Decrease In Dry Density Research Articles

INVESTIGATION ON THE SWELLING PROPERTIES AND MICROSTRUC-TURE MECHANISM OF COMPACTED GAOMIAOZI BENTONITE

Bentonite has the property of swelling when meeting water. It is a desirable buffer/backfill material in the deep geological disposal for high-level radioactive waste. The expansibility is one of the most important properties for bentonite as the buffer/backfill material, and is influenced by a number of factors. For study the expansibility of bentonite, Gaomiaozi(GMZ)bentonite was taken as the research object. Gaomiaozi(GMZ)bentonite had been proposed as the first choice of buffer/backfill material for the high-level radioactive waste disposal in China. Its expansibility was studied by the constant volume swelling test method which is one of the commonest methods for measuring the swelling pressure of bentonite. In these tests, water content and dry density were chosen as the control variable. Two types of dry density and three types of water content were adopted in the tests. Results of the swelling tests show that the shape of swelling curves and the maximum swelling pressure depend on the water content and dry density of the bentonite samples. There are conspicuous double-peak shapes of the swelling curve for the samples with low dry density. When the dry density is high, the swelling curves have different shapes with different water contents. The curve's shapes change from double-peak to smooth curve with the water content increasing. For analysis of the results of swelling tests, the mercury intrusion porosimetry(MIP)test has been carried out. MIP test results indicate that the pore size distribution curves of samples also depend on the water content and dry density, with the volume of inter-aggregate pores increasing as the water content or dry density decreases. In accordance with the relevant researches, the swelling curve of GMZ bentonite is deeply influenced by the volume of the inter-aggregate pores. When meeting water, the bentonite aggregates absorb water and swell quickly. When the inter-aggregate pores are large enough, there will be sufficient space for swelled aggregates to form a provisional structure. The provisional structure will collapse with the swelling pressure reach the limit load. Then the measured pressure fall and inner structure of bentonite recombination. The hydration is continuous so that the curve will get the second peak. Therefore, a double-peak structure can be observed when the space of inter-aggregate is great. With the volume of inter-aggregate pore decrease, the swell curve of bentonite changes from a double-peak structure to a smooth curve.

Soil aggregation and root growth of perennial grasses in a constructed clay minesoil

Studying constructed soils (anthropogenic) in mined areas provides an opportunity to expand the existing knowledge about the formation and stabilization of aggregates, due to the magnitude of ecosystem disruption, that creates a “zero time” scenario. The aim of this study was to evaluate the relationship between the aggregation and the root growth of perennial grasses 103 months after the reconstruction of a constructed minesoil, in a coal mining area located in Candiota/Rio Grande do Sul State, Brazil. The evaluated plant species were Hemarthria altissima, Paspalum notatum cv. Pensacola, Cynodon dactylon cv. Tifton, and Urochloa brizantha. The grass roots promoted the recovery of the soil physical condition in the 0.00–0.10m layer, with a decrease in dry bulk density and an increase in soil macroporosity related to the formation of new aggregates. The decrease in root development of all species below 0.10m depth is the result of the restrictive soil physical conditions, with high bulk density and low macroporosity related to aggregates formed originally by compression. The results of root and soil attributes found in this study suggest a different soil-aggregation hierarchy in compacted constructed minesoils, where first a disintegration occurs of large cohesive aggregates formed by compression followed by a re-aggregation process, with sequential re-formation and stabilization of aggregates. The Urochloa brizantha showed a greater root density, volume, length and area, thus presenting a greater potential to recover the physical attributes of the degraded areas, especially those in the compacted layer below 0.10m depth. The recommendation of this and other species in the reclamation of constructed soils after coal mining should take into account the thickness of the topsoil layer because the roots of these species can grow into the overburden layers and thus accelerate the sulfurization process. The recovery of physical attributes of the constructed minesoil, especially below the 0.00–0.10m layer, is a slow process, possibly due to the low accumulation rates of organic carbon in this layer.

Effect of fly ash, construction demolition waste and lime on geotechnical characteristics of a clayey soil: a comparative study

Improvement of strength and subgrade characteristics of soil by stabilization is one of the popular techniques nowadays. The use of construction demolition (C&D) waste in soil stabilization is still under research as much work has not been done in this area. This paper presents a comparative study of utilization of fly ash, C&D waste and lime in soil stabilization. A number of tests such as differential free swell, pH, compaction, unconfined compressive strength (UCS) and California bearing ratio (CBR) were conducted to study the effect of addition of fly ash, C&D waste and lime on geotechnical characteristics of soil. Based on results, it is concluded that differential free swell and maximum dry density decrease, whereas pH, UCS and soaked CBR value increase with addition of fly ash, C&D waste and lime. The increase in UCS is almost the same for lime and C&D waste at 7 days which indicates that the usage of C&D waste compared with that of lime is economical, whereas if used in pavement subgrade lime is better material because of higher CBR value. The UCS at 28 days is more for fly ash compared with that for lime and C&D waste.

