Silty Sand

Coarse-grained soils are a type of soil frequently found in civil engineering projects. The mechanical characterization of these soils is very difficult because of the presence of large-sized elements that disturb or prevent the realization of the tests. However, there is still no rational procedure to characterize coarse soils and determine their mechanical characteristics (cohesion and friction angle) for the calculation of slope stability or structures. The objectives of the research work are to contribute to the improvement of the knowledge of the mechanical behavior of matrix coarse-grained soils and to propose a rational procedure to characterize them. In order to achieve these objectives, it is important to understand the influence of the fundamental parameters related to the mode of reconstitution on the mechanical behavior of the coarse soils: volume fraction, particle size distribution and spread, consolidation level, and the initial state of the matrix. Tests are carried out using the large-sized triaxial testing device in drained conditions. With natural coarse-grained soils, it is very difficult to conduct repeatability tests to validate the results. For this reason, we will study a particular category of coarsegrained soils composed of inclusions (coarse elements) within a fine sandy matrix (matrix coarse-grained soils), using a reference soil composed of a mix of sand and gravel. The results show that for both states of sand compaction (ID=0.4 and ID = 0.8), the shear strength of the soil increases with the increase in the proportion of gravel. This increase is more marked in the case of uniform 8/10 mm gravel. Thus, the size of inclusions has no significant influence on the value of qmax.

The scarcity of competent soils in the desired locations has forced geotechnical engineers to look for soil stabilization that is sustainable and environment-friendly. In this regard, bio-cementation technology has received a lot of interest in this area because of its benefits over traditional soil stabilization techniques. The present study aims to examine the influence of the bio-cementation technique with and without Rice Husk Ash (RHA) on the permeability property of silty sand. Biocemented soil samples were prepared with various combinations of the bacterial solution (0.5, 1.0, and 1.5 optical density (OD)) and cementation solution (0.5, 1.0, and 1.5 molarity) at 0, 3, 7, 14, and 28 curing days. The RHA, an agricultural waste with good pozzolanic qualities, was added to the control soil and the biocemented soil samples at 5, 10, and 15% by weight. A falling head permeability test was employed in this study. The test results showed that the permeability of the soil decreased when the bio-cementation technique, with or without RHA, was applied. The permeability of the soil decreased with increasing BS and CS concentrations in all curing days. A greater decrease in the permeability value was seen when the RHA additive was added to the bio-cemented soil. The results of the micro-analysis tests were also in support of this reduction. Overall, the addition of RHA up to 10% with 1.0 OD BS and 1.0M CS at a 14day curing period was noted to optimally reduce the permeability property of the soil.

This paper presents an experimental study of natural Camargue silty sand mechanical behavior. The analysis of test results was based on the use of the equivalent intergranular void ratio instead of the global void ratio. The calculation of equivalent intergranular void ratio requires the determination of parameter b which represents, physically, the fraction of active fines participating on the chain forces network, hence on the soil strength. A new formula for determining the parameter b using an approach based on the coordination number distribution and probability calculation is proposed. The validation of the developed relationship was done through back-analysis of published datasets in literature on the effect of fines content on silty sand behavior. It is shown that the equivalent intergranular void ratio calculated with the b value obtained by the new formula is able to provide a strong correlation, not only at the critical state, but also at the onset of instability of various silty sands, in different terms such as peak deviator stress, peak stress ratio or cyclic resistance. Therefore, it is suggested that the use of the equivalent void ratio concept and the new formula that we have put forward for b determination is highly desirable in predicting of silty sand behavior.

The occurrence of liquefaction phenomenon may be induced in the event of a large magnitude earthquake but sometimes loose, saturated and poorly graded sand may be subjected to liquefaction due to the vibration produced by other sources. Liquefaction could cause damage to building and infrastructure due to sudden increase of pore pressure in the loose layers of saturated sand causing the loss of bearing capacity and shear strength. Defence Housing Authority (DHA) is the well planned residential scheme established by Pakistan Army along the coastal belt of Karachi. The soil occurring in DHA is fine grained, poorly graded and mainly comprises of sandy silt and silty sand of Recent age, where water table is encountered at very shallow depth. Hence, it is important to assess the geotechnical behavior of the soil in DHA area, where most of the high rise buildings and mega civil structures are being constructed. In present study, seismic soil liquefaction was evaluated at 15 sites (30 bore holes) in DHA by using simplified empirical method in terms of Factor of Safety (FS). The Relative Density (RD) was determined with the help of Standard Penetration Test (SPT) data. Grain size analysis was also carried out on each borehole samples. The results revealed that the DHA area is vulnerable to liquefaction during severe seismic event of magnitude between 6.5 and 7.5 in Karachi.

The occurrence of liquefaction phenomenon may be induced in the event of a large magnitude earthquake but sometimes loose, saturated and poorly graded sand may be subjected to liquefaction due to the vibration produced by other sources. Liquefaction could cause damage to building and infrastructure due to sudden increase of pore pressure in the loose layers of saturated sand causing the loss of bearing capacity and shear strength. Defence Housing Authority (DHA) is the well planned residential scheme established by Pakistan Army along the coastal belt of Karachi. The soil occurring in DHA is fine grained, poorly graded and mainly comprises of sandy silt and silty sand of Recent age, where water table is encountered at very shallow depth. Hence, it is important to assess the geotechnical behavior of the soil in DHA area, where most of the high rise buildings and mega civil structures are being constructed. In present study, seismic soil liquefaction was evaluated at 15 sites (30 bore holes) in DHA by using simplified empirical method in terms of Factor of Safety (FS). The Relative Density (RD) was determined with the help of Standard Penetration Test (SPT) data. Grain size analysis was also carried out on each borehole samples. The results revealed that the DHA area is vulnerable to liquefaction during severe seismic event of magnitude between 6.5 and 7.5 in Karachi.

