Geo-environmental Projects Research Articles

Effect of Dynamic Loads on the Long-Term Efficiency of Liner Layers

The liner layers of natural sand-clay mixtures are extensively used in a range of geotechnical and geoenvironmental projects. In many of these projects, these layers are exposed to dynamic loads or waves due to natural seismic earthquakes or due to human activities, such as machine vibrations, traffic repeated loads, and other impact loads. The permeability of liners is a key property and should be adequately designed to sustain these loads during their lifetime of serviceability. This study sought to evaluate the possible effects of dynamic loads on the efficiency of two different sand-expansive clay (SCL) liners during their lifetime. This was achieved through experimental tests for two series; the first series was subjected to dynamic loads (up to 500 cycles) using the triaxial dynamic system and then tested for permeability for a long period of up to 100 days. The permeability results were compared with the second series tested without being subject to dynamic loads. The dynamic properties for both liners, such as the shear modulus (G), damping ratio (D), and degradation index (δ) were determined and discussed. The results indicated that both materials showed significant degradation with an increase in cycles of dynamic loads; most of the degradation took place during the first 100 cycles. In consequence, the dynamic loads induced a significant effect on the performance of the liners during their lifetime (reducing the permeability by more than six times). These effects were time-dependent and should be taken into account during the design phases.

Predictive model for water retention curve of water-absorbing polymer amended soil

Water-absorbing polymer (WAP) amendment is emerging as a sustainable soil management technique in various geoenvironmental projects for controlling the subsurface water flow in the vadose zone. The addition of WAP can alter the pore structure and improve water-retention characteristics of the soil. The existing water-retention characteristic curve (WRCC) models for polymer-amended soils are complex and require a number of empirical parameters, which cannot be easily obtained through simple laboratory experimentation. The current study proposes a simple predictive WRCC model for WAP-amended soils based on the understanding that WAP particles absorb and retain water within their polymer structure and therefore influence the void ratio. The proposed model captures the change in the void ratio of the amended soil through a modified phase relationship for predicting WRCC. The performance of the model was validated for four different textured soils with varying WAP concentrations. The comparison between measured and predicted WRCC indicates that the proposed model can capture the changes in the void ratio as well as the WRCC with adequate accuracy.

Strain-softening failure mode after the post-peak as a unique mechanism of ruptures in a frozen soil-rock mixture

A large number of traffic systems in China pass through a large area of frozen soil, most of which contains frozen soil–rock mixtures (FSRMs). For a profound understanding of the mechanical behaviours and damage mechanisms of geotechnical and geoenvironmental projects, it is necessary to understand the stress–strain characteristics and failure modes of FSRMs. This study focuses on the uniaxial compression strength (UCS), Young's modulus, and complete stress–strain curve under loading, considering the post-peak behaviour. More than 250 FSRM specimens were tested for UCS evaluations, while considering the effects of different freezing temperatures (−5, −10, −20, −30, and − 40 °C), initial water contents (15.0, 25.0, and 30.0%), and volumetric block proportions (0, 30, 40, 50, and 100%). The stress–strain curve of the FSRM was characterised by six distinct stress levels and deformation stages, different from those of rock or soil in the normal state. Particularly, the turning point from volume compression to expansion was observed after the post-peak, at which superficial cracks were initiated. Ice crystals provided ductility of the FSRM and maximised its load capacity to prevent premature cracks on the FSRM surface. The block stone hindered the linear propagation of cracks. The failure patterns of the FSRM for the UCS evaluation could be classified into four types. The UCS was influenced by mainly the strength of the mixture composed of ice crystals and soil particles and friction and occlusal strength between blocks. Notably, the gradual thawing of the FSRM might cause the largest deformation at the bottom of the active layer in summer and autumn, according to the experimental results. Thus, it is very important to understand the strength characteristics, deformation stages, and failure patterns associated with the geomechanical behaviour of the FSRM for engineering design and applications in a permafrost region.

