6: PILE FOUNDATIONS
- Page ID
- 123557
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- 6.1: Introduction to Part 6
- This page discusses the limitations of shallow foundations due to soil conditions and economic factors, necessitating deep foundations like piles. Piles efficiently transfer loads through inadequate soil to stable layers, critical in scenarios involving low-strength soils, high lateral loads, scour risks, seismic concerns, nearby excavations, and expansive soils. They are also employed for slope stabilization and excavation support in various geotechnical contexts.
- 6.2: Common pile types
- This page discusses two primary types of piles based on construction methods: displacement (driven) piles that compact the ground during installation, and non-displacement (drilled shafts) piles formed by drilling and filling with concrete. Displacement piles include preformed, driven cast in place, and screwed cast in place categories, while non-displacement piles are classified as supported or unsupported.
- 6.3: Installation of driven piles
- This page discusses the installation of driven piles using impact hammers, emphasizing the importance of factors such as load support, noise, and alignment. It mentions the use of a continuous-flight auger for pre-drilling and highlights the shift toward steam or pneumatic hammers in modern projects to enhance productivity.
- 6.4: Construction of drilled shafts
- This page outlines three methods for constructing non-displacement piles across different soil conditions: dry construction using a temporary casing for stable soils, wet construction involving slurry to stabilize the shaft before concrete placement, and casing construction for loose soils to avoid caving. Key factors for successful implementation include careful design and selection of concrete and reinforcement materials to ensure structural integrity and environmental compliance.
- 6.5: Load transfer mechanisms
- This page explains pile classification based on load transfer to subsoil: friction piles depend on skin friction, while end-bearing piles transfer loads to a firm layer below. All piles utilize both mechanisms, though classification hinges on skin friction's dominance. Negative skin friction can add load in settling soils, and laterally loaded piles counter forces via bending and passive earth pressure.
- 6.6: Pile driving effects
- This page discusses the effects of pile driving, which creates dynamic impact loads that generate stress waves in piles and surrounding soil, leading to deformation and increased pore water pressures, particularly in fine-grained soils. The installation results in a stress state similar to undrained shear conditions, causing significant strain. Afterward, pore pressure dissipation alters soil strength and skin friction resistance, with residual stresses remaining below the pile toe.
- 6.7: Piles subjected to axial compressive loads - general concepts
- This page discusses the mechanics of load transfer in piles, emphasizing skin friction and end-bearing. It notes that the soil's stress-strain response initially resembles oedometer test results but is affected by dynamic loads during installation. As loads increase, potential failure mechanisms emerge, and idealized models may not accurately depict real-world conditions. It highlights that minor displacements mobilize skin friction, while end-bearing resistance requires larger movements.
- 6.8: Load and Resistance Factor Design of piles subjected to axial compressive loads according to AS2159
- This page discusses the design capacity of piles under axial compressive loads as per AS2159. It emphasizes that the ultimate geotechnical strength and a reduction factor, based on a risk assessment of geological complexities and design methods, determine capacity. Factors rated on a scale of 1 to 5 contribute to the geotechnical strength reduction factor. Additionally, systems with different levels of redundancy have varying φgb values to enhance structural safety.
- 6.9: Ultimate geotechnical strength of piles subjected to axial compressive load under undrained conditions (α-Method)
- This page discusses the α-Method for estimating short-term axial collapse load of piles in fine-grained saturated soils under undrained conditions, focusing on total stresses. It combines skin friction and end-bearing resistance, using a Coulomb friction model with an adhesion factor linked to soil shear strength. Various estimation methods exist for the adhesion factor, emphasizing the importance of pile driving effects on soil.
- 6.10: Ultimate geotechnical strength of piles subjected to axial compressive load under drained conditions (β-Method)
- This page discusses the β–Method for estimating collapse loads of piles in coarse and fine-grained soils under drained conditions. It utilizes effective stress analysis, differentiating between skin friction and end-bearing calculations. Skin friction depends on effective stress and friction angle, while end-bearing resistance parallels shallow foundation techniques.
- 6.11: Ultimate geotechnical strength of piles subjected to axial compressive load from SPT test results
- This page discusses estimating pile collapse loads in homogeneous coarse-grained soil using SPT test results, eliminating the need for detailed soil parameter interpretation. It provides outdated formulas for calculating skin friction and end-bearing resistance based on average SPT values, considering pile length and diameter. The range of relevant blow counts for accurate assessments is outlined, along with references to the geometry of the potential failure surface beneath the pile toe.
