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Rodrigo Salgado - One of the best experts on this subject based on the ideXlab platform.
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Effect of loading direction on the Shaft Resistance of jacked piles in dense sand
Géotechnique, 2019Co-Authors: Ayda Galvis-castro, Rodrigo Salgado, Ruben D. Tovar-valencia, Monica PrezziAbstract:The design of piles subjected to tensile loading is usually done by applying a correction factor on the Shaft Resistance calculated for compressive loading, but experimental data on what this corre...
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Experimental Study of Shaft Resistance of Model Piles in Fluidized and Nonfluidized Fine Sand
Journal of Offshore Mechanics and Arctic Engineering, 2017Co-Authors: Larissa De Brum Passini, Fernando Schnaid, Rodrigo SalgadoAbstract:Torpedo piles installed by dynamic penetration have been used as anchors in the Brazilian offshore oil production infrastructure practice for two decades. Dynamic penetration aided by fluidization of the soil during pile penetration is now being contemplated as a method of installation that would allow deeper penetration. The two key design questions in connection with torpedo piles are how far they penetrate and what their pullout capacity is. In a companion paper, the authors addressed the first question, whereas in the present one the second question is attended through laboratory tests using model piles, essentially pipes simulating torpedo piles without wings. The model piles were installed in two different ways: by fluidization, which enabled the piles to sink by their own weight, and by monotonic jacking. Pullout tests were then performed on the model piles in both fluidized and nonfluidized sandy soils prepared at two initial relative densities. Results from the laboratory tests indicate that Shaft uplift capacity of fluidized piles is essentially independent of the sand initial relative density. The measured values of the coefficient of lateral earth pressure (Ks) derived from the fluidized model tests are lower than those reported for other methods of pile installation, in some cases being lower than K0. Finally, the Shaft Resistance of fluidized piles increases after installation as the soil reconsolidates and particles rearrange.
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closure to Shaft Resistance of drilled Shafts in clay by tanusree chakraborty rodrigo salgado prasenjit basu and monica prezzi
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Prasenjit Basu, Rodrigo Salgado, Tanusree Chakraborty, Monica PrezziAbstract:The authors have derived relationships to determine the variation of Shaft Resistance with depth over the length of a drilled Shaft pile during different stages of its construction and installation in clay soils through the use of critical-state soil parameters in a one-dimensional, axisymmetric, finite-element analysis (FEA). Their work was aimed at determining a rational approach to the calculation of Shaft Resistance of drilled Shafts, which so far has been based on empiricism. The validity of the developed relationships was evaluated against available results of full-scale load tests and FEA predictions and found to be generally in good agreement. A particularly important and commendable aspect of the authors’ developmental work is the influence of the method of pile installation on the alpha factor (a, Shaft friction coefficient) used in determining the unit Shaft Resistance based on the drained and undrained shear strength of the soil. Certain simplifying assumptions were imposed by the authors on the mechanisms of installation of a drilled Shaft, which, for the most part, appear to be reasonable. The development of the authors’work covers normally consolidated, lightly overconsolidated, and highly overconsolidated clays, and incorporates both drained and undrained behavior of the soils in the determination of an alpha factor, which at present is used to determine Shaft Resistance from the undrained shear strength in a total stress design approach in pile design. In general, the process of removal and reinsertion of the auger during the installation of a drilled Shaft pile results in severe shear straining of the side walls of the drilled Shaft. This can be conceptualized to create a somewhat polished surface of the side wall, hence affording a soil-contact surface with the pile that derives its Shaft Resistance to movement of the pile on loading, based on its criticalstate or residual friction angle depending on the magnitude of the effective normal stress. However, in reality the friction angle influencing the Shaft Resistance also would depend on the nature/consistency of the clay soil (i.e., whether normally consolidated, lightly overconsolidated, or heavily overconsolidated). As a result, some aspects of the assumptions made by the authors require further elaboration for a clearer understanding of the behavior of the soil influencing the Shaft frictional Resistance resulting from the mechanism of installation of a drilled Shaft pile, as outlined subsequently. The installation process of a drilled Shaft pile in clay results in the pile wall undergoing several insertions and removal of the auger to effect a pile to the desired depth because the actual auger is normally a short length of the auger system of which the kellybar attachment is the longest component. The auger is extended from the kellybar as the augering process occurs to effect pile construction to a desired depth. The authors’work, however, appears to indicate that the drilled Shaft installation results from a one-stage insertion and removal of the auger. For normally consolidated and lightly overconsolidated saturated clays, the augering method, while causing roughness at the drilled Shaft wall by the leading end of the auger on its insertion, also causes removal of the rough interface when the auger progresses with depth, and further on auger removal by the soil that adheres to the auger during the removal phase. This soil is often in a softened state, and, in the process of removal of the auger, results in the interface of the drilled Shaft wall being smeared with softened clay. Shaft Resistance is afforded in this case by the friction between the soil surface of the drilled Shaft wall and soil adhering to the pile Shaft. This process would engage the residual friction angle of the soil through soilto-soil shearing contact, which can result in a minimum value of the residual friction angle. On the other hand, when the clay is highly overconsolidated, the drilled Shaft wall becomes scored on insertion of the auger. This scoring is not readily filled with softened soil as the clay is not as pliable as the case of the normal or lightly overconsolidated soil; hence, there is much more roughness at the interface between the constructed Shaft and the adjacent soil. This roughness ensures that failure occurs within the soil immediately in contact with the pile rather than through soil-to-soil shearing contact. In this case, the friction angle would likely trend toward the critical-state friction angle. However, it also often is noted that, for heavily overconsolidated clays (e.g., clay shales), an insert (back scratcher) is attached to the auger, which ensures that the Shaft wall is scored or ribbed beyond the diameter of the auger to ensure that grooves thus formed during insertion and removal would allow for rough interface surfaces to occur when the concrete is poured. This situationwould result in failure taking place within the soil as the process does not contribute to the vertical shearing of the soil as in the case of augering. Thus, in such cases, the Shaft Resistance should be governed by the peak friction angle rather than the critical-state or residual friction angle of the clay. This discussion indicates that the proposed alpha (a) values in the derived relationships in Eqs. (4) and (5) of the authors’ paper should recognize the variation of possible friction angles resulting from the nature/consistency of the clay soils in which the drilled Shafts are being constructed. The discusser would appreciate if the authors can comment on whether a computer program like FLAC3D also would be suitable to simulate the loading and unloading of the soil that occurs during the installation process of auger insertion and removal. Overall, the paper has provided a more rational approach to the derivation of a values that can be determined for both drained and undrained loading, which otherwise conventionally were associated with determining the Shaft Resistance based on the undrained shear strength of the soil.
