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

In this research work, the remediation of a clay soil contaminated with dimethyl phthalate ‎was ‎studied by using electrokinetic method. Contaminated soil was made with the ratio ‎of 0.04 mg/g. ‎Non-ionic (Tween 80) surfactant and solution of 0.1 M NaOH were ‎used as anolyte. A reference ‎test was also considered with distilled water as ‎anolyte and catholyte. pH and EC and volume of ‎flow out fluid were measured ‎during the tests in both electrode reservoirs. At the end of each test ‎the shear ‎strength, pH, EC and degree of remediation of soil was measured at different ‎distance ‎from anode. The removal of contaminated was measure by a GC (Gas ‎Chromatography) apparatus. ‎The results showed that the amount of flow out fluid ‎for NaOH was nearly 20% more than the ‎solution of Tween 80 and distilled water. The ‎results also indicated that the strength of soil for ‎different solution is increased ‎by increasing the distance from anode. The value of it around the ‎cathode for ‎solution of NaOH was 14 kPa that was about 50 and 57% more than the distilled ‎water ‎and Tween 80. It was found that the degree of remediation at cathode is less than ‎anode. The ‎percentage of remediation for Tween 80 solution around the anode and ‎cathode were 53.88 and ‎‎16.5% respectively but for NaOH they changed to 50.82 and ‎‎23.26 near anode and cathode ‎reservoir. It was resulted that the effectiveness of NaOH ‎solution in remediation of soil was more ‎than the other used solutions.

Increased production of lignocellulosic waste and its incineration by farmers have raised bio-environmental concerns. Reusing these fibers to change the mechanical properties of loose soil can reduce these problems. It should be noted that the use of natural fibers has received more attention due to its compatibility with the environment and the realization of sustainable geotechnical goals. The reinforcement effect of rice straw fibers on the mechanical behavior of clayey soils stabilized with cement has been investigated. Studying the effect of different percentages of mixing these fibers on the compressive strength of clayey soils stabilized with different amounts of cement through performing unconfined compressive strength test and evaluation of the effect of the so-called fibers on the results of standard compaction test form the basis of laboratory research in this project. cement can be used as an additive along with fiber reinforcement to create the required cohesion to increase the compressive strength of the sample. The results of unconfined compressive strength on the uncured samples stabilized with different amounts of cement (4%, 8% and, 12%), and reinforced with different amounts of rice straw fibers (0.25% and, 1%) show that at a constant content of cement, increasing the fiber percentage can increase the compressive strength up to 148% and also, at a constant content of fibers, increasing the cement percentage can increase the compressive strength up to 183%.

The presence of petroleum products (crude oil pollutions) in clay with low limit liquid (CL) due to physical and chemical processes causes changes in the stress-strain curve, wedge rupture, plastic zone and, strain energy compared to unpolluted soil. These changes often reduce the safety factor against failure, increase the plastic zone, and Decreased soil slope stability. So far, the effect of crude oil pollution on soil shear strength parameters has been tested by direct shear test and the modulus of subgrade reaction has been tested by plate loading test for different types of clay and sandy soils. In this study, the effect of changes in crude oil pollution in the range of 0 to 16% (0-4%-8%-12%-16%) on clay soil slope stability has been done by numerical modeling of finite element method in ABAQUS software. The height of the clay slopes is 10 m, 13 m and, 16 m and, the slope angle of the slope is 53 degrees. The results of this study show that increasing crude oil pollution reduces slope stability. It is predicted that with the increase of crude oil pollution in the range of 0 to 16%, the safety factor of clay slope stability will decrease by 72%. Also, increasing only 4% of crude oil pollution in clay soil slope (12% to 16% of crude oil pollution), causes a 2 to 3 times increase in horizontal displacement and a 3 to 4 times increase in vertical displacement.

