Sharif Digital Repository

Geotextiles are one of the most widely used materials in filtration and drainage applications. Since geotextiles are exposed to different stresses and hydraulic gradients, thier hydraulic behavior in real situations is of great importance. In this study, filtration and drainage of several nonwoven needle-punched geotextiles with different properties and unit masses per area of 200g/m2, 400g/m2, 500g/m2 and 800g/m2 under various confined stresses and hydraulic gradients are investigated. To get to these aims, permittivity and transmissivity apparatuses were designed and built in the course of this investigation. Then samples which were emerged for at least 24 hours were tested under different... 

The behavior of pile foundations under earthquake loading is an important issue that affects the performance of structures. Design procedures have been developed for evaluating pile behavior under earthquake loading; however, the application of these procedures to cases involving liquefiable ground is uncertain. The performance of piles in liquefied soil layers is much more complex than that of non-liquefying soil layers because not only the superstructure and the surrounding soil exert different dynamic loads on pile, but also the stiffness and shear strength of surrounding soil diminishes over time due to both non-linear behavior of soil and pore water pressure generation. In this... 

Piles are usually used in groups. The complicated interaction between piles on the one hand and between piles and their surrounding soil on the other hand, have made it difficult to recognize mechanisms that influence the pile group behavior and analyze it accurately. In this research, three dimensional models in ABAQUS software were used to investigate response of single piles and pile groups under lateral loading in clayey soils. Configuration of piles in a group, connection of piles to the pile cap, pile spacings, and pile cross section were taken into consideration as some important factors affecting response of pile groups. All the modeled piles were categorized as long piles. In order... 

Study of fluid flow through the porous fractured media is used in many branches of science such as oil production, environment, water resources, geotechnics and mining, and the results of these researches are useful for industries.The porous fractured media consist of two main parts each having different roles. The first is the fracture networks that act as channels to conduct the fluid in the media, and the second is the porous media that act as a storage space for the fluid. The differences of dimensions and ability of fluid conduction between these two parts would cause the flow analysis to be performed in a heterogeneous and non-isotropic media. Moreover, the irregular networks of... 

A considerable number of engineering applications deal with flow of fluid(s) through particulate porous media. For certain engineering problems, fluid flow may displace and even dislodge the solid particles from the mass where a fluid-particle flow occurs. The complexity of involving processes which should be studied at the scale of moving particles transforms the analyses of these problems towards a difficult engineering task. Characteristics of solid grains such as size and shape and properties of the flowing fluid(s) such as viscosity and surface tension play essential roles in the behavior of fluid-particle systems. Also, when fluid flows through porous media, secondary processes such as... 

Effects of temperature on the behavior of soils and rocks have been studied widely in recent years. Following the need for understanding the effects of temperature on the behavior of clayey soils, several experimental and numerical studies on thermo-mechanical behavior of clayey soils have been carried out and a number of thermo-mechanical constitutive models have been developed for saturated and unsaturated clayey soils. In this research, a two-yield surface thermo-plastic constitutive model developed by Abuel-Naga et al. (2007, 2009), has been chosen for THM analysis of the behavior of saturated clayey soils. This constitutive model is based on Modified Cam-Clay (MCC) model. The MCC model... 

Dynamic compaction (DC), as a method of deep improvement of soft soils, recently has been used increasingly worldwide. The method involves application of high energy by dropping heavy tamper on surface of the soil. The majority of previous studies on DC are concentrated on dry soils. Observations show that DC treatment in saturated soils is also effective, but little studies in this area are available. A fully coupled dynamic finite element code, PISA, has been used in order to clarify the ambiguities in process and to predict the strain/displacement filed in the ground, determine depth and degree of improvement, and also calculate the pore pressure variation during the process. Because the... 

Rubble-mound breakwaters are one of the most customary breakwaters, which make a calm and safe area for ships to berth. To protect these structures from sea wave attacks, armour layers consisting of rocks or concrete blocks are put on their outer surface. Providing the stability of the armour layer is an important procedure in the design of breakwaters. Until now, design of the armour layer is based on the empirical formulae and physical modeling tests. The current research aims to study the stability of the armour layer by the numerical method and employing the commercial code FLOW-3D. In the present research, the effect of geometrical parameters such as breakwater slope and armour diameter... 

Sand production in petroleum industry is a phenomenon of solid particles being produced together with reservoir fluid. This phenomenon is costing industry billions of dollars every year. Corrosion of the pipelines and other instruments, sand-oil separation cost, possible wellbore choke and repeated shut-in and clean-up of the wellbore are some of examples of the costs. On the other hand, a controlled sanding or even sand production invocation has proved to be very effective in increasing production rate, especially in heavy oil recovery, asphalt wells and low PI wells. Discovering the best sand controlling procedure in oil extracting wells, parameters that have the most important effects on... 

Fluid flow in porous media is a common phenomenon in the nature, in many fields of science and engineering such as flow of water in the soil, migration of contaminants in the soil, petroleum reservoir engineering, semi?olten magma flow in the crust, water flow in plants, blood flow in body tissues, etc. In many cases, the porous structure of the medium and fluid flow pattern are very complex because of the inherent problems of fluidAluid and fluidsolid interactions. Also, secondary issues such as intrinsic permeability and tortuosity of porous media, and relative permeability of two phase flow, increase the complication of the analyses. Studying these types of phenomena in the nature or even... 

