فهرست مطالب yaser jafarian

Using a simple shear test, it is possible to investigate the behavior and recognition of soil resistive parameters. Cementation is one of the subsets of soil remediation that falls into the category of physical and chemical remediation that binds soil particles together and prevents the breakdown of the soil skeleton and increases shear strength (Consoli, 2009; Finn, 2002). The behavior of soil resistance parameters is investigated using simple shear tests. Shear stresses in the soil can be divided into static and dynamic (Li et al, 2016). One of the best ways to reduce cement consumption and production is to use pozzolanic materials, especially natural pozzolans, and replace them with cement. Pozzolans are widely used in the cement and concrete industry (Rahgozar et al, 2018). Micro-silica, perlite, methakaolin and zeolite are the most well-known natural pozzolans. Since the cost of producing pozzolans other than zeolite is almost high, their use would not be economical on a large scale. Zeolite mainly contains silica, and aluminum oxide, which reacts with calcium oxide and thereby increases the strength of the resulting compound. The addition of zeolite improves the spatial structure properties of the zeolite, as well as reduces the porosity of the resulting mixture (El Mir and Nehme, 2017). This paper presents the results of laboratory investigations on the shear strength of cemented sand and the effect of zeolite replacement on cement. To achieve this purpose, mineral zeolite, Shahroud cement, and Babolsar sand were used.

High pressure and temperature in earth crust lead to fracture and microcracks in rocks. Direct access to earth crust rocks at great depths is very costly and in most cases impossible. The study of the condition of rocks at great depths is often done using indirect methods such as seismic waves. The results of these studies are compared with the results of laboratory studies of wave velocities in different rocks and the conditions of the rocks are simulated. At high depths, hydrostatic stress is applied to the rocks of earth crust, and tectonic, earthquake and other stresses cause it to be anisotropic. The main purpose of this study is to investigate the change in compressive wave velocity due to change in compressive stress in rocks. In first, a cylindrical core of different stones with a length to diameter ratio of 2 to 2.5 is prepared according to the standard test method (ASTM D4543) and their dimensions and weight are determined. after measuring the unconfined compressive strength of cores according to standard test method (ASTM D2938), the hydrostatic pressure of 50% to 95% of it is applied to the rock samples prepared from the earth. This pressure is applied to the cores by using the Hoek cell (for lateral pressure) and the axial load machine and using ultrasonic device, determine the compressive wave velocity (ultrasonic pulse) is determined according to the standard test method (ASTM D2845) in the axial direction of the sample. Then, the wave velocity was measured during decreasing the lateral pressure (increasing deviatoric stress) in a stepwise manner, the wave velocity measured at each step. In the following, comparative diagrams of compressive wave velocity (Vp) with density (ρd), uniaxial compressive strength (UCS) and the effect of hydrostatic stress (σhyd) and deviatoric stress (σdev) on P-wave velocity in each sample are drawn. The results show linear relationships between compressive wave velocity and physical properties of rock samples, also the P-wave velocity at hydrostatic pressure is the highest and as the lateral pressure decreases (increasing the deviatoric stress), the velocity also decreases.

The shortcoming of loose sandy soils in terms of shear strength besides placement of a huge number of structures on them drive the critical requirement for exploring the shallow foundations treatment, their positioning and shapes. In this regard, stabilization of loose sandy soils through fabricating cement and an appropriate additive is one of a promising solution. Hence, in this study, a series of unconfined compressive strength tests have been conducted to find out the mechanical properties of zeolite cemented sand composites. Afterwards, 1g small scale tests have been performed to measure the behavior of shallow foundations placed on the stabilized ground. The main aims of this study are enhancing the bearing capacity and conversely decreasing the settlement of foundations attributed to the chemical reactions between sand, cement and zeolite particles. The results demonstrate that placing a zeolite pad with B/3 thickness underneath the shallow foundation, which contain 3% and 7% cement content, increases their bearing capacity in a range between 11% and 23% respectively compared to those of without a zeolite pad. This is followed by respectively 44% and 67% enhancement in the bearing capacity through doubling the thickness of the zeolite pad. Considering the cement content as a comparing factor between the samples, increasing in the resistant coefficient is in a range between 9% to 23%, while it is constantly 6% for the decreasing coefficient. In summary, this stabilization approach improves the behavior of shallow footing on loose soils.

Adjacency and interfering of footings are a matter of importance in geotechnical engineering. The researchers have focused on the adjacency of the footings by several approaches, but the mechanism of nearby footings under unequal and non-simultaneous surcharges have not been explored to date. In this study, two series tests were conducted using small scale 1g models to investigate the behavior of the two adjacent footings under reinforced and unreinforced soil conditions. The footings were installed with different spacing and rested on loose saturate sand. The ultimate bearing capacity, settlement, and tilting of footings were evaluated when the footings are rested on unreinforced sand as well as the sand bed reinforced by concrete pedestals. The results indicate that reinforcing the new footing by three concrete pedestals in the spacing to footing's width ratio (S/B) of 0 (i.e., two coherent footings) results in 67% increase of the bearing capacity of the new footing compared to that of the unreinforced condition. Also, the settlement and tilting of the old footing adjacent to the new footing decrease respectively up to 250% and 600% in comparison to those of the unreinforced condition.