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Recent Advances in Calculation of Shaft Resistance of Drilled-Displacement Piles
Geo-Congress 2014 Technical Papers, 2014Co-Authors: Prasenjit Basu, Monica Prezzi, Rodrigo SalgadoAbstract:Drilled-displacement (DD) piles are a distinctive class of auger piles installed by using specially designed drilling tools. Although these piles are increasingly being used in different parts of the world, the available design methods rely on empirical rules. This paper outlines a promising approach to quantify Shaft Resistance of DD piles installed in sand. Finite element analyses (FEAs) performed in this study use a two-surface, plasticity-based constitutive model for sand and involve three distinct analysis stages: pile installation, removal of drilling tool from the ground, and loading of the pile. Based on FEA results, a set of equations that can be used in calculation of the limit unit Shaft Resistance of DD piles in sand is proposed. Moreover, the Shaft Resistance available for a DD pile is compared with that available for a nondisplacement (e.g., drilled Shaft) and a full-displacement pile installed by monotonic jacking.
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Shaft Resistance and Setup Factors for Piles Jacked in Clay
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Prasenjit Basu, Rodrigo Salgado, Monica Prezzi, Tanusree ChakrabortyAbstract:AbstractInstallation of a displacement pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile. When a displacement pile is installed in saturated clay, significant excess pore pressure develops. As the excess pore pressure dissipates over time, the effective stresses in the soil surrounding the pile and the pile capacity increase. This paper investigates jacking of piles into clay using finite-element analysis. A two-surface plasticity-based constitutive model for clays was implemented in the finite-element code Solid Nonlinear Analysis Code. Based on the numerical results, equations are developed for quantifying the effects of undrained and residual shear strength on the Shaft Resistance of jacked piles in clay. The gain in Shaft Resistance over time is assessed and setup factors are proposed that can be used to estimate the gain in Shaft Resistance as a function of time after installation of a jacked pile in clay. Good agreement was obtaine...
Monica Prezzi - One of the best experts on this subject based on the ideXlab platform.
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Effect of loading direction on the Shaft Resistance of jacked piles in dense sand
Géotechnique, 2019Co-Authors: Ayda Galvis-castro, Rodrigo Salgado, Ruben D. Tovar-valencia, Monica PrezziAbstract:The design of piles subjected to tensile loading is usually done by applying a correction factor on the Shaft Resistance calculated for compressive loading, but experimental data on what this corre...
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closure to Shaft Resistance of drilled Shafts in clay by tanusree chakraborty rodrigo salgado prasenjit basu and monica prezzi
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Prasenjit Basu, Rodrigo Salgado, Tanusree Chakraborty, Monica PrezziAbstract:The authors have derived relationships to determine the variation of Shaft Resistance with depth over the length of a drilled Shaft pile during different stages of its construction and installation in clay soils through the use of critical-state soil parameters in a one-dimensional, axisymmetric, finite-element analysis (FEA). Their work was aimed at determining a rational approach to the calculation of Shaft Resistance of drilled Shafts, which so far has been based on empiricism. The validity of the developed relationships was evaluated against available results of full-scale load tests and FEA predictions and found to be generally in good agreement. A particularly important and commendable aspect of the authors’ developmental work is the influence of the method of pile installation on the alpha factor (a, Shaft friction coefficient) used in determining the unit Shaft Resistance based on the drained and undrained shear strength of the soil. Certain simplifying assumptions were imposed by the authors on the mechanisms of installation of a drilled Shaft, which, for the most part, appear to be reasonable. The development of the authors’work covers normally consolidated, lightly overconsolidated, and highly overconsolidated clays, and incorporates both drained and undrained behavior of the soils in the determination of an alpha factor, which at present is used to determine Shaft Resistance from the undrained shear strength in a total stress design approach in pile design. In general, the process of removal and reinsertion of the auger during the installation of a drilled Shaft pile results in severe shear straining of the side walls of the drilled Shaft. This can be conceptualized to create a somewhat polished surface of the side wall, hence affording a soil-contact surface with the pile that derives its Shaft Resistance to movement of the pile on loading, based on its criticalstate or residual friction angle depending on the magnitude of the effective normal stress. However, in reality the friction angle influencing the Shaft Resistance also would depend on the nature/consistency of the clay soil (i.e., whether normally consolidated, lightly overconsolidated, or heavily overconsolidated). As a result, some aspects of the assumptions made by the authors require further elaboration for a clearer understanding of the behavior of the soil influencing the Shaft frictional Resistance resulting from the mechanism of installation of a drilled Shaft pile, as outlined subsequently. The installation process of a drilled Shaft pile in clay results in the pile wall undergoing several insertions