The effect of freeze–thaw cycles on physical and mechanical properties of granitoid hard rocks

This paper presents the influence of freeze–thaw cycles on physical and mechanical properties of Alvand granitoids hard rocks, in the west of Iran. For this purpose, three different types of Alvand granitoid rocks were selected and studied. For assessment of freeze–thaw weathering effects, a long-term freeze–thaw test was carried out for 300 cycles. P-wave velocity, porosity, water absorption, dry density, uniaxial compressive strength, and tensile strength of specimens were determined prior to doing the test and after every 50 cycles. The results of this study show that, by increases in the number of freeze–thaw cycles, uniaxial compressive strength, tensile strength, dry density, and P-wave velocity decreases, whereas the water absorption and porosity increases. P-wave velocity and tensile strength were also suggested as the best indicators to assess the effects of freeze–thaw cycles on the physical and mechanical properties of the studied granites.

Behavior of cement-stabilized fiber-reinforced pond ash, rice husk ash–soil mixtures

In order to study the effect of addition of rice husk ash, pond ash, cement and fiber on the compaction and strength behavior of clay, a series of tests were performed. Modified proctor tests were conducted to evaluate the compaction behavior, while unconfined compression tests (UCS) and split tensile strength (STS) tests were conducted to evaluate the strength properties of clay. For testing purpose specimens were prepared with different amount of admixtures. Pond ash (PA) and rice husk ash were added to clayey soil at ranges of 30–45% and 5–20%, respectively. Polypropylene fibers of length 6 mm and 12 mm are used in this study with different contents as 0, 0.5, 1.0 and 1.5% by dry weight of mix whereas cement contents used are 0, 2 and 4%. To study the effect of curing on strength property, the specimens were cured for 7, 14, and 28 days and tested. Test results have shown that the maximum dry density decreases and optimum moisture content increases with the addition of admixtures, but fiber inclusion have marginal effect. The results shows that the inclusion of fiber reinforcement within un-cemented and cemented soil caused an increase in the UCS, STS and axial strain at failure, decreased the stiffness and the loss of post-peak strength, and changed the cemented soil brittle behavior to a more ductile one. Strength of clay improves by the addition of admixtures and fibers. The study has shown that combination of clay, RHA, PA, cement and fiber can be used as light weight fill material in different structures like embankment, retaining wall etc.

Compaction characteristics of fine grained soil and rice husk ash mixture

This study presents the compaction characteristics of fine grained soil and rice husk ash (RHA) mixture. Three types of fine grained soils viz., montmorillonite clay, kaolinite clay, and one local soil has been used in the present study. From the compaction tests results it is observed that with increase in RHA content (0–30%) maximum dry density (MDD) decreases and also optimum moisture content (OMC) increases irrespective of types of fine grained soil. Based on the experimental data, a number of linear regression models have been developed to estimate MDD and also OMC of fine grained soil and RHA mixture. Empirical models also presented to estimate dry density in terms of water content of dry side of optimum or water content of wet side of optimum, compaction energy, RHA content, and also specific gravity of fine grained soil and RHA mixture. The above models may be useful for the field engineers within the range of compaction energy from 300 kJ m−3 to 2700 kJ m−3, RHA content from 0%–30%, specific gravity of fine grained soil and RHA mixture from 2⋅311–2⋅750, and OMC for soil from 16⋅8%–37⋅0%.

The Tests on the Lime-Treated Expansive Soils Compaction Characteristics

The compaction characteristics of the lime-treated expansive soils from the planning airport in China's Ankang were studied through the heavy compaction tests. The results show that all these elements such as lime content, water content, soil height, wetting time have a certain effect on dry density. As the lime quality ratio increases, the optimum water content under heavy compacting standard of improved soils increases but the maximum dry density decreases. With the increase of lime content, the effect of water content on dry density decreases while the water content near to its optimum value. Soils with the lower height have higher dry density when compaction energy, lime content and water content unchanged. As the wetting time increases, the maximum dry density shows a decreasing tendency until after 48 h it remained stable. It indicates that with the same lime content the order of primary factors influence on dry density are water content, wetting time, soil height. Finally, the lime stabilizing principle to expansive soil is explained through by applying scanning electron microscope technique.

