Pile Shaft Research Articles

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.

Torsional installation and vertical tensile capacity of helical piles in clay

Helical piles are being increasingly considered for offshore applications as they avoid the acoustic emissions associated with pile driving, and they provide additional capacity relative to a driven pile. In this paper, the installation and tensile capacity of helical piles is considered through a combination of centrifuge experiments and large-deformation finite-element analyses within a coupled Eulerian–Lagrangian framework. The experiments provide a basis for validating the numerical simulations, but also quantify the expected installation torque and undrained tensile capacity, including the variation with time after installation. The numerical simulations extend the parameter space investigated experimentally, considering the number of helices, their spacing and pitch, in addition to the ratio of pile shaft to helix diameter and the profile of undrained shear strength. Mechanisms revealed through the numerical simulations are reflected in a new analytical model for calculating undrained tensile capacity, which is seen to agree reasonably well with the numerically and experimentally determined capacities.

Effect of degradation on geotechnical behavior of glauconite sands from the U.S. Mid-Atlantic Coastal Plain

Glauconite sand is a challenging sediment that can pose risks to foundation installation and performance due to its tendency to transform from coarse-grained material into fine-grained material due to particle crushing. Glauconite is characteristically green iron potassium mica and smectite often found in sand-sized peloidal form. It forms under reducing conditions within marine depositional environments below wave base and has been found in coastal plain and offshore regions of the U.S. This paper presents an overview of the geological basis for glauconite sand formation, describes its depositional environment and maturation process, and summarizes the state of knowledge of geotechnical challenges in glauconite sands. Laboratory test results are presented for glauconite sands collected from the U.S. Atlantic coastal plain, showing that initial sample conditions, drying methods, and degradation methods affect the initial, temporary, and long-term geochemical and mechanical characteristics of glauconite sands. The degree to which particles crush or degrade from their natural peloidal form to clay-size particles is linked to maturity and depositional method. Intentionally degraded specimens used in laboratory testing can simulate the effect of pile driving through creation of a shear zone of degraded soil along the pile shaft, and quantify its impact on soil-structure interface strength.

Centrifuge modelling of piled foundations in swelling clays

A study aimed towards assessing the variation in shaft capacity of piled foundations in swelling clays is presented. At the clay's in-situ water content, the results of pull-out tests on short-length piles revealed no dependency of shaft capacity on overburden stress. Conversely, after achieving a targeted value of swell, a strong dependency on overburden stress was observed. In upper portions of the profile where swell can occur relatively freely, swell-induced softening results in a reduction in pile shaft capacity. However, at greater depths where swell is largely suppressed, so too are the effects of swell-induced softening. For this reason, shaft capacity at depth was found to remain relatively constant before and after swell. The results of an instrumented pile test revealed an overriding dependency of lateral induced swell pressure on the magnitude of heave which has occurred. Irrespective of the level of overburden stress, lateral pressures against the pile were found to increase at early stages of the swelling process, but then reduce as swell continued and softening began to occur. Such a result highlights the importance of carefully considering the level of swell at which shaft capacity should be assessed if a conservative design is to be obtained.

Homogeneity of Bored Piles According to Results of Four-Channel Cross-Well Ultrasonic Monitoring

The homogeneity of the structure of the boired pile shaft has been studied based on the results of four-channel inter-well ultrasonic (US) monitoring. The actual lengthy of the piles has been determined with the detection of defragmentation of the pile shaft, the compressive defects have been determined, and continuity defects have been identified based on a joint analysis of data from the method of interwell ultrasonic monitoring. The use of four channels allows to control separately the peripheral and central areas of the pile in six directions. The data of the seismoacoustic method coincided with the parameters of ultrasonic monitoring in terms of identifying zones of concrete heterogeneity, reducing the pile cross section, etc. For all of the listed piles, data are not registered by the named test methods indicating defragmentation of the pile shaft – the presence of sections in the cross sections of which there is no concrete at all. These test methods for all piles confirmed the compliance of their actual length with the design values. A significant defect in the continuity of the concrete of the 40op pile, according to the data of ultrasonic monitoring and seismoacoustic method, was registered in the interval of marks – (17.5–18) m, manifesting itself a sa decrease in the propagation velocity of the ultrasonic pulse from 25 to 50 % in two sounding directions, inclu-ding diametrical. This defect can be interpreted as a decrease in the effective section of the pile to 25–50 % of the average value. Defective sections of piles were found in their upper part at depth marks from 0 to –1.5 m, counting from the end surface of the head. At the same time, differences in the physical and mechanical parameters of concrete at these marks were also observed within the cross section of piles [1–5].

