Sharif Digital Repository

The ground experiences various hydraulic conditions under climate and groundwater level changes, and it becomes dry or wet frequently. The states of pore-water within the geomaterial, being signified in terms of suction and saturation degree, change during these variations, and consequently affect the soil behavior. The main objective of this research is investigation the effect of anisotropic loading induced by rotation angel of principal axes parameter under unsaturated conditions . Hence, shear strength of firoozkooh silt, in terms of deviatoric stress at failure under monotonic loading under different values of rotation angel of principal stress axes parameter and confining stress have... 

The increase in the amount of groundwater exploitation and climate changes has made land subsidence into one of the environmental problems and has caused many problems in various infrastructures such as urban areas, residential buildings, and vital arteries such as power transmission lines. Many areas of the country, especially areas with smooth topography such as plains where alluvium accumulates, due to excessive exploitation of groundwater resources and climate changes, are facing a decrease in the level of groundwater, an increase in the thickness of the unsaturated layer, and as a result, progressive subsidence. In particular, the destructive effects of land subsidence on power... 

In many of the geotechnical engineering projects, such as embankments in earth dams and roads, the soil bears anisotropic loading. Even that the behavior of this material depends on the anisotropic loading, not many researches have investigated the effects of this phenomenon. The main objective of this research is investigation the effect of anisotropic loading induced by rotation angel of principal axes parameter under unsaturated conditions. Hence, shear strength of firoozkooh silt, in terms of deviatoric stress at failure under monotonic loading under different values of rotation angel of principal stress axes parameter and confining stress have been studied. For this purpose, silty... 

A physical model has been developed in the advanced soil mechanic lab of the sharif university of technology. This model has been used to investigate the thermo-hydro-mechanical behavior of the group energy pile, which was embedded in the unsaturated silty sand soil. This model contains a steel soil box, 4 aluminum piles, strain gauges, the total pressure cells, the thermocouples, and the mechanical load. Three sets of tests were conducted on these piles. In the first the thermal cycles were applied on 1 pile and in the second and third tests, the number of the energy piles was 2 and 3, respectively. The result has shown there was a permanent settlement at the end of the thermal cycles.... 

Shear modulus and damping ratio are the most important parameters for evaluating and designing the performance of geotechnical systems under dynamic loads. According to the definition, the secant shear modulus is the slope of the hysteresis shear stress-shear strain loop. Also, the damping ratio indicates the dissipation of wave energy during propagation in the soil. This research presents an experimental laboratory study on the effect of non-plastic fines content and hydraulic hysteresis on the Gmax of unsaturated sand-silt mixtures. A significant part of the previous research has been done to determine Shear modulus and damping ratio parameters. It has been done in completely saturated or... 

In many of the geotechnical engineering projects, such as embankments in earth dams and roads, the soil bears anisotropic loading. Even that the behavior of this material depends on the anisotropic loading, not many researches have investigated the effects of this phenomenon. The main objective of this research is investigation the effect of anisotropic loading induced by mean principal stress parameter under unsaturated conditions. Hence, shear strength of firoozkooh silt, in terms of deviatoric stress at failure under monotonic loading under different values of intermediate stress parameter and saturation degree have been studied. For this purpose, silty samples have been prepared with... 

Oil pollutants are among the important sources of pollution in countries with oil and gas industries such as Iran. Soil pollution by these pollutants is one of the environmental issues and hazards. All kinds of organic and inorganic pollutants in the soil may penetrate the underground water or enter the atmosphere in the form of gas, which respectively enters the food chain through absorption by plants or enter the body of living organisms through breathing. They include humans, which are a threat to the health and life of living beings. For example, many of these pollutions cause diseases such as cancer, suppression of the body's immune system, or even obesity; therefore, it is necessary to... 

Shear modulus and damping ratio are the most important parameters for evaluating the performance of geotechnical systems under seismic and dynamic loads. According to the definition, secant shear modulus is the slope of the hysteresis shear stress-shear strain loop and damping ratio indicates the dissipation of wave energy during propagation in the soil. These parameters depend on stress state, shear strain and void ratio of the soil. Shear strain amplitude has an important effect on the behavior of shear modulus and damping ratio and it is necessary to study the behavior of these parameters in the range of small to large strains. In addition to dynamic loading, climate change and wet and... 

Given that highly deformable natural deposits such as collapsible and swelling soils make up more than one-fifth of the land surface and are generally in unsaturated conditions, behavioral measurement of this type of soil including accurate measurement of its hydraulic properties is important. The challenges of designing and implementing construction infrastructure, along with the most reported financial losses due to the presence of these soils, double the importance of studying the behavior of these soils. The large volume changes of these soils in contact with water (equivalent to a volumetric strain of more than 5%) has been a major challenge for researchers in predicting the... 

In all five continents, existence of collapsible soils such as Loess has been reported. These kinds of soils have mutual properties such as open structure, high void ratio and low dry density. Collapsible soils are always at risk of experiencing significant reduction in volume due to increasing water content or degree of saturation. Hence, this kind of soil can lead to serious problems including reduce of load bearing capacity, excessive deformation and failure of foundations.Collapsible soils exist in several regions of Iran. Consequently, researching their properties is a key point of geotechnical studies in our country. Hence, in past 10 years, several studies have been conducted by... 

