Role of critical volumetric water content and net overburden pressure on swelling or collapse behavior of compacted soils

Time domain reflectometry (TDR) can be used to determine the volumetric water content of soils. This note describes the utilization of a TDR miniprobe in triaxial testing. The TDR performance was examined with a series of tests that not only proved its reliability but also resulted in two empirical correlations. Using these correlations, the degree of saturation and volumetric water content during triaxial testing could be determined. The TDR was then put to use in a laboratory program designed to investigate the response of loose gassy sand under static and cyclic loading. Because of the TDR measurements it was possible to determine the degree of saturation and void ratio of the gassy specimens. The TDR miniprobe proved to be accurate, simple to use, and inexpensive to build.Key words: time domain reflectometry, TDR, triaxial testing, gassy, unsaturated.

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Numerical simulation of coupled liquid water, stress and heat for frozen soil in the thawing process

Engineering Computations ◽

10.1108/ec-03-2021-0138 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Wei Xiao ◽

Enlong Liu ◽

Xiao Yin ◽

Guike Zhang ◽

Chong Zhang ◽

...

Keyword(s):

Numerical Simulation ◽

Water Content ◽

Coupled Model ◽

Frozen Soil ◽

Water Migration ◽

Overburden Pressure ◽

Content Type ◽

Thawing Process ◽

Sample Water ◽

The One

PurposeThe purpose of this paper is to perform the thermo-hydro-mechanical (THM) numerical analysis in order to study the thawing process for frozen soil and to predict the thawing settlement.Design/methodology/approachA new one-dimensional multi-field physical coupled model was proposed here to describe the thawing process of saturated frozen soil, whereby the void ratio varied linearly with effective stress (Eq. 10) and hydraulic conductivity (Eq. 27b). The thawing process was simulated with different initial and boundary conditions in an open system with temperature variations. The mechanical behavior and water migration of the representative cases were also investigated.FindingsThe comparisons of representative cases with experimental data demonstrated that the model predicts thawing settlement well. It was found that the larger temperature gradient, higher overburden pressure and higher water content could lead to larger thawing settlement. The temperature was observed that to distribute height linearly in both frozen zone and unfrozen zone of the sample. Water migration forced to a decrease in the water content of the unfrozen zone and an increase in water content at the thawing front.Research limitations/implicationsIn this study, only the one-directional thawing processes along the frozen soil samples were investigated numerically and compared with test results, which can be extended to two-dimensional analysis of thawing process in frozen soil.Originality/valueThis study helps to understand the thawing process of frozen soil by coupled thermo-hydro-mechanical numerical simulation.

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

10.5194/egusphere-egu21-4564 ◽

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

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.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.We carried out water retention and hydraulic conductivity measurements with two tensiometers introduced in two different heights in a cylindrical compartment (250 cm&#179;) containing a loamy sand, either with or without the introduction of a 20 &#181;m 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 &#181;m d-1 at 20% volumetric water content.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.We conclude that water extractability from soils distant to roots can be facilitated under dry conditions when AMF hyphae are present.&#160;

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Studies on Water in Barnacle Muscle Fibres II. Role of ions and Organic Solutes in Swelling of Chemically-skinned Fibres

Journal of Experimental Biology ◽

10.1242/jeb.90.1.43 ◽

1981 ◽

Vol 90 (1) ◽

pp. 43-63

Author(s):

M. E. CLARK ◽

J. A. M. HINKE ◽

M. E. TODD

Keyword(s):

Water Content ◽

Fibre Volume ◽

Tween 20 ◽

Muscle Fibres ◽

Skinned Fibres ◽

Organic Solutes ◽

Net Charge ◽

Trimethylamine Oxide ◽

Organic Solute

Single muscle fibres from the giant barnacle, Balanus nubilis, were chemically skinned (2% Tween 20), then equilibrated for 40 h in salt solutions ranging in ionic strength from 0·025 to 0·6M at pH 7·0. The water content of the fibres and the net charge on the myofilaments increased with increasing salt concentration. Cation accumulation in the fibres was about equal to anion exclusion at all salt concentrations. When an organic solute (trimethylamine oxide, glycine, alanine, serine, proline, or glycerol) in the concentration range from 0·1 to 0·6 M was added to the salt solution, cation accumulation increased and water content decreased. Myofilament architecture was disrupted when the fibres were equilibrated in high salt (> 0·4 M) solutions and preserved when 0·5 M-triethylamine oxide was also added. The results are consistent with the view that organic solutes enhance the association between the fixed charge sites and their counterions. This hypothesis is examined quantitatively using the Oosawa relationship between the volume and the counterion association for cylindrical polyelectrolytes. The results illustrate that organic solutes can influence fibre volume in a way other than through osmo-regulation.

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