Research on Dynamic Pile-Driving Formula Parameters and Driving Feasibility of Extra-Long PHC Pipe Piles

Prestressed high-strength concrete (PHC) pipe pile has the advantages of high single pile bearing capacity, a wide range of applications, good driving resistance, fast construction speed, etc. It has been widely used in high-rise buildings, bridges, ports, and other industries. The application of extra-long PHC pipe piles with a length of more than 50 m is increasing. However, there are few studies on the drivability and hammering criteria of extra-long PHC piles. To analyze the drivability of extra-long piles and predict their bearing capacity, in this paper, high-strain dynamic tests were carried out on 14 test sections with the pile foundation of Temburong Bridge in Brunei as the research background. The hammer stop control criteria calculated according to the Hiley formula would lead to excessive hammering. Three types of damage occurred during construction: pile shaft breakage, weld tearing, and pile head breakage. The weight and drop height of the piling hammer selected for this project were appropriate, and the extra-long test piles can be hammered to the design depth. The values of Cp (Compression of the pile) and n (the efficiency of the blow) were fitted based on the dynamic test data, which provided a more accurate reference for the selection of subsequent piling parameters of the project. It provides a more accurate calculation method for predicting the bearing capacity of extra-long PHC piles and provides control criteria for pile stopping and a scientific basis for their design and construction.

Experimental Investigation on Jacked Pile-Sinking and Capacity-Induced Pore Pressure and Effective Radial Stress at the Pile-Clayey Soil Interface

Based on research into how static pressure piles sink in saturated cohesive soil, alterations caused by a rise in pore stress during the load process between the pile and the earth as well as the effects of a variation in valid radial thrust on the project are thoroughly studied. These changes are of great importance for the application and practice of practical projects. Microtest components are embedded on the surfaces of open and closed piles, and test research is conducted using a large-scale system and double-deck open and closed pipe piles. Finally, complete consideration is given to how variations in effective radial stress. Through this test, it was determined that as the pile’s buried depth gradually grows, so do the valid radial thrust and excess pore pressure. However, the quantity of the superfluous pore water stress for a closed pile is higher than for an open pile. And the higher half has substantially lower effective radial thrust and overall surplus pore stress than the lower part does. The pile penetration depth is constant, and the value of h/L of the pile shaft is also rising, the occurrence of “lateral pressure degradation” of earth load between pile and earth is becoming increasingly prominent. The maximum ratio of the excess pore stress to the valid soil pressure between the pile and earth contact is 62.1% for an exposed pile and 52.1% for a sealed pile. At the interface, the effective radial stress is about 3.76∼5.46 times that of the remaining pore water stress. Therefore, under changing pile penetration depths, the value of h/L will have an impact on the pile’s and the soil’s additional pore water pressure or excellent soil pressure. The test results have a significant impact on how static pressure piles are built and how bearing capacity is designed in real-world applications.

Bearing behavior of monopile-friction wheel hybrid foundation under combined horizontal-torsional loads in sand soil

The monopile-friction wheel hybrid foundation withstands various loads in the marine environment, such as the vertical load (V) transmitted from the superstructure, horizontal loads (H) caused by wind or wave, torsional loads (T) caused by rotating structures. In this article, 1 g model tests are used to investigate the behavior of the monopile-friction wheel hybrid foundation under independent horizontal load (H) or torsional load (T), and combined loads (H-T) in sand soil, respectively. The failure envelopes of H-T loading plane are obtained from the measured load–displacement data with the simplified calculation equations presented as well. Finally, we also discuss quantitatively the influences of the pre-vertical loads, foundation geometry and loading eccentricity on the bearing capacity of the hybrid foundation via the three-dimensional finite element method. The results indicate that the displacement response of the hybrid foundation under independent loading is significantly different from that subjected to combined loads (H-T). The torsional bearing capacity of the hybrid foundation can be significantly improved by 6.6–33.34% under pre-horizontal load. The horizontal bearing capacity of the hybrid foundation decreases sharply after the pre-torsional load reaches a certain value, which decreases by about 20%. The presence of a friction wheel improves the torsional/bending moment distribution of pile shaft.

