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

In the current study, using a physical model, the behaviour of anchors with horizontal end plates at shallow depths has been investigated. In this research, the effect of various factors such as the buried depth of the end plate, the diameter of the end plate, the type of soil, and the geocell and geotextile have been investigated. Based on the load-displacement curve obtained in the experiments, the results have been investigated. The results show that the rupture mechanism and the obtained load-displacement curve are a function of the conditions in the tests. For example, the shape of the load-displacement curve when there are geocells and geotextiles is completely different from the normal state (without geocells and geotextiles). On the other hand, the results show that the maximum value of the upward force obtained for the normal state is a function of the diameter of the plate and the buried depth so that its value increases with the increase of the diameter and depth of the plate. The effect of depth is much more important in the presence of geocell and geotextile on the results. The results obtained on different tested soils show that the pull-out force of the anchor is a function of the shear resistance parameters of the soil. As the sand friction angle increases, the force has increased. The results indicate that with the increase in the depth and diameter of the plate, the effect of sand on the maximum pullout force has increased. The results show that with the addition of a layer of geocell or geotextile, the tensile force of anchors increases significantly, and the combination of two layers of geocell and geotextile causes a significant increase in the pull-out Capacity.

Understanding the behavior of the pile group near the slope is an important factor in designing a structure adjacent to the slope. There are very little research on the vertical capacity and efficiency coefficients of pile group near slope, so the study about the behavior of pile group adjacent of the slope is very important. The purpose of this study is to investigate and compare the bearing capacity and efficiency coefficient of vertical pile group under axial loading in the near sandy slopes in two modes of free horizontal movement and no free horizontal pile movement by testing the physical model of pile group. Also in the this study, horizontal force applied to the pile group with free lateral movement is investigated with the FLAC3D software. For this purpose, a series of experiments were performed on the physical model of 2 × 2, 2 × 1, 3 × 1 and 3×3 pile groups adjacent to the dry sandy slope without horizontal displacement and the results were obtained with previous research of other researchers in which the lateral displacement of the pile group has been free, compared. The results of the physical model tests show that the bearing capacity and efficiency coefficient of the pile group is dependent on the pile distance, the pile group configuration, and the liner pile-group direction relative to the slope direction. Also, the results of the physical model tests show that the bearing capacity and efficiency coefficient of the pile group with free lateral movement have higher values than the pile group without lateral movement. Numerical analysis results show that the lateral force applied to the pile group decreases by increasing the spacing of the piles, and the ratio of horizontal force to axial force in the linear pile group decreases with increasing number of piles.

In this research, dilation effect related to density and confining stresses during liquefaction on structural settlement is investigated using OpenSees. Therefore, a sand layer with different dilation angles and surface load is considered. The numerical model presented in this research, calculated the excess pore water pressure based on fully coupled effective stress analysis during seismic loading. Model parameters were selected and verified using the results of VELACS centrifuge tests. The results show that by increasing the dilation angle, the pore water pressure decreases and the liquefaction-induced settlements decrease. The decreasing trend of settlement with increasing dilation angle tends to a constant value, so that at high densities with increasing dilation angle, little changes in settlement is observed. Also, the dilation angle is calculated based on the preshear mean effective stresses and compared with the dilation angle caused by the stresses during liquefaction. The comparison shows that for relative densities less than 60%, the dilation angle obtained from preshear effective stress is more than the confinig stress based method during liquefaction.

Several factors affect the bearing the load of natural and engineered embankments and slopes including the crude oil leakage, leading to a severe decrease in resistance. This is especially important for oil-rich countries, such as Iran, which have several crude oil resources. The main purpose of this study is to investigate the load bearing the load (i.e. load versus settlement) and strain-stress behavior of crude oil contaminated sandy soils using California Bearing Ratio (CBR) Test. In this paper, 10 different types of sand with different characteristics used. At first, a series of CBR experiments performed for natural sands (i.e. clean sands) and then contaminated sands with 6% crude oil tested under similar conditions and densities to obtain the reduction in bearing the load of crude oil contaminated sands quantitatively. Experimental results showed that bearing the load of sand containing 6% of crude oil decreased at least 50% compared to clean sands and the stress-strain diagram of these contaminated soils would decrease significantly. Based on the results of investigation, it can be stated that particle shape(sharpness or roundness), coarse particle ratio,and finally the type of aggregation influences the resistance of crude oil contaminated sands. It was also found that standard Ottawa sand had 83% reduction in strength and sand with a coarse particle had 57% decrease in strength. Sand contaminated with crude oil experience a severe loss of bearing capacity,so in designing foundations and engineering structures, greater safety factors should be considered, where there is a risk of crude oil leakage.

