End-bearing Capacity Research Articles

Analysis of the End-Bearing Capacity of Piles in Sand Under Limited Region Failure by a Mixed Zero-Extension Line Method

Analysis of the End-Bearing Capacity of Piles in Sand Under Limited Region Failure by a Mixed Zero-Extension Line Method

Evaluation of side and tip resistances for barrette piles using CYCU/Barrette/Side&Tip/64

This study focuses on evaluating the side and tip resistances for barrette piles under compression loading. An extensive dataset from field load tests, designated as CYCU/Barrette/Side&Tip/64, was utilized for analysis. These data were categorized into drained and undrained soils, based on the predominant soil conditions along the pile shaft. In contrast, tip resistance depended on the soil (drained or undrained) or rock condition at the pile tip. Eight interpretation methods were employed to evaluate the measured side and tip resistances of each load test. The predicted side resistance was calculated using the classical α and β methods developed for more common piles such as drilled shafts. For the prediction of tip resistance, end-bearing capacity models for a drilled shaft resting on soil or socketed in rock are considered. Subsequently, a comparison was made between the measured and predicted capacities. Based on these analyses, it was observed that the measured side resistance is the main contributor to the overall capacity of barrette piles. The percentage of measured side resistance ranges from around 80% to 90%. In addition, the predicted side resistance calculated using the α and β methods is smaller than the measured side resistance interpreted using the L2 criterion. To reduce this prediction bias, the adhesion factor (α) and stress factors (K/Ko) for barrette piles were adjusted. For the tip resistance, the trend is opposite – predicted values are larger than the measured values for barrette piles resting on soil or socketed in rock. Another approach to correct for prediction bias called the generalized model factor is presented.

Evaluation of Design Parameters (α and β) for Analysis and Design of Piles on Soft Clays

This paper presents the analyses of 12 prestressed concrete instrumented test piles (TPs) that were driven in different bridge construction projects of Louisiana as part of a load testing program. The 12 TPs were driven mainly in cohesive soils. Detailed soil characterizations including both laboratory and in situ tests were conducted to determine the different soil properties. The TPs were instrumented with vibrating wire strain gauges to be able to calculate the distribution of skin friction and end-bearing capacities separately. Static load tests and dynamic load tests were conducted on each TP after end of driving to calculate the ultimate load capacity. Fifty six soil layers exhibiting clayey soil behavior and sandy soil behavior dominated the remaining 15 soil layers. The total stress parameter (α) and the effective stress parameter (β) were back-calculated for each soil layer. The α values ranged from 0.22 to 1.80, and the β values ranged from 0.11 to 0.83. Regression analyses were performed on 42 soil layers (75% data) to develop an empirical model to predict α as a function of undrained shear strength. The remaining 25% of the data were used to verify the developed model, and good agreement was observed between the measured and predicted values.

The pullout capacity of OMNI-Max anchors in sand

As the latest development and benchmark of a gravity installed anchor (GIA), the OMNI-Max anchor stands as a cutting-edge achievement and benchmark, finding increasingly widespread use within mooring systems due to its exceptional operational performance and adaptability. Notably, while investigations into the pullout capacity of OMNI-Max anchors have been conducted extensively in clay, the relevant studies are seldom observed in sand. Actually, the mechanical properties of sand are quite different from those of clay, and sand is also widely distributed in seabed soil. Full knowledge of OMNI-Max anchors not only in clay but also in sand is necessary to a wider application of the anchors. In the present work, the large deformation finite element (LDFE) method is adopted combined with the coupled Eulerian-Lagrangian (CEL) technique to study the end-bearing characteristics of the OMNI-Max anchor in sand seabeds. A bounding-surface plasticity model is taken as the constitutive model to capture the characteristics of sand. Through investigation and analysis, OMNI-Max anchors are closely related to the anchor embedment depth, the soil relative density, the anchor orientation, the loading angle and the bearing area, so the working conditions related to these five factors are designed and calculated. An explicit expression of the end-bearing capacity factor is finally derived to provide a simple and fast tool of evaluating the pullout capacity of the anchor in sand under multiple factors. Validation cases and orthogonal tests have confirmed the effectiveness and applicability of the explicit expression.