Lateral spreading is a common mode of earthquake-induced failure that usually occurs as a result of liquefaction in gently sloped sandy layers. Numerical simulation of this phenomenon requires fully coupled analysis of displacement of solid sand particles and pore water pressure under seismic loading. Predicting occurrence of initial liquefaction and sub-sequent ground movement requires employing an efficient and robust constitutive model that can predict the undrained behavior of saturated sand under different conditions. In this study, a fully coupled finite element code “PISA” utilizing a critical state two-surface plasticity constitutive model, proposed by Manzari and Dafalias (1997),... 

Lateral Spreading, which usually occurs as a consequence of liquefaction in gently sloped loose saturated sand layers, is known to be a major source of earthquake-induced damages to structures such as bridge piers, quay walls, pipelines and highway/railway. Therefore, evaluation of liquefaction potential and using appropriate methods for prediction of the adverse events of lateral spreading is of great importance. In this study, numerical modeling has been used to study of lateral spreading phenomenon behind rigid waterfront structures. In order to perform a numerical modeling of lateral spreading and also designing the structures exposed to its effects, the interaction of the soil solid... 

Hydraulic fracturing is a process during which a viscous fluid under relatively high pressure and flow rate is injected into a wellbore to induce and propagate a system of cracks in the ground.Hydraulic fracturing of underground formations has been widely used in different fields of
engineering, such as petroleum engineering, geotechnical engineering, environmental engineering, mining engineering,and so on.Despite the technological advances in the techniques of in-situ hydraulic fracturing, the industry lacks a realistic and reliable numerical model to design cost - effective and efficient hydraulic fracturing treatment.This is due to the complex interaction and strong coupling between... 

Settlement and tilt of structures due to liquefaction of subsoil layers is a major cause of damage during earthquake. Among different soil profile type, two layered soil is very common which was reported many times in differen earthquakes. Settlement of structures was measured by means of empirical methods before which were not viable because they do not consider different effective parameters. Consequently, different experimental studies performed to shed light on different aspects of liquefaction phenomena. In these studies, researchers consider some of the main parameters which have effect on the soil, otherwise, they neglected some important factors. So, numerical procedure is more... 

Although unsaturated soils exist all around the world, civil engineers are not familiar with unsaturated soil behavior; consequently, the soil structures they design may neither be safe nor economical. Thus, implementing unsaturated soil constitutive models to practical computer softwares can be very beneficial for geotechnical engineers. Geotechnical engineering softwares normally consider soil in saturated or dry conditions. So, their built-in constitutive models do not usually consider unsaturated soils. In this study, Barcelona Basic Model (BBM), which is developed using critical states soils mechanics principles, is implemented to the FLAC2D software. This model can simulate complex... 

Flows in porous media exist in many practical and research fields including water flow in soil, transport of pollution in soil, oil recovery engineering, and etc. Studying the multi-phase flows seems being too complex due to the interactions between fluids or between fluid and media in the porous media, wetting tendency of fluids, intrinsic permeability of the porous media, tortuosity of the flow’s path and etc. Hence, the field and laboratory studies of multi-phase flows is difficult, if not impossible. While numerical methods can handle many of these complexities, many of them are unable to simulate the micro-scale flows. On contrary, Lattice Boltzmann has no such shortcomings and even is... 

Because of seismic flexibility, aesthetics, economic advantage and rapid construction of reinforced soil walls, application of these walls has raised tremendously since 1970’s. The early reinforced soil retaining walls used metallic srips to reinforce the soil with precast concrete panels as facing, however, since 1990’s using of geosynthetics to reinforce these walls with modular concrete block facing have replaced the old fashion. In this study, a finite difference code was developed in FLAC software. After verification of the numerical modeling procedure, a wall with 3.6m height reinforced by geosynthetics was simulated. In the course of numerical simulations the stage of counstruction,... 

The exploitation of oil and gas were changed dramatically with the advent of hydraulic fracturing. By using enhanced oil recovery methods in unconventional reservoirs, USA could raise the rate of production in comparison with the rate of consumption. Hydraulic fracturing is one of the enhanced oil recovery methods.The purpose of this research is the study of the effects of geomechanical parameters in the characteristics of the cracks induced by hydraulic fracturing in unconventional oil reservoirs. The minimum in-situ stress and tensile stress of rock can be overcome by injecting fluid and thus the rock will be cracked. Changes in geomechanical parameters such as modulus of elasticity,... 

Rubble mound low-crested breakwaters protect the structures and ships in the port against wave attacks. Due to the overtopping, these structures provide a more attractive landscape and helps preserve the port's environment. Stability of low-crested breakwaters relies on the stability of the armor layer against the wave action, requiring the choice of the appropriate diameter for the armour blocks. For cubic armours that are of interest to the designers, there is currently no design relationship, and they inevitably use formulae specified for high-crested breakwaters that may not be in the safe side. The conventional method for determining the required armour diameter for a breakwater is... 

Sand production is a phenomenon of producing solid particles together with the reservoir fluid. Material degradation is a key process leading to sanding. Drilling operation, cyclic effects of shut-in and start-up, operational conditions and reservoir pressure depletion may gradually lead to sandstone degradation around perforations and boreholes. Sand production is a major issue and has an adverse impact on production cost that gas and petroleum industry have faced for decades. Corrosion of the pipelines and surface facilities, sand-oil separation cost, repeated shut-in and clean-up of the wellbore are some of the examples. On the other hand, a controlled sanding could be beneficial in...