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Such parameters as cement content, cement type, relative density, grain size distribution, and moisture condition can influence the mechanical behaviors of Fiber-Reinforced-Cemented-Sand (FRCS). Va...

Due to the economic and tourist importance of Bandar-e Anzali coastal zone and also the high seismic risk in this area, this article provides an experimental seismic study using shaking table test on the sandy soil of Bandar-e Anzali. Modeling the laboratory conditions and applying seismic forces were carried out using a transparent tank on a shaking. Additionally, digital instrumentations of horizontal displacement transducers, pore water pressure gauge and data entry device via computer were used. In this study, data collection was conducted by creating saturated samples with relative densities of 20%, 30% and 50% and accelerations of 0.15 g, 0.3 g and 0.53 g and the variation of pore water pressure, horizontal displacement and settlements were measured. The results indicate the high effect of input acceleration on the occurrence of liquefaction and amount of the settlements, especially in low relative density. The effect of higher density on reducing the liquefaction potential and settlement is also significant.

This study was conducted on durability of the clayey-sand stabilized using the copper slag (CS)-based geopolymer against wetting-drying (W-D) cycles. In this investigation, the mix of 0, 10, and 15% CS and alkaline activator liquid was used. In this solution, the ratio of NaOH to Na2SiO3 is 70:30 and the weight ratio of CS to solution is 1:1. To evaluate the effects of CS content and NaOH concentration (8 M and 11 M) on the strength, durability, and microstructural variation, a series of experiments were conducted after different cycles. The tests carried out for this purpose include standard proctor compaction test, unconfined compressive strength (UCS), Atterberg limits, accumulative loss of mass, swell and shrinkage, ultrasonic P-wave velocity, pH, toxicity characteristic leaching procedure (TCLP), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) tests. The UCS results demonstrated a remarkable reduction in cycle 2 due to W-D cycles, followed by a decrease in further cycles. As a result of Atterberg limits, lower PI leads to the lower potential to swell or shrinkage; thus, the lower loss of soil mass with a higher amount of CS content is obtained. The microstructure analysis showed that with the increase in cycle number, the abundance of microcracks and voids were increased. Moreover, dissolved geopolymerization products leached due to wet cycles and formed gel becomes weaker. The results showed that all the chosen mixtures were durable and endured all 12 W-D cycles. Furthermore, their mass loss was lower than allowable mass loss content of ASTM D559, suggesting that this stabilization method was appropriate for this soil.

Liquefaction is a phenomenon that occurs in loose saturated granular soils during seismic loading. In this study, the control volume finite-element method (CVFEM) and local radial basis fun...

Recent researches indicated that the topography is one of the factors affecting the wave propagation pattern (i.e., the amplification or de-amplification). In recent years, many researchers investigated the effect of the tunnels on the wave propagation pattern in the free-field. Although in the construction of the roads in mountainous areas, tunneling for passing through slopes is unavoidable, the role of the tunnel in seismic behavior of slopes has been less concerned. In this study, the structural behavior of the tunnel lining and the amplification pattern in slopes in the presence of horseshoe tunnels, subjected to Ricker incident in-plane shear wave (SV), has been evaluated using the ABAQUS software. Several parameters affecting this phenomenon are accounted for such as the overburden, the distance of tunnels from the slope surface, and the dip angle of slope and bedrock. Results show that the presence of the horseshoe tunnels has a significant effect on the seismic response of the slopes. In comparison to the free-field, the amplitude of the seismic response was increased approximately 30 and 70% for the upstream and the inclined surface of the slope, respectively.

