Shaft Resistance Of Piles Research Articles

Analysis of pile shaft resistance embedded in unsaturated clayey soils

ABSTRACT The finite element analysis was carried out to investigate the performance of pile foundations with dimensions (0.6 × 12) m in diameter and length, respectively, which is embedded in fully and partially saturated soils within Baghdad city. The behaviour of partially saturated clay is investigated through many factors, such as the degree of saturation, water table depth, clay shear strength, negative pressure head, soil density, permeability function, volumetric water content function, and unsaturated soil modulus (H). This study examined the adhesion factor (α) in piles at different water tables, saturation degrees, and the impact of partial soil saturation on the final shaft resistance. It is concluded that the pile capacity rises as the soil becomes partially saturated due to the water table dropping at varying depths and saturation levels. The study determined that the respective degrees of saturation and reduction of the water table in the three soils significantly influenced the skin friction values caused by partial soil saturation. The shaft resistance increases quickly when the water table is dropped to 2 and 4 metres. It is discovered that when matric suction is increased to a particular value, the shaft resistance decreases.

Response of piled raft foundations using the disturbed state concept theory: Analysis and interpretation

In nearshore and marine environments, challenges arise from loading conditions, subsoil profiles, and dynamic soil states influenced by continuous wave action. Piles in such settings face complex interactions due to soil vulnerability to loading and over-consolidation. Accurate estimation of pile shaft and base resistances, as well as raft-soil interface stiffness, is crucial. The paper introduces the disturbed state concept for analysing piled raft foundations under vertical loading. This theory assumes interface strength between piles and soil follows an exponential distribution, expressed through the Weibull function. Interaction between piles is established using a modified displacement factor, which is a modified form of Mindlin's solution. Raft-soil interaction is modelled with springs connected to the pile head. The load transfer model exhibits both softening and hardening responses. Validation against numerical and field experimental studies demonstrates close agreement within a 5%–15% error range. Parametric investigation analyses load-settlement response, percentage of load on pile base with settlement increase, and axial load transfer along pile length under varying conditions. The impact of limiting pile-soil relative movement on piled raft response is also explored.

Why pile-supported building settled continuously after water level was stabilized during dewatering: Clues from interaction between pile and multi aquifers

Dewatering in a multi-layered aquifer-aquitard system often causes groundwater drawdowns in multiple aquifers, which together lead to obvious settlement of adjacent pile-supported building. This paper documents an in-situ pumping test conducted in a multi-aquifer system. It indicates that an adjacent pile-supported building settled continuously after water level was stabilized. To clarify the possible reasons for this phenomenon, a series of numerical models were established, validated and employed to explore the load transfer behaviour between pile and multi-aquifers during different dewatering conditions. Results indicate that the appearances of several aquitards in the multi-aquifer system significantly block the hydraulic connection between different aquifers, leading to non-synchronized developments of groundwater drawdown and pile shaft resistance at different soil layers during pit dewatering, which eventually causes the lagging settlement of the building. In practical pit dewatering in multi-aquifer system, engineers should appropriately increase the monitoring time for the deformation of adjacent pile-supported buildings for avoiding missing the maximum settlement.

Analysis of pile end bearing capacity in Holocene interlayered silty deposits based on CPT soil behavior type index

The existing correlations between pile and cone penetration test (CPT) results often lack versatility for silty geomaterials, as they were primarily developed for clays or sands. To establish meaningful correlations, it is essential to understand the geology of the environment under examination. The CPT and its derived parameters, including the Soil Behavior Type (SBT) index, have proven to provide reliable soil information, particularly in the field of pile foundation engineering. This paper presents the findings and interpretations from several pile load tests conducted alongside field cone penetration tests on a Holocene saline interlayered silty formation, a distinct condition encountered in practice. Various CPT-based pile design methods were employed to evaluate pile capacity based on CPT results. As observed, predictions for pile shaft resistance in this geological formation remained consistent across all methods, while notable variations emerged in estimating pile end bearing. This was inferred to be a result of limited research on pile end bearing capacity in the literature, leading to proposals of broad ranges for pile influence zone and toe coefficient values, as well as various CPT tip resistance averaging techniques across different methods. Consequently, to improve accuracy, modifications based on site-specific test data may be necessary. Drawing from the assessments, effective modifications involved considering the SBT index near the pile tip. Subsequently, the current study introduces a new region-specific adjustment to the widely recognized Enhanced Unicone method based on the SBT index, resulting in a more accurate estimate of pile end bearing in such interlayered silty contexts, with less scatter compared to other available approaches.