- 6.12: Ultimate geotechnical strength of piles subjected to axial compressive load from CPT test results
- This page outlines various methodologies for estimating the collapse load and capacity of driven piles using Cone Penetration Test (CPT) data. It highlights Schmertmann's and the LCPC method for calculating skin friction resistance and end-bearing resistance. Additionally, the UWA-05 method emphasizes installation effects and provides detailed formulas applicable to various pile types.
- 6.13: Design of drilled shafts socketed in soft rock to resist axial compressive loads
- This page discusses the design methods for drilled shafts socketed in soft rock, particularly in Australia, indicating that traditional methods are inadequate. It highlights the Rowe and Armitage method, focusing on meeting settlement criteria and managing axial loads, including the importance of modeling the shaft-rock interface and adjusting for site conditions.
- 6.14: Ultimate geotechnical strength of drilled shafts subjected to axial compressive loads
- This page discusses estimating the collapse load of drilled shafts using modified analytical methods for driven piles, specifically the α-Method and β-Method. It highlights necessary adjustments for calculating skin friction and end bearing resistance due to soil disturbance during excavation. The α-Method uses a conservative adhesion factor, while the β-Method applies specific formulas for coarse-grained soils based on SPT data.
- 6.15: Ultimate geotechnical strength of piles subjected to axial tensile loads
- This page discusses the calculation of uplift resistance in piles without enlarged bases, emphasizing the importance of skin friction resistance and the pile's dead weight. In soft fine-grained soils, skin friction is treated similarly to compression friction, decreasing under drained conditions due to the Poisson effect, with reduction factors between 0.75 and 0.85.
- 6.16: Static pile load tests
- This page outlines static load testing methods for assessing pile geotechnical strength, emphasizing full-scale experiments with load-settlement curves for design verification. It details various loading stages, monitoring techniques, and distinguishes between proof and ultimate tests.
- 6.17: Pile driving formulas
- This page presents an alternative method for assessing the collapse load of driven piles through the correlation with the energy expended during driving. It includes the historical Engineering News (EN) Record formula, which has been refined to better reflect modern pile driving technology and factors like hammer efficiency. The derived equations are key in determining if piles have reached adequate geotechnical strength at specific depths.
- 6.18: Pile group effects on ultimate geotechnical strength
- This page discusses the use of group piles supported by a concrete cap for foundations, highlighting their lateral stiffness under heavy loads and during seismic events. It emphasizes that pile group efficiency varies due to factors like soil types and spacing. The importance of addressing potential block-type failures and excess pore pressures during construction is noted, along with recommendations for adjusting spacing and efficiency.
- 6.19: Immediate settlement of single piles
- This page reviews current methods for predicting the settlement of single piles, focusing on simplified mathematical models based on elasticity theory, which assume linear behavior and no slippage at the soil-pile interface. It highlights the distinction between elastic and consolidation settlements, discusses the influence of soil and bedrock stiffness on end-bearing piles, and notes that for slender piles, increasing diameter or stiffness is more effective in reducing settlement than length.
- 6.20: Immediate settlement of pile groups
- This page explores how pile group interactions and stress overlapping affect pile settlements under axial loads. It identifies two main predictive methods: approximate methods for rigid caps, which assume equal load distribution, and the elasticity method that considers load distribution with interaction factors. Both methods seek to accurately estimate settlements while considering variables like pile spacing and count.
- 6.21: Consolidation settlement of pile groups
- This page discusses the effects of friction piles on soft clay layers, highlighting that they can induce consolidation settlement beneath the pile toe. It emphasizes the need to account for both this settlement and group settlement.
- 6.22: Negative skin friction effects
- This page discusses negative skin friction during construction, particularly near completed piles, leading to soil settling more than the piles and counteracting their resistance. The "neutral plane" is vital for understanding friction zones. It outlines influencing factors and mitigation methods, highlighting the importance of careful analysis in engineering practices. Negative skin friction is a critical consideration in related contexts.
