scholarly journals Investigation on Compressibility and Microstructure Evolution of Intact Loess During Wetting Process

2021 ◽  
Author(s):  
Tao Jian ◽  
Ling-wei Kong ◽  
Wei Bai ◽  
Zhi-liang Sun
Keyword(s):  
Water Content ◽  
Pore Space ◽  
Experimental Studies ◽  
Vertical Stress ◽  
Dry Density ◽  
Compression Index ◽  
Rapid Reduction ◽  
Before And After ◽  
Wetting Process ◽  
Intact Loess

Abstract Loess is widely deposited in arid and semi-arid areas and is characterized by low dry density, developed pore space, and loose structure, which is not commensurate with that high structural strength and shear strength in the dry state. Many natural phenomena and experimental studies show that intact loess is very sensitive to the change of water content, with slight increases in water content causing a rapid reduction in strength. Abundant information is available in the literature for collapsibility of loess; however, the research on the evolution of loess compressibility during wetting is still minimal, which is very helpful to understand the loess collapsible deformation caused by long-term irrigation. In this paper, the evolution of compressibility of intact loess during wetting are studied by oedometer test, and the microstructure and pore size distribution (PSD) is characterized on intact loess specimens with different water content before and after oedometer tests by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) methods. The results show that the compression index (Cc) and secondary compression index (Cα) of intact loess depend on water content and vertical stress and change abruptly after the vertical stress exceeds the yield stress. The Cα/Cc values of the intact loess are not constant, which increased with the vertical stress to peak and then gradually decreased and tend to 0.025. Both wetting and loading can cause microstructural damage to the intact loess, in which loading leads to the collapse of the overhead structure and transformation from a bimodal PSD into a single PSD, and wetting intensifies the collapse of microstructure to form a compacted interlocking structure and promotes the transformation of medium pores into small pores.

scholarly journals Irreducible water saturation in snow: experimental results in a cold laboratory

1998 ◽  
Vol 26 ◽  
pp. 64-68 ◽  
Author(s):  
Cécile Coléou ◽  
Bernard Lesaffre
Keyword(s):  
Water Content ◽  
Water Saturation ◽  
Experimental Studies ◽  
Homogeneous Layer ◽  
Radius Of Curvature ◽  
Dry Density ◽  
Saturated Layer ◽  
Irreducible Water Saturation ◽  
Wet Snow ◽  
Water Saturated

The porosity of wet snow is often about 50%; however, liquid water generally fills less than 10% of this pore volume. In order to relate the irreducible water content trapped in snow to its characteristics, we have conducted experiments in a cold laboratory. The results show that irreducible water content, expressed as per cent of mass, depends only on porosity. Experimental studies were restricted to homogeneous wet snow samples. Therefore, we can only achieve a valid result in natural snowpacks when applying to an homogeneous layer of wet snow. Nevertheless, the results may be incorporated into snow-cover energy-balance models to improve the retention and percolation predictions. The thickness of the water-saturated layer observed at the base of the sample in our experiments, was related to the ratio of the mean convex radius of curvature to dry density.

scholarly journals Irreducible water saturation in snow: experimental results in a cold laboratory

1998 ◽  
Vol 26 ◽  
pp. 64-68 ◽  
Author(s):  
Cécile Coléou ◽  
Bernard Lesaffre
Keyword(s):  
Water Content ◽  
Water Saturation ◽  
Experimental Studies ◽  
Homogeneous Layer ◽  
Radius Of Curvature ◽  
Dry Density ◽  
Saturated Layer ◽  
Irreducible Water Saturation ◽  
Wet Snow ◽  
Water Saturated

The porosity of wet snow is often about 50%; however, liquid water generally fills less than 10% of this pore volume. In order to relate the irreducible water content trapped in snow to its characteristics, we have conducted experiments in a cold laboratory. The results show that irreducible water content, expressed as per cent of mass, depends only on porosity. Experimental studies were restricted to homogeneous wet snow samples. Therefore, we can only achieve a valid result in natural snowpacks when applying to an homogeneous layer of wet snow. Nevertheless, the results may be incorporated into snow-cover energy-balance models to improve the retention and percolation predictions. The thickness of the water-saturated layer observed at the base of the sample in our experiments, was related to the ratio of the mean convex radius of curvature to dry density.

scholarly journals Research of Temperature Conditions of Organic Sediments Formation in the Productive Formation at Paraffinic Oil Well Production