Processes and impacts of acid discharges on a natural substratum under a landfill

Analyses of substratum samples under a landfill were performed to assess the pollution impact of waste over a clay–sand material after nine years of exposure. These samples presented different illite/kaolinite ratios and an acid pH, especially low near the waste/soil contact in a 1–1.5m soil thickness with low density and despite the basic pH of the collected actual methanogenic leachate. This study has raised the effects of a presumably acid stage in the waste leachate on the substratum final quality of clay and its physical–chemical properties as an attenuation buffer. These effects were the dissolution of carbonate minerals, decrease of dry density, increase of hydraulic conductivity, release of metals and formation of clays with low cationic exchange capacity (CEC) as kaolinite. The large presence of H+ and Al(OH)3−xx+ depleted the neutralizing capacity of the substratum and occupied exchangeable sites, decreasing therefore the available sites for retaining leachate pollutants, which traveled further than the first-meter depth of the substratum. In order to combat and prevent pollution as well as to preserve the good barrier properties under new landfills it is proposed to select illitic materials better than kaolinitic substratum, to avoid acid landfilling and if not possible to add lime.

Compaction Characteristic of Lime Modified Expansive Soil

Through compaction test discussed about the compaction characteristics of expansive soil by lime modified in middle of Shandong province. The results show that the optimum moisture content is lower when the expansive soil is cured by dry compaction method, and the maximum dry density is higher. Compaction curve appeared the phenomenon of two peaks when expansive soil is cured by wet compaction method.Lime content of lime improved expansive soil, particle size composition, age and compaction function have influence on compaction curve.With the increase of the quantity of lime, the optimum moisture content increases, the maximum dry density decreases. With the age growth, the optimum moisture content increase slightly,the maximum dry density decreases slightly. The bigger the compaction work, the smaller moisture content is, the larger the maximum dry density is.

Study on the Physics and Mechanical Properties of Freeze-Thaw Soil and Undisturbed Soil

The parameter of the undisturbed soil cannot be used simply in the engineering for the characteristics varied considerably. So the physics and mechanical characteristics of freeze-thaw soil are very important in the freezing method engineering. The physics and mechanical properties of freeze-thaw soil and undisturbed soil are compared by the experiment. And the data of test are shown that after the samples are frozen and thawed, density, dry density decrease and plastic limit decrease, void ratio increase a little, other physicals are similar. Permeability of mild clay greatly increased. Compressibility of mild clay decrease, but compressibility of fine sand increase. This can be used reference to model test, numerical analysis and project designing.

Study on the Physics and Mechanical Properties of Freeze-Thaw Soil and Undisturbed Soil

The parameter of the undisturbed soil cannot be used simply in the engineering for the characteristics varied considerably. So the physics and mechanical characteristics of freeze-thaw soil are very important in the freezing method engineering. The physics and mechanical properties of freeze-thaw soil and undisturbed soil are compared by the experiment. And the data of test are shown that after the samples are frozen and thawed, density , dry density decrease and plastic limit decrease, void ratio increase a little, other physicals are similar. Permeability of mild clay greatly increased. Compressibility of mild clay decrease, but compressibility of fine sand increase. This can be used reference to model test, numerical analysis and project designing.

Cover Crops and their Effects of Time Harvesting on the Control of Weed in Citrus Orchards in Northern Iran

Weed are one of the most important problems in newly established orchards.Weed compete with young trees of citrus trees can reduce the growth. In order to investigation of effect of cover crops (Vicia sativa L. and Trifoliumalexandrinum L.) to control weed in citrus orchards in northern Iran, This studywas conducted by randomized complete block design with thirteen treatment and three replication (8 treatments of the two cover crop with different harvest times, two treatments of herbicide, plowing and weeding and treatment of control). The results of this study showed, berseem clover to common vetch has better performance in reduced weed . There was a noticeable decrease of dry and wet weight and density of weed in harvest and drop off residuesof berseem clover on fifth of April.spring is the best time to harvest it. When we use common vetch as a cover crop, the best time to harvesting is the middle spring.

