Behavior Of Cohesive Soils Research Articles

Geophysics-based approach to predict triaxial undrained and drained compressive behavior in soft soils

Geophysical measurements such as shear wave velocity are typically used to characterize subsurface conditions. Since the shear wave velocity can be measured both in the field and in the laboratory, there is continuous interest in using shear wave velocity to define the stress state of the soil. This study aimed to develop a geophysics-based approach to predicting the triaxial behavior of cohesive soils. Laboratory tests with bender elements were performed for silt-predominant samples from the state of Kentucky. A function to relate mean effective stresses and shear wave velocities was adapted from the measured behavior to predict undrained and drained triaxial behavior. Using the previous function in conjunction with a hypoplastic model for soft soils expressed in stress invariants, the deviatoric strains, volumetric strains, and excess porewater pressures developed during shearing were predicted. The proposed methodology performed very well in simulating the various soils under undrained and drained conditions.

Coupled Effect of Granite Sand and Calcium Lignosulphonate on the Strength Behavior of Cohesive Soil

This paper assesses the significance of stabilizing clay soil with calcium lignosulphonate (CLS) and granite sand (GS). Unconfined compressive strength (qc) and hydraulic conductivity (K) are taken as performance indicators and the effect of varying dosages of GS (30%, 40%, and 50%) and CLS (0.5%, 1%, 1.5%, and 2%) at different curing periods on qc and K are examined. The best fit regression equations have been proposed to relate qc and K of untreated clay soil and stabilized clay using GS and CLS. The proposed nonlinear regression equations provide details of experimental data and aid in estimating qc and K very efficiently and reliably for targeted geotechnical applications from a sustainable perspective.

Determination of the coefficient of consolidation by piezocone tests under partially drained conditions

Dissipation tests after piezocone penetration are used widely to estimate the consolidation behaviour of cohesive soils. Interpretation of dissipation tests is complicated in intermediate soils, such as in silts and silty clays, since the accumulated pore pressures and the subsequent dissipation response are affected by the partially drained conditions. The influence of partial drainage on dissipation response is investigated using a large-deformation finite-element approach within the framework of effective stress analysis. The numerical approach is validated by comparison with the existing centrifuge tests where dissipation tests were performed after undrained and partially drained penetrations. The numerical results provide insights to quantify the effects of drainage conditions, including distribution of pore pressures prior to dissipation and then the operative coefficient of consolidation, ch, against various penetration velocities. The time corresponding to a given degree of dissipation is found to be increased with reducing normalised penetration velocity, as the gradients of normalised pore pressures are reduced in the radial direction before dissipation. The ratio between ch and the coefficient of consolidation can be described through a unique backbone curve. A new approach estimating the coefficient of consolidation from a dissipation test following partially drained penetration is proposed for practical applications.

Creep behavior of cohesive soils associated with different plasticity indexes

Creep behavior of cohesive soils associated with different plasticity indexes

NUMERICAL SIMULATION OF JET EXCAVATION IN CONDUCTOR JETTING OPERATIONS IN SUBMARINE SOIL: MESH ANALYSIS

The more complex exploration techniques and operations in deepwater environment are, the higher become the financial costs involved in the process. The rent of an offshore rig, for instance, can cost hundreds of thousands of dollars per day. Therefore, improving deepwater drilling efficiency can lead to significant cost savings. The drilling process of an oil well starts with the initial drilling, which is the operation to accommodate the conductor casing. Among the techniques to set the conductor casing, jetting operations have become popular in submarine environments where the seafloor sediments allow the technique to be used. In these environments, the submarine soil consists of a deformable body displaying a behavior that falls between a linear elastic solid and viscous fluid. Therefore, its behavior is governed by general theory of rheology, and it can be described as highly viscous non-Newtonian fluid. Despite the lack of comprehensive investigations, promising works can be carried out by considering cohesive soil behavior as viscous fluid. Problems of this type can be solved using computational fluid dynamics (CFD), a powerful software which solves complex fluid mechanics equations. Thus, this work numerically evaluates the excavation mechanism in conductor jetting operations in submarine soil during the first 30 seconds of examination, considering soil as viscous fluid of Herschel-Bulkley. Ansys Fluent®, which is a CDF software based on the finite-volume method, was applied to simulate the jetting excavation process. The results indicate that all meshes generated in the development of this work have an excellent quality, and they also show that the greater the mesh refinement is, the higher the accuracy and robustness of the model will be. However, the computational cost to simulate the model increases exponentially with the increase in number of elements, highlighting the importance of properly balancing mesh refinement and computational effort. When analyzing the results, we could also identify the excavation profile made by the bit jet, which presented an almost symmetrical shape.