and removal of the auger to effect a pile to the desired depth because the actual auger is normally a short length of the auger system of which the kellybar attachment is the longest component. The auger is extended from the kellybar as the augering process occurs to effect pile construction to a desired depth. The authors’work, however, appears to indicate that the drilled Shaft installation results from a one-stage insertion and removal of the auger. For normally consolidated and lightly overconsolidated saturated clays, the augering method, while causing roughness at the drilled Shaft wall by the leading end of the auger on its insertion, also causes removal of the rough interface when the auger progresses with depth, and further on auger removal by the soil that adheres to the auger during the removal phase. This soil is often in a softened state, and, in the process of removal of the auger, results in the interface of the drilled Shaft wall being smeared with softened clay. Shaft Resistance is afforded in this case by the friction between the soil surface of the drilled Shaft wall and soil adhering to the pile Shaft. This process would engage the residual friction angle of the soil through soilto-soil shearing contact, which can result in a minimum value of the residual friction angle. On the other hand, when the clay is highly overconsolidated, the drilled Shaft wall becomes scored on insertion of the auger. This scoring is not readily filled with softened soil as the clay is not as pliable as the case of the normal or lightly overconsolidated soil; hence, there is much more roughness at the interface between the constructed Shaft and the adjacent soil. This roughness ensures that failure occurs within the soil immediately in contact with the pile rather than through soil-to-soil shearing contact. In this case, the friction angle would likely trend toward the critical-state friction angle. However, it also often is noted that, for heavily overconsolidated clays (e.g., clay shales), an insert (back scratcher) is attached to the auger, which ensures that the Shaft wall is scored or ribbed beyond the diameter of the auger to ensure that grooves thus formed during insertion and removal would allow for rough interface surfaces to occur when the concrete is poured. This situationwould result in failure taking place within the soil as the process does not contribute to the vertical shearing of the soil as in the case of augering. Thus, in such cases, the Shaft Resistance should be governed by the peak friction angle rather than the critical-state or residual friction angle of the clay. This discussion indicates that the proposed alpha (a) values in the derived relationships in Eqs. (4) and (5) of the authors’ paper should recognize the variation of possible friction angles resulting from the nature/consistency of the clay soils in which the drilled Shafts are being constructed. The discusser would appreciate if the authors can comment on whether a computer program like FLAC3D also would be suitable to simulate the loading and unloading of the soil that occurs during the installation process of auger insertion and removal. Overall, the paper has provided a more rational approach to the derivation of a values that can be determined for both drained and undrained loading, which otherwise conventionally were associated with determining the Shaft Resistance based on the undrained shear strength of the soil.
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Recent Advances in Calculation of Shaft Resistance of Drilled-Displacement Piles
Geo-Congress 2014 Technical Papers, 2014Co-Authors: Prasenjit Basu, Monica Prezzi, Rodrigo SalgadoAbstract:Drilled-displacement (DD) piles are a distinctive class of auger piles installed by using specially designed drilling tools. Although these piles are increasingly being used in different parts of the world, the available design methods rely on empirical rules. This paper outlines a promising approach to quantify Shaft Resistance of DD piles installed in sand. Finite element analyses (FEAs) performed in this study use a two-surface, plasticity-based constitutive model for sand and involve three distinct analysis stages: pile installation, removal of drilling tool from the ground, and loading of the pile. Based on FEA results, a set of equations that can be used in calculation of the limit unit Shaft Resistance of DD piles in sand is proposed. Moreover, the Shaft Resistance available for a DD pile is compared with that available for a nondisplacement (e.g., drilled Shaft) and a full-displacement pile installed by monotonic jacking.
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Shaft Resistance and Setup Factors for Piles Jacked in Clay
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Prasenjit Basu, Rodrigo Salgado, Monica Prezzi, Tanusree ChakrabortyAbstract:AbstractInstallation of a displacement pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile. When a displacement pile is installed in saturated clay, significant excess pore pressure develops. As the excess pore pressure dissipates over time, the effective stresses in the soil surrounding the pile and the pile capacity increase. This paper investigates jacking of piles into clay using finite-element analysis. A two-surface plasticity-based constitutive model for clays was implemented in the finite-element code Solid Nonlinear Analysis Code. Based on the numerical results, equations are developed for quantifying the effects of undrained and residual shear strength on the Shaft Resistance of jacked piles in clay. The gain in Shaft Resistance over time is assessed and setup factors are proposed that can be used to estimate the gain in Shaft Resistance as a function of time after installation of a jacked pile in clay. Good agreement was obtaine...
