جستجوی مقالات مرتبط با کلیدواژه « بهسازی خاک » در نشریات گروه « عمران »

Due to the fast growth of urban and industrial facilities, the necessity of construction in new land becomes inevitable. Most of these lands were left as a result of the existence of weak layers that make them unsuitable for construction. One the methods in treatment of such lands that have weak clay layers is the application of surcharge with or without prefabricated vertical drains or vacuum. In this literature first a brief description of the vacuum and surcharge preloading is presented and then a case history was investigated by finite element method that consists of only vacuum and prefabricated vertical drains without embankment. Based on the results the application of vacuum preloading alone even in the absence of surcharge, would give satisfactory results, especially where the application of surcharge preloading is not possible due to the unavailability of suitable loading material or the existence of sensitive buildings or infrastructures. The results of this literature can be used by consulting companies or personals who are active in land reclamation, especially in offshore regions.

Soil pollution by oil hydrocarbons is one of the most important kinds of pollution. In this study, clay soil from the CL class were contaminated with gasoil synthetically in 3, 6 and 9 percent by weight, and then the soil containing 6 percent of pollution reinforced with polypropylene fibers at amounts of 0.25, 0.5, 0.75 and 1 percent by weight. According to the results in all samples, Atterberg limits were reduced compared to the base soil. By increasing the percentage of contamination from 0 to 6 percent, the liquid limit and plastic index of the contaminated samples decreased. Moreover by increasing the amount of contamination to 9 percent, these values increased. Investigation of changes trend and amount of compaction characteristics (maximum dry density and optimum moisture) of samples also showed that with soil contamination, maximum dry density and optimum moisture content, had an upward and descending trend compared to the corresponding values in base soil, respectively. According to the results, the presence of contaminant in the soil was led to a decrease of consolidation coefficient, decrease of void ratio, increase of coefficient of volume compressibility and increase of permeability coefficient. The highest rate of decrease in consolidation coefficient (equivalent to 1.7 percent) and the highest increase in permeability coefficient (equivalent to 23.01 percent) was related to the contaminated sample reinforced with 0.75 percent by weight of fibers.

Injection soil improvement is one of the methods of modifying the properties of the site of construction projects or existing structures. Several stabilization techniques are available to improve such conditions, including compaction, consolidation, mechanical stabilization, and cement injection into the soil. The injection is often done by filling cavities and fractures with grout or cement mortar. Despite almost the same principles, injection methods have different equipment and procedures. These methods have their characteristics and advantages due to insufficient bearing capacity, shrinkage swelling, settling, and durability. This study intended to review the studies and methods of improving alluvial soils using the cement injection method. After reviewing the results of this study, we can get three main factors: percentage of cement, setting time (sample age), and percentage of coarse soils have a very effective and controlling role in the strength of soil-cement samples, but the effect of these three factors is not the same in increasing strength. The results of such experiments can be used as a basis for quality control of cement injections in porous media, especially in coarse-grained alluvial sediments and jointed and crushed rocks. The resistance of coarse-grained alluvial sediments with the potential for spillage can be increased, during or after tunnel excavation, by adding a minimum percentage of injected cement to the desired strength or design strength, which is essential from the technical and economic justification of injection projects.

Various improvement methods have been proposed to improve the mechanical and physical characteristics of soil for the construction and the other similar matters. One of the improvement methods is using of the environmentally-friendly elements such as Persian herbal gum as a renewable hydrocolloid biopolymer. Regarding this, in the present laboratory study, the effect of adding this gum to the Firouzkooh sand (No 161) was investigated. Persian gum-water mixture was added in different percentages relative to the weight of dry soil, and the created samples were subjected to unconfined compressive strength test to identify the optimal conditions of the composition. In spite of the variability of the weight percentages of water and gum added to the soil, the effect of the weight of the soil, curing temperature (room or oven temperature), and curing time (7 to 56 days) were investigated. To interpret the effect of Persian gum addition, several scanning electron microscope tests were performed on selected dry samples. The results clearly revealed an increase in the unconfined compressive strength of the samples improved with Persian gum up to 4 MPa due to the presence of many carboxyl and hydroxyl groups in the gum. Samples cured at room temperature with relative humidity of 15% displayed lower unconfined compressive strength than similar samples cured in an oven temperature due to the hydrophilic properties of herbal gum and increased flexibility of the created bonds.

