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

In this study, the improvement of a clay soil contaminated with MTBE (methyl tert-butyl ether) using magnesium oxide and hydrated lime was studied. Soil contaminated with MTBE was prepared in the laboratory, then mixed with different percentages of magnesium oxide and hydrated lime. Natural soil was also mixed with the same percentages used with the desired additives. Atterberg limits, compaction, Unconfined compressive strength, and SEM tests were performed on all samples. To determine the strength, the samples were prepared by static method and tested after 7, 14, and 28 days of curing time. The results showed that magnesium oxide and lime both increase the strength and E50 and thus improve natural and contaminated soil, which is a function of the percentage of used additives and curing time. The Comparison of improvement results showed that the final strength in natural soil is higher than in contaminated soil. In addition, the comparison of the results showed that lime has less effect on soil improvement compared to magnesium oxide. The SEM results also showed that the increase in strength is due to the cement materials produced during the carbonation process, which makes the particles paste to each other and make a rigid body.

Nowadays new materials for improving bearing capacity of soils are widely used. Kind of new materials used in this regard are geosynthetics. Geofoam panel type of geosyntethic materials is useful and alternative for backfill in retaining wall or pavement layers. Main idea in this research is study geofoam particles and moisture effects on improvement bearing capacity of clayey soil. Geofoam particles effects on clay in 0.05, 0.1, 0.2, and 0.3% percent were considered. Also, moisture were changed in 10, 12, 14, 16, 18 and 20 percent in specimens. In order to evaluating geofoam particles influence in geotechnical properties of clayey soil some laboratory tests such as compaction, uniaxial strength, direct shear and permeability tests were performed. Results of this study showed that clay specimens with 0.05% geofoam particles along with 14 % water content have optimum geotechnical behavior. As, maximum dry density went up, permeability decreased and shear strength of specimens increased.

Liquefaction is one of the most damaging geotechnical phenomena in soils. This phenomenon occurs in saturated, sandy soils that are loose-grained and subject to dynamic loading. When the pore water pressure increases, the effective stress becomes zero and the total stress is equal to the pore water pressure. In this case, the soil is no longer resistant and the sand becomes liquid. This causes damage to the soil and has the risk of liquefaction, so in this case a material is required to improve the strength parameters of the soil. This paper presents the methods used to improve liquid soils, their application and the soils suitable for each method. The method used in this study is a desk and laboratory investigation of the available sources. According to the results of this study, the selection of suitable methods for wetland soil improvement methods includes soil replacement, dehydration, site reinforcement, injection, thermal, geosynthetic, blasting and vibrocondensation.

Geotechnical and engineering structures transfer their loads to soil by foundation. Therefore, structures should be constructed on soil with high bearing capacity. Demand for suitable soil in civil engineering projects is high, but soil with high quality in terms of bearing capacity provides from long distance and uses. Although, this operation is extensive and time consuming. Social, economical and environmental challenges have been caused researchers find new method for improving soil behavior in terms of bearing capacity and strength. In the other side, waste materials such as plastic, wood, glass and etc. in terms of high volume production due to urban development and urbanization with high cost in disposal and maintenance have been caused serious researches for application of recycled waste materials in soils for improvement performed. Polyethylene Terephthalate (PET) is one of the waste material which is permanent and causes environmental pollution. As regard to supply and demand of plastic waste (PET) is increasing, so recycling and re-use is one of the major purpose in engineering and environmental protection (John and Rodwan, 2012). Nowadays, about the use of waste plastic strip and PET different studies have been performed such as (Sivakumar Babu and Vasudevan, 2008), (Sivakumar Babu and Chouksey, 2011), (Dutta et al., 2012) and (Soltani-Jigheh, 2014) can be mentioned. Main idea of this research is evaluation of flexible waste plastic strips (PET=Polyethylene Terephthalate) effects on mechanical and geotechnical behavior of fine-grained soil.

In the present century, the use of various petroleum products and fossil fuels has been an integral part of industry and human progress. Nowadays the major concern, in addition to the use of petroleum products, is their uncontrolled diffusion in various parts such as extraction, processing, transfer and use. The other problem with the utilization of these products has arisen in the field of geotechnical engineering includes environmental pollution and the creation of problematic contaminated soils. Many solutions to these problems have been investigated and presented separately. In the present study, the microbiologically induced calcium carbonate precipitation (MICP) method, as a solution to purify contaminated soils and to improve its reduced bearing capacity with two petroleum products, diesel and engine oil, has been proposed. The bacterium used in this process was Sporsarcina pasteuri, which was added to the contaminated soil as a flocculate bacterium. In two stages; purification evaluation (using chromatographic results) and geotechnical improvement (using direct shear and permeability test results) were performed. With the aid of FTIR (Fourier-transform infrared spectroscopy) analysis and chromatographic diagrams, a reduction of peaks of the identified components in the treated sample in comparison to the standard sample (prepared from diesel or engine oil) was observed. On the other hand, improving the geotechnical properties of contaminated soils was one of the most important effects observed in the treated samples.