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Closure to “Shaft Resistance of Drilled Shafts in Clay” by Tanusree Chakraborty, Rodrigo Salgado, Prasenjit Basu, and Mônica Prezzi
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Prasenjit Basu, Rodrigo Salgado, Tanusree Chakraborty, Monica PrezziAbstract:The authors have derived relationships to determine the variation of Shaft Resistance with depth over the length of a drilled Shaft pile during different stages of its construction and installation in clay soils through the use of critical-state soil parameters in a one-dimensional, axisymmetric, finite-element analysis (FEA). Their work was aimed at determining a rational approach to the calculation of Shaft Resistance of drilled Shafts, which so far has been based on empiricism. The validity of the developed relationships was evaluated against available results of full-scale load tests and FEA predictions and found to be generally in good agreement. A particularly important and commendable aspect of the authors’ developmental work is the influence of the method of pile installation on the alpha factor (a, Shaft friction coefficient) used in determining the unit Shaft Resistance based on the drained and undrained shear strength of the soil. Certain simplifying assumptions were imposed by the authors on the mechanisms of installation of a drilled Shaft, which, for the most part, appear to be reasonable. The development of the authors’work covers normally consolidated, lightly overconsolidated, and highly overconsolidated clays, and incorporates both drained and undrained behavior of the soils in the determination of an alpha factor, which at present is used to determine Shaft Resistance from the undrained shear strength in a total stress design approach in pile design. In general, the process of removal and reinsertion of the auger during the installation of a drilled Shaft pile results in severe shear straining of the side walls of the drilled Shaft. This can be conceptualized to create a somewhat polished surface of the side wall, hence affording a soil-contact surface with the pile that derives its Shaft Resistance to movement of the pile on loading, based on its criticalstate or residual friction angle depending on the magnitude of the effective normal stress. However, in reality the friction angle influencing the Shaft Resistance also would depend on the nature/consistency of the clay soil (i.e., whether normally consolidated, lightly overconsolidated, or heavily overconsolidated). As a result, some aspects of the assumptions made by the authors require further elaboration for a clearer understanding of the behavior of the soil influencing the Shaft frictional Resistance resulting from the mechanism of installation of a drilled Shaft pile, as outlined subsequently. The installation process of a drilled Shaft pile in clay results in the pile wall undergoing several insertions and removal of the auger to effect a pile to the desired depth because the actual auger is normally a short length of the auger system of which the kellybar attachment is the longest component. The auger is extended from the kellybar as the augering process occurs to effect pile construction to a desired depth. The authors’work, however, appears to indicate that the drilled Shaft installation results from a one-stage insertion and removal of the auger. For normally consolidated and lightly overconsolidated saturated clays, the augering method, while causing roughness at the drilled Shaft wall by the leading end of the auger on its insertion, also causes removal of the rough interface when the auger progresses with depth, and further on auger removal by the soil that adheres to the auger during the removal phase. This soil is often in a softened state, and, in the process of removal of the auger, results in the interface of the drilled Shaft wall being smeared with softened clay. Shaft Resistance is afforded in this case by the friction between the soil surface of the drilled Shaft wall and soil adhering to the pile Shaft. This process would engage the residual friction angle of the soil through soilto-soil shearing contact, which can result in a minimum value of the residual friction angle. On the other hand, when the clay is highly overconsolidated, the drilled Shaft wall becomes scored on insertion of the auger. This scoring is not readily filled with softened soil as the clay is not as pliable as the case of the normal or lightly overconsolidated soil; hence, there is much more roughness at the interface between the constructed Shaft and the adjacent soil. This roughness ensures that failure occurs within the soil immediately in contact with the pile rather than through soil-to-soil shearing contact. In this case, the friction angle would likely trend toward the critical-state friction angle. However, it also often is noted that, for heavily overconsolidated clays (e.g., clay shales), an insert (back scratcher) is attached to the auger, which ensures that the Shaft wall is scored or ribbed beyond the diameter of the auger to ensure that grooves thus formed during insertion and removal would allow for rough interface surfaces to occur when the concrete is poured. This situationwould result in failure taking place within the soil as the process does not contribute to the vertical shearing of the soil as in the case of augering. Thus, in such cases, the Shaft Resistance should be governed by the peak friction angle rather than the critical-state or residual friction angle of the clay. This discussion indicates that the proposed alpha (a) values in the derived relationships in Eqs. (4) and (5) of the authors’ paper should recognize the variation of possible friction angles resulting from the nature/consistency of the clay soils in which the drilled Shafts are being constructed. The discusser would appreciate if the authors can comment on whether a computer program like FLAC3D also would be suitable to simulate the loading and unloading of the soil that occurs during the installation process of auger insertion and removal. Overall, the paper has provided a more rational approach to the derivation of a values that can be determined for both drained and undrained loading, which otherwise conventionally were associated with determining the Shaft Resistance based on the undrained shear strength of the soil.
Guo-liang Dai - One of the best experts on this subject based on the ideXlab platform.
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A review of research on the Shaft Resistance of rock-socketed piles
Acta Geotechnica, 2020Co-Authors: Guo-liang Dai, Wei-ming Gong, Qi Zhang, Asadul Haque, Ranjith Pathegama GamageAbstract:Shaft Resistance generally dominates at the service loads of rock-socketed piles and therefore is always a topic of large research interest. This paper reviews the research progress that has been made in the last four decades in understanding the shear mechanism of the pile–rock interface and in calculating the Shaft Resistance. First, particular attention is given to notable previous studies of the shear mechanism and the method for calculating the shear strength at the pile–rock interface. Next, some commonly used design methods and many empirical correlations between the ultimate Shaft Resistance fsu and the unconfined compressive strength σc of the intact rock are summarized, and the factors considered in these design methods (e.g., roughness, joints, discontinuities, smear, construction, and disturbance) are compared. Also, the factors that influence the Shaft Resistance of rock-socketed piles are summarized. Then, by evaluating briefly the existing theoretical methods, the limitations of elastic normal stiffness and the two-dimensional shear model are discussed. Finally, combined with a comparison between the elastic and elastoplastic solutions of the normal stress increment with the radial displacement increases and an analysis of paths of radial and tangential stress and possible crack formation of the bore wall during expansion, three modification methods using the elastoplastic solution to calculating the increment of normal stress are proposed to calculate shear strength at the pile–rock interface and some suggestions are also made for future research to optimize the calculation of Shaft Resistance.
