Shear strength characteristics of sand-mixed with granular rubber

Waste materials such as waste tires, rubbers, and plastic materials are normally produced in every society, entering the environment and causing serious problems. These problems may be somehow reduced by finding applications for them in engineering, for example, as lightweight materials for backfill in geotechnical projects. To this aim, this paper demonstrates how shear strength characteristics of sand mixed with various percentages of waste garden hose grains are altered. A relatively, uniform sand has been mixed with waste hose grains in loose and slightly compacted states. Waste hose grains were prepared with special popular machinery in a local area. Various sand-rubber mixtures having 0%, 10%, 15%, 20%, 50%, 70%, and 100% waste hose particles by weight were chosen. The rubber grains were distributed in the sand such that uniform mixtures are obtained. In order to compare the shear strength of different sand-rubber samples, two compaction states were considered. The results show that the influencing parameters on shear strength characteristics of sand-rubber mixtures are normal stress, mixture unit weight, and rubber content. With the selected waste hose particles, compaction states, and rubber contents, the initial friction angle φ₁ does not change significantly. However, an apparent cohesion appears in the mixtures. From environmental point of view and due to lightweight material for the sand-waste hose particles, it may be useful to use such materials in corresponding geotechnical projects. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental Study on Effect of Waste Plastic Bottle Strips in Soil Improvement

With rapid advancements in technology globally, the use of plastics such as polyethylene bags, bottles etc. is also increasing. The disposal of thrown away wastes pose a serious challenge since most of the plastic wastes are non-biodegradable and unfit for incineration as they emit harmful gases. Soil stabilization improves the engineering properties of weak soils by controlled compaction or adding stabilizers like cement, lime etc. but these additives also have become expensive in recent years. This paper presents a detailed study on the behavior and use of waste plastic in soil improvement. Experimental investigation on reinforced plastic soil results showed that, plastic can be used as an effective stabilizer so as to encounter waste disposal problem as well as an economical solution for stabilizing weak soils. Plastic reinforced soil behaves like a fiber reinforced soil. This study involves the investigation of the effect of plastic bottle strips on silty sand for which a series of compaction, direct shear and California bearing ratio (CBR) tests have been performed with varying percentages of plastic strips and also with different aspect ratios in terms of size. The results reflect that there is significant increment in maximum dry unit weight, Shear Strength Parameters and CBR value with plastic reinforcement in soil. The quantum of improvement in the soil properties depends on type of soil, plastic content and size of strip. It is observed from the study that, improvement in engineering properties of silty sand is achieved at 0.4% plastic content with strip size of (15 mm?×?15 mm).     

Physical and Compaction Behaviour of Clay Soil–Fly Ash Mixtures

At present, nearly 100 million tonnes of fly ash is being generated annually in India posing serious health and environmental problems. To control these problems, the most commonly used method is addition of fly ash as a stabilizing agent usually used in combination with soils. In the present study, high-calcium (ASTM Class C—Neyveli fly) and low-calcium (ASTM Class F—Badarpur fly ash) fly ashes in different proportions by weight (10, 20, 40, 60 and 80 %) were added to a highly expansive soil [known as black cotton (BC) soil] from India. Laboratory tests involved determination of physical properties, compaction characteristics and swell potential. The test results show that the consistency limits, compaction characteristics and swelling potential of expansive soil–fly ash mixtures are significantly modified and improved. It is seen that 40 % fly ash content is the optimum quantity to improve the plasticity characteristics of BC soil. The fly ashes exhibit low dry unit weight compared to BC soil. With the addition of fly ash to BC soil the maximum dry unit weight (γ_dmax) of the soil–fly ash mixtures decreases with increase in optimum moisture content (OMC), which can be mainly attributed to the improvement in gradation of the fly ash. It is also observed that 10 % of Neyveli fly ash is the optimum amount required to minimize the swell potential compared to 40 % of Badarpur fly ash. Therefore, the main objective of the study was to study the effect of fly ashes on the physical, compaction, and swelling potential of BC soils, and bulk utilization of industrial waste by-product without adversely affecting the environment.     

