Pore Water Distribution Research Articles

Quantifying pore-level non-uniformity of pore-water distribution in unsaturated soils

Quantifying the magnitude and distribution of degree of saturation (Sr) in unsaturated soils is crucial to understand the grain-scale hydromechanical behavior, but it has been a major experimental challenge. This study proposes a new method to quantify the pore-water distribution non-uniformity, in terms of Sr, based on three-dimensional (3D) X-ray computed tomography images. The algorithm constructs vectors that consider the 3D spatial distribution of Sr for each REV. A weighted water distribution tensor (G, characterizing the spatial distribution of Sr) was derived to calculate a scalar parameter A that represents the non-uniformity. Application of the algorithm on sand samples demonstrated that the Sr distributions could be highly non-uniform at different drying states. The algorithm captured pore-water transport between the dilated and non-dilated zones of samples subjected to pre-peak shearing. The evolution of A with matric suction and axial strain showed potential in incorporating the pore-water distribution into microstructure-based constitutive models.

Migration Rules and Mechanisms of Nano-Biochar in Soil Columns under Various Transport Conditions.

Compared to traditional biochar (BC), nano-biochar (NBC) boasts superior physicochemical properties, promising extensive applications in agriculture, ecological environments, and beyond. Due to its strong adsorption and migration properties, NBC may carry nutrients or pollutants to deeper soil layers or even groundwater, causing serious environmental risks. Nevertheless, the migration rules and mechanisms of NBC in soil are still unclear. Therefore, this study employed soil column migration experiments to systematically explore the migration rules and mechanisms of NBC under various flow rates, initial soil water contents, soil depths, and soil textures. The results showed that regulated by smaller particle size differences and greater surface charges, NBC exhibited a stronger migration ability compared with traditional BC. As the soil texture transitioned from fine to coarse, the migration capability of NBC significantly improved, driven by both pore structure and interaction forces as described by the DLVO theory. The migration ability of NBC was also greatly boosted as the soil transitioned from saturated to unsaturated conditions, primarily because of preferential flow. When the flow rate increased from 70% KS to 100% KS and 130% KS, the migration ability of NBC also increased accordingly, as changes in injection flow rates altered the velocity distribution of pore water. NBC in 25 cm soil columns was more prone to shallow retention compared with 10 cm soil columns, resulting in weaker overall migration ability. In addition, through fitting of the two-site kinetic model and related parameters, the penetration curves of NBC under various variable conditions were effectively characterized. These findings could offer valuable insights for NBC's future efficient, rational, and sustainable utilization, facilitating the evaluation and mitigation of its potential environmental risks.

A fully coupled micro-hydromechanical (micro-HM) model for partially saturated soils based on DEM

A fully coupled micro-hydromechanical (micro-HM) model is developed for partially saturated soils in this study by integrating two-dimensional pore morphology (PM) approach and discrete element method (DEM). In the proposed model, the PM approach is employed to predict the tentative water distribution. The porous media marching cubes (PMMC) algorithm is adopted to evaluate the interphase interfaces and to further calculate the capillary forces. The combined effects of interparticle contact forces and the capillary forces on the motion of particles are handled by DEM. The developed model was then employed to conduct a series of numerical biaxial shear tests on a partially saturated soil with real particle shapes. The typical macroscopic responses such as stress–strain relationship, volume change, and saturation change can be well simulated by the micro-HM model. Based on the micro-HM model, a novel equation is proposed to directly evaluate the effective stress from the pore water distribution. The effective stress parameter and the suction contribution to effective stress calculated by the new equation well matches the experimental data, thus confirming the validity of the micro-HM model and the new equation of effective stress. The microscopic responses are then revealed and discussed through the proposed model.

Hydrogeological characterization of low permeability medium for conceptualization of a mine site in Eastern Turkey