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Experimental Investigations of Capacity Response of Root Piles on Combination of O-Cell Test and Conventional Head-Down Test Methods
Innovative Solutions for Deep Foundations and Retaining Structures, 2020Co-Authors: Xiao-juan Li, Guo-liang Dai, Wei-ming Gong, Ming-xing ZhuAbstract:This paper introduces installation procedures of root piles, and then presents the results of an experimental study on the behavior of a root pile in Chizhou Yangtse River Bridge. In order to investigate the capacity response of root piles and the effect of roots on Shaft Resistance, O-cell test and conventional head-down test were conducted on a root pile, with diameter of 1.8 m and length of 49 m. The pile was instrumented with strain gauges along the steel bars of pile in load tests to measure the load distribution along the length of the test pile, as well as its Shaft Resistance. The research demonstrates that the existence of roots affects the value of average compressive stiffness in O-Cell test, and also changes the transform character of axial loads significantly; the difference between the Shaft Resistance with roots and that without roots is increase with the increase of load; the existence of roots increased Shaft Resistance at pile section with roots, but it decreased Shaft Resistance at the adjacent segments without roots, These positive and negative effects are influenced by the distribution of roots and loading strategy.
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A new method for predicting the ultimate Shaft Resistance of rock-socketed drilled Shafts
Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, 2020Co-Authors: Wei-ming Gong, Qi Zhang, Ranjith Pathegama Gamage, Guo-liang DaiAbstract:Data from 187 loading tests on rock-socketed Shafts are used to develop a new relationship between the ultimate Shaft Resistance fsu and unconfined compressive strength σc of intact rock. The adhes...
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Effect of Vertical Shaft Resistance on the Lateral Behavior of Large-Diameter Pile Foundation
Springer Series in Geomechanics and Geoengineering, 2018Co-Authors: Ming-xing Zhu, Guo-liang Dai, Zhi-hui WanAbstract:Current research gradually recognizes that resisting moment Ms, induced by vertical Shaft Resistance developed on the passive side of pile Shaft, has non-ignorable influence on the lateral bearing characterize of large-diameter pile embedded in stiff soil layers. This work firstly presents numerical solution for resisting moment which is suitable for any type of side friction models. Accordingly, a series of analytical expressions for resisting moment versus slope are established with hardening and softening τ-s curve models (i.e., Shaft Resistance). Furthermore, the comparison of case study indicates that the influence of Shaft resisting moment cannot be ignored for large-diameter pile embedded in stiff soil material. Finally, parametric study is performed and results reveal that for hardening τ-s curve, resisting moment Ms will increase with increase of pile diameter, equivalent limit friction τu,eq and as decreasing critical displacement seu; for softening τ-s model, Ms will increase with increasing pile diameter, ratio of residual-critical displacement to peak displacement and ratio of residual Shaft friction to maximum Shaft friction.
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Full-Scale Field Study on Large-Diameter Post-grouting Drilled Shafts
Proceedings of GeoShanghai 2018 International Conference: Advances in Soil Dynamics and Foundation Engineering, 2018Co-Authors: Guo-liang Dai, Zhi-hui WanAbstract:In this article, full-scale field tests were conducted to observe the field performances of large-diameter drilled Shafts for three combined side-and-tip grouting Shafts and one side-grouting Shaft in extra-thick fine sand layer. The load-displacement response, Shaft Resistance, and mobilized unit tip Resistance were discussed. Comparing with the test results before and after grouting shows that the ultimate bearing capacity, the total Shaft Resistance and the base Resistance of the Shaft after grouting at the Shaft side alone are increased by 41.54%, 51.85%, and 1.27%, respectively, whereas the ultimate bearing capacity, the total Shaft Resistance and the base Resistance of the Shaft after grouting at the Shaft tip and side are increased by 66.03–73.49%, 46.72–56.91%, and 137.87–139.17%, respectively. Consequently, the bearing behavior of the combined-grouting Shaft is obviously better than that of the side-grouting Shaft. Additionally, the strengthening effect of the soil improvement at the Shaft tip due to tip grouting on mobilizing Shaft Resistance, and meanwhile, the unit tip Resistance can also be enhanced by the surrounding soil improvement due to side grouting.
Prasenjit Basu - One of the best experts on this subject based on the ideXlab platform.