It is well accepted that rainfall could play a significant role in instability of slopes. The main objective of the presented study is to quantify the influence of varying characteristics of water flow, its associated changes of pore-water pressures and shear strength on the stability of simplified, but inhomogeneous, slope geometries. The commonly used van Genuchten model was used to describe the Soil Water Characteristic Curve (SWCC) mathematically. In the context of this study, the influence of different hydraulic behaviour of soil layers, i.e. different SWCC, on the factor of safety (FoS) is evaluated by means of fully coupled flow-deformation analyses employing the finite element method. To quantify the slopes' factor of safety during rainfall events after specified times of infiltration or evaporation, the strength reduction method was applied. In addition to various combinations of soil layers, the influence of a water bearing high permeable soil layer between two less permeable soil layers, a situation which is often encountered in practice, on the factor of safety has been investigated.

The present paper describes a new triaxial apparatus which allows the measurement of low strain stiffness by means of both bender elements and resonant column test. In a previous paper Squeglia et al. (2009) described the innovative use of bender elements as receivers for the measurement of shear wave velocity. The proposed technique is synthetically described with the further development of apparatus which allow to perform resonant column test during a triaxial test. Since the apparatus has not been designed as a resonant column device, some critical points have been dealt with. Some tests have been dedicated to solve the problem of apparatus calibration, in particular it was not clear which type of restraint was introduced by some mechanical details concerning the ram for application of axial load. After calibration, some results have been presented. Tests carried out with the new apparatus have been compared with results of tests carried out with a Drnevich type resonant column apparatus showing a good agreement.

In this study we investigate the effect of prior seismic shaking on the monotonic shear strength of saturated Ottawa Sand 20/30. We perform a series of stress-controlled undrained cyclic triaxial tests with different seismic intensities intentionally without causing failure, followed by drainage of the excess pore pressure and an undrained monotonic loading test to determine the undrained shear strength. The experimental data show that small to moderate seismic events that do not fail the specimen can significantly increase undrained shear strength without much change in relative density. One prior seismic event with peak ground acceleration ~ 1.3 m/s 2 may increase the undrained shear strength of a specimen at ~ 10 m depth by around 30%. The results also show that as the intensity of the shaking increases, the increase in the monotonic shear strength increases. However, the strengthening effect does not increase with the number of seismic events although a small degree of global densification in the sample is observed. The results of this paper will help assess the change in static slope stability after a single or multiple small to moderate events occurred without causing initial instability.

In this study we investigate the effect of prior seismic shaking on the monotonic shear strength of saturated Ottawa Sand 20/30. We perform a series of stress-controlled undrained cyclic triaxial tests with different seismic intensities intentionally without causing failure, followed by drainage of the excess pore pressure and an undrained monotonic loading test to determine the undrained shear strength. The experimental data show that small to moderate seismic events that do not fail the specimen can significantly increase undrained shear strength without much change in relative density. One prior seismic event with peak ground acceleration ~ 1.3 m/s 2 may increase the undrained shear strength of a specimen at ~ 10 m depth by around 30%. The results also show that as the intensity of the shaking increases, the increase in the monotonic shear strength increases. However, the strengthening effect does not increase with the number of seismic events although a small degree of global densification in the sample is observed. The results of this paper will help assess the change in static slope stability after a single or multiple small to moderate events occurred without causing initial instability.

One of the most economical and viable methods of soil improvement is dynamic compaction. It is a simple process that uses the potential energy of a weight (8 tonne to 36 tonne) dropped from a height of about 1 m to 30 m, depending on the project requirement, on to the soil to be compacted hence densifying it. However, dynamic compaction can only be applied on soil deposits where the degree of saturation is low and the permeability of the soil mass is high to allow for good drainage. Using dynamic compaction on saturated soil is unsuitable because upon application of the energy, a part ACKNOWLEDGMENTS I would like to extend special thanks to Dr. Leon van Paassen who gave me the opportunity to work with him on this project. He acted not only as my professor and mentor on the project, but also as a teammate and a friend. I would also like to thank my two other committee members, Dr. Edward Kavazanjian and Dr. Claudia Zapata for their constant support on the project from time and again, which helped me immensely in the completion and presentation of my project. I would also like to take this opportunity to thank Peter Goguen and Jeffrey Long, the lab managers for Geotechnical Engineering laboratories at Arizona State University for their constant support with all my lab tests. My heartfelt thanks to all the members of the Engineering Research Center, Center for Bio-mediated and Bio-inspired Geotechnics (CBBG), especially, Liya Wang, Dr. Nariman Mahabadi, Daehyun Kim, Caitlyn Hall, for their help and support, academically or otherwise during the period of my project. My sincere thanks to all the authors of the publications, whose works I have referenced in this thesis. Lastly, I would like to thank the National Science Foundation Geomechanics and Geosystems Engineering and Engineering Research Center programs under grant number ERC-1449501 for their support of this project. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect those of the NSF.