The laminar shear boxes (LSBs) are commonly preferred for geotechnical physical modeling over the fixed wall boxes; the latter may suffer from problems associated with wave reflection. This paper mainly describes the seismic response of a uniform layer of loose saturated and dry sands in rigid and flexible boundary conditions. A lightweight LSB was recently designed and fabricated by the authors for physical modeling of geotechnical earthquake engineering problems. To investigate the boundary effect on the seismic response of level ground, a series of shaking table tests were conducted with both LSB and rigid wall containers in identical conditions. The seismic performance of the free-field ground in the experiments is evaluated in terms of time histories, shear stress–strain hysteresis loop, and dynamic soil properties. The dynamic movements of all layers in the LSB, captured by image processing techniques, are compared with that of the rigid end-wall condition. The results demonstrate that acceleration and settlement of the ground surface are highly affected by artificial boundaries in both dry and saturated sands. It is shown that the hysteresis loops estimated from the LSB tests are more compatible with the cyclic behavior of sands, compared with those of the rigid box tests.

Results of several cyclic triaxial and resonant column experiments on calcareous sand were presented by the authors in a preceding paper to obtain the shear modulus and damping ratio of the sand under various effective confining pressures and relative densities. The calcareous sand was taken from Bushehr, one of the most strategic ports of Iran in the Persian Gulf. This technical note compares dynamic properties of this coastal sand with a comprehensive database compiled from the experiments on various siliceous sands. The discrepancy observed between the experimental results of the calcareous sand and those of the siliceous sands is demonstrated. These differences can be attributed to the grains’ shape, mineralogy, and texture of the calcareous and siliceous sands. The comparative study provides useful insights into the dynamic properties of the studied calcareous sand.

Seismic loads may damage municipal solid waste landfills (MSWLF) through the relative movements within the waste, bottom lining system, cover system, foundation, and interfaces. The smooth synthetic materials might be placed beneath the structures to provide seismic protection by absorbing the imparted energy of earthquakes through the sliding mechanism. In the present study, experimental investigations were conducted in order to evaluate role of in-soil base isolation on seismic response of the Kahrizak MSW landfill. Shaking table tests were conducted on the MSW embankment isolated by semi-elliptic shaped liners and subjected to harmonic sinusoidal base excitations. Furthermore, the shaking table model was simulated by numerical analysis. The results of the isolated and non-isolated cases are compared in terms of permanent displacement and seismic response. Subsequently, the behavior of the numerical model was evaluated for different parameters. A reasonable agreement was found between the results of the physical model and the numerical model in prototype scale. The efficiency of in-soil isolation increases with increasing the amplitude of input motion. The results show that increasing the shear modulus reduces the amount of spectral amplification and relative displacement. It was also observed that as the age of the MSW increases, base isolation increases the displacement and crack width. Moreover, employing flat liner facilitates the movement of the ridge to the sides; and the concave liner prevents the wedge to move and, hence the quantity of settlement is reduced.

The interference of two nearby footings has been challenging due to the lack of suitable construction sites. Therefore, engineers are often forced to place footings at close spacing, which results changing of the ultimate bearing capacity, the settlement, and the tilt based on the considered spacing. In this study, two series of 1 g model test were conducted on two interfering parallel strip footings rested on the Babolsar saturated sand with different safety factors considered for the previously constructed footing (named as the old footing). The footings are loaded unequally and non-simultaneously to simulate mechanism of the new and the old footing with different surcharge and construction orders. The results are presented in the form of non-dimensional interference factors for ultimate bearing capacity and settlement of interfering footings versus isolated footings. It is demonstrated that the interference effect on the performance of isolated footings is considerable. Moreover, by decreasing the S/B ratio (i.e., spacing divided by footing width) from 1 to 0, the settlement ratio increases more than five times. Furthermore, in both series of tests, more than 300% increase in the tilting degree of the old footing was resulted due to the interference with the new footing in the ratio of S/B = 0 compared with S/B = 1. It demonstrates the perilous effect of the old footing tilting caused by the new footing adjacency. Moreover, applying different safety factors for the old footing has no dramatic effect on the tilting of the old footing enforced by the adjacent new footing.

Seismic loads may damage municipal solid waste (MSW) landfills through the relative movements within the landfill system. These movements can disrupt performance of drainage and gas collection systems, thereby resulting in environmental pollution. The smooth synthetic materials might be placed beneath the structures to provide seismic protection by absorbing the imparted energy of earthquakes through the sliding mechanism. It has been found that a high strength geomembrane placed over the other smooth and lubricated geomembrane sheets constitutes an efficient seismic liner. In the present study, experimental investigations were conducted to evaluate role of in-soil base isolation on seismic response of the Tehran MSW landfill. Results of geophysical and geotechnical investigations in the landfill site are presented in detail. Shaking table tests were conducted on the MSW embankment isolated by semi-elliptic shaped liners and subjected to harmonic sinusoidal base excitations. The results for the isolated and non-isolated cases are compared in terms of permanent displacement and seismic response. It has been observed that at all elevations the spectral accelerations within the waste decreased by base isolation, especially for the more intense excitations. Results of the present study demonstrate a suitable application of geosynthetic liners for seismic retrofitting of landfills.