Pile foundations are widely used to ensure the stability of structures subjected to seismic excitation. Numerous structures and foundations in soil-pile-structure systems have been destroyed during occurrence of earthquakes. Because of complexities involved in soil-pile interaction problems and the lack of precise methods, it is necessary to use numerical methods for analyzing soil-pile interaction problems. There are several factors affecting the dynamic response of a pile in soil-pile system. These factors can be divided into three main categories: geometrical factors, material properties, and load characteristics. Studying the effects and importance of these factors in the response of the pile will help geotechnical engineers to optimize their design. In this research, three-dimensional modeling has been developed using FLAC3D computer program, and the effects of various soil and pile properties on the dynamic behavior of a single pile in clayey soils are evaluated. One of the most important subjects in the numerical modeling of soil-pile system dynamic response is the constitutive model considered for the soil. This strongly affects the accuracy of results. In this study a softening model has been used for the behavior of the soil under dynamic loads.Sinusoidal harmonic loading has been applied to the model base as the acceleration time history, and the variations of bending moments, shear forces, and displacements along the pile are obtained for all analyses carried out in this study.The results show that kinematic interaction coefficient depends on the loading characteristics and in the high frequencies head pile response is lower than free field.

Soil tensile strength is important in different geotechnical structures such as earth dams, roads, airports, landfills, and retaining walls. There are several experiments to study the tensile behavior of soils with different advantages and disadvantages. One of the methods used to investigate soil tensile behavior is tensile hollow cylinder apparatus, which has seldom been used. In this research, a hollow cylindrical device to measure the tensile properties of soil was built and operated. This device can apply tensile stress evenly to the entire soil sample so that stress concentration does not occur at any point in the sample.  After designing, manufacturing, and assembling the apparatus, validation tests were performed to ensure the device was operating well. The results of the repeatability tests show the accurate performance of the device. Also, in this study, the effect of plasticity index (PI) on the tensile behavior of kaolinite clay was investigated. Clayey soils with plasticity indices of 10 and 24% were selected. The results show that for clays with a similar mineral, the tensile strength increases and the tensile failure strain decreases with increasing the plasticity index.

Investigation and evaluation of damages to surrounding structures and also estimation of rupture levels by considering the amount of deformations and the amount of adjacent gates are important issues in the nailing system in urban areas. In this research, we tried to evaluate the axial force of the nails and the deformation in concave and convex dams; in sandy and clay soils. In this regard, numerical modeling is carried out using the Abaqus CAE software in the soil environment and parametric studies are carried out for different corner angles in the excavation under the service load. The results of this study indicate the effect of concave cortical deterioration and the damaging effect of the convex corners, which is in contrast to the concave hedge, in gondolas with sandy soil as well as clayey soil. The maximum axial force of the nails in the clay soil is less than that of the sandy soil, which decreases with the approach to the hollow corner. For maximum seating and horizontal displacement of the Goodwall wall, there is also a turning point between the angular angles of 130 ° to 150 °, with a good turnaround. By comparing and analyzing land surface levels and rupture levels, we will find that the maximum level of earth's summation in sandy soils will be the highest level of rupture, and in clay soils, ground-level landings in the location of critical burst surface changes It is noteworthy.

According to statistics, internal erosion and piping have been known as the main causes of the destruction of earth and rock-fill dam. In earth dams, hydraulic fracturing and internal erosion are two interdependent phenomena. Hydraulic fracturing causes expansion of the cracks. The flow of water in cracks causes the leaching of soil, materials and internal erosion occurs.The Bidwaz dam is an earth and rock-fill dam. About seven and a half years after the start of the first impounding, a subsidence appeared on the upstream face of the dam body. This dam is located in a narrow valley; therefore, hydraulic fracturing and internal erosion are proposed as one of the main causes of subsidence.Using the concepts of fracture mechanics is one of the prediction methods in hydraulic fracturing. Fracture mechanics is the field of mechanics concerned with the study of the crack propagation in materials. Fracture toughness modes I and II are two important parameters of materials in fracture mechanics, which can be determined by the method provided in ASTM E399.In this study, through 3-point and 4-point bending tests, the tensile strength, mode I and mode II fracture toughness of core's soil at different moisture contents are evaluated. Due to the low tensile strength of the soil, the direction of load is perpendicular to that of weight to reduce the influence of the weight. The ability to perform experiments is provided by making some changes in direct shear apparatus.Moisture content is the most important factor affecting the tensile strength and fracture toughness of soil. Experiments have been conducted with different moisture contents to evaluate the effect of this parameter. The results show that based on the moisture content, soils can be divided into three categories: 1. Brittle, 2. Semi-brittle, and 3. Elastic-Plastic. Increasing the moisture content reduces tensile strength and increases flexibility.In general, fracture toughness of mode 1 is obtained to be more than that of mode 2. Therefore, the probability of crack expansion with tensile mechanism is less than shear mechanism. At the end, based on the results of laboratory tests, mode I and II interaction diagram has been plotted as a fracture criterion at different moisture contents.

