Journal of Engineering Geology

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In tunnelling in soil mass, in groundwater existing mode, liquefaction, elastic displacements and settlement in soils upon the tunnel, are the risks may attack the excavated underground space stability. In this case study that were performed on second line of Mashhad city subway route, information catched from Standard Penetration Test, in situ and laboratorial tests, were used to optimum numerical values search for soil engineering parameters that could optimize the TBM stationing level. In order to this goal attaining, intelligent, numerical and probabilistic methods were used and the reliability of intelligent and numerical methods with the Safety Factors of tunnel stability, investigated simultaneously. The results were denoting the accordance of intelligent models such as Genetic Algorithm (GA) and Multi objective Genetic Algorithm with Finite Element model's output. So these models could be complement of each others in planning and designing of tunnels and using of them advised in tunneling and excavations.

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Due to the increasing importance of geomorphologic conditions on the seismic ground response, the effect of liquefiable soils on seismic ground surface response is discussed. At first, the equivalent linear analysis based on total stress model in the frequency domain is carried out and then the nonlinear analyses based on total stress, effective stress model and considering the pore water pressure development in time domain are done in order to evaluate the differences between the several types of ground response analysis methods. DEEPSOIL.Ver5 software is used based on the latest achievements and various techniques in both solution domains. LNG port project in Assaluyeh, situated in south of Iran, is considered as a case study. Due to lack of the real data recorded near-field fault at the project site, the simulated method is used in order to create the artificial earthquake. Also three far-field earthquakes have been selected based on conventional seismic hazard studies for the seismic ground response analysis. Then, in order to better understanding of the obtained responses, the resulted responses spectra are compared with the acceleration design spectra provided in some valid codes. The result of this study indicates that the pulse effect in the horizontal component of acceleration perpendicular to the fault plane direction, affects severely the surface ground response of the near-field earthquake. The obtained results of the nonlinear modeling of the soil with excess pore water pressure build-up in the time-domain are extremely different from those of frequency-domain responses based on the equivalent linear method. In addition, because of the inherent linearity of equivalent linear analysis which can lead to spurious resonances in ground responses, the peak ground acceleration in the time-domain is lower than the frequency-domain.

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Marly rocks of Abtalkh formation were classified by Q, RMR, RSR and RQD rock mass classification systems using 222 meters logs from exploratory boreholes in Doosti dam site. The results show that the RMR is the most suitable method for classification of studied rock masses and has highest correlation coefficient with RQD. The validity of different Q-RMR equations was studied using error ratio (ER). Cameron et al. (1981) and Morno (1982) equations have lowest ER and highest validity for studied marlstones. Bieniawski (1989) and Cameron (1981) relationships are lower and higher limits of equations for marly rocks respectively. 

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Objective of the present research is to identify, analyze, and assess risk of Paveroud Dam during construction phase. Following collection and analysis of the information related to environmental conditions of the area of study and technical specifications of dam construction, a list of probable risk factors was prepared in the form of a questionnaire, and for verification, the questionnaires were provided to a group of specialists consisting of elites and professors specialized at the disciplines relevant to environment and civil engineering. Number of questionnaires was determined based on Cochran’s formula. In the first step, the expert group in the research was asked to score in Likert scale format so as to analyze the acquired responses and the risks present in the region. Having analyzed the scores using the findings of PHA method, TOPSIS technique was applied to prioritize the identified risks of Paveroud Dam. The results indicated that erosion had the highest priority among 36 risk factors. After prioritization among the risk factors, risk was also assessed using RAM-D technique in which “impact on Sorkhabad Protected Zone with 9 scores, “erosion” with 6 scores, and “work at high elevation” with 3 scores were recognized as three major risks of Paveroud Dam. In order to mitigate the effects of dam risks during construction phase, environmental management planning is crucial, and for this purpose, risk mitigation choices were recommended at the end aimed at coping with the identified risks.

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Subsurface flow contributes considerably to river flow and plays an important role in river sediment loads. This research has been focused on investigation of soil properties and bankstream slope on seepage erosion. For this purpose a series of lysimeter experiments were performed for four different slopes of bankstream by varying the soil grain sizes. The obtained results indicate that Reynolds number in porous medium plays an effective role in depth of scour hole in noncohesive layer. It was observed that the time of beginning of sediment motion decreases with an increase in the soil grain size.

