Probabilistic analysis of drilled shaft service limit state using the "<i>t</i>–<i>z</i>" method

Misra, Anil; Roberts, Lance A.

doi:10.1139/t06-074

Cited by 35 publications

(9 citation statements)

References 7 publications

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“…The solution to the equilibrium equation, assuming non-linear behavior of the springslider system, is presented elsewhere (Misra and Roberts 2006). However, for completeness, there are a number of additional parameters necessary to utilize the t-z model approach.…”

Section: Analysis Of Load Test Datamentioning

confidence: 99%

Support of Structures in Expansive Shale Using Recycled Plastic Piles

Roberts

Brandner

2010

DFI Journal - The Journal of the Deep Foundations Institute

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Expansive soil formations can be found throughout the United States. When subjected to wetting, these formations have the potential to swell and exert large uplift forces on buildings and foundations. Lightly loaded structures, such as single family residences founded in areas of expansive soils, can be significantly damaged due to uplift movement from swelling actions. Designing an economical deep foundation that can resist uplift forces is critical to prevent damage to these structures. The current solutions to control uplift due to swelling soils, such as over-excavation and replacement of the expansive material or the use of drilled shafts can be costly. Piles made from recycled polymer materials could provide a solution. Due to a lower coefficient of friction along the interface of the soil-pile interface compared to traditional pile materials, solid recycled plastic piles can allow expansive soils to move nearly independently from the pile when wetted. This results in a much smaller magnitude of uplift force being transferred to the structure, which minimizes the risk of significant structural damage from excessive movements. This paper presents the results of research conducted on the use of recycled plastic piles in an expansive shale environment. The preliminary phase of the project involved the installation of six recycled plastic piles at a test site on the South Dakota School of Mines and Technology campus. Two of the piles were subjected to a full-scale compression load test in order to determine ultimate capacity. The remaining four piles were subjected to long-term monitoring of uplift movement during the course of the project. A concrete anchor was also installed at the test site for uplift monitoring. Data gathered during the field and laboratory testing was utilized in a non-linear soilstructure interaction model to predict the displacement behavior and internal stresses within a plastic pile and concrete anchor subjected to uplift forces from the swelling shale. While more research is needed to further understand the application for recycled plastic piles, the results from this research indicate that their use is a viable alternative for support of lightly loaded structures in expansive soil environments.

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Section: Analysis Of Load Test Datamentioning

confidence: 99%

Support of Structures in Expansive Shale Using Recycled Plastic Piles

Roberts

Brandner

2010

DFI Journal - The Journal of the Deep Foundations Institute

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“…Using the load-displacement data obtained from the Monte Carlo simulations, it is possible to calculate load capacity frequency diagrams for the drilled shafts based upon an allowable displacement of 10 mm and 20 mm (Misra & Roberts, 2006). Fig.…”

Section: Reliability Indexmentioning

confidence: 99%

“…If one assumes that the load acting on the drilled shaft is deterministic, the probability of service limit state failure can be determined using Fig. 4 by determining the cumulative frequency corresponding to the value of the deterministic load (Misra & Roberts, 2005, 2006. Alternatively, if the load acting on the drilled shaft is assumed to be probabilistic, then the area where the load and load capacity histograms overlap, marked by the shaded area in Fig.…”

Section: Reliability Indexmentioning

confidence: 99%

“…Therefore serviceability limit state design of foundations cannot be performed in a manner analogous to that for strength, with the probability distribution for estimated displacement of the foundation being compared with the probability distribution for tolerable movement of the structure. It is therefore useful to determine the load capacity histogram at which the displacement of the foundation is equal to an allowable displacement (Misra & Roberts, 2005, 2006.…”

Section: Introductionmentioning

confidence: 99%

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Service limit state resistance factors for drilled shafts

