جستجوی مقالات مرتبط با کلیدواژه "marl" در نشریات گروه "عمران"

The expansion of oil-dependent industries has caused a growing rate of oil extraction and increasing oil- and its derivatives-contaminated water and soil. The impacts and damages caused by oil pollution on human resources, water, and the environment have been very complicated. Oil and its derivates leakages into the soil can change its physical and mechanical properties. Oil-contaminated lands are thought of as the main challenge to the environment. Fuel and oil-reserve sites are common oil leak sites that may penetrate the soil. However, most Bandar Abbas refineries are situated on marl soil beds. Marl is composed of clay, and calcium carbonates of varying degrees of 20-65%, which, having been hardened, are converted into marl soil, thus becoming physically stiff and impermeable. Marl soil has high stiffness and shear strength under dry conditions, as these properties experience lower rates under wet conditions. The volatile behavior of the marl soil in water and organic pollutants makes it problematic when used in geotechnical projects. Thus, the present research takes a microstructural approach to investigate the geotechnical properties and environmental geotechnics of the marl soil contaminated with varying degrees of crude oil.

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).

Marl soils with their complex behavior can be found in different parts of the world, such as Spain, the United States, Italy, Britain, France, Canada, and the Gulf states. In Iran, also, Marls can be located in abundance in the marginal zones of the East Azerbaijan Province, Persian Gulf, Hormozgan, and Qeshm Island. Marl soils' engineering behavior and durability in dry and wet conditions are entirely different and cause challenges in construction projects. Marl-like soils are widely observed in different parts of the world. The behavioral characteristics of marl typically depend on the distribution and size of the particles and their plastic properties. Under dry conditions, the deformation of marl soil is due to the breakdown of particles and creating a new structure. However, when this type of soil is exposed to moisture, the aggregate bond will degrade and cause swelling in the soil and, at the same time, a change in its hardness and strength on the other hand, many polluting industries are located on marl soils. Usually, the pollution caused by these industries changes the pH and creates acidic and alkaline conditions in marl soils. Therefore, this study aims to study the effect of initial pH on the durability of marl soils from a microstructural perspective.

In this regard, marl soils with different initial pHs were prepared by adding 1 M sodium alkali hydroxide (NaOH) and hydrochloric acid (HCl). Changes in geotechnical and geoenvironmental characteristics were investigated by macrostructural experiments (Atterberg Limits, permeability, and unconfined compressive strength, durability, and water absorption testing) as well as microstructural experiments (Laser diffraction particle size analysis (PSA), X-ray diffraction (XRD), X-ray fluorescence (XRF), carbonate percentage determination and scanning electron microscopy (SEM) images) and the effect of initial soil pH change on marl engineering behavior was investigated.

One of the most important results of the present paper is the durability and stability of marl soils with initial pH ≤4 against moisture. Based on the SEM images and XRF analysis results, the formation of magnesium chloride in the structure of palygorskite and sepiolite has caused the stability of marl soils with initial pH≤ 4. Also, the initial strength of marl soil does not affect the durability of indentation.

Shallow foundation construction on soft and loose soils results in unacceptable deformation, high strain, and failure. Therefore, the implementation of shallow foundation on this type of soil can cause problems in terms of bearing capacity and settlement. Therefore, soil improvement is a logical and appropriate way. Geocell is a series of three-dimensional cells and its main application is to reinforce loose soils. Due to the mechanism of geocell interaction with the soil, the use of geocell reinforcement makes it possible to achieve a greater bearing capacity. In this study, using Abaqus finite element software, the effect of geometrical of geocell on the increase of bearing capacity of shallow foundation resting on saturated marl soil has been investigated. Also, using the analysis of the designed numerical models results, a correlation for homogeneity of the improved soil with geocell reinforcement has been presented instead of considering the soil reinforcement relations. The correlation coefficient and the presented diagram illustrate the high capability of the proposed correlation to estimate the equivalent shear strength to the geocell reinforced soil environment. The analysis results show that by increasing the geocell height for greater than , where S and B are the foundation settlement and the foundation diameter, respectively, the effect of the geocell height on increasing the bearing capacity is noticeable and it is more noticeable in looser soils. Moreover, by increasing the geocell pocket size up to (m) and the geocell length by twice the foundation diameter, there is an increase in the bearing capacity of the foundation and then, there is no noticeable change in the bearing capacity. With an increase in the length of the geocell, it can be stated that the optimal length of the geocell layer is about twice the diameter of the foundation. In order to produce a correlation for estimating the equivalent shear strength of the soil environment reinforced with geocell, a number of numerical models were designed.

Marly soils have a relatively good resistance in the dry state, but these characteristics tend to significant degradation in contact with water (Ouhadi & Yong, 2003, Hosseini et al. 2012). The Failure to identify the behavior of clayey fine-grained soils, and especially marls, can challenge the structures constructed on such soils. Because of the extent and distribution of this type of soil in many regions of Iran, especially in southern Iran, and the high potential for the construction of hydraulic structures in these areas, it is necessary to study the behavior of these soils. Accordingly, the purpose of this study is to investigate the geotechnical characteristics of marl soils and provide a solution for improving the engineering properties of these soils.