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closure to Shaft Resistance of drilled Shafts in clay by tanusree chakraborty rodrigo salgado prasenjit basu and monica prezzi
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Prasenjit Basu, Rodrigo Salgado, Tanusree Chakraborty, Monica PrezziAbstract:The authors have derived relationships to determine the variation of Shaft Resistance with depth over the length of a drilled Shaft pile during different stages of its construction and installation in clay soils through the use of critical-state soil parameters in a one-dimensional, axisymmetric, finite-element analysis (FEA). Their work was aimed at determining a rational approach to the calculation of Shaft Resistance of drilled Shafts, which so far has been based on empiricism. The validity of the developed relationships was evaluated against available results of full-scale load tests and FEA predictions and found to be generally in good agreement. A particularly important and commendable aspect of the authors’ developmental work is the influence of the method of pile installation on the alpha factor (a, Shaft friction coefficient) used in determining the unit Shaft Resistance based on the drained and undrained shear strength of the soil. Certain simplifying assumptions were imposed by the authors on the mechanisms of installation of a drilled Shaft, which, for the most part, appear to be reasonable. The development of the authors’work covers normally consolidated, lightly overconsolidated, and highly overconsolidated clays, and incorporates both drained and undrained behavior of the soils in the determination of an alpha factor, which at present is used to determine Shaft Resistance from the undrained shear strength in a total stress design approach in pile design. In general, the process of removal and reinsertion of the auger during the installation of a drilled Shaft pile results in severe shear straining of the side walls of the drilled Shaft. This can be conceptualized to create a somewhat polished surface of the side wall, hence affording a soil-contact surface with the pile that derives its Shaft Resistance to movement of the pile on loading, based on its criticalstate or residual friction angle depending on the magnitude of the effective normal stress. However, in reality the friction angle influencing the Shaft Resistance also would depend on the nature/consistency of the clay soil (i.e., whether normally consolidated, lightly overconsolidated, or heavily overconsolidated). As a result, some aspects of the assumptions made by the authors require further elaboration for a clearer understanding of the behavior of the soil influencing the Shaft frictional Resistance resulting from the mechanism of installation of a drilled Shaft pile, as outlined subsequently. The installation process of a drilled Shaft pile in clay results in the pile wall undergoing several insertions and removal of the auger to effect a pile to the desired depth because the actual auger is normally a short length of the auger system of which the kellybar attachment is the longest component. The auger is extended from the kellybar as the augering process occurs to effect pile construction to a desired depth. The authors’work, however, appears to indicate that the drilled Shaft installation results from a one-stage insertion and removal of the auger. For normally consolidated and lightly overconsolidated saturated clays, the augering method, while causing roughness at the drilled Shaft wall by the leading end of the auger on its insertion, also causes removal of the rough interface when the auger progresses with depth, and further on auger removal by the soil that adheres to the auger during the removal phase. This soil is often in a softened state, and, in the process of removal of the auger, results in the interface of the drilled Shaft wall being smeared with softened clay. Shaft Resistance is afforded in this case by the friction between the soil surface of the drilled Shaft wall and soil adhering to the pile Shaft. This process would engage the residual friction angle of the soil through soilto-soil shearing contact, which can result in a minimum value of the residual friction angle. On the other hand, when the clay is highly overconsolidated, the drilled Shaft wall becomes scored on insertion of the auger. This scoring is not readily filled with softened soil as the clay is not as pliable as the case of the normal or lightly overconsolidated soil; hence, there is much more roughness at the interface between the constructed Shaft and the adjacent soil. This roughness ensures that failure occurs within the soil immediately in contact with the pile rather than through soil-to-soil shearing contact. In this case, the friction angle would likely trend toward the critical-state friction angle. However, it also often is noted that, for heavily overconsolidated clays (e.g., clay shales), an insert (back scratcher) is attached to the auger, which ensures that the Shaft wall is scored or ribbed beyond the diameter of the auger to ensure that grooves thus formed during insertion and removal would allow for rough interface surfaces to occur when the concrete is poured. This situationwould result in failure taking place within the soil as the process does not contribute to the vertical shearing of the soil as in the case of augering. Thus, in such cases, the Shaft Resistance should be governed by the peak friction angle rather than the critical-state or residual friction angle of the clay. This discussion indicates that the proposed alpha (a) values in the derived relationships in Eqs. (4) and (5) of the authors’ paper should recognize the variation of possible friction angles resulting from the nature/consistency of the clay soils in which the drilled Shafts are being constructed. The discusser would appreciate if the authors can comment on whether a computer program like FLAC3D also would be suitable to simulate the loading and unloading of the soil that occurs during the installation process of auger insertion and removal. Overall, the paper has provided a more rational approach to the derivation of a values that can be determined for both drained and undrained loading, which otherwise conventionally were associated with determining the Shaft Resistance based on the undrained shear strength of the soil.
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Recent Advances in Calculation of Shaft Resistance of Drilled-Displacement Piles
Geo-Congress 2014 Technical Papers, 2014Co-Authors: Prasenjit Basu, Monica Prezzi, Rodrigo SalgadoAbstract:Drilled-displacement (DD) piles are a distinctive class of auger piles installed by using specially designed drilling tools. Although these piles are increasingly being used in different parts of the world, the available design methods rely on empirical rules. This paper outlines a promising approach to quantify Shaft Resistance of DD piles installed in sand. Finite element analyses (FEAs) performed in this study use a two-surface, plasticity-based constitutive model for sand and involve three distinct analysis stages: pile installation, removal of drilling tool from the ground, and loading of the pile. Based on FEA results, a set of equations that can be used in calculation of the limit unit Shaft Resistance of DD piles in sand is proposed. Moreover, the Shaft Resistance available for a DD pile is compared with that available for a nondisplacement (e.g., drilled Shaft) and a full-displacement pile installed by monotonic jacking.
