جستجوی مقالات مرتبط با کلیدواژه « Stabilization » در نشریات گروه « عمران »

Geopolymers produced by the reaction between solid aluminosilicate and alkaline metal solution have been classified as the third generation binders after lime and portland cement. In current study, the application of the above method to modify the behavior of the yellow marl soil of Tabriz has been evaluated by unconfined compression tests. For this purpose, zeolite and metaclay have been used as sources of silica alumina and sodium hydroxide solution has been used as an alkaline activator. The results of tests have shown the very appropriate effect of the geopolymerization mechanism in treatment the resistance of carbonated clay soil. Meanwhile, the zeolite geopolymer samples have higher resistance than the metaclay ones in all combinations and curing times. The effect of alkaline solution concentration on the strength of zeolite and metaclay geopolymer samples was not the same, so that in the metaclay samples, increasing the molarity of alkali had a negative effect on results. Also, the results show that the rate of change of resistance with time depends on the concentration of alkaline solution so that the treatment effect reduces with inhancement of alkali content. In the optimal sample of zeolite geopolymer (15% zeolite, 12 M alkaline), the uniaxial resistance is about 90.2 kg/cm2, which is about 26 times yellow marl one wherease the optimal metaclay geopolymeric matrix (15% matrix, 4 M alkaline solution) has obtained an unconfined compression strength of about 17.86 kg/cm2. Also in the geopolymer samples, the failure strain has declined by 50% compared to the pure soil.

Saline soils are one of the types of problematic soils which are very vulnerable to dissolution and swelling phenomena. This type of soil has been observed in many parts of Iran and has been used as road subgrade. To enhance the resistance properties of salt beds, various methods are usually used, including chemical stabilization, and the geotechnical properties of stabilized salt beds are evaluated with field and laboratory tests. However, estimation of some main parametersو required for road design, such as modulus of resilience, is dependent on the use of three-dimensional cyclic tests, which requires spending considerable time and cost. This article’s aim is to investigate the traffic loads effect on saline soil subgrade stabilized with cement and carbonated waste, by modeling the modulus of resilience parameter via finite elements method. The natural saline soil of this research was stabilized with different percentages of type 2 Portland cement and a type of carbonated waste, without treatment or treated with two different stabilization methods. Then, several resistance tests such as direct shear test, unconfined uniaxial compressive strength and California bearing ratio (CBR) were done on the samples. The obtained shear strength parameters were used in the modeling of the modulus of resilience. Considering the inherence of traffic loading and the type of test, after examining various soil constitutive models, the small strain hardening soil constitutive model was chosen for this analysis. After performing the modeling steps, including determining the model parameters, developing and running the model, analysis of the results showed that modulus of resilience has exponential relationship with the sum of the main axial and confining stresses. The model coefficients’ relationship was determined and shown using multiple regression analyses. Also, the correlation between modulus of resilience and California bearing ration (CBR) are presented.

One of the suggested techniques to inhibit the spread of contaminants in the soil is cement-based stabilization/solidification. The production of hydration products and the attainment of an alkaline pH are the two primary processes in this method. In natural conditions, contaminants enter the soil simultaneously and in combination with each other. The simultaneous presence of organic and heavy metal contaminants alters how the soil-cement system interacts with each contaminant. The objective of this study is to compare the leaching and retention amount of cadmium and phenol separately and simultaneously in cement-based stabilization/solidification. In this context, the TCLP test has been used to assess the leaching amount of phenol and cadmium, as well as their retention capacity in single and combined systems. An X-ray diffraction test was also carried out to examine the microstructure of the stabilization/solidification process. The results indicate that the retention percentage of phenol in the presence of cadmium did not differ much compared to the single system, while the amount of cadmium retention decreased in the presence of phenol. In a combined system, the simultaneous presence of phenol and cadmium causes a reduction in the intensity of the C-S-H peak compared to single systems. However, the presence of cadmium had a greater effect on reducing the intensity of the C-S-H peak than phenol. Furthermore, in the presence of cadmium, the amount of phenol extracted during the TCLP test has increased compared to the single system.