One of the most economical and viable methods of soil improvement is dynamic compaction. It is a simple process that uses the potential energy of a weight (8 tonne to 36 tonne) dropped from a height of about 1 m to 30 m, depending on the project requirement, on to the soil to be compacted hence densifying it. However, dynamic compaction can only be applied on soil deposits where the degree of saturation is low and the permeability of the soil mass is high to allow for good drainage. Using dynamic compaction on saturated soil is unsuitable because upon application of the energy, a part ACKNOWLEDGMENTS I would like to extend special thanks to Dr. Leon van Paassen who gave me the opportunity to work with him on this project. He acted not only as my professor and mentor on the project, but also as a teammate and a friend. I would also like to thank my two other committee members, Dr. Edward Kavazanjian and Dr. Claudia Zapata for their constant support on the project from time and again, which helped me immensely in the completion and presentation of my project. I would also like to take this opportunity to thank Peter Goguen and Jeffrey Long, the lab managers for Geotechnical Engineering laboratories at Arizona State University for their constant support with all my lab tests. My heartfelt thanks to all the members of the Engineering Research Center, Center for Bio-mediated and Bio-inspired Geotechnics (CBBG), especially, Liya Wang, Dr. Nariman Mahabadi, Daehyun Kim, Caitlyn Hall, for their help and support, academically or otherwise during the period of my project. My sincere thanks to all the authors of the publications, whose works I have referenced in this thesis. Lastly, I would like to thank the National Science Foundation Geomechanics and Geosystems Engineering and Engineering Research Center programs under grant number ERC-1449501 for their support of this project. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect those of the NSF.

In this study, since the city of Bartin in Northwest Turkey on the Black Sea is in the first-degree seismic zone and its residential area only occupies 7% of the total acreage that is expected to expand with newly flourishing urbanization, soil samples were obtained from a total of five different locations where there are open areas for the construction of dwellings. Engineering properties of the soils were assessed by laboratory experiments and the allowable bearing capacity and elastic settlement (Schmertmann method) values of the soils were calculated. The results showed that calculated settlement values are very high and can damage the foundation systems of any building constructed in future; therefore, allowable settlement value was fixed at 50 mm and allowable bearing capacities of the soils were obtained from back calculations by using the Schmertmann method. The aim of calculating allowable bearing capacity modified by settlement analysis is to propose a procedure about the foundation designs of the building laying on compressible sandy soils.

One case of seepage regime identification in earthen dam on the basis of visual and instrumental observations is considered in terms of data ambiguity and uncertainty regarding either dam condition, soils permeability or seepage control and drainage features operability both in dam body and foundation. The technique of identification of dam fill hydraulic conductivity based on correlation analysis of piezometric readings is proposed. Contour maps of groundwater levels were examined. As well as simulation modelling was performed in order to determine the most probable seepage computational model of earth dam corresponding in the best way to monitoring data. While simulating special attention was being payed to seepage control and drainage features performance. Thus it was approved that earth dam seepage regime meets the criteria of safety against seepage.

The strength of levees can be affected during fluctuations in the water table. It is also possible for the climate to have an influence on the position of the water table in an earth levee. Traditional methods have resulted in approximate methods for dealing with the transient fluctuations of the water table in a levee. These approximations are generally accepted in engineering practice but the question can be rightfully raised as to how these approximations compare to a rigorous transient combined seepage and slope stability analysis. Software technology has significantly changed in recent years and is now at the point where it is much easier to perform transient seepage analyses. There are new questions that can be asked. Does an effective stress analysis diverge significantly from the 3-stage Duncan (1990) analysis? If so, under what conditions? This paper compares the Duncan (1990) three-stage methodology for analyzing rapid drawdown scenarios to a combined transient seepage and slope stability analysis. Traditional limit equilibrium methods will be utilized in the slope stability analysis and the accommodation of saturated and unsaturated pore-water pressures will be considered. Analyses of a number of typical cross-sections will be considered in order to determine the potential influence of geometry. The intent of the paper is to illustrate scenarios under which the Duncan (loc. cit.) methodology produces similar results to the results of a more rigorous analysis.

This paper uses the San Luis Dam upstream slide to evaluate the pore-water pressures at failure and progression of the phreatic surface through the fine-grained core for drawdown stability analyses. The hydraulic conductivity and compressibility parameters of saturated and unsaturated soils are calibrated using the reservoir hydrograph and 13 piezometers in order to evaluate the pore-water pressures at failure. The analyses show unsaturated and transient seepage analyses can be used to estimate pore-water pressures during drawdown for various stability analyses and evaluate the progression of the phreatic surface through the fine-grained core. The transient results also indicate the van Genuchten parameter α significantly influences unsaturated soil response during drawdown. Different meshing techniques can produce consistent moisture content profiles in two different seepage software packages, but in situ measurement of moisture content and suction pressure is recommended to develop an unsaturated and transient seepage model.

Geosynthetic encased stone columns are often designed using the conventional framework of saturated soils ignoring the influence of in-situ unsaturated soil conditions. This article evaluates the performance of stone columns with and without geosynthetic encasement extending the mechanics ofunsaturated soils. The focus of numerical simulations was directed towards understanding the influence of matric suction on the confining support offered by the surrounding soil to stone columns with and without geosynthetic encasement. Investigations were extended considering the stiffness and the length of the geosynthetic encasement. The numerical studies suggest the load-carrying capacity of stone columnincreased with an increase in the matric suction in the boundary effect and the primary transition zone. However, the contribution of matric suction towards load-carrying capacity starts reducing from the secondary transition zone. The information on boundary effect and transition zones can be...

Coal ash is recognized as an alternative fill material to the conventional natural soils near a coal fired thermal power station where its large deposits are available. This paper presents experimental investigations on footings on coal ash subjected to loads. A series of laboratory model tests on varying sizes of footings were conducted. The conventional bearing capacity evaluation methods applied for natural soils do not consider progressive failure. These effects are explained based on the non-linear strength behavior of the granular soil and occurrence of progressive failure. The classical bearing capacity theory was applied in relation to the relative dilatancy of coal ash to describe this phenomenon. Few novel observations presented here show that the extent of progressive failure of ash fills is a compressed function of material characteristics of the ash, size and depth of footing and the settlement ratio.