Advancing Rock-Socketed Pile Design with a Unified Interface Shear Strength Framework for Soft Rocks

The shaft resistance of rock-socketed piles (RSPs) is primarily influenced by the interactions between the pile, rock and any soft interface materials. This study presents a fundamental experimental and numerical investigation to predict the shaft resistance of model RSPs in soft rocks through a comprehensive shear strength framework incorporating the major variables such as roughness and smear fabric. By calibrating the Discrete Element Method (DEM) results with the experimental outcomes, this study evaluates the load-resistance attributes of RSPs in three different soft rocks for a wide range of roughness and smear configurations. The interface roughness effect of the RSPs in terms of the friction coefficient was correlated with the ultimate shaft resistances, uniaxial compressive strength and Young’s modulus of the rock. The study then incorporated the effect of smear fabric (placement, thickness and area proportion) in the shear strength framework of clean shafts. Comprehensive review of the DEM results revealed that the socket roughness effect diminishes at a critical roughness factor (RF)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$({\ ext{RF}})$$\\end{document} of 0.4, beyond which the smear predominantly influences the shaft capacity. Following this, the effects of roughness and smear fabric were incorporated into a single equation representing the interface shear strength of RSPs, where the existence of smear results in a maximum reduction of up to 75% of the ultimate shaft resistance. The distinctive feature of this unified interface shear strength framework lies in its integration of the new smear fabric parameter and the linkage to the mechanical properties of soft rocks, which is the limitation of the earlier studies. It thereby sets a strong base for future studies aimed at advancing the pile-rock interface models.

Mechanical resistance behind fiber-reinforced polymer pile: Role of clay minerals

Due to the geotechnical design requirements of the fiber-reinforced polymer (FRP) pile embedded in clay, interface friction evolution between the FRP pile and clay plays a crucial role in determining the pile shaft resistance. It is observed from the experimental evaluation that the earth pressure and shear rate affect the pile-soil interface behavior. In this study, a cross-linked epoxy resin is created to contact a siloxane surface of kaolinite in the molecular dynamic simulation. The interfacial accommodation between kaolinite and epoxy resin is studied. In order to investigate the effect of normal stress and sliding velocity on nanoscale friction characteristics, the steered molecular dynamics is utilized to simulate the sliding of the kaolinite model on the surface of the epoxy resin. Simulation results show that the calculated peak interface shear coefficient decreases nonlinearly as the normal stress increases, which follows a logarithmic relationship consistent with the FRP-soil interface shear test. On the other hand, it is observed that two distinct velocity regions, slow pulling mode (5–200 m/s) and fast pulling modes (300–800 m/s), are well fitted by extended Bell theory. The stick–slip motion is only found in slow sliding velocity mode. This increasing tendency of the energy barrier with the normal stresses indicates that higher pulling forces are required for the FRP to slide along the soil at higher normal stress. The present work provides a fundamental understanding of the friction mechanisms between kaolinite and epoxy resin.