- 6.23: Lateral loading of piles – General considerations
- This page discusses the advantages of pile foundations over shallow footings in resisting lateral forces from seismic activity and other loads. It highlights the complexity of soil-structure interactions and the historical development of methodologies for designing piles against lateral loads. Key factors include reaction modulus and p-y curves for soil resistance. The classification of pile failure modes into “short” and “long” influences design preferences to prevent catastrophic failures.
- 6.24: Broms method – Piles in undrained soil
- This page covers geotechnical strength and bending moments in both short and long piles under lateral loads. It details the estimation of ultimate soil reaction and maximum bending moments for short free-head piles, while also describing similar procedures for fixed-head piles. Additionally, it addresses calculating pile head deflection and the coefficient of subgrade reaction, important for different soil types and load conditions.
- 6.25: Broms method – Piles in drained soil
- This page analyzes pile behavior under drained loading conditions, focusing on short and long piles with varying head fixity. It details calculations for ultimate soil reactions, collapse lateral loads, and maximum bending moments, highlighting considerations for potential failure modes. The text also estimates lateral deflection under serviceability loads and offers methods for determining the coefficient of subgrade reaction for piles in varying soil conditions.
- 6.26: Rigorous elasticity method for estimating pile deformations
- This page discusses Brom's approximate method for estimating pile head deflection, based on empirical formulas. It compares this with a more rigorous approach by Zheng et al. (2024), which models soil as an elastic medium and evaluates stiffness components of floating piles under serviceability conditions.
- 6.27: Numerical beam-on-nonlinear Winkler spring methods for the analysis of piles subjected to lateral loading
- This page discusses analytical methods for pile analysis in various soil conditions, emphasizing the use of numerical approaches like beam-on-nonlinear Winkler models for multilayered soils. It details the derivation of p-y curves tailored for soft and stiff clay, as well as sand, addressing factors such as soil behavior, pile geometry, and loading types.
- 6.28: Pile group effects on the lateral load response of piles
- This page discusses how pile-to-pile interactions affect the lateral load response of a pile group connected by a rigid cap, which experiences uniform deflection under lateral loading. The arrangement of piles and other factors require the application of a reduction factor (βg) to adjust single pile p-y curves, varying by geometry, spacing, and load direction. A thorough evaluation must consider all interactions among group members to accurately determine the collective response of each pile.
- 6.29: References
- This page compiles references and standards on the planning, design, and construction of foundations and offshore platforms, emphasizing pile design and soil mechanics. It includes guidelines from the American Petroleum Institute and Australian/New Zealand standards.
- 6.30: Additional problems
- This page discusses problems in designing and analyzing pile foundations per AS2159, covering calculations for short-term bearing capacities of different piles, embedment depths for offshore structures, and settlement criteria for pre-stressed concrete piles. It presents results that indicate required bearing capacities, embedment depths, and conditions for meeting settlement criteria, including data on applied loads and material properties.
- 6.31: Example 6.1
- This page discusses estimating the design bearing capacity of a single cylindrical pile in uniform clay using the α-Method and ICP method per AS2159. It highlights calculations for skin friction and end-bearing resistance, revealing that the pile functions as a friction pile. The α-Method yields higher skin friction values than the ICP method, which factors in installation effects.
- 6.32: Example 6.2
- This page analyzes the design bearing capacity of concrete piles using the α- and β-Methods according to AS2159, considering a multilayered soil profile. It includes calculations for short-term and long-term loading, emphasizing skin friction and end bearing resistances in clay and sand layers.
- 6.33: Example 6.3
- This page covers the numerical estimation of a single pile's ultimate geotechnical strength in homogeneous soil, focusing on undrained behavior. It generates a load-displacement curve using PLAXIS to model soil-pile interaction, considering shear stress and slippage. The study compares numerical results with the α-method, noting the importance of parameter selection for accurate ultimate strength predictions, while acknowledging that the α-method provides reasonable estimates.
- 6.34: Example 6.4
- This page provides an overview of numerical methods for estimating geotechnical strength of piles in multilayered soil under diverse loading conditions. It discusses load-displacement curves for both short-term and long-term analyses using models like Mohr-Coulomb for different conditions. The analysis is divided into three stages: geostatic stress, construction influences, and loading effects.