The presence of heavy metal contaminants in clays causes changes in soil properties, which increases the risk of contaminant transport into the clay layer. Various techniques have been developed recently to remediate contaminated soil. These methods include electrokinetics, biological treatment, and immobilization. Among them, cement-based stabilization/solidification technique is very common. Generally, cement-based systems are frequently used because of their affordability and great durability. This method uses the two mechanisms of chemical stabilization and physical solidification to retain heavy metals and decrease the mobility of contaminants. Even though several researches have been performed to address the different aspects of cement-based solidification/stabilization, there has been a lack of research on the stabilization/solidification of heavy metals in the presence of two different heavy metal ions. Therefore, the objective of this study is to determine to what extent the pH variations affect lead and cadmium retention and release in single and double-component cement-based stabilization/solidification systems. To accomplish the aforementioned objective, first, the retention capacity of lead and cadmium, in cement-based S/S of contaminated bentonite in single and double-component heavy metal systems is investigated. The effect of pH on the stabilization/solidification process was determined by conducting a series of XRD tests in order to investigate and differentiate the stabilization and solidification mechanisms. In the next step, the amount of released cadmium and lead ions during the TCLP test was determined in single and double-component systems in order to investigate the effect of pH and the simultaneous presence of lead and cadmium in the release of these heavy metals. According to the achieved results, the maximum retention capacities of lead and cadmium occur in the pH ranges of 8.5 to 11 and 10 to 12, respectively. Furthermore, retention in the double-component system is always lower than that of the single-component system, assuming a similar initial concentration. In addition, XRD results illustrate that the intensity of the peaks of cadmium and lead chemical compounds has increased for the samples their pHs take place in the safe zones. This indicates an increase in the contribution of the stabilization mechanism. According to the results of this paper, at a similar contaminant concentration, the intensity of the C-S-H peak increases with an increase in cement percentages. This indicates progress in the contribution of the solidification mechanism in the retention of heavy metals. Still, the release of these heavy metals is always lower than the maximum allowable value reported by the US EPA in the above-mentioned pH ranges. Moreover, the results of this research show that the amount of released cadmium and lead in the double-component system is more than that of the single-component system, assuming similar initial concentrations. Based on the definition of the safe zone, in the defined pH range, the contaminant is retained during the TCLP test mainly by chemical stabilization (precipitation). In fact, in the above range, an increase in the amount of cement has not shown a significant effect on the amount of heavy metal desorption. This finding is supported by the results of retention tests.

Using new and environmentally friendly materials to stabilize problematic soils is one of the challenges facing geotechnical engineers. Nanoclays are highly reactive due to their high specific surface area, low specific gravity, fine particles, and are also considered as an effective and environmentally friendly stabilizer due to their uniformity with soil materials. In the present study, the effect of Nanoclay on the behavioral properties of Kermanshah's clay fine-grained soil has been evaluated. For this purpose, after having conducted index and identification tests on the natural soil, Nanoclay was added to the studied soil with 0.5, 1, 2, and 4 percent by weight of the dry soil, and Atterberg, consolidation, unconfined compressive strength and California bearing ratio tests were conducted on these samples in curing periods 1, 14, 28 and 60 days. Also, the durability of the stabilized samples was investigated by applying wet-dry cycles, and to investigate the effect of Nanoclay on the soil microstructure, imaging was captured from unstabilized and stabilized samples by scanning electron microscopy. The results show that the stabilization performance is significantly dependent on the amount of Nanoclay and curing periods. Also, according to the results, the optimal amount of Nanoclay is 4%, and the presence of this amount of Nanoclay and increasing curing periods has increased the plastic index, compressive strength and soil bearing ratio and decreased the coefficient of consolidation, settlement, Compression, permeability, and soil swelling. It is noteworthy that soil durability against environmental conditions has also increased.