The mining site in Eastern Anatolia of Turkey were encounter a significant risk of slope instability within the operational area. One of the processes that govern slope stability is the pore water pressure distribution. The conceptualization and characterization of porous media serve as fundamental prerequisites for the implementation of numerical methods aimed at predicting pore water distribution. This study aims to characterize the hydrogeological properties of water bearing rocks in the active mining site in Eastern Anatolia of Turkey. A total of 21 wells and drill holes were drilled in the study area to conduct in-situ tests, monitoring, and sampling. The large diameter wells drilled in surrounding the carbonate rocks were to determine the groundwater flow and boundary conditions and also wells tapped metasediments and diorite unit for hydraulic testing. The lugeon tests and installation of vibrating wire piezometers were carried out at small diameter drill holes to obtain localized hydraulic conductivity of metasediments and diorite at different depths and monitoring pore water pressure distribution along some critical cross-sections. The results obtained from these tests are used for developing hydrogeological conceptual model for groundwater flow. The results of in-situ tests show that the metasediment and diorite units act as a single hydrostratigraphic unit. The metasediments and diorite have high total porosity and low specific yield indicating that the pore water is retained by electrostatic forces in the medium and it resists flow due to low hydraulic conductivity. The vertical variation in hydraulic conductivity values indicates that the medium is highly heterogeneous.

NMR-based pore water distribution characteristics of silty clay during the soil compaction, saturation, and drying processes

The pore water distribution (PWD) of soil provides key information about soil shear strength, hydraulic conductivity, and water-retention ability. The PWD characteristics of the soil depend on the specimen preparation conditions (i.e., the variations in initial water content or compaction degree) and drying-wetting processes, which were investigated by using the nuclear magnetic resonance (NMR) technique. The NMR T2 spectrum is mathematically transformed into the PWD curve to more accurately quantify the variations in pore water content stored with pores of different radii. The pore water in silty clay can be categorized into strongly bound water, intra-aggregate pore water, and inter-aggregate pore water, which are identified by the pore radius of <0.05 μm, 0.05-1.0 μm and >1.0 μm, respectively. The effects of compaction degree and initial water content on the PWD of the soil exhibit distinctions. For unsaturated compacted specimens, the PWDs remain unaffected by changes in compaction degree, while an increase in initial water content promotes the formation of clay aggregates, thereby increasing the maximum water-holding pore radius and the intra-aggregate pore water content. For saturated compacted specimens, the inter-aggregate and intra-aggregate pore water content increases with a decrease in the compaction degree, while the changes in the PWD shape from unimodal to bimodal with an increase in the initial water content. During the soil drying process, inter-aggregate pore water is rapidly drained, the intra-aggregate dominant pore water content increases first and then decreases, and the strongly bound water content remains constant. The relationship between the cumulative pore water distribution curve and the soil-water characteristic curve (SWCC) can be established through the Young-Laplace theory. The SWCC can be well predicted by using the envelope of the cumulative pore water distribution curves during soil drying.

Influence of bank slope on sinuosity-driven hyporheic exchange flow and residence time distribution during a dynamic flood event

Abstract. This study uses a reduced-order two-dimensional (2-D) horizontal model to investigate the influence of the riverbank slope on the sinuosity-driven hyporheic exchange process along sloping alluvial riverbanks during a transient flood event. The deformed geometry method (DGM) is applied to quantify the displacement of the sediment–water interface (SWI) along the sloping riverbank during river stage fluctuation. This new modeling approach serves as the initial step focusing on the impact of the bank slope on the hyporheic exchange flux (HEF) and the residence time distribution (RTD) of pore water in the fluvial aquifer for a sinuosity-driven river corridor. Several controlling factors, including sinuosity, alluvial valley slope, river flow advective forcing and duration of flow, are incorporated into the model to investigate the effects of bank slope on aquifers of variable hydraulic transmissivity. Compared to simulations of a vertical riverbank, sloping riverbanks were found to increase the HEF. For sloping riverbanks, the hyporheic zone (HZ) encompasses a larger area and penetrated deeper into the alluvial aquifer, especially in aquifers with smaller transmissivity (i.e., due to increased hydraulic conductivity or reduced specific yield). Furthermore, consideration of sloping banks as compared to a vertical riverbank can lead to both underestimation and overestimation of the pore water travel time. The impact of bank slope on residence time was more pronounced during a flood event for high-transmissivity aquifer conditions, while it had a long-lasting influence after the flood event in lower-transmissivity aquifers. Consequently, the impact of bank slope decreases the travel time of water discharging into the river relative to base flow conditions. These findings highlight the need for (re)consideration of the importance of complex riverbank morphology conceptualization in numerical models when accounting for the HEF and RTD. The results have potential implications for river management and restoration and the management of river and groundwater pollution.

