Sharif Digital Repository

The effects of liquefaction induced lateral spreading on the piles of a dolphin-type berth were investigated using 1 g large scale shake table testing accompanied by numerical simulations. For this purpose, various aspects of the response of the soil and the pile group to lateral spreading were considered. The results indicated that large bending moments were induced in the piles during lateral spreading and the downslope piles of the group received greater bending moments than the upslope one. The monotonic components of bending moments in the piles were reasonably predicted by the displacement based numerical approach using p-y springs when they were properly tuned for strength reduction... 

Liquefaction is a phenomenon through which saturated sandy soil loses its shear strength and turns into a liquefied state. One of the most detrimental consequences of liquefaction is the reconsolidation volumetric settlements after the earthquakes, which is due to the dissipation of excess pore pressure caused by earthquakes. Severe floods can follow these settlements in free fields such as grounds close to the sea or rivers. Several researchers studied this phenomenon using data obtained from experiments in the lab or observations in the fields. Previous works were mainly based on a limited number of experimental observations and considered loadings and boundary conditions that were... 

In this study, a fully coupled dynamic finite element model was employed for numerical simulation of the response of level to gently sloping saturated sand layers subjected to cyclic loading. This model utilized a critical state two-surface-plasticity constitutive model to simulate the cyclic behavior of sandy soil. Moreover, a recently proposed variable permeability function was implemented in the numerical model to reflect the effects of soil permeability variations during the liquefaction phenomenon. The numerical model was validated by simulating a number of well-documented geotechnical centrifuge tests with different relative density of sand, base acceleration time history, and surface... 

Supersonic gas separator is proposed for methane purification. One-dimensional analysis is performed to examine the design aspects associated with the converging-diverging nozzle and the liquid separation chamber. The results indicate that at low swirl intensities, the separation chamber length is about 100 times of the nozzle throat. Increasing the swirl intensity would lower this length sharply and it will be less than 10 for swirl intensity of unity which is equivalent to a swirl angle of 45°. In addition, a sensitivity analysis of the separator performance to the inlet conditions like the temperature, pressure, and composition of the mixture is carried out. It is observed that increasing... 

During recent years, extensive studies have been conducted around the world documenting liquefaction induced lateral spreading and its effects on deep foundations. This study is aimed to numerically model a shaking table experiment, to investigate the effect of lateral spreading on piles and also to assess the capability of an advanced critical state two-surface plasticity model in predicting soil and pile responses to lateral spreading. Changes in permeability of the soil layers during the shaking are also accounted for using the software's built-in programming language, FISH. Numerical results showed that the onset of liquefaction occurs after just a few cycles from the beginning of the... 

Due to its unique properties, helium has wide application in different industries and scientific fields, which has turned it into a strategic material. Helium liquefaction plants include wide temperature range from 300 k to 4.2 k, so these plants have high energy consumption. A lot of studies have done to optimize the operation of these cycles. In this research, an exergy analysis is performed for a liquid helium production plant. The optimal performance of 3 and 4 stage cycles is extracted using parametric study and the results are compared with those of Collins dual-expander cycle. The results show that by increasing the number of cooling stages, not only the compressor optimum discharge... 

Due to its unique properties, helium has wide application in different industries and scientific fields, which has turned it into a strategic material. Helium liquefaction plants include wide temperature range from 300 k to 4.2 k, so these plants have high energy consumption. A lot of studies have done to optimize the operation of these cycles. In this research, an exergy analysis is performed for a liquid helium production plant. The optimal performance of 3 and 4 stage cycles is extracted using parametric study and the results are compared with those of Collins dual-expander cycle. The results show that by increasing the number of cooling stages, not only the compressor optimum discharge... 

Geotechnical design codes have been shifted from classical limit equilibrium analysis toward the performance-based procedures. In foundation design, settlement is the most representative parameter for its performance. Settlement of shallow foundations subjected to earthquake loading and its consequences is one of the most outstanding issues which should be considered in designing different structures. In this study, settlement of shallow footing on two-layered subsoil strata under earthquake loading is of concern. The numerical study presented in this research by means of a 3D dynamic fully coupled u-p analysis, addresses the effect of different parameters on shallow foundation settlement... 

The volume change that occurs due to membrane penetration into peripheral voids of gravelly specimens during hydrostatic compression test in a conventional triaxial apparatus is studied by performing a set of hydrostatic compression tests on gravelly specimens with different initial relative densities. During the isotropic loading on the specimens, the total volume changes of the specimens were determined by measuring the amount of water seeping out of the specimens at different loading steps. Image processing technique was implemented simultaneously to determine the skeletal volume changes of the specimens. In this regard specimens were compressed to isotopic pressures from 10 to 500 kPa... 

A fully coupled numerical analysis using Biot's theory with u-p formulation considering variable permeability during liquefaction is used in this study to simulate liquefaction induced lateral spreading phenomenon. A centrifuge test performed on liquefiable soil at Rensselaer Polytechnic Institute is simulated using the developed model. The numerical results are in good agreement with experimental observations. A number of numerical simulations under different geometric, site-specific, and ground acceleration parameters have been carried out in the course of this study. Based on the statistical analysis conducted on the results of 31 different models, a new relation is proposed for... 