Water Retention Characteristics of Fly Ash–Bentonite Mix

The use of sand–bentonite mixes as hydraulic barrier in municipal and hazardous landfills are established in the literature. Environmental awareness and stringent rules on river conservation has restricted the free availability of construction sand making it non-viable for massive geo-environmental projects such as waste containment. Following the same philosophy for which sand was used in bentonite, this study propose to replace the former with fly ash. Apart from being an alternate material to sand, this proposition would ensure mass utility of waste fly ash for environmentally advantageous waste containment project. For this purpose, it is important to study the unsaturated characteristics of fly ash–bentonite mix, which is not reported in the literature. This study explores the influence of fly ash properties and its classification on the water retention characteristics curve (WRCC) of fly ash–bentonite mixes. The extent of variability in WRCC attributed to different sources of fly ash were quantified to investigate whether there is a possibility of generalizing the unsaturated behavior of fly ash–bentonite mixes. In addition, the influence of bentonite water content on the WRCC of mixes were studied and compared with the previously published results in the literature. It was found that at high suction (> 105 kPa), all the WRCC of FA–B mixes merges together and is mainly dominated by the water retention of bentonite only. It was also established from this study that any types of fly ashes irrespective of its source can be used in this application if compacted at optimum moisture content.

Adsorption behavior of Na-bentonite and nano cloisite Na+ in interaction with Pb(NO3)2 and Cu(NO3)2·3H2O contamination in landfill liners: Optimization by response surface methodology

Contamination of soils and water with Pb (II) and Cu (II) ions are very common in geo-environmental projects, but despite investigations of soil-contaminant interactions, the actual process of the interaction involving heavy metals and Nano-clays has not been extensively investigated. Lead can enter the food chain through contaminated soil. Lead poisoning can affect the blood circulation, kidneys, and peripheral and central nervous systems especially in adults. Accumulation of Cu (II) in the human body causes brain, skin, pancreas and heart diseases.In this study, a wide range of the adsorbent / electrolyte and heavy metal concentration was considered to compare the interaction process of Pb (II) and Cu (II) contaminants with Nano cloisite Na+ (NCNa) and bentonite. This classification of materials has a unique functionality which may have widespread applications, due to their novel or significantly enhanced properties to use in the Geo-environmental projects. A series of experiments was carried out using a range of Pb (II) and Cu (II) contaminant concentrations from 25 to 275 cmol kg-soil−1, under a range of contaminant/absorbent ratios from 0.01 to 0.02. Response surface methodology (RSM) was used to optimize the results. Generally, the results showed an increase in adsorption with increasing the adsorbent / electrolyte ratio up to 0.015. Bentonite adsorbed up to %50 of the Pb (II) while the concentration was 150 cmol/kg.soil. This amount was %40 for the NCNa in a constant ratio of adsorbent/electrolyte. Also the behavior of bentonite clay adsorbents was likely to favor adsorption of Pb (II) rather than Cu (II), as indicated in the previous research found.

Role of the location and size of soluble particles in the mechanical behavior of collapsible granular soil: a DEM simulation

Collapsing soil structure caused by mineral dissolution is a challenge to geoenvironmental projects. Although the parameters affecting the macro-response of collapsible soil have been addressed experimentally, the micromechanical behavior of soluble soil is unclear. The aim of this study was to simulate the dissolution behavior of a granular assembly at the particle level. A DEM code was developed that considers both localized and random dissolution as well as the particle size distribution and stress level. The effect of particle dissolution was simulated by considering the role of particle size in the load-bearing skeleton. The results show that mechanical behavior of a granular assembly is strongly influenced by the location and percentage of dissolution of particles. The loss of the soluble particles decreases physical contact and transfers to neighboring particles due to the arching forces around the voids, as in a honeycomb structure. However, if the soluble areas cut across the load-bearing force chains, a honeycomb fabric cannot form because of the lack of an arching effect, leading to the collapse of the structure and large volume change. Particle loss of up to 3% will not have a serious impact on the mechanical behavior of the granular assembly. After fine particle dissolution of a binary mixture, the arching effect around them decreases the volumetric strain in comparison with the dissolution of coarse particles. Also, during dissolution, the high stress level will decrease the peak friction angle, but the opposite is true for the post-dissolution behavior above 12% strain.