Studying the piled raft behavior has been the subject of many types of research in the field of geotechnical engineering. Several studies have been conducted to understand the behavior of these types of foundations, which are often used for uniform loading on the raft and piles with the same length, while generally the transition load from the upper structure to the foundation is non-uniform and the choice of uniform length for piles in the above model will not be optimally economic and practical. The most common method in identifying the behavior of piled rafts is the use of theoretical relationships and software analyses. More precise identification of this type of foundation behavior can be very difficult due to several influential parameters and interaction of set behavior, and it will be done by doing time-consuming computer analyses or costly full-scale physical modeling. In the meantime, the technique of artificial neural networks can be used to achieve this goal with minimum time consumption, in which data from physical and numerical modeling can be used for network learning. One of the advantages of this method is the speed and simplicity of using it. In this paper, a model is presented based on multi-layer perceptron artificial neural network. In this model pile diameter, pile length, and pile spacing is considered as an input parameter that can be used to estimate maximum settlement, maximum differential settlement, and maximum raft moment. By this model, we can create an extensive domain of results for optimum system selection in the desired piled raft foundation. Results of neural network indicate its proper ability in identifying the piled raft behavior. The presented procedure provides an interesting solution and economically enhancing the design of the piled raft foundation system. This innovative design method reduces the time spent on software analyses.

Geotechnical engineers deal with uncertainties in different projects. These uncertainties can be captured using nondeterministic approaches. Although during the last two decades numerous p...

The injection of cementitious materials into soil is one of the solutions to increase the mechanical and shear properties of the soil. In this study, the microfine cement grout with the water to cement ratio of 0.6 and different replacement percentages of 0, 0.5, 1, 1.5, and 2% of nanosilica was used to improve the mechanical and shear properties of the soil. For this purpose, the in situ injections into the coastal sand were performed and the SPT test was done at the depths of 2, 4, and 6 m and distances of 35, 70, and 100 cm to the injection center. The results of this study showed that the injection efficiency decreases with increasing the depth. Also, the maximum increase rate of penetration number (N1)60 in this study due to the addition of nanosilica was equal to 42%. On the other hand, the role of nanosilica in improving the strength increases with increasing the distance to the injection center.

Stabilization of the soil on the site is one of the methods used to improve the mechanical properties of soils. On the other hand, the replacement of cement by other materials for reducing the environmental issues has always been of interest to engineers. The soil is compacted after mixing with the stabilizing agent. The application of compaction energy can cause the grains to fail. By performing the standard compaction and subsequent soil grading tests, this study investigated the effects of different factors such as compaction moisture, cement percentage, percentage of coal waste, and grading method on the grain failure after compaction. The results of this study showed that increasing the cement weight ratio increases the maximum dry density and reduces the optimum moisture content. The increase in the weight ratio of coal waste for the sample with 3% cement increases the maximum dry density. However, for the sample with 6% cement, the addition of coal waste up to 10% increases the dry density and then reduces the density. All percentages of moisture in the compaction test result in a smaller size of sand grains due to the grain failure. On the other hand, up to the near optimum moisture, increasing the moisture will reduce the failure of grains. The grain failure rate increase is in the primary moisture contents. Also, increasing the moisture content for a mixture with 3% cement reduces the grain size, and for the mixture with 6% cement, it increases the grain size (reducing the rate of grain failure). Finally, it could be stated that the addition of coal waste has a significant effect on the change in the behavior of soil stabilized with cement in the area of grain failure.

Soft soil layer can significantly increase destruction during ground motions. Although, earthquake waves pass through mainly rocky media to reach ground surface, they often transit through a thin l...

The reinforcement of structural elements and construction materials using natural fibers has gained popularity among researchers and industries due to environmental concerns and financial problems of synthetic fibers. The contribution of natural fibers as soil reinforcement elements enhances the shear strength properties as the stresses in the soil mobilize tensile resistance in the fibers. Despite the specific limitations of direct shear test, it is considered as one of the most commonly used techniques that gives the design engineers a quick measure of soil strength properties when a certain fine content exists in the soil mixture. Therefore, this study is intended to present the results of a series of large-scale direct shear tests on compaction characteristics and shear strength properties of kenaf fiber reinforced soil. A total number of 128 tests have been carried out to determine the compaction and shear strength characteristics of unreinforced and reinforced sand-clay mixtures. Subsequently, the influence of kenaf fiber reinforcement on the stress-displacement relationship, volume change, ductility and failure state of reinforced soil was evaluated. Based on the results, the addition of a certain amount of kenaf fiber to the sand-clay mixture enhances the mixture ductility, improves the shear strength parameters, and ultimately makes it an appropriate candidate to be used in construction projects such as pavement layers, slope protection, embankment, and building foundation.