Suitable tensile strength is one of the important parameters in soils subjected to tensile stress. In recent years, biopolymer materials have been widely used to control cracking and increase the tensile strength of soil. In this laboratory study, the tensile strength of sand treated with Persian gum was investigated. For this purpose, the effect of parameters of initial relative dry density of soil, materials mixing method, temperature and humidity of curing place and curing time on the tensile strength of treated samples was evaluated by indirect tensile test. After examining the results, it was found that adding a uniform gum-water solution (including 2% gum and 16% water related to the weight of dry soil) to the dry soil was the best mixing method and the initial relative density of 50% for the soil was the optimal density to obtain the highest tensile strength. Also, there is a direct relationship between the increase in temperature and the decrease in humidity with the increase in tensile strength, so that when the temperature increases from 25 degrees in the room to 50 degrees in an oven and the relative curing humidity environment decreases from seventy to fifteen and then to zero percent, the maximum tensile strength of treated samples increases from 154 to 270 and 442 kPa respectively.

In recent years soil reinforcement and improvement techniques have gained widespread applications in different aspects of geotechnical engineering. It is apparent that reinforcing/stabilizing a weak/problematic soil is more economical than replacing it with select fills. A contemporary method of soil reinforcement/ improvement is the application of fibers-natural or synthetic (polymeric) with random distribution within the soil (Hejazi et al. 2012). More recently, there has been a trend in utilization of recycled fibers for soil reinforcement/improvement purposes (Valipour et al. 2021). This treatment dwells on the application of Recycled Tire Polymer Fibers (RTPFs) for enhancing the shear strength of Babolsar sand.

In this literature a case study that includes surcharge and prefabricated vertical drains (PVDs) was introduced and verified using finite element program Geostudio 2018R2. Based on the verified model, the lateral displacement and horizontal strains were calculated. It was shown that the safe zone for this special case study is 40 m that is approximately equal to the length of the constructed embankment. In urban areas as a result of the existence of water and wastewater pipes, optical fibers, oil and gas transition lines or trenches and excavations, these infrastructures are in serious danger due to the lateral displacements and horizontal strains. The same case is true for constructions in industrial areas. Since the mentioned infrastructures do have special importance in passive defense doctrine, exclusive attention should be considered by the owners, consultants and contractors in such projects all phases including preliminary investigation, during the construction and after the compilation of the treatment process in the case of permanent embankment. It was shown that due to the obstacles related to surcharge and PVDs treatment, this method is not suitable in urban areas.

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.

Many improvement methods have been proposed in the world which is one of the most common methods of chemical stabilization using lime or cement, which are not compatible with the environment. Therefore, nowadays, the use of pozzolans and geopolymeric cements instead of Portland cement has attracted the attention of various researchers. In this study, the stabilization of sandy soil in Ahvaz city with the help of metakaolin as an additive has been investigated. In this research, the effect of different amounts of variables such as the percentage of metakaolin, the ratio of sodium silicate to sodium hydroxide, the concentration of sodium hydroxide, and the ratio of alkaline activator solution to the additive at the curing ages of 7 and 28 days have been discussed. Samples are subjected to unconfined uniaxial compressive strength (UCS) evaluation and microstructural investigation, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyzes are used. The results of this research show that in order to achieve optimal resistance, it is necessary to mix 20% metakaolin, the ratio of sodium silicate to sodium hydroxide is 2.5, the concentration of sodium hydroxide is 12 Molar, and the ratio of activator solution to additive is 0.5. The strength of the sample with 28-day curing reaches about 5 MPa, which is about 3 times more than cement samples and 23 times more than unstabilized soil, which can be seen in the microstructural analysis of the presence of N-A-S-H gel as the main factor in increasing the strength in the geopolymerization process.