3D analytical modeling of moving‐loading induced pile‐group behavior in stratified cross‐anisotropic poroelastic water‐saturated soils based on two stage theory

AbstractThe aim of this paper is to propose a two‐stage theory‐based analytical method for the dynamic performance of pile groups in layered poroelastic saturated cross‐anisotropic soils induced by moving loadings. Among them, the free‐field vibrational analysis of saturated soils is performed by the analytical element‐layer approach (ALEA) and Fourier transformation. Based on the free‐field response, the boundary element (BE) solution for the soil resistance at the soil‐pile interface is derived utilizing the two‐stage theory. Simultaneously, the finite element (FE) solutions for the pile shaft resistance and deformation of pile groups are derived based on the Timoshenko beam theory. Finally, the FE‐BE coupled dynamic equation for deformations and internal loadings of the soil‐pile system is obtained. Thereafter, the reliability of the proposed method is validated by comparing with existing solutions and FE data from ABAQUS. Based on the derived solutions, a comprehensive parametric study is performed to examine the effects of loading amplitude, force speed, soft soil‐layer stiffness, soil anisotropy, and pile length on the dynamic responses of pile groups.

Numerical study on vibratory extraction of offshore wind turbine monopile foundations under sandy seabed condition

The wind industry has experienced a rapid growth in Europe over the last decades. The early generation turbines were designed for a life of 20–25 years. Decommissioning of offshore wind turbines is becoming more important since many of these installed assets are approaching their end of lifetime. In this study, using vibratory extraction of monopile foundations instead of current practice of cutting them is investigated numerically. Correct estimation of extraction force helps operators to choose suitable vibro-hammer and vessel (or crane-barge), which leads to reduction of decommissioning costs. A Coupled Eulerian-Lagrangian (CEL) approach of ABAQUS/Explicit combined with a modified Mohr-Coulomb (MMC) model are used to find the pile shaft resistance during total removal operation under saturated dense sand condition. The MMC model captures the nonlinear pre-peak hardening and post-peak softening of the dense sand which is not modelled by conventional Mohr-Coulomb model. The VUSDFLD subroutine, which is a user-defined framework, has been used to implement the MMC model into CEL analysis. A parametric study is conducted to analyze how the characteristics of the vibro-hammer, such as its frequency, eccentric moment, and the extraction rate influence the results. The present numerical results show that using proper frequency results in reduction of soil resistance to less than 25% of the initial resistance. However, appropriate hammer with enough eccentric moment and suitable extraction rate, are vital to ensure soil degradation. The results show that the proposed methodology is both robust and straightforward and it has the potential to reduce computational time which is efficient for engineering applications.

Field Measurement and Theoretical Analysis of Sidewall Roughness on Shaft Resistance of Rock-Socketed Piles

Sidewall roughness is a key factor influencing the shaft resistance of rock-socketed piles. Owing to the difficulties in onsite measuring and the inconsistency in quantitatively characterizing the roughness degree of sidewalls, existing approaches for estimating the shaft resistance of rock-socketed piles often cannot take this factor into account. Based on the measured surface curves of the 68 sockets in No. 6# and 7# group piles of the Chishi Bridge on the Ru-Chen Expressway in China, sidewall roughness is described by introducing the roughness factor (RF) based on the Horvath and Monash models, respectively, while a statistical analysis of the sidewall roughness in rock-socketed sections is also conducted. In addition, an analytical solution to the shaft resistance of rock-socketed piles with consideration of sidewall roughness and the relative settlement of the pile–rocks interface (∆s), is proposed and further compared with the field load tests. The results showed that: the RF obtained by the Horvath model is bigger than that obtained by the Monash model; the larger RF is, the bigger the mobilized shaft resistance; the analytical solution generally overestimates the mobilized shaft resistance of rock-socketed piles under the same ∆s, and the deviation is less than 15% if ∆s is larger than 3.00 mm. The Horvath model is recommended to quantitatively characterize the roughness degree of sidewalls for its good operability in practice.