Effect of Humic Acid on Physical and Engineering Properties of Lime-Treated Organic Clay

The study of lime stabilisation has been established for a long time and its implementation in geotechnical engineering has improved regularly. The present work deals with the stabilisation of organic clay using hydrated lime, which resulted in three favourable combinations of artificial organic clay. The idea of using artificial organic clay is to reduce possible inconsistencies that may happen during testing and to ensure the repeatability of the results of the test. This is vital for comparative study that involves varying additive contents and curing periods. Due to the complex nature of natural soils, a series of experiments was carried out using the manufactured kaolin which represents the clay mineral and different commercial humic acid contents (0.5%, 1.5%, and 3%), which are the main constituents of organic matter that impede the lime stabilisation process. The amount of hydrated lime (5%, 10% and 15% based on dry weight of soil) was taken beyond the initial consumption of lime (ICL) value. Results are presented in three aspects: (1) behaviour of physical properties, (2) shear strength development and (3) microstructure changes due to shear strength. Results produced by physical testing show that the presence of humic acid has a drawback effect on untreated and limetreated organic clay. The decrease in specific gravity value is accompanied by a decrease in dry density and strength of kaolin prepared with higher humic acid content. Plasticity of untreated organic clays also decreases with increased humic acid content. Some notable increases in shear strength at 7 days curing period were observed in the limetreated sample for up to 5% lime content. However shear strength of lime-treated organic clay decreased at longer curing periods. A slight decrease in shear strength occurred for samples treated with 0.5% and 1.5% humic acid. The significant decrease in shear strength can be observed at 3% humic acid content. Thus it can be concluded that lime stabilisation is not effective with the presence of more than 1.5% humic acid at longer curing periods. A microstructure analysis was carried out on untreated and limetreated specimens at OLC (5%) with 1.5% and 3% humic acid content at a 14 days curing period, which represent the duration of the modification process. The findings reveal that the fabric of untreated organic clay for both specimens prepared at different humic acid contents reveals no apparent aggregations. More pore spacing was clearly observed for lime-treated clay minerals with 1.5% humic acid than for 3% humic acid soil structure. Flocculating structure was more visible at lower humic acid contents with particles dispersed by large openings.

Effect of seasonal frost conditions on the permanent strain behaviour of compacted unbound granular materials used as base course

Frost action affects permanent strain behaviour of unbound granular materials' performance by causing an increase in saturation degree as well as a decrease in density. This research aims to improve the understanding on how the base granular materials' permanent strain behaviour changes through seasons. In order to characterise this behaviour, eight permanent strain tests were performed at various water contents, densities and test conditions. Freeze and thaw cycles, for drained and undrained testing conditions, were applied to samples to measure the contribution of frost action to the plastic deformation mechanisms. From the obtained results, it is concluded that the effect of the freeze–thaw cycle on the permanent strain behaviour of unbound granular materials used as pavement base is mostly explained by the increase of water content and, to a lesser extent, by the decrease of dry density.

Influence of using rice husk ash in soil stabilization method with lime

In clayey lands, swelling problem causes vertical displacements on road subbase, and finally, failure in pavement occurs due to lack of appropriate drainage systems. One popular and inexpensive method of soil stabilization is using lime. Investigations indicate that based on environmental and atmospheric conditions, the chemical reaction of lime and clayey soil is not accomplished well, owning to low temperature and high humidity. This paper aims to investigate the influence of adding rice husk ash on the reaction between soil and lime and lime reaction and determine soil physical and mechanical characteristics. Therefore, sufficient laboratory soil tests, such as Atterberg limits, compaction, California bearing ratio (CBR), and direct shear test are carried out, and the results are analyzed. The results generally indicate that adding lime and rice husk ash (RHA) causes a decrease in dry density and an increase in optimum water content. Increasing lime and RHA causes a decreasing rate in soil liquid limit and plastic limit. Adding lime and RHA to the soil causes a decrease in deformability of soil samples and gives more brittle materials. Also, this action causes an increase in shear strength. Moreover, increasing in CBR amount under the influence of increasing RHA is one of the main results of this paper.

Experimental study of the effect of fines content on dynamic compaction grouting in completely decomposed granite of Hong Kong

This paper addresses the effects of fines contents on the mechanical behavior of CDG (completely decomposed granite) during dynamic compaction grouting. The first set of tests involved adding different amounts of kaolin clay into CDG to study the effects of fines contents on the compaction characteristics, permeability, consolidation behavior and shear strength of soils. It is found that, as the fines content increases, the dry density decreases, however the optimum water content increases. In addition, the permeability decreases due to reduction of void ratio, and the coefficient of consolidation increases with higher fines content. Furthermore, with increasing fines contents, the shear stress tends to be constant after it reaches the peak strength. However, when reaching the peak value, the shear stress reduces with further adding of fines content. In the second set of tests, the dynamic compaction grouting tests are carried out to study the effect of fines content on the compaction efficiency of Hong Kong CDG. It is found that, the compaction efficiency increases with increasing fines content, and reaches the peak compaction efficiency when the fines content reaches 6%, and then the compaction efficiency drops abruptly from a peak value of 0.55–0.25 when the fines content increases from 6% to 8%. However, when the fines content increases from 8% to 41%, the compaction efficiency decreases very slowly.