The geotechnical properties of hydrophilic (wettable) sands have been widely discussed in the literature. However, sands may gain hydrophobic (non-wettable) property after certain processes. Available studies regarding the response of hydrophobic sands mostly focused on its environmental and hydrological aspects. The current state of knowledge about the geotechnical aspects of hydrophobic sands is quite limited and consists of the results of a limited number of direct shear tests. To close this gap, a comparative laboratory testing program consisting of 18 static strain-controlled consolidated undrained triaxial shear tests was designed. Tests were performed on fully saturated hydrophilic and hydrophobic reconstituted Kızılırmak sand samples of different relative densities with pore water measurements. Additionally, soil classification tests including specific gravity , minimum void ratio and maximum void ratio determination and sieve analysis were performed. Hydrophobic samples wer...

Coarse-grained soils are a type of soil frequently found in civil engineering projects. The mechanical characterization of these soils is very difficult because of the presence of large-sized elements that disturb or prevent the realization of the tests. However, there is still no rational procedure to characterize coarse soils and determine their mechanical characteristics (cohesion and friction angle) for the calculation of slope stability or structures. The objectives of the research work are to contribute to the improvement of the knowledge of the mechanical behavior of matrix coarse-grained soils and to propose a rational procedure to characterize them. In order to achieve these objectives, it is important to understand the influence of the fundamental parameters related to the mode of reconstitution on the mechanical behavior of the coarse soils: volume fraction, particle size distribution and spread, consolidation level, and the initial state of the matrix. Tests are carried ...

Although in situ measurements in modern frequently occurring turbidity currents have been performed, the flow characteristics of turbidity currents that occur only once every 100 years and deposit turbidites over a large area have not yet been elucidated. In this study, we propose a method for estimating the paleohydraulic conditions of turbidity currents from ancient turbidites by using machine learning. In this method, we hypothesize that turbidity currents result from suspended sediment clouds that flow down a steep slope in a submarine canyon and into a gently sloping basin plain. Using inverse modeling, we reconstruct seven model input parameters including the initial flow depth, the sediment concentration, and the basin slope. A reasonable number (3500) of repetitions of numerical simulations using a one-dimensional layer-averaged model under various input parameters generates a dataset of the characteristic features of turbidites. This artificial dataset is then used for supervised training of a deep-learning neural network (NN) to produce an inverse model capable of estimating paleo-hydraulic conditions from data on the ancient turbidites. The performance of the inverse model is tested using independently generated datasets. Consequently, the NN successfully reconstructs the flow conditions of the test datasets. In addition, the proposed inverse model is quite robust to random errors in the input data. Judging from the results of subsampling tests, inversion of turbidity currents can be conducted if an individual turbidite can be correlated over 10 km at approximately 1 km intervals. These results suggest that the proposed method can sufficiently analyze field-scale turbidity currents.

Coarse-grained soils are a type of soil frequently found in civil engineering projects. The mechanical characterization of these soils is very difficult because of the presence of large-sized elements that disturb or prevent the realization of the tests. However, there is still no rational procedure to characterize coarse soils and determine their mechanical characteristics (cohesion and friction angle) for the calculation of slope stability or structures. The objectives of the research work are to contribute to the improvement of the knowledge of the mechanical behavior of matrix coarse-grained soils and to propose a rational procedure to characterize them. In order to achieve these objectives, it is important to understand the influence of the fundamental parameters related to the mode of reconstitution on the mechanical behavior of the coarse soils: volume fraction, particle size distribution and spread, consolidation level, and the initial state of the matrix. Tests are carried ...

Coarse-grained soils are a type of soil frequently found in civil engineering projects. The mechanical characterization of these soils is very difficult because of the presence of large-sized elements that disturb or prevent the realization of the tests. However, there is still no rational procedure to characterize coarse soils and determine their mechanical characteristics (cohesion and friction angle) for the calculation of slope stability or structures. The objectives of the research work are to contribute to the improvement of the knowledge of the mechanical behavior of matrix coarse-grained soils and to propose a rational procedure to characterize them. In order to achieve these objectives, it is important to understand the influence of the fundamental parameters related to the mode of reconstitution on the mechanical behavior of the coarse soils: volume fraction, particle size distribution and spread, consolidation level, and the initial state of the matrix. Tests are carried ...

The geotechnical properties of hydrophilic (wettable) sands have been widely discussed in the literature. However, sands may gain hydrophobic (non-wettable) property after certain processes. Available studies regarding the response of hydrophobic sands mostly focused on its environmental and hydrological aspects. The current state of knowledge about the geotechnical aspects of hydrophobic sands is quite limited and consists of the results of a limited number of direct shear tests. To close this gap, a comparative laboratory testing program consisting of 18 static strain-controlled consolidated undrained triaxial shear tests was designed. Tests were performed on fully saturated hydrophilic and hydrophobic reconstituted Kızılırmak sand samples of different relative densities with pore water measurements. Additionally, soil classification tests including specific gravity , minimum void ratio and maximum void ratio determination and sieve analysis were performed. Hydrophobic samples wer...

With the alarming growth in vehicle population in world, scrap tires are beginning to pile up. The paper presents an engineering overview of use of shredded scrap tires chips with fly ash, lime and gypsum mix. It has been observed that the tensile load, diametral strain and toughness characteristics of the reference mix mixed with dry tire chips can be increased by providing surface treatment of tire chips with carbon tetra chloride, sodium hydroxide and water. Beside this, it has been observed that curing methods and curing periods has also prominent effect on the tensile and toughness characteristics of reference mix mixed with dry/treated tire chips. As the composite formed by mixing fly ash, lime and gypsum with treated tire chips has shown increased toughness characteristics, hence the composite material find new application in those construction where there is more requirement of toughness characteristics. Utilizing some portion of these wastes like fly ash and tire chips in this way will reduce the quantity of the waste-requiring disposal. Moreover, the disposal in this way will be in an environmental friendly manner.

