جهانگیر خزائی

Toppling failure is a common failure mode in natural and artificial rock slopes, which has always been associated with serious injuries to humans in road trenches, tunnels, dams, and mines. In this research, it has been tried to investigate the effect of cross joints with inverted layers on the toppling failure of rock slopes and horizontal displacements on the slope surface, in this regard numerical modeling using discrete element software. (UDEC) has been carried out in the rock to study the toppling failure mechanism, surface displacements, investigation of yield levels and the formation of tensile cracks, and parametric studies for cross joints with inverted layers and with different numbers in the rock slope. A total of six rock slope models were analyzed (three different models for the case of one cross-joint and three other models for the number of cross-joints). The results of this research show that the mechanism of failure in this type of slopes is stepped, unlike soil slopes, and when the first tensile crack reaches the surface, the toppling area is formed. The presence of cross joints causes more instability, which will increase the surface displacements much more compared to the model without cross joints. The length of the rock layers and the number of joints can simultaneously have their effects on toppling failure; The speed of movement of the layers also confirms this. The sliding zone is also formed in these models, which resists the toppling failure to a certain extent, so it is necessary to know these zones to stabilize the inverted rock slopes.

Using new and environmentally friendly materials to stabilize problematic soils is one of the challenges facing geotechnical engineers. Nanoclays are highly reactive due to their high specific surface area, low specific gravity, fine particles, and are also considered as an effective and environmentally friendly stabilizer due to their uniformity with soil materials. In the present study, the effect of Nanoclay on the behavioral properties of Kermanshah's clay fine-grained soil has been evaluated. For this purpose, after having conducted index and identification tests on the natural soil, Nanoclay was added to the studied soil with 0.5, 1, 2, and 4 percent by weight of the dry soil, and Atterberg, consolidation, unconfined compressive strength and California bearing ratio tests were conducted on these samples in curing periods 1, 14, 28 and 60 days. Also, the durability of the stabilized samples was investigated by applying wet-dry cycles, and to investigate the effect of Nanoclay on the soil microstructure, imaging was captured from unstabilized and stabilized samples by scanning electron microscopy. The results show that the stabilization performance is significantly dependent on the amount of Nanoclay and curing periods. Also, according to the results, the optimal amount of Nanoclay is 4%, and the presence of this amount of Nanoclay and increasing curing periods has increased the plastic index, compressive strength and soil bearing ratio and decreased the coefficient of consolidation, settlement, Compression, permeability, and soil swelling. It is noteworthy that soil durability against environmental conditions has also increased.

The process of biomineralization as a method of biological soil improvement refers to a set of biochemical reactions in which the sediment formed by bacteria causes the grains of soil to graft and thus improve its properties. In the present study, after optimizing the precipitation conditions, the effect of the sample making method on the biological improvement of Kermanshah clay fine-grained soil with two bacteria Bacillus megaterium and Lysinibacillus boronitolerans was studied. The results show that the method of sample making (in terms of adding biocementation solutions) has a significant effect on the improvement of compressive strength of samples. The maximum improvement of soil compressive strength (up to 2.68) occurred for Bacillus megaterium in adsorption method. In general, the addition of solution to the soil by adsorption method has been more effective in the proper placement of sediment between soil grains than the mixing and injection method. It has been more effective and in fact the solutions have been allowed to move between the soil grains to the corners where the grains join, thus resulting in the formation of effective sediment at the grains joint. Also, biological stabilization of the consolidation test sample reduced the soil void ratio change from 0.584 to 0.354 and the compression index from 0.077 to 0.038. The addition of biocementation solutions to the sample of atterberg limits test sample reduced the plasticity index from 26 to 19.