The rigid base proximity (such as stiff rock) under a relatively thin sand stratum and employing a 3D reinforcement (e.g. geocell) can tend to significant improvement in the bearing pressure of shallow footings. In this study, the behavior of circular footings located on unreinforced and geocell-reinforced thin sand layer was investigated. The simultaneous or individual effect of footing dimensions, sand layer thickness, and geocell reinforcement on the bearing pressure and settlement was studied by conducting large-scale model tests. The influence of soil layer thickness on footing behavior was elucidated by considering optimum dimensions and location for geocell reinforcement. Based on the results, improvement in the bearing capacity and settlement reduction for both unreinforced and reinforced footing bed was seen when the sand layer thickness is lower than two times of the footing width. Additionally, the effectiveness depth of the rigid base for both cases was obtained two times of footing width. The combination of geocell reinforcement and rigid base as lateral and vertical confinement factors, led to increase in the bearing capacity and settlement reduction at the failure point up to 45% and 53%, respectively. The tests results were served to define new factors extending classical bearing capacity equations for footings located on thin soil at reinforced and unreinforced cases. The comparision of this study’s achievement with the previous investigations confirmed their good agreement.

This article addresses the question of how the use of helical piles will improve the uplift capacity and displacement. Shahriar sand has been used with the relative density of 70% and the compression operation has been performed using hammering. The universal Zwick/Roell Z160 apparatus has been employed for tensile. With regard to the dimensions of the apparatus, the sand container was designed and physical modeling of the helical pile has carried out using dimensional analysis and nondimensionalization by Buckingham π theorem. After fabricating of the pile sample with pitch of 13, 20 and 25 mm, the behavior of simple and helical piles were investigated and the effect of pitch was examined. The maximum uplift capacity and its associated displacement were extracted and analyzed. The results show that the maximum uplift capacity of helical piles with pitch of 13, 20 and 25 mm in comparison with the simple pile increased 453.57%, 518.66% and 436.24%, respectively. When the ratio of the pitch/central shaft diameter is between 1 and 1.5, the tensile capacity is improved by the generated friction and the weight of sand on the blade as a resisting factor. By increasing the ratio of S/d to 1.92 the blade torsional angle increases and the sand weight on the blades decreases. Therefore, the uplift capacity is reduced compared to the previous two. The outputs show that the displacements of helical piles are approximately equal.

Penetration tests are one of important geotechnical insitu tests by which, different soil parameters can be estimated. The advantages of these tests are easiness, high speed, and repeatability. In this research, a penetrometer called as “Manual Dynamic Penetrometer (MDP)” is utilized to perform tests on dry Firoozkuh Sand with three different relative densities. The MDP is similar to other penetrometers used in geotechnical engineering, but the dimension is different which causes to generate more power to penetrate into the soil with deeper layers. The aim of this research is to investigate the effect of cone geometry as well as applied energy on test results. To do so, three different cone diameters and cone apex are considered. In addition, the mass of the hammer is also changed in three different values. The comparison of results indicate that the come apex does not influence the penetration value; however, the cone diameter plays the role. It is also seen that the applied energy has direct relationship with the penetration. Since the mechanism of the cone penetration is similar to that of pile driving, it was also shown that it is possible to estimate the residual internal friction angle of the soil by using empirical formula proposed by Meyerhof.

Construction wastes can be found easily and are increasing by the developing of cities. Lack of sufficient knowledge and facilities for recycling these materials causes deposition of these materials and unfavorable scenes in suburban regions. Settlement of these materials makes some troubles for building constructions on them. Prevalence of disease, growing of vermin and also the low potential of these materials for raising plants are some of the problems which are the motivation for many scientific researches about recycling of these materials. In this study first brick, gypsum and cement contained wastes were collected and then 200 samples with 3, 6 and 12 percent of cement in 4 groups with different mixture of wastes were made. Compressive and indirect tensile strength tests and the test of durability against freezing and thawing were conducted to evaluate these materials to be used in stabilized base and subgrade layers. The results show that many mixtures of these materials have sufficient compressive strength and durability to be used in base and subgrade layers according to highway construction codes.

Carbon fiber polymer reinforcement sheets are available in two types of unidirectional and bidirectional woven sheets. Since the carbon fibers are one-directional tensile elements, any material produced from fibers will be anisotropic material. In this research, the anisotropy of the interface behavior between Carbon Fiber Polymer Reinforcements (CFRP) and sand was investigated at the laboratory. The main objective of this study was to evaluate the effect of the moisture content of the soil and the direction of the shear force on the interface behavior of sand and CFRP. The soil used in this study was a sandy silt collected from Joupar road in Kerman. Two types of CFRP sheets including unidirectional and bidirectional woven carbon fiber polymers were used in this study. The soil samples were prepared with different water contents ranging from 8.5 to 14.5% with a similar dry unit weight of 19.3 kN/m3. The direct shear test device with a modified shear box used to perform the interface shear tests under 50, 100, and 150 kPa of vertical stresses with 1mm per minute shearing rate. For unidirectional CFRP sheets, two series of parallel and perpendicular and for bidirectional CFRP sheets, two series of diagonal and parallel interface shear tests with different water contents of the sand were conducted. The results of these investigations showed that the interface behavior of sand and CFRP was anisotropic and was dependent on the direction of the shear displacement. For both unidirectional and bidirectional CFRP sheets, the interface friction angle was maximum when the shear direction was perpendicular to the fibers direction. The variation in the interface friction angle in the direction of the shear force in the unidirectional CFRP sheets was more considerable when compared to bidirectional CFRP sheets. The interface friction angle between sand and bidirectional CFRP sheets was larger than that between unidirectional sheets. Increasing the moisture content reduced the interface friction angle for both types of CFRP sheets; however, its reducing effect was much more considerable for unidirectional CFRP sheets.