A Critical Review on Filter Design Criteria for Dispersive Base Soils

Dispersive soils have become common materials for the construction industry. Highly susceptible to internal erosion and piping, dispersive soils must only be used with specific engineering measure in order to avoid failures that were often catastrophic. In an earth dam, clayey soils are used for the core and sandy materials are used for the filter to retain the eroded core soils and prevent their migration. In the absence of first-rate core material, dispersive soils have been used instead. This paper provides a review of the current knowledge and experiences regarding filtration of core soils, particularly the dispersive ones. The engineering problems associated with the use of dispersive soils are discussed and significant findings from previous studies on protective filters are summarized. It is worthy to note that the current review considers both, the conventional, rather empirical filter design criteria based on particle sizes and the current, quite theoretical state-of-the-art filter design criteria based on constriction sizes, with discussion given on the advantages and disadvantages of both. The information provided by this review should be handy for the study, design, construction, and operation of related geotechnical and geo-environmental projects.

Treatment of dispersive clay soil by ZELIAC

Dispersive clays are prone to erosion and could cause significant problems in geotechnical and geo-environmental projects. In this research, a new additive - the ZELIAC – was investigated for treating a Malaysian dispersive clay soil where an appreciable decrease in dispersivity was achieved due to treatment with 8% ZELIAC. The curing time was found to be significant that after 28days, the initially dispersive samples became non-dispersive. Furthermore, due to the treatment, the samples had increased unconfined compressive strength (UCS), permeability, and optimum moisture content; and decreased fines content, plasticity index, maximum dry density, and compressibility index. The UCS increased nearly 7.3 times for sample treated with 8% ZELIAC and cured for 90days. The X-ray fluorescence (XRF) results showed a cementitious structure with calcium content 10.8 times more in the treated sample than in the untreated one, reflecting the constructive cation exchange reaction taking place during the curing process. The sodium ion was noticeably replaced by calcium ion which resulted in a decreased thickness of the diffused double layer and the subsequent reduction in the dispersivity of the sample. These results were also reflected by the lower peak intensity as measured by the X-ray diffraction test (XRD) for the treated sample, as compared to the higher peak intensity for the un-treated sample. Finally, the SEM images indicate that the flocculated structures of the treated dispersive clay were surrounded by the ZELIAC particles. Thus, the ZELIAC was proven to be effective in improving the studied Malaysian dispersive clay.

Numerical simulation of porosity and tortuosity effect on the permeability in clay: Microstructural approach

This study presents an analysis of the association between the coefficient of permeability of active clays and their porosity and tortuosity. Montmorillonite was selected because it is used as a barrier in geo-environmental projects and its sensitive structure results in wide variations in permeability when in contact with pore fluids. The microstructural approach was selected for a numerical simulation using the discrete element method (DEM). A DEM code was developed by considering the mechanical force, diffuse double-layer repulsion, and van der Waals attraction as the inter-particle interaction. The coefficient of permeability was calculated by simulating consolidation tests, and the DEM simulations were compared with the experimental data. The results show that the coefficient of permeability decreased as the void ratio decreased. At the same void ratio, there was a deviation between the coefficient of permeability for clay–electrolyte systems caused by the micro-fabric and variations in tortuosity. Micro-fabric evolution during loading showed that increasing the stress state caused a reorientation of the particles perpendicular to the direction of loading and increased the anisotropy of the particle orientation, increasing the tortuous flow path. A dispersed or oriented structure can occur at the same void ratio for different clay–electrolyte systems, causing variations in the coefficient of permeability.

Evaluation of Measurement Methodologies Used for Establishing Water Retention Characteristic Curve of Fly Ash

AbstractFly ash (FA) has potential applications in geotechnical and geoenvironmental projects, where its water retention characteristic curve (WRCC) is important. The main objective of this study was to establish the inherent range of measured suction of FAs using four different tools: tensiometer (TM), matric potential sensor, equitensiometer (EQT), and WP4 dew point potentiameter with a varying measurement range. Based on the measured results, the variability of WRCC equation parameters of four FAs collected from different thermal power plants were studied. Further, the sensitivity of a different range of measured suction on WRCC equation parameters of FA was investigated. The study indicated that the possible range of measurable suction for FA is 1 to 1000 kPa, which can be measured conveniently with an EQT. The parameters of FA were not influenced by high suction measurements (>1000 kPa) of WP4. The suction data (>1000 kPa) obtained using the WP4 can be appended with a low-suction-range instrument such as a TM for a better representation of the WRCC of FA. However, the study indicated that WRCC parameterization of FA is influenced more by the low range of suction.