This study presents the experimental results and numerical analyzes on the conical and pyramidal shell foundations located on loose unreinforced and reinforced with geogrid sand. The results have been compared with the values studied for flat circular and square foundations. Laboratory studies were performed on different types of shell foundations with different apex angles using small-scale physical modeling. In order to extend of study for determination of the effect of various conditions of foundation’s depth to width ratio and the number of geogrid layers on bearing capacity ratio, numerical analyses have been done by limit analysis method. The results have shown that, in general, increasing the depth of the foundations and the use of reinforcing structures ameliorate the geotechnical performance of foundations in both flat and shell models, although this enhancement is more evident in plane foundations. The load bearing capacity for the foundations with 180°, 120°, 90°, and 60° apex angles is put up to 40%, 36%, 32%, and 28%, respectively by rising in the foundation depth to Df/B=0.5, and is raised to 76%, 67%, 61%, and 55%, respectively by the growth of the foundation depth to Df/B=1.0. The use of geogrids increases the bearing capacity of plane foundations more than the shell foundations. The use of a single geogrid layer increased the bearing capacity of the foundations on the soil surface by an average of 79%, while the use of two layers of geogrid increased the bearing capacity by 86%, reflecting the fact that the use of two layers of geogrid will not significantly improve the bearing capacity in comparison to the condition when the soil is reinforced with a single geogrid layer. Bearing capacity of buried foundations with Df/B=0.5 is increased to 50% and 53% by using a single geogrid layer and double geogrid layer, respectively, and with Df/B=1.0 is increased to 28% and 30% by using a single geogrid layer and double geogrid layer, respectively, in comparison to foundations which are built on surface unreinforced soil. For foundations on the soil surface with 180°, 120°, 90°, and 60° apex angles, using a single geogrid layer increases the average bearing capacity to 99%, 81%, 75%, and 60%, respectively, and the use of two layers of geogrid increases to 110%, 90%, 78%, and 62%, respectively. These conditions are less pronounced for buried foundations and the increase in load bearing capacity for footings with all apex angles is about 50% for Df/B=0.5 and 29% for Df/B=1.0. The use of two layers of geogrid will have less impact on the foundations with smaller apex angles.

Investigation and evaluation of damages to surrounding structures and also estimation of rupture levels by considering the amount of deformations and the amount of adjacent gates are important issues in the nailing system in urban areas. In this research, we tried to evaluate the axial force of the nails and the deformation in concave and convex dams; in sandy and clay soils. In this regard, numerical modeling is carried out using the Abaqus CAE software in the soil environment and parametric studies are carried out for different corner angles in the excavation under the service load. The results of this study indicate the effect of concave cortical deterioration and the damaging effect of the convex corners, which is in contrast to the concave hedge, in gondolas with sandy soil as well as clayey soil. The maximum axial force of the nails in the clay soil is less than that of the sandy soil, which decreases with the approach to the hollow corner. For maximum seating and horizontal displacement of the Goodwall wall, there is also a turning point between the angular angles of 130 ° to 150 °, with a good turnaround. By comparing and analyzing land surface levels and rupture levels, we will find that the maximum level of earth's summation in sandy soils will be the highest level of rupture, and in clay soils, ground-level landings in the location of critical burst surface changes It is noteworthy.

Soil friction angle is one of the basic parameters in determining the shear strength of coarse-grained soils, which is often determined in the laboratory by spending a time and cost, and the use of field experiments has solved this problem. In this regard, Standard Penetration Test (SPT) is one of the most practical field tests that is commonly used in granular soils. In recent years many researches are proposed that present the correlation SPT and shear wave velocity, undrain shear strength and friction angle. Many correlations between SPT and soil friction angle are proposed but most equation with SPT numbers greater than 35 predict the right answers. The correlation between SPT results and soil bearing capacity has been studied and reported by various researchers.  In additional, some correlation between SPT and Soil friction angle have been proposed that each of those evaluated the material of specific area. In this paper new practical equation is proposed that presents an acceptable result in all SPT numbers. With use of this equation, the results can be predicted more accurately.

Current design of Geo synthetic-reinforced soil (GRS) walls, shows that the horizontal deformations in the walls increases rapidly with height. To take advantage of both the aesthetics and the economics of GRS walls while considering high heights, multi-tiered walls are often used. In this context, 12 models of the walls were constructed and their performance was determined under static loading. This study presents a series of model tests on the GRS walls in a tiered configuration, to evaluate the effects of factors, including the offset distance between adjacent tiers and number of tiers, on the lateral displacements of the wall facing and ultimate bearing capacities of the strip footings on the multi-tiered GRS walls. The ultimate bearing capacity and wall deflection can be significantly improved by increasing the number of tiers wall and increase of tier-offset. Interaction between the upper and lower walls significantly influences the tier-offset, and the interaction between the walls, significantly increase in the horizontal deformation in the wall face for the upper wall. With an increase in the offset distance, the lateral displacement decreased significantly, particularly in the upper tier. The experimental results showed that, the Performance in Four layers of reinforcement, and two tier walls, the optimum offset distance obtained for D/H= 0.35. When the offset becomes significantly large, each tier functions independently