Study on Effect of Particle Size Distribution on Water-Retention Capacity of Coral Sand from Macro and Micro Perspective

The reclamation coral sand (CS) layer is the survival environment for island reef vegetation in the South China Sea. The root system within the CS bed draws water necessary for vegetation growth, implying that the water-retention capacity of CS plays a pivotal role in determining vegetation viability. Particle size distribution (PSD) significantly influences the water-retention capacity of geomaterials. This study examines the impact of PSD on the water-retention capacity of CS from both macro (soil–water characteristic curve, SWCC) and micro (pore water distribution) perspectives using the pressure plate test and nuclear magnetic resonance technique, and an F&amp;X model was used to analyze the SWCC of CS. The findings indicated that the F&amp;X model aptly describes the SWCC of CS with different PSDs. Both the air entry value and residual water content rise with an increased content of fine grains (d &lt; 0.25 mm), suggesting that the presence of fine grains augments the water-retention capacity of CS. It is considered that a size range of d = 0.075–0.25 mm predominantly impacts the water-retention capacity of CS. The PSD primarily influences the water-retention capacity by affecting the pore size distribution of CS. The volume of small pores swells with the surge of fine-grain content, while the maximum pore size contracts with increasing fine-grain content. Limited pore connectivity in CS means macropores can retain water even under high suction, bolstering the water-retention capacity of CS. These findings offer theoretical guidance for selecting gradation parameters for the planting layer on island reefs.

Microscopic moisture localisation in unsaturated materials using nuclear magnetic resonance relaxometry

Due to the detrimental effects of moisture in the built environment, there is a continuous interest in non-destructive experimental techniques that quantify and/or localise moisture in materials. Most existing experimental techniques, however, typically focus on macroscopic moisture contents in samples rather than the microscopic distribution of water in the individual pores of building materials. For the latter, a popular method such as X-ray computed tomography is not readily applicable, due to the gap between its spatial resolution limit and the typical pore sizes of building materials. Nuclear magnetic resonance (NMR) relaxometry is capable of measuring water in pores of both the nanometer and micrometer scale and is therefore an interesting possibility. While most NMR research focusses on water-saturated materials or overall moisture contents, this study determines the size distributions of the water islands in unsaturated materials with NMR, and compares results to X-ray computed tomography (XCT) images and pore network model (PNM) simulations. Results on unsaturated materials show that NMR focusses on the biggest water islands (i.e. in capillary filled pores) and disregards the hydrogen nuclei in smaller water islands (i.e. stored in pore corners). NMR relaxometry is therefore only adept at providing very rough estimates of the size of water-filled pores, especially since post-processing of the NMR experiments to obtain these water island size distributions involves a lot of uncertainty.

Fast-nondestructive measurement of axial slice water content and water distribution with NMR SFG-MSCPMG sequence

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 (ρ2) of clays are obtained. With ρ2 = 41.90 μm/s the T2 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 T2 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.

Determination of nuclear magnetic resonance T2 cutoff in remoulded loess by the freezing point

AbstractProton nuclear magnetic resonance (NMR) is widely applied to characterize the microscopic properties of hydrogen‐containing porous media. The transverse relaxation time cutoff (T2c) value is the crucial parameter for the quantitative analysis of NMR data. Currently, there is no universal method for the determination of the T2c in clayey soils. This study aimed to develop a laboratory method for determining the T2c of remoulded loess by the freezing point of loosely bound water. Malan loess, a kind of typical clayey silt, was used as test material. Based on the soil freezing characteristic, NMR measurements were performed on remoulded loess with different macro‐parameter controls during the cooling process to obtain the T2 spectrum at each target temperature. By analysing the variation of unfrozen water content with temperature reduction, the freezing point of loosely bound water and the T2c value within the freezing‐point range was determined. The freezing point of loosely bound water in remoulded loess is about −3 to −5°C and that of firmly bound water is less than −5°C. Accordingly, the T2c value of remoulded loess is determined to be 1.5–1.8 ms. The assessment of heating and cooling process and different methods for determining the T2c shows that the laboratory method by the freezing point is effective and reliable, and the T2c determined by statistical methods is worthy of further study and improvement. The saturated permeability of remoulded loess is evaluated according to the determined T2c, and two NMR‐based permeability equations can well reflect pore water distribution in remoulded loess, but to a certain extent, both equations ignore soil microstructure, pore connectivity and chemical effects of pore solution. The laboratory method by the freezing point and the determined T2c value of remoulded loess fill the gap of NMR measurement in loess analysis and are of great significance for low‐plastic clays and clay types.