2021 ◽  
Vol 21 (2) ◽  
pp. 84-93
Author(s):  
Mikhail S. Sandyga ◽  
◽  
Ivan A. Struchkov ◽  
Mikhail K. Rogachev ◽  
◽  
...  
Keyword(s):  
Free Volume ◽  
Pore Space ◽  
Experimental Studies ◽  
Saturation Temperature ◽  
Reservoir Rock ◽  
Core Material ◽  
Reservoir Rocks ◽  
Temperature Conditions ◽  
Before And After ◽  
Paraffinic Oil

The paper presents the studies results of the temperature conditions for the formation of organic (asphalt-resin-paraffinic) deposits in the productive formation during the downhole production of paraffinic oil, including the results of experimental studies to assess the temperature of oil saturation with paraffin in the pore space of reservoir rocks. The studies were carried out in order to substantiate and develop a technology for preventing such deposits in the "reservoir - well" system. The results of filtration and rheological studies showed that for the same oil, the wax saturation temperature in the pore space of the reservoir rock could exceed the value of this parameter in the free volume. It was found that for the investigated solutions (models of highly paraffinic oils), the phase transition of paraffin from liquid to solid state, the formation of wax crystals in the pore space occured at a temperature 3-4° C higher than in the free volume. The results of tomographic studies of the core material, performed before and after filtration of a paraffin-containing solution through it with a decrease in temperature, showed that the open porosity of rock samples decreased on average four times due to the clogging of their pore space with paraffin. Based on the results of the filtration experiment and computed tomography, a digital core model was created, which allowed modeling the fluid flow in the pore space of the rock before and after the formation of paraffin deposits in it. The calculations results of the changes dynamics in the thermal field around the injection well confirmed the probability of cooling the bottomhole zone of the well to a temperature equal to the temperature of the onset of wax crystallization, as well as the probability of the cold water front advancing to neighboring production wells, which could cause a significant decrease in the productivity due to the formation of paraffin deposits in pore space of reservoir rocks. The research results are recommended to be taken into account when developing oil fields in conditions of possible formation of organic (asphalt-resin-paraffinic) deposits in the productive formation. This will make it possible to more reliably predict and effectively prevent its formation in the "reservoir - well" system.

scholarly journals The effect of clay water content in the Jet Erosion Test

2019 ◽  
Vol 92 ◽  
pp. 02016
Author(s):  
Raniero Beber ◽  
Alessandro Tarantino ◽  
Matteo Pedrotti ◽  
Rebecca Lunn
Keyword(s):  
Water Content ◽  
Soil Mechanics ◽  
Dominant Role ◽  
Dry Density ◽  
Surface Erosion ◽  
Surface Boundary ◽  
Surface Boundary Conditions ◽  
Unsaturated Soil Mechanics ◽  
Wetting Process ◽  
Particle Configuration

The understanding of the onset of breaching induced by surface erosion is fundamental to enable definition of the level of protection afforded by embankments and provision of standards for the design of new structures and the upgrading of existing ones. Compacted embankment materials are generally partially saturated due to seasonal variation in the water content. At the onset of the overflow process embankments undergo to a wetting process due to the changes at the outer surface boundary conditions (i.e. overflow). Erosion behaviour is known to be a counterbalance between gravity forces and shear erosion forces. However, as the particle size decreases (i.e. clayey soils), gravitational forces become negligible and electrochemical interaction between particles play a dominant role. Clay microstructure (e.g. particle configuration and inter-particle forces) changes with the hydro-mechanical stresses history. Thus, it is necessary to consider the microstructural changes in particle configuration to understand the influence of microstructure on the macroscopic behaviour of clay during erosion. Upon wetting, clay have a swelling/collapse behaviour. This research presents experimental results on erosion of clay samples compacted at the same initial dry density but with different compaction water content. The influence of different wetting times on erosion is also investigated. We show that for a given as-compacted water content, the longer the wetting stage, and hence the higher the sample water content, the more erodible the samples. Additionally, for samples compacted at the same dry density, the ones compacted on the dry side of optimum are more erodible than samples compacted at the optimum water content, despite the lower water content at formation. We hypothesise that this may be due to the formation of a different initial microstructure in sample on the dry side of optimum (i.e. bi-modal pore size distribution). Our results contribute to the fundamental understanding of time-dependent mechanisms that influence erosion of clay embankments during overflow and, hence, to embankment failure. In addition, these tests show how basic concepts of unsaturated soil mechanics can serve as a guide to ‘design’ the compaction conditions of embankment material.

