Soil Cap Research Articles

Comparison of the adhesion and shear tensile strength of needle-punched GCLs

This paper will show the correlation between the shear tensile test and the direct shear test within the field of geosynthetic clay liners (GCLs). It will be proven that the former may serve as a substitute for the latter, but only for the adhesion value.GCLs are clay mineral sealing layers widespread used. They can be used in waste and contaminated soil caps and closures, landfill base liners, gas and vapor seals, vertical barriers, etc. GCLs often have bentonite encased between two geotextile layers connected by fibers, either by needle-punching or stitch-bonding. The results from peel tests and shear box tests are currently used for establishing the internal shear failure of GCLs.This paper analyzes the mechanical shear behavior of needle-punched GCLs (NP GCLs) in a zero stress condition. On the one hand, a large direct shear test (ASTM 6243-09) on NP GCLs specimens was used to study its shear behavior, specifically, assessing the adhesion value. On the other hand, the shear tensile test, showed by Maubeuge and Ehrenberg (Maubeuge, K.P., Ehrenberg, H., 2000. Comparison of peel bond and shear tensile test methods for needle-punched geosynthetic clay liners. Geotextiles and Geomembranes 18(2–4), 203–214), was used to study the shear tensile strength. Comparing both test methods, an average shear tensile value of 32 kPa was obtained which is closer to the average adhesion value of 30 kPa. The dominant failure mechanisms are not depending on the test conditions (e.g. dry or hydrated conditions). However, it strongly depends on the type of carrier geotextiles and their connections.

Lateral resistance of pile cap – an experimental investigation

The pile foundation resists not only the loads from the superstructure, but also the large lateral forces from other sources such as earthquakes, wind, wave, etc. The pile cap is a crucial structural element in a pile foundation that is often massive and deeply buried, and design to provide significant resistance under the lateral loads. In this paper, a comprehensive experimental study of pile cap resistance under lateral load is presented. The parametric study of pile–soil–cap interaction under lateral load is performed on different pile groups. This study shows that the pile cap contributes approximately good amount of lateral resistance.

Parametric study of pile cap lateral resistance: finite element analysis

Analytical studies using finite element analysis of pile cap resistance under lateral load is seldom reported in literature. Recently, presents the results of experimental study on model piles to show the effect of pile cap elevation below the ground surface and pile spacing on lateral resistance of single pile and pile groups driven in sand. From their parametric study, they concluded that the lateral carrying capacity of single pile and pile groups increase as the pile cap depth below the ground surface increases and as the spacing between piles in the group increases. The objective of this study is to study pile–soil–cap interaction under lateral load considering different influences parameter and thus quantifying the lateral resistance for different conditions. Finite element modeling and analysis is performed for three different spacings, namely 3D, 5D, and 9D for RCC pile with 300, 400, and 500 mm diameter. It is observed that pile cap has lateral resistance varying from 35·42 to 44·06% implies good agreement with the findings of .

Evaluation of liquefaction in Karasu River floodplain after the October 23, 2011, Van (Turkey) earthquake

The eastern shore of Lake Van was shaken by a powerful earthquake (M w 7.2) on October 23, 2011. The epicenter of the earthquake was located at about 30 km north of the Van Province, which is one of the main cities in the Eastern Anatolia. The Van Province and particularly its largest district Ercis were adversely affected by the earthquake, and unfortunately, a total of 600 people lost their lives. Besides severe constructional damages and building collapses, ground deformations were widespread at many locations nearby the Lake Van and Karasu River floodplain. Numerous sand boils and lateral spreading cracks were observed at the left and right embankments of the Karasu River, which is one of the major streams in the region. In this study, field observations on liquefaction and lateral spreading features triggered by the M w 7.2 Van earthquake are initially presented. Then, the results of subsurface investigations including trial pits, drillings and geophysical surveys on specific large-scale sand boils are explained. Subsequently, liquefaction back-analysis is performed considering the gathered subsurface data. The analysis indicates that the liquefaction occurred in a shallow zone with approximately 4 m thickness in the investigated area. The Liquefaction Potential Index method reveals high liquefaction potential for the analyzed sand boil location. In addition, the effect of cap soil thickness on liquefaction is once more validated by this case.