One of the geotechnical engineering strategies for dealing with weak soils in a construction site is to alter their mechanical properties with the assistance of soil improvement techniques. The present study examined the effect of the addition of nano calcium carbonate (0, 0.4, 0.8 and 1.2% by weight of the soil) as a stabilizing nanoparticle and carpet waste fibers (0, 0.2, 0.4, and 0.6% by weight of the soil) as a reinforcement agent on the soil behavior. A total of 52 unconfined compressive strength tests, 52 ultrasonic pulse velocity tests, 12 unconsolidated undrained (UU) triaxial tests, and 8 Atterberg limit tests were performed to investigate the effect of fiber and nanoparticle contents and treatment time on the geotechnical properties of the clayey soil. The results showed that the addition of nanoparticles to the clayey soil reduces its liquid limit and increases its plastic limit. The best improvement in the soil strength, which was about 100%, was observed in the 42 days old sample with 1.2% nano calcium carbonate content. The combined use of fibers and nanoparticles also led to significant strength improvement. The addition of carpet waste fiber was found to increase the soil stiffness. Increasing the carpet waste fiber content above the 0.2% did not have much impact on the maximum strength, but significantly improved the residual strength. The addition of carpet waste fibers up to 0.2% increased the velocity of ultrasonic waves, but further increase in the fiber content resulted in reduced velocity. The paper provides a number of equations that express the relationship between the unconfined compressive strength and the ultrasonic pulse velocity for the clayey soils with different additive contents. The provided equations can be used to estimate the success of stabilization and strength improvement efforts based on the results of non-destructive ultrasonic pulse velocity test. The results of unconsolidated undrained triaxial tests showed that the used fibers alter the sample behavior in high strains. Also, the use of nano calcium carbonate and carpet waste fibers together almost doubled the undrained cohesion.

Composite clay is a mixture of clay and coarse-grained materials which can particularly be applied in practice as the core of earth dams and the platform for construction of buildings and roads. They are especially used when the appropriate materials are not available or the present mixed soils have not the required properties. The soil strength measurement for various types of soils including the cohesive and gravelly soils is an important issue in geotechnical engineering. Therefore, this paper is intended to compare the resistance of samples with different percentages of clay and gravel with a maximum grain size of 19 mm by performing large-scale direct shear tests. The samples consisted of clay and gravel with the gravel content of 30%, 50%, 70% (by dry weight of clay), respectively. First, to ensure the required compaction, modified Proctor compaction tests were performed. Then, large scale direct shear tests were conducted on the samples to measure the shear strength properties of soil. The results clearly reveal that by increasing the percentage of gravel in the mixture, the maximum dry density increased and the optimum moisture content decreased. It was also observed that increasing the gravel content leads to an increase in the soil internal friction angle and shear strength.

In this study, 72 consolidated drained triaxial tests have been carried out to evaluate the effect of relative density, weight ratio of fibers, weight ratio of cement and confining pressure on the ...

Composite soils are a mixture of fine- and coarse-grained soil with a proportion that improves the density, permeability and strength properties of the mix. When the underlying soil does not provide adequate settlement and load carrying properties, composite soil as a cushion layer beneath the shallow foundation can be used. Thus, this paper investigates the influence of using gravel-clay and sand-clay mixture under the shallow foundation subjected to eccentric vertical load. Field investigations and experimental testing were first conducted to evaluate the in-situ soil properties and available fine- and coarse-grained material in Babol, Iran. Then, three-dimensional finite element method was employed to predict the behavior of the eccentrically loaded shallow foundation resting on the composite soil in terms of bearing capacity improvement B C I and normalized average settlement, R a v g of the foundation, based on the data collected in previous stage. According to the results, foundation over sand-clay mixture (SCM) showed a comparatively better performance in comparison with gravel-clay mixture (GCM). Ultimately, nonlinear regression technique was utilized to incorporate the effect of cushion layer in the relationship to calculate the bearing capacity reduction factor.

In this study, the effect of Kenaf fibre and cement on the mechanical behaviour of Babolsar sand was investigated by consolidated drained triaxial compression tests. Kenaf fibres with a length of 1...

