Experimental evaluation of salinity geosynthetics capillary barriers

2021 ◽  
pp. 1-27
Author(s):  
A. Bouazza
Keyword(s):  
Experimental Evaluation ◽  
Preventive Measures ◽  
Saline Water ◽  
Capillary Rise ◽  
Water Entry ◽  
Upward Flow ◽  
Wetting Front ◽  
Capillary Barrier ◽  
One Dimensional ◽  
Capillary Barriers

This paper explores the transient upward flow of saline water in one-dimensional soil and soil-geosynthetics columns to evaluate preventive measures to mitigate salinity rise. Unsaturated soil concepts are utilised to elucidate the salinity movement through geotextile and geocomposite drain interfaces. The presence of a geotextile layer slowed down the capillary rise of the saline water. However, it did not prevent the breakthrough of the saline water due to the hydrophilicity of the geotextile and the suction at the geotextile base being close to the geotextile's water entry suction value.  In contrast, using a geocomposite drain mitigated the upward saline wetting front. It acted as a salinity capillary barrier due to the initial hydrophobicity of its geotextile component and the air gap present in the geonet core.

The rate of water entry into dry sand and calculation of the advancing contact angle

Soil Research ◽  
1963 ◽  
Vol 1 (1) ◽  
pp. 9 ◽  
Author(s):  
WW Emerson ◽  
RD Bond
Keyword(s):  
Contact Angle ◽  
Capillary Rise ◽  
Applied Pressure ◽  
Water Entry ◽  
Water Repellent ◽  
Maximum Height ◽  
Wetting Front ◽  
Vertical Column ◽  
Advancing Contact Angle ◽  
Dry Sand

For water entry into a vertical column of dry sand, the height of capillary rise, h, is defined for the present purposes as the maximum height of capillary rise in the sand, below which the moisture content is uniform. Previous experimental results on water entry into dry sand have been reviewed to show the validity and usefulness of this definition. The rise of the wetting front into a vertical column of sand was measured, the rate of rise of the wetting front was plotted against the reciprocal of the height of rise, and 1/h was found by extrapolating the line to zero rate of rise. For water-repellent sand a positive hydrostatic head was applied to the base of the sand to obtain an adequate number of points for the extrapolation. This pressure was adjusted so that the initial rate of advance of water into the sand was about equal to that of water into the ignited sand with no positive applied pressure. The advancing contact angle averaged over the wetted surface area of the sand was then calculated from the ratio of the values of h obtained with sand before and after ignition. The contact angle of a water-repellent sand has been shown to be higher than 90�. This explains the difficulty experienced in the field of wetting these sands. Two remedial measures are suggested: one is to cultivate and mix the soil to give a uniform average contact angle, the other is to cut slots so that a positive hydrostatic pressure can be applied to the deeper patches of high contact angle sand.

Geotextiles to Mitigate Frost Effects in Soils: A Critical Review

1996 ◽  
Vol 1534 (1) ◽  
pp. 5-11
Author(s):  
Karen S. Henry
Keyword(s):  
Field Trials ◽  
Frost Heave ◽  
Laboratory Research ◽  
Capillary Barrier ◽  
Subgrade Soil ◽  
Capillary Barriers ◽  
Geotechnical Structures ◽  
Barrier Performance ◽  
Base Course ◽  
Selection Of

The use of geotextiles to mitigate frost effects in soils has been studied, but few techniques have been developed. Guidelines developed for the placement of granular capillary barriers are presented to serve as preliminary guidelines for geotextile capillary barriers. Laboratory research shows that pore size distribution, wettability, and, for some geotextiles, thickness influence capillary barrier performance in a given soil. Geotextiles that easily wet do not reduce frost heave and may even exacerbate it. On the basis of the literature reviewed, guidance for selection of geotextile capillary barriers in field trials is given. If geotextiles function as capillary barriers during freezing and reinforce or separate and filter the subgrade at the base course interface during thaw, then the potential exists for their use in a combination of functions to reduce frost-related damage in geotechnical structures. It was found that properly designed geotextiles have the potential to reduce frost heave by functioning as capillary barriers, they can be filters for capillary barriers, and they can provide reinforcement or separation or filtration (or all of these) of the subgrade soil to reduce thaw-related damage.