Numerical Simulation of Tortuosity Effect on the Montmorillonite Permeability

This study analyzed the association between the coefficient of permeability of clayey sealing materials and their tortuosity. Montmorillonite was selected because it is used as a barrier in geo-environmental projects and its sensitive structure results in wide variations in permeability when in contact with pore fluids. A DEM code was developed by considering mechanical force, diffuse double layer repulsion, and Van der Waals attraction as the inter-particle interaction. The coefficient of permeability was calculated by simulating a consolidation test and the DEM simulations were compared with experimental data. The results showed that the coefficient of permeability decreased as the void ratio decreased. At the same void ratio, there was a deviation between the coefficient of permeability for clay-electrolyte systems caused by the micro-fabric and variations in tortuosity. Micro-fabric evolution during loading showed that increasing the stress state caused reorientation of the particles perpendicular to the direction of loading and increased anisotropy of the particle orientation, increasing the tortuous flow path.

Assessing the anion type effect on the hydro-mechanical properties of smectite from macro and micro-structure aspects

The expansivity of clayey soils is a complicated phenomenon which may affect the stability of geotechnical structures and geo-environmental projects. In all common factors for the monitoring of soil expansion, less attention is given to anion type of pore space solutions. Therefore, this paper is concerned with the impact of various concentrations of different inorganic salts including NaCl, <TEX>$Na_2SO_4$</TEX>, and <TEX>$Na_2CO_3$</TEX> on the macro and microstructure behavior of the expandable smectite clay. Comparison of the responses of the smectite/NaCl and smectite/<TEX>$Na_2SO_4$</TEX> mixtures indicates that the effect of anion valance on the soil engineering properties is not very pronounced, regardless of the electrolyte concentration. However, at presence of carbonate as potential determining ions (PDIs) the swelling power increases up to 1.5 times compared to sulfate or chloride ions. The samples with <TEX>$Na_2CO_3$</TEX> are also more deformable and show lower osmotic compressibility than the other mixtures. This demonstrates that the barrier performance of smectite greatly decreases in case of anions with the non-specific adsorption (e.g., <TEX>$Cl^-$</TEX> and <TEX>$SO{_4}^{2-}$</TEX>) as the salinity of solution increases. Based on the results of the X-ray diffraction and sedimentation tests, the high soil volumetric changes upon exposure to carbonate is attributed to an increase in the repulsive forces between smectite basic unit layers due to the PDI effect of <TEX>$CO{_3}^{2-}$</TEX> and increasing the pH level which enhance the buffering capacity of smectite. The study concluded that the nature of anion through its influence on the re-arrangement of soil microstructure and osmotic phenomena governs the hydro-mechanical parameters of expansive clays. It seems not coinciding with the double layer theory of the Gouy-Chapman double layer model.

Pozzolanic consolidation of stabilized soft clays

The presence of soft clays underlying foundations has been responsible for failures in several geotechnical and geo-environmental projects. The three aspects of this study dealing with the stabilization of a soft clay through the addition of cement and lime include: (a) determination of the optimum proportions of both cement and lime needed to obtain a stabilized soil, (b) the phenomenon of pozzolanic consolidation which occurs in the cement–lime stabilized soft clay, and (c) using knowledge of the pre-consolidation stress and compression index of the stabilized soft clay as a practical criterion for determination of the optimum additive percentage in soft clays stabilization. The experimental research program designed to investigate the behavior of the soft clay before and after stabilization involved a series of tests that included sedimentation testing, cation exchange capacity measurement, X-ray diffractometry, unconfined compression and consolidation tests. The results indicate that pozzolanic reaction creates a form of pre-consolidation in the cement–lime stabilized soft clay. The reduction in soil settlement is attributed to the pozzolanic reaction in soil-additive interaction resulting in an increase in pre-consolidation stress of stabilized soil. The test results show that pozzolanic consolidation causes an increase in initial pre-consolidation stress of 70kN/m2 for a soft clay soil to 375kN/m2 for the stabilized soil with 6% lime, and to 385kN/m2 for stabilized soil with 6% cement. The series of XRD experiments conducted are used to study the micro-structural aspects of the stabilized soil. The results show that pozzolanic consolidation not only improves strength behavior of clay soils in general, but also reduces the potential for large settlements of the stabilized soft clays — indicating that there is considerable merit in using the consolidation behavior of the stabilized soft clays as a means for determining the required percentages of additives for cement–lime stabilization of soft clays and soft soils in general.