Evaluation of bagasse ash treated lateritic soil as a potential barrier material in waste containment application

Laboratory tests were conducted on a reddish-brown lateritic soil treated with up to 12 % bagasse ash to assess its suitability in waste containment barriers applications. Soil samples were prepared using four compaction energies (i.e. reduced Proctor, standard Proctor, West African Standard or ‘intermediate’ and modified Proctor) at ?2, 0, 2 and 4 % moulding water content of the optimum moisture content (OMC). Index properties, hydraulic conductivity (k), volumetric shrinkage and unconfined compressive strength (UCS) tests were performed. Overall acceptable zones under which the material is suitable as a barrier material were obtained. Results recorded showed improved index properties; hydraulic conductivity and UCS with bagasse ash treatment up to 8 % at the OMC. Volumetric shrinkage strain increased with higher bagasse ash treatment. Based on the overall acceptable zone obtained, an 8 % optimal bagasse ash treatment of the natural lateritic soil makes it suitable for use in waste containment barrier application.     

Desiccation-Induced Volumetric Shrinkage of Compacted Foundry Sand Treated with Cement Kiln Dust

Foundry sand, an industrial waste, was treated with up to 12 % cement kiln dust content at comparative energy levels of British standard light, West African standard or “intermediate” (WAS) and British standard heavy (BSH) efforts at molding water contents ?2, 0, 2, 4 and 6 % of optimum moisture content. Samples were extruded from the compaction molds and allowed to air dry in the laboratory in order to assess the effect of desiccation-induced shrinkage on the material for use as a hydraulic barrier in waste containment application. Results recorded show that volumetric shrinkage strain (VSS) values were large within the first 5 days of drying; VSS values increased with higher molding water content, water content relative to the optimum moisture content. VSS generally increased with higher initial degree of saturation for all compactive efforts, irrespective of the level of cement kiln dust (CKD) treatment. A compaction plane of acceptable zones for VSS based on the regulatory value is ≤4 %. The influence of CKD treatment generally showed a decrease in the desiccation-induced volumetric shrinkage strain with increasing CKD content. This is largely due to the pozzolanic input of CKD. Finally, only the BSH compactive effort gave successful results of volumetric shrinkage strain at CKD treatment content of between 4 and 8 %, while 12 % CKD content produced successful volumetric shrinkage strain results at WAS and BSH compactive effort, respectively.     

轻量砂变形及强度特性三轴试验研究

通过三轴试验系统研究了新型土工材料--轻量砂的变形及强度特性。结果表明,不同的配比、龄期使轻量砂具有不同的原生结构强度,围压使不同原生结构强度的土样处于剪胀或剪缩状态,导致发生应变硬化、应变软化以及相应状态下孔压的3种对应形态变化。变形模量随EPS（发泡聚苯乙烯）球粒掺入比的增大而线性减小,随水泥掺入比、龄期增大而线性增大,相同配比的土样变形模量与围压关系不大;三轴抗压强度随EPS球粒掺入比增大而呈负指数关系减小,随水泥掺入比、龄期、围压增大而线性增大,存在水泥掺入比阀值;土骨架转换效应对于土样强度的影响很大,造成了土体单轴、三轴抗压强度分带,高水泥掺入比能够大大弱化EPS颗粒的土骨架效应。结合前人成果,系统地研究了轻量砂密度、无侧限抗压强度的影响因素,引入材料学中比强的概念,提出了单价比强图结合配方公式的方法,对轻量土砂进行配方优化。分析了轻量土砂应力-应变关系转型问题,提出采用无侧限抗压强度来表征不同配比、龄期轻量土砂的原生结构强度。通过试验与数理统计,建立临界围压与原生结构强度的关系,为数值模拟计算与建立本构模型奠定了基础。     

Response of vegetation pattern to different landform and water-table depth in Hailiutu River basin,Northwestern China