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The Sharbyan river is located in the Sharbyan village, Sarab, East Azarbaijan province. This river alluvials are supplied from rock units belonging to Oligo-miocene and Miocene, including conglomerate, sandy lime, limestone, marl and shale. These deposits are used as raw materials of producing hot asphalt in two asphalt plants that have been built in the vicinity of this river, and the produced asphalt is used mainly in the neighbor provinces that have rather cold climate. Combined analysis of the sediments indicate high level of silica, around 60 percent, for which  the prepared asphalt  is prone to stripping phenomenon in the cold seasons. During this process, the moisture penetration in aggregates and asphalt mixtures, causes weakening bitumen-asphalt materials bounding and finally asphalt demolition.  The role of sediments and its impact on the quality of asphalt has not been studied in this area, therefore, the solutions for dealing with this phenomenon is also examined and presented. This study is based on the conventional sedimentology methods, different standards of ASTM, AASHTO and Ministry of Roads and Urban Development guidelines. In this study, the combined effects of hydrated lime (lime filler) and natural filter materials with different proportions was used to deal with the stripping phenomenon, and  the parameters of strength, softness, indirect tensile strength, asphalt quality and durability criteria, have been appraised. The results show that these parameters are improved using additives in various proportions and the produced asphalt quality and durability is better. The results illustrate, when the lime is used in its maximum ratio of 3%, stripping score is 1 and is disappeared by other parameters improvement

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Soil nailing is a prevalent method for temporary or permanent stabilization of excavations which, if it is used for permanent purposes, the seismic study of these structures is important. There are a few physical models, with limited information available, for the study of behavior of soil nailed walls under earthquake loading. Numerical methods may be used for the study of effects of various parameters on the performance of soil nailed walls, and this technique has been used in the current paper. In this research, the effects of various parameters such as the spacing, configuration, and lengths of nails, and the height of wall on seismic displacement of soil nailed walls under the various earthquake excitations were studied. To investigate the effects of the configuration and the lengths of nails on the performance of these structures, two configurations of uniform and variable lengths of nails have been used. To study the effects of the spacing between nails and the height of the wall the spacings of 2 and 1.5 meters and the heights of 14, 20, and 26 meters have been considered. The seismic analysis has been carried out using the finite element software Plaxis 2D. To analyze the lengths' of nails, it was assumed that the safety factors of stability of different models are constant, and the limit equilibrium software GeoSlope was used. After specification of the lengths of nails based on constant safety factor of stability, the deformations of the models under several earthquakes records were analyzed, and recommendations were made on minimizing the deformations of soil nailed walls under seismic loading.

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Because most part of Iran country is located in a dry climate, construction of water conveyance tunnels is inevitable. One of the major challenges in the construction of these tunnels is inflow of water into the tunnel during the construction and operation phase. The Rozieh water conveyance tunnel whose length is 3200 meters is a part of water conveyance project to the Semnan city and it is located 30 k NE of Semnan city. In accordance with the drilled boreholes, the tunnel route has been classified into eight zones from the geotechnical view. Then the permeability coefficients of host rock were calculated using back analysis approach on the basis of numerical simulation results and water inflow quantity during the construction phase. A parametric study was done on the lining and cement injection zone permeability and the thickness of cement injection zone. According to this study, the effect of injection zone thickness variation on the water inflow quantity is negligible. So with the assumption of 3 meters thickness for the injection zone, the permeability coefficient of host rock after injection were evaluated. Dependent on the initial rock permeability, cement injection could reduce the rock permeability 10 to 1000 times. In addition, the water inflow into the tunnel was calculated using hydro-mechanical coupling analysis. According to this analysis, the water inflow calculated by the hydro-mechanical coupling analysis is 50 to 70 percent less than the hydraulic analysis.

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The Bakhtiari dam has located on Bakhtiari River in province of Lorestan. In order to access the crest of the dam, the excavation of a spiral tunnel is being studied. There are other access tunnels which are branched from this tunnel in different levels and are connected to grout galleries. According to the fact that this tunnel will also be used during the operation of the dam,The correct determination of mechanical parameters of rock masses for tunnel design and stability Analysis is very important. In order to analyse the stability of the underground rock structures, the mechanical and engineering parameters of the rock mass must be known. Accurate rock mass properties can only be obtained from large in situ tests. Such tests are seldom carried out as they are very expensive and time consuming. Sensitivity analysis of parameters can be applied for the optimisation of testing schemes. Sensitivity analysis helps to avoid mistakes due to subjective conjecture. In this article, after the introduction of regional geology and determination critical section on the tunnel path, the mechanical parameters of the rock mass surrounding the tunnel are modelled and analyzed by using FLAC3D software (numerical finite difference method). Parameters conducted in the analysis include the elasticity modulus (E), cohesion of the rock mass (C), friction angle (ϕ), coefficient of lateral stress (K) and tensile strength (&sigmat). Ultimately, according to the result of numerical modelling and parametric analysis, parameters affecting the stability are prioritized. The result of analysis showed that in this project, tensile strength of the rock mass does not affect the stability of the tunnel, and Also, in order of priority, E, ϕ, C, k parameters are important in design. The amount of field tests for rock parameters can be rationalised according to their sensitivity factors.