In-situ subaqueous capping of mercury-contaminated sediments in a fresh-water aquatic system, Part II-evaluation of sorption materials

The function and longevity of traditional, passive, isolation caps can be augmented through the use of more chemically active capping materials which have higher sorptive capacities, ideally rendering metals non-bioavailable. In the case of Hg, active caps also mitigate the rate and extent of methylation. This research examined low cost, readily available, capping materials for their ability to sequester Hg and MeHg. Furthermore, selected capping materials were evaluated to inhibit the methylation of Hg in an incubation study as well as the capacity of a selected capping material to inhibit translocation of Hg and MeHg with respect to ebullition-facilitated contaminant transport in a column study. Results indicated that bauxite had a better capacity for mercury sorption than the other test materials. However, bauxite as well as soil capping materials did not decrease methylation to a significant extent. Materials with larger surface areas, higher organic matter and acid volatile sulfide (AVS) content displayed a larger partitioning coefficient. In the incubation experiments, the presence of a carbon source (lactate), electron acceptor (sulfate) and the appropriate strains of SRB provided the necessary conditions for Hg methylation to occur. The column study showed effectiveness in sequestering Hg and MeHg and retarding transport to the overlying water column; however, disturbances to the soil capping material resulting from gas ebullition negated its effectiveness.

Dynamic response of vertically loaded helical and driven steel piles

The dynamic performance of helical piles is of significant interest because such piles can offer an efficient alternative to conventional piling systems in many applications where the foundation is subjected to dynamic loads. This paper presents the results of full-scale dynamic vertical load tests on a 9.0 m double-helix, large-capacity helical pile and a driven steel pile of the same length and shaft geometry. Comparing the results is considered necessary to evaluate, qualitatively and quantitatively, the dynamic performance characteristics of large-capacity helical piles. The test piles were closed-ended steel shafts with an outer diameter of 324 mm. The piles were subjected to harmonic (quadratic) loading of different force intensities acting within a frequency range that covered the resonant frequencies of the tested pile–soil–cap systems. The dynamic and static properties of the subsurface soil adjacent to the test piles were determined using the seismic cone penetration technique and the conventional soil boring and testing methods. In addition, field observations are compared with calculated responses using the program DYNA 6 to better understand the pile–soil interaction for the case of helical piles. The effects of soil nonlinearity and pile–soil separation were accounted for in the analysis by employing a weak boundary zone around the piles in the analytical model. The experimental results show that the dynamic behaviour of helical piles is essentially the same as that of driven steel piles with the same geometric properties (without the helix plates). In addition, it was demonstrated that the program DYNA 6 can accurately simulate the behaviour of both helical and driven piles.

Initial seedling growth rates in a semi-dwarf spring wheat collection.

A relationship was observed between seedling growth rate and seedling emergence under conditions of soil capping. Coleoptile and root growth rates were strongly influenced by the origin of the seed sample and the genotype involved, whereas genotype × environment interactions were small and not significant. A test-cross analysis revealed the presence of strong epistatic effects for the characters coleoptile growth rate and coleoptile diameter. Both additive and dominance variation contributed strongly to the total genetic variation for coleoptile growth rate, while the - dominance appeared to be ambidirectional. Genetic variation for coleoptile diameter was found to be predominantly additive. Whereas both traits were expected to respond well to selection, no consistent correlations with simple plant characteristics could be established, a situation that may limit the utilization of the observed genetic differences through indirect selection.