Modeling of Grout Returned Height for Postgrouting at Pile Tip Considering the Soil Unloading and Time-Dependent Behavior of Cement Viscosity Effects

Postgrouting at the pile tip can improve the behavior of pile shaft resistance through the grout returned along the pile shaft. The soil radial unloading effect that existed in the bored pile shaft soil and the cement viscosity with time-dependent behavior affect the grout diffusion. A grout returned height model for postgrouting at the bored pile tip considering the soil unloading effect and time-dependent behavior of cement viscosity was proposed to analyze the grout returned diffusion behaviors. The reliability of the grout returned height model was compared and verified with a series of model bored pile tests and the measured results of the field case. The analysis results showed that considering the influence of pile shaft soil unloading for bored piles and the time-dependent behavior of cement viscosity in the grout returned height model is essential for analyzing the grout returned diffusions. A parametric study with the proposed model was performed, and the effects of soil unloading degree, the grout flow rate, the grouting pressure, and the pile scaling effect on the grout returned height were analyzed.

Unsupervised machine learning for detecting soil layer boundaries from cone penetration test data

AbstractCone penetration test (CPT) data contains detailed stratigraphic information that is useful in a wide variety of applications. Separating a CPT profile into discrete layers is an important part of many analyses such as critical layer selection in liquefaction triggering analysis, effective stress seismic ground response analysis, analysis of pile shaft and tip resistance, and soil‐pile interaction analysis. The discretization of the profile into layers is often done manually, relying on the judgment of the analyst. This manual approach is cumbersome for datasets that include large numbers of CPT profiles (such as the Next Generation Liquefaction [NGL] database and the New Zealand Geotechnical Database) and it may not be consistent or repeatable because different analysts may discretize a given CPT log in different ways. To overcome these difficulties, we present an approach to automatically divide a CPT profile into discrete layers. Automated layer detection is performed using an unsupervised machine learning technique called agglomerative clustering in combination with two cost functions to identify an optimal number of layers. The algorithm is illustrated using CPT profiles from the NGL database, where the approach is being used in the development of liquefaction triggering and manifestation models. Although the algorithm shows promise for replicating our judgment regarding layering, we recommend visual review of the layering produced by the algorithm to check for reasonableness given the site geology and intended use of the CPT data.

Seasonal variation of the shaft resistance of CFA piles in unsaturated soil: a case study

Excessive settlements or failure of piles observed in some Brazilian unsaturated soil sites indicates that the shaft resistance can vary with the seasonal variability of top soil water content, especially in the case of foundations of transmission towers or installed at the periphery of buildings, situations in which the soil is more susceptible to suction fluctuation due to the higher exposure to rainfall action. The objective of the research described in this paper was to provide field evidence with the purpose of alerting practising engineers and to help researchers to better understand the contribution of matric suction on pile capacity. For this aim, the seasonal variability of the shaft resistance of Continuous Flight Auger (CFA) piles in a typical Brazilian unsaturated tropical soil was evaluated by performing axial tensile load tests on eight instrumented CFA piles in different periods of the year. Soil suction was monitored throughout the period of tests, and the results indicate that the shaft resistance of the pile upper part varies considerably during the year and tends to decrease with decreasing soil suction. This work provides valuable insights into the application of unsaturated soil mechanics, which is usually disconnected to classical geotechnical practice.

Investigation of the dynamic vertical behaviour of a floating pile embedded in unsaturated poroelastic half-space

This paper proposes an analytical solution for investigating the dynamic vertical behaviour of a floating pile in unsaturated poroelastic half-space by considering the dynamic properties of the soil below the pile base. The pile shaft resistance is derived by applying Hankel integral transformation to the governing equations, and the pile base resistance is derived by introducing the potential function and operator decomposition methods. The dynamic interaction between the soil and the pile is considered by virtue of the impedance function. To account for the mixed boundary conditions of the pile-soil interface, an analytical solution for the vertical dynamic response of a floating pile is derived in the frequency domain. Additionally, by utilizing the inverse Fourier transform and convolution theorem, a quasi-analytical solution for the velocity response of the floating pile is derived in the time domain. Furthermore, the derived solution is verified through comparisons with existing solutions available in the literature. Finally, a parametric study is performed to investigate the influence of saturation and intrinsic permeability on the dynamic flexibility coefficient of porous unsaturated half-space, the influence of saturation on the dynamic impedance of the soil layer, and slenderness ratio on the vertical behaviour of floating pile and end-bearing pile.