Today, soil and groundwater contamination by toxic and dangerous pollutants has been raised as a global environmental problem. Soil contamination by heavy metals, especially cadmium (Cd), is a big problem with harmful effects on human health and the earth's ecology. This heavy metal also affects the geotechnical properties of the soil, leading to irreparable effects on the soil beneath structures. One of the efficient and economical methods to rehabilitate soil contaminated with Cd is the stabilization of this toxic metal in the soil by zero-valent iron nanoparticles. The present study is conducted on the effect of heavy metal cadmium contamination on some geotechnical characteristics of soil using Etterberg limit tests (liquid limit and plastic limit), uniaxial compressive strength (UCS), and compaction. Next, this contamination is stabilized in soil by using zero-valent iron nanoparticles, and the characteristics of the modified soil are examined. For this purpose, these nanoparticles were prepared by reducing Ferric Chloride (FeCl3) with sodium borohydride (NaBH4) in a vacuum environment. The laboratory results illustrate the high efficiency of these synthesized nanoparticles in removing ionic cadmium in the sample so that the amount of absorbable Cd in the samples was significantly reduced by using them in optimal conditions. The results show a very high effect in changing the amount of kaolinite and cadmium and the presence of nanoparticles on the soil’s geotechnical parameters. Also, the results of the unconfined compression tests showed that the uniaxial stress of samples with iron nanoparticles increased by 45.6, 63, 67.1, and 67.7%, respectively,

Marl or marl clays are named for carbonated soils with the amount of carbonate in varying proportions from 20 to 55% (Elert et al., 2017). Marls are one of the most important problematic soils that not only the problem of volume changes but also their bearing capacity is lower than coarse-grained beds, so not meet the load-bearing goals of engineering structures. Different improvement methods are proposed to improve the engineering characteristics of problematic soils, the most common is using of lime for this purpose in clayey soils (Al-Mukhtar et al., 2012 and Obuzor et al., 2012) But this substance is less effective in marls (Ghobadi et al., 2014 and Ureña et al., 2015). According to the history of soil modification, the geopolymerization method can be introduced as the third generation of cementation methods after lime and cement (Li et al., 2010). Geopolymers are alkaline activated bonds with low calcium and medium to high aluminum produced by the reaction between alkaline hydroxide solution and materials containing alumina silicate (Provis et al., 2009 and Yung-Ming et al., 2016).The purpose of this research is using the geopolymerization technique to stabilize Tabriz carbonate clay with the approach of controlling deformations and increasing strength. To achieve this outcome, laboratory studies have been carried out on Tabriz green marl with alkali activated zeolite and metaclay as sources of alumina silicate to form cemented bonds. The alkali activator used in this study is sodium hydroxide with different concentrations to achieve optimal results. For this purpose, multiple tests of uniaxial compressive strength have been used to evaluate the strength of stabilized soil. The effective parameters studied in the current research can be referred to the weight percentages of materials containing alumina silicate (zeolite and metaclay), curing time and molarity of the alkaline solution (NaOH).

One of the most important reasons for the instability and failure of river bridges is the scouring around its piers and abutments during floods. In the recent years, the issue of local scouring has been widely studied by various researchers and different methods have been proposed to control scouring, such as the use of riprap, gabion, collars, concrete blocks, sacrificial piles, groove and cables. In this article, firstly, various methods of protection against scouring have been introduced and previous studies have been reviewed. In the following, from a practical and executive point of view, the use of riprap, concrete blocks, gabion and the construction of apron and cut off wall, which are among the existing and common methods to reduce bridge scouring in the presence of shallow foundations (foundations without piles) are reviewed and compared. All the mentioned methods are classified in the category of bed-armoring. The design and executive considerations are presented in each case and the advantages and disadvantages of each method are stated. Finally, according to the different conditions of the river and the bridge structure, the most appropriate method has been proposed in terms of execution, economy and maintenance.