This paper attempted to show the application of particle swarm optimization in the prediction of the compressive strength of cement sandy soil from the curing period, porosity of sample and percent...

To evaluate the behavior of cemented clay treated reinforced with copper sludge, 63 ultrasonic pulse velocity tests were conducted. The copper sludge content, curing period and moisture content wer...

To evaluate the effect of non-plastic fines on liquefaction resistance of Babolsar sand, a series of undrained static and cyclic triaxial tests alongside a series of numerical analysis were carried out. The cyclic triaxial tests were conducted in stress-controlled conditions with 1 Hz frequency at 0.35 constant cyclic stress ratio for 50 kPa and 0.25 for 100 and 200 kPa confining pressures. The samples contained 0%, 10%, 20%, 30% and 40% of fine grains. The numerical analysis was performed by a finite difference method, and Finn’s constitutive model was applied to investigate the liquefaction resistance of the mixtures. The tests’ results showed that the number of cycles leading to liquefaction of a sand–silt mixture decreases after increasing fine-grained percentage. Poorer performance in compression and better performance in tension was observed in this situation. The test outcomes also showed that dominant behavior of the mixtures changes from sand to silt at 20% fines content. It was observed from the test results and the numerical analysis that in low percentages of silt, the behavior of the sand–silt mixture is similar to those of the clean sand sample. But by increasing silt, the mixture’s behavior becomes more dependent on contacts between fine and granular particles. The concept presented by Thevanayagam was used to check the contacts between fine and coarse particles. It was also observed that the Finn constitutive model is in good consistency with the test results as long as the behavior of the sand is dominant in the mixture.

During earthquake loading, seismic evaluation of site dynamical analysis is the most serious issue in geotechnical earthquake engineering. Seismic waves pass through soils and rocks to reach the ground surface; hence, their characters play an important role in surface strong ground motion parameters. There are numerous techniques for the estimation of local site effect. This study aims at the comparison of different local site effect estimation methods in Babol city, Iran, with high thickness of the alluvial layer (80 m). Babol strong motion records have been used in this study. The obtained results from strong ground motions data were compared with other methods. The results reveal that for a site with high thickness of alluvial layer deposits, the microtremor measurement method is the best way for estimating site effect. Moreover, the numerical site response analysis based on the International Building Code and National Earthquake Hazards Reduction Program may not provide accurate results for alluvial layers at deep solid foundation, where an obvious rock-soil interface cannot be detected within 30 m.

One major step in evaluating the site response is estimation of the shear wave velocity and fundamental frequency. Various methods are available for evaluating the site effect, of which the ambient noise measurement method is a prevalent one. The method is quick with low cost; it is nondestructive and gives precise results. In the present research, to assess the site response in Babol City, measurements of ambient noise were performed at 60 points and the data were analyzed by Nakamura method. Also, at 8 sites, measurements of the ambient noise were done by applying SPAC method and the data were analyzed to obtain the shear wave velocity. In addition, equivalent-linear method was performed using the shear wave velocity as well as geotechnical and geological data of those 8 sites. Furthermore, the artificial neural network (ANN), with different input data, was trained and then was utilized to predict the fundamental frequency. The fundamental frequencies acquired from ambient noise, ANN and equivalent-linear method were compared to each other to investigate reliability of the results. The results showed that most parts of the study area have a fundamental frequency less than 1 Hz, while higher frequencies could be observed in some northwestern and southern parts of the city. Finally, it is shown that, the ambient noise measurements were highly useful for evaluating the site effect and estimating important seismic parameters (fundamental frequency and shear wave velocity).

This study aims to evaluate the effects of cement on the mechanical behavior of loess and clayey soil, and various laboratory tests have been conducted to do so. Such laboratory tests as standard proctor compaction, large-scale direct shear, and consolidated-drained triaxial were performed. In current research, the cement percentages were 0, 4, and 8%—by dry weight of soil. The samples were cured for 7 days. Results of the investigation showed that cement treatment improves mechanical behavior remarkably; however, it changes the samples behavior from ductile to brittle and alters the failure mode. Additionally, the enhancement depends to the soil type. With increasing percentage of cement, the stress-strain behavior of specimens tends towards the behavior expected of over-consolidated soils.