Aggregate slaking during rapid wetting: Hydrophobicity and pore occlusion

2008 ◽  
Vol 88 (1) ◽  
pp. 85-97 ◽  
Author(s):  
Hafida Zaher ◽  
Jean Caron
Keyword(s):  
Organic Matter ◽  
Management Strategies ◽  
Water Entry ◽  
Paper Sludge ◽  
Silty Clay ◽  
Clay Loam ◽  
Wetting Front ◽  
Clay Loam Soil ◽  
Silty Clay Loam ◽  
Loam Soil

The slaking process after rapid wetting is a key factor controlling soil structural stability in dry soil, and an understanding of the relative importance of the different mechanisms involved in slaking may help in the design of management strategies aimed at maintaining a stable surface soil structure. Slaking has been linked to, among other factors, rapid pressure build-up in aggregate, and previous work has emphasized the role of organic matter to hamper that pressure build-up, possibly due to hydrophobicity, reducing rapid water entry within aggregates and hence the build-up. This study emphasizes this latter aspect linked to slaking. The evolution of the intra-aggregate pressure, the matter lost by slaking and the expelled air after rapid wetting of two soils of different textures (clay loam soil and silty-clay loam soil) amended with different types of paper sludge were studied. Hydrophobicity effects were also studied using a tensio-active solution. The results of these experiments showed that when aggregates were submitted to sudden wetting, those treated with paper sludge had an improved resistance to the destructive action of rapid wetting. The lower pressures measured in the aggregates from the amended soils and having less slaking resulted most likely from slow water entry and reduced swelling. Detailed investigation on the link between hydrophobicity and water entry revealed that the true hydrophobic effect (modification of contact angle) was non-existent for the silty-clay loam and minor for the clay loam. This study, rather, suggests that changes in the water potential at the wetting front following organic matter addition and aggregate immersion most likely depend on pore occlusion and on changes in pore surface roughness. Key words: Aggregate stability, organic matter, slaking, pressure, swelling, wettability

Flume-scale laboratory study of rainfall-runoff responses in Devon silt and capillary barrier profiles

2020 ◽  
pp. 1-10
Author(s):  
Ahlam Abdulnabi ◽  
G. Ward Wilson
Keyword(s):  
Water Balance ◽  
Rainfall Intensity ◽  
Mine Waste ◽  
Ground Surface ◽  
Time Lapse ◽  
Rainfall Runoff ◽  
Wetting Front ◽  
Capillary Barrier ◽  
Infiltration Capacity ◽  
Water Balance Components

The design of soil covers for mine waste reclamation requires comprehensive water balance calculations at the ground surface and the subsurface. To achieve a determinate water balance equation, rainfall-runoff quantities need to be predicted or measured. The parameters that control rainfall runoff were investigated by performing rainfall-runoff experiments on Devon silt and capillary barrier profiles at different saturation stages. A rainfall simulator apparatus was employed to measure water balance components at different rainfall intensities during each test; the apparatus’ design is presented. The rainfall intensity and the saturated hydraulic conductivity of the soil govern runoff volumes and rates in the saturated profiles. The rainfall intensity and infiltration capacity of the soil govern runoff volumes and rates in the unsaturated profiles. The capillary barrier effects are evaluated and discussed by comparing time-lapse photographs of the wetting front during each test with changes in matric suction and volumetric water content measurements.

Field measurements of water storage capacity in a loess–gravel capillary barrier cover using rainfall simulation tests

2017 ◽  
Vol 54 (11) ◽  
pp. 1523-1536 ◽  
Author(s):  
Liang-tong Zhan ◽  
Guang-yao Li ◽  
Wei-guo Jiao ◽  
Tao Wu ◽  
Ji-wu Lan ◽  
...  
Keyword(s):  
Storage Capacity ◽  
Water Storage ◽  
Field Measurements ◽  
Test Site ◽  
Water Entry ◽  
Rainfall Event ◽  
Capillary Barrier ◽  
Water Storage Capacity ◽  
Artificial Rainfall ◽  
Compacted Loess

A 30 m long × 20 m wide capillary barrier cover (CBC) test site was constructed at the Jiangcungou landfill in Xi’an, China. The cover consisted of a compacted loess layer with a thickness of 0.9 m underlain by a gravel layer. After the cover surface was kept bare and exposed to natural climate conditions for nearly 5 months, one artificial rainfall event was implemented at the site. Vegetation was established at the test site after the first rainfall event. Four months later, a second artificial rainfall event was applied to the surface of the vegetated site. The pore-water pressures (PWPs) and volumetric water contents (VWCs) of the cover were monitored using jet-filled tensiometers and time-domain reflectometry moisture probes, respectively. Surface runoff and percolation were measured using field collection devices. The field measurements demonstrated a more rapid response of PWPs to the rainfall compared to the response of the VWCs. Percolation was observed when the PWPs near the interface reached the water-entry value of the gravel at local points. At that moment, the measured VWC near the interface was less than the VWC according to the water-entry value. The observation indicated that preferential flows took place in the compacted loess during the rainfall. As a result, the maximum water storage capacity was not reached at the onset of percolation. When percolation ceased, the average PWP near the interface decreased below the water-entry value, while the VWC near the interface was higher than that at the onset of percolation. Water storage at the completion of percolation was approximately 5% greater than that at the onset of percolation. Compared with the monolithic loess cover, the loess–gravel CBC increased the available water storage capacity by 41% at the completion of percolation. Vegetation had an insignificant influence on water storage capacity.

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