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The Schmidt hammer provides a quick and inexpensive measure of surface hardness that is widely used for estimating the mechanical properties of rock material such as uniaxial compressive strength and Young’s modulus. On the other hand, Schmidt rebound hardness can be used for a variety of specific applications. In the mining industries, it is used to determine the quality of rock, which is common practice when constructing rock structures such as those found in long wall mining, room and pillar mining, open-pit mining, gate roadways, tunnels, dams, etc. However, a number of issues such as specimen dimensions, water content, hammer type, surface roughness, weathering, testing, data reduction and analysis procedures continue to influence the consistency and reliability of the Schmidt hammer test results. This paper presents: a) a critical review of these basic issues and b) avaluate the effect of temperature, moisture and uniaxial compressive stress on Schmidt hammer hardness. It was found that water content has a significant effect on the Schmidt rebound hardness (SRH) of rocks. So that increase of water content substantially reduced the SRH of samples. Temperature also had a considerable influence on the SRH. However, relationship between SRH decreases with increasing temperature for tested samples were linear. Also tests results showed that uniaxial loading of samples increases the SRH values.

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There are various methods for the analysis of the interactional behavior of the surrounding land, using the lining structure which is the most common method of deigning lining structure tools for the static loads by using the hyper static methods. In recent years, there has been a question that depicts whether this method provides the best results in designing the tunnel structure or not.Due to the nonlinear behavior of the earth surrounding the lining structure, utilizing the lining method could lead to conservative results in the design. If it is possible to somehow find the forces caused by the real behavior of the land surrounding the lining structure influencing the structure and conduct the design based on them, more optimal results would be obtained. This study is based on the actual behavior of the land surrounding the lining structure and the displacement of the structure caused by forces with linear behavior in the static design according to the non-linear behavior of the land around the tunnel structure. The behavior is modeled using the non-linear programs and the forces affecting the lining of the structure will be inference. Also there is a case study based on this method in which the soil interaction with the tunnel analysis and designing the lining structure was first performed and eventually the obtained results were compared with the hyper static method. In this paper, analysis of maintenance system with lower thicknesses considering land-shield, indicated that applying the reinforced concrete with 40cm thickness has the potential to tolerate the applied load but lining with 45cm thickness is capable of tolerating the loads of design and it can be concluded that applying the simulation method combined with the soil and structure besides considering the nonlinear behavior of the soil leads to more economical results in a project. 

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This research focuses on the identification and description of various features of pseudokarst in different parts of Alvand granitic batholith, Hamedan, west of Iran. In the literature, karst features have been presented as specific types of terrain or landscapes with particular characteristics suites of well-known surface and subsurface dissolutional forms. Whereas, pseudokarst refers to non-dissolutional surface or subsurface features and landforms created in different areas such as slopes, coastal lines crushed stone areas, lava tubes and permafrost regions. In this research, a comprehensive field investigation program has been carried out. During the field investigations, the most important features of pseudokarst in Alvand granitic batholith have been recognized and classified. Results show a wide range of pseudokarst features in the Alvand granitic rock masses. These landforms are created by erosion, weathering processes and some holes caused by rock block movements along the rock slopes. Some of the most important forms and features of the pseudokarst in the studied area are consist of tafoni, genama, pseudokarren, talus caves, caves associated with the residual blocks and erosional forms along joints and fractures within the granitic rock masses

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Evaluation of the excavation-induced ground movements is an important design aspect of supporting system in urban areas. This evaluation process is more critical to the old buildings or sensitive structures which exist in the excavation-affected zone. Frame distortion and crack generation are predictor, of building damage resulted from excavation-induced ground movements, which pose challenges to projects involving deep excavations. Geological and geotechnical conditions of excavation area have significant effects on excavation-induced ground movements and the related damages. In some cases, excavation area may be located in the jointed or weathered rocks. Under such conditions, the geological properties of supported ground become more noticeable due to the discontinuities and anisotropic effects. This paper is aimed to study the performance of excavation walls supported by nails in jointed rocks medium. The performance of nailed wall is investigated based on evaluating the excavation-induced ground movements and damage levels of structures in the excavation-affected zone. For this purpose, a set of calibrated 2D finite element models are developed by taking into account the nail-rock-structure interactions, the anisotropic properties of jointed rock, and the staged construction process using ABAQUS software. The results highlight the effects of different parameters such as joint inclinations, anisotropy of rocks and nail inclinations on deformation parameters of excavation wall supported by nails, and induced damage in the structures adjacent to the excavation area. The results also show the relationship between excavation-induced deformation and the level of damage in the adjacent structure.

