DEM-aided method for predicting the hydraulic properties with particle-size distribution of porous media

2019 ◽  
Vol 36 (5) ◽  
pp. 1716-1743 ◽  
Author(s):  
Han-Cheng Dan ◽  
Zhuo-Min Zou ◽  
Jia-Qi Chen ◽  
An-Ping Peng
Keyword(s):  
Particle Size ◽  
Porous Media ◽  
Hydraulic Conductivity ◽  
Hydraulic Properties ◽  
Volume Fraction ◽  
Size Distributions ◽  
Content Type ◽  
Unsaturated Hydraulic Conductivity ◽  
Critical Volume Fraction ◽  
The Relationship

Purpose The soil water retention curve (SWRC) and unsaturated hydraulic conductivity (UHC) are crucial indices to assess hydraulic properties of porous media that primarily depend on the particle and pore size distributions. This study aims to present a method based on the discrete element model (DEM) and the typical Arya and Paris model (AP model) to numerically predict SWRC and UHC. Design/methodology/approach First, the DEM (PFC3D software) is used to construct the pore and particle size distributions in porous media. The number of particles is calculated according to the AP model, which can be applied to evaluate the relationship between the suction head and the moisture of porous media. Subsequently, combining critical path analysis (CPA) and fractal theory, the air entry value is applied to calculate the critical pore radius (CPR) and the critical volume fraction (CVF) for evaluating the unsaturated hydraulic conductivity. Findings This method is validated against the experimental results of 11 soils from the clay loam to the sand, and then the scaling parameter in the AP model and critical volume fraction value for many types of soils are presented for reference; subsequently, the gradation effect on hydraulic property of soils is analyzed. Furthermore, the calculation for unbound graded aggregate (UGA) material as a special case and a theoretical extension are provided. Originality/value The presented study provides an important insight into the relationship between the heterogeneous particle and hydraulic properties by the DEM and sheds light on the directions for future study of a method to investigate the hydraulic properties of porous media.

Hyphal colonization of Rhizophagus irregularis increases unsaturated hydraulic conductivity of a loamy sand distant from roots

2021 ◽  
Author(s):  
Michael Bitterlich ◽  
Richard Pauwels
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Hydraulic Properties ◽  
Volumetric Water Content ◽  
Rhizophagus Irregularis ◽  
Loamy Sand ◽  
Soil Hydraulic Properties ◽  
Unsaturated Hydraulic Conductivity ◽  
Soil Hydraulic ◽  
Root Exclusion

<p>Hydraulic properties of mycorrhizal soils have rarely been reported and difficulties in directly assigning potential effects to hyphae of arbuscular mycorrhizal fungi (AMF) arise from other consequences of AMF being present, i.e. their influence on growth and water consumption rates of their host plants that both also influence soil hydraulic properties.</p><p>We assumed that the typical nylon meshes used for root-exclusion experiments in mycorrhizal research can provide a dynamic hydraulic barrier. It is expected that the uniform pore size of the rigid meshes causes a sudden hydraulic decoupling of the enmeshed inner volume from the surrounding soil as soon as the mesh pores become air-filled. Growing plants below the soil moisture threshold for hydraulic decoupling would minimize plant-size effects on root-exclusion compartments and allow for a more direct assignment of hyphal presence to modulations in soil hydraulic properties.</p><p>We carried out water retention and hydraulic conductivity measurements with two tensiometers introduced in two different heights in a cylindrical compartment (250 cm³) containing a loamy sand, either with or without the introduction of a 20 µm nylon mesh equidistantly between the tensiometers. Introduction of a mesh reduced hydraulic conductivity across the soil volumes by two orders of magnitude from 471 to 6 µm d<sup>-1</sup> at 20% volumetric water content.</p><p>We grew maize plants inoculated or not with Rhizophagus irregularis in the same soil in pots that contained root-exclusion compartments while maintaining 20% volumetric water content. When hyphae were present in the compartments, water potential and unsaturated hydraulic conductivity increased for a given water content compared to compartments free of hyphae. These differences increased with progressive soil drying.</p><p>We conclude that water extractability from soils distant to roots can be facilitated under dry conditions when AMF hyphae are present.</p><p> </p>