In performance-based geotechnical earthquake engineering, the required degree and spatial extent of ground densification for mitigation of liquefaction beneath a structure should be determined based on the acceptable levels of performance of foundation. Currently, there is no solution for evaluation of the amount of settlement and tilt of footings constructed on a densified ground which is surrounded by a liquefiable soil. This implies the need for numerical procedures for simulation of seismic behavior of shallow foundations supported on both liquefiable and densified subsoil. In this paper, the dynamic response of shallow foundations on a densified ground is studied using a 3D fully... 

Performance-based design (PBD) has become increasingly important in recent years, especially for the design of foundations rested on sub-soils that are susceptible to liquefaction at seismically active areas. Shallow foundations may fail due to excessive settlement because of liquefaction of the underlying loose saturated cohesion-less sands. Building codes usually do not address the issue of liquefaction-induced settlement of shallow foundations. In this paper, a framework is proposed for calculating the liquefaction-induced settlement of shallow foundations resting on heterogeneous two-layered liquefiable soil by conducting a series of 3D. hydro-mechanical dynamic analyses in a fully... 

The lateral movement of a liquefiable soil layer on gentle slopes is the most visible and devastating type of liquefaction-induced ground failure. Recent earthquakes have shown that this phenomenon causes severe damages to coastal structures, pier of the bridges and life-lines by exerting large lateral forces on the structures. In this paper coupled dynamic field equations of extended Biot's theory with u-p formulation are used for simulating the phenomenon and the soil behavior is modeled by a critical state two-surface plasticity model for sands. Furthermore, in this study variation of permeability coefficient during liquefaction is taken into account. The permeability coefficient is... 

Abstract 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 quay walls, bridge piers, pipelines, and highway/railways. Therefore evaluation of the liquefaction potential and using appropriate methods for prediction of the adverse consequences of lateral spreading is of great importance. In this study, numerical modeling has been used to study lateral spreading phenomenon behind rigid waterfront structures. Coupled dynamic field equations of the extended Biot's theory with u-P formulation are used for simulating the phenomenon. A fully coupled... 

It is well established that the main mechanism for the occurrence of liquefaction under seismic loading conditions is the generation of excess pore water pressure. The growth of the excess pore water pressure of saturated sand is dependent on several factors. Changing the inclination and magnitude of the major principal stress with respect to the depositional direction in most cases will increase the collapse potential and brittleness as well as reduce the shear strength and shear stiffness. An experimental program was carried out to study the variation of pore water pressure of cross-anisotropic deposits under anisotropic cyclic loading. A total of 30 undrained cyclic tests were performed... 

In the current research, the main concern is to verify the behavior of gravelly soils. To that matter, with taking use of CU triaxial tests and variations in parameters of interest, gradation, relative density, isotropic pressure and anisotropy of consolidation during the tests, the effects on the steady state condition and monotonic liquefaction of gravelly soils are investigated. The test results indicated that as the isotropic pressure increases, percentage increase of steady state strength resulting from the increase of relative density will decrease. Moreover, with the increase of anisotropy of consolidation, the effect of relative density on steady state strength and built-up pore... 

Several methods have been used for the evaluation of liquefaction potential, among which the simplified method is mostly used. In this method, which is mainly based on standard penetration test (SPT), cone penetration test (CPT) and shear wave velocity (Vs) measurement, a boundary curve is provided to separate the liquefiable and non-liquefiable soil zones. Vs measurement is a good alternative method of penetration-based methods (SPT and CPT). This is especially true in micro-zonation of liquefaction potential. Although relatively large studies have been carried out to establish the correlation between Vs and liquefaction resistance for sands; there are uncertainties about the effects of... 

Numerical simulation of liquefaction-induced lateral spreading in gently sloped sandy layers requires fully coupled dynamic hydro-mechanical analysis of saturated sandy soil subjected to seismic loading. In this study, a fully coupled finite element model utilizing a critical-state two-surface-plasticity constitutive model has been applied to numerically investigate the effects of surface/subsurface geometry on lateral spreading. Using a variable permeability function with respect to excess pore pressure ratio is another distinctive feature of the current study. The developed code has been verified against the results of the well-known VELACS project. Lateral spreading phenomenon has been... 

Liquefaction-induced lateral spreading has imposed severe damages to many important structures supported on pile foundations during past earthquakes. As a result, evaluation of pile response to lateral spreading is an important step towards safe and resistant design of pile foundations against this destructive phenomenon. Current paper aims to study the response of a group of piles subjected to liquefaction-induced lateral spreading using a large scale 1-g shake table test. General test results including time-histories of accelerations, pore water pressures, displacements and bending moments are presented and discussed in this paper. In addition, distribution of lateral soil pressure on... 

The soil permeability coefficient plays a key role in the process of numerical simulation of the liquefaction phenomenon. Liquefaction causes a considerable increase in soil permeability, due to the creation of easier paths for water flow. The work presented in this paper tries to investigate the effects of permeability coefficient on the results of numerical modeling of the liquefaction phenomenon. To do this, a fully coupled (u-P) formulation is employed to analyze soil displacements and pore water pressures. Two different versions of a well-calibrated critical state bounding surface plasticity model, which possesses the capability to utilize a single set of material parameters for a wide...