Effects of Pore Water on the Heterogeneity in Nanopore Structures of Deep Marine Shales: A Multifractal Study on As-Received Shale Samples from the Southern Sichuan Basin, China

Shale strata generally contain a certain amount of pore water that accompanies the whole diagenetic and thermal evolution processes of shales. The distribution and occurrence characteristics of pore water significantly influence the nanopore structures of shales, which subsequently affects the accumulation and production of shale oil and gas resources. Based on a set of fresh Wufeng–Longmaxi (WL) shale samples from the deep marine strata in the southern Sichuan Basin, this study investigated the effects of pore water on the pore heterogeneity of shales by a multifractal method. The results show that (1) the deep WL shales have low pore water content (CPW) and water saturation (SEW), with average values of 7.47 mg/g and 35.21%, respectively, and the CPW and SEW of the shales are mainly controlled by clay mineral content. (2) Under dried conditions, the pore heterogeneity of high-probability measure areas has negative relationships with the clay mineral content and pore volumes with pore widths of 4–10 nm, and the pore connectivity is mainly controlled by clay mineral content. Under as-received conditions, however, the pore heterogeneity of low-probability measure areas and pore connectivity have positive relationships with clay mineral content and pore volumes with pore widths less than 4 nm. (3) Under as-received conditions, the pore water mainly occupies the nanopore with pore widths less than 4 nm and reduces the effective pore spaces and connectivity, which reduces the pore heterogeneity of high-probability measure areas and enhances the pore heterogeneity of low-probability measure areas.

A new domain model for estimating water distribution in soil pores during the drying and wetting processes

It is well known that both the soil-water characteristic curve (SWCC) and hydraulic conductivity function (HCF) of unsaturated soils are hysteretic. Modeling the hysteresis behavior of unsaturated soil is crucial for understanding the hydraulic properties of unsaturated soil and solving geotechnical problems in practice. There have been two types of models, the empirical model and the domain model, proposed to describe SWCC hysteresis. The results from the empirical model are subject to the model parameters, and the domain model has a physical theoretical background. However, the application of the domain model requires calibration using experimental data. In this technical note, a new domain model is proposed for estimating the water distribution in soil during both the drying and wetting processes. Consequently, the main wetting curve and the drying scanning curve can be estimated using the proposed domain model in this study. The estimated results from the proposed model agree well with the experimental data (a total of 16 sets) from different studies. The method proposed in this technical note provides a reliable approach for estimating water distribution in pores with different sizes for various types of soil.

Effect of aggregate size on water distribution and pore fractal characteristics during hydration of cement mortar based on low-field NMR technology

The influence of aggregate size (AS) on the hydration of cement mortar is very important for improving the quality and stability of cement mortar. This study aims to study the effect of AS on water distribution and pore structure characteristics on the early-age hydration of cement mortar by low-field NMR technology. The hydration degree and fractal dimension of the hydration process were calculated by the T2 spectrum. The water distribution models at different times and locations during the hydration process were established based on the MRI bitmap data. The variation law of water volume at different locations was studied. The results indicate that: In the process of hydration, some of the water is consumed by the hydration reaction, and some of the water oozes out. The water in the large pores flows to the small pores under the action of hydrostatic pressure. AS affected the uniformity of the cement mortar at the initial state, and the gradation of the sand could improve the uniformity. The smaller AS was, the more complex the pore water distribution and changed during hydration. The bleeding mass was directly proportional to the porosity and inversely proportional to the specific surface area of particles. The effect of porosity on bleeding mass was more significant than AS. Pore fractal dimension was negatively correlated with aggregate diameter. In the initial stage, when the aggregate composition became complex, the change of fractal dimension with time also became complex. The fractal dimension increased gradually with the increase of hydration time. The gel pores (G) did not have fractal characteristics from beginning to end, capillary pores (C) and transition pores (T) had fractal characteristics after a particular time of hydration reaction. Although the air-voids (A) had fractal characteristics from beginning to end, they were not continuous.