In this paper, the comparison between the behavior of pile groups with two types of connector plugs into the cap clamped and has been joint and seismic response of pile groups with shear force, axial force, vertical displacement, horizontal displacement of the torque moment in the pile is measured. For this purpose, three-dimensional dynamic finite element software Ansys 3D under earthquake loads in use and the results were compared with each other. Finally, comparing the behavior of pile groups in both study with two types of connector shows a joint connection for minimizing vertical displacement and fixed connection to minimize the axial and shear force and bending moment is right. It means that the fixed connection have a better operation than the joint connection. because the joint connection have a better operation just at the vertical displacement and optimizes it. But fixed connection have a better operation at most of outputs.Keywords: pile, pile cap, dynamic analysis, liquefaction.

Due to the increasing production of plastic materials, there is an international concern about disposal or recycling of plastic waste in the world. One of the ways to reuse plastic waste is to use it in the engineering works to modify mechanical properties of loose soils. The purpose of this research is to find a way to reuse a particular kind of plastics (bottles of dough, soft drinks, mineral water, etc.) in geotechnical works to improve soil.In this paper, the mechanical behavior of Anzali Port sand, reinforced with 1×1 cm polyethylene terephthalate crumbs and 1×5cm strips, to 0, 0.1 , 0.5 , 1 and 2% and polyethylene terephthalate fibers to 0 and 0.1 and 0.5% of the dry weight of the soil which were arranged separately, was evaluated. Samples were prepared at the relative density of 75%. The effects of parameters such as dimensions, the weight percentage of reinforcers in the soil and vertical stress were investigated. The results of the experiments showed that although the polyethylene terephthalate crumbs and strips improve the mechanical behavior of sandy soil, but the effect of fiber reinforcers on soil mechanical properties has been much higher. Also, the optimum percentage of polyethylene terephthalate crumbs and strips reinforcers was 1% of sand dry weight. The comparison between reinforced and unreinforced samples showed that reinforced specimens had more ductility and resistance.

Soils, which show a large amount of volume reduction and cause a series of sudden settlements on the surface of the earth, due to the increase of moisture, are referred to as collapsible soils. In many different countries, the immediate settlements of these soils, especially in warm and arid areas, have caused the formation of subsidence and sinkhole. These soils always create inappropriate conditions for the construction of structures such as buildings, road projects, foundations, water channels and other civil engineering projects. The occurrence of such sinkholes in parts of Iran and other parts of the world is one of the geotechnical problems of the above problematic soils. Several sink holes have formed in the northern sector of Hamedan. The soil types in this area include sandy and clayey soils which have low dry density. Generally, collapsible behaviour of soils can be evaluated by the use of odometer test. According to the ASTM standard (D5333-03), the collapse index (Ie) is used to determine the magnitude of collapsible possibility during saturation at 200 kPa in a simple odometer device. The purpose of this study was to investigate the effect of changing the order of clay and sand layers on the collapsible behavior mechanism of collapsible soils and on the changes in the collapse index. To achieve the above mentioned objective, the sandy soil was used from the northern areas of Hamadan and kaolinite clay (Super Zenouz of Tabriz) used to make the samples in three single-layer, two-layer and three-layer systems in specific molds made to a height and diameter of 5 cm in the odometer apparatus. Accordingly, in the present laboratory study on these two types of soil, considering the different arrangements of clay and sandy layers, at each stage of the specimen preparation, specimens were prepared in three different series with a dry unit weight of 1.3, 1.5 and 1.7 g per cubic centimeter in a odometer metal molds. By carrying out a series of odometer experiments, it was found that the sandy soils of the study area alone did not have a high percentage of the collapse index. However, with the presence of clay layers in such soils, the collapse index increases, so that collapse index at a unit weight of 1.3 g per cubic centimeter in the sample made in a single-layer system (fine-grained sand sample) reached from 3.8% to 8.7% in the sample made in the presence of a clay in the two-layer system, (the lower layer of the fine-grained sand and the upper layer of clay). Based on the results obtained from this study, the mechanism of collapse can significantly being influenced by the order of layering in that with increasing dry unit weight, the effect of the ordering of the layers on the value of the collapse index decreases. The results of this paper shows that in specimens made with a density of 1.7 g per cubic centimeter, the collapse index of all samples are almost similar values. In other words, the collapsible behaviour of soils is a function of soil dry density.