Microbially-induced calcium carbonate precipitation is a low-cost, environmentally friendly, novel ground improvement technique that has received much attention in recent years. Most studies on biological soil stabilization have investigated the mechanical and hydraulic behavior of soils in dry and saturated conditions. However, the behavior of soils stabilized by this method in the unsaturated state should be of immense concern through the extent of unsaturated soils in nature. Therefore, this study aims to investigate the effects of microbially-induced calcium carbonate precipitation on the soil-water retention curve and changes of small strain shear modulus of unsaturated cemented and... 

Loess with a dispersion potential is one of the problematic soils of Iran. This study aims to investigate the impact of dispersion potential on the water flow in a three-phase medium and determine the effect of salinity on the stability of an unsaturated railway embankment by employing the soil-water retention curves of the materials. To satisfy this objective, the natural dispersive loess of the Chabahar region is desalinated in this study and the hydraulic properties of both saline and desalinated soils are comprehensively investigated. First, the soil-water retention curves of the materials are measured through the filter paper test method. Afterward, the saturated hydraulic conductivity... 

Shear modulus and damping ratio are of the most important parameters for geotechnical structures during dynamic and seismic loading. Secant shear modulus is the slope of hysteresis shear stress-shear strain loop, and damping ratio is indicative of dissipation of waves energy during propagation in the soil. These parameters mainly depend on void ratio, stress state, and shear strain of the soil. Climate changes cause some drying and wetting process which changes the soil state from saturated to unsaturated form. Previous researches indicated that the shear modulus and damping ratio change with the amount of matric suction. During the drying process, the matric suction increases,therefore,... 

The deposits in many regions in Iran, particularly eastern zones like Golestan, Semnan, Yazd, Kerman, Hormozgan, Sistan and Baluchestan provinces consist of deposits of loess, which are categorized as collapsible soils. This kind of soil show sufficient shear strength and low deformability in dry or natural condition. However, if a structure is built on the soil and water seeps or infiltrates into the soil due to several reasons such as sewer leakage, water seepage or heavy precipitations in a way that its moisture reaches to a critical value, the interparticle bonds may break or the present suction in the soil may decrease in a way that the soil experiences sudden collapse, which may result... 

In this research an analytical and semi analytical solution to the differential eqautions derived from coupled analysis of heat transfer, moisture transfer and solid deformation in porous materials is presented. In first section, differential equations derived from Hydro-mechanical analysis of an unsaturated soil layer with limited thickness was considered and it is assumed that pore air pressure is equal to atmospheric pressure. To solve the system of equations laplace transform is used.In second section, the effect of daily changes in temperature on transient heat and moisture transfer in semi infinite layer is studied in three dimension. Energy conservation equation and pore liquid mass... 

Evaluation of the seismic-induced settlement of an unsaturated soil layer depends on several variables, among which the small strain shear modulus, Gmax, and soil’s state of stress have been demonstrated to be of particular significance. Recent interpretation of trends in Gmax revealed considerable effects of the degree of saturation and hydraulic hysteresis on the shear stiffness of soils in unsaturated states. Accordingly, the soil layer is expected to experience different settlement behaviors depending on the soil saturation and seasonal weathering conditions. In this study, a semi-empirical formulation was adapted to extend an existing Gmax model to infer hysteretic effects along... 

The seismic behavior of pile-supported systems has been an active area of research over the past decades. However, focus has mostly been on evaluating the seismic response of structures embedded in either dry or fully saturated, especially liquefying soil conditions. In this study, a series of dynamic centrifuge tests have been conducted to investigate the effects of soil’s degree of saturation on the seismic behavior of pile-supported superstructures. The scaled physical model tests were carried out on two distinct pile-mass systems embedded in uniform sand layers. A steady state infiltration technique was used to control matric suction profiles in the sand layer prior to shaking. The... 

The subsidence phenomenon in the past years has caused many problems and issues for the agricultural lands, roads, power transmission lines, energy etc., due to different reasons including over use of groundwater resources and changes in climate. This phenomenon has been observed in different plains of the country including the Khorasan, Kerman, Hamedan, Ghazvin and Isfahan plains and has caused many damages to infrastructure and agricultural products in the mentioned regions. In this research the main factors which have affected the subsidence phenomenon especially reduced ground water table and climate changes in Ardebil plain, are taken into account and some studies which comprise... 

The main purpose of this study is to develop the Hollow Cylinder Apparatus (HCA) for unsaturated testing on granular materials and to investigate the effect of stress anisotropy on dynamic parameters of soils like shear modulus and damping ratio. Direction of loading and the magnitude of intermediate principal stress have significant effect on the anisotropic response of soils. In many of in-situ loading the direction of major principal stress does not coincide with deposition direction of soil or because of the three dimensional loading condition of soil, the effect of the intermediate principal stress cannot be ignored. On the other hand, in many areas, soils are in unsaturated condition.... 

Loess soil layers in semi-arid to arid areas have been deposited through the accumulation of aeolian sediments, resulted in a special metastable and open structure being usually unsaturated in nature. Since naturally occurred loess is widespread, it has been recently considered as a promising resource for constructing earth-fill structures. However, due to different microstructures of intact and recompacted loess, different responses to hydraulic and mechanical loading would be expected. Up to now, the hydro-mechanical behavior of loess from different perspectives has not been linked to its microstructural characteristics. The current research, therefore, aims to provide insight into the...