Research Progress on the Influence of Thermo-Chemical Effects on the Swelling Pressure of Bentonite

The swelling pressure of bentonite changes dramatically due to diffused nuclear radiation heat and underground osmosis, causing the failure of the buffer isolation layer in deep geological repositories for the disposal of high-level radioactive waste. A detailed overview of the relevant research results on the swelling pressure variation of bentonite under thermo-chemical effects is presented in this paper. The results showed that the values of the swelling pressure obtained by different test methods are dissimilar. The swelling pressure of bentonite decreased with the increasing pore solution concentration; nevertheless, the effect of temperature on the swelling pressure is still controversial. At the micro-level, crystal layer swelling and double- layer swelling are generally considered to be the main factors affecting the swelling pressure; the pore structure and water distribution of bentonite will change owing to thermo-chemical effects. At the macro-level, involving intergranular stress, a mechanical parameter was proposed to explain the mechanism of the changes in the swelling pressure of bentonite. Finally, future research directions for the study of the evolution of bentonite swelling properties under thermo-chemical effects are proposed, based on the current research results.

Microscopic occurrence and movability mechanism of pore water in deep shale gas reservoirs: A typical case study of the Wufeng-Longmaxi Formation, Luzhou block, Sichuan Basin

Water in pore system (i.e., pore water) is of great significance for shale gas exploration and exploitation. However, the microscopic occurrence and movability mechanism of pore water is still unclear. In this study, the pore water of deep shale gas reservoirs of the Wufeng-Longmaxi Formation in the Luzhou block was quantitatively evaluated by a new theoretical approach. The microscopic distribution and movability of pore water were investigated by combining NMR technology and theoretical models, and then the influencing factors were discussed. The results show that the signal amplitude of dry shale originates from clay minerals and organic matter. For clay minerals, illite has the greatest influence on the signal amplitude, followed by illite-smectite mixed layer and chlorite. Pore water mainly exists in an adsorbed phase, with an average adsorbed ratio of 69.26%, and an average adsorption thickness (H) of 0.5392 nm. Adsorbed and free water coexist in pores of 3–100 nm, and have equivalent content and saturation in pores of 10 nm and 6–7 nm, respectively. The specific surface area and pore volume control the occurrence of adsorbed and free water respectively. With the increase in average pore size, the water-holding capacity of pore system weakens. Adsorbed water mainly occurs in pores related to organic matter and quartz, while free water tends to occur in clay minerals pores. The adsorption affinity of spherical pores is the strongest, followed by cylindrical and slit pores. The effective pore size threshold available for fluid flow in spherical, cylindrical, and slit pores is 6H, 4H, and 2H respectively. With increasing centrifugal pressure difference, the water saturation decreases, the adsorbed ratio and mobility increase. Shale with higher pore volume has stronger mobile potential and mobility. Clay minerals are essential for pore water movability, while organic matter and brittle minerals inhibit pore water movability. This study offers a novel approach for quantitatively characterize the occurrence and transport of pore water and potentially has wide application prospects.

Study of the groundwater regime in unsaturated slopes prone to landslides by multidisciplinary investigations: Experimental study and numerical modelling

The triggering of shallow landslides in granular deposits is highly controlled by the groundwater regime, namely, the pore water pressure distribution, which directly affects soil shear strength. The slope hydraulic state is usually variable over time and space due to the high variability of atmospheric loads at the ground surface and local geologic conditions, such as stratigraphic irregularities and preferential groundwater flow paths. The unfavourable combination among critical geomorphological and topographical settings with stratigraphic and hydrogeological features are commonly recognized as predisposing factors of flowslides and debris flow occurrences.This paper proposes a multidisciplinary approach that combines geological, geophysical and geotechnical investigations to identify the role of local geological and geotechnical factors on the groundwater regime in slopes prone to flow-like landslides. The study is based on seasonally repeated electrical resistivity tomography measurements integrated with geotechnical numerical modelling of hydraulic phenomena affecting the soil cover. The latter is used to analyse the effects of the stratigraphic variability in terms of the geometry, continuity, and thickness of the soil horizons on the groundwater regime over time. The proposed approach has been applied to a test site located on the northern slope of Faito Mt. in the Lattari/Sorrento Peninsula mountain chain (southern Italy), an area historically affected by many rapid instability phenomena, such as flow-like landslides and flash floods. Both geophysical and geotechnical models obtained for the test site were cross-checked and validated, providing significant insights into the hydraulic response of the soil cover to rainfall and its hydraulic interaction with the underlying bedrock. Specifically, the integrated approach proved that i) the buried paleo-morphology of the bedrock severely affects the pore water distribution in the soil cover and ii) ashy soil fills the upper karst portion of the bedrock, providing a hydraulic connection of the water flow infiltrating from the topsoil downwards.

