanda's largest river, is facing stress from both human activities and climate change. These factors have a substantial contribution to the water processes, making it difficult to effectively manage water resources. To address this issue, it is important to find out the most accurate techniques for simulating hydrological processes. This study aimed to calibrate the SWAT model employing various algorithms such as GLUE, ParaSol, and SUFI-2 for the simulation of hydrology in the basin of the Nile Nyabarongo River. Different data sources, such as DEM, Landsat images, soil data, and daily meteorological data, were utilized to input information into the SWAT modeling process. To divide the basin area effectively, 25 sub-basins were created, with due consideration of soil characteristics and the diverse land cover. The outcomes point out that SUFI-2 outperformed the other algorithms for SWAT calibration, requiring fewer computing model runs and producing the best results. ParaSol established residing the least effective algorithm. After calibration with SUFI-2, the most sensitive parameters for modeling were revealed to be (1) the Effective Channel Hydraulic Conductivity (CH K2) measuring how well water can flow through a channel, with higher values indicating better conductivity, (2) Manning's n value (CH N2) representing the roughness or resistance to flow within the channel, with smaller values suggesting a smoother channel, (3) Surface Runoff Lag Time (SURLAG) quantifying the delay between rainfall and the occurrence of surface runoff, with shorter values indicating faster runoff response, (4) the Universal Soil-Loss Equation (USLE P) estimating the amount of soil loss. The average evapotranspiration within the basin was calculated to be 559.5 mma-1. These calibration results are important for decision-making and updating policies related to water balance management in the basin.

Effect of Bentonite Admixture Content on Effective Porosity and Hydraulic Conductivity of Clay-based Barrier Backfill Materials

Clay-based barrier wall has been diffusely employed as vertical barriers. Nevertheless, there were few project practices of these walls in China. And few research have been performed to study the impact on the permeability of the addition of domestic bentonites. To solve this problem, the influences of bentonite level on hydraulic conductivity, porosity and clay-bound water of soil-bentonite admixtures have been assessed employing a flexible-wall test and water centrifugal dewatering experiment with various bentonites. The outcomes revealed that as barrier walls are constructed by blending bentonite and Fujian standard sandy soil, there is a critical bentonite level of the smallest porosity. If the bentonite level is less than the critical bentonite content, hydraulic conductivity is reduced quickly, while if the bentonite level is greater than the critical bentonite content, hydraulic conductivity is reduced gently. Additionally, as the bentonite level grew, the clay-bound water centage of the admixtures continually improved. Supposing that the clay-bound water enclosed the clay grains, a near computation approach of the effective porosity is put forward and showed that the effective porosity decreased with bentonite content. Additionally, an exponential relationship was found between the effective porosity and the permeability.

Calibration and validation of hillslope runoff and soil loss outputs from the Water Erosion Prediction Project model in Minnesota agricultural watersheds

AbstractThere is growing interest in studying the impact of alternative agricultural management practices on runoff and soil loss under future climate change scenarios. In order to address this interest, it is important to demonstrate that runoff and soil loss can be accurately simulated under existing climates based on comparisons between modeled and experimental results. This study calibrates and validates the Water Erosion Prediction Project (WEPP) model to quantify the accuracy of predicting growing season runoff and soil erosion in agricultural hillslopes based on comparisons with experimental data from five Minnesota hydrologic unit code 12 watersheds. In order to accurately predict runoff and soil erosion in each watershed, the baseline effective hydraulic conductivity (Kbe), interrill and rill erodibility (EIR and ER), and monthly precipitation standard deviations (Pstdev) were calibrated in WEPP using observed runoff and total suspended solids data from five Minnesota Discovery Farms field sites. Before calibration, Nash–Sutcliffe model efficiency (NSE) and percent bias (PBIAS) values for predicted versus measured monthly average total runoff (Ravg‐T), runoff ratios (RRT), and total soil loss were generally not in acceptable ranges. After calibration, the NSE values showed very good fits between measured and predicted monthly Ravg‐T (0.64–0.98), RRT (0.66–0.93), and soil loss (0.58–0.80). PBIAS values were also within acceptable ranges for Ravg‐T and RRT (±25%) and soil loss (±55%), except for RRT at site BE1. NSE and PBIAS values during validation were within acceptable ranges, except for RRT at site BE1. These findings suggest that the WEPP hillslopes calibrated in this study are sufficiently robust to accurately predict monthly runoff and soil erosion in Minnesota agricultural fields during the growing season.

Effective governing equations for dual porosity Darcy–Brinkman systems subjected to inhomogeneous body forces and their application to the lymph node

We derive the homogenized governing equations for a double porosity system where the fluid flow within the individual compartments is governed by the coupling between the Darcy and the Darcy–Brinkman equations at the microscale , and are subjected to inhomogeneous body forces. The homogenized macroscale results are obtained by means of the asymptotic homogenization technique and read as a double Darcy differential model with mass exchange between phases. The role of the microstructure is encoded in the effective hydraulic conductivities which are obtained by solving periodic cell problems whose properties are illustrated and compared. We conclude by solving the new model by means of a semi-analytical approach under the assumption of azimuthal axisymmetry to model the movement of fluid within a lymph node.