Population growth and the attributed increase in housing demand are the cause of an acute shortage of suitable land for construction. As such, it has become a business strategy in construction sector to find optimum solutions in terms of modification and improvement of inferior lands. One readily available solution to address this issue is decreasing the settlement of strip footings and improving their load bearing capacity through embedding cemented zeolite pads underneath the strip footings. Therefore, here, a series of small scale 1g model tests have been conducted with the aim of evaluating the behavior of the strip footings reinforced with zeolite-cemented pad. For practical purposes, Babolsar sand (in dry and saturated conditions) has been selected as the case study. The pads are placed underneath the foundations and in direct contact with the sand. The results demonstrate that placing a pad with one third thickness of the foundation's leads to an increase in the bearing capacity of both dry and saturated conditions. This increase is in the range between 30% to 91% under the dry condition and between 23% to 67% under the saturated condition. Also, this reinforcement causes clear increase in settlement reduction ratio of the dry condition in the range between 35% to 60% and in the 29% to 49% range for the saturated condition.

Saturated loose soils have constituted superficial layers of the ground in vast regions of the country. For instance, geotechnical site investigations have revealed that shoreline of the Mazandaran Sea involves thick layers of uniform sand mixtures. Presence of such soil deposits in the northern and southern Iran, which are prone to seismic activity, may produce severe damages due to liquefaction occurrence. To prevent earthquake damages to the structures relied on liquefiable soils two strategies might be preferred: (1) improvement of liquefiable soil and ceasing liquefaction, and (2) bypassing the liquefiable layer via deep foundations. The latter strategy aims to transfer the superstructure load to the underlying stiff layer by end-bearing piles while raft foundation is also required because the superficial liquefiable soil may be unable to provide sufficient bearing capacity due to seismic pore pressure generation. In pile-raft systems passing through the liquefiable layer it seems that the liquefiable layer has less influence to the response of the system. However, several interactions in the environment such as pile-liquefiable soil, pile-pile, pile-raft, and raft-liquefiable soil could result in a sophisticated problem; affecting the amplification of the upward propagating seismic waves. Amplification of seismic wave denotes variations of amplitude and frequency content of upward propagating wave passing through the reinforced liquefiable soil layer. It is expected that the pile-raft system in conjunction with the liquefiable layer considerably change seismic response of the ground compared with the free-field liquefiable ground in the absence of pile-raft system. In the design of routine projects for which the national seismic building code is employed, there is no clear recommendation to account for the influence of pile-raft on the site amplification factors. The currently used building codes have poorly addressed the problem; and thus, considerable researches might be required. The aim of this paper is to study the characterization of seismic wave amplification by considering the presence of piled raft. To achieve this goal three-dimensional numerical modeling of piled raft and free-field in both liquefied and dry sand deposit is used. Results of some centrifuge experiments of a piled raft structure on liquefied sand are used to evaluate the predictive capabilities of the numerical model constructed in OpenSees, as a state-of-the-art numerical tool. Fully-coupled solid-fluid 3D nonlinear numerical simulations were performed in OpenSees, in combination with the pressure-dependent-multiyield soil constitutive model that enables dynamic effective-stress modeling of soil liquefaction in addition to embedded pile and superstructure elements. The numerical simulation results demonstrated reduction of seismic wave amplification in liquefied sand versus dry sand due to reduction of soil strength and increase damping. In both liquefied and dry state, the presence of piled-raft increases the soil stiffness and seismic wave amplification. The level of site amplification depends on many factors such as lateral stiffness of the pile-raft system and characteristics of input motion. Parametric study was then carried out to address these factors. Results of this study indicate that amplification factor decreases due to the presence of liquefied soils. However, the decrease of amplification factor at the free-field is larger than pile-raft foundation. Furthermore, amplification factor increases due to increase of pile stiffness, amplitude and period of input motion. Therefore, the site-specific analysis might be necessary to account for the presence of piled-raft system in the sites involving thick sand layers.

Two adjacent footings behave often differently from a single footing. Nowadays, with the scarcity of suitable land for construction purposes and population growth in the coastal zone of Caspian Sea, construction without considering the interference of the footings is increasing. This issue has been further complicated due to the unequal and non-simultaneous loading of the adjacent footings. In other words, initially, the light or old footing has been constructed, and then the heavy or new footing will be constructed adjacent to the old footing. This is also true in ports where containers are stacked side by side. In this study, the influence of unreinforced concrete pedestals on improvement of saturated loose sandy soil is investigated through modeling the small-scale 1g tests. The main focus was on the load bearing capacity, settlement and tilt of the light footing nearby the heavy footing, when the pedestals are placed beneath the heavy footing. Results of this study illustrated that with fixed diameter pedestals (D=5 cm), increasing the pedestal length (L) from 15 to 25 cm, as refining factor of the soil underneath the heavy footing, led to 18 and 38 percent decrease in settlement and tilt of the light footing nearby the heavy one, respectively, when the S/B ratio was zero.