Misra¹,

Roberts²

2009

Géotechnique

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The analysis of bored piles, or drilled shafts, at the service limit state is important when foundation settlements are critical to the operation of a structure. The t-z method is a widely used soil-structure interaction model for the analysis of drilled shaft settlement. In current practice, nominal values of soil stiffness and strength parameters are used to determine settlement based upon the t-z method. However, the nominal values can vary from one designer to another, making the results somewhat inconsistent. By considering reliability-based design principles, probabilistic relationships can be incorporated into the settlement analysis of the drilled shaft, and thus design uncertainty can be quantified. Following this approach, load and resistance factor design (LRFD) procedures may be utilised and resistance factors established for use in design. Using a t-z model and the Monte Carlo simulation process, probability distributions are determined for drilled shaft capacity at the service limit state. Resistance factors are calculated based upon these relationships. The drilled shaft geometry and the shaft/soil interface parameters are varied so that their effects on the resistance factors may be understood.KEYWORDS: limit state design/analysis; numerical modelling; piles; settlement; soil/structure interaction L'analyse de pieux forés, ou d'arbres percés, à l'état limite de service est importante lorsque le tassement des fondations joue un rôle critique dans l'utilisation d'une structure. La méthode t-z est un modèle très répandu d'interaction sol -structure pour l'analyse du tassement des arbres percés. Dans les applications actuelles, on utilise des valeurs nominales de rigidité du sol et des paramètres de résistance afin de déterminer le tassement sur la base de la méthode t-z. Toutefois, les valeurs nominales peuvent varier d'un concepteur à un autre, en produisant ainsi des résultats quelque peu irréguliers. En examinant des principes conceptuels basés sur la fiabilité, des rapports probabilistes peuvent être incorporés dans l'analyse du tassement de l'arbre foré, et on est alors en mesure de quantifier l'incertitude conceptuelle. En suivant ce principe, il est possible d'utiliser des procédures d'étude du facteur de charge et de résistance, et d'établir des facteurs de résistance, qui seront utilisés dans la conception. On procède à la détermination de distributions de la probabilité en appliquant le modèle t-z et la technique de simulation Monte-Carlo, pour la capacité des arbres percés à l'état de service limite. Des facteurs de résistance sont calculés sur la base de ces rapports, et on varie la géométrie des arbres percés et les paramètres d'interface arbre/sol afin de comprendre leurs effets sur les facteurs de résistance. INTRODUCTIONThe geotechnical design of drilled shafts, also known as bored piles, has traditionally followed the allowable stress design (ASD) methodology at the axial ultimate limit state, assuming full resistance of the soil along the length of the shaft and at the tip. In the ...

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“…Fenton and Griffiths (2007) and Haldar and Babu (2007) analyzed the random response of pile foundations under vertical load. Hu et al (2008) and Misra and Roberts (2006) performed probabilistic and reliability analysis of static pile capacity considering uncertainties in loading conditions, pile material and section properties, and soil-pile interaction characteristics using the Finite Difference Method (FDM) and derived closed form solutions for the soil-pile interface load-displacement behavior. While most probabilistic methods of pile analysis have considered the variability of soil and pile properties, their results were mainly focused to the evaluation of probability of failure or reliability index in comparison to the target values, without making further recommendations to the specific factor of safety to be used in order to provide design options that are not only safe but more economical.…”

Section: Introductionmentioning

confidence: 99%

Probabilistic evaluation of economical factor of safety for the geotechnical design of pile axial load capacity

Kim

Mission

2011

KSCE J Civ Eng

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The inability to evaluate the effects of the various uncertainties due to spatial and material variability of the soil and pile properties in the axial load capacity of a pile foundation had led some designers to adopt higher global factors of safety in design, which may be conservative and uneconomical if it were not properly evaluated. In addition, the use of lower factors of safety in pile design is often traditionally justified only by the performance of specific pile load tests. This study presents the application of probabilistic analysis based on Stochastic Finite Element Method (SFEM) and Monte Carlo Simulation (MCS) in the selection of economical factors of safety for the geotechnical design of pile axial load capacity. The SFEM is implemented by a coupling between the reliability algorithm with the MCS technique in MATLAB ® and the OpenSees finite element program. A probabilistic method of pile analysis evaluates the risk, reliability, or probability of failure associated with the selection of lower factors of safety in design. The results of a probabilistic method of pile capacity evaluation then provide guidance in the selection of a more reliable, unconservative, and economical factor of safety at an acceptable level of risk by making cost comparisons with available options for design.

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Probabilistic analysis of drilled shaft service limit state using the "t–z" method

Cited by 35 publications

References 7 publications

Support of Structures in Expansive Shale Using Recycled Plastic Piles

Support of Structures in Expansive Shale Using Recycled Plastic Piles

Service limit state resistance factors for drilled shafts

Probabilistic evaluation of economical factor of safety for the geotechnical design of pile axial load capacity

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