The spatial distribution of vegetation pattern and vegetation cover fraction (VCF) was quantified with remote sensing data in the Hailiutu River basin, a semiarid area in North China. The moderate resolution imaging spectroradiometer normalized different vegetation index (NDVI) values for 4 years from 2008 to 2011 and field observation data were used to assess the impact of climate factors, landform and depth to water table on vegetation distribution at large scale. In the VCF map, 74 % of the study area is covered with low and low–medium density vegetation, 24 % of the catchment is occupied by medium–high and high-density vegetation, and 2 % of area is bare soil. The relationship between NDVI and climate factors indicated that NDVI is correlated with relative humidity and precipitation. In the river catchment, NDVI increases gradually from landform of sand dune, eolian sand soil to river valley; 92.4 % of low NDVI from 0.15 to 0.3 is mostly distributed in sand dunes and the vegetation type is shrubs. Crops, shrubs and some dry willows dominate in eolian sand soil and 82.5 % of the NDVI varies between 0.2 and 0.35. In the river valley, 70.4 % of NDVI ranges between 0.25 and 0.4, and grass, dry willow and some crops are the main plants. Shrubs development of Korshinsk peashrub and Salix psammophila are dependent on groundwater by analyzing NDVI response to groundwater depth. However, NDVI of Artemisia desertorum had little sensitivity to groundwater.     

Influence of size of granulated rubber on bearing capacity of fine-grained sand

Nowadays, in most of the advanced and developing countries, waste tires have caused serious environmental problems such as fire and environmental contamination. For reusing them in an appropriate and beneficial way, waste tires have been utilized as a lightweight fill material in geotechnical engineering applications such as highway embankments. In this study, Babolsar fine-grained sand and granulated rubber with sizes in the ranges of 1 to 4, 1 to 9, and 4 to 9 mm were used. A series of model footing tests on reinforced sand with different sizes of granulated rubber were carried out. According to the results, 4- to 9-mm granulated rubber had the highest effect on enhancement of bearing capacity and reduction of fine-grained sand settlement. The results showed that sand-granulated rubber mixtures with granulated rubber in the range of 4 to 9 mm and content of 10% by weight of mixture can increase the bearing capacity of sand up to 50%. In addition, for this mixture, a series of laboratory tests were conducted to determine the optimum width and depth of the reinforcement layer consisting of sand-granulated rubber mixture. The results indicate that the optimum width and the most effective depth of this mixture are 5B and 1B, respectively (where B is the footing width).     

Sorption of Cd<Superscript>2+</Superscript> ions onto zeolite synthesized from perlite waste

In this work, the studies on the formation of zeolites from expanded perlite waste and their use in the sorption process of Cd²⁺ ions will be reported. Such approach is innovative and has not been investigated elsewhere. The results of the synthesis of zeolites from aluminosilicate waste using hydrothermal method were presented. By-product from the process production of expanded perlite was used as the starting material. Theoretical and practical aspects of Cd²⁺ ions sorption process onto material synthesized in selected conditions (a material with good sorption capacity can be obtained by 24 h reaction of 1 g of perlite waste in 10 mL of 4.0 M NaOH solution with at 70 °C) will be presented. The atomic absorption spectroscopy has been used as the main method, from which the effective cation exchange capacity as well as the proportion of ion exchange to chemisorption in the sorption process have been determined. Structural analyses of the sample before and after sorption process have been also carried out by the mid-infrared spectra measurement, especially pseudolattice range of the spectra was analyzed in detail in which changes caused by ion exchange of non-tetrahedral ions have been observed.     

掺绿砂改良膨胀土室内试验研究

绿砂高额的处理费用与其具有的再利用潜力相比,使绿砂再利用的研究得到重视,尤其对公路路基改良具有很大的利用潜力。针对膨胀土路基的胀缩问题,围绕绿砂及膨胀土-绿砂混合物进行一系列室内土工试验,探讨绿砂作为公路膨胀土路基改良剂的可行性。在不同含水率及不同配比条件下,对绿砂以及绿砂改良后膨胀土的基本物理性质、击实特性、力学特性等进行室内对比试验分析。分析结果表明,绿砂改良膨胀土试样的强度主要取决于试样的含水率、掺砂率;随着掺砂率的增加,塑性指数逐渐降低,最佳含水率也随之减小,最大干密度增大的幅度变化很小,无侧限抗压强度先降低而后提高,其后又降低。     

Effect of fines content and void ratio on the saturated hydraulic conductivity and undrained shear strength of sand–silt mixtures