Historical development of soil-water physics and solute transport in porous media

2007 ◽  
Vol 7 (1) ◽  
pp. 59-66 ◽  
Author(s):  
D.E. Rolston
Keyword(s):  
Porous Media ◽  
Hydraulic Conductivity ◽  
Solute Transport ◽  
Soil Water ◽  
20Th Century ◽  
Water Flow ◽  
Unsaturated Soils ◽  
Transport Processes ◽  
Transport In Porous Media ◽  
Unsaturated Hydraulic Conductivity

The science of soil-water physics and contaminant transport in porous media began a little more than a century ago. The first equation to quantify the flow of water is attributed to Darcy. The next major development for unsaturated media was made by Buckingham in 1907. Buckingham quantified the energy state of soil water based on the thermodynamic potential energy. Buckingham then introduced the concept of unsaturated hydraulic conductivity, a function of water content. The water flux as the product of the unsaturated hydraulic conductivity and the total potential gradient has become the accepted Buckingham-Darcy law. Two decades later, Richards applied the continuity equation to Buckingham's equation and obtained a general partial differential equation describing water flow in unsaturated soils. For combined water and solute transport, it had been recognized since the latter half of the 19th century that salts and water do not move uniformly. It wasn't until the middle of the 20th century that scientists began to understand the complex processes of diffusion, dispersion, and convection and to develop mathematical formulations for solute transport. Knowledge on water flow and solute transport processes has expanded greatly since the early part of the 20th century to the present.

Effect of cultivation on the relationship between root length density and unsaturated hydraulic conductivity in a moderately swelling clay soil

Soil Research ◽  
1989 ◽  
Vol 27 (4) ◽  
pp. 645 ◽  
Author(s):  
SA Prathapar ◽  
WS Meyer ◽  
FJ Cook
Keyword(s):  
Surface Layer ◽  
Hydraulic Conductivity ◽  
Root Length ◽  
Root Length Density ◽  
Pore Characteristics ◽  
Soil Matrix ◽  
Wheat Field ◽  
Natural Pasture ◽  
Unsaturated Hydraulic Conductivity ◽  
The Relationship

Few studies have examined the effect of cultivation on the relationship between the presence of roots and unsaturated hydraulic conductivity in the soil matrix. Roots change soil pore characteristics by modifying pore diameter and pore continuity. Thus, the presence of roots may be expected to affect the hydraulic conductivity in saturated and unsaturated phases. In situ measurements of unsaturated hydraulic conductivity (Ku) at 0.04 m suction and root length density (Lv) of a moderately swelling soil were made in a wheat field and in a natural pasture field at 0, 0.25 and 0.4 m depths to determine their inter-relations. The Ku value decreased significantly with depth and the surface layer of the wheat field had the highest value (0.28 m day-1). The pasture field had high Lv at the surface layer (7.3 cm cm-3), but values decreased to less than those in the wheat field at 0.4 m depth. There was a distinct positive correlation between Lv and Ku, with the slope of the linear regression line being greater in the wheat field than in the pasture field. The cause of the relation is probably due to the common pore characteristics which influence Ku and Lv.