Advances in agronomic management of phytoremediation: methods and results from a 10-year study of metal-polluted soils

Among green technologies addressed to metal pollution, phytoextraction has received increasing attention in recent years as an alternative to physical and chemical methods of decontamination. Since 1998, as part of an Italian multidisciplinary research team on phytoremediation, we have been carrying out several agronomic investigations with field crops in agricultural soil and pyrite waste, both markedly contaminated by heavy metals. Phytoextraction was rarely an efficient process, requiring a long time even to remove merely the bioavailable metal fraction, but the great metal stock in roots suggests exploring the effectiveness of long-term in planta stabilisation. Poor above-ground productivity was the main factor constraining metal removals, especially in wastes. Without assisting the process, only zinc (Zn), manganese (Mn) and copper (Cu) were harvested by the canopy in substantial amounts, with an estimated maximum of ~8 kg of metals from an hectare base with rapeseed in the agricultural soil and only 0.33 kg with fodder radish in pyrite waste. Root growth was a key trait in species and genotype selection, in view of the close relationship between root length and metal uptake. The auxins, humic acids and chelators tested on the model plant fodder radish generally increased metal concentrations in plant tissues, but reduced growth and removals. It is currently concluded that phytoremediation efficiency with crop species may be improved through increased productivity by suitable soil management, involving mineral and organic fertilisation, contaminant dilution, soil capping, and metal immobilisation with inorganics and biochar.

Bearing capacity of a square model footing on sand reinforced with shredded tire – An experimental investigation

Recycling rubber from waste tires has become one of the major challenges worldwide. The use of waste tires in geotechnical applications may be feasible as an alternative way to consume the huge stockpile of scrap tire, with a better understanding of the behavior of rubber–soil mixture. The objective of this study was to investigate the feasibility of using rubber shreds, randomly distributed into the soil, as soil reinforcement beneath the footing. A series of laboratory tests were conducted to obtain the bearing capacity of a square footing rested on shredded rubber-reinforced soil. The results show that the efficiency of rubber reinforcement was increased by addition of rubber content, the thickness of rubber-reinforced soil layer and the soil cap thickness up to the optimum values of these parameters, after that, with a further increase in each of these parameters, the bearing capacity decreases. For the optimum value of rubber content of 5% at footing settlement level of 5%, the maximum improvement in bearing capacity of rubber-reinforced bed was obtained as 2.68 times of the unreinforced bed. This value of improvement was achieved using the optimum thickness of reinforced layer of 0.5 times of footing width and the optimum thickness of soil cap of 0.25 times of footing width. The findings strongly suggest the use of rubber shreds obtained from non-reusable tires as a viable alternative way for improving the soil behavior, particularly when environmental interest is considered.

Use of Biosolids for Phytocapping of Landfill Soil

Conventional clay capping for post-closure management of landfill commonly cracks and deteriorates over time. As a consequence, water ingress into waste increases as a function of time, potentially causing a range of environmental issues. An alternative approach is known as phytocapping, which utilizes select plant species to control cap stability and moisture percolation. In this study, growth of Arundo donax L. (giant reed), Brassica juncea (L.) Czern. (Indian mustard), and Helianthus annuus L. (sunflower) on a landfill site was studied with different biosolid amendment rates (0, 25, and 50 Mg ha−1). Cultivation of the landfill cap and amendment with biosolids significantly improved the characteristics of the soil. Growth of each plant species increased due to biosolid addition. Giant reed produced the largest biomass in the 50 Mg ha−1 biosolid amendment rate (38 Mg ha−1 dry weight). The high pH and clay content of landfill cap soil, and the low metal concentrations of the biosolid resulted in low heavy metal (copper, zinc, cadmium, and lead) accumulation in leaves of most treatments. The improvement in growth and limited uptake of metal contaminants to plant shoots indicated that biosolid application to landfill clay caps improves the application of phytocapping of old landfill sites.