Temperature changes the engineering behavior of clay soils. Clay soils are used as a protective cover for burial of high-level wastes (HLWs), where the soil is exposed to medium to high temperature regimes. Marls are a type of sedimentary deposits consisting of clay minerals and calcium carbonate. These two components can substantially influence the behavior of marl soils from an engineering standpoint. The present study focuses on the engineering characteristics of marl soils under various temperature regimes with an emphasis on the microstructural changes in permeability coefficient, settlement, and compressive strength Therefore, after determining the geotechnical properties of the marl soil, its samples were exposed to temperatures from 25℃ to 900℃. The changes in marl soil properties were analyzed via mechanical tests (measuring permeability, consolidation, and uniaxial compressive strength), and microstructural tests (measuring pH and X-Ray diffraction), and scanning electron microscopy (SEM). The microstructural analysis of marl soil samples indicates that due to the deterioration and formation of new minerals as well as soil particle arrangement and microscopic texture; temperature regimes increase the permeability coefficient. However, at 700℃ the formation of cement compounds reduces permeability coefficient by an approximate factor of 50,000.

Marls are among sedimentary deposits that generally contain 35 to 65 percent of clay minerals and calcium carbonate. The presence of clay minerals in marls has significant effect on reduction of slake durability index of marls. Hence, marls stabilization is important. Furthermore, the presence of carbonate as one of the main components of marls has drastic influence on engineering behavior of soils. Heat, both in transient or constant forms, results in physical, mechanical and microstructural alternation of soils, especially the engineering properties of clay soils. Accordingly, the purpose of this study is to investigate the effect of heat treatment on strengthening parameters of marls, microstructural perspective. Impression of heat treatment on behaviors of marls, using macrostructure tests (Unconfined Compressive Strength, Atterberg Limit, Granularity, Slaking, Water Absorption and Linear Shrinkage) and microstructural tests (pH and X-ray diffraction) have been assessed. For this purpose, the specimens are exposed to heating surfaces (25 to 900 °C). examinations with emphasize on microstructural alternations of marls on specified temperatures and effect of temperature variations on mechanical and strengthening specifications of soil, have been conducted. According to the results, on 700°C marl soils have the best compressive strength of 27.69 Kg/cm2 and durability against moisture.

Marlies are of problematic soils, which easily eroded when exposed to water flow and create problems in the sustainability of the developmental projects substrate. Using additives such as lime, cement and nanoparticles is one of the methods for soil chemical modification. The present study investigates the effect of lime and nano-SiO2 on the engineering properties of marl soil and formation of new compounds due to the stabilization process. In this regard, after determining the geotechnical properties of Marl soil, the improvement of engineering properties of the samples stabilized with different percentages of lime and nano-SiO2 has been evaluated at the end of the treatment period. In order to identify present minerals in the soil and investigate the formation of calcium silicate hydrate compounds in the reaction of soil with lime and nano-SiO2, the X-Ray Diffraction (XDR) test was conducted. The results showed that the presence of nano-SiO2 in the limestone system led to the uniform distribution of cement (C-S-H) compounds in the soil. Based on the results, with increasing the treatment time, lime participation in pozzolanic reactions was increased, also, the results obtained from the Atterberg limits test showed a diminution in the paste limit of the marl sample with increasing lime and nano-SiO2 values.

Marls are problematic soils, which easily erode if they are exposed to water flow and problems in the stability of the bedding of construction projects can be occurred. One of the methods for soil chemical modification is the use of additives such as lime, cement and nanoparticles. The effect of adding nano-SiO2 on the lime performance on the enhancement of the improvement process of the marl soil engineering properties and the formation of new compounds due to the stabilization process has been investigated in the present study. In this regard, after determining the geotechnical properties of Marl soil, improvement of engineering properties of samples stabilized with various percentages of lime and nano-SiO2 after the end of the curing period was analyzed by performing large-scale experiments (Atterberg limits, aggregation, deposition and unconstrained compressive strength (UCS), and microstructure ((pH) and X-ray diffraction (XRD)). According to the results of this study, the presence of nano-SiO2 in the marl-lime soils system has led to increased pozzolanic activities and growth of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) nanostructures and uniform distribution of these nanostructures. The compressive strength of the modified samples with the combination of nanosilica and lime proportional to the increased nano-silica additive has a quite ascending trend. Based on the results of the present study, the development rate of improvement of marl soil engineering properties in a modified specimen with 6% lime and 1% nano-SiO2 increased the compressive strength in the first 7 days by 18.45 kg/cm2 and the compressive strength increased by 18 times compared to the reference specimen.

Using the Soil Nailing due to its numerous advantages, the traditional approach is to stabilize the excavation walls fitted. Due to the different behavior of marl soils in short and long-term and fundamental role of friction between soil cement grout around the walls were nailed, In this study, tensile strength and creep behavior of soil nails to maintain green marl are discussed. Therefore, the number 6 nails diameter of 11 cm and a length of 4 m in vertical and 2 achieve the same as the horizontal at an angle of 15 degrees to the horizon scale has been constructed and the effect of Drillings Type on the tensile strength and creep behavior were investigated. the results indicates 20 to 25% increasing in tensile strength of nails in vertical mode and 15% increasing in a horizontal mode implemented with non-smooth drill compared to smooth drill.