Improvement of sands is frequently carried out by cement together with several other additives. The common additives have high manufacturing costs and negative environmental impacts during their manufacturing process and recycling in nature. Zeolite as a mineral substance for cement replacement can improve the strength parameters of a treated sand, without the negative deficiencies of the common additives. In this study, unconfined compression strength (UCS) and small-scale 1g model tests were conducted to evaluate the mechanical features of zeolite-treated sand and to study the behavior of shallow foundations rested on zeolite pad, respectively. The results of this study demonstrate that the UCS of the cemented sand samples increase when the cement is replaced by zeolite at an optimum proportion of 40% with 14 and 28 days curing times. Adding this amount of zeolite to cemented sand mixture causes an increase in terms of the improvement rate between 40% and 125% and increases the bearing capacity ratio (BCR) of the strip foundation treated by zeolite pad in the range of 11% and 420%. In addition, zeolite pad leads to decline the settlement of the treated strip footing from 16% to 86% in terms of the settlement reduction ratio (SRR).

Reliable and accurate assessment of dynamic soil behavior curves is necessary for the solution of many soil dynamic problems, such as the site response analysis. The shear modulus and damping curves of silicate soils under different conditions have been investigated by many geotechnical researchers.
Carbonate sediments are located in temperate and tropical areas and cover approximately 40% of the ocean surface. This type of soil is typically observed near offshore hydrocarbon industries, such as the Persian Gulf. Carbonate sand is the accumulation of pieces of carbonate materials; it usually originates from reworked shell fragments and skeletal debris of marine organism. Foundation problems associated with carbonate soil deposits, particularly as experienced by the offshore hydrocarbon industry have led to significant research focused on understanding the behavior of these soils.
This study focuses on evaluation of dynamic properties of Bushehr calcareous sand. The shear modulus and damping ratio of the tested sand was measured at small to large shear strains using resonant column and cyclic triaxial tests. The calcareous sand specimens were tested by a fixed-free type of resonant column apparatus (SEIKEN model). By using the resonant column apparatus, shear modulus and damping ratio of the calcareous sand for the shear strain amplitude ranging from about 10-4 % to 10-2 % were measured. The cyclic triaxial tests were conducted using a fully automated GDS triaxial testing apparatus. The cyclic tests were done on samples with shear strain amplitudes ranging from about 10-2 % to 1 %. The procedure used to perform the dynamic and cyclic tests was the multi-stage strain-controlled loading under undrained condition.
The tests were conducted in three levels of initial effective mean confining pressure equal to 40, 200, and 400 kPa. The sand specimens were constructed in relative densities lower than 50 or 80 percent, depends on the initial effective stress, in order to acquire the target relative densities (i.e. 50 or 80 percent) after consolidation.
The experimental results indicate that with an increased shear strain amplitude, shear modulus decreases and damping ratio increases. This trend, which was observed for all the tests, is typical behavior of soils under dynamic loading, as observed in the previous studies.
The effect of mean effective confining pressure and relative density on the normalized shear modulus (G/Gmax) curves of the Bushehr calcareous sand was investigated. Gmax is the small-strain shear modulus measured at shear strain amplitude about 10-4 %. The increase in mean effective confining pressure causes the normalized shear modulus to increase; however, it is more pronounced in low effective confining pressure. Changes of the normalized shear modulus curves (G/Gmax-γ) at the range of σ'm=200-400 kPa is less than that at the range of σ'm=40-200 kPa. Normalized shear modulus curves are almost independent of the changes in relative density of the sand.
The results also indicate that the increased amount of initial mean effective confining pressure leads to the smaller damping ratio for the tested sand. It is also observed that damping ratio curves (D-γ) are not affected strongly by relative density changes.
Comparison of the tests results with the ranges and models recommended by the previous researchers reveals that the normalized shear modulus and damping ratios of the studied calcareous sand are somewhat inconsistent. In fact, there might be a necessity to modify the previous recommendations for accurate prediction of the dynamic behavior curves of calcareous sands.

Newmark sliding block method is commonly used for estimating earthquake-induced permanent displacement of earth slopes and embankments. Since this method is a simplified dynamic analysis procedure with acceptable accuracy, it has been received considerable attention among the geotechnical practitioners. However, it has some shortcomings such as neglecting system response and sliding mass rotation. Hence, researchers have proposed modified procedure to enhance the realistic features of this method. The effect of sliding mass rotation, which sets the block in a gentler condition, was previously considered by continuous increment of yield acceleration. Since the sliding mass is three dimensional in reality, smaller permanent displacement is expected when the width of block is accounted for. In this paper, width of the rotating-sliding mass is taken into account in the coupled and decoupled solution of block sliding equations. The results show that the width of the slip zone is effective on the resulting displacements. With a constant slip length, whatever slip width is reduced, yield acceleration increases and consequently difference between the modified decoupled (or modified coupled) and decoupled (or coupled) increases.