The possibility of confronting unsuitable soils in the construction site prompted the engineers to find a way to change inappropriate features of the natural soils. The process of changing the natural soil properties is referred to as soil improvement. Since the used soil from the site is exposed to sequential freeze and thawing conditions, it affects the mechanical and physical properties of the natural soil, leading to a reduction in strength and increase in volume change and mass loss. In this study, the effect of lignosulfonate (2% weight ratio of soil as an optimum content), stabiliser and PP fibers (0, 0.4, and 0.8% weight ratio of stabilised soil) as reinforcement on the freeze-thaw durability of clayey sand was investigated. For this purpose, unconfined compressive strength, durability, ultrasonic pulse-velocity, Atterberg limits and, standard compaction tests have been performed. First, the effect of the lignosulfonate addition and optimal content (0,1,2,3,4%) in different curing times (2,7 and 28 days) to natural soil has been investigated. Then freeze and thaw cycles have been performed on both lignosulfonate treated and untreated soils. Also, to improve the lignosulfonate tread soil behaviour, the addition of fiber with different content (0.4 and 0.8%) with a length of 12 mm has been investigated. The results of this study showed that the addition of lignosulfonate improves the durability of clayey sand. The stabilised samples containing 2% lignosulfonate resisted 12 freeze-thaw cycles, and the sample behaviour was improved by adding 0.4 and 0.8% fiber to the stabilised samples. By increasing the freeze and thaw cycles, the strength and stiffness of the samples decrease gradually until the cycle number gets to the critical value of steady-state of soil behaviour, which is 12 cycles. Hence, the lignosulfonate-stabilised samples exhibited acceptable behaviour under Freeze-thaw durability cycles. This indicates that a lignosulfonate stabiliser is appropriate in the areas where there is a potential for frost and exhibits good behaviour. Furthermore, the results of ultrasonic pulse velocity (UPV) tests showed that it could be used as a non-destructive test to control the durability of lignosulfonate-stabilised soils.

In this study, the effect of an additive with nano-montmorillonite brand on the process of self-healing on clay soil was considered. Laboratory tests include Atterberg limits and unpressurized comp...

The design of high-rise buildings often necessitates ground excavation, where buildings are in close proximity to the construction, thus there is a potential for damage to these structures. This paper studies an efficient user-friendly framework for dealing with uncertainties in a deep excavation in layers of cemented coarse grained soil located in Tehran, Iran by non-deterministic Random Set (RS) method. In order to enhance the acceptability of the method among engineers, a pertinent code was written in FISH language of FLAC2D software which enables the designers to run all simulations simultaneously, without cumbersome procedure of changing input variables in every individual analysis. This could drastically decrease the computational effort and cost imposed to the project, which is of great importance especially to the owners. The results are presented in terms of probability of occurrence and most likely values of the horizontal displacement at top of the wall at every stage of construction. Moreover, a methodology for assessing the credibility of the uncertainty model is presented using a quality indicator. It was concluded that performing RS analysis before the beginning of every stage could cause great economical savings, while improving the safety of the project.

International audience; Background: During an earthquake, significant damage can result due to instability of the soil in the area affected by internal seismic waves. Liquefaction is known as one of the major causes of ground failure due to the earthquake. Various procedures have been classified for assessing liquefaction phenomenon into two main groups, including the deterministic and probabilistic approaches. Results: Four deterministic methods and one probabilistic approach, which is a reliability procedure are considered for assessing the liquefaction potential in Babol City. The main purpose of this comprehensive research is to evaluate the liquefaction potential and to determine the validation and accuracy of the reliability approach. For this purpose, 60 boreholes including almost 600 field records in different parts of Babol City are analyzed and liquefaction and nonliquefaction areas are identified. Microzonation maps are provided by result analysis of the deterministic and probabilistic procedures. Finally, a 2D borderline, including (CSR) and (N spt) is obtained by analyzing all data. Conclusions: The present study illustrates that the evaluation of liquefaction potential by using reliability approach is accurate and this procedure can be recognized as one of the best methods for assessing liquefaction. The map obtained utilizing a reliability approach and the borderline provided in this study, can be utilized for recognizing liquefaction and non-liquefaction areas based on different safety factor and probabilistic procedures.

