Assessment of different agents for stabilisation of a clay soil Estabragh, A. R.; Jahani, A.; Javadi, A. A. ...
International journal of pavement engineering/The International journal of pavement engineering,
01/2022, Letnik:
23, Številka:
2
Journal Article
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The effects of different agents on stabilisation of a clay soil were investigated through a series of laboratory experiments. The selected agents were cement, Ground Granulated Blast Furnace Slag ...(GGBS), mixture of GGBS and MgO (Magnesia) (GGBS:MgO) and mixture of GGBS, MgO and cement (GGBS:MgO:Cement). Mixtures of GGBS:MgO and GGBS:MgO:Cement were prepared at ratios of 3:1 and 3.0:0.5:0.5 by weight respectively. 5%, 10% and 15% of these agents were mixed with soil samples. Atterberg limits and standard compaction tests were conducted on the mixtures. Also, unconfined compressive strength (UCS) tests were performed on compacted samples from the natural soil and the above mixtures at curing times of 7, 14 and 28 days. The results showed that all the used agents cause increase in the strength of the samples and the amount of increase is dependent on the percent of the agents and the curing time. It was revealed that the activation of GGBS with MgO and MgO:Cement is effective in increasing the strength in comparison with GGBS alone. Based on the scanning electron microscopy (SEM) results, it was found that the increase in strength of stabilised soil is resulted from bonding between soil particles and stabilizing agents.
The effect of thermal history on the properties of bentonite was studied through a number of experimental tests. The desired thermal history was created on samples of bentonite by keeping them at a ...fixed temperature (50, 100, 150, 200 and 250 °C) for a specific duration (3, 7, 14 and 30 days). Standard compaction, Atterberg limits, free swelling and swelling pressure tests were carried out on the samples on the dry side of optimum, optimum and wet side of optimum of the compaction curve with desired thermal history. In addition chemical tests were carried out on the flooding water at the end of the swelling test. The results showed that the changes in compaction characteristics were not considerable but the Atterberg limits, free swelling and swelling pressure of the soil were changed due to the thermal history in comparison with the soil without any thermal history. The magnitudes of free swelling and swelling pressure were dependent on the location of prepared sample on the compaction curve. In addition, the changes in Atteberg limits and swelling parameters (amount of free swelling and swelling pressure) were functions of magnitude of temperature and duration of time that the sample experienced the temperature in its temperature history. The effects of temperature and also duration of exposure of the soil to temperature was discussed with the aid of the Diffuse Double Layer (DDL) theory. It was found that the temperature may change the gradation of soil due to cementation of particles as a result of formation of some salts and oxides that help to paste the particles together and change the properties of the soil.
Four new species of Lasiodiplodia; L. citricola, L. gilanensis, L. hormozganensis and L. iraniensis from various tree species in Iran are described and illustrated. The ITS and partial translation ...elongation factor-1α sequence data were analysed
to investigate their phylogenetic relationships with other closely related species and genera. The four new species formed well-supported clades within Lasiodiplodia and were morphologically distinct from all other known species.
In this paper, the effect of glycerol solution on the behaviour of a sediment of a clay soil and its treatment was investigated through a programme of experimental tests. Laboratory tests were ...conducted to study settlement of the clay soil in water and in solutions of glycerol with different concentrations. Also, treatment of the sediments deposited in water and solutions of glycerol was investigated by adding 5%, 8% and 10% cement to these sediments. Atterberg limits, compaction and unconfined compression tests were conducted on treated and untreated sediments. Comparison of the results showed that the behaviour of the sediments that were deposited in water and in different solutions of glycerol are not the same. The results also indicted that the cement is effective in the treatment of sediments deposited in solutions of glycerol and for a given percent of cement and curing time, the degree of treatment is dependent on the percent of glycerol in the solution. Increasing the concentration of glycerol decreases the strength of the sediment with time. Based on SEM analysis, it was found that the fabric of the soil deposited in water is different from those of the soils deposited in solutions of glycerol.
The effect of lime on the yield stress, and more generally the presence of structure in the soil, is usually not accounted for in the design of geotechnical structures. As a result the potential of ...lime treatment or of a structured soil has not been fully exploited. This paper presents a new formulation to account for the effect of structure on the mechanical behaviour for structured soils. A constitutive model is proposed in the framework of the Modified Cam Clay model to describe the behaviour of lime treated soils. The new formulation introduces a limited number of additional parameters, all of which have a physical meaning and can be obtained from an isotropic compression test. Due to similarity in behaviour of lime treated soils and naturally structured soils, the formulation can be applied to both types of soil. It is shown that the proposed model can successfully reproduce the main features of both structured soils such as maximum rate of dilation at softening and degradation at yield. The model can be applied for any structured material regardless of the origin of cementation.