Experimental Study on the Difference Mechanism of Shaft Resistance between Uplift Piles and Compressive Piles

To study the formation mechanism of the lower shaft resistance of uplift piles compared to compression piles, the additional stress caused by uplift and compressive piles in the soil is obtained through indoor model tests with embedded micro earth pressure cells. The study shows that the uplift pile has an unloading effect in pile side soil, and the compressive pile has a loading effect in pile side soil. Closer to the loading point, the unloading effect of the uplift pile and the loading effect of the compressive pile becomes more obvious. The unloading effect decreases the shaft resistance of the uplift pile, and the loading effect increases the shaft resistance of the compressive pile. The tests also reveal that the distribution range of additional stress caused by a single pile is within 6 d from the axis of the pile. After considering the effects of loading and unloading of a single pile, the calculated uplift pile bearing capacity is close to the values of formulas such as Meyerhof and Deshmukh and the measured value.

Soil resistance during vibratory driving in sand

A mechanism to explain pile shaft resistance during vibratory driving is discussed. One hypothesis is that horizontally oscillating stresses temporarily reduce shaft resistance. Vibration measurements were conducted in medium-dense to dense sand during vibratory driving. A large compaction probe was installed by a vibrator with variable frequency. The driving process and ground response were documented in detail. Geophones were installed on and below the ground surface. Horizontal ground vibrations were measured at three levels below the ground surface. The difference in vibration response of the ground during driving at a high frequency (27 Hz) and at the system resonance frequency (15 Hz) showed the effect of the vibrator operating frequency on penetration speed and emitted ground vibrations. Horizontal stress pulses are emitted along the probe shaft, which can temporarily reduce static horizontal stresses acting against it. This phenomenon can explain the temporary reduction of shaft resistance and efficiency of vibratory driving in granular soils. As a result of these pulses, the horizontal stresses are increased permanently. Using a monitoring and process control system, the system resonance frequency can be determined in the field – a critical parameter for vibratory driving resistance, emission of ground vibrations and vibratory compaction of granular soils.

Effects of soil unloading and grouting on the vertical bearing mechanism for compressive piles

The present study conducts a series of model cast-in-place piles tests to analyze the vertical bearing characteristics and the grout returned diffusion mechanism along the pile shaft of tip post-grouting piles with different grouting and pile shaft soil unloading conditions. The model test results show that the pile tip post-grouting technology can improve the weak difference in the bearing characteristics and axial force distribution of the pile foundation caused by pile shaft soil unloading. The pile shaft resistance can be improved by the returned grout in the pile shaft. The pile shaft resistance will mainly bear the pile top load when the pile top load and the grouting volume are relatively small, and the pile tip resistance will mainly bear the pile top load with the increases of the pile top load and the grouting volume. The grouting return height increases with the increase in pile shaft soil unloading degree, and the analyzed values of the grouting returned height based on the pile bearing characteristic results are close to the measured values. The grouting diffusion mechanism of the cement on the pile tip and pile shaft soil during the pile tip post-grouting process is revealed.

Full-scale field test study of bearing characteristics of post-grouting pile for offshore wind turbines

Full-scale load tests were conducted on a combined steel pipe and bored pile foundation used for offshore wind turbine in Fuqing Xinghua Bay. Due to the complex geological conditions of the project, lengthening the bored pile will cause it to exceed the steel pipe pile so much that there are construction risks such as collapsed holes, hence, combined tip-and-side post-grouting was used to improve the bearing characteristics of the pile foundations. The results of double-level O-cell bi-direction tests before and after grouting on test pile SZ32 are reported. Comparing the test results before and after grouting shows that post grouting can significantly enhance the bearing capacity of the pile foundations. Furthermore, the relative displacement required to mobilize the shaft resistance of the test pile is significantly reduced by the post grouting craftwork. Additionally, the core samples obtained from the coring tests showed that the cement grout was distributed from 0.5 D below the pile tip to 5.3 D above the pile tip, respectively. Finally, the results could be applied to similar foundation design used in offshore wind turbine.

