جستجوی مقالات مرتبط با کلیدواژه « shear strength parameters » در نشریات گروه « عمران »

Due to the ever-increasing growth of fossil pollution in the air of big cities or any other place, the resulting rain will be acidic. The reason for the formation of acid rain particles is nitrogen group compounds. That is, the combination of existing water with nitrate causes the phenomenon of acid rain. The soil may be exposed to various pollutants over time, including acidic pollutants and its shear resistance changes.Therefore, this issue is investigated in this research. On the other hand, investigating the behavior of soil under the effect of acidic contamination is so important because the excessive using of the sand-bentonite mixture in the Landfills. According to this subject in this research Sand of Firoozkooh with different percentages (0, 10%) Bentonite to carry out the undrained consolidated triaxial tests is use to investigate the effect of nitrat acid solution with (1,3)pH for investigating the influence of acidic contamination on shear strength parameter. Results that comes out from experiments indicates that Presence of acid lead to reduction of shear strength of clean sand. Although in sand-bentonie mixture with pH=3 shear strength increased but rising of acid in pH=1 lead to decrease of shear strength. Also presence of acid make the positive pore pressure higher.

In this paper, the effect of various parameters on the shear strength parameters of soil reinforced with ceramic fibers coated with nano-silica and kaolin particles has been investigated using the results of direct shear tests. The effect of the ceramic fiber content, fiber length, the nano-silica and kaolin contents and the content of fibers coated with nano-silica and kaolin on the shear strength parameters of reinforced silty sand has been investigated. The microscopic structure of the samples and the interaction of nano-silica, kaolin and fibers have also been examined with Scanning Electron Microscope (SEM). The results show that the shear strength parameters of the samples increase by adding ceramic fiber, nano-silica or kaolin particles to the natural soil. The length of ceramic fibers does not have a significant effect on the shear strength parameters of fiber-reinforced specimens, and 0.5% fiber content was recognized as the optimal fiber content. The samples containing kaolin particles have a higher shear strength than those containing nano-silica particles for a constant content of additive. The coating of fibers with kaolin has a greater effect on increasing the shear strength parameters of the samples.

In road projects, a suitable base for project execution is essential. Many of the soil types, such as wind sand, are not suitable for road building, and there is a need to carry out operations to prepare these soils for the base. In many cases, there is a need to switch to bed soil, but it is costly and will prolong the execution time of the project. Since it is challenging to reach ideal soil for road construction projects, soil improvement is being carried out. This is done in different ways, one of which is adding different materials to the soil. In this study, this method is used to stabilize the wind sand of Yazd. Two different types of glass fibers (type E and AR) have been used in this study. In order to perform the compressive test, the soil with both types of glass fibers was mixed in different percentages of 0.25, 0.5, 0.75, and 1 percent. The results showed that the percentage of optimum moisture increased by increasing the percentage of glass fibers. It should be noted that glass fibers did not affect the maximum dry soil weight. The direct shear test was done with the same percentages used in the compressive experiment. In this experiment, adding 0.75 and 0.5 percent of the type of AR and E to soil was selected as optimal for internal friction angle and cohesion, respectively. Also, using glass fibers of type AR in the studied soil had better results.

By the expansion of the industrial zones, heavy metals enter the environment through industrial wastewater or leakage from storage tanks, which contaminates the soil and groundwater. The leakage of heavy metals such as lead, zinc, cadmium and etc. is not only an environmental crises, but also causes changes in soil shear resistance parameters. Type of soil and initial concentration of contamination are most prominent parameters that affect the behavior of contaminated soils.In this research, with Triaxial tests, the behavior of sandy soils with different percentages of kaolinite in two cases of non-contaminated and contaminated with lead is investigated. It can be seen that by increasing the lead concentration, the hydrogen bonding between kaolinite particles reduce and it decreases the resistance of contaminated soils. By increasing the concentration of heavy metals up to 20,000 ppm, the shear resistance of clayey sand with 15% and 25% kaolinite decreases by 18% and 24%, respectively. Then, to investigate the effect of clay minerals on contaminated soils, the shear resistance parameters of soil with kaolinite and soil with bentonite are compared. The results show, with variation of clay minerals in contaminated soils, resistance parameters have different behavior. Increasing the lead concentration in bentonite causes a flocculated structure, thus the shear strength increased. In soils with bentonite, shear strength parameters increase 20% to 30% with increasing the lead nitrate concentration

Petroleum contamination in soils induced by oil products such as crude oil, gasoline, and motor oil is an issue raised widely in oil-rich countries like Iran. Contaminated soil with oil products is considered as a common environmental problem, but under the physical-chemical processes that occurred between these contaminants and soil, new geotechnical behavior is expected, which can reduce the soil bearing capacity, change the soil strength parameters and vary engineering and geotechnical properties of soil. Once the leakage occurs, resulted by self-gravity, the oil flows towards the groundwater level, which will cause soil-saturation with this hydrocarbon liquid. In spite of this, lateral propagation of the liquid may result in a wider scale of contamination. Oil pollution near the shore, contaminates the soil across the entire coastline. In this case, to account for the pollution of soil, regarding the environmental conditions, soil type, and type of contaminants the geotechnical properties are revised. The largest oil contamination in soil occurred in recent decades due to the Persian Gulf war in Kuwait, where a volume of 9 million cubic meters of soil in 19.05 million square meters was contaminated to oil; about 69 lakes were created to gather the diffused crude oil. Another case is the destruction of tanks of the refinery of Tehran and Abadan in the war between Iran and Iraq, which caused intense oil-pollution.

Problematic soils are those that make the construction of foundations extremely difficult. Some problematic soils loss their strength, at saturated conditions. As silty soil and quicksands have low strength at saturated condition, it seems that stabilizing of these soils is necessary. In literature, stabilizing these soils by cement is more effective. On the other hand, by developments in nanotechnology within last three decades, researchers discovered a material with unique properties, named as carbon nanotube. The carbon nanotubes has very high strength even higher than steel, high elastic module and toughness and other unique properties. Within last three decades, many studies are concerned about applying this material in cement composites, but only we can find a few works related to use this material in soil stabilization. Since carbon nanotube attract each other, we should separate nanotube particles. In this study, different values of ultrasonic energy and polycarboxilate based super plasticizer solution was used to overcome carbon nanotubes agglomeration problem. As it is not possible to use carbon nanotubes in dry state, to investigating the effect of carbon nanotubes on the soils, the aqueous solution of carbon nanotube was added to the soil, using wet mix method. The samples were cured in water for 7 days. After performing direct shear test the shear strength and its parameters were evaluated.