Distribution and occurrence of pore water and retained oil in nanopores of marine-terrestrial transitional shales during oil generation and expulsion: Implications from a thermal simulation experiment on shale plug samples

The distribution and occurrence of pore water and retained oil in shale nanopores is a key scientific issue confronting the evaluation, exploration and development of shale hydrocarbon resources. At present, however, relevant researches are scarce, especially on marine-terrestrial transitional (MTT) shales. In this study, a thermal simulation experiment was performed on a set of water-saturated shale plug samples prepared from a low-maturity MTT shale. The pore water and retained oil contents of the artificially matured samples were quantified, and the pore structures under moist, dried, and solvent extracted conditions were investigated. The results show that the pore water content of the shale decreases with Ro increasing from 0.75% to 0.97% and then increases with Ro further increasing to 1.53%, which exhibits a negative correlation with the retained oil content during the oil generation and expulsion. The pore water occurs mainly in filling, adsorption and water-cluster states in micropores (<2 nm), small non-micropores (2–10 nm), and large non-micropores (>10 nm), respectively. The retained oil is mainly in a filling or dissolved state in the micropores and small non-micropores and in an oil-cluster state in the large non-micropores. The pore water and retained oil in shale micropores are stored in the inorganic matter (IM) and organic matter (OM) micropores, respectively. During oil generation and expulsion, the IM micropores are fully saturated by the pore water that is barely expelled, and most of the pore water is stored in non-micropores, especially in large non-micropores. With increasing maturity, the distribution of retained oil in nanopores changes obviously. The retained oil in non-micropores tends to be stored in the large non-micropores at low-maturity stages, occurs uniformly in both the small and large non-micropores at mature stages, and is dominantly reserved in the small non-micropores and micropores at high-maturity stages. These results have significances for understanding the accumulation mechanism of shale oil and gas resources under geological conditions and evaluating their resource potential.

NMR-based analysis of pore water state of unsaturated compacted bentonite considering the saline effect

Understanding the saline effect on the pore water state of unsaturated compacted bentonite at the microscale is critical for evaluating the performance of barrier materials in nuclear waste geological repositories. In this paper, the pore water redistribution and pore water state of unsaturated compacted bentonite considering the saline effect is investigated via nuclear magnetic resonance (NMR) technique. It is found that, with increasing pore water salinity, the pore water content decreases and pore water is distributed in smaller pores, which is consistent with the swelling deformation behavior of bentonite at the macroscale and the diffuse double layers (DDL) theory at the microscale. In addition, the saline effect on pore water distribution is weakened with the increase in matric suction due to the shrinkage deformation of bentonite during drying. Then, the saline effect on the pore water state of unsaturated compacted bentonite is discussed via the concept of effective activation energy. It is shown that the drainage of pore water and increased pore water salt concentration (or the increase of matric suction and osmotic suction) both elevate the effective activation energy of bentonite, decreasing pore water mobility. The saline effect on the permeability coefficient of bentonite is also discussed. For bentonite under larger matric suction and osmotic suction conditions, the permeability coefficient is smaller.

Change in size distribution of porewater and entrapped air with progression of water infiltration in sandstone

Change in size distribution of porewater and entrapped air with progression of water infiltration in sandstone

A nuclear magnetic resonance based quantification of pore water distribution in unsaturated soils

This study presents a novel approach to quantify the distribution characteristics of pore water in unsaturated soil by using the nuclear magnetic resonance (NMR) technology. The SWCC and NMR T2 curves under different matric suction were measured during the drying process of soil specimen, and a conversion relationship between T2 and pore radius r of was determined. The method using capillary drainage model to simulate soil drying process was feasible, and pores of unsaturated soil were divided into saturated pore, unsaturated pore, and dry pore when the suction exceeded the air entry value. Pore water distribution curve based on T2 well described the distribution characteristics of pore water in unsaturated soil; the quantification of pore water distribution was realized through a defined index named pore water damage potential (Mcp), and a good mathematical relationship was observed between the relative damage degree and the matric suction. By introducing the Mcp, a modified VG model that reflected the characteristics of pore water distribution was in a good quantitative agreement with the experimental observations. The results achieved provided a valuable reference for revealing the internal mechanism of SWCC and establishing mechanical model of unsaturated soil based on pore water distribution.