Scaling effects on the seismic response of a closed-end pipe pile embedded in dry and saturated coarse grain soils

Foundations can be subjected to dynamic or seismic loads depending on their applications and the site being constructed in. The researchers concentrated their works on investigating the reasons of the significant damage of piles during seismic excitation. Based on the findings of laboratory experiments and other numerical analyses, such failures were referred to as the kinematic impact of the earthquake on piles since they were associated with discontinuities in the subsoil because of sudden changes in soil stiffness. The current work investigates the seismic response of closed-end (CE) pipe pile using three-dimensional finite element analysis, including the impact of the scaling-up model, acceleration-time history of the ground motion, and ground conditions. The numerical model is developed using a variety of scaling rules and the outputs of the available laboratory tests. The current results showed that the saturated sand models have larger pile deformation factors than dry sand models. Pile frictional resistance was evaluated numerically, and the entire findings were evaluated against the earlier work. Mainly, the frictional resistance around the pile shaft was lower than that at the pile tip, and the frictional resistance factor on the soil surface of dry soil models was larger than that of saturated soil models. Owing to the acceleration amplifications, the pile and soil suffered cycles of compression and tension stresses. A hysteresis loop is broader and flatter on the x-axis as the shear strain increases serve to identify the shear stress–strain plane behavior. The main outputs of the scaled models were normalized to provide a deep insight of model to prototype scaling effects.

Experimental Study on Cumulative Deformation of Pile Group in Saturated Clay under Horizontal Cyclic Loading

In order to investigate the cumulative deformation of the pile group in saturated clay under horizontal cyclic loading, a series of 1g model tests were conducted using the self-made loading equipment in this paper. Firstly, the loading equipment and testing procedure are introduced. Then, the cumulative deformation of the pile group, the dynamic response of the soil, and the bending moment of the pile shaft under horizontal cyclic loading are studied. Finally, the horizontal cyclic stiffness of the pile group is analyzed based on the experimental results. It can be found that the cumulative displacement, the rotation angle of the bearing platform, the pile shaft bending moment, and the pore water pressure can attain 90% of the peak values within the first 1000 cycles, and the growth rate slows down in subsequent loading cycles. Moreover, the bending moment of each pile increases with the burial depth and gradually decreases after the peak values. Notably, the horizontal cyclic stiffness of the pile group grows with the cycle loading times and decreases with the loading amplitude.

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.

Axial cyclic loading of piles in low-to-medium-density chalk

Comprehensive field investigations into the axial cyclic loading behaviour of open steel pipe piles driven and aged in low-to-medium-density chalk identify the conditions under which behaviour is stable, unstable or metastable. Post-cycling monotonic tests confirmed that stable cycling enhanced pile capacity marginally, while unstable cases suffered potentially large losses of shaft capacity. Metastable conditions led to intermediate outcomes. The patterns by which axial deflections grew under cyclic loading varied systematically with the normalised loading parameters and could be captured by simple fitting expressions. Cyclic stiffnesses also varied with loading conditions, with the highest operational shear stiffnesses falling far below the in situ seismic test values. The monotonic and cyclic axial responses of the test piles were controlled by the behaviour of, and conditions within, the reconsolidated, de-structured, chalk putty annuli formed around pile shafts during driving. Fibre-optic strain gauges identified progressive failure from the pile tip upwards. Large factors of safety were required for piles to survive repetitive loading under high-level, two-way conditions involving low mean loads, while low-amplitude one-way cycling had little impact. A simple ‘global’ prediction procedure employing interface shear and cyclic triaxial tests is shown to provide broadly representative predictions for field behaviour.

Lateral kinematic response of offshore pipe piles to S‐wave seismic excitation

AbstractThis paper presents an analytical study on the lateral kinematic response of offshore pipe piles subjected to vertically propagating S‐wave seismic excitation. Both the kinematic interaction of the pipe pile with the soil and seawater are considered. The lateral resistances of the outer and inner soil are obtained based on the confined viscoelastic dynamic continuum models, while the hydrodynamic pressures of the seawater are based on the inviscid incompressible fluid theory. The pile response is then obtained by utilizing the continuity condition at the soil‐pile and seawater‐pile interfaces along the pile shaft. The derived solution is employed to investigate the sensitivity of the seismic response of pipe piles to certain key problem parameters, such as length of pile segment embedded in seawater, the relative stiffness of the pile and soil and the pile radius ratio. We demonstrate that the partially embedded piles are much more flexible compared with fully embedded piles when subjected to S‐wave excitation, resulting more strong motion transferred to the superstructures and the existence of seawater will amplify the seismic responses of offshore pipe piles.