Temporary soil improvement methods have always been a concern of geotechnical engineers. Today, the use of methods such as nailing and anchorage is one of the common methods in Iran, while in developed countries, new methods such as artificial ground freezing are also used. The reason for the increasing use of artificial ground freezing, in addition to technical, economic and environmental benefits, is its ability to be used in all boundary conditions and all types of soils. Due to the insignificant laboratory study on the behavior of frozen clay, in this paper, after conducting initial experiments, over 130 unconsolidated-undrained triaxial experiments have been performed on clay samples prepared from the Shurabil Lake site (located in Ardabil). In these triaxial experiments, the effect of freezing, temperature decrease, strain rate increase and confining pressure increase on stress-strain behavior of saturated clay samples has been completely investigated. The results of this study show that decreasing the temperature significantly increases the shear strength and modulus of elasticity of frozen clay samples. Also, due to the presence of ice matrix in the structure of frozen clay, the effect of strain rate is to a large extent, which leads to an increase in shear strength and modulus of elasticity of the samples. Also, all samples showed strain hardening behavior and none of the samples showed brittle rupture. Therefore, the use of artificial ground freezing method in clay soils can be used.

Soil improvement has long played an important role in civil sciences, especially in geotechnics. However, with the passage of time and the lack of resilient lands for the construction of more advanced construction structures, engineers in this field decided to use new methods to stabilize and reinforce problematic soils. Also in recent years, environmental problems such as the increase of waste and industrial waste and their release into the living environment have created problems for the life of living Creatures. In these circumstances, geotechnical engineers have tried to use these materials in construction projects to protect the environment and, also, due to the very low cost of waste materials, reduce the economic costs of soil improvement projects. As a result of this study, granular soil is reinforced in two loose and semi-dense states using Polymeric industrial waste material called full ethylene-vinyl acetate (EVA). The experiments were performed at different weight percentages of EVA (0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 3 and 4), without adding moisture and using the CBR device. The results show that soil CBR has increased significantly with the use of these additives, and its effect on the soil increases with the reduction of the specific weight of the soil.

Based on a case study, the soil improvement operation under single foundations of a settled concrete structure has been presented using injected micropiles. Based on this, the effect of using micropiles in controlling the stress-deformation field created in the soil of the concrete structure has been studied. In order to evaluate the situation of the settlements, the necessary information was collected, including subsurface identification using geotechnical boreholes and settlement monitoring operations. The survey results before the soil improvement operations indicated the settlement of individual foundations and the continuity of the settlements. After the soil improvement operation, this trend reached zero. Using the Abaqus finite element software, a set of numerical analyses was performed on a concrete structure built on a loose foundation prone to destructive deformations in structural load-bearing members such as columns. In these simulations, in order to obtain the optimal performance of micropiles, the parameters of depth, diameter, and several micropiles were examined. The necessity of this research includes the decision to improve the soil of a settled concrete structure in the vicinity of the excavation based on the micropiles method or the destruction of the structure. The obtained results showed that the parameters of the length and number of micropiles have the greatest effect on the control of the deformation field and settlement of the structure. Also, the results show that the effect of the structure weight parameter on the interaction between the micropiles and the structure is significant.