The hydraulic conductivity represents an important indicator parameter in the generation and redistribution of excess pore pressure of sand–silt mixture soil deposits during earthquakes. This paper aims to determine the relationship between the undrained shear strength (liquefaction resistance) and the saturated hydraulic conductivity of the sand–silt mixtures and how much they are affected by the percentage of low plastic fines (finer than 0.074 mm) and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests carried out on samples reconstituted from Chlef river sand with 0, 10, 20, 30, 40, and 50 % non-plastic silt at an effective confining pressure of 100 kPa and two initial relative densities (D _r = 20, 91 %) are presented and discussed. It was found that the undrained shear strength (liquefaction resistance) can be correlated to the fines content, intergranular void ratio and saturated hydraulic conductivity. The results obtained from this study reveal that the saturated hydraulic conductivity (k _sat) of the sand mixed with 50 % low plastic fines can be, in average, four orders of magnitude smaller than that of the clean sand. The results show also that the global void ratio could not be used as a pertinent parameter to explain the undrained shear strength and saturated hydraulic conductivity response of the sand–silt mixtures.     

Impact of wetting–drying cycles on the hydraulic conductivity of liners made of lime-stabilized sand–bentonite mixtures for sanitary landfills

In this study, an investigation was performed to determine if lime-stabilized sand–bentonite mixtures are appropriate for the construction of sanitary landfills liners. For this aim, the hydraulic conductivity tests were conducted in the laboratory on sand–bentonite mixtures and lime-stabilized sand–bentonite mixtures to evaluate the effect of wetting–drying cycles. The hydraulic conductivity tests were performed to see if their hydraulic conductivities are affected by wetting–drying cycles. First series of specimens have been prepared as a mixture of sand and bentonite only. In the first series of specimens, sand was mixed with bentonite in proportions of 20, 30, 40, and 50 %. In the second series of the specimens, lime in proportions of 1, 2 and 3 % by weight was added to the mixtures of sand–bentonite in proportions of 20, 30, 40, and 50 %. From the results of the tests, it was observed that while optimum water content increased, maximum dry density decreased with addition of lime to the sand–bentonite mixtures. Generally, the hydraulic conductivity increased with the addition of lime to the mixtures but at low percentages of lime (1–2 %), however, slight decreases in k were recorded. It was also observed that the wetting–drying cycles on the permeability test indicate cure effect on specimens with addition of lime which resulted in decreased the hydraulic conductivity.     

Potential Application of Lateritic Soil Stabilized with Cement Kiln Dust (CKD) as Liner in Waste Containment Structures

This study evaluates the applicability of residually derived lateritic soil stabilized with cement kiln dust (CKD), a waste product from the cement manufacturing process as liner in waste repositories. Lateritic soil sample mixed with 0–16 % CKD (by dry weight of the soil) was compacted with the British Standard Light, West African Standard and British Standard Heavy compaction efforts at water contents ranging from the dry to wet of optimum moistures. Geotechnical parameters such as Atterberg limits, compaction characteristics, hydraulic conductivity, unconfined compressive strength and volumetric shrinkage strain were determined. Results indicate that the plasticity index, the maximum dry unit weight and hydraulic conductivity together with the volumetric shrinkage decreased with increased amount of CKD while the optimum moisture content and unconfined compressive strength increased with higher CKD content for all the efforts. When measured properties were compared with standard specifications adopted by most environmental regulatory agencies for the construction of barrier systems in waste containment structures, the resulting values showed substantial compliance. Besides developing an economically sustainable liner material, the present study demonstrated effective utilization of an industrial by-product otherwise considered as waste by the producers, in addition to a systematic expansion in the use of the lateritic soil for geotechnical works.     