Comparison between Theoretical and Experimental Behavior of Shallow Foundation in Cohesive Soil

This paper discusses a finite element analysis of shallow footing subjected to axial loading rested on different types of cohesive soil by using a computer program called PLAXIS-3D (V.20) software. The behavior of cohesive soil is simulated using several constitutive models (Mohr-Coulomb model, Hardening soil model, and Hardening soil with small strain stiffness model in order to find the best match between theoretical and experimental results).Two cases are considered square and rectangle. Moreover, some parameters that affect the load settlement relation curve; such as internal friction angle and soil modulus elasticity were investigated. It was found that the simulation by the Hardening soil model with small strain stiffness gives better results in both cases of the square and rectangle (C=25) and square footing (C=70). It was also observed that increasing the foundation width led to increases in bearing capacity, however, there was an increase of bearing capacity to about (9.45 %) for an increase in footing width of (6.25), so it was about (17%) for (12.5). For square footing in stiff clayey soil, the bearing capacity of the soil increases to about (23%) when the range of the modules of elasticity of soil increases from (10000 to 30000KN/m2).

Anisotropic Behavior of Cohesive Soils by Considering Effect of Gradation and Plasticity Characteristics

In practice, strength of soils commonly is measured isotropically, while for accurate design of structure foundations and earth structures, it is essential to consider the effect of anisotropy phenomenon on the mechanical behavior of the soils. In previous research, the effect of anisotropy on shear strength of sandy soils has been known and there is some limited work on cohesive soil. Moreover, anisotropy impact is not known on shear-induced pore water pressure. In this research, a series of triaxial tests were carried out on the undisturbed samples of different fine-grained soils, taken at different directions in the sites. The samples were consolidated under effective isotropic stresses of 200, 300, 500 and 700 kPa, and loaded in undrained condition. The results revealed that the behavior of all soils significantly depends on the sample orientation in the field. As the direction of samples changed from “perpendicular to bedding orientation” to “parallel to bedding orientation”, the shear strength decreased gradually and it has the minimum value at anisotropy angle of 72°, 59° and 90° for red clay, yellow marl and olive marl, respectively. The reduction rate completely depends on the soil plasticity and level of confining pressure.

Study of Stress- Strain Behaviour of Cohesive Soil Mixed With Granite Dust under Triaxal Test

Study of Stress- Strain Behaviour of Cohesive Soil Mixed With Granite Dust under Triaxal Test

Study on the Effects of Grouting and Roughness on the Shear Behavior of Cohesive Soil-Concrete Interfaces.

Grouted soil–concrete interfaces exist in bored piles with post-grouting in pile tip or sides and they have a substantial influence on pile skin friction. To study the effect of grouting volume on the shearing characteristics of the interface between cohesive soil and concrete piles with different roughness, grouting equipment and a direct shear apparatus were combined to carry out a total of 48 groups of direct shear tests on cohesive soil–concrete interfaces incorporating the grouting process. The test results showed that the shear behavior of the grouted cohesive soil–concrete interface was improved mainly because increasing the grouting volume and roughness increased the interfacial apparent cohesion. In contrast, increasing the grouting volume and roughness had no obvious increasing effects on the interfacial friction angle. Interfacial grouting contributed to the transition in the grouted cohesive soil from shrinkage to dilation: as the grouting volume increased, the shrinkage became weaker and the dilation became more obvious. The shear band exhibited a parabolic distribution rather than a uniform distribution along the shearing direction and that the shear band thickness was greater in the shearing direction, and it will become thicker with increasing grouting volume or roughness. The analysis can help to understand the shear characteristics of soil–pile interface in studying the vertical bearing properties of pile with post-grouting in tip or sides.

Behavior of Cohesive Soil Reinforced by Polypropylene Fiber

For any land-based structure, the foundation is very important and has to be strong to support the entire structure. In order for the foundation to be strong, the soil underneath it plays a very critical role. Some projects where the soil compacted by modifying energy is insufficient to achieve the required results, so the additives as a kind of installation and reinforcement are used to achieve the required improvement. This study introduces an attempt to improve cohesive soil by using Polypropylene Fiber instead of conventional kinds used in soil stabilization. Three different percentages (0.25%, 0.5%, and 0.75% by dry weight of soil) and lengths (6, 12, and 18) mm of fiber are mixed with cohesive as a trial to enhance some properties of clay. The results of soil samples prepared at a dry density at three different water conditions (optimum water content, dry side, and wet side) showed that the increase of the percentage and length of polypropylene fiber causes a reduction in the maximum dry density of soils. Soil cohesion increases with the increase of PPF up to 0.5% then decreased. The length of Polypropylene fiber has a great effect on the cohesion of soil and adding 0.5% Polypropylene fibers with a length of 18mm to the soils consider the optimum mix for design purposes to improve the soil. Finally, the soil reinforced by PPF exhibits a reduction in the values of the compression ratio (CR) and accelerates the consolidation of the soil.