Deep excavation have a direct effect on stresses and strains of surrounding soil, and it leads to the change in static and dynamic response of adjacent structures of the excavation. In this study the effects of urban rail ramp permanent excavation on Hamyari response, has been investigated. Consideration of soil-structure-groove interaction has a great effect on the structure response, including increased range of internal motion of foundation and floors, reducing the base shear, and increasing the natural period of the structure. The three-dimensional study has considered a nonlinear behaviour for soil and steel materials and also, semi-infinite elements have been used for viscose boundaries. The use of semi-infinite boundaries has shown a desirable performance in seismic analysis of soil environments. Placement of the building near the entrance ramp of Kermanshah metro and consideration of soil-structure interaction near the excavation, lead to the 8.98% increasing in the first period of the structure, decreasing 19.37% base shear of the Structure against the rest rigid condition, and also increasing the lateral displacement of floors, especially higher floors, and this increment in the roof floor compared to the rigid base and soil-structure interaction are 89.89% and 14.25%, respectively. Also, consideration of soil-structure interaction adjust excavation for building compared to the case with soil-structure interaction and without the excavation effect, leads to the 1.09% increasing in the first period of the structure and 10.27% decreasing in base shear, and also increasing of acceleration response spectrum.

The application of artificial simulations in predicting the behavior of materials, especially when we have real results, is very important in terms of time and cost. Therefore, in this study the data collected from unconfined compressive strength test on stabilized soil samples with lime, waste industrial and sodium silicate by neural network (GRNN) and genetic algorithm (GEP) have been investigated. Moreover, based on the results of unconfined compressive strength for the limited percentages of the experiment, simulation has been performed and verified. Then, with the development of the neural network and genetic algorithm for different states and percentages of mixing in stabilized soil, the optimized mixing percentage has been set. According to the results of genetic algorithm model, the optimal mixing design for this type of clay is 6% lime, 6% industrial waste, and 1.5% sodium silicate. The results of neural network had better predictive power than the genetic algorithm, so that the best prediction for the 90-day model of the neural network with R2 and RMSE values is 0.998 and 0.019, respectively, and the least prediction for the 7-day model of genetic algorithm with R2 and RMSE is 0.967 and 0.059, respectively.

Shallow foundations are among the most common typesof foundations used to support mid-rise buildings in ar-eas with high seismic hazard. Recent studies have indi-cated that dynamic interaction of soil-foundation andbuilding can a ect the seismic response of structuresduring an earthquake. Therefore, the foundation fea-tures can also change the dynamic characteristics, suchas natural frequency and damping of the soil-foundation-structure system. In this research, a 14 story momentresistant frame building built on shallow foundationswith various dimensions has been considered and thethree dimensional prototype of all three components ofsoil-foundation-structure system has been modeled byABAQUS nite element software. Also modal analysiswas performed to calculate the natural frequencies ofeach model. In the present study, in nite boundarieswere applied in order to simulate free eld conditionand appropriate contact elements were used to modelthe slip and separation phenomena between foundationand soil elements. To do so, nite element direct modelswere developed. Cone model, as one of the approximatemethods that considers SFSI with practical engineeringprecision was veri ed and then applied in the series ofsimulations. An assessment procedure was applied tocheck the accuracy of Cone model as an approximatemethod in comparison with direct method. Structuralresponses including lateral deformation, drift, rotationand shear force distribution were studied for all cases in-cluding xed-base, cone model and SFSI direct models.Modal analysis implies that SFSI can reduce the natu-ral frequencies of the building. The results show thatshallow foundation size, due to the interaction betweensoil, foundation and structure, in uences the dynamiccharacteristics and seismic response of building. As aresult, engineers should carefully consider these param-eters to ensure the safety and economic seismic design.Cone Model with an appropriate engineering precision,functionality and high analysis speed is capable of assess-ing dynamic sti ness of soil due to the soil-foundation-structure interaction phenomena.

In practice, the numerical simulation of soil nailing wall is often performed to evaluate the performance and stability. Use one or two stairs, while in the metropolitan area, despite the space constraints, it is possible to reduce deformations and increase safety factor excavation nailing method that justifies the use of this technique is relatively new. In the present study investigated The effect on the stabilization excavation stairs by nailing taking into account the behavioral models Mohr-Coulomb soil and HS and HSsmal to Software finite element is discussed. Use one or two stairs ratio to the nailing vertical wall with regard to behavioral models Mohr coulomb and HS and HSsmall soil maximum of horizontal and vertical and horizontal deformations of the top edge of the excavation is severely reduced Also uses a two-stairs soil nailing safety factor in the wall, with all models of behavior is considered to increase the equally.