Pullout Response of Uniaxial Geogrid in Tire Shred–Sand Mixtures

Use of tire shred–soil mixtures as backfill materials in mechanically stabilized earth walls has several advantages over other backfill materials: (1) good drainage, (2) high shear strength, and (3) low compacted unit weight. This paper presents the results of laboratory pullout tests performed on uniaxial geogrid embedded in tire shred–sand mixtures. The effects of tire shred size, tire shred–sand mixing ratio and confining pressure on the interaction between the geogrid and tire shred–sand mixtures are evaluated. Three sizes of tire shreds are considered: tire chips (with 9.5 mm nominal size), tire shreds 50-to-100 mm long and tire shreds 100-to-200 mm in length, with mixing ratios of 0, 12, 25 and 100 % of tire shreds in the mixtures (by weight). Based on compaction testing of a number of mixtures, the optimal mixing proportion of tire shreds and sand was found to lie between 25/75 and 30/70 (by weight of tire shred and sand); this is equivalent to approximately 40/60 and 50/50, respectively, by volume of tire shreds and sand. The pullout resistance of a geogrid embedded in tire shred–sand mixtures is significantly higher than that of the same geogrid embedded in tire shreds only. The size of the tire shreds has negligible effect on the pullout resistance of a geogrid embedded in mixtures prepared with either low (12/88 mix) or high (100/0 mix) tire shred content. However, when the 25/75 mixture is used, greater geogrid pullout resistance was obtained for the geogrid embedded in tire chip–sand mixtures than in tire shred–sand mixtures.     

Effect of Random Inclusion of Wheat Straw Fibers on Shear Strength Characteristics of Shanghai Cohesive Soil

The effect of random inclusion of wheat straw (fibers) on shear strength characteristics of Shanghai cohesive soil is presented in this paper. 1 year old natural wheat straw (fibers) with four section lengths of 5, 10, 15, 20 mm (aspect ratio: l/d = 1.67, 3.33, 5, 6.67) are used as reinforcement and specific Shanghai cohesive soil is used as medium. Locally available cohesive soil is compacted with standard Proctor’s maximum density with low percentage of reinforcement (0.1–0.4 % of wheat straw sections by weight of oven-dried soil). A series of direct shear tests were conducted on unreinforced as well as reinforced soil to investigate the shear strength characteristics of wheat straw-reinforced soil. The test results show that the inclusion of randomly distributed wheat straw sections (fibers) in soil increases the shear strength to one degree or another. It is noticed that the optimum wheat straw (fiber) content for achieving maximum shear strength is 0.3 % of the weight of oven-dried soil for wheat straw fiber length 15–20 mm (aspect ratio: 5–6.67).     

Rheological characteristics of mixed kaolin–sand slurry,impacts of pH,temperature, solid concentration and kaolin–sand mixing ratio

Significant amount of slurry waste is produced from mineral processing plants globally constituting high levels of both kaolin and sand in aqueous suspension. Large quantities of slurry and mine tailings require efficient handling, transportation and storage system. The transportation and treatment of kaolin–sand slurry is dependent on its rheological behaviour which is a function of temperature, total solid concentration and pH. In this study, the effects of total solid concentration, pH and temperature on rheological behaviour of kaolin–sand mixture were investigated. These parameters were varied to analyse the viscosity, yield stress, flow index and shear force requirements of the mixed kaolin–sand suspension as a function of these varying parameters. Experimental rheological investigation conducted on rotational stress-controlled rheometer equipped with Peltier concentric cylinder system showed that the kaolin–sand mixture suspension is shear thickening in nature. The shear stress-rate rheograms for the kaolin–sand suspension can be modelled by the Herschel–Bulkley model with high levels of accuracy for pH range of 4–11, temperature range of 20–50 °C and solid concentration of 5–50 %. Solid concentration of the suspension was found to significantly affect the rheological behaviour of the mixture where higher kaolin–sand slurry concentration resulted in greater viscosity and the trend becoming less predictable for solid concentration greater than 50 % by weight. pH was another factor affecting the rheological behaviour of kaolin–sand slurry. pH of 3 or less resulted in the dramatic increase of viscosity of the suspension possibly due to the isoelectric point of the mixture system found between pH of 3 and 4.     

Laboratory Characterization of Cemented Tailings Paste Containing Crushed Waste Rocks for Improved Compressive Strength Development

This paper aims at investigating some physical and mechanical characteristics of cemented tailings paste incorporating different amounts of crushed waste rocks (hereinafter called paste aggregate fill, PAF) for underground stope filling. Different mixture formulations were prepared with three classes of crushed waste rocks (or aggregate) grain size, namely 0/10, 0/15 and 0/20 mm. The amount of crushed waste rocks in the PAF mixtures ranges from 10 to 50% by volume (% v/v) (or 8–45% by mass, %m) of dry mill tailings and crushed waste rocks. The results show that the addition of crushed waste rocks in cemented tailings paste mixtures allows a significant unconfined compressive strength (UCS) development after 28 and 90 days of curing. The highest UCS was obtained from the mixtures containing 50% v/v of crushed waste rocks of class of size 0/15 mm. The PAF mixtures with the coarser crushed waste rocks (class of size of 0/20 mm) exhibit some particles segregation.     