The Caspian Sea is regularly visited by many tourists and the surrounding lands are densely populated. Accordingly, many tall buildings and heavy structures are constructing over this coastal area. The region is overlaid by poorly graded clean sand which seems to be susceptible to liquefaction occurrence. However, there is no documentation and field observation to ensure liquefaction triggering in the uniform rounded- shape deposits of the region during an actual earthquake. Hence, lots of research works are expected to be carried out to recognize cyclic behavior of these coastal deposits before the probable scenario earthquake and the consequent disaster happen. The undrained shear strength of granular soils is one of the most important parameters to evaluate flow liquefaction, which is prone to produce beneath the shallow foundations bearing considerable levels of static shear stress. Mechanism of flow liquefaction is commonly studied using triaxial apparatus to obtain a better understanding of the parameters controlling the phenomenon. Soils experiencing the flow type of liquefaction commonly undergo large deformations because the driving stresses tolerated by the soil exceed the shear strength reduced by generation of excess pore pressure in earthquake condition. There exist numerous studies for evaluation of undrained behavior of mixed soils comprising of gravels, sands, silts, and clays. Majority of the previous studies have focused on the homogeneous mixtures of soils while natural soils are generally found in the nature with levels of non-homogeneity. In this study, mechanical behaviors of homogeneous and heterogeneous mixtures of the Babolsar sand and gravels are compared under different conditions such as initial effective stress, relative density, and heterogeneity. Several triaxial experiments were conducted to evaluate effects of stratified sedimentation and increase of heterogeneity on undrained shear strength and pore pressure development of sand-gravel mixtures in various relative densities and confining pressure. A simple formula has been defined to specify level of heterogeneity of the sample, which varies from zero to one percent. The results demonstrate that shear strength, the potential of pore water pressure, and internal friction angle of homogeneous samples are quite different from heterogeneous samples. The undrained shear strength of sand-gravel mixtures increases with increasing degree of heterogeneity even in identical gravels content. Excess pore water pressure in sand - gravel mixed samples with higher degrees of heterogeneity reduces and tends towards dilative behavior, with respect to the more homogeneous samples. The undrained shear strength of the samples is proportional to initial relative density and effective confining pressure, as expected and observed in other granular materials. It is found from the results of the tests that the type of mixed sedimentation has significant impact on the soil's friction angle. In fact, increase of heterogeneity level increases the internal friction angle of the mixed soils while the gravels content is kept identical.

Knowledge of the dynamic behavior curves of soils is important for designing various geotechnical structures subjected to different kinds of vibrations, including earthquakes. Reviewing the previous studies on soil dynamic behavior shows that most of the studies have focused on the siliceous soils. Geological studies suggest that vast areas of the earth in the tropical regions are covered by calcareous deposits. Large areas of the southern Iran, which are seismic-prone based on the recent earthquake activities, are also covered by calcareous soils. Foundation problems associated with carbonate soil deposits, particularly as experienced by the offshore hydrocarbon industry have led to significant research focused on understanding the behavior of these soils. Origination of calcareous soils from processes and minerals different than those known for the silicate soils clarifies the necessity for comprehensive research on geotechnical properties of such soils. The wide variation of the origin of calcareous soils, due to their offshore locations and the related fauna that make their formation, merit more research into the behavior of these soils from various regions.
In the current research, shear modulus and damping ratio of Hormuz calcareous sand and Babolsar siliceous sand were measured and compared. An identical grains size distribution curve was synthetically attained for the tested sands. The soils are classified as poorly graded sand (SP) according to the USCS (ASTM D2487). The shear modulus and damping ratio values were calculated at small and large shear strains using resonant column and cyclic triaxial tests. The calcareous and siliceous soil specimens were tested by a fixed-free type of resonant column apparatus (SEIKEN model). By using the resonant column apparatus, shear modulus and damping ratio of the calcareous and siliceous sands were measured for the shear strain amplitude ranging from about 10-4 % to 10-2 %. The cyclic triaxial tests were conducted using a fully automated GDS triaxial testing apparatus. The cyclic tests were done on the samples with shear strain amplitudes ranging from about 10-2 % to 1 %. The procedure used to perform the resonant column and cyclic triaxial tests was the multi-stage strain-controlled loading under undrained condition.
The results for both calcareous and siliceous sands indicate that the shear modulus (G) decreases and damping ratio (D) increases with an increase in shear strain amplitude (γ), as expected. Moreover, the shear modulus of tested soils increases with the increase of effective confining pressure (σ'0). Further, the tests results indicate that the increased amount of effective confining pressure leads to the smaller damping ratio for the Hormuz and Babolsar sands. The shear modulus of Hormuz calcareous sand is higher than that of the Babolsar siliceous sand while grains size distribution, effective confining pressure, and void ratio of both soils were identical. It is evident from the resonant column and cyclic triaxial tests that the Hormuz calcareous sand has lower values of damping ratio (D) in comparison to the Babolsar siliceous sand. Finally, dynamic behavior curves of the studied sands are compared with the available relationships. These comparisons indicate that the available relationships are unable to accurately assess behavior of the tested calcareous sand.