This paper presents the results of effect of inclusion of water, sodium hydroxide and carbon tetrachloride treated tire chips on Compressive load, tensile load, axial strain, diametral strain, toughness index and post peak behaviour of the reference mix containing fly ash + 8% lime + 0.9% gypsum for a curing period varying from 7 to 180 days using three different curing methods. The results of this study revealed that the axial/diametral strain, axial/tensile load of reference mix mixed with dry tyre chip can be increased with the treatment provided on dry tyre chips. The axial/diametral strain, axial/tensile load, toughness index improves with the change in curing method and curing period. Potential use of this relatively new constructional material can be road pavement having light traffic.

Liquefaction is one of the most devastating instabilities in saturated granular materials and is the major cause of damage to the ground and earth structures during earthquakes. Field observations of liquefactioncase histories triggered by strong earthquakes evidence the development of large deformations and strength loss due to the pore water pressure build-up for a broad range of saturated soils. Earlier experimental attempts to study the liquefaction phenomenon of soils date back to the 1960's, nevertheless, soil liquefaction is still one of the most difficult phenomenon to assess, as it is strongly acted by different factors, such as relative density, confining pressure, fine content, overconsolidation, stress or strain amplitude and loading path. Hence, predicting the occurrence of liquefaction of soils is a critical aspect of geotechnical earthquake engineering practice. The goal of this research is to identify factors affecting liquefaction resistance of silty-sands and ...

Several hydraulic loadings impose earthen levees to time-dependent variably saturated seepage conditions. The main objective of this study is to improve the analysis of levees under transient seepage with the use of unsaturated soil mechanics. An extensive set of laboratory testing, field monitoring and numerical modeling are performed to analyze a silty sand setback levee located near Seattle, WA. In-situ data obtained from field monitoring are used to monitor suction and effective stress within the levee’s embankment and foundation over the past two years. Soil samples taken from the site are used to perform index, water retention, and unsaturated multi-stage triaxial tests in the laboratory. A finite element model of transient seepage under saturated-unsaturated conditions is then developed and calibrated to reasonably match the field data. The results highlight the need to consider unsaturated soil mechanics along with climatic variables and soil-atmosphere interaction when anal...

The appropriate choice of shear strength of liquefied sands is an important component in seismic slope stability evaluation. Several factors affect the undrained steady-state strength (S us) of sands. The steady-state strengths of 24 sandy soils were analyzed. It is shown that fines content, relative density, and friction angle play important roles affecting S us. Fines content was found to be the major factor affecting S us. This was verified experimentally for one sand. When the S us data for sands were grouped into (a) relatively clean sands (Ͻ12 percent fines), (b) silty sands (12 to 50 percent fines), and (c) silts or sandy silts (Ͼ50 percent fines), at the same relative density, relatively clean sands showed the highest S us. Silts showed the lowest S us. Silty sands showed intermediate strengths. Lower-bound S us-relative density relationships were established for relatively clean sands and silty sands. The appropriate choice of shear strength of liquefied sands is an important component in seismic slope stability evaluation. It is well recognized that several factors may significantly affect the in situ postliquefaction shear strength of sands. At present, it is mostly determined by three methods: (a) steady-state strength (S us) testing in the laboratory, followed by making appropriate corrections to the field void ratio condition taking relevant factors into account (1), (b) back-calculated residual strength (S r) correlation with equivalent clean sand standard penetration test blow count [(N 1) 60-CS ] on the basis of past case studies (2,3), and (c) the normalized strength ratio approach (4-6). The S us approach for seismic stability analysis is based on the assumption that seismic flow deformation is affected primarily by one mechanism, based on the concept of steady-state deformation (1), except for possible differences due to the shearing mode. If the back-calculated S r data are also affected only by the latter mechanism, then practically, S r and S us should be the same, except for possible differences due to stress path effects. In a real field problem several mechanisms (2,7-9) may influence the operative strength. The back-calculated S r (2) may collectively reflect the effects of different mechanisms, if present, in each case history. At present the relationship between S r and S us or their relationship with postliquefaction strength is not clear. In general, past studies (2) indicate that the back-calculated residual strengths are smaller than typical laboratory S us values obtained for different sands at comparable relative densities. It is suspected that different mechanisms that might have been operative under given site conditions could have affected the residual strength, accordingly resulting in a different S r compared with the S us (2). There is concern among practitioners that the use of S us determined from laboratory tests may be unsafe (10). Having observed such differences, in general, there is consensus among researchers that within the limitations of current understanding of the factors affecting the postliquefaction strengths of sands,

This Soil stabilisation is a broad topic, but it is especially important when it comes to sandy soil. It aims to increase the strength of soil and escalate the confrontation to softening by tying the soil particles together. The paper's main goal was to investigate the use of pine needles to stabilise sandy soil. The index qualities of both the parent soil and the pine needle-treated soil were discovered. The addition of pine needles results in an increase in OMC and a decrease in MDD. As a result, the strength of this combination does not suffer from the reduction in MDD when compared to virgin soil. In comparison to UCS test findings of virgin soil, UCS increased with pine needle.

This paper monitored a structured silty soil based on the geological setting of the area. The depositions develop other formation characteristics that have been established under the influences of the geological conditions in the study location. The behaviour of flow net condition are determined by such characteristics and the study has express the behaviour of flow net in terms of effect from alluvia deposition. The predominant parameter in the flow net is the permeability of the soil, which plays major role on the direction of flow. The combination of flow lines and equipotential lines develop the flow net. From the simulation, it was observed that linearization of the flow net was predominant and these may be based on the alluvia influence based on the geological setting. Thorough expression of the flow net was expressed through development of mathematical modeling method and a model was generated to monitor the deposition of fluid flow direction in the formation. The developed m...