Cement-based stabilization/solidification is a commonly used method to prevent the transportation of heavy metal ions in soils. The main objective of this paper is to investigate the controlling mechanisms in cement-based stabilization/solidification of Pb ion-contaminated bentonite under two different curing conditions: closed and open systems. In an open system, the stabilized/solidified sample continues to have access to free water, while in a closed system, the stabilized/solidified sample is prevented from accessing any external water after initial mixing. To achieve this objective, a series of geo-environmental experiments, including pH, solubility measurements, TCLP, and XRD, were performed. In the first step, the bentonite sample was contaminated with 100 cmol/kg-soil of lead nitrate. After achieving equilibrium, the contaminated sample was stabilized/solidified with 15% cement. The results indicate that when 15% cement is applied to the contaminated bentonite, the pH ranges from 10.5 to 11.5, which is a safe domain for lead precipitation. In other words, the minimum required percentage of cement for stabilization/solidification is the quantity in which the pH of the system is in the necessary range for heavy metal precipitation. This quantity is generally a function of the type and concentration of the heavy metal contaminant. According to the experimental results of this research, the method of curing does not have a noticeable impact on the stabilization process of stabilized/solidified contaminated bentonite. However, the XRD results show that more pozzolanic components have formed in the closed system. Therefore, the achievement of EPA criteria for TCLP experiments in cured samples in the closed system is attributed to the more significant progress in pozzolanic interaction and more formation of C-S-H and C-A-S-H components at 28 days for cured samples under closed conditions.

Stabilizing materials can be used as a soil improvement technique when dealing with inappropriate soils. This study investigates the effects of wetting and drying cycles on the clayey soil stabilized with Calcium Lignosulfonate and also polyethylene fibers. For this purpose, unconfined compression strength and durability of the prepared samples under wetting and drying cycles are investigated. Atterberg limit tests, standard compaction tests and unconfined compression tests have been performed on the prepared samples. Also, the optimum curing duration for soil stabilized with lignosulfonate is investigated. The results show that lignosulfonate-stabilized clay was not sufficiently durable against wet and dry cycles. Based on this result, the stabilization of clay with lignosulfonate stabilizer has a great weakness that is the main drawback to the use of this stabilizer. Addition of 4% polyethylene fibers increases the durability of stabilized samples up to 600% against wet and dry cycles. Also, adding polyethylene fibers to stabilized clay soil with lignosulfonate reduces the weight loss of the materials (70%).

Heavy metals are found in high concentrations in industrial wastewater and cause damage to humans and other organisms by entering to water, soil and food chain. Stabilization and solidification is a common process in the treatment of sludge containing heavy metals. In this study, solidification/stabilization of ceramic tile industry sludge was investigated using cement and additives like water, lime, microsilica and ordinary clay.

In this study, by designing the tests by response surface methodology, the effect of different additives on compressive strength and metals concentration after pollution leakage test was investigated. So, hazardousness of wastes after stabilization and solidification and the samples tolerance against the environmental loads was evaluated.

Results showed the highest value compressive strength in high amounts of cement. Decreasing the amount of waste and replacing more lime, clay and microsilica, the compressive strength was increased. In optimal mode, by 5.77% lime, 8.69% clay, 4.35% microsilica and 51.84% cement, the maximum compressive strength was achieved about 116 kg/cm2. The minimum concentration of Cr was 0.0782 mg/L and resulted from 11.23% lime, 21.31% clay, 10.65% microsilica and 27.46% cement. Minimum Pb concentration (0.0043 mg/L) was obtained in 11.23% lime, 21.31% clay, 4.35% microsilica and 33.76% cement.

The more efficiency on compressive strength is related to cement. In addition, applying the lime, clay, microsilica and cement concluded the effective reduction of Cr and Pb concentration in leaching the stabilized samples.