The empirical models of liquefaction-induced lateral ground deformation have the most common applications for the routine projects. Beside the inherent uncertainties of such models, estimation of geotechnical, geometrical, and design earthquake parameters also involves measurement errors. These sets of error may considerably affect the final estimation of ground deformation and lead to questionable designs. Several empirical models are in-use in the current practice; however, a comprehensive study seems to be required in order to evaluate and compare their performances. This papers aims to present: (1) parametric study of the available empirical models of lateral spreading, consideration of the most recent database, and developing a new empirical model, and (2) Reliability analysis of the developed model through FORM, SORM, and Monte Carlo methods. In the first part, unreliable data points with only one observation borehole located farther than 5m from the point of ground deformation are removed from the database. The new empirical model has acceptable accuracy compared with the previous models. In the second part, effect of the geotechnical parameters variability in the estimated values of ground deformations are estimated and the results are presented in terms of probability of exceedence from a certain level of permissible displacement versus the ground slope.

Complete recognition of calcareous sediments engineering behavior considering their local expansion and wide variety of engineering properties is very important. In south parts of Iran, there are some carbonate hydrocarbon reservoirs which are covered by calcareous deposits. Hormuz Island in is one of the most strategic areas in Hormuz Strait between the Persian Gulf and Oman Sea. In this study, a series of undrained monotonic and cyclic simple shear tests was performed on saturated Hormuz calcareous sand specimens using hollow cylinder torsional apparatus. The tests were carried out on specimens with various relative densities under different effective consolidation stresses. Based on the results, pore pressure generation, shear strain development, stress–strain characteristics of the specimens are presented and compared with the technical literature. In addition, dissipation of strain-based energy during the cyclic loading and its relation to excess pore water pressure is described. The cyclic resistance curves of specimens with different initial conditions are plotted. Also the results of monotonic and cyclic tests are compared together for better interpretation of Hormuz calcareous sand under undrained torsional loading.

Bearing capacity failure and seismically induced settlement of buildings with shallow foundations rested on liquefied soils have resulted in significant damage in recent earthquakes. Engineers still largely estimate seismic building settlement using procedures developed to calculate post-liquefaction reconsolidation settlement in free-field. They commonly disregard residual strength of liquefied soil in their design procedures. Previous studies of this problem have identified important factors involving shaking intensity, the liquefied soil’s relative density and thickness and the building weight and width. Newly studies have also showed that shear deformation combined with localized volumetric strains during partially drained loading are dominant mechanisms. Bearing capacity degradation due to high excess pore pressure development also has been reported in previous studies.
Two series of physical modelling experiments involving shallow footing rested on liquefied sand have been performed to identify the mechanisms involved in liquefaction-induced building settlements and bearing capacity degradation. Experiments have performed on Babolsar sand with moderate relative density in a box with two plexiglass sides to observe sand deformations. Earthquake waves can cause pore pressure build up in saturated sands but complete liquefaction always do not occur. Anyhow excess pore pressure generation can cause bearing capacity degradation and excessive settlements. Various pore pressure ratios have been generated by static seepage through box base to assess bearing capacity degradation and excessive settlements before and in complete liquefaction conditions.
First series of experiments are consisted of 8 tests related to bearing capacity measurements of square and spread foundation in pore pressure development conditions. Results show bearing capacity reduction due to excess pore pressure development, but there is remarkable strength even in complete liquefaction that is related to post-liquefaction strength of liquefied sand. Square foundations are more affected than spread footings by excess pore pressure ratios. Foundation’s loading behaviour and Shape factors are not affected by excess pore pressure ratios. Pore pressure decreased with loading increscent under the middle of foundation because of particle rearrangement and always was below the induced excess pore pressure. Complete liquefaction has never observed under footing.
Safety factor selection is a challenging step in shallow foundation designs for engineers because of its economical view. Recent studies show the important role of shear deformations in shallow foundations as discussed before. In second test series of this experimental study, foundations firstly loaded to some safety factors and then its settlements due to pore pressure build up has measured, loading then increased to complete bearing capacity failure. This series are consisted of 12 tests for two types of foundations and various excess pore pressures, only shear deformations are assessed in this series because there is no volumetric deformation as excess pore pressure is constant during the tests. Results show increase of foundation settlements with safety reduction progressively, settlements for safety factors below 2 are negligible.