HYDRAULIC PROPERTIES OF DISTURBED AND UNDISTURBED SOILS

1970 ◽  
Vol 50 (3) ◽  
pp. 431-437 ◽  
Author(s):  
C. F. SHAYKEWICH
Keyword(s):  
Hydraulic Conductivity ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Available Water ◽  
Unsaturated Hydraulic Conductivity ◽  
Direct Measurements ◽  
Undisturbed Soils ◽  
Reliable Procedure ◽  
Sample Disturbance ◽  
High Suction

Studies showed that sample disturbance influenced water retention, lower limit of available water and unsaturated hydraulic conductivity. Significant differences in water retention due to sample disturbance occurred more frequently at low than at high suction. Results showed that sample disturbance may influence unsaturated hydraulic conductivity by changing area of water flow and/or tortuosity. A modified Millington and Quirk method did not adequately predict measured hydraulic conductivity, in either disturbed or undisturbed soils. In view of theoretical objections to extension of capillary theory to the dry end of the available water range, and the relative ease of direct measurements, it is suggested that direct measurement is the only reliable procedure available.

scholarly journals Soil-Water Characteristic Curves And Hydraulic Conductivity of Gaomiaozi Bentonite Pellet-Contained Materials

2021 ◽  
Author(s):  
Jianghong Zhu ◽  
Zhenyan Su ◽  
Huyuan Zhang
Keyword(s):  
Particle Size ◽  
Hydraulic Conductivity ◽  
Soil Water ◽  
Dry Density ◽  
Characteristic Curves ◽  
Factors Affecting ◽  
Unsaturated Hydraulic Conductivity ◽  
Long Time ◽  
Soil Water Characteristic Curves ◽  
High Level

Abstract The bentonite pellet-contained material (PCM) is a feasible material for the joint sealing of high-level radioactive waste repository. During the operation of the repository, the PCM will be unsaturated for a long time, and its water retention and permeability directly affect the buffer barrier seepage, nuclide migration, and joint healing. Moreover, the particle size of bentonite pellets and dry density are important factors affecting the performance of PCM. In this work, the pressure plate method and vapour equilibrium technique were utilized to test the soil-water characteristic curves (SWCCs) of the PCMs with different particle sizes and dry densities. The unsaturated hydraulic conductivity of the PCMs was predicted by combining the SWCC model and saturated hydraulic conductivity. The results showed that in the low suction range (20–1150 kPa), the dry density and particle size had a negative correlation with the water content at the same suction. In the high suction range (4200–309000 kPa), the dry density and particle size had little effect on the SWCC. The Gardner model was appropriate for describing the SWCC of PCM. In addition, the hydraulic conductivity of the PCM decreased with the increase in dry density, while increased with the increase in particle size. The influence mechanism of the SWCC and hydraulic conductivity was further discussed based on the scanning electron microscopy images and pore size distribution curves.

scholarly journals An experimental approach for determining unsaturated hydraulic properties of rock fractures

2004 ◽  
Vol 35 (3) ◽  
pp. 251-260 ◽  
Author(s):  
Hu Yunjin ◽  
Su Baoyu ◽  
Mao Genhai
Keyword(s):  
Hydraulic Conductivity ◽  
Capillary Pressure ◽  
Water Flow ◽  
Hydraulic Properties ◽  
Experimental Approach ◽  
Single Fracture ◽  
Rock Fractures ◽  
Unsaturated Hydraulic Conductivity ◽  
Connected Channels ◽  
Theoretical Saturation

An experimental approach for determining the unsaturated hydraulic properties (the relations between capillary pressure, saturation and unsaturated hydraulic conductivity) of rock fractures is developed and tested. Applying this approach to a single fracture, and with only water flowing, the capillary pressure–saturation and unsaturated hydraulic conductivity–capillary pressure relationships of the fracture during drainage and imbibition can be determined simultaneously. To facilitate the test of the validity of the experimental approach and to elucidate the characteristics of water flow in unsaturated fractures, an analogous fracture with parallel, connected channels of different apertures was fabricated. Experiments of unsaturated water flow in the analogous fracture were carried out. Some characteristics of water flow in unsaturated fractures (hysteresis between drainage and imbibition, etc.) were elucidated. Comparison of measured saturation values and theoretical saturation values corresponding to different apertures at the beginning of drainage and imbibition shows that the experimental approach presented in this paper is valid.

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