Mechanical Response Analysis for an Active–Passive Pile Adjacent to Surcharge Load

Due to the complexity of pile–soil interaction, there is little research on active–passive piles that bear the pile-top load transmitted from the superstructure and the pile shaft load caused by the lateral soil movement around the pile simultaneously. The purpose of this study is to analyze the displacement and internal force of active–passive piles. Most of the pile design codes in China use the elastic resistance method to describe the relationship between the lateral soil resistance and the horizontal displacement of the pile, but this is not accurate enough to analyze the internal force and deformation of the pile when the pile displacement is large. For this case, the passive load on the pile shaft caused by the adjacent surcharge load can be described in stages, and the p–y curve method can be used to express the relationship between the lateral soil resistance and the horizontal displacement of the pile. Additionally, taking both the active load (vertical force, horizontal force, and bending moment on the pile top) and the passive load into account, the deflection differential equation of the pile shaft is herein established, and a corresponding finite difference method program is implemented to obtain the calculations pursuant to the equation. The correctness of the analysis method and program was verified by two test cases. The results show that our calculation method can effectively judge the flow state of the soil around piles and accurately reflect the nonlinear characteristics of pile-soil interaction. Moreover, the influence depth of the pile displacement under the passive pile condition caused by the adjacent load is significantly greater than that under active pile condition, and the maximum pile-bending moment appears near the interface of soft and hard soil layer.

Performance of fin pile subjected to torsional loads embedded in dry sand

Torsional capacities of shaft piles with fins are experimentally examined. For comparison, model experimental tests were performed on conventional piles without such fins to investigate the behaviour of fin piles on the torsional capacity under diverse parameters. The influence of such fins, which are constructed at the top of the shaft with various values of width and length, was investigated. The test results elucidated that the fin efficiency of torsional capacities of fin piles ameliorates with the increase both of fin width/pile diameter ratio (Wf/Dp) and sand relative density. The adopted fins of the shaft play a vital function in its torsional capacity. This is thought to be because the section modulus of a fin pile shaft is augmented at the top of the shaft owing to the presence of fins, which lead to a soil–pile–fins interaction. In addition, augmenting the fin width will provide an appreciably higher soil resistance and a stiffer performance due to an augmentation of the passive zone of earth pressure in front of the shaft compared with conventional piles. This leads to amelioration in the torsional capacity for fin piles.

Field tests on large-scale instrumented piles driven in chalk: results and interpretation

The design of large open steel piles driven at chalk sites suffers from considerable uncertainty, leading to major difficulties in many significant onshore and offshore projects. This paper describes recent instrumented driving, monotonic testing to failure, and restrike tests conducted on large open steel piles driven in primarily low- to medium-density chalk at a site in North-western France. The experiments are described and interpreted with reference to a high-quality site characterisation, dynamic and static methods of test analysis, and alternative predictive design approaches. Important new conclusions flow regarding driving behaviour, the set-up that took place over up to 65 days after installation and the resistances available under compression and tension loading. Surprisingly large differences are shown between tension and compression shaft capacity, which are postulated to be due to Poisson straining in the steel pile shaft and its interaction with the surrounding chalk mass. The field tests contribute to building a high-quality dataset that allows proposed axial capacity design methods to be tested and potentially refined to provide reliable and representative design tools.

Cyclic overlay model of p–y curves for laterally loaded monopiles in cohesionless soil

Abstract. The bearing behaviour of large-diameter monopile foundations for offshore wind turbines under lateral cyclic loads in cohesionless soil is an issue of ongoing research. In practice, mostly the p–y approach is applied in the design of monopiles. Recently, modifications of the original p–y approach for monotonic loading stated in the API regulations have been proposed to account for the special bearing behaviour of large-diameter piles with small length-to-diameter ratios. However, cyclic loading for horizontally loaded piles predominates the serviceability of the offshore wind converters, and the actual number of load cycles cannot be considered by the cyclic p–y approach of the API regulations. This research therefore focuses on the effects of cyclic loading on the p–y curves along the pile shaft and aims to develop a cyclic overlay model to determine the cyclic p–y curves valid for a lateral load with a given number of load cycles. A stiffness degradation method (SDM) is applied in a three-dimensional finite element model to determine the effect of the cyclic loading by degrading the secant soil stiffness according to the magnitude of cyclic loading and number of load cycles based on the results of cyclic triaxial tests. Thereby, the numerical simulation results are used to develop a cyclic overlay model, i.e. an analytical approach to adapt the monotonic (or static) p–y curve to the number of load cycles. The new model is applied to a reference system and compared to the API approach for cyclic loads.