Improvement of physical, mechanical and strength behavior of cohesive soils with natural pozzolana and brick dust

This research project seeks to improve soil properties through experimentation with geotechnical purposes. For this, will be used natural volcanic pozzolana in 5%, 10%, 15% and brick dust in 10% giving it a second reuse. The soil improvement will be analyzed with the proposed additions and its influence on the results. It is concluded that the addition improves the behavior of the soil by decreasing its plasticity index, increases the compaction index and improves the geotechnical parameters.

SIMULATING THE BEHAVIOR OF SOFT COHESIVE SOILS USING THE GENERALIZED BOUNDING SURFACE MODEL

The Generalized Bounding Surface Model (GBSM) for saturated cohesive soils is a fully three­dimensional, time and temperature-dependent model that accounts for both inherent and stress induced anisotropy. To better simulate the behavior of cohesive soils exhibiting softening, the model employs a non­associative flow rule. The GBSM synthesizes many previous bounding surface constitutive models for saturated cohesive soils and improves upon their predictive capabilities. For those cases where the use of the more complex forms of the GBSM is not justified, the model can be adaptively changed to simpler forms, thus reducing the number of associated parameters, giving flexibility to the simulations and reducing the computational cost. Following a brief overview of the GBSM, the model's performance in simulating the response of soft, saturated cohesive soils is assessed under both axisymmetric and true triaxial conditions.

Undrained Pore Pressure Development on Cohesive Soil in Triaxial Cyclic Loading

Cohesive soils subjected to cyclic loading in undrained conditions respond with pore pressure generation and plastic strain accumulation. The article focus on the pore pressure development of soils tested in isotropic and anisotropic consolidation conditions. Due to the consolidation differences, soil response to cyclic loading is also different. Analysis of the cyclic triaxial test results in terms of pore pressure development produces some indication of the relevant mechanisms at the particulate level. Test results show that the greater susceptibility to accumulate the plastic strain of cohesive soil during cyclic loading is connected with the pore pressure generation pattern. The value of excess pore pressure required to soil sample failure differs as a consequence of different consolidation pressure and anisotropic stress state. Effective stresses and pore pressures are the main factors that govern the soil behavior in undrained conditions. Therefore, the pore pressure generated in the first few cycles plays a key role in the accumulation of plastic strains and constitutes the major amount of excess pore water pressure. Soil samples consolidated in the anisotropic and isotropic stress state behave differently responding differently to cyclic loading. This difference may impact on test results analysis and hence may change the view on soil behavior. The results of tests on isotropically and anisotropically consolidated soil samples are discussed in this paper in order to point out the main features of the cohesive soil behavior.

A cohesive discrete element based approach to characterizing the shear behavior of cohesive soil and clay-infilled rock joints

The mechanical behaviour of the infilled rock joints is highly concerned in rock joint studies due to its involvement in a wide range of mining collapses. In this study, a new cohesive constitutive model was employed and used in discrete element method (DEM) simulation to analyse the failure mechanism of infilled rock joints numerically. The exponential softening responses of the model in mixed mode loading conditions allow more realistic modelling of clay-infilled rock joints, which is more phenomenologically promising than the use of the current constitutive models in PFC2D such as the parallel bond model (PBM). The proposed model is implemented in DEM commercial codes (PFC2D) as a user-defined contact constitutive model. In parallel with this theoretical development, experimental works on shear behaviour of infilled materials and infilled rock joints under different normal loads are also carried out for the calibration of the cohesive model, and validation of the DEM based approach, respectively. Simulation results show excellent agreement with experimental counterparts demonstrating the effectiveness of the proposed cohesive model in reproducing the shear properties of clay-infilled rock joint. The proposed cohesive DEM framework, therefore, will facilitate better understanding of the shear mechanism of cohesive infilled rock joints.

Experimental Studies on Effect of Load Repetition on Dynamic Characteristics of Saturated Ahmedabad Cohesive Soil

The present study investigates the hysteresis response, stiffness degradation/cyclic softening and energy dissipation features of Ahmedabad cohesive soil. Saturated specimens of Ahmedabad cohesive soil were reconstituted using slurry consolidation technique at different void ratios to perform the following series of tests, strain-controlled cyclic triaxial tests, shear strength, and compressibility tests. Load repetition exhibited significant degradation in shear modulus of slurry consolidated cohesive soil specimens under cyclic loading conditions. A maximum stiffness degradation of 78% was observed for the specimen possessing minimum initial void ratio. Hysteresis response of Ahmedabad soil revealed alteration in the rotation angle of hysteresis loops and their sizes with varying initial void ratios of the Ahmedabad cohesive soil. A substantial influence of initial void ratio on the energy dissipation behavior of cohesive soil was depicted in the present study. The cumulative energy dissipation of the specimen prepared with lower initial void ratio was obtained to be 7.1 times higher than the specimen possessing maximum initial void ratio.