In dynamic analysis, modeling of soil medium is ignored because of the infinity and complexity of the soil behavior and so the important effects of these terms are neglected, while the behavior of the soil under the structure plays an important role in the response of the structure during an earthquake. In fact, the soil layers and soil foundation structure interaction phenomena can increase the applied seismic forces during earthquakes that has been examined with different methods. In this paper, effects of soil foundation structure interaction on a steel high rise building has been modeled using Abaqus software for nonlinear dynamic analysis with finite element direct method and simulation of infinite boundary condition for soil medium and also approximate Cone model. In the direct method, soil, structure and foundation are modeled altogether. In other hand, for using Cone model as a simple model, dynamic stiffness coefficients have been employed to simulate soil with considering springs and dashpots in all degree of freedom. The results show that considering soil foundation structure interaction cause increase in maximum lateral displacement of structure and the friction coefficient of soil-foundation interface can alter the responses of structure. It was also observed that the results of the approximate methods have good agreement for engineering demands.

Effect of ground deformation on adjacent building caused by excavation is one of the main concerns in the construction of underground facilities in urban areas. The performance of soil nail walls is significantly affected due to the complex mutual interaction between its main components including the native soil, the reinforcement (nails) and the facing. Additionally, various other factors, such as the construction sequence, the installation method of nails, the connection between the nails and the facing, are also likely to influence the behavior of the soil nail walls. In practice, to study the complex soil-structure interaction and assess the performance of soil nail walls, often numerical simulations are performed. It is well established that the accuracy of numerical simulations depends significantly on the constitutive soil model used. In the present study, excavation in soft and stiff clay using hardening soil model, softening soil model, and Mohr-Coulomb model and also in loose and dense sand using hardening soil model and Mohr-Coulomb model is simulated using the finite element software ``Plaxis''. According to the results, considerable dependency of deformation of ground and side wall of excavation on the selected constitutive model is obvious. Based on obtained results, Mohr-Coulomb model predicts swilling at ground surface for points around the side wall. Hardening soil model and Mohr-Coulomb model predict maximum and minimum lateral deformations of side wall, respectively, but the deformation trends of side wall are quite different due to the two models. The modeling results of loose and dense sands show the amount of predicted swilling at the bottom of the excavation using Mohr-Coulomb model is more than hardening soil model result. In this study, the maximum and minimum amounts of swilling at bottom of the excavation for soft clay are calculated by Hardening soil model and softening soil model, respectively. The results of stiff clay show the maximum and minimum amounts of swilling at bottom of excavation and near the side wall predicted by hardening soil model and Mohr-Coulomb model, respectively, but away from the side wall, softening and hardening soil models predict maximum and minimum amount of swilling, respectively.

Behavior of braced excavation in a cohesive-frictional soil has been evaluated by present paper. Two groups distinct analyses based on plastic calculations and consolidation calculations were implemented by considering time intervals of staged excavation. In order to investigation of time effect and pore water pressure impact on the staged excavation phases, numerical modeling has been conducted by help of consolidation and plastic analyses. In major of former analysis and before present study numerical analyses of staged excavation procedure have selected without considering the effect of time and in form of plastic analyses, while pore water pressures were also ignored. In this, paper thereto the time effect other effects such as length of time interval, kind of analysis depending on drainage conditions, constitutive modeling for soil and location of ground water table were considered. Two dimensional finite element analyses in PLAXIS 2D software are the basis of the numerical calculations of present study. Excavation bracing selected as a kind of concrete facing wall and grouted soil nailing. The results of this research show that the values of excavation wall lateral displacement and soil heave in bottom of the excavation in consolidation analysis by considering time effect in comparison with plastic analysis often reduced approximately 20%.
It seems that effect of time and staged excavation just with implementation of numerical deflection analysis depending on the time such as consolidation analysis with creep models can be evaluated and these conditions in plastic numerical analysis with staged excavation without creep (time-depended) models is meaningless. Soft soil creep model (i.e. SSC model) for considering time effect in plastic and consolidation analyses has been used by authors. The results of present paper show that neither consideration of analyses that consider time interval nor analysis such as consolidation analysis that considers time are not adequate, but soil constitutive model that defines the material behavior must be contains time and also in their mathematic equations structure parameters such as time, strain rate and stress rate that vary with time must be taken into account. Present paper analyses show that consolidation analysis by considering time effect obtain less wall deflections by comparison with plastic analyses.
However, from present study outcomes can conclude that the plastic analyses also by considering constitutive model that contain time can take into account time effects in stress-strain calculations. On the other hand, responses of plastic analyses by comparison with consolidation analyses always are preservative and show more values. Therefore, in structural designing of bracing of an excavation, reliance on results obtained from plastic analysis is preservative and real values of time-dependent deflections of wall and bottom of excavation via consolidation analyses are obtainable. This paper has recommended that both plastic and consolidation analyses for designing of braced cut were considered by engineers and optimum system between those according to the economically advantages and disadvantages be selected. Because, occasionally reliance on plastic preservative analyses lead to imposition of high values of design and construction costs on a certain project that is revealed by implementation of consolidation analyses that those are not necessary. At the end of the paper, verifications and comparisons are related to the topic of present study have been carried out by authors and the obtained results have been compared with together and then are investigated with the obtained results by present study.