The size and shape of soil particles reflect the formation history of the grains. In turn, the macroscale behavior of the soil mass results from particle level interactions which are affected by particle shape. Sphericity, roundness and smoothness characterize different scales associated to particle shape. New experimental data and data from previously published studies are gathered into two databases to explore the effects of particle shape on packing as well as small and large-strain properties of sandy soils. Data analysis shows that increased particle irregularity (angularity and/or eccentricity) leads to: an increase in emax and emin, a decrease in stiffness yet with increased sensitivity to the state of stress, an increase in compressibility under zero-lateral strain loading, and an increase in critical state friction angle φcs and intercept Γ with a weak effect on slope λ. Therefore, particle shape emerges as a significant soil index property that needs to be properly charact...

Frost-heave and thaw-weakening phenomena in frost susceptible soils are intricately tied to many intrinsic thermal properties of the porous media. When the porous medium is subjected to below sub-zero temperatures, the phase changes start to take place at the freezing point where the pore water is converted to ice. This paper presents a novel chemical stabilization approach using calcium nitrate to lower the freezing point of the porous media in the frost-susceptible soils. Calcium nitrate is extensively used in the agriculture industry as a nitrogen fertilizer, as an admixture in concrete, and wastewater treatment facilities. Despite its many successful applications in various disciplines, the use of calcium nitrate as a stabilizer to frost-susceptible soil is not very well understood. In this study, silty sand (SM), a highly frost-susceptible soil, was considered for evaluating the feasibility of using calcium nitrate as a chemical stabilizer to lower the freezing point. Characterization studies were performed on the treated and untreated soil samples, and different percentages of calcium nitrate were added to the soil, and their freezing points were measured. It was observed that the freezing point has significantly lowered with the addition of calcium nitrate to the soil, and a threshold value was selected based on the rate of freezing point depression rate analysis.

This paper presents the effect of coir fibres on the compaction and unconfined compressive strength of a bentonite-lime-gypsum mixture. The coir fiber content varied from 0.5 to 2 %. The results indicated that the dry unit weight and the optimum moisture content of a bentonite – lime mix increased with the addition of gypsum. The unconfined compressive strength of the bentonite increased with the increase in the lime content up to 8 %. Beyond 8 %, the unconfined compressive strength decreased. The dry unit weight of the reference mix decreased, and the optimum moisture content increased with the addition of coir fibre. The unconfined compressive strength of the bentonite + 8 % lime mix increased up to 4 % with the gypsum. Beyond 4 %, the unconfined compressive strength decreased. The unconfined compressive strength of the reference mix increased with the addition of coir fibre up to a fibre content of 1.5 %. The unconfined compressive strength of the reference mix-coir fibre composi...

This paper presents the results of effect of inclusion of water, sodium hydroxide and carbon tetrachloride treated tire chips on Compressive load, tensile load, axial strain, diametral strain, toughness index and post peak behaviour of the reference mix containing fly ash + 8% lime + 0.9% gypsum for a curing period varying from 7 to 180 days using three different curing methods. The results of this study revealed that the axial/diametral strain, axial/tensile load of reference mix mixed with dry tyre chip can be increased with the treatment provided on dry tyre chips. The axial/diametral strain, axial/tensile load, toughness index improves with the change in curing method and curing period. Potential use of this relatively new constructional material can be road pavement having light traffic.

In all civil engineering structures, load is transferred to the soil. Load carrying capacity of soil depends upon the shear strength characteristics of soil. Angle of friction and cohesion are two shear strength parameter according to the Mohr–Coulomb theory. In case of granular soil mainly frictional and interlocking resistance mobilize between particles contributes for load carrying capacity of soil. This resistance mainly depends upon the particle size distribution, moisture content, and compaction state of granular soil. In this study, a regression model is established for the prediction of the shear strength parameter of granular soil. This model has taken average particle size, coefficient of uniformity, relative density as variable parameter for the prediction. The mathematical expression is found satisfactory for the prediction of shear strength parameter of soil.

Although in situ measurements observed on modern frequently occurring turbidity currents have been performed, the flow characteristics of turbidity currents that occur only once every hundreds of years and deposit turbidites over a large area have not yet been elucidated. In this study, we propose a method for estimating the paleo-hydraulic conditions of turbidity currents from ancient turbidites by using machine learning. In this method, we hypothesize that turbidity currents result from suspended sediment clouds that flow down a steep slope in a submarine canyon and into a gently sloping basin plain. Using inverse modeling, we reconstruct seven model input parameters including the initial flow depth, the sediment concentration and the basin slope. Repeated numerical simulation using one-dimensional shallow water equations under various input parameters generates a dataset of the characteristic features of turbidites. This artificial dataset is then used for supervised training of a deep learning neural network (NN) to produce an inverse model capable of estimating paleo-hydraulic conditions from data of the ancient turbidites. Only 3,500 datasets are needed to train this inverse model. The performance of the inverse model is tested using independently generated datasets. Consequently, the NN successfully reconstructs the flow conditions of the test datasets. In addition, the proposed inverse model is quite robust to random errors in the input data. Judging from the results of subsampling tests, inversion of turbidity currents can be conducted if an individual turbidite can be correlated over 10 km at approximately 1 km intervals. These results suggest that the proposed method can sufficiently analyze field-scale turbidity currents. 1 Introduction Turbidity currents are sediment-laden density flows that occur intermittently in deep sea environments (Talling, 2014). Turbidity currents are the main drivers of mass circulation processes in deep sea environments. In fact, estimating the flux of organic carbon transported and buried by turbidity currents is particularly necessary to understand the carbon cycle processes (Buscail and Germain, 1997; Heussner et al., 1999). In addition, the deposits of turbidity currents, i.e., turbidites, form a submarine fans 1