Buried Pipes in Rubber-Soil Backfilled Trenches under Cyclic Loading

AbstractIn geotechnical engineering, recycled tires are used in lightweight fills, backfill materials, highway embankments, soil reinforcement, and soil-retaining walls. The rubber-soil mixture can exhibit a greater capacity for energy absorbency than soil alone under cyclic loading and tends to decrease the stress and shocks transferred into the ground. The shear strength and energy absorbance of the rubber-soil mixture is highly dependent on the size of the rubber fragments and the proportion in the soil. In this paper, soil surface settlement, pipe deflection, and pressure distributed over a pipe placed in a trench and subject to cyclic loading were investigated as a function of chipped and shredded rubber used as backfill. The observed responses show that the shredded rubber-soil mixture used over the pipe is more effective in reducing these three parameters when covered by a soil cap, than when using the same soil alone for the whole of the fill. Also, using the rubber-soil mixture in the whole of ba...

Simulation of Soil Behavior under Blast Loading

A viscoplastic cap model was previously developed to address the high strain rate effect on soil behaviors. Although the model is an improvement over the inviscid cap model, it does not update soil density and bulk modulus as the shock wave propagates through the soil. Further, soil should be modeled as a three-phase porous media to accommodate various degrees of water saturation. This is especially true for the soil mass surrounding the source of energy release because each of the three phases responds differently to shock loading. A revised cap model comprising a Gruneisen equation of state for each of the three phases has been developed. These equations of state for solid, water, and air have been integrated with the viscoplastic cap model to simulate behaviors of soil with different degrees of water saturation. Numerical results from this revised soil cap model compared closely with experimental data from explosive tests in both dry and saturated soil.

Phosphogypsum Capping Depth Affects Revegetation and Hydrology in Western Canada

Phosphogypsum (PG), a byproduct of phosphate fertilizer manufacturing, is commonly stacked and capped with soil at decommissioning. Shallow (0, 8, 15, and 30 cm) and thick (46 and 91 cm) sandy loam caps on a PG stack near Fort Saskatchewan, Alberta, Canada, were studied in relation to vegetation establishment and hydrologic properties. Plant response was evaluated over two growing seasons for redtop ( L.), slender wheatgrass ( (Link) Malte ex H.F. Lewis), tufted hairgrass ( (L.) P. Beauv.), and sheep fescue ( L.) and for a mix of these grasses with alsike clover ( L.). Water content below the soil-PG interface was monitored with time-domain reflectometry probes, and leachate water quantity and quality at a depth of 30 cm was measured using lysimeters. Vegetation responded positively to all cap depths relative to bare PG, with few significant differences among cap depths. Slender wheatgrass performed best, and tufted hairgrass performed poorly. Soil caps <1 m required by regulation were sufficient for early revegetation. Soil water fluctuated more in shallow than in thick caps, and water content was generally between field capacity and wilting point regardless of cap depth. Water quality was not affected by cap depths ≤30 cm. Leachate volumes at 30 cm from distinct rainfall events were independent of precipitation amount and cap depth. The study period had lower precipitation than normal, yet soil caps were hospitable for plant growth in the first 2 yr of establishment.

Bauxite Processing Residue: A Critical Review of Its Formation, Properties, Storage, and Revegetation

Bauxite is processed in alumina refineries by the Bayer process in which Al-containing minerals are dissolved in hot NaOH. The insoluble solids (bauxite processing residue mud and sand) are washed, sometimes partially neutralized (using CO2 or seawater treatment), and deposited in impoundments surrounding the refinery using either wet (15–30% solids) or dry (50–65% solids) disposal techniques. Revegetation strategies for impoundments include constructing a soil cap over the mud deposit, amending the mud with residue sand and other materials or revegetating the sand fraction that surrounds and covers the mud deposit. Major limitations to plant growth in residues include salinity, sodicity, alkalinity, Al toxicity, and deficiencies of macro- and micronutrients. Physical properties are also problematic since residue mud consolidates to form a solid mass that waterlogs easily or dries to form a massive structure, while sand has a very low water holding capacity. Gypsum amendment reduces pH, displaces Na with Ca and tends to improve porosity. Organic amendments supply nutrients, increase CEC, and improve physical conditions while inorganic fertilizers supply essential nutrients. An integrated approach using all of the previously mentioned amendments as well as saline sodic-tolerant plant species is likely to increase the success of revegetation compared to use of only 1 or 2 techniques. There are very few reports on microbial activity in residue but since it is heat and chemically treated, activity is likely to be initially very low. Organic residue addition provides a substrate for heterotrophic microbes and provide the beginnings for a below-ground living ecosystem. Inoculation of plants with appropriate mycorrhiza and legumes with Rhizobium might also increase plant establishment and growth. These aspects deserve future examination. Although much research has concentrated on the establishment phase of revegetation, little consideration has been given to the subsequent growth and self-propagation of the introduced species, changes in residue properties during weathering and leaching of alkalinity from residue over time. These facets need careful study before definitive statements can be made regarding the sustainability of various revegetation strategies.