Improving the physical properties of soil using industrial waste has always been of interest to researchers And it becomes more important when Accumulation of huge volume of borrowed Soil resulting from the development of Civil projects Due to improper engineering characteristics For reuse in Civil projects Cause a lot of problems. On the other hand Given that Iran is one of the hubs of steel production and Huge volumes of steel furnace slag are produced and accumulated annually in this country, It is necessary for the optimal recycling of this waste Conduct comprehensive research in various fields of science and technology. One of the goals for the optimal use of this waste, Their use is in soil improvement for use in road construction. The present study is based on the improvement of accumulated fine-grained soil in Mobarakeh Steel area Using processed steel slag in the size of 0 to 25 mm , Has been studied For use in road construction. Engineering properties of loan soil in Mobarakeh Steel Plant (Saba area), Includes Liquid Limit and Plasticity Index , classification and seive size, After sampling from different parts, Preparation and testing in the laboratory Was initially examined According to the specifications of road building materials, Soil unsuitable for use in road construction was identified. Eventually, by performing step by step experiments, Soil engineering properties were modified using different percentages of steel slag And achieve a suitable mixture for use in road construction. Also compare the geotechnical properties of soil samples to the samples of soil and slag mixture obtained Showed that these properties improved significantly by increasing the percentage of slag.

Preloading is a well-known and classic way for soil treatment in engineering practice. For south part of Iran, this method is an economic and also effective way for soil treatment. In this method, the preloading is done using vertical drains to accelerate the consolidation and also a surcharge that is embankment. The preloading induces the required settlement to weak and compressible layers and hence the settlement would be reduced considerably after the compilation of the main structure and also the risk of differential settlement in the future would be decreased considerably. In this article the Mahshahr clarifying unit has been modeled and then the results were compared with instrumentation on site.

The addition of glass fibers has been used to stabilize the unsuitable clay of Rey city to reduce the subsidence in the strip foundations due to the improvement of resistance parameters. The combination of glass fibers with clay and the effect of using this additive on the stabilization of clay fine-grained clay (CL) were investigated in the laboratory. Soil samples in the natural state as well as in the combined state with different percentages of glass fibers equal to 0.2, 0.4 and 0.6, 0.8 and 1% of the dry weight of the soil were used for laboratory tests including standard compaction test, California load ratio test and direct cutting. Were located. The results show a decrease in unit weight of maximum soil volume and an increase in optimum moisture content, as well as a California load-bearing ratio by adding this material to the clay. The amount of adhesion and the internal friction angle resulting from the direct shear test increase with increasing percentage of glass fibers. After laboratory studies, the effects of using modified soil with improvement depths of one meter, two meters, four meters for strip foundations with widths of 0.75, 1.50 and 2.25 meters with the help of Plaxis2D software show that by increasing the percentage of mixing glass fibers In fine-grained clay soils, the amount of foundation deposition is reduced, while the reduction of foundation deposition on soil mixed with 0.8% glass fibers is more than soil mixed with 1% glass fibers. The reduction rate of the strip foundation with a width of 0.75 m with a mixing percentage of 0.8 glass fibers and a depth of improvement of 4 m is 1.57 cm. ،he reduction rate of the desired foundation with widths of 1.5 and 2.25 meters is equal to 2.29 and 2.72 cm, respectively

High plasticity clay soils are one of the problematic soils for engineering projects, especially for road construction. Electro-osmosis is one of the methods for improving the characteristics of the soft and fine grained soils. In this method applying the electric field cause changes in microstructure of the soil and modify the physical and chemical properties of the soil. Injecting chemical solution into soil during the electro-osmosis process adopted for enhance the efficiency of the treatment in recent years. The effect of injection of strontium solutions on chemical and geotechnical characteristics of soil was investigated. A layer of the soil was impacted in a tank for obtaining density and field moisture content. Direct current was applied through the soil under voltage gradients of 0.5, 1, and 2 (V/cm) for periods of 7, 14, and 28 days, with and without the injection of strontium solution. Stainless steel electrode was exerted for treatment. The results demonstrated the increases in compressive strength and reduction of the moisture content of the soil. From the results it is noted that injecting strontium increases the compressive strength and volume of drained water compare to electro-osmosis process in absence of strontium. Chemical analysis of the soil before and after the treatment identifies the ionic migration, ionic exchanges and changes in chemical composition of the soil. These chemical changes lead to changes in structure and properties of the soil. The scanning electron microscopy (SEM) images exhibited the changes of the microstructures including flocculation and agglomeration and confirm the validity of physical results. At last, the result of California bearing ratio (CBR) showed that electro osmosis chemical treatment is feasible method to increase the properties of the soil to meet the requirements for subgrade constructions.