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Shaft Resistance and Setup Factors for Piles Jacked in Clay
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Prasenjit Basu, Rodrigo Salgado, Monica Prezzi, Tanusree ChakrabortyAbstract:AbstractInstallation of a displacement pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile. When a displacement pile is installed in saturated clay, significant excess pore pressure develops. As the excess pore pressure dissipates over time, the effective stresses in the soil surrounding the pile and the pile capacity increase. This paper investigates jacking of piles into clay using finite-element analysis. A two-surface plasticity-based constitutive model for clays was implemented in the finite-element code Solid Nonlinear Analysis Code. Based on the numerical results, equations are developed for quantifying the effects of undrained and residual shear strength on the Shaft Resistance of jacked piles in clay. The gain in Shaft Resistance over time is assessed and setup factors are proposed that can be used to estimate the gain in Shaft Resistance as a function of time after installation of a jacked pile in clay. Good agreement was obtaine...
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Closure to “Shaft Resistance of Drilled Shafts in Clay” by Tanusree Chakraborty, Rodrigo Salgado, Prasenjit Basu, and Mônica Prezzi
Journal of Geotechnical and Geoenvironmental Engineering, 2014Co-Authors: Prasenjit Basu, Rodrigo Salgado, Tanusree Chakraborty, Monica PrezziAbstract:The authors have derived relationships to determine the variation of Shaft Resistance with depth over the length of a drilled Shaft pile during different stages of its construction and installation in clay soils through the use of critical-state soil parameters in a one-dimensional, axisymmetric, finite-element analysis (FEA). Their work was aimed at determining a rational approach to the calculation of Shaft Resistance of drilled Shafts, which so far has been based on empiricism. The validity of the developed relationships was evaluated against available results of full-scale load tests and FEA predictions and found to be generally in good agreement. A particularly important and commendable aspect of the authors’ developmental work is the influence of the method of pile installation on the alpha factor (a, Shaft friction coefficient) used in determining the unit Shaft Resistance based on the drained and undrained shear strength of the soil. Certain simplifying assumptions were imposed by the authors on the mechanisms of installation of a drilled Shaft, which, for the most part, appear to be reasonable. The development of the authors’work covers normally consolidated, lightly overconsolidated, and highly overconsolidated clays, and incorporates both drained and undrained behavior of the soils in the determination of an alpha factor, which at present is used to determine Shaft Resistance from the undrained shear strength in a total stress design approach in pile design. In general, the process of removal and reinsertion of the auger during the installation of a drilled Shaft pile results in severe shear straining of the side walls of the drilled Shaft. This can be conceptualized to create a somewhat polished surface of the side wall, hence affording a soil-contact surface with the pile that derives its Shaft Resistance to movement of the pile on loading, based on its criticalstate or residual friction angle depending on the magnitude of the effective normal stress. However, in reality the friction angle influencing the Shaft Resistance also would depend on the nature/consistency of the clay soil (i.e., whether normally consolidated, lightly overconsolidated, or heavily overconsolidated). As a result, some aspects of the assumptions made by the authors require further elaboration for a clearer understanding of the behavior of the soil influencing the Shaft frictional Resistance resulting from the mechanism of installation of a drilled Shaft pile, as outlined subsequently. The installation process of a drilled Shaft pile in clay results in the pile wall undergoing several insertions and removal of the auger to effect a pile to the desired depth because the actual auger is normally a short length of the auger system of which the kellybar attachment is the longest component. The auger is extended from the kellybar as the augering process occurs to effect pile construction to a desired depth. The authors’work, however, appears to indicate that the drilled Shaft installation results from a one-stage insertion and removal of the auger. For normally consolidated and lightly overconsolidated saturated clays, the augering method, while causing roughness at the drilled Shaft wall by the leading end of the auger on its insertion, also causes removal of the rough interface when the auger progresses with depth, and further on auger removal by the soil that adheres to the auger during the removal phase. This soil is often in a softened state, and, in the process of removal of the auger, results in the interface of the drilled Shaft wall being smeared with softened clay. Shaft Resistance is afforded in this case by the friction between the soil surface of the drilled Shaft wall and soil adhering to the pile Shaft. This process would engage the residual friction angle of the soil through soilto-soil shearing contact, which can result in a minimum value of the residual friction angle. On the other hand, when the clay is highly overconsolidated, the drilled Shaft wall becomes scored on insertion of the auger. This scoring is not readily filled with softened soil as the clay is not as pliable as the case of the normal or lightly overconsolidated soil; hence, there is much more roughness at the interface between the constructed Shaft and the adjacent soil. This roughness ensures that failure occurs within the soil immediately in contact with the pile rather than through soil-to-soil shearing contact. In this case, the friction angle would likely trend toward the critical-state friction angle. However, it also often is noted that, for heavily overconsolidated clays (e.g., clay shales), an insert (back scratcher) is attached to the auger, which ensures that the Shaft wall is scored or ribbed beyond the diameter of the auger to ensure that grooves thus formed during insertion and removal would allow for rough interface surfaces to occur when the concrete is poured. This situationwould result in failure taking place within the soil as the process does not contribute to the vertical shearing of the soil as in the case of augering. Thus, in such cases, the Shaft Resistance should be governed by the peak friction angle rather than the critical-state or residual friction angle of the clay. This discussion indicates that the proposed alpha (a) values in the derived relationships in Eqs. (4) and (5) of the authors’ paper should recognize the variation of possible friction angles resulting from the nature/consistency of the clay soils in which the drilled Shafts are being constructed. The discusser would appreciate if the authors can comment on whether a computer program like FLAC3D also would be suitable to simulate the loading and unloading of the soil that occurs during the installation process of auger insertion and removal. Overall, the paper has provided a more rational approach to the derivation of a values that can be determined for both drained and undrained loading, which otherwise conventionally were associated with determining the Shaft Resistance based on the undrained shear strength of the soil.