Biodiesel production from three mixes of oils with high free fatty content: quality evaluation and variable analysis

Due to the excessive use of fossil fuels around the world, more environmentally friendly alternatives have been studied. Technologies for the production of ethanol, biogas and biodiesel are focusing on the importance of improving costs and efficiency. Biodiesel can be used in automotive internal combustion, is biodegradable and has no presence of metals, however, it lacks competitiveness versus petrodiesel mainly by the high cost of the pure oils used for its production. The aim of this study was to obtain biodiesel from oil samples with high content of free fatty acids (>1 %) obtained from three fast food restaurants using their molecular weight and acidity index values in order to neutralize the free fatty acids in a one-step reaction and perform a screening for optimal conditions for transesterification. The experimental design consisted of two reaction times (60 and 90 min); four methanol–oil molar ratios—6:1, 10:1, 15:1 and 20:1; and two catalysts (NaOH and KOH) at three concentrations 0.5, 1 and 1.5 % with a constant temperature of 60 °C and 500 rpm. The optimum conditions for the different waste cooking oil feedstocks were established reaching a final yield up to 85.53 % of biodiesel, concluding that there is viability of production through the use of this raw material and free fatty acids neutralization technique, obtaining a biofuel that meets international quality standards.     

Preparation of Uniform Sand Specimens Using Stationary Pluviation and Vibratory Methods

Relative density is an important state parameter that influences the soil behavior. Preparation of sand specimens with uniform density is critical during large-scale laboratory testing in geotechnical engineering. In this study, the details of a stationary air pluviation device used to prepare uniform sand specimens in a large-size test chamber with dimensions equal to 900 mm × 900 mm × 1000 mm (in length, width, and depth) are provided. The proposed device is found to be simple to construct due to presence of only two diffuser sieves with an ability to produce uniform sand beds in a reasonably quick time. Prior to construction of full-scale pluviation device, a scaled-down model of the device with plan dimensions equal to 300 mm × 300 mm is fabricated to perform calibration studies. The range of densities of two gradations of Indian Standard sand (IS Grade II and IS Grade III) obtained using this device for various heights of fall of sand particles and passing through different opening sizes are provided. Relative density in the range of 53–99 % and 74–99 % is achieved for IS Grade II and III sands, respectively. The spatial uniformity in densities is also assessed, and the coefficient of variation (COV) in the density is found to be less than about 7 %. In addition to pluviation method, uniform sand beds are also prepared using pneumatically-operated vibratory method. The target relative density of sand bed is achieved by adjusting the pressure of compressed air inside the vibrator, and the maximum relative density of IS Grade II and Grade III sands from vibratory method is found to be higher than that from pluviation method for the range of pressures chosen in the study.     

废旧轮胎胶粉-黏土混合土的击实性能

废旧轮胎橡胶颗粒用于填埋场衬垫材料改性,有望提高衬垫系统的有效性。击实性能是衬垫设计和施工的基础,但目前缺乏针对性研究,击实机理不够明确。开展废旧轮胎胶粉-黏土混合土的击实试验研究,探讨橡胶颗粒粒径、掺入比等因素对混合土击实性能的影响规律和压实机制。研究表明,当橡胶掺入比从0增大到25%时,胶粉-高岭土的最优含水率增大,胶粉-红黏土的最优含水率减小,变化在2.4%范围内; 混合土的最大干密度从1.65gcm-3减小至约1.40gcm-3; 试验选用的橡胶颗粒粒径对最优含水率和最大干密度差异不显著。在击实过程中橡胶颗粒回弹和橡胶颗粒比表面积变化两种效应下,最优含水率随橡胶掺入比的增加表现出减小(大颗粒时)、不变和增加(小颗粒时)的变化规律,并与基质土的性质密切相关。给出了初步设计时改性黏土含水率和干密度的控制方法,能够基本满足规范中对压实黏土的含水率和压实度的要求,且其渗透系数小于1.010-7cms-1。