Toxic effect of heavy metals on aquatic environment

The indiscriminate discharge of industrial effluents, raw sewage wastes and other waste pollute most of the environments and affect survival and physiological activities of target organisms. Metals in particular have a tendency to accumulate and undergo food chain magnification. Heavy metals affect all groups of organisms and ecosystem processes, including microbial activities. The bioaccumulation of trace elements in living organisms and biomagnification in them describes the processes and pathways of these pollutants from one trophic level to another, exhibiting the higher bioaccumulation ability in the organisms concerned. Some of these organisms, like fishes, are consumed by human beings. They could also cause catastrophic diseases like Minamata and Itai-Itai. Remediation approaches such as excavation and land fill, thermal treatment, electroreclamation and soil capping have been proposed depending on the extension, depth and kind of contamination, but all are expensive and environmentally destructive. Hence, reduction of toxic elements in aquatic environment can be progressively monitored by currently accepted and updated methods.© 2010 International Formulae Group. All rights reserved.Keywords: Heavy metals, effluents, Minamata, Itai-itai, Remediation, antacids.

Assessment of a Reclamation Cover System for Phosphogypsum Stacks in Central Alberta, Canada

Phosphogypsum (PG), a byproduct of the phosphate fertilizer industry, was produced and stockpiled at the Agrium Fort Saskatchewan facility from 1965 to 1991. Upon decommissioning, the outer slopes of the PG stacks were reclaimed by applying 15 cm of topsoil and planting a non-native seed mix. Physical, chemical, and hydrologic evaluations of the cover system confirmed that plants were successfully growing in various soil capping depths and were often rooting more than 200 mm into the PG. Percolation past the substrate into PG during a typical storm event was low (< 10 mm), and runoff from the stacks was negligible. Runoff quality met most guidelines, but some parameters, including fluoride, were up to 18 times higher than provincial or federal guidelines for soil and water quality. However, the cover system, when applied appropriately, does meet basic reclamation objectives. The exceedances are found in areas where the cover system has been compromised by erosion or mixing or in areas where the cover system has not been fully applied, such as roads or the inner basin. In areas where the cover system has been applied successfully, basic reclamation requirements are met.

Influence of exsolved gases on slope performance at the Sarnia approach cut to the St. Clair Tunnel

In 1993, over 100 years after the completion of the original St. Clair Tunnel and its approach cuts, work commenced on the new St. Clair Tunnel. The new tunnel used the existing approaches, but required additional excavation to widen and deepen the original cuts. In Sarnia, the new work initiated unusual deep-seated deformations on the south slope of the approach. Effective stress finite element analysis (FEA), using an elliptical cap soil model coupled with Biot consolidation theory, was used to model the 1993 construction, but initial predictions were unable to capture the trend of deformations noted in the field. Naturally occurring gases are frequently encountered near the base of the overburden in the Sarnia area and this phenomenon was observed during drilling investigations in the Sarnia approach cut. Including the effects of the presence of exsolved natural gases in fine-grained soils subjected to unloading in the FEA results in substantially better predictions in the trend of deformations on the slopes of the approach cut.