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Consolidated-drained triaxial compression tests were conducted to compare the stress-strain and volume change response of sands and clayey sands reinforced with discrete randomly distributed poly-propylene fibers. The influence of various test parameters such as fiber content (0.0%, 0.5% and 1.0% by weight), clay content (0%, 10% and 20% by weight), relative density (50% and 90%) and confining pressure (100 kPa, 200 kPa and 300 kPa) were investigated. It has been observed that addition of clay particles to the sands decreased the shear strength of samples. Also, increase in clay content reduced dilation and increased compressibility of the mixed soil. Addition of the fiber to both sands and clayey sands samples improved the shear strength and increased ductility and axial strain at failure point. 

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Free vibration of soil often occurs during earthquakes. Since the vibration caused by earthquake does not have (steady state harmonic vibration) continuity, the alluvium vibrates with its natural frequency between two natural seismic waves. This study evaluates the effect of piles on the period of free vibration of a soil layer using numerical method. In the first stage, using analytical equations for calculation of vibration period of a soil layer and a column with continuous mass, the results were analyzed by the software. In the second step, piles with the same dimensions and distance were added step by step, and the vibration period for the soil layer with piles was calculated. The friction or floating effects of the piles on alluvial soil vibration period was also examined. The results show that as the number of piles increases, the differences between the results of one dimensional analysis of alluvium soil and the results of the software become different, and this creates the need for specific arrangements for seismic analysis of this kind of alluvium (with inserted piles). The results also suggest that end-bearing piles have a greater effect on alluvial soil vibration period, and with increased amount of the floating of these piles, these effects decline.

 

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Durability is a significant parameter in engineering geology and it shows the extent of the degradability of rocks as the result of mechanical and chemical breakdowns. This phenomenon is closely linked to the composition, porosity and texture of rocks. To understand the relationship between the chemical composition of rocks and their durability the mineralogical properties of the rocks along with durability tests under both acidic and alkaline pH environments were determined. Five samples of limestone and three samples of marl were analyzed. The results revealed that rocks containing high levels of CaCo3 were affected in the acidic conditions while rocks containing high levels of SiO2 were not affected by variance in the pH of the environment. These second groups of rocks were more dependent on the texture of their constituent minerals.

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./files/site1/files/6Extended_Abstract.pdfExtended Abstract
(Paper pages 115-134)
Introduction
Different factors should be considered in investigating soil- structure interaction for which we can refer to underground layers material properties, site shape and topography and entry motion. It has been showed that seismic waves will be reflected and makes more strange seismic waves in comparison with the state of without slope. To investigate the topography effects the various assumptions such as considering the rigid and compliant bedrock, half space, stimulations with different frequencies, slopes with different angles, different heights of slopes, and soil type were evaluated.  In this study topography effects on interstory drift of three structures with steel moment resistant frame system is considered, for this aim 6 combined model of soil- structure and topography is investigated. Three structures of 6, 9 and 12 story placed in near and far from of crest of a slope and 10 earthquake on bedrock has been applied to models. Interstory drift is considered as a criteria for investigating topography effect.
Material and Methods
This paper examines 3 planar steel moment resistant frame (SMRF) which have been previously designed by Karavasilis et al (2007) according to EC3 and EC8. These structures have 3 bays, and 6, 9, 12 stories. The length of each bay and the height of each story are 5 and 3 m, respectively. Furthermore, the amount of dead and live loads are considered in accordance with the current study (Minasidis et al 2014). The study frames were modeled in ABAQUS software in the form of two-dimensional (Figure 2). A36 steel is used in the models and the yield strength of steel is 235 MPa. Modeling of the behavior of steel was implemented using the yield criterion of VON MISES and taking into account the non-linear behavior of materials and Poisson's ratio of 0.3. A kinematic material hardening of 3% is assumed for the nonlinear elements and a Rayleigh damping of 5% is assumed for the first two modes of each frame.
In this study,   a slope with α=20 is considered. The characteristics of the slope and the soil of the region are obtained by borehole in different point based on Ghanbari et al 2011 study.