The increasing population of the world indicates the development of urban areas, and consequently the use of appropriate methods to improve sandy soils in these areas, led engineers to think of inventing methods to improve the properties of sandy soils. One of these efficient methods to modify the behavior of unsuitable soils in geotechnical engineering is to change the properties of problematic soils, which is called improvement. In this regard, sandy soil is improved by adding materials to improve mechanical properties (compressibility, hardness, shear strength, permeability, etc.). In this study, the undeniable role of nanoparticles in the improvement of sandy soil and the effect of nanosilica along with bacteria in the biological improvement of soil samples that have not been tested, was investigated (Dejong et al., 2010). Controlling the distribution at the site of bacterial and reactant activity and the results of calcium carbonate distribution and related engineering properties below the soil surface is a major challenge for future improvements, especially if bioremediation in a surface or deep soil system (To replace the method of deep soil improvement with artificial lime). In order to commercialize the bioremediation process, further optimizations in the performance of the biological deposition process (improving the effective use of bacteria, reactants and reducing heterogeneity) should be done (Sharma et al., 2016). Therefore, the aim of this study was to investigate the compatibility of nanosilica with bacteria in order to be able to use minerals to increase the strength of biologically improved soil properties.

According to the expansion of cities, the necessity of high-rise buildings construction and the need to retrofitting the old buildings is inevitable, particularly in metropolises such as Mashhad with expanded urban areas and neighbor areas of Imam Reza shrine built on the fine-grained deposits, the necessity of improvement and reinforcement of soil is evident. Nanotechnology can be significantly efficient as one of the most useful modern technologies in the recent century to meet the needs of the construction industry. The technology has a significant effect on the improvement of strength and mechanical parameters of soil because of a considerable increase in particle surface. In this regard, this study has investigated the effect of adding clay nanoparticles of type Montmorillonite and Silica of type "S" on the strength and mechanical parameters of silty-clay soils adjacent to Imam Reza's Shrine using laboratory studies. The results showed a significant increase in shear and compressive strength parameters and a decrease in settlement of soil in the Nanosilica-improved samples compared to nanoclay-improved ones. In this way, adding 1% nanosilica and 2.5% nanoclay could cause a 620 and 134% increase in bearing capacity of silty-clay soil, respectively.

The improvement of soil treatment by additives is one of the most critical issues in geotechnical engineering. Typical additives such as cement, lime, fly ash, and bitumen have been investigated in the past. Nanomaterials have unique features. The application of this type of material has led to a significant development in other branches of engineering. However, in geotechnical engineering, the investigation of the effects of this type of material is a new subject. Hence, in the present research, the effects of nano clay on geotechnical parameters of clayey sand are investigated. The principal purpose of investigation in this scale is the creation of new compounds with changes in ingredients and the detection of a new class of materials with new functions. These types of researches can make an appropriate base for future researches in this context. The Atterberg limits test and direct shear tests were carried out on different types of clayey sand. Various percentages of nano clay were used in the study. Ball mill was applied for uniform dispersion of nanoparticles. Also, in order to obtain optimum water content and maximum specific weight for prototyping, a standard compaction test was carried out on samples without nano clay particles. Based on the results, in general trends of tests, liquid limit and plastic limit are increased by increasing nano clay. The plasticity index has decreased when the percentage of the nano clay is increased by up to 1%. The plasticity index has increased again in a higher percentage of nano clays (more than 1%). Also, the shear strength of clayey sand in direct shear tests is improved in a specific percentage of nano clay. The optimum percentage of the nano clay for the friction angle φ is 1% in the direct shear test, and its best percentage for the cohesion C is 4%. Also, nano clay has a negative effect on the shear strength of pure sand. Therefore, according to the results of experiments, nanoparticles can be an acceptable choice for improving the geotechnical properties of clayey sand soils.