Numerical Modelling of Displacement Pile Resistance in Sand Ground. Part 1: Soil Physical Model, Calibration of Model Parameters

Accuracy of numerical modelling of ground resistance of the displacement pile highly depends on proper evaluation of its states: prior loading and its changes during the loading. Evaluation of initial ground stage, its subsequent changes caused by pile installation and, finally, evolution of the loaded pile resistance are the modelling stages that require validation with specialized test results performed under controlled laboratory conditions. Selection of the proper physical soil model and its parameters should be also done in accordance with the relevant soil tests results. The first paper briefly introduces testing results of a displacement pile prototype. Tests were conducted in the created sand deposit in the laboratory pit. Determining pile resistance and ground stress-strain distribution in the vicinity of the pile allows selecting the physical model for the soil. Numerical calibration of the parameters for the physical model of the selected soil was performed. The second, following paper will introduce analyses of pile resistance. It involves creation of a discrete model and its parameters, numerical modelling of pile resistance against vertical load. The pile ground resistance modelling applying the physical model of the selected soil includes the following stages: evaluation at rest stage and assessment of residual effects of installation and displacement pile loading resistance. Numerical analyses results were validated with displacement pile prototype testing results.

Effect of Competent Caliche Layers on Measuring the Capacity of Axially Loaded Drilled Shafts Using the Osterberg Test

This study investigates the effect of the location of an O-cell hydraulic jack along the length of a drilled shaft in a full-scale Osterberg test performed in soils containing layers of caliche. The location of the hydraulic jack with respect to caliche layers influences the measurements obtained from the Osterberg test and the subsequent interpretation of drilled shaft capacity. In this study, drilled shaft capacities were derived utilizing data from 30 Osterberg full-scale field load tests in soils containing caliche layers. The hydraulic jack was placed at the midpoint of the drilled shaft length. Additionally, the Osterberg test data was used to calibrate a numerical model by Plaxis finite element software for drilled shaft analysis. Using the calibrated model, several scenarios of hydraulic jack location were simulated. The scenarios included hydraulic jack locations at several distances above and below a caliche layer. The results of the simulations indicate that in cases where the O-cell was installed far from the caliche layer, the Osterberg tests results showed lower pile resistance capacity compared to the top-down test. However, in cases where the O-cell was installed close to the caliche layers, the Osterberg tests results showed comparable pile resistance capacity compared to the top-down tests. This study recommends installing the hydraulic jack as close as possible to the caliche layers for more reliable interpretation of the Osterberg field tests which leads to a cost-effective design approach by reducing the required shaft length.

Development of a Pile Mooring System for Large Scale FSRUs

In this paper, a pile mooring system is introduced as an alternative mooring solution for FSRU. Also, the methodologies of mooring analysis and structural analysis to verify a design of pile mooring system are introduced. The mooring performance of pile mooring system can be assessed by coupled mooring analysis considering stiffness of pile, resistance of soil and hull interface mechanism. The structural integrity of pile, foundation and hull interface can be assessed by non-linear contact finite element analysis. Using these methods, the basic design of pile mooring system for 160,000-CBM large scale FSRU is developed considering practical environmental conditions.

Geomaterial classification criteria for design and construction of driven steel H-piles

Methodologies are proposed to develop criteria for classifying geomaterials into soils, intermediate geomaterials (IGMs), and hard rocks to achieve efficient driven pile designs. IGMs were categorized into IGM-soils and IGM-rocks to reduce the uncertainties in pile resistance estimations associated with properties ranging from soils to rocks. A boundary between soils and IGM-soils was established based upon the performance of two static analysis methods measured in terms of the coefficients of variation between measured and estimated shaft resistances. A boundary between IGM-rocks and hard rocks was established by limiting the geotechnical resistance in IGM-rocks to the compressive strength of a steel pile. Finally, a geomaterial classification flowchart and sample design charts are proposed to facilitate the classification of geomaterials specifically for the design and construction of driven steel H-piles. The proposed framework can be adapted for other driven pile types.

A model for ultimate bearing capacity of piles in unsaturated soils under elevated temperatures

Geo-energy applications such as energy piles can expose unsaturated, deep foundation soils to elevated temperatures. This paper presents a closed-form equation for the ultimate bearing capacity of piles in unsaturated soils subject to elevated temperatures under drained conditions. For this purpose, a temperature-dependent effective stress model was incorporated into calculations of skin resistance and end bearing resistance of piles. The proposed temperature-dependent model is an extension of the modified β method for determining the ultimate pile bearing capacity of unsaturated soils under drained conditions. Employing the proposed model, a parametric study was carried out to evaluate the ultimate pile bearing capacity for hypothetical clay and silt soils at temperatures ranging from 25 °C to 55 °C. For both clay and silt, the results indicated that the ultimate pile bearing capacity varies with an increase in temperature. Different trends with temperature were observed for clay and silt. A monotonic increase in pile resistance was observed in clays. For silt, the pile resistance increased at relatively low matric suction whereas it decreased at higher matric suctions.

Piles and lateral loads: comparison of calculation methods

Introduction. Calculation and analysis of pile resistance to loads remains to be a relevant problem in geoengineering. The design of pile foundations is currently performed using diverse analytical, empirical and numerical methods. However, the reliability of these methods remains to be a topic of interest among researchers and designers. This research paper analyses methods used for calculating the lateral-load capacity of piles in comparison with field-test data. Materials and methods. The paper dwells upon the development of reliable analytical expressions based on mathematical models of the pile–soil interaction. Main existing mathematical models of the soil environment, including the Mohr – Coulomb elastic ideal plastic model and the hardening soil model (HSM) were analysed. A particular attention was paid to a variety of factors affecting the pile–soil interaction, such as natural factors, pile types, pile sinking depth and technology, configurations of loads, as well as time-changed processes. A comparison of methods for calculating the lateral-load capacity of piles was conducted. To that end, calculations using the Mohr – Coulomb model and the local elastic strain theory (still required by building codes) were performed. High-level solid elements were used to develop and compute a finite-element pile-in-soil model in a spatial setting. Another model on the basis of parametric pile elements was designed using the MIDAS software. Results. It is established that the use of numerical calculation methods for evaluating the capacity and movements of pile foundations provides results comparable to those of field tests. These methods demonstrate a higher reliability compared to standardized analytical techniques. Conclusions. The reliability of numerical calculations of pile resistance to lateral impact is shown to be sufficiently high, thus being feasible for use in geoengineering. The use of these methods should be based on advanced non-linear soil models, such as HS, CamClay, etc.

Target geotechnical reliability for redundant foundation systems

Geotechnical support systems (e.g., deep and shallow foundations) generally involve at least some redundancy. For example, if a building is supported by np separate foundations, then failure (e.g., excessive settlement) of a single foundation will generally not result in failure of the building if the building is able to shed the load from the failed foundation to adjacent foundations. This load-shedding ability lends the foundation system redundancy — system failure only occurs if multiple foundations fail. This paper investigates the relationship between the level of geotechnical redundancy, individual foundation reliability, and system reliability for deep foundations (piles). In the particular case where the pile resistance remains constant after achieving its ultimate capacity (at a certain displacement), the relationship between individual and system reliabilities is computed theoretically. The more general case, where the load carried by the pile reduces after exceeding its ultimate capacity, is investigated by Monte Carlo simulation. Charts relating system and individual reliability indices are presented, which can be used to aid in the design of individual piles as part of a pile support system.