The effect of liquefaction depth on co-seismic and post-seismic settlements of shallow foundation has been studied using three centrifuge test series. The models were constructed in 1/80 scale and subjected to the centrifugal acceleration of 80g. They involved two rigid foundations with two different static surcharges and sufficient spacing to minimize the interaction. Poorly graded sand known as No. 306 sand with a relative density of 55% was used. The model was excited with a 15-cycle sinusoidal base motion having constant amplitude and 2 Hz frequency. In the free-field, liquefaction occurred in the shallower layers first, propagated rapidly to the deeper layers. The full depth of soil profile was liquefied in the strongest event. The liquefied depths were about 2.4 m and 7.2 m for amax=0.04g and amax=0.07g, respectively. Liquefaction caused severe deterioration of soil stiffness resulted in significant decay of accelerations. After excitation ceased, upward seepage from deeper layers enforced the shallower layers to remain in liquefied state for longer time. The free-field settlement commenced immediately after the first cycles and accumulated until excitation ceased. Its rate stopped for a while. The free-field settlement began again and continued up to full EPWP dissipation. Large negative EPWP was observed beneath the foundations, which are attributed to the deviatoric stress induced by their surcharge and soil dilation due to lateral movement of subsoil. Amplification was observed in acceleration time histories within the foundation soil, which is attributed to the negative EPWP generated in this zone. Large horizontal and vertical hydraulic gradient was developed during shaking, causing water flow towards the foundations. Once the water pressure equalized in each level, reconsolidation commenced. The foundations settled linearly with time during shaking with decreasing rate after excitation ceased. The extent of liquefaction had a major impact on the foundation settlement in this period. The higher the extent of liquefaction, the more the foundation settlement occurred. It seems that partial bearing failure and the inertial forces are two dominant mechanisms. The settlement and EPWP time histories can be separated into three different phases: (1) shaking, (2) progressive failure, and (3) reconsolidation. The rate of settlement significantly decreased during the second phase. Previous researchers noted that most of foundation settlement occurs during shaking period, but the results of this research show that most of the foundation settlement occurs after shaking. Foundation settlement continued progressively due to partial bearing failure and strength loss in the foundation soil. It seems that liquefaction extent and soil permeability have major impact on Phase (2). The thicker the liquefied layer or the lower the permeability of foundation soil, the longer time the foundation has to settle. Although the foundation settlement is significant in this phase, it has been neglected in geotechnical designs. The foundation settlement mechanisms are clearly different from that of the free-field. Volumetric-induced deformations are dominant mechanisms in the free-field, whereas, deviatoric-induced strains are the main cause of foundation settlement. It seems that the widely used procedure for the estimation of liquefaction-induced settlements of shallow foundations that is based on volumetric strains might be revised.

Currently, there is no reliable design procedure which considers all aspects of liquefaction effects on shallow foundations. There are many light and heavy structures resting on saturated sand with high liquefaction potential in seismic areas. The aim of this experimental and numerical study is to evaluate the performance of two shallow foundations with different contact pressures in liquefaction. The results of the centrifuge experiment of shallow foundations with surcharges of three-story and nine-story buildings on liquefiable sand are presented in detail. Although entire soil profile is liquefied, no liquefaction is observed under the foundations. There is a clear difference in settlement mechanisms observed beneath the shallow foundation and in the free-field. The heavy foundation fluctuated more strongly compared with the lighter one. The effect of soil permeability and contact pressure on foundation response is investigated during numerical study. Subsequently, the experiment is simulated two dimensionally using a fully coupled nonlinear constitutive model (UBCSAND) implemented in a finite-difference program, FLAC-2D. The results show that settlement of foundations increased with the increase of soil permeability. Trends of excess pore water pressure are captured reasonably by the soil model, but the settlement mechanisms are different. The soil model underestimates total liquefaction-induced settlement of shallow foundation, especially for light foundation.

In this study, the role of input motion characteristics on the amount of residual settlement of shallow foundations relied on liquefiable soil is investigated. First, two-dimensional numerical model is created using finite difference software FLAC-2D, and the UBCSAND constitutive model. After verification of the numerical model with the results of a centrifuge test, behavior of foundation is investigated under different earthquake loadings. To evaluate the effect of the input motion characteristics on foundation settlement, three records from Irpinia 1980, Northridge 1994, and Landers 1992 earthquakes are used. The frequency contents of these records are considerably different. These records are scaled to five levels of PGA (including 0.05g, 0.1g, 0.2g, 0.3g, 0.45g) to be used in the analyses. The results of the analyses demonstrate that the amounts of foundation settlement for the same PGA in three records are considerably different. Therefore, the use of PGA alone might be insufficient to predict the amount of foundation settlements. This fact is shown in Figure (1a). Figure (1b) illustrates the amounts of foundation settlement against the mean period of records at different PGA levels. It is observed that the mean period of records which indicates their frequency content, has a significant influence on the values of foundation settlements. It is concluded from the numerical analyses that the seismic parameters associated with ground velocity have better correlation with settlements of foundation. For example, the amounts of foundation settlements against the peak ground velocity (PGV) of the input motion are shown in Figure (2). This result reveals a high correlation between the ground velocity and the residual settlement of foundation, irrespective of frequency content and PGA of the earthquake records. It can be concluded from the results that both PGA and mean period of input motions have significant influence on the amounts of the foundation settlement, but they cannot be a good criteria for evaluating the amounts of the foundation settlements alone. In contrast, velocity-type parameters that are called intermediate-frequency intensity measures can be appropriate for prediction of foundations settlement in liquefaction condition. These results have been achieved for conditions of the calibrated foundation with its certain inherent parameters such as natural frequency content. For other conditions such as larger foundations’ width or sand density, more detailed studies are required.