Figure1. Growth percentage in average amount of interstory drift
The desired slope has a height of 30 m. The depth of the bedrock is considered equal to 60 m. The numerical analyses were performed with the Finite element method, for nonlinear soil with VS=238 m/s, Poisson’s ratio v=0.35 and mass density ρ=1800 kg/m3. Moreover, to estimate the distribution of response, 10 records located on the bedrock (shear wave velocity is more than 650 m/s) have been used. To reduce the near source effect records are selected in such a way that they have no pulse in velocity time history and Distance from source to site greater than 10 km considered
Result
Result showed that interstory drift of structures increases due to topography effects, but this increase varies for different structures and earthquakes. Growth percentage in average amount of interstory drift are 25, 15 and 6 percent for structures with 6, 9 and 12 story respectively. Also for structure 9 and 12 story, interstory drift was decrease in some stories.
 

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./files/site1/files/1.pdfExtended Abstract
(Paper pages157-174)
Introduction
Considering the fact that the estimation of mode  fracture toughness by testing is time-consuming and expensive. It might be associated with certain practical difficulties. Therefore, many researchers have attempted to propose experimental relationships in order to capture these problems. Gunsallus et al. (1984) and Bhagat (1985) experimentally found that mode  fracture toughness is related to tensile strength. Whittaker et al. (1992) have also proposed a number of relationships between mode I fracture toughness, tensile strength, point load index, uniaxial compressive strength and the velocity of sound waves. Bearman (1999) obtained an experimental relationship between mode I fracture toughness and point load index, while Brown et al. (1997) presented an experimental relationship between this parameter and density. Up to now no significant research effort has been made in this field in Iran, only Ayatollahi and Fatehi addressed rock fracture toughness. Although, Ayatollahi has not presented any experimental relationships. In the present research the three-point bending test was used on a cylindrical specimen containing a straight crack in order to determine the mode  fracture toughness, and the Brazilian test was employed to determine tensile strength.
Materials and Methods
The tests were carried out on six types of rocks, namely gray sandstone,
tuff, lithic tuff, travertine, andesite, and limestone. Sandstone, travertine, and limestone are sedimentary rocks, while andesite is an extrusive igneous rock, and tuff and lithic tuff are pyroclastic rocks (pyroclastic rocks resulting from volcanic eruptions that harden by sedimentation). Therefore, the studied rocks have different origins. In order to carry out the Brazilian and the three-point bending test, cores were prepared from these blocks. In order to perform the three-point bending test, specimens with diameter of 73 mm with a thickness of 30 mm were used. The samples were cut in two semicircular by a cutting machine, and a notch with length of 15 mm is created by a diamond saw.  Notch is vertical in the center of the semicircular samples.
The Brazilian test was performed on disc shaped specimens. In order to perform the Brazilian test, specimens with diameter of 51 mm and thick of 25 mm were used. The specimens are carefully placed under the curved jaws of the machine and then loaded until fracture.
Results and Discussion
A summary of the Brazilian and the three-point bending test results are presented in Table 1. The average value of test result pertaining to each rock is reported in Table 1.
Table 1. Summary of the Brazilian and the three-point bending test results

Specimen	Tensile Strength (MPa)	Fracture Toughness (MPa√m)
Limestone	3.74	1.23
Sandstone	7.14	1.63
Tuff	16.36	2.17
Lithic Tuff	4.34	1.01
Andesite	13.25	1.86
Travertine	8.27	1.14

In this study, it was attempted to propose an experimental relationship between mode I fracture toughness and the tensile strength of the rock.
In order to determine the relationship between the tensile strength and the fracture toughness, the tensile strength vs. fracture toughness diagram was plotted in Excel to obtain Eq. 1 and the coefficient of determination (R²) (Figure 1).

The coefficient of determination (R²) in Eq. 1 shows that almost 80 percent of the mode I fracture toughness variations can be estimated using the linear relationship (Eq. 1). The relationship is applicable for determining the mode I fracture toughness resulting from the three-point bending test on semicircular specimens containing a straight crack.

In the following, the results of this study are compared to those reported by Whittacker (1992) and Zhang (2002).
In order to examine the accuracy of the presented relationships, the Root Mean Square Error (RMSE) measure was used which is computed from Eq. 2. In the best case, RMSE is zero. 

In the relationships,   represents the fracture toughness obtained from testing while  is the fracture toughness estimated using the relationships.
Comparison of the obtained results indicate that the proposed relationship has the capability of precise estimation of the mode I fracture toughness of rocks.
Conclusion
Given the many difficulties associated with the direct estimation of fracture toughness, indirect estimation methods have been proposed. One of such methods is the estimation of mode I fracture toughness using tensile strength. A linear relationship with a coefficient of determination of 0.7977 was proposed. The accuracy of this relationship has been verified by comparing its results to those from previous studies.