Design Engineering to Control Geological Environmental Problems of Limestone Mine in Fengshan, Guangxi

Geo-environmental treatment projects had not been implemented in many old mines of China. Those mines environment has got increasingly deteriorated. So the government provides specialized policies and funding to solve the environmental problems of those mines. Based on the characteristics of the geological environmental treatment projects of old mines, the paper puts forward the principle and index of the treatment projects design and applies in the design of Fengshan limestone mine, Guangxi. It indicated that: (1)The geological environment problems are complex and diverse, and the treatment projects involve a multi-disciplinary cross which are environmental geology, ecology geology, geotechnical engineering, environmental engineering and landscape works. It needs to consider the follow key indicators: Geo-environment problems, Feasibility, Benefit, and social demand. (2) the limestone mine in FengShan is high 134m, and there had happened a collapse which had 2.1×104 m3, and killed 6 people. The geo-environment problems include rockfall, rock collapse, land and vegetation destruction, and landscape damage. The mine local in the Leye-Fengshan International Geological Park in Guangxi, the requests for travel security and sight-viewing environment are extremely high. Therefore, drainage, anchoring, rockfalls platforms and rock carvings would be implemented for the purpose of transforming the mine into a sight spot in the park.(3) The treatment projects eliminate the geo-hazard and build the world-class carving attractions reflect the benefit of the project management from the environment, economy and society aspects.

Numerical simulation of pore fluid characteristic effect on the volume change behavior of montmorillonite clays

The aim of this paper is to analyze the association between the volume change in clayey sealing materials and pore fluid chemistry under different stresses. Montmorillonite is considered because it is commonly used as a barrier in geo-environmental projects. Microscopic observations are numerically simulated using a discrete element method (DEM). A DEM code has been developed by considering both mechanical and diffuse double layer repulsion as interparticle interactions. The results show that volume change behavior is strongly influenced by the type of the electrolyte and its concentration. An increase in the valance of exchangeable cation and electrolyte concentration cause a reduction in the thickness of DDL and soil compressibility. The DEM simulations are compared with theoretical and experimental data, and their agreements are reported. It is concluded that DEM is a virtual laboratory for simulating the microstructural behavior of clay.

Analysis of Dispersivity Behavior of Clay Minerals by Fuzzy Computational System and Experimental Methods

In general, dispersive soils may cause some geotechnical problems, although in a geo-environmental context they can be used as an excellent contaminant absorbent due to their large surface area and well exposed clay particles to soil pore fluid. Because of this environmental application, using dispersive clay is common in many landfill projects. On the other hand, the dispersivity behavior of soils is known to be a function of clay mineral and concentration of salt in pore fluid. Most previous studies have based their experimental research on pure clayey soils such as montmorillonite, illite or kaolinite. Considering the fact that from a realistic point of view, there are very few cases of single clay mineral application in geo-environmental projects, there is a need to pay more attention to the behavior of soils which are composed of different minerals. This research investigates the role of mineral type and concentration of pore fluid on dispersivity performance of smectite, illite, kaolinite and their mixtures by means of turbidity, XRD and atomic adsorption tests. In addition, in this article a fuzzy set method based on laboratory tests is developed, with an aim to predicting the geo-environmental behavior of clay minerals mixtures. The system introduced is verified by a database which is compiled from laboratory tests. The results indicate that this system provides extensive knowledge concerning the necessary salt concentration required to disperse pure clay minerals and their mixtures. Furthermore, the numerical results generate some applicable graphs to estimate the required concentration of salt to disperse clayey soils with a view to using it in geo-environmental projects.

A Laboratory Procedure for Measuring High Soil Suction

AbstractMeasurement of soil suction is important for geotechnical and geoenvironmental projects involving unsaturated soils. Most of the methodologies developed for measuring soil suction are limited to low range of suction (&amp;lt;1500 kPa). Those methodologies that can measure high suction (&amp;gt;1500 kPa) are costly, time intensive and require skilled person for suction measurement. Therefore, a simple, cost-effective and relatively less time consuming measurement methodology has been proposed in this study for easy and quick measurement of high range of soil suction. The instrument essentially consists of a commercially available relative humidity sensor secured in a fabricated relative humidity box. The total suction for three soils measured using the proposed methodology has been compared with the conventional filter paper method. The study demonstrates the usefulness and advantage of the proposed cost-effective methodology for measuring high range of soil suction, in a relatively less time.