In this research, effects of pine tree sawdust on geotechnical properties of two types of kaolinite clayey soil was evaluated. So that, sawdust in 3, 6 and 9 percent (by weight) in dry condition randomly mixed with two kaolinite clayey soil with different plasticity index. Compaction, uniaxial, permeability (falling head) and consolidation tests were performed on specimen. Results showed while 3% sawdust mixed to samples, 24% minimum void ratio (emin) decreased in kaolinite clay with high plasticity index. Also, in this condition, increasing of bearing capacity and strength, ductility and decreasing in water absorbing have been happened

Removal of petroleum hydrocarbons from contaminated soil using electrokinetic method or biological processes has been considered in recent century. The most limiting factors in the electrokinetic process are extreme changes in pH around the electrodes and non-polarity of some pollutants. On the other hand, the key factor of biological treatment is simultaneous presence of microorganisms, pollutants (carbon source of microorganisms), electron acceptors, and essential nutrients for microorganisms’ growth. But in fine-grained soils with low permeability, it is difficult to uniformly distribute bacteria, electron acceptors and nutrients, or making pollutants available for microorganisms. To solve these problems, bioelectrokinetic method is used to eliminate the limitations of both biological and electrokinetic processes in treatment of fine-grained soil contaminated with organic compounds. In this integrative approach, the biological method has a role in biodegradation of pollutants. Whiles, the electrokinetic process can direct and accelerate the transfer of pollutants and microorganisms. The aim of this study is determining the equations and conditions governing on bioelectrokinetic process in removal of crude oil from clayey soil. For this reason, the numerical method of FTCS finite-difference was applied for modeling the pollutant biodegradation and transmission in clayey soil under electric field. In order to develop and validate the model, the first step was to set up a bioelectrokinetic system in a laboratory scale. In this study, each test was conducted in cylindrical cell made of Plexiglas with the length and diameter equal to 55 and 5 cm respectively, for 35 days. They were performed in various conditions of pollution amount and electric field intensity in the presence of Pseudomonas Putida strain. On the other hand, after determining and combining the governing equations on the electrokinetic and biodegradation system, the numerical solution of the equation was coded using Matlab software. In suggested mathematical model, the parameters like initial concentration of crude oil, voltage gradient, time step and spatial step were assumed as variables and parameters related to reactor, soil and pollutant such as the length of reactor, soil porosity and tortuosity, ion mobility, diffusion coefficient and electroosmosis permeability coefficient were considered as constants. In continue, by comparison the result of numerical solution of the suggested model with the experimental results, the same trend was observed in changes in crude oil concentration between the two. Because of differences between the model results and laboratory data and to make more accordance between the two, the modifying factor was used as the factor of microorganism transfer under electric field. In this way, by addition of modifying coefficient in model, a better accordance between them was observed and this difference reduced to minimum. Modeling results showed that electroosmosis, diffusion and electromigration mechanisms, unlike biodegradation, had little impact on the transmission and removal of oil from soil. According to the numerical solution, similar to bioelectrokinetic data, increasing the initial concentration of oil and voltage gradient caused the increase in removal efficiency of oil. In addition, the model has been able to predict the residual crude oil concentration after bioelectrokinetic treatment with a good accordance.