 

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./files/site1/files/4.pdfExtended Abstract
(Paper pages 225-246)
 Introduction
Soil has always been a major material in civil projects. Due to progress in science, different studies on the behavior of soil and its engineering characteristics have been conducted. As mentioned, there are different types of soil in nature; a small change in their structure and fabric under different environmental conditions or loading causes high deformation and settlements, which result in a reduction of strength and bonding between soil particles. Also, in this regard, some soft soils exist that are mostly composed of clay particles, with small shear strength and big settlement under low stress. With respect to the above-mentioned characteristics, these soils are referred to as problematic soils. The problematic soils consist of a silicate combination, whose major parts are clay minerals formed under weathering of rocks. Additionally, the precipitation of some soils and ground activity near the surface causes them to become problematic (Beckwith and Hansen [1]). Principally, in engineering, those soils on which construction is not safe, and which are affected by different environmental conditions, are defined as problematic soils. Collapsible soils are some of the most important of these problematic soils. The collapsibility phenomenon is defined as a sudden collapse of soil caused by the loss of the shear strength of soils. The collapsible potential depends on the initial void ration of soils. A few silty strata that are exposed to arid weather are susceptible to considerable volume decrease or collapse under soil saturation. Therefore, it is possible that surface water penetration in an irrigation form, pipe leakage and rise in ground water level may lead to great settlement.
In the last decade, the use of nanotechnology based on the science of production and nano-scale particles usage has become prevalent in many sciences. It can be said that nanoparticle application has made considerable progress, apart from nanotechnology, in recent years and has been one of its main aspects of this study. In this regard, the variety of nanoparticle depends on different applications.
The use of nano-materials has drawn the attention of various researchers in geotechnical engineering. One of the important nano-materials is nanoclay which, with respect to its characteristics, has had a wide range of applications in soil improvement techniques. Taha and Taha [2] and Majid et al. [3] have studied the effects of nano-materials, such as nanoluminum, nanocopper and nanoclay, on the swelling and shrinkage behavior in fine grain-size soils. Also, the compressive strength and permeability of soils increase and decrease with the addition of nanoclay, respectively, and are subjected to change of elastic to plastic behavior (Burton et al. 2009 [4], Gallagher and Lin [5], Persoff et al. [6]).
In this research, the main objective is to investigate the addition of nanoclay on the behavior of fine grain-size soil with experimental studies and to evaluate the different parameters on the soils’ modification mechanisms.
Material and methods
Given the importance of this subject and the practical use of the results of this research in the improvement of problematic soils, as well as the field assessment conducted, it was observed that, in many parts of the main irrigation channels of Gonbad dam in northeastern Iran, which is an arid and semi-arid region of Iran, due to the specific geotechnical conditions and loess soils, large and non-uniform subsidence of soil has occurred around dewatering channels. This has caused large cracks to occur in the concrete channel coverage and subsoil and the surrounding wall soil, which ultimately will lead to the destruction of large parts of the channel mentioned above. Remarkably, given the nature of loess soils in the study area, dangers such as collapsibility, dispersivity, landslides, sinkholes and subsidence can be noted. In order to evaluate the effect of soil improvement with the help of nanoclay in field conditions, all the tests and geotechnical studies on soil samples located in the channels were performed under valid standards. In this regard, a number of exploratory boreholes were bored in the walls and floors of the considered channel. During this procedure, sampling was carried out in different depths of layers of soil in order for laboratory tests to be carried out and for identification of the soil. The undisturbed samples were also taken by a Shelby Tube Sampler for necessary tests. In order to determine the initial physical and mechanical properties of the used soils, various tests such as particle size analysis, Atterberg limits, specific gravity and standard compaction were conducted. Table 1 summarizes the characteristics of the used soils.
Table 1. Soil  specifications

Incheberon Area	Gonbad    Area	Soil Properties
CL-ML	CL-ML	Unified soil classification system
2.55	2.54	Particle specific gravity
18	16	Plastic limit (%)
23	22	Liquid  limit (%)
5	6	Plasticity index (%)
86	95	Passing No. 200 sieve (%)
0.04	0.006	Average particle size  (D50) (mm)
16	15	Optimum water content (%)
1.60	1.54	Maximum dry unit weight (g/cm3)

The nano-materials used in this study have comprised nanoclay prepared by Sigma-Aldrich Company Ltd with the brand clay montmorillonite K(10).
Results and discussion
By adding nanoclay to the soil, it is observed that the liquid limit and plasticity limit of samples gradually increases as can be seen in Figure 1.