This study investigated the potential effect of the non-woven geotextile reinforcing of the clayey sand treated with the copper slag (CS)-based geopolymer. To this end, preliminary tests such as standard compaction, P-wave velocity, pH, and Atterberg limits (Plasticity index) were conducted on variously treated samples. In addition, complementary tests including unconfined compressive strength (UCS), unconsolidated-undrained compression triaxial (UU), and scanning electron microscopy (SEM) analysis were performed on the reinforced samples. Furthermore, 0, 10, and 15% of CS and 0, 2, 4, 8, 12, and 16 M (M) NaOH concentrations were utilized in the investigation. The alkaline-activator solution (AAS) contained 70% of Na2SiO3 and 30% of NaOH, and the weight ratio of CS-ASS was one. Subsequently, the selected samples were reinforced with 0, 1, 2, and 3 non-woven geotextile (NWG) layers by various arrangements. The results indicated the acceptable increase in the peak, residual strength, and failure axial strain. The UU results further demonstrated the improvement in shear parameters. The negligible and significant increases in the internal friction angle and the undrained cohesion were evaluated, respectively. The microstructural analysis elaborated the three mechanisms of geotextile, which helps to improve the mechanical behaviour of the reinforced samples. These mechanisms include contact, bending action, and interweaving action; interweaving action plays a vital role in the strength enhancement of samples.

Every year, numerous casualties and a large deal of financial losses are incurred due to earthquake events. The losses incurred by an earthquake vary depending on local site effect. Therefore, in order to conquer drastic effects of an earthquake, one should evaluate urban districts in terms of the local site effect. One of the methods for evaluating the local site effect is microtremor measurement and analysis. Aiming at evaluation of local site effect across the city of Babol, the study area was gridded and microtremor measurements were performed with an appropriate distribution. The acquired data was analyzed through the horizontal-to-vertical noise ratio (HVNR) method, and fundamental frequency and associated amplitude of the H/V peak were obtained. The results indicate that fundamental frequency of the study area is generally lower than 1.25 Hz, which is acceptably in agreement with the findings of previous studies. Also, in order to constrain and validate the seismostratigraphic model obtained with this method, the results were compared with geotechnical, geological, and seismic data. Comparing the results of different methods, it was observed that the presented geophysical method can successfully determine the values of fundamental frequency across the study area as well as local site effect. Using the data obtained from the analysis of microtremor, a microzonation map of fundamental frequency across the city of Babol was prepared. This map has numerous applications in designing high-rise building and urban development plans.

An experimental program was conducted to explore the impact of nanosilica on the microstructure and mechanical characteristics of cemented sandy soil. Cement agent included Portland cement type II. Cement content was 6% by weight of the sandy soil. Nanosilica was added in percentages of 0%, 4%, 8% and 12% by weight of cement. Cylindrical samples were prepared with relative density of 80% and optimum water content and cured for 7 d, 28 d and 90 d. Microstructure characteristics of cement-nanosilica-sand mixtures after 90 d of curing have been explored using atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. Effects of curing time on microstructure properties of cemented sandy soil samples with 0% and 8% nanosilica have been investigated using SEM test. Unconfined compression test (for all curing times) and compaction test were also performed. The SEM and AFM tests results showed that nanosilica contributes to enhancement of cemented sandy soil through yielding denser, more uniform structure. The XRD test demonstrated that the inclusion of nanosilica in the cemented soil increases the intensity of the calcium silicate hydrate (CSH) peak and decreases the intensity of the calcium hydroxide (CH) peak. The results showed that adding optimum percentages of nanosilica to cement-stabilized sandy soil enhances its mechanical and microstructure properties.

Helical piles, which have been widely applied as a deep foundation system from small to large load ranges, are very suitable for different kinds of applications. Therefore, concerns about t...