Hydrologic and water quality modelling of bioretention columns in cold regions

AbstractBioretention is widely used in urban sustainable stormwater management; however, limited numerical research has been conducted on its performance in cold regions, particularly for winter snowmelt, spring runoff and summer large storms (>50 mm) for urban flood mitigation. In this study, HYDRUS 1D was used to explore these knowledge gaps. The model was comprehensively calibrated and validated against 2‐year hydrologic and water quality data of four bioretention columns with different designs under lab‐simulated cold region conditions. The Morris method was used to measure the sensitivity and interaction of the calibrated hydraulic parameters. The model revealed that the effective hydraulic conductivity (KS) values of the soil media were similar for winter snowmelt and spring runoff when the soil temperature was around −0.5°C. Preferential flow is likely to occur in soil media during winter or spring in cold regions. The summer modelling showed that bioretention could substantially reduce peak flow, ponding depth and duration for large storm events (even for a 1:100 local storm with 83.4 mm in 4 h). The water quality modelling confirmed experimental results that the bioretention effectively removed phosphate and ammonium but had leaching issues for chloride and nitrate. Finally, optimization and recommendations for bioretention columns were provided.

The Impact of Land-Use and Climate Change on Water and Sediment Yields in Batanghari Watershed, Sumatra, Indonesia

The Batanghari River flows from the province of West Sumatra into the West Coast of Jambi, with the main river extending up to 870 km. Also, the Batanghari watershed Land use changes have shown a decreasing forest cover and an increasing agricultural area. Therefore, this study aims to calculate the impact of land use and climate change on water and sediment yield using Soil and Water Assessment Tools (SWAT) hydrological modeling. Land-use change analysis was performed with projections in 2040 while, near future and future climate projections under Representative Concentration Pathway (R.C.P.) 4.5 and 8.5 were used for global climate change scenarios. The results show a changing pattern of growing agricultural area and decreasing forest area in 1990, 1997, 2005, 2015, and 2040. SWAT hydrological model used for the simulation was calibrated automatically with SWAT-CUP and the results were validated on good criteria. The sensitivity analysis results showed that effective hydraulic conductivity in main channel alluvium (CH_K2) and Base flow alfa factor (Alfa_BF) formed the most sensitive parameters for discharge. Furthermore, the model simulation showed an increase in surface runoff and a decrease in lateral flow and base flow due to land-use changes, which increased sediment loading over time. The impact of climate change on water and sediment yield increased the average flow discharge ratio, resulting in more frequent droughts and floods events.

Rock fragments influence the water retention and hydraulic conductivity of soils

AbstractRock fragments (RFs) influence soil hydraulic properties (SHPs), and knowledge about the SHPs of stony soils is important in vadose zone hydrology. However, experimental evidence on effective SHPs of stony soils is still scarce and mostly restricted to water‐saturated conditions and low volumetric contents of RFs. We examined the influence of RFs on SHPs through a series of measurements. Stony soils were prepared by packing 250‐cm3 cylinders with soils of two textures (sandy loam and silt loam) and with different volumes of RFs (up to 50% v/v) with a diameter of 8–16 mm. Samples were prepared in a way that the background soils (diameter smaller than 2 mm) had identical bulk density. The simplified evaporation method was used to determine the effective SHPs of stony soils. We used the obtained SHP data to evaluate the performance of models, which predict the effective SHPs of stony soils from SHPs of the background soil. The results highlight the systematic dependency of SHPs on volumetric content of RFs. The difference between modeled and measured SHPs was substantial for cases in which the soil contained a high amount of RFs. Accounting for the moisture content of RFs improved the prediction of the effective water retention curve of stony soils compared with a simple scaling that used only the content of RFs. Among the evaluated models for the effective hydraulic conductivity, the model based on the general effective medium theory showed the best performance, particularly for low RF contents.

Performances of the Soil–Bentonite Cutoff Wall Composited with Geosynthetic Clay Liners: Large-Scale Model Tests and Numerical Simulations

The geosynthetic clay liner (GCL) overlap plays a key role in maintaining hydraulic performance of the barrier systems, e.g., the bottom liner and cover systems. However, its influences on the behavior of the vertical barrier have been rarely investigated. This paper aims to address this issue using the large-scale model test and 3-dimensional finite element (FE) modeling. In the model test, the GCL overlap at the width of 500 mm was tested under a constant hydraulic head of 1 m and confining stress ranging from 10 to 150 kPa using a newly developed large-scale apparatus. Compared with the flexible wall permeameter, this apparatus could guarantee full field-scale GCL overlap to be tested. Results showed that the effective hydraulic conductivity of the GCL overlap decreased from 10−8 to 10−9 cm/s as the confining stress increased from 10 to 150 kPa. The addition of supplemental bentonite paste in between the overlap with a water-to-bentonite ratio of 19:1 contributed to reducing the effective hydraulic conductivity by 60% compared with that for a GCL overlap without bentonite paste. The breakthrough time for the soil-bentonite (SB) cutoff wall composited with GCLs was 64% longer in comparison with that for the single SB wall. Additionally, the breakthrough after 50 years is made for the entire depth of the single SB wall while at the depth no more than 0.9 m for the composite wall with bentonite paste at the GCL overlap. With consideration that the depth of the groundwater table is generally greater than 1 m, the GCL–SB composite cutoff wall will exhibit a good performance in containing groundwater contaminants in the field, especially when applying bentonite paste at the GCL overlap.