Figure 1. Effect of nanoclay addition on the Atterberg limits test of soil samples
Based on the obtained results by adding different amounts of nanoclay to the soil, the maximum dry density and optimum moisture content decreased and increased, respectively. By adding nanoclay to the soil, strain increases at the moment of failure due to increased plasticity and changes in soil structure. It is worthy to note that the unconfined compressive strength in samples stabilized with nanoclay has been increased in comparison with the plain soil.  Plain and improved soil samples were tested with different amounts of nanoclay under unconsolidated undrained conditions at different confining pressures.
To study the impact of nanoclay on the collapsibility potential of the soil, double consolidation tests were conducted to determine the deformation of plain and stabilized samples with various amounts of nanoclay under different vertical pressures. The test results showed that adding nanoclay has reduced the collapsibility potential of samples.
Conclusions
Due to existence of large areas of collapsible soils in Iran, improvement of these soils is necessary in civil projects. With considering the advances of nanotechnology sciences, in this research aiming to understand the impacts of different amounts of nanoclay on above mentioned soils have been studied. The soil samples used in experiments were collected from Golestan province including Boston dam of Gonbad and Incheboron near Gorgan city. In order to assessment of geotechnical behavior of soils, samples were mixed with varying percentages of nanoclay and different tests such as Atterberg limits, standard compaction, unconfined compressive strength, unconsolidated undrained triaxial and double consolidation were conducted. The results showed that nanoclay particles have a significant effect on the plasticity and strength behavior of used soils. Also, it was found that collapsibility index of soils decrease with adding nanoclay and it depends on the type of soil. 
Keywords: Nanoclay,‎‏ Collapsibility, Improvement, Fine-grained Soils.
 
1. Beckwith, C., Hansen, L.A., Identification and characterization of the collapsible alluvial soils of the western United States, Foundation Engineering, Current Principles and Particles, ASCE, (1989) 143-160.
2. Taha, M.R., Taha, O.E., Influence of nano-material on the expansive and shrinkage soil behavior, Journal of Nanoparticle Research Vol. 14(10) (2012) 1-13.
3. Majeed, Z.H., Taha, M.R., Jawad, I.T., Stabilization of soft soil using nanomaterils, Research Journal of Appiled Sience, Engineering and Technology Vol. 8(4) (2014) 503-509.
4. Burton, C., Axelsson, M., Gustafson, G., Silica sol for rock grouting: laboratory testing of strength, fracture behavior and hydraulic conductivity, Tunneling and Underground Space Technology (2009) 603-607.
5. Gallagher, P.M., Lin, Y., Column testing to determine colloidal silica transport mechanisms, Proceedings Sessions of the Geo-Frontiers Congress of Innovations in Grouting and Soil Improvement, Texas Vol. 162 (2005) 1-10.
6. Persoff, P., Apps, J., Moridis, G., Whang, J.M., Effect of dilution and contaminants on strength and hydraulic conductivity of sand grouted with colloidal silica gel, Journal of Geotechnical and Geoenvironmental Engineering Vol. 125 ( 6) (1999) 461-469.

 

 