1, 2, 3. Department of Civil Engineering, Imam Khomeini international university Received: 3 April 2017 Revised: 17 Oct 2017 Abstract Materials such as waste tire chips were widely used to improve the strength of soil. The objective of this study is to discuss the residual strength or steady-state behavior of sand-waste tire chip mixtures. A series of undrained monotonic triaxial compression tests were conducted on reconstituted saturated specimens of sand and sand-tire chip mixtures with variation in the tire-chip contents from 0 to 4 percentages by dry weight of soil. The specimens are prepared using dry deposition method of preparation. The influence on residual resistance of varying confining pressure (100, 200, and 300 kPa) and sand mixture relative density (40, 65, and 80%) were evaluated. Tests results showed that by increasing the tire chip contents, the residual strength increased and steady-state lines move to the right of log Sus-e diagram. Also, the residual resistance i...

An innovative specimen reconstitution technique for sandy and silty soils that simulates underwater deposition is presented and evaluated. The technique is an upgraded version for triaxial testing of the well-established slurry deposition method. This novel setup integrates the reconstitution mould and the mixing tube into a single unit to avoid transferring the sample from the mixing tube to the mould. This subtle, but critical, modification enables reconstitution of very loose specimens as sample transfer disturbance, which can be significant, is eliminated. The quality of specimens prepared by the new reconstitution method was assessed by experiments on a clean sand from the UK (Ham River sand) and a silty sand from Norway (Øysand). The method, as any slurry-based procedure, is capable of producing homogeneous specimens with high initial degree of saturation, even in the absence of back pressure. The procedure is shown to be suitable for sands with or without fines. Moreover, the...

Geotechnical properties of hydrophilic (wettable) sands have been widely discussed in the literature. However, sands may gain hydrophobic (non-wettable) properties after being exposed to a hydrophobic agent in the nature. The number of available studies regarding the response of hydrophobic sands is very limited, and mostly focus on their environmental and hydrological aspects. To close this gap, a controlled laboratory testing program, consisting of 18 monotonic strain-controlled consolidated undrained triaxial shear tests, was designed. Tests were performed on fully saturated hydrophilic and hydrophobic reconstituted Kızılırmak sand samples of different relative densities with pore water measurements. Hydrophobic samples were prepared by using 1 and 2 % WD-40 lubricant by mass. The effect of hydrophobic agent was assessed by comparing the stress-excess pore water pressure-strain responses of hydrophobic sand samples with those of conventional (hydrophilic) sand samples. Test results revealed that addition of hydrophobic agent increases the dilatancy of sands at low confining stresses (~100kPa) by decreasing the excess pore water pressure generation. At higher confining stresses (~400kPa) this effect is less pronounced. Moreover, the addition of hydrophobic agent up to 2% by mass does not systematically and significantly change the effective angle of shearing resistance of sand samples, independent of their initial relative density and confining stress levels.

This paper presents the results of effect of inclusion of water, sodium hydroxide and carbon tetrachloride treated tire chips on Compressive load, tensile load, axial strain, diametral strain, toughness index and post peak behaviour of the reference mix containing fly ash + 8% lime + 0.9% gypsum for a curing period varying from 7 to 180 days using three different curing methods. The results of this study revealed that the axial/diametral strain, axial/tensile load of reference mix mixed with dry tyre chip can be increased with the treatment provided on dry tyre chips. The axial/diametral strain, axial/tensile load, toughness index improves with the change in curing method and curing period. Potential use of this relatively new constructional material can be road pavement having light traffic.

This paper presents the results of effect of inclusion of water, sodium hydroxide and carbon tetrachloride treated tire chips on Compressive load, tensile load, axial strain, diametral strain, toughness index and post peak behaviour of the reference mix containing fly ash + 8% lime + 0.9% gypsum for a curing period varying from 7 to 180 days using three different curing methods. The results of this study revealed that the axial/diametral strain, axial/tensile load of reference mix mixed with dry tyre chip can be increased with the treatment provided on dry tyre chips. The axial/diametral strain, axial/tensile load, toughness index improves with the change in curing method and curing period. Potential use of this relatively new constructional material can be road pavement having light traffic.

This paper presents the effect of coir fibres on the compaction and unconfined compressive strength of a bentonite-lime-gypsum mixture. The coir fiber content varied from 0.5 to 2 %. The results indicated that the dry unit weight and the optimum moisture content of a bentonite – lime mix increased with the addition of gypsum. The unconfined compressive strength of the bentonite increased with the increase in the lime content up to 8 %. Beyond 8 %, the unconfined compressive strength decreased. The dry unit weight of the reference mix decreased, and the optimum moisture content increased with the addition of coir fibre. The unconfined compressive strength of the bentonite + 8 % lime mix increased up to 4 % with the gypsum. Beyond 4 %, the unconfined compressive strength decreased. The unconfined compressive strength of the reference mix increased with the addition of coir fibre up to a fibre content of 1.5 %. The unconfined compressive strength of the reference mix-coir fibre composi...

This study examines the influence of the fly ash material on the shear strength characteristics and stress–dilatancy response of two categories of sands with different maximum grain sizes (Dmax = 4.00 mm and 0.63 mm) mixed with four fly ash fractions (FA = 0, 5, 10 and 15%). To achieve this goal, a series of direct shear tests was carried out on reconstituted samples at an initial relative density (Dr = 90%) and subjected to three normal stresses (σn = 100, 200 and 300 kPa). The obtained test results show that the fly ash content enhances greatly the shear strength characteristics of the granular soils. It is found for a given normal stress, the peak friction angle and maximum dilatancy angle increase with the increase of fly ash content. In addition, the excess friction angle (ϕex) increases with the increase of the maximum dilatancy angle (ψmax) of the tested materials. New developed strength-dilatancy equations incorporating the influence of fly ash proportions were proposed for the tested materials. In general, it is found that these strength-dilatancy equations could well predict the mechanical characteristics and shearing response of the different sand classes mixed with various proportions of fly ash leading to a systematic better understanding of the tested soils to be used in the road embankment constructions.