Method for Calculating Vertical Compression Bearing Capacity of the Static Drill Rooted Nodular Pile

The static drill rooted nodular (SDRN) pile is a new kind of composite pile foundation made by inserting a precast nodular pile into the cemented soil. Based on the tests and analysis on the mechanism characteristics of these two kinds of interfaces, which are between the pile and cemented soil, and between the cemented soil and soil, this paper proposes a calculation method for the ultimate vertical bearing capability of the SDRN pile considering two failure modes. When the precast pile and surrounding cemented soil fails as a whole, the diameter of the cemented soil pile is taken to calculate the ultimate shaft resistance, and the shaft resistance of the SDRN pile is about 1.05∼1.10 times that of the bored pile in the same soil layer. When the core precast pile fails in penetration mode, the diameter of the core pile is taken. The pile shaft resistance takes that of displacement piles in the same soil layer. The lower nodular pile shaft resistance should consider the squeezing effect of nodular joints. Besides, the improvement of pile tip resistance due to the expanded cemented soil should also be taken into consideration. The result is the smaller value calculated according to these two failure modes. The ultimate bearing capacity of a SDRN pile calculated by the theoretical method is not only compared with the field test result, but also the simulation result of a 2D model pile built by PLAXIS finite element software. In addition, the finite element simulation is also confirmed to be an effective way to investigate the mechanism characteristics of SDRN piles more thoroughly.

Prediction of Pile Shaft Capacity in Tension Based on Some Direct CPT Methods-Vistula Marshland Test Site.

This paper presents different CPT methodologies for the prediction of the pile shaft resistance in tension on the example of three reference screw piles of the Jazowa test site in Poland. The shaft capacity was estimated based on the cone resistance, sleeve friction and CPT excess pore water pressure. Three piles with a diameter of 0.4 m and the length varied from 8 m to 14.6 m were subjected to static load tests in tension. Their results were used to determine the ultimate bearing capacity of the reference piles. The pile shaft resistance was estimated according to the AFNOR standard, Doan and Lehane 2018 centrifuge tests based method (Delft University of Technology approach), the Modified Unicone method, KTRI (Kajima Technical Research Institute) and LCPC (Laboratoire Central des Ponts et Chaussées) method. Then, the ultimate bearing capacity determined in static load tests was compared to the estimated values according to five different methods. The best estimation, fitting almost perfectly to static load test values, was obtained with the AFNOR method, whereas the other predictions significantly underestimated the ultimate bearing capacity.

Performance analysis of a jacked-in single pile and pile group in saturated clay ground

When a pile is installed into saturated clay ground, the “setup” effect may occur due to ground consolidation, which changes pile performance. Although this phenomenon has been observed both in the field and laboratory, its numerical simulation is still challenging. In this work, pile installation effects on the behaviors of jacked-in piles were investigated through three simulation techniques by a three-dimensional finite element analysis program, PLAXIS 3D. A constitutive model called the soft soil creep model was used to describe the soil behavior based on soil parameters obtained from laboratory tests. The behaviors of single piles were first investigated with or without the consolidation process after pile installation to evaluate the pile setup effect. Then, a pile group comprising 4 piles was analyzed using the consolidation process to verify the applicability of the three simulation techniques. The calculated results were compared with the corresponding experimental results. The calculated results using three techniques generally agreed well with the experimental results in terms of initial stiffness and pile shaft resistance. Both the measured and calculated results indicate that ground consolidation caused by pile installation significantly increases the pile bearing capacity and especially, the pile shaft resistance. Therefore, the pile setup effect can be reasonably simulated by the three proposed techniques.