scholarly journals Local radon flux maxima in the quaternary sediments of Schleswig–Holstein (Germany)

2021 ◽  
Author(s):  
Johannes Albert ◽  
Maximilian Schärf ◽  
Frieder Enzmann ◽  
Martin Waltl ◽  
Frank Sirocko
Keyword(s):  
Water Content ◽  
Pore Space ◽  
Mineralogical Composition ◽  
Fault System ◽  
Near Surface ◽  
Salt Diapirism ◽  
The North ◽  
Radon Flux ◽  
Published Evidence ◽  
Tectonically Active

AbstractThis paper presents radon flux profiles from four regions in Schleswig–Holstein (Northern Germany). Three of these regions are located over deep-rooted tectonic faults or salt diapirs and one is in an area without any tectonic or halokinetic activity, but with steep topography. Contrary to recently published studies on spatial patterns of soil radon gas concentration we measured flux of radon from soil into the atmosphere. All radon devices of each profile were deployed simultaneously to avoid inconsistencies due to strong diurnal variations of radon exhalation. To compare data from different seasons, values had to be normalized. Observed radon flux patterns are apparently related to the mineralogical composition of the Quaternary strata (particularly to the abundance of reddish granite and porphyry), and its grain size (with a flux maximum in well-sorted sand/silt). Minimum radon flux occurs above non-permeable, clay-rich soil layers. Small amounts of water content in the pore space increase radon flux, whereas excessive water content lessens it. Peak flux values, however, are observed over a deep-rooted fault system on the eastern side of Lake Plön, i.e., at the boundary of the Eastholstein Platform and the Eastholstein Trough. Furthermore, high radon flux values are observed in two regions associated with salt diapirism and near-surface halokinetic faults. These regions show frequent local radon flux maxima, which indicate that the uppermost strata above salt diapirs are very inhomogeneous. Deep-rooted increased permeability (effective radon flux depth) or just the boundaries between permeable and impermeable strata appear to concentrate radon flux. In summary, our radon flux profiles are in accordance with the published evidence of low radon concentrations in the “normal” soils of Schleswig–Holstein. However, very high values of radon flux are likely to occur at distinct locations near salt diapirism at depth, boundaries between permeable and impermeable strata, and finally at the tectonically active flanks of the North German Basin.

The effects of aquatic therapy on mobility of individuals with neurological diseases: a systematic review

2014 ◽  
Vol 29 (8) ◽  
pp. 741-751 ◽  
Author(s):  
Andresa R Marinho-Buzelli ◽  
Alison M Bonnyman ◽  
Mary C Verrier
Keyword(s):  
Randomized Controlled Trials ◽  
Gait Speed ◽  
Neurological Diseases ◽  
Dynamic Balance ◽  
Experimental Studies ◽  
Controlled Trials ◽  
Aquatic Therapy ◽  
Randomized Controlled ◽  
Randomized Studies ◽  
Before And After

Objective:To summarize evidence on the effects of aquatic therapy on mobility in individuals with neurological diseases.Data sources:MEDLINE, EMBASE, PsycInfo, CENTRAL, CINAHL, SPORTDiscus, PEDro, PsycBITE and OT Seeker were searched from inception to 15 September 2014. Hand-searching of reference lists was performed in the selected studies.Review methods:The search included randomized controlled trials and quasi-experimental studies that investigated the use of aquatic therapy and its effect on mobility of adults with neurological diseases. One reviewer screened titles and abstracts of retrieved studies from the search strategy. Two reviewers independently examined the full texts and conducted the study selection, data extraction and quality assessment. A narrative synthesis of data was applied to summarize information from included studies. The Downs and Black Scale was used to assess methodological quality.Results:A total of 116 articles were obtained for full text eligibility. Twenty studies met the specified inclusion criteria: four Randomized Controlled Trials (RCTs), four non-randomized studies and 12 before-and-after tests. Two RCTs (30 patients with stroke in the aquatic therapy groups), three non-randomized studies and three before-and-after studies showed “fair” evidence that aquatic therapy increases dynamic balance in participants with some neurological disorders. One RCT (seven patients with stroke in the aquatic therapy group) and two before-and-after tests (20 patients with multiple sclerosis) demonstrated “fair” evidence on improvement of gait speed after aquatic therapy.Conclusion:Our synthesis showed “fair” evidence supporting the use of aquatic therapy to improve dynamic balance and gait speed in adults with certain neurological conditions.