The behaviour of expansive soil with different flooding fluid, i.e. distilled water and solution of glycerol with different percentages of glycerol (10%, 20%, 30% and 40%) was studied through a ...number of cyclic wetting and drying tests. Experimental tests were conducted on compacted samples of the expansive soil in a modified oedometer with different flooding fluids under a surcharge pressure of 10 kPa. The vertical and radial deformations of the samples were determined during different stages of wetting and drying. The results showed that during cycles of wetting and drying, the deformation of the soil decreased with increasing the number of cycles for all flooding fluids. The magnitude of deformation for samples flooded with a solution of glycerol is less than distilled water and this reduction is a function of glycerol concentration. The equilibrium condition of samples with glycerol solution is reached in fewer cycles than distilled water. The results also indicated that the swelling-shrinking deformation was nearly the same when the equilibrium condition was attained. Comparison of the results showed that by increasing the percent of glycerol, these curves were contracted. Furthermore, the paths of wetting and drying converged to an S-shaped curve at equilibrium condition.
The survey for DUST in Nearby Galaxies with Spitzer (DUSTiNGS) has identified hundreds of candidate dust-producing asymptotic giant branch (AGB) stars in several nearby metal-poor galaxies. We have ...obtained multi-epoch follow-up observations for these candidates with the Spitzer Space Telescope and measured their infrared (IR) light curves. This has allowed us to confirm their AGB nature and investigate pulsation behavior at very low metallicity. We have obtained high-confidence pulsation periods for 88 sources in seven galaxies. We have confirmed DUSTiNGS variable star candidates with a 20% success rate and determined the pulsation properties of 19 sources already identified as thermally pulsing AGB stars. We find that the AGB pulsation properties are similar in all galaxies surveyed here, with no discernible difference between the DUSTiNGS galaxies (down to 1.4% solar metallicity; Fe/H = −1.85) and the far more metal-rich Magellanic Clouds (up to 50% solar metallicity; Fe/H = −0.38). These results strengthen the link between dust production and pulsation in AGB stars and establish the IR period-luminosity relation as a reliable tool ( 4%) for determining distances to galaxies, regardless of metallicity.
The survey for DUST in Nearby Galaxies with Spitzer (DUSTiNGS) identified several candidate Asymptotic Giant Branch (AGB) stars in nearby dwarf galaxies and showed that dust can form even in very ...metal-poor systems ( ). Here, we present a follow-up survey with WFC3/IR on the Hubble Space Telescope (HST), using filters that are capable of distinguishing carbon-rich (C-type) stars from oxygen-rich (M-type) stars: F127M, F139M, and F153M. We include six star-forming DUSTiNGS galaxies (NGC 147, IC 10, Pegasus dIrr, Sextans B, Sextans A, and Sag DIG), all more metal-poor than the Magellanic Clouds and spanning 1 dex in metallicity. We double the number of dusty AGB stars known in these galaxies and find that most are carbon rich. We also find 26 dusty M-type stars, mostly in IC 10. Given the large dust excess and tight spatial distribution of these M-type stars, they are most likely on the upper end of the AGB mass range (stars undergoing Hot Bottom Burning). Theoretical models do not predict significant dust production in metal-poor M-type stars, but we see evidence for dust excess around M-type stars even in the most metal-poor galaxies in our sample ( ). The low metallicities and inferred high stellar masses (up to ∼10 ) suggest that AGB stars can produce dust very early in the evolution of galaxies (∼30 Myr after they form), and may contribute significantly to the dust reservoirs seen in high-redshift galaxies.
The critical state concepts have been investigated for an overconsolidated unsaturated silty soil through a comprehensive set of controlled suction triaxial laboratory experiments. The experimental ...tests were conducted in a specially designed double-walled Bishop and Wesley triaxial cell on samples of unsaturated silty soil. Isotropic loading, unloading, and triaxial drained shear tests were performed on samples of unsaturated silty soil with different overconsolidation ratios at various suctions. The data from the triaxial tests were used in the development of a critical state framework for overconsolidated unsaturated silty soil. The framework is defined in terms of four state variables: mean net stress (p'), deviator stress (q), suction (s), and specific volume (v). The results show that the critical state lines in q:p' space for different soil suctions are not parallel and merge with each other. The slopes and intercepts of these lines are functions of suction. However, the critical state lines are nearly parallel in the v - ln p' plane except under saturation conditions, and the slope and intercept of these lines are also functions of suction.
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