Earthquake has left much life and property damages. The occurrence of such events necessitates the execution of plans for combating the earthquakes. One of the most important methods for combating earthquakes includes assessing dynamic characteristics of soil and site effect. One of the methods by which one can state dynamic characteristics of the soil of an area is the measurement of microtremors. Microtremors are small-scale vibrations that occur in the ground and have an amplitude range of about 0.1–1 microns. Microtremor measurement is fast, applicable, cost-effective. Microtremor measurements were taken at 15 stations in the Babol, north of Iran. Regarding H/V spectral ratio method, peak frequency and amplification factor were calculated for all microtremor stations. According to the analysis, the peak frequency varies from 0.67 to 8.10 Hz within the study area. Also, the authors investigated the validity of the results by comparing them with SESAME guidelines and geotechnical conditions of study area. The microtremor analysis results are consistent with SESAME guidelines and geotechnical condition of study area. The results show that the microtremor observations are acceptable methods for assessing dynamic characteristics of soil and site effect in the Babol City.

In recent years, large steps have been taken in the field of nanotechnology, and many nanotechnology-based breakthroughs have been made in geotechnical engineering. It is apparent that nanomaterials will be used to improve the geotechnical properties of soils in the near future, extensively. In this paper, we discussed previous studies on the use of nanoparticles in soil, their properties, their effects on soil and the equipment used in nanotechnology. A new categorization was introduced and the significant effects of nanoparticles on the properties of soil were studied. According to the new categorization, clay particles vary between 0.1 and 2 μm, while nanosol contains particles in the range of 1–100 nm.

In this study, a series of unconfined compression tests have been performed to determine the effect of polyvinyl alcohol (PVA) fiber inclusion on deformation characteristics of cemented sand. The cement contents were 2, 4, and 6% by weight of the dry sand and samples were cured for 7 days. PVA fibers with a length of 12 mm and a diameter of 0.1 mm were added to sand-cement mixtures at a weight ratio of 0.0%, 0.3%, 0.6% and 1% (dry wt.). The compression stress-axial strain, secant modulus of elasticity (E50), tangent modulus of elasticity (Etan), failure mode, energy absorption capacity (EA), energy base index, strain base index, deformability index and axial strain at peak strength of the samples were described. Tests results show that addition of cement to sand increased stiffness and unconfined compression strength (UCS), and leading to a brittle behavior. Moreover, addition of PVA fibers to cemented sand increased the UCS and axial strain at peak strength and increased softening stress after th...

Helical piles have been increasingly used as a deep foundation system for small to large load ranges. They are suitable for various applications, including residential housing, solar farms, utilities, retrofitting projects, power transmission lines, oil facilities, and industrial applications. Hence, many researches have been conducted recently on qualifying and quantifying axial capacities and performance characteristics of helical piles. This paper discusses design considerations, installation procedures, and results of full-scale field load tests. In this study, axial static loading tests on single, double, and triple helix helical piles under grouted and un-grouted conditions have been conducted. The field study has been performed on two different soil types including sand and silty clay soil to investigate the behavior of helical piles. Results showed that in the silty clay soil, grouted and un-grouted helical piles had a similar performance while grouted piles showed greater axial compressive strength. In the sandy soil, cylindrical performance in helical piles was not satisfactory and in triple-helix piles, the axial compressive strength was less than that of double-helix piles even though the number of helixes has been increased.

In recent years, due to the growth of the world population, suitable lands for construction and building are being reduced, gradually; hence, researchers have continuously sought to increase the bearing capacity and resistance of soil and improve its properties. One of the effective methods for improvement of the soil bearing capacity and reduction in foundation settlement is the implementation of micropiles below them. In this study, the seismic response of micropiles under real seismic loading was performed using finite element software. The stabilized soil behavior was modeled as elastoplastic along with Rayleigh damping, and micropiles were modeled as elastic beam elements by considering the interaction between soil and structure. The parametric study aims to focus on how to connect micropiles with foundation and effect of earthquake intensity. The results of the analysis show that decreased stiffness of the micropiles foundation system against the applied forces affects the values of lateral displacement and bending moment. Also, it is found that the Arias intensity of an earthquake is important parameter in characterizing of an earthquake nature influence on pile performance in soil.