Torque-Transferring Characteristics of Offshore Tetrapod Piled Jacket Foundations in Dense Sand

Tetrapod piled jacket (TPJ) foundations that support offshore wind turbines (OWTs) tend to be subjected to significant torque that is caused by eccentric loading from wind, waves, or accidental vessel impact. This paper presented a comprehensive three-dimensional (3D) numerical analysis to investigate TPJs performance under torsional loading, which considered the distribution of local torque and rotation over pile shafts and the underlying torsional load transfer mechanism. A modified Mohr–Coulomb (MMC) model for dense sands was implemented in ABAQUS/Standard that captured the evolution of the friction and dilation (ψ) angles against the accumulated plastic shear strain (γp). The results showed that the torque that was imposed at the head of a TPJ foundation could trigger soil reactions of torsional resistance (τs) and horizontal force (Hp) in individual piles; higher pile spacing-to-diameter ratios (S/D) mitigated the influence of torsional loads. A pressure-dependent torsional load transfer model was proposed that considered the effects of the pile–sand relative stiffness and sand’s relative density (DR). The model could be employed to predict TPJs response under torsional loading and improve their practical design.

Installation Effects and Behavior of a Driven Prestressed High-Strength Concrete Nodular Pile in Deep Saturated Soft Clay

This paper investigated the installation effects of a driven prestressed high-strength concrete (PHC) nodular pile in deep soft clay through full-scale tests, and the behavior of a driven PHC nodular pile is analyzed based on the field test results. The test results demonstrated that the driven PHC nodular pile installation process induced significant disturbance in the surrounding soil. The excess pore water pressures (Δu) that were induced by the installation of a driven PHC nodular pile were larger than the Δu that were induced by the installation of a driven PHC pipe pile. The driven PHC nodular pile installation caused significant Δu in the soil down to 2 m below the pile base, and the Δu became much smaller in the soil at 4 m below the pile base. The Δu dissipated slowly in the soft clay layers, and the Δu in the surficial soil layers dissipated faster than that in the deep soil layers. The nodules along the PHC nodular pile shaft could increase the pile shaft capacity. The measured shaft resistances of 350(400)-mm PHC nodular piles were 1.17–1.18 times the calculated shaft resistances of 350-mm PHC pipe piles in soft clay layers.

Effect of Underreamed Pervious Concrete Columns on Load-Carrying Capacity of Loose Cohesionless Soils

Weak confinement governs the bulging failure of granular columns. Pervious concrete columns have granular columns like drainage with stiffness of concrete column are thus independent of the confinement from the weak surrounding soil can be treated as an alternative solution. Moreover, it is well established that under-reaming bulb enhances the bearing resistance to the pile shaft. Therefore, the present experimental and analytical study investigates circular pervious concrete column (CPCC) and under-reamed pervious concrete column (UPCC) in improving the bearing capacity of loose pond ash fill. CPCC and UPCC are constructed in a model pond ash fill subjected to vertical loading. The load-carrying capacity, settlement failure mechanism, and consolidation parameters were examined. Theoretical analysis for evaluating the load-carrying improvement factor (LCF) with nondimensional parametric variation of area replacement ratio (Ra), underreamed bulb ratio (Br), and length ratio of the column (RL) was also done. Efficacy of CPCC was also numerically studied (Plaxis 3D). Experimental results show that the vertical settlement is reduced by 52.8% with CPCC and UPCC. UPCC renders higher load-carrying capacity than CPCC. Both CPCC and UPCC undergo deformation at depth of 4D during failure. For the same area replacement ratio (Ra), the experimental and theoretically computed values are found in good agreement. The rate of consolidation is reduced from 53 to 23 days by using CPCC signifying its drainage potential.