- 6.35: Example 6.5
- This page explains how to estimate the ultimate geotechnical strength (Qf) of a pile under axial compressive load using Standard Penetration Test (SPT) results, detailing the calculation for skin friction resistance (Qsf) from average SPT values and end-bearing resistance (Qb) from nearby SPT data. It emphasizes the importance of making conservative assumptions and applying risk ratings within non-site-specific methodologies.
- 6.36: Example 6.6
- This page discusses estimating the geotechnical strength of driven concrete piles under axial loads using CPT results, comparing the Schmertmann and Bustamante & Gianeselli methods for calculating skin friction in sand and fine-grained layers. It highlights the uncertainties of empirical methods and calculates end-bearing resistance based on cone resistance and empirical factors.
- 6.37: Example 6.7
- This page analyzes the design bearing capacity of a four-pile group for an offshore foundation, using the α-Method to assess ultimate geotechnical strength. It emphasizes factors like block-type failure and pile group efficiency, specifying a geotechnical strength reduction factor of 0.60. The findings indicate that block-type failure results in higher strength compared to individual piles, underscoring the importance of design bearing capacity in the evaluation process.
- 6.38: Example 6.8
- This page compares two methods for calculating settlement of a driven solid concrete friction pile in homogeneous soil: Poulos (1998), which assumes infinitely deep soil, and Zheng et al. (2023), which accounts for finite soil layers. The pile head stiffness is estimated using specific parameters, resulting in varying settlement values.
- 6.39: Example 6.9
- This page examines settlement calculations for end-bearing piles in layered soil using two methods: Poulos and Davis (1991) for rigid bedrock and Zheng et al. (2023) for two-layered soil. It presents an example with specific parameters to illustrate how different modulus values impact settlement estimates.
- 6.40: Example 6.10
- This page examines the settlement of six concrete piles under a vertical load of 3000 kN in deep clay, comparing a rigid pile cap scenario with a flexible one. The rigid cap leads to uniform settlement of 36.6 mm per pile, while the flexible cap results in differential settlement, where mid piles settle more than corner piles, highlighting important design considerations for the pile group.
- 6.41: Example 6.11
- This page analyzes negative skin friction on drilled shafts through numerical simulation under varying loads. It highlights the elevation changes of the neutral plane with uniform surcharge and vertical loads and uses a drained Mohr-Coulomb model to simulate clay response. Findings indicate that the neutral plane rises with added load, eliminating negative skin friction at collapse load, while surcharge enhances bearing capacity by increasing effective stresses along the shaft.
- 6.42: Example 6.12
- This page analyzes the geotechnical strength and deflection of a steel pipe pile in stiff clay under lateral loads. It specifies key parameters and calculates collapse lateral loads for short and long-pile failure modes, identifying long-pile failure as critical with a collapse load of 1333.6 kN. Additionally, it estimates the pile head deflection for a service load that is half of the collapse load using the modulus of subgrade reaction.
- 6.43: Example 6.13
- This page presents a study on the geotechnical strength and deflection of a 10 m steel pipe pile in drained sand under lateral loads. It finds that the maximum bending moment for short-pile failure surpasses the yield moment, leading to reliance on long-pile equations. The critical collapse lateral load is identified as 343.8 kN, with a serviceability load of half this value. The estimated pile head displacement is minimal, indicating stability under the examined conditions.
- 6.44: Example 6.14
- This page discusses the calculation of deflection and rotation of a concrete pile in soil, using Zheng et al. (2024) method. It considers a solid pile under lateral load with fixed and free rotation scenarios. The aim is to determine the pile head's deflection and bending moment for the fixed case, and deflection and rotation for the free case, utilizing stiffness and compliance matrices.
- 6.45: Example 6.15
- This page analyzes a 0.6 m diameter, 10 m long concrete pile embedded in layered soil (stiff clay and dense sand) under lateral loads of 100 kN and 200 kN. It employs the beam-on-nonlinear Winkler spring method and Finite Element Method to assess lateral deflection, bending moments, shear forces, and structural capacity. The findings confirm that the pile can safely support the loads, provided geotechnical reduction factors are applied to meet relevant standards.
- 6.46: Example 6.16
- This page details the estimation of the p-y curve reduction factor (βg5) for pile #5 under lateral loads, addressing both weak and strong axis loading conditions. It highlights the importance of accounting for interactions between pile #5 and adjacent piles, providing equations and figures to assist in calculating individual interaction factors and the overall reduction factor for each loading direction.