Liquefaction of sandy porous soil under earthquake waves is the most important feature governing the serviceability of underground pipelines. In this study, an artificial neural network (AN...

During history, soil was always considered as the cheapest materials, but natural soil exist in site that may not be suitable for construction, and weakness is one of the main faults of soil mechanical characteristics against tension. With purpose of increasing strength and stability of soil particles, nowadays, soils reinforcement method is studying by several researchers. The main purpose of this research is study of effect of using polyvinyl alcohol (PVA) fiber on Babolsar sand behavior. Twelve consolidated drained triaxial (CD) test were conducted on samples with four confining pressures 50, 100, 300, and 500 kPa and three fiber contents (0, 0.5, and 1%). The experimental results indicate that fiber reinforcement improves the mechanical properties of sand. Adding PVA fiber to sand increases maximum shear strength, axial strain at failure point and decrease of strength loss after peak strength. Failure strain and strength increases by increasing confining pressure.

Geotechnical engineers have long used the lumped factor of safety approach in design of retaining walls. In recent years, uncertainty inherent in soil properties has caught more attentions from researchers, thus reliability analyses are used widely. In short, combining the probabilistic and deterministic analysis is common practice nowadays and failure probability calculated by risk analysis is a kind of complement of safety factor. In this paper, reliability analysis of a deep excavation is presented using two probabilistic methods called Point Estimate Method (PEM) and Monte Carlo Simulation (MCS) method. Horizontal displacement of the excavated wall, as well as safety of factor, are adopted as a basis for assessing the performance stability of the system. The paper explains why probabilistic analysis with numerical methods is challenging, and how PEM and MCS can be used to calculate the statistical moments of output variables and to estimate probability of failure. The results are presented and compared in terms of statistical moments, probability of occurrence and most likely values at every stage of construction.

This paper presents a procedure to compute the values of degradation factors of p-y curves in the pseudo-static analysis of piles in liquefiable soils. Three-dimensional finite-element model was used for the computation of p and y values using OpenSees computer package. The piles were modeled using beam-column elements and elastic section. The soil continuum was modeled using brick elements and a two-surface plasticity model. By comparing the results of models in two cases of liquefiable and non-liquefiable, values of degradation factors were obtained. Validation of the degradation factors computed was conducted through the centrifuge test results. The simulation results showed a similar trend between degradation factor variation in different densities and sands. With increasing depth, the degradation factor increased. By comparing the results of pseudo-static analysis with the centrifuge test results, it was concluded that the use of the p-y curves with computed degradation factors in liquefiable sand gave reasonable results.

Piled raft foundations are the composite construction of a spread foundation and a few number of piles that are usually used in soft soils to compensate the weakness of a raft in satisfying the design requirements. Due to the complex behaviour of piled raft, it is necessary to take into account a number of factors such as pile geometry and arrangement, raft thicknesses, soil properties and loading condition in the design. In this study, a parametric study has been conducted by a three-dimensional finite-element method considering the full interaction between the components of piled raft foundation. The underlying soil consists of Babol clay in drained condition with various stiffness and plasticity, determined from the results of a geotechnical investigation. The results of numerical analyses show that the bearing capacity of piled raft obviously increases with increasing pile length, pile spacing and raft thickness, especially in stiff clay. The effect of load type is more significant for the differentia...

In our research, we apply numerical modeling for prediction of liquefaction of sands during and after dynamic loading. In numerical modeling, to properly simulate the generation, redistribution, and dissipation of excess pore water pressure during and after dynamic loading, it is important to use a suitable constitutive model for soil. In this article, Dafalias and Manzari’s model [2004] (a critical state bounding surface plasticity model) was used to model the behavior of saturated sand due to relatively simple of formulations and a unique set of input parameters for a wide range of initial stress and void ratio. The attention in this article is on Babolsar sand. After calibration model parameters for Babolsar sand, the analysis of liquefaction using the modeling of a centrifuge test and predictions of model was carried out. The results indicate a reasonable performance of the model for prediction of behavior of types of sands. Also, Babolsar sand has more prone to dilatancy than Nevada and Toyoura sands.