Homogenization of spatially variable hydraulic conductivity in the presence of a geotechnical structure

This paper proposes a novel homogenization method for spatially variable hydraulic conductivity (k). The main novelty is that it can characterize the effective hydraulic conductivity “felt” by a geotechnical structure for steady state flow problems, whereas the prevailing homogenization method does not address the existence of a geotechnical structure or complex boundary conditions. An engineer can apply this relatively simple method to determine a characteristic value that is consistent with both physics and spatial variability. The proposed method is based on a weighted geometric average (GA) with weight proportional to the degree of mobilization, which can be approximately determined at a modest cost using a single deterministic finite element analysis. Monte Carlo simulation of a flow problem in a spatially variable medium requires costly repeated runs of a random finite element analysis. Based on the results from numerical examples, it is shown that the proposed method is superior to the prevailing homogenization method based on uniform GA when a geotechnical structure or complex flow boundaries are present. The proposed method reduces to the prevailing method for an example where there is no geotechnical structure. The applicability of the proposed method is verified by a real pumping test case study.

Calibration, validation, and evaluation of the Water Erosion Prediction Project (WEPP) model for hillslopes with natural runoff plot data

The Water Erosion Prediction Project (WEPP) model has been widely used for estimating runoff and soil loss. The evaluation of the latest version (version 2021.133) under a range of environmental conditions can provide confidence to its users. The objectives of this study were to evaluate the WEPP model for runoff and soil loss predictions using 1159 plot years of rainfall-runoff events data from field experimental plots with various climates, soils, topographies, and crops. WEPP runoff and soil loss predictions were compared to the observations before and after input parameter calibration. The results showed good predictions of runoff and soil loss were obtained with both the uncalibrated and calibrated WEPP model for all considered scales with Nash-Sutcliffe model efficiencies (NSE) over 0.4. The calibration of input baseline effective hydraulic conductivity (ke), baseline critical shear stress (τc), baseline rill erodibility (kr), and baseline interrill erodibility (ki) improved WEPP model performance with NSE values of 0.98 and 0.91 for average annual runoff and soil loss predictions, respectively. The WEPP model tended to underestimate the runoff and soil loss for large events with runoff over 100 mm and soil loss over 120 t/ha. Good event runoff and soil loss predictions (NSE ≥0.4) were obtained for the most common cropping/management systems considered, including corn, cotton, tilled fallow, and wheat after calibration. This study illustrates the most recent WEPP model's performance for runoff and soil loss predictions, and provides a comprehensive set of results.

Two-dimensional model of flow and transport in porous media: Linking heterogeneous anisotropy with stratal patterns in meandering tidal channel deposits of the Venice Lagoon (Italy)

Understanding the internal structure of permeable and impermeable sediments (e.g. point-bars and tidal-flat deposits) generated by the evolution of meandering tidal channels is essential for accurate modeling of groundwater flow and contaminant transport in coastal areas. The detailed reconstruction of stratal geometry and hydraulic properties from measurements must be accompanied by depositional history information. In this work, we use high resolution reconstructions of ancient tidal channels of the Venice Lagoon (Italy) to drive 2D simulations of groundwater flow and transport, showing the importance of incorporating information on the sediment accumulation processes into the hydraulic characteristics and how horizontal anisotropy emerging from these processes significantly influences transport. Effective hydraulic conductivity is modeled with a heterogeneous 2D anisotropic tensor with principal directions aligned with observed sedimentation sequences. Comparison of flow and solute dynamics simulated using reconstructed and theoretical hydraulic properties show drastically different pathways of solute propagation.

Evaluating Spatial-Temporal Clogging Evolution in a Meso-Scale Lysimeter

When surface water infiltrates soil, the fine soil particles carried in water gradually clog soil pores and form a low-permeability soil layer. Clogging impacts the variations in pore water pressure heads in soil and effective hydraulic conductivity. However, few studies have connected field measurements of pore water pressure heads to clogging in soil. This study proposed a diagram to demonstrate the relationship between the normalized pore water pressure head (λ) and effective hydraulic conductivity (Keff) based on a conceptual 1-D vertical infiltration model. The coevolution of λ and Keff indicated the occurrence of clogging and its location relative to the pore-pressure measurement point. We validated the λ-Keff diagram based on a series of numerical simulations of infiltration experiments in a lysimeter. The simulation results showed that the proposed diagram not only indicated the occurrence of clogging but also the development of the unsaturated zone beneath the upper clogging layer. Furthermore, we used a diagram to analyze the spatiotemporal changes in permeability in a lysimeter during three cycles of physical infiltration experiments. The experimental data presented with λ-Keff diagram indicated cracking on the soil surface, and clogging gradually developed at the bottom of the lysimeter.

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.