Shear strength is the most important property of soil for determining the ground's stability. This paper focuses on the effect of strain rate on shear strength parameters of sands in wet condition. Locally available red soil has been used in this study to assess the role of strain rate at different density. The index properties like specific gravity, compaction characteristics of soil are obtained. Direct shear tests are performed on soils compacted to various densities and each of their results are observed at different shear deformation rates of 1.25, 0.25, 0.05 and 0.01 mm/min. The test results show apparent cohesion increases and decrease with strain rate and the peak friction angle is maximum at a higher strain rate. The magnitude of decrease or increase in each of shear strength parameter varies with relative density.

Massive utilization of pond ash in earth works requires thorough understanding of its geotechnical characteristics, especially strength characteristics. Here in this paper, a detailed experimental study carried on the strength and other geotechnical characteristics of pond ash samples, collected from inflow and outflow points of two ash ponds in India, are presented. Strength characteristics were investigated using consolidated drained (CD)

Shear strength of silty sand depends not only on silt percentage but also on other factors like its source, gradation and hydrological parameters (difference in altitude of origin and fall of river, length of traverse, mean discharge, catchment area and basin characteristics etc.). Other parameters affecting the strength characteristics are methods of testing, sample preparation, confining pressure, the state of denseness or overburden pressure and the critical angle of internal friction. In the present work the values of shear strength parameters Q af and R af obtained from triaxial test results of silty sand obtained from Yamuna river basin and Ottawa river basin has been compared. Triaxial tests on silty sand were carried out in the lab at different relative density and confining pressure. The review of past works on silty sand indicates that strength parameter of clean sand and silty sands often evaluated corresponding to relative density containing significant percentage of fin...

The strength behavior of silty sand can be interpreted from its relative compaction, mean confining pressure and relative dilatancy. The present work considers triaxial test results on silty sand at different relative compaction and confining pressure. The review of past results on shear testing indicates that strength parameter of clean sand and silts are often considered corresponding to relative density. There are serious problem associated with the estimation of relative density of the soil containing significant percentage of plastic and non-plastic silt. In fact, presence of plastic fines disallows the investigator to interpret relative density. Therefore it is pertinent to use relative compaction of the soil as considered in the present study to interpret the strength parameter of the soil containing fines. This concept is used for an analytic simplicity for generic application. This relative density assumption for the soil containing significant percentage of fines often lea...

PurposeThis paper aims to develop a unified framework for modelling triaxial deviator stress – axial strain and volumetric strain – axial strain behaviour of granular soils with the ability to predict the entire stress paths, incrementally, point by point, in deviator stress versus axial strain and volumetric strain versus axial strain spaces using an evolutionary-based technique based on a comprehensive set of data directly measured from triaxial tests without pre-processing. In total, 177 triaxial test results acquired from literature were used to develop and validate the models. Models aimed to not only be capable of capturing and generalising the complicated behaviour of soils but also explicitly remain consistent with expert knowledge available for such behaviour.Design/methodology/approachEvolutionary polynomial regression (EPR) was used to develop models to predict stress – axial strain and volumetric strain – axial strain behaviour of granular soils. EPR integrates numerical...

The present study aims at the investigation of composite mix of fly ash-lime-gypsum prepared reinforced with jute fibres. The aim of the present study was to investigate the effect of jute length, content, curing methods and curing periods in the reference mix having proportion 1:8:1.5 of flyashlime-gypsum mix. The fly ash for the investigation was derived from ACC Cement Plant, Gagal, Distt. Bilaspur, Himachal Pradesh. Whereas, materials like lime, gypsum and jute fibres were procured from the local market. The jute fibres having proportion of 5% to 10% by weight of reference mix was added in the reference mix. Split tensile tests were performed on the prepared samples for a curing period of 28 days to determine the strength characteristics. Further, to analyse the mineralogical aspect, X-Ray Diffraction (XRD) was carried out on the specimens of fly ash-limegypsum composite reinforced with jute fibres. The specimens were cured with the help of two different curing methods i.e. self curing method and burlap curing method. The study had revealed that split tensile strength test of fly ash-lime-gypsum composite mix increased with the inclusion of jute fibres. A prominent increase in split tensile strength was observed with the use of burlap curing method in comparison to self curing method. Further, the increase in split tensile strength was highest with the inclusion of 8% of 20mm size jute fibres at 28 days of curing in the flyash-lime-gypsum mix. The composite material as derived can have potential use as building material in the construction industry. The use of waste material in this regard will also be in the environmental friendly manner.

The main feature of the shallowest quaternary basin of the well-renowned historic city of Venice, Italy and its surrounding lagoon, is the presence, apparently without any regular trend in depth and site, of a predominant silt fraction. This is always combined with clay and (or) sand, forming a chaotic and erratic interbedding of different sediments whose mineralogy is however variable in a relatively narrow range due to a unique geological origin and a common depositional environment. After a brief description of the basic soil indexes of the Venice lagoon soil, the present study, based on a comprehensive geotechnical laboratory investigation, describes the range of variation of the most relevant time-independent geotechnical properties. Moreover, a new grain size index, combining the geometrical characteristics of the particle distribution, is introduced. It is shown that the soil response at large and very small strains can be related to this grain size index, which appears to be able to include the influence of the soil grading on the description of the overall mechanical behavior.