Many road pavement maintenance projects are carried out at very high costs. Accordingly, the present study aims to provide a software model for prioritizing road pavement improvement projects using fuzzy hierarchical analysis. The criteria selected in this study include route length, current condition of the road, transverse slope, road drainage, traffic volume, traffic composition, route width and whether it is two-way or one-way. There are about 18 selected streets in Aq Qala city. After entering the criteria and options, improvement prioritization is done for pavement projects using hierarchical analysis method. The results indicate that North Khomeini Street is in the first priority and Esteghlal Street is in the last priority of improvement. Then, they are weighted according to the selected criteria, which are of quantitative and qualitative type, experts’ opinion, and pairwise comparisons. The results show that the current road condition criterion has the highest weight and the transverse slope criterion has the least importance. The criteria are divided into two descriptive-analytical and spatial categories, and their discrepancy rate is 0.03 and 0.02, respectively. The overall discrepancy rate is 0.03, which is less than the allowable limit.

Due to the rapid changes in the environment and business, only organizations in this environment will survive that are active and able to respond quickly to environmental requirements. Therefore, it is very important to pay attention to value engineering programs and plans in organizations and construction projects in order to improve and improve the quality level and improve products and services. Using value engineering in executive projects can become a tool for managing and controlling costs, given the complexity of the work, especially in large-scale development projects. Valuable engineering can improve and enhance the quality of new processes at any stage of an implementation project. Given that the Stone Creativity Phase is the cornerstone of value engineering projects, any improvement and reduction in cost and value created by system reform is due to the production of valuable ideas in the Value Engineering Creativity Phase. . In this research, while reviewing articles, books and valid standards through library studies, presenting and analyzing the current situation of value engineering in various construction projects, examining the obstacles facing the application of this methodology and implementing strategies to eliminate this damage. And the correct use and outcome of value engineering have been proposed.

Improvement of soils with the additives is one of the methods for surface or deep soil treatment. Improvement of soil by additives is one of the most important issues in geotechnical engineering. Typical additives such as cement, lime, fly ash and some nano materials have been previously investigated but pozzolanic materials, especially zeolite, which have unique features, have been less considered in geotechnical engineering. Due to the lack of sufficient studies on the effect of zeolite on soil properties and chemical properties of these materials, this study examines the effects of zeolite on soil strength parameters. In this paper, the effect of a type of zeolite called Clinoptilolite on the strength parameters of clayey sand soil has been studied. For this purpose, after conducting the identification tests on clayey sand (a mixture of clay and 161 Firoozkooh sand), the Atterberg limit test was performed on natural and stabilized samples with 5, 15 and 25\% Clinoptilolite. Also, uniaxial compressive strength test was taken into on samples with 0, 5, 10, 15, 20 and 25\% additive and curing times of 7, 14 and 28 days. The results showed that the atterberg limit increased with increasing the percentage of Clinoptilolite. Furthermore, the uniaxial compressive strength of the soil increased with increasing the amount of Clinoptilolite and curing times. The highest strength occurred at 25\% additive and 28 days. The failure behavior of the samples showed that with increasing time and percentage of the additive brittle failure was occurred and after brittle fracture the uniaxial strength decreases with high speed. Also, with increasing curing time, the failure plan in the samples becomes clearer. The results of this research are based on the laboratory test on a clayey sand soil with the engineering specifications presented in the study and may be different for other soils of this type. These results are also laboratory tests and may have a significant difference in soil conditions.

Nowadays new materials for improving bearing capacity of soils are widely used. Kind of new materials used in this regard are geosynthetics. Geofoam panel type of geosyntethic materials is useful and alternative for backfill in retaining wall or pavement layers. Main idea in this research is study geofoam particles effects on improvement bearing capacity of sand. Geofoam particles effects on sand in 0.05, 0.1 and 0.15% percent were considered and sand was considered in granular and angular conditions. In order to evaluating geofoam particles influence in geotechnical properties of sandy soils some laboratory tests such as compaction, direct shear (in vertical stresses 1,2 and 3 kG/cm2) and permeability tests were performed. Results of this study showed that with increasing 0.15% percent geofoam in sandy soils maximum dry density went up, permeability decreased and shear strength of specimens increased. Although, geofoam particles is more effective in angular sandy soil than granular sand.