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./files/site1/files/2.pdfExtended Abstract
(Paper pages175-200)
Introduction
In weak soils with low bearing capacity, the load transfer is done using piles. Therefore, by creating an interposed layer separating the pile from the raft, reactions between raft and pile head will be reduced and the load-bearing role of shallow soil will be more than contact pile situation. Normally, the pile head and shallow soil have a settlement equal to the raft. Thus, the relative settlement of pile and soil in pile head is equal to zero and at the bottom is high and the body friction mobilizes upward. In addition, a portion of load is tolerated by shallow soil and the other portion is tolerated by the pile head, which would be transferred to deeper soil layers. In noncontact state, with the formation of a hard soil layer on which the raft is located, soil mechanical parameters will be improved; while in contact state, the settlement will be decreased by reducing the amount of transferred load to the shallow soil. The transferred load to the shallow soil increases vertical and horizontal stress around piles, so bearing capacity of piles is increased.
Methodology
In this study, a parametric study has been performed concerning contact and noncontact piles using finite element software namely, ABAQUS/CAE software version 6.13.1 and the obtained results were compared (with what? The sentence is incomplete). Thus, simulations are is done for states of 0, 1, 4 and 9 piles for each of the contact and noncontact piles (total of 8 simulations). In the present research two models were taken to investigate the optimum mesh sizes, 12 models for parametric studies on parameters of piles’ length, piles’ diameter, thickness of the raft and interposed layer and one model for verification study. Models in both contact and noncontact have been considered with a one meter interposed layer. Raft width and thickness were selected 7.5 and 1.6 m, respectively. Width and depth of the soil mass used in the model were 32 and 26 m, respectively, and the distance between the bottom of the pile and the soil mass was 13 m. In all cases, the diameter of piles was 0.5 m and distance between piles were 5 and 2.5 m in 4 and 9 states, respectively. The geotechnical parameters and model dimensions used, were selected according to the Fioravante & Girettis (2010) [1]. Sand and silica-sand with the defined properties were used for the soil mass and the interposed layer, respectively. Since Drucker-Prager criteria has better ability to express the behavior of coarse-grained soils, this criterion was used in the modeling [2]. The purpose of this study is to investigate the influence of interposed layer on bearing capacity and settlement of pile. Hence, because of simplifying the process of modeling, parameters of main soil and interposed layer are mostly similar. Piles and raft are made of concrete with an elasticity modulus of 21 GPa, Poisson's ratio of 0.2 and density of 2300 kg/m³. The crack growth analysis with the compressive stress-plastic strain was used to express the fracture behavior of concrete [2, 3 & 4]. In the present study, frictional and vertical contacts between surfaces were considered for conducting interactions between different materials. For frictional contact, the penalty formulation with the fixed friction coefficient of tanδ was used where δ is the angle of friction. The penalty formulations and hard contact were applied between two surfaces for the normal contact. Interactions were considered in the modeling including raft-soil mass, raft-interposed layer, pile-raft, interposed layer-soil mass, interposed layer-pile and the soil-pile [5 & 6]. Coefficient of soil lateral pressure used in this study corresponds to k₀=0.65 which is introduced in many geotechnical conditions [7]. A uniform distributed vertical load 500 kPa was applied on the raft. For getting results in every portion of loading time, this amount is applied in order of 5 kPa in each time interval. To accelerate the process of analysis and because of the symmetry of all models in two directions of X and Y, the quarter model technique was used, so that movements in the direction perpendicular to the sheet and rotation around perpendicular axes on the sheet were not allowed on the border of symmetry. The boundaries of the models due to the enough distance from the piles were considered in a way that lateral displacement and rotation around the vertical axis was not allowed. Furthermore, the bottom of the soil mass was considered as complete fix due to the enough distance from the pile foot.
Conclusion
In this research, a numerical – parametric study is performed on special kind of piles named noncontact piles and results are compared with contact piles. Results of this study can be summarized as follows:
1. By increasing the number of piles from 1 to 9, the settlement reduced more in a noncontact state showing more effectiveness of implementing 9 contactpiles and thus requiring more piles in this case.
2. Soil surface stress differences in noncontacts states from 4 to 9 piles was less than contact state (approximately 1/7) indicating that more piles is needed to conduct the contact state.
3. Stress changes in the soil under the pile in noncontact state by adding piles from 1 to 4 was higher than adding piles from 4 to 9 indicating the suitability of using 4 noncontact piles; while, in the contact state, the stress changes in the soil under the pile in both cases from 1 to 4 piles and from 4 to 9 piles was noteworthy showing the necessity of using the ninth pile.
4. Unlike the states of 4 and 9 piles, the negative friction in noncontact state and 1 pile was seen along the piles, which can be due to the fewer piles and the effect of interposed layer density as well as soil mass at greater depthsbecause of lesser effect of piles in load-bearing.
5. The ratio of heads load in the contact to the noncontact piles was about 2.5 to 4 reflecting the positive impact of using interposed layer on load reduction and smaller cross-layer design for piles. In addition, the ratio of heads load in the contact to the noncontact piles was higher for 4 piles than 9 piles that represented the suitability of using 4 piles.
6. Based on the results of geometric parametric studies it is found that:
(A) By resizing the elements from 0.25 to 0.5 m, the results had not changed and only time of analysis was increased.
(B) Among three values of 0.5, 1 and 1.5 m for interposed layer thicknesses, the thickness of 1 m was enough and had a good effect on the stress distribution and involving shallow soil in bearing vertical stress.
(C) The raft thickness of 1.6 m was appropriate so that with this thickness, the resultant effect of increasing vertical loads (raft weight) and increased rigidity due to increased raft thickness caused the stress and settlements remain in a reasonable range.
(D) Due to the increased friction by increasing in diameter, the optimal diameter of 0.5 m was achieved for piles which reduced the settlement by receiving more load.
(E) Among three pile lengths of 10, 19 and 25 m, the optimal length was 19 m; so that by further increase in the length, stresses and settlements were not noticeably changed.In total, noncontact piles had better performance compared to contact piles in similar conditions.
Reference
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