Clayey soils usually have low bearing capacity, high compressibility, shrinkage and swell characteristics. Several methods have been adopted to improve the geotechnical properties of such soils. Soil stabilizing by chemical materials is one of the most common methods for treating fine grained soils. Lime has been used to improve some mechanical and plastic properties of fine grained soils since many years ego. In recent years some studies has been also carried out to investigate the influence of adding pozzolany materials on the geotechnical properties of lime – treated clayey soils. Geotechnical behavior of clayey soils depends on chemistry of pore fluid. When drinking water is used to provide the needed moisture of soil in the laboratory, it will be lead to incorrect interpretation in engineering properties of soil where specific water such as sea water is utilized. Therefore, if the undrinkable water has been used to provide soil moisture, it is necessary to examine the behavior characteristics of the materials by the same water. For example, presence of some sulphates in the soil stabilized with lime leads to problems such as reduction of strength and increase of swelling in clay. In this laboratory study, effect of sea water on strength of stabilized kaolinite has been investigated by conducting several unconfined compression tests. The specimens were prepared at fore percentage of lime and pozzolan (i. e. 0%, 1%, 3%, 5%) by weight of dry soil and distilled water and three saline water which were taken from Caspian Sea, Persian Gulf and Urmia Lake. for every combination, weight of each material was determined exactly based on the optimum moisture content and maximum dry density which is obtained from the standard proctor compaction test. Clay and lime and pozzolan were mixed in dry condition properly and then water was added gradually. Afterwards, the mixtures were kept in plastic bags for 24 hours. Weight of each specimen was determined in accordance with given specific volume and obtained maximum dry density from compaction test. This weight was divided into four portion and each portion was compacted in 20 mm layer in a PVC mold. The specimens were cured in a oven having a temperature about 35 C for 3, 7 and 14 days. After each curing time a extruder was used to remove the specimens from the molds with constant rate vertically to avoid bending and formation of tensile cracks. Then the specimens were immediately tested under strain controlled at constant loading rate of 1. 0 mm per minute, according to requirements of ASTM D 2166. For each combination, three specimens were examined to assure repeatability of results. The results of conducted experiments indicate that unconfined strength of samples without additives (lime and pozzolan) prepared by sea water are higher than specimens containing distilled water. For the samples containing Urmia lake water, the unconfined strength were higher than the other samples. Also, for the specimens in which additive has been used, the strength of the samples containing Caspian Sea and Persian Gulf water were more than that with distilled water and the strength of samples containing Urmia lake water was less because of differences in the concentration of salts existed in the water. Finally, the results show that water minerals are higher in Urmia lake water, Persian Gulf and Caspian Sea, respectively.

Drying of soils and shrinkage cracks is a crucial issue in geotechnical and geo-environmental engineering. Better understanding of the soil cracking process is essential in analyzing desiccation effects on buildings integrity. In this study, cracking behavior of the clay due to desiccation investigated experimentally at different temperatures on thin clay layer. Experimental tests carried out on the clay slurry saturated with water content about 60%, (1.5 times of its liquid limit). In this study, the clay supplied from clay mine in Abadeh, a city in Fars province in Iran.
Experimental results showed that the critical water content, which corresponds to the initiation of desiccation crack increases when the temperature rises. In addition, the number of produced cracks decreases by increasing the temperature. This phenomenon can be attributed to the reduction of water surface tension force or voids central tendency in soil mass. Also, the width of crack opening decreases by increasing the temperature.

With regard to cross the railway tracks and roads paved most original and non-original geological sequences with dominant lithological clay, silt, marl and Physical and chemical characteristics of soils, Possible ways to increase the strength of fine-grained soils against stress in compression, tension and shear at different axis (a-axis) or the all-round use. In this study, a sample of random and systematic path of clay used for established and strengthened platform, try it with tests to determine the bearing CBR in both wet and dry clay without lime (natural) and lime percentages of 2 and 5, the optimum amount of lime to stabilize and strengthen the substrate with known test results to determine the amount of change in transportation mode (with lime and without lime) were identified. However technically soils were also tested and evaluated. The importance of this study is to determine the amount of materials and how to strengthen the project's context; especially in the area of excavation of clay sequence is obvious.

Due to the positive effects of adding lime in fine-grained soils and reinforcing these soils with polypropylene fiber, durability evaluation of stabilized or reinforced soils especially in cold regions where are more exposed to periodical freezing and thawing cycles is still necessary. In this research, 12 different treatments were prepared by using three levels of lime (0, 2 and 4 percent by weight of dry soil) and four levels of polypropylene fiber (0, 0.25, 0.5 and 1 percent by weight of dry soil). Each treatments with three replications has been cured for 28 days and undergoes numerous cycles of freezing and thawing including 0, 1, 4, 7 and 10 cycles, then unconfined compressive strength of the specimens were determined. According to results of various tests, it was found that using 4% lime with 0.5% polypropylene fibre is the most appropriate combination for making strongest and most durable mixture, as unconfined shear strength of test samples do not change after taking numerous cycles of freezing and thawing.