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Shaft Resistance of Drilled Shafts in Clay
Journal of Geotechnical and Geoenvironmental Engineering, 2013Co-Authors: Tanusree Chakraborty, Rodrigo Salgado, Prasenjit Basu, Monica PrezziAbstract:ThecurrentstudyexaminesandquantifiesthelimitShaftResistanceofdrilledShaftsinstalledinclaythrough finite-elementanalyses that use an advanced two-surface-plasticity constitutive model for clay. The clay constitutive model used in this study reproduces the mechan- ical responseofclaysundermultiaxial loadingconditions,predictsbothdrainedandundrainedbehavioratsmallandlargestrains,andcaptures the drop in strength toward a residual value at very large shear strains. One-dimensional finite-element analyses are performed to simulate the essential stages of the installation and loading of drilled Shafts in clay for different initial stresses, different overconsolidation ratios, and dif- ferent values of the difference between the critical-state and the minimum residual friction angles. On the basis of these simulations, equations for the Shaft friction coefficient are proposed that can be used in the calculation of the Shaft Resistance of drilled Shafts in clay. Predictions using theproposedequationscomparewellwiththedataderivedfromdifferent fieldpileloadtestsondrilledShafts.DOI:10.1061/(ASCE)GT.1943- 5606.0000803. © 2013 American Society of Civil Engineers. CE Database subject headings: Drilled Shafts; Piles; Clays; Numerical models; Plasticity; Finite element method; Constitutive models. Author keywords: Drilled Shaft; Nondisplacement piles; Shaft capacity; Clay; Numerical modeling and analysis; Two-surface plasticity.
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Analysis on Shaft Resistance of the steel pipe prebored and precast piles based on field load-transfer curves and finite element method
Soils and Foundations, 2020Co-Authors: Hyun Kim, Sangseom Jeong, Jongjeon ParkAbstract:Abstract Shaft Resistance is the major source of bearing capacity and has a critical effect on settlement of prebored and precast pile (PPP). In this paper, the load-transfer behavior and Shaft Resistance of steel pipe PPP was observed based on real scale pile loading tests. The main focus was on determining the load transfer mechanism and establishing a framework on Shaft behavior of steel pipe PPPs. 10 cases of real scale field loading tests were carried out on the fully instrumented steel pipe PPPs, and the load transfer mechanism was observed based on the obtained load-transfer (t-z) curves along the Shaft. In addition, the failure surface along the pile Shaft was clarified based on the nine small-scale pile loading test results. By analyzing the load-transfer (t-z) curves, it was shown that steel pipe PPP showed two distinctive types of curves related with two different types of failure characteristics – elasto-perfectly plastic and brittle behavior – along the Shaft, and this was validated by using intensive finite element analysis. From this, the Shaft behavior of the steel pipe PPP can be classified and can be used in analyzing the Shaft behavior along the Shaft. Moreover, the range and the lower 95% value of the Shaft Resistance of the steel pipe PPP will be stated for different types of soil the pile is socketed, which can be used as a guideline of PPP design.
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Load–settlement behavior of rock-socketed drilled Shafts using Osterberg-Cell tests
Computers and Geotechnics, 2009Co-Authors: Hoonil Seol, Sangseom JeongAbstract:Abstract Osterberg-Cell (O-Cell) tests are widely used to predict the load–settlement behavior of large-diameter drilled Shafts socketed in rock. The loading direction of O-Cell tests for Shaft Resistance is opposite to that of conventional downward load tests, meaning that the equivalent top load–settlement curve determined by the summation of the mobilized Shaft Resistance and end bearing at the same deflection neglects the pile-toe settlement caused by the load transmitted along the pile Shaft. The emphasis is on quantifying the effect of coupled Shaft Resistance, which is closely related to the ratios of pile diameter to soil modulus (D/Es) and total Shaft Resistance to total applied load (Rs/Q) in rock-socketed drilled Shafts, using the coupled load-transfer method. The proposed analytical method, which takes into account the effect of coupled Shaft Resistance, was developed using a modified Mindlin’s point load solution. Through comparisons with field case studies, it was found that the proposed method reasonably estimated the load-transfer behavior of piles and coupling effects due to the transfer of Shaft shear loading. These results represent a significant improvement in the prediction of load–settlement behaviors of drilled Shafts subjected to bi-directional loading from the O-Cell test.
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Shaft Resistance characteristics of rock socketed drilled Shafts based on pile load tests
Journal of the Korean Geotechnical Society, 2007Co-Authors: Hoonil Seol, Sangseom JeongAbstract:Behavior of rock-socketed drilled Shafts subjected to axial load was investigated on the basis of pile load tests. The emphasis was laid on analyzing the shear load transfer characteristics from the Shafts to surrounding rock. Field load tests were performed on nine test Shafts under various conditions such as weathering of rock mass, borehole roughness, pile diameters, and loading directions. The borehole roughness at each test site was profiled using a laser borehole profiler. In order to evaluate and to propose ultimate Shaft Resistance() of drilled Shafts in rock of Korean peninsular, also, database of pile load tests was developed by reviewing various literature and technical reports.