Factors affecting the skid resistance are devided into three categories: weather conditions, traffic fluctuations and parameters related to vehicle. One of the factors related to the pavement is the average depth of coarse texture. The main objective of this study is to obtain an average depth of pavement texture. In order to achieve this goal, an appropriate aggregation was selected from the Iran’s road pavement Regulations (open and continuous gradation 5). Some samples were made by Marshall Test using the selected gradation and six different types of pure bitumen 60-70 with the percentage of 4, 4.5, 5, 5.5, 6, 6.5% and calcareous mountain broken materials. After analyzing the results for each sample, the optimum bitumen percentage was obtained for each sample. Regarding the optimum bitumen, gyratory samples were made. The coarse texture effect on these samples was investigated through sand spread method (based on ASTM E965-96) and the most appropriate gradation was selected regarding the skid rtesistance. The results showed that an average depth of open coarse is better than continuous course. Also porous asphalt could be an appropriate option to eliminate the phenomenon of skid resistance due to possess suitable vacuum drainage and continuous transverse surface water.

The seismic performance of quay walls is found to be strongly dependent on liquefaction occurrence. Besides, in some existing walls that were designed without consideration of the liquefaction hazard, due to the relatively long length of quay walls, the orientation of soil strata probably caused the liqueable layers to appear unavoidably neighboring the wall roots. In this paper, the dynamic response of anchored sheet pile quay walls embedded in liquefaction susceptible soil was investigated numerically, utilizing the strain space plasticity model for cyclic mobility available in the DIANA nite element program. Based on the results, the extension of liqueable soil around the wall root leads to the "failure at embedment" mode. Deformed mesh indicates that the most visible deformations are localized in loose soil around the embedded section. Beside the noticeable heave of the seabed, its seaward displacement causes a signicant reduction in its supporting role for the embedded section, and leads to the large tilt of the wall. Consequently, an active wedge, extending from the embedded section to the back of the anchors, is formed. Moving along this wedge, the anchors endure signicant overturning. The mentioned deformation shape was previously observed in shaking table tests conducted by the authors. The leeward section of the loose layer is recognized as the most vulnerable zone against liquefaction. Besides the eect of soil softening in this zone, dynamic active pressure behind the wall causes the bottom of the wall to experience higher displacement than its top. The time history of monotonic bending moment infers that considerable moment is applied to the wall root by the loose section behind the root. This moment is the main reason for the "escape" of the wall root. The remediation method, by deep vibro-compaction of the weak area, is considered as a liquefaction countermeasure. The eectiveness of soil improvement in zones adjacent to the embedded section is discussed, based on analytical dynamic responses. Implemented countermeasures are found to considerably reduce deformations in the wall; however, in order to prevent failure at embedment, improvement of soil located behind the wall root is more eectual. The compacting of this section not only reduces driving moment applied to the wall root, but also creates resistant moment against root escaping. In addition to the impact of base acceleration amplitude, the optimum extension of improved zones is introduced.

improvement is essential. In cases where weak soil is improved by a replacing method, the improvement depth, due to the stress distribution pattern, is of great importance. However, in some cases, it is very dicult or too expensive to provide enough improvement depth. Hence, additional bearing capacity or other improvement methods are required. Using a geogrid to reinforce soil is an eective alternative way to improve the bearing capacity more eectively and economically. In this paper, the eect of replacing a loose layer by a dense one on the bearing capacity and settlement of a strip footing has initially been investigated. Then, the in uence of a geogrid layer placed on the interface of loose and dense layers is analyzed and investigated using nite dierence FLAC  software. The numerical model is veried and calibrated using experimental data from a physical model developed in the Soil Laboratory of Amirkabir University. Analyses results show that increasing the depth of compacted soil layer by more than  times the width of the foundation, does not have a considerable eect on the ultimate bearing capacity of strip footings, and only settlements will decrease. Using a geogrid layer between loose and compacted soil will improve the bearing capacity greatly, for a modied depth less than  times the width of the foundation 'The most ecient improvement in this method is when the geogrid layer is placed on the boundary of loose and dense layers at a depth of  the foundation width. The eciency of reinforcement is reduced by increasing the improvement depth. Using a reinforced layer with a width of less than  times the foundation width is not recommended.

During recent earthquakes، it was observed that liquefaction can cause severe damages to several countries'' infrastructures including the buildings، bridges، road and railways in the form of significant settlement and the relevant shear failures of subgrade soil. Amongst the various rehabilitation methods of the soils tending to be liquefied، utilization of the stone column have encountered with more attention because of its beneficial characteristics from both technical and economical points of view. One of the major issues in this matter is their efficiency in liquefaction mitigation in the single and group forms. For this purpose the current study has dedicated to numerical investigation of the problem of stone column efficiency in dissipating the excess pore water pressure during the earthquake excitation، and The reliability of the numerical modeling is verified via a centrifuge test results of VELACS project. a three dimensional analysis is carried out using FLAC3D. Also، effects of various parameters such as stone column diameter، stone columns distances on the liquefaction resistance of NEVADA sand soil are investigated.