Effect of Soil Moisture Content and Dry Density on Cohesive Soil–Geosynthetic Interactions Using Large Direct Shear Tests

Geosynthetics have increasingly been used to reinforce many earth structures and are now a well-accepted means to improve engineering properties of various types of soil. However, most previous studies and applications of geosynthetic stabilization are confined to noncohesive soils. Few research efforts have been dedicated to the feasibility and benefits of geosynthetic reinforcement on cohesive soils. This paper presents the results of an extensive laboratory testing program using a large direct shear device, in which four different soils including one sand and three clays of different plasticities were reinforced by three different geogrids and one woven geotextile. Reinforcement mechanisms were analyzed and the soil-geosynthetic interface parameters were obtained from the testing results. The increase in molding moisture content and/or decrease in dry density caused an appreciable reduction in interface shear resistance, which suggests that it should be more rational to use interface parameters of soils at their 95% maximum dry density and moisture content 2% above their optimum values. This study also provides a basis for future research and modeling the behavior between cohesive soils and geosynthetics.

Lime stabilisation of the chicoco mud of the Niger Delta

Chicoco mud is a very soft and extremely compressible organic marine mud found extensively and to considerable depths within the saline tidal flat or mangrove swamp of the Niger delta region in southern Nigeria. Natural chicoco mud is highly compressible barely able to support an average human weight but air-dried chicoco has been used successfully by the natives for shore protection, etc. especially if placed above water. In this study, varying percentages (ranging from 1% to 9%) of industrial and locally produced (from periwinkle shells) slaked-lime were used to stabilise chicoco. It was observed that neutralisation of acidic “air-dried” chicoco by basic lime inhibited the expected ion-exchange reaction and its attendant improvement in mechanical properties. As a result and as lime (industrial or locally-produced) content increases, maximum dry density (MDD) decreases, optimum moisture content (OMC) decreases while unsoaked CBR maximises within low lime content of about 4%. Also, significant improvement in all three parameters (MDD, OMC and CBR) was recorded with saltwater addition. However and with maximum unsoaked CBR of only 12.5%, lime-stabilised chicoco can only produce subgrade materials in roadworks, i.e. not unsuitable for sub-base and base-course materials.Keywords: chicoco mud, Niger delta, lime, periwinkle, stabilisationGlobal Journal of Engineering Research Vol.4 (1&2) 2005: 69-73

An Investigation into the Geotechnical Properties of Soil-Tyre Mixtures

The work presented in this paper investigates the potential of using waste shredded tyre in soil-tyre mixtures for specific engineering applications. Bentonite, kaolin and kaolin-lime were used as the base clayey soil types. Soil-tyre mixtures containing up to 20% tyre were tested for compaction, unconfined compression strength, permeability and leachability. The results show that the compacted dry density, strength and permeability decrease with the introduction of the tyre and decrease further as the amount and size of tyre particle is increased. The permeability results, which contradict other published work, could mean possible application as landfill cover and landfill liner material. The TCLP leaching test indicated higher concentrations of heavy metals in the leachates than drinking water standards with the exception of one of the kaolin-lime-tyre mixtures. Results from less severe leaching tests than the TCLP test should be investigated before firm conclusions are made. These results are encouraging for use of waste shredded tyre in soil-tyre mixtures. It could prove to be both economical and a safe method of the disposing of rubber.

Use of rice husk ash for soil stabilization

Rice husk is one of the largest farm refuse in Malaysia and is put into use as a fuel. building bricks, among other things. A large quantity is being disposed off by dumping or by burning and is becoming a menace. An attempt has been made in this investigation to make use of the rice husk ash to stabilize clayey soil along with lime. The effect of the quantity of the admixture of lime and rice husk ash on soil index properties, compaction and strength characteristics are studied. The influence of the ratio of the quantities oflime and rice husk ash for a given quantity of admixture on the soil behaviour are also investigated. It has been found that there is a decrease of maximum dry density and an increase of optimum water content when the soil is treated with the admixture oflime and rice husk ash. The plasticity index of the soil is decreased by treating the soil with the admixture oflime and rice husk ash. The effect is more significant after a curing period of 28 days. It has also been found that there is an optimum quantity admixture at which the soil attains peak strength. The peak strength increases as the curing time increases.