Karst development and hydrogeology of Konarsiah salt diapir, south of Iran

The Konarsiah salt diapir is located in the Simply Folded Zone of the Zagros Mountain in the south of Iran. The salt rocks in Konarsiah diapir belong to the Hormuz Formation (Upper Precambrian–Middle Cambrian). Salt extruding from two nearby vents along the same fault have merged into a single body. The grey salt is covered by brown residual cap soils (4–32 m) and blocks (up to tens of meters) of the low-solubility components of the Hormuz Formation. The visible karst features are extensive sinkholes, a few shafts, and inlet caves. Sinkholes are mainly due to soil-cover and caprock collapse and do not show any preferential spatial pattern. Several maps, including salt outcrops, thickness of the mantling soils, salt table (the contact elevation between salt layer and cap soil), and sinkhole distribution are presented. The diapir has been divided into four zones based on the surface slope, cap soil thickness, sinkhole area ratio, and the size and density of sinkholes. Surface slope and cap soil thickness are the main parameters that differentiate the sinkholes. The general direction of groundwater flow is downslope towards the adjacent Konarsiah Plain in the south with diversions towards brine springs, and adjacent alluvium and karst aquifers. The type of groundwater flow is dominantly diffuse. Cave and conduit development is inhibited due to rapid saturation of recharge water with respect to halite. The numerous discharging zones and the constant flow rate of brine springs confirm a diffuse flow model proposed for the hydrology of the Konarsiah salt diapir.

Rehabilitation of a tailing dam at Shimen County, Hunan Province: Effectiveness assessment

This study was conducted to assess the effectiveness of phytoremediation on a tailing dam located in Shimen County, Hunan Province. Quadrat survey method was employed to investigate and sample the dominant plant species growing on the rehabilitated tailing dam. The fertilities of the soils were assessed, and concentrations of arsenic and other heavy metals in the plant and soil samples were measured. The results showed that no difference was found on the effect of soil capping with top and non-topsoils for rehabilitation of plants on the tailing dam. After rehabilitation, stable vegetation coverage types were established, 39 plant species were found to grow on the tailing dam, and the minimal area for plant communities was 30 m 2. The dominant plant species were planted Pteris vittata and natural colonizing Miscanthus sinensis. The contents of organic matter, nitrogen and phosphorus in the soils were low, while the potassium content was at a middle level; however, plots where Legumina plants grew were found to have higher level of nitrogen and phosphorus in the growing soils. Arsenic (As) and Cadmium (Cd) concentrations in the soils were 8 and 7 times of the grade III value of the National Standard for Soil Quality (GB15618-1995), respectively; while in tailings these were 81 and 68 times. The available As concentration in the soils ranged as 3.7–29.5 mg kg −1, whereas the available As concentration in tailings was as high as 61.1 mg kg −1. Concentrations for most of the heavy metals were in the normal range of terrestrial higher plants, except As and Cd in P. vittata and M. sinensis, and As in the roots of M. sinensis. It is concluded that phytoremediation project has reduced the ecological and health risks caused by the tailing dam to the ambient environment. However, the plants growing on the tailing dam which contained high As and Cd should be kept from entering into food chain in order to protect the health of local residents.

Phytocapping: an alternative technique for landfill remediation

An alternative technique of landfill remediation known as 'Phytocapping' was trialled at Rockhampton, Australia. Twenty one tree species were established on two types of phytocaps (thick cap; 1400 mm soil and thin cap; 700 mm). The trial was monitored for plant growth, transpiration loss, canopy rainfall interception and methane oxidation. The results show that the tree species can intercept ca. 30% of the rainfall and they transpire 1-2 mm day−1. The phytocaps also lowered methane emission by 4-5 times compared to an adjacent non-vegetated landfill. The HYDRUS 1D simulation revealed a percolation rate of 16.7 mm yr−1 in thick phytocap and 23.8 mm yr−1 in thin phytocap. These values are significantly lower than those expected from compacted clay capping (78 mm yr−1; i.e. 10% of the rainfall). Overall, this study demonstrated that the phytocaps are effective in minimising percolation of water into buried waste. Further research is being conducted (http://www.wmaa.com.au/aacap/aacap.html), to seek approval of regulatory authorities to use phytocapping as an alternative technique of landfill remediation.