Shear Strength and Deformation Behaviour of Glass Fibre-Reinforced Cohesive Soil with Varying Dry Unit Weight

Proctor compaction and consolidated undrained triaxial tests were carried out to investigate the effects of glass fibre reinforcement on the shear strength and deformation behaviour of a cohesive soil under different compaction states. The fibre diameter was 0.15 mm, varying in length from 10 to 30 mm, and in content from 0 to 4% by weight of the dry soil. The separate and joint effects of fibre content, fibre length, confining pressure and dry unit weight on the deviator stress response, pore water pressure response, deformation mode, stiffness and shear strength of the specimens were evaluated. The shear strength of the reinforced soil increases with the moulding dry unit weight, though the optimum fibre content and fibre length remain the same for all dry unit weights. Multiple-regression statistical analysis was carried out to develop an expression for predicting the major principal stress at failure of the glass fibre-reinforced cohesive soil.

Dynamic properties and liquefaction behaviour of cohesive soil in northeast India under staged cyclic loading

Estimation of strain-dependent dynamic soil properties, e.g. the shear modulus and damping ratio, along with the liquefaction potential parameters, is extremely important for the assessment and analysis of almost all geotechnical problems involving dynamic loading. This paper presents the dynamic properties and liquefaction behaviour of cohesive soil subjected to staged cyclic loading, which may be caused by main shocks of earthquakes preceded or followed by minor foreshocks or aftershocks, respectively. Cyclic triaxial tests were conducted on the specimens prepared at different dry densities (1.5 g/cm3 and 1.75 g/cm3) and different water contents ranging from 8% to 25%. The results indicated that the shear modulus reduction (G/Gmax) and damping ratio of the specimen remain unaffected due to the changes in the initial dry density and water content. Damping ratio is significantly affected by confining pressure, whereas G/Gmax is affected marginally. It was seen that the liquefaction criterion of cohesive soils based on single-amplitude shear strain (3.75% or the strain at which excess pore water pressure ratio becomes equal to 1, whichever is lower) depends on the initial state of soils and applied stresses. The dynamic model of the regional soil, obtained as an outcome of the cyclic triaxial tests, can be successfully used for ground response analysis of the region.

Energy-based analysis of permanent strain behaviour of cohesive soil under cyclic loading

In this paper the original results of uniaxial cyclic compression test on cohesive soil are presented. The shakedown phenomena in cohesive soil are described. Energy-based method highlights the change of soil material behaviour from plastic shakedown through plastic creep shakedown to incremental collapse. The samples were cyclically loaded under undrained conditions with the constant amplitude of stress in one-way test procedure. In this study the energy-based method was presented as a proper method to categorise response of cohesive soil to cyclic loading in uniaxial conditions. A shakedown criterion factor, SE, was introduced to help understand the shakedown phenomena in cohesive soil. In cohesive soils the absence of a limit between plastic shakedown and plastic creep shakedown was pointed out.

Strength and Deformation Behavior of Fiber-Reinforced Cohesive Soil Under Varying Moisture and Compaction States

An experimental study was carried out to investigate the effects of glass fiber reinforcement on the strength and deformation behavior of a cohesive soil under different compaction states by means of unconfined compression tests. The specimens were prepared with varying fiber contents, fiber lengths, dry unit weight and moisture content other than maximum dry unit weight and optimum moisture content of the soil. From the test results, peak strength, failure axial strain, secant modulus and energy absorption capacity of the reinforced soil specimens were calculated and compared with that of the unreinforced soil. The results showed that the relative benefits of fiber reinforcement are highly dependent on the moisture content and dry unit weight of the soil specimens. The peak strength of the reinforced soil specimen increases gradually with increase in dry unit weight, whereas the improvement of peak strength with moisture content occurs up to optimum moisture content. The brittle failure pattern with a single distinct shear plane of the unreinforced soil specimens is gradually transformed to multi-shear failure pattern along with barreling shape at low fiber content, and then to plastic bulging failure with a network of minor fissures at higher fiber content.

General response observed in cyclically loaded cohesive soils

<p>The response of cohesive soils subjected to cyclic loading is affected by different factors; the most important are soil type, stress or consolidation history, and specific test conditions. To better understand the behavior of cohesive soils subjected to cyclic loading, beginning in early 1960’s, a rather substantial body of experimental work has been performed. This has involved different types of soils, tested at different values of overconsolidation ratio, and subjected to different cyclic loading histories. This paper compiles the most important findings of the aforementioned experimental work on cohesive soils. It summarizes the general behavioral trends observed for cyclically loaded cohesive soils. Besides, several key characteristics of cyclically loaded cohesive soils that any rational mathematical simulation must account for have been identified, thus offering the general trends that should be taken into account in the development of new constitutive models used in predicting the response of such soils.</p>