The diverse carbonate materials found in Iran exhibit varied physical, mechanical, and chemical behaviors, making their stabilization a subject of great interest. Further research is necessary to investigate their properties. The engineering properties of problematic soils, like carbonate sand, can be enhanced by using suitable chemical soil stabilizers. Colloidal nano-silica solution injection in carbonate soils is highly beneficial, especially in small pores where injecting cement slurry is not feasible. Colloidal nano-silica is a suspension of silica nanoparticles in water, having viscosity similar to water, facilitating injection into such soils. Moreover, it is environmentally and chemically non-toxic. In this study, carbonate soil with varying silt contents (0%, 10%, 20%, 30%, and 40%), different nano-silica concentrations (10%, 20%, and 30%) and an average density of 50% were investigated for injectability along the Persian Gulf coast (Bushehr port). Injection was possible at a pH of about 6.5 with all concentrations, especially at 30%. Unconfined compression tests were carried out at different silt contents, curing periods, and nano-silica concentrations to determine the optimal injection concentration. The results showed that the unconfined compression resistance increased with higher concentrations of nano-silica, with 30% concentration demonstrating the best performance. Injecting colloidal nano-silica in carbonate soils, particularly silty sand, can serve as a stabilizing agent in construction.

Tabriz marl soil are Lake Carbonated sediments. The percentage of organic matter in this soil is less than 6%; and does not fit into the classification of organic soils. The carbonate content of this soil is from 10 to 35%. The classification of this soil is mostly CH and in some cases MH (Mahouti and Katabi, 1397). Dredged soil is not much different from conventional fine-grained soil and can be used in a variety of applications with stabilization. Due to poor geotechnical properties; they are stabilized for use in dredging materials in engineering applications (Chan and Shahri, 2016). To stabilize the soil; Stable stabilizers (such as steel slag and industrial waste) have been proposed to replace cement. In the meantime, the environmental compatibility (safety in terms of pH and harmful substances, such as heavy metals and toxic substances) of BOF slag (as soil stabilizer and filler) has been confirmed. Therefore, the use of steel slag; In addition to reducing project costs and environmental problems caused by lime and cement production (reducing CO2 emissions and energy consumption), it does not pollute the environment and eliminates the problem of accumulation of by-products of the industry (Proctor et al., 2000; Motz and Geiseler, 2001; Kang et al., 2019).

Global oil production exceeds two million tons per year, contaminating the soil around oil facilities. Consequently, the soil’s geotechnical properties are modified. Since Iran is an oil-rich country with numerous refineries and oil extraction facilities, it is crucial to study the mechanical behavior of contaminated clay soils. This study examines the stabilization of oil-contaminated clay (CH) soils in the Masjedsoleyman contaminated clay soils by adding lime. To this end, laboratory tests were conducted to determine the chemical properties, Atterberg limits, standard compaction, and unconfined compressive strength (UCS) of the soil and conduct a microstructural analysis. As a result, 144 contaminated soil samples (76 mm in height and 38 mm in diameter) containing 0, 4, 7, and 10% oil were synthesized by adding 0, 3, 6, and 9% lime. The samples were subjected to unconfined strength tests and microstructural analyses after 1, 14, and 28 curing days. The results of the standard compaction test revealed that the optimum moisture content (OMC) of samples with greater oil contamination decreased by 44.4%, while their maximum dry density (MDD) increased. The unconfined compressive tests indicated that adding 6% lime resulted in the highest unconfined strength (416.6%) compared to other cases. As curing time increased for lime-stabilized samples, the unconfined compressive strength of the samples improved due to the cementation of lime particles with clay soil. The microstructural analysis results demonstrated that the 7% oil-contaminated clay soil had a laminar and discontinuous structure and numerous porous spaces between soil particles. However, longer curing times reduced the porosity and cavities in samples stabilized with different lime percentages. This confirmed the high cation exchange capacity of lime and the presence of pozzolanic reactions, which increased the unconfined compressive strength of the samples. Overall, this study demonstrates the efficacy of adding lime in stabilizing the contaminated clay and the potential use of stabilized contaminated clay as an alternative construction material and practice in the environmental protection of sites.