Soil water dynamics after fire in a Portuguese shrubland

2006 ◽  
Vol 15 (1) ◽  
pp. 99 ◽  
Author(s):  
Joaquim S. Silva ◽  
Francisco C. Rego ◽  
Stefano Mazzoleni
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Plant Community ◽  
Root Distribution ◽  
Control Plot ◽  
The Other ◽  
Water Dynamics ◽  
Soil Water Dynamics ◽  
Surface Layers ◽  
Before And After

This paper presents a study where soil water content (SW) was measured before and after an experimental fire in a shrubland dominated by Erica scoparia L. in Portugal. Two plots were established: one was kept as a control plot and the other was burned by an experimental fire in June 2001. Measurements were taken before fire (2000), and after fire (2001, 2002, and 2003) at six depths down to 170 cm, from June to December. Measurements before fire allowed comparison of the two plots in terms of the SW differential, using 2000 as a reference. Results for 2001 showed that SW decreased less during the drying season (June–September) and increased more during the wetting season (October–December) in the burned plot than in the control plot. The magnitude of these effects decreased consistently in 2002 and 2003, especially at surface layers. The maximum gain of SW for the total profile in the burned plot was estimated as 105.5 mm in 2001, 70.2 mm in 2002, and 35.6 mm in 2003. The present paper discusses the mechanisms responsible for the increase in SW taking into account the characteristics of the plant community, including the root distribution, and the results of other studies.

Application of Thermo-Frictional and Chemical-Thermal Methods Treatments for Surface Strengthening of Materials

2021 ◽  
Vol 1038 ◽  
pp. 93-99
Author(s):  
Alexander Levterov ◽  
Julia Nechitailo ◽  
Tatyana Plugina ◽  
Oleg Volkov
Keyword(s):  
Cross Sections ◽  
Experimental Studies ◽  
Metallographic Analysis ◽  
Thermal Treatments ◽  
Strengthening Effect ◽  
Thermal Methods ◽  
Surface Strengthening ◽  
Before And After ◽  
The Cross

In the article, the issues of using the methods of thermo-frictional and chemical-thermal treatments for surface strengthening of steel tools were disclosed. 65G steel and U8A steel were considered. A flat graver and a cylindrical root roller were considered to be tools in need of hardening. The nature of the jewellery work using such a tool has been described. Hardening techniques, experimental studies and macro photographs of the samples were presented in this article. A detailed metallographic analysis and measurement of the microhardness of the cross-sections of the prototypes after their strengthening using various methods was carried out. The metallographic nature of the reinforcement with the formation of surface "white layers" was shown. Comparison of the properties of the samples before and after strengthening was carried out. Conclusions about the strengthening effect of the thermo-frictional and chemical-thermal methods of strengthening were made.

scholarly journals Simulating microbial degradation of organic matter in a simple porous system using the 3-D diffusion-based model MOSAIC

2014 ◽  
Vol 11 (8) ◽  
pp. 2201-2209 ◽  
Author(s):  
O. Monga ◽  
P. Garnier ◽  
V. Pot ◽  
E. Coucheney ◽  
N. Nunan ◽  
...  
Keyword(s):  
Experimental Data ◽  
Organic Matter ◽  
Water Content ◽  
Microbial Degradation ◽  
Diffusion Processes ◽  
Pore Space ◽  
High Water Content ◽  
Porous System ◽  
Micro Computed Tomography ◽  
Bacterial Strains

Abstract. This paper deals with the simulation of microbial degradation of organic matter in soil within the pore space at a microscopic scale. Pore space was analysed with micro-computed tomography and described using a sphere network coming from a geometrical modelling algorithm. The biological model was improved regarding previous work in order to include the transformation of dissolved organic compounds and diffusion processes. We tested our model using experimental results of a simple substrate decomposition experiment (fructose) within a simple medium (sand) in the presence of different bacterial strains. Separate incubations were carried out in microcosms using five different bacterial communities at two different water potentials of −10 and −100 cm of water. We calibrated the biological parameters by means of experimental data obtained at high water content, and we tested the model without changing any parameters at low water content. Same as for the experimental data, our simulation results showed that the decrease in water content caused a decrease of mineralization rate. The model was able to simulate the decrease of connectivity between substrate and microorganism due the decrease of water content.

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