Landslide is considered as one of the reasons of natural resources loss in mountainous areas, leading to sever property damages and casualties worldwide (Fele Gray et al., 2013: 228). According to the United Nations’ report, landslide damages in developed countries is as equal as 1 to 2 percent of their gross domestic product, GDP (Lerouil, 2006: 198). The most well-known natural factors affecting the landslide are rainfall, lithology, slope etc. (Talebi and Niazi, 2011: 66). Moreover, road-building is considered as an effective human factor in the occurrence of landslides (Kelarestaghi, 2002: 5). In a research on the spatial association between the occurrence of landslides and roads in the forest regions, Larsen and Parks (1997) revealed that road building will increase the effect of the landslide by 5 to 8 percent.
In spite of providing several methods regarding the stabilization of landslide by different researchers, there is no unified consensus. Ramezani and Ibrahimi (2009) stated that, unlike the landslides made by non-natural factors, it is not often easy to control the ones made by natural factors.
In the present study, considering the uncertainties about a convenient and practical method to stabilize the landslide occurred on the kilometer 194 of the railway Malayer – Kermanshah (located between Aran, Kangavar and Ahangaran-e Sahne village), first, the stability of the aforesaid landslide will be discussed. Then, the geometry of landslide in different states including the present slope (unstable), the slope with modified geometry (the proposed method in this study), the modified slope proposed by consultant engineer, and the stabilized slope by pile system is modeled in FLAC 3D software, considering soil characteristics determined by the soil mechanics laboratory. Besides, the results will be evaluated and compared in order to choose the most appropriate method for landslide stabilization.
Materials and In this study, stability of a particular slope having different boundary condition has been modeled and analyzed using version 3 of FLAC 3D. In fact, geometry of slope was modeled in different conditions including unstable slop, slope with modified geometry (method proposed in this study), modified slope using proposed method by consulting engineers (Hexa Consulting Engineers, 2011), and stabilized slope using the pile systems (case studied in Malayer - Kermanshah railway). The soil characteristics were determined by soil mechanics laboratory. Moreover, the Mohr-Columb model, as the most practical model in soil slope modeling, was used. For the sake of validation, slope modeling was analyzed in Geoslope software version 2007 (limit equilibrium methods) in both natural and stabilized modes. Furthermore, the behavior of the progressive landslide was monitored using five stable monitoring points in different locations. The monitoring points were installed from bottom to the top of the slope which were mapped during four consecutive months, from September to December 2012, with ten-day intervals. Numerical findings were confirmed by comparing not only the consecutive mappings but also the latest and first mappings.
Slope analysis of the status quo proved the maximum displacement of 185 cm and a safety coefficient of slope stability of 1.26. High values of displacement marks the instability of the slope in this particular case. Slope modeling, after geometric correction, revealed a decrease in the displacement up to 71 cm, and an increase in the safety coefficient to 1.61. The proposal of the project consulting engineer suggested the slop adjusting and a concrete gallery implement to cross the railway track. In this case, the displacement in the gallery wall in the middle of the wall and the corners is 40-50 cm and 30-40 cm respectively, which may cause severe damages to the side of the gallery in case of landslide activity. Besides, the maximum displacement of the slope in this case is a bit more than 95 cm. In terms of stability safety, it should be noted that the maximum displacement in this case is less than 100 cm, so the amount of displacement is legal but on the edge of insecure borders. This condition can be soften by applying the procedures such as drainage. In the case of the pile application for stabilization, the largest landslide displacement was about 30cm, which was quite in a normal range, although it needs considerable operating expenses.
The findings of this study revealed that gallery implement method proposed by the project consulting engineer and stabilization method with piles are the most appropriate method for stabilizing the slope. The aforesaid method not only is economical, but also preserved the environment with the least interface in nature. Moreover, its safety and output are confirmed by the analytical model in FLAC 3D software. In the proposed method, geometric correction with drainage is cheaper, the displacement is lower, and the possibility of damage to the embankment is less. Moreover, in case of damage, it is easier to repair. Combining this method with Bio-engineeringmethods, such as planting of vetiver grass can increase the slope stability.