Influence of Potential Determining Ions on the Microstructural Performance and Contaminant Adsorption of a Homoionic Illitic Clay

Contaminant adsorption properties of clays are markedly influenced by the type of clay minerals, the nature of the exchangeable ions, and the type of clay microstructure present. Clay soils, due to their high buffering capacity and low permeability, are very helpful materials as barriers in waste disposal projects. On the other hand, the different microstructures of clay soils, due to their different surface areas and the different quantity of these surfaces exposed to the water, cause different contaminant attenuation levels for clay minerals. Even though the dispersive structures of soils might cause some geotechnical problems, in geo-environmental projects they might be of use as an excellent contaminant absorbent due to the fact that their clay particles are well-exposed to the soil pore fluid. The present study investigates the role of various types and concentrations of pore fluid on the microstructure and contaminant adsorption of illite. A series of pH measurements, a turbidity experiment, an XRD analysis, batch equilibrium testing and soil adsorption evaluation were performed to achieve the aforementioned objective. Homo-ionic illite mineral was prepared and some experiments were performed on it to support the findings. The results of this study show that although the theoretical calculation of the double layer theory does not take into account the effect of different anion types on the variation of the thickness of double layer, the anion type has a major impact on the microstructure variations of clay minerals. In addition, the turbidity measurement and the monitoring of XRD peak intensity of the major basal spacings of illite are appropriate tools for evaluating its dispersivity behaviour. It is shown that the PDI treated illite has more capacity for adsorption of heavy metal contaminant than that of illite or Ca–illite. It is concluded that the observed geo-environmental behaviour is noticeably a function of changes in the microstructure of illite.

The formation of ice from the infiltration of water into a frozen coarse grained soil

Understanding the formation of pore ice in coarse grained soils is important to geotechnical and geo-environmental projects such as the construction of roads, airstrips and gravel foundations as well as the treatment of contaminated soils in the arctic, sub-arctic, alpine and northern regions. The amount of pore ice present impacts the strength characteristics of the soils as well as the flow of fluid through soil. Tests have been conducted to qualify the impact of gradation, temperature, compaction and initial moisture content on the formation of pore ice in coarse grained soils. The purpose of this study was to prepare a conceptual model of the freezing mechanism in coarse grained soils and to qualify the parameters that influence the ice formation. Results from this study indicate that the presence of fine particles in a coarse grained soil greatly impact the depth at which the pore space initially becomes saturated with ice. A conceptual model was developed and its application is shown with regards to the process of thaw weakening in roads and the creation of preferential flow paths in permeable reactive barriers.

Assessment of the stability of a dispersive soil treated by alum

Dispersive soils have been responsible for failures in several geotechnical and geoenvironmental projects. Chemical treatments have been used to overcome deficiencies in the dispersive performance of these types of soils. Alum (aluminum sulfate {Al 2(SO 4) 3·18H 2O}) is commonly used for the treatment of these types of soils. The interaction of soil–additives during the treatment process is a physico-chemical phenomenon. In this paper, the fundamental aspects of interaction between dispersive soil and alum are examined and evaluated. Bentonite samples were laboratory dispersed with the use of different concentrations of sodium sulfate (Na 2SO 4). Alum was then used to control their dispersivity performance. A set of physico-chemical experiments including Atterberg limits, permeability, consolidation, double hydrometer, ion exchange, and pH measurement were performed to investigate the fundamental mechanism of soil–alum interaction. XRD and SEM testing were performed to support the findings. Double hydrometer testing indicates that the application of 1.5% aluminum sulfate caused a noticeable decrease in dispersivity potential. The results obtained indicate that the addition of alum causes a decrease in the pH level of dispersive bentonite. In this process, a distinguishable change in the engineering properties of soil occurred, including a reduction in liquid limit and an increase in hydraulic conductivity. In fact, the replacement of sodium ions by aluminum ions in the double layer of the clay particles resulted in a decrease in the thickness of the particles' double layers. It is concluded that two different phenomena were responsible for overcoming soil dispersivity: ion exchange and pH effects.