As a disastrous cyclic response of soils، liquefaction commonly takes place in the saturated soils overlaid in seismic regions. Earthquake excitation in loose deposits enforces the soil particles to displace towards a more compacted state. This tendency causes generation of excessive pore water pressure when drainage is prevented or its rate is less than the generation rate. Comprehensive laboratory investigations have been carried out so far in order to capture cyclic behavior of silicate soils. However، cyclic behaviour and liquefaction resistance of calcareous soils has not been fully recognized as well. Calcareous soils evolve from biological resources due to the physiochemical process of marine organisms. Such soils have excessive crushing capability; and thus، their mechanical behaviour is expected to be different than that of terrestrial soil deposits. The current study presents results of several undrained cyclic tests on isotropically and anisotropically consolidated samples of Boushehr calcareous sand. The tests were conducted via a triaxial machine in strain-controlled condition. Bulk samples of the sand were gathered from the coast of Boushehr city located in the southwest of Iran، north bank of Persian Gulf. The sand samples were reconstituted with dry deposition method of sample preparation under various initial relative densities and confining pressures. The consolidation phase of the tests was performed in drained condition for either isotropically or anisotropically consolidated samples. The cyclic loading phase of the tests was conducted by multi-stage procedure in order to recognize soil potential for excess pore water pressure generation. Various levels of controlled cyclic axial strains were applied on the sample in each stage of the cyclic loading phase and the samples were allowed to be drained at the end of each stage. The results are presented in terms of threshold shear strain and dissipated strain energy concept. Comparison is made between the tests results and those reported by the previous studies. The results revealed that liquefaction resistance of the studied sand increases with increasing initial relative density and effective confining pressure whereas the samples with high initial effective stress never liquefied even after one hundred cycles of loading. Relationships between excess pore water pressure and the normalized number of cycles as well as the normalized dissipated strain energy are studied and compared with the relationships presented by the previous researchers for silicate sands. According to the results، such relationships are strongly affected by type of cyclic loading i. e. strain or stress-controlled when excess pore water pressure is correlated to the normalized number of cycles. In fact، evaluation of excess pore pressure is more reasonable to be done with the normalized strain energy in order to minimize the influence of loading type. The threshold shear strain for the studied sand was found to be 0. 015% which is comparable with this value for silicate sands.

Recent advances in evaluation of earthquake-induced permanent displacement of earth systems are addressed herein. Currently, seismic design of geotechnical structures emphasize on the quantification of system performance with the prescribed levels of permanent displacements. Accordingly, evaluation of earthquake-induced permanent displacement in geotechnical structures such as earth embankments and slopes is a topic of consideration for the geotechnical engineers. Different studies are available for estimating earthquake-induced permanent deformation of earth slopes and embankments. In general, these studies can be divided into three categories: analytical and semi-analytical, empirical and semiempirical, and numerical studies. Analytical and semi-analytical studies are simplified dynamic methods based on Newmarkian rigid block analogy. Based on this analogy, the rigid block displaces once the exciting acceleration exceeds the critical (or yield) acceleration. The original Newmarkian analogy assumes the sliding mass as the rigid block directly subjected to the input acceleration. The decoupled analysis is based on a rigid block but dynamic response of the system is calculated to obtain the equivalent acceleration as the input motion for the sliding block analysis. The decoupled analysis does not consider dynamic response of the slipped mass, while this response affects the overall behavior of the system. In a fully coupled analysis, dynamic response of the sliding mass and the permanent displacement are modeled together so that the effect of sliding displacement on the ground motions is taken into account. Through the empirical approaches, researchers developed correlations to predict seismicallyinduced displacement of slopes using databases of field case histories. These studies make clear that traditional rigid block analysis does not yield acceptable results for the seismic performance of large engineered earth structures. Besides, they provided detailed treatments of specific combinations of site and shaking conditions that are and are not adequately modeled by rigid-block analysis. Furthermore, other semi-empirical correlations have been presented based on the results of the analytical and semianalytical approaches. The third category aims to incorporate advanced constitutive models and numerical procedures such as finite difference, finite element, discrete element, and hybrid methods. This category soon began to be applied to slopes, particularly earth dams, and it provided a valuable tool for modeling the static and dynamic deformation of soil systems. However, advanced constitutive models, which are capable for simulation of soil behavior under dynamic loading, commonly require many parameters such as a high density of high-quality data and sophisticated soil-constitutive models. This problem may prevent prevalent usage of the advanced numerical approaches for estimation of earth slope displacement. For this reason, use of simplified method is preferable for evaluation of seismic permanent displacement. In this paper, major studies and recent developments on the methods of seismic slope displacement are explained based on the aforementioned categories. Moreover, advantages and disadvantages of the recent approaches are explained.