Road slope stabilization is one of the most common issues in reducing financial and life risks. Use of efficient and cost effective approaches for stabilizing earth slopes is a crucial matter. Due to Road growth, stabilizing of endanger slopes and insuring its safety is one of the basic concerns for engineers. With regard to regional condition, site importance, economical status, and many other factors, using common methods of stabilizing are diverse. One of these appropriate approaches for reinforcing earth slopes is the use of stone columns. Using stone columns, which, besides its simplicity and comfort implementation, is also very economical. The object of this research is presentation of experimentally and numerically investigates stone column stabilization of earth slopes, and investigates case studies about using stone columns in road slopes stabilization.

In order to mitigate the environmental impact of iron ore tailing (IOT) and also to reduce the use of natural aggregates, these materials can be used as road materials after stabilization with chemical additives. In this research, the feasibility of using Golgohar IOT, stabilized with 4, 6 and 8% of Portland cement as road base materials, has been investigated. To this end, modified Proctor compaction test, unconfined compressive strength (UCS) test and durability against freezing and thawing (F-T) cycles test were conducted on IOT samples stabilized with different percentages of Portland cement. Results of compaction testing on the samples showed that increasing the percentage of cement increases the optimum moisture content (OMC) and decreases the maximum dry density (MDD). In the next stage, IOT were stabilized using 4, 6 and 8% of Portland cement and UCS samples were fabricated with three different compaction moistures (dry side, optimum moisture content and wet side) and cured for 7, 28 and 56 days. The results showed that with increasing the percentage of cement from 4 to 8% for all curing times, the UCS increased between 1.45 to 2.15 times. Also, the 28-day UCS and 56-day UCS are about 1.73 times and 2.34 times the 7-day UCS, respectively. It was also found that the UCS increases with decreasing moisture content. The results of durability tests against (F-T) cycles on the samples showed that with increasing the percentage of cement, the durability of stabilized materials increases, so that in samples with higher percentage of cement, the lowest percentage of weight loss and volume reduction is observed. Finally, it was found that IOT stabilized with at least 4% of Portland cement provides the necessary strength and durability criteria for use as stabilized base layer.

In two decades, the roads of the roads in the desert areas of the desert have also been changed. Fiber-reinforced soil behavior modification studies have been performed by compaction, uniaxial compressive strength, and California load-bearing ratios. In this research, studies were performed on soil stabilization of constructing roads in sandy loam soils using cellulose nanofibers. The aim of this study was to stabilize the cracked pavement bed and strengthen it by adding nanocellulose to the soil. Physical and mechanical tests were performed to find the type of soil in the area and the effectiveness of nanocellulose. Samples in these experiments were combined with 0.5, 1 and 1.5% nanocellulose, The results obtained from the experiments showed that the addition of nanocellulose increased the liquid and plastisite between 21 to 27% and 60 to 65% and decreased the plastisite index between 25 to 40%, respectively. Optimal moisture and dry specific gravity increase and decrease, respectively. The uniaxial strength of the samples increased between 30 and 85% and the maximum CBR number up to 12 times., and the soil strength class in all samples was changed to "very good" subgrade for use in pavement. The rupture zone energy results also show that the increase in nanocellulose has a positive effect on the modified specimens and delays the occurrence of rupture cracks due to loading and volumetric changes. The response Surface statistical method was also used to predict objective variables.

Construction wastes can be found easily and are increasing by the developing of cities. Lack of sufficient knowledge and facilities for recycling these materials causes deposition of these materials and unfavorable scenes in suburban regions. Settlement of these materials makes some troubles for building constructions on them. Prevalence of disease, growing of vermin and also the low potential of these materials for raising plants are some of the problems which are the motivation for many scientific researches about recycling of these materials. In this study first brick, gypsum and cement contained wastes were collected and then 200 samples with 3, 6 and 12 percent of cement in 4 groups with different mixture of wastes were made. Compressive and indirect tensile strength tests and the test of durability against freezing and thawing were conducted to evaluate these materials to be used in stabilized base and subgrade layers. The results show that many mixtures of these materials have sufficient compressive strength and durability to be used in base and subgrade layers according to highway construction codes.