Loading Rate Effect on the Pullout Capacity of OMNI-Max Anchors in Clay Coupled With Multiple Factors

Abstract As the latest development of gravity installed anchors (GIAs), the OMNI-Max anchor has drawn much attention from worldwide due to its unique behavior in the seabed. The pullout capacity of OMNI-Max anchors is a key index in engineering. However, most of the relevant studies were carried out under a quasi-static condition, which do not actually meet the installation and operation requirements. In practice, the anchor may be subjected to both long-term and short-term sharp loading during mooring. As an important environmental variable, it is essential to evaluate the effect of loading rate on the pullout capacity. Since the bearing capacity of OMNI-Max anchors is affected by many factors, it is also essential to explore systematically the coupling effects of the loading rate and other factors, including the anchor embedment depth, the anchor orientation, the bearing area, the loading angle, and the soil strength. Based on the coupled Eulerian–Lagrangian (CEL) technique, numerous analytical cases are designed and calculated by the large deformation finite element (LDFE) method. The loading rates span four orders of magnitude from the quasi-static velocity to 10 m/s (about one anchor length per second), covering a wider range in pulling out of GIAs. The end-bearing capacity factor changes remarkably with the pullout velocity for OMNI-Max anchors, and the increase can even reach more than twice of that in a quasi-static condition. As a result, a succinct explicit expression is constructed in terms of the loading rate and multiple factors, which can be effectively utilized to calculate the end-bearing capacity factor of OMNI-Max anchors in clay under complex conditions.

An Experimental Study on Estimation of the Lateral Earth Pressure Coefficient (K) from Shaft Friction Resistance of Model Piles under Axial Load

Estimating a pile shaft’s frictional capacity is challenging and has been a controversial subject among researchers. In this study, the shaft friction resistance of non-displacement (pre-installed) model piles under axial load was investigated. Four different model piles were used, including steel, timber, and two composite piles (FRP and PVC filled with concrete). The angle of interface friction (δ) between test sand, and pile materials was determined using an interface shear test (IST) at four relative densities. Axial pile load experiments were implemented in a soil tank and piles were embedded into loose to very dense sand. Model pile load tests were performed in such a way that there was no end (point) bearing capacity (only friction was generated), and lateral friction resistance between the pile material and the soil along the pile shaft formed the complete bearing capacity of the model pile. According to experimental results, it was observed that, with increasing sand relative density and surface roughness of the pile material, the shaft friction resistance of the model pile increases. A back-calculation analysis was also performed to find the values of lateral earth pressure coefficient (K) using Burland’s (1973) equation with the help of measured shaft friction capacity of the model pile load test. By performing multivariate regression analysis, an equation was obtained between the back-calculated lateral earth pressure coefficient (K) and other parameters. The obtained equation was used to calculate the K values given in other studies in the literature. It was determined that the obtained equation was in good agreement with the data in other studies. This equation can be beneficial in practice and can be advantageous for further study in the future.

Ultimate bearing capacity of intact rocks at tip of large-diameter rock-socketed piles considering internal micro-cracks

In the design of large-diameter rock-socketed piles, the ultimate bearing capacity of intact rocks under the pile tip (qb ) is often required to be predicted, especially for rock-socketed end-bearing piles. Existing approaches for calculating qb establish an empirical relation with the macroscopic parameters of rock layers, but the research on the microscopic parameters inside intact rocks is insufficient. This study provides a theoretical method for calculating qb from a micro perspective and implements it in MATLAB, in which the integral stress of the Mindlin solution within the circular region at the pile base was selected as the stress state of the theoretical calculation regions, and the tension– or compression–shear mixed mode I–II criterion was selected as the failure criterion of micro-cracks inside intact rocks. Six model piles with measured ultimate end-bearing capacities were analyzed to validate the proposed solution. The results showed that the failure ranges of intact rocks under an identical base load for analytical analyses are comparable with those obtained by model tests, which confirms the rationality of the theoretical approach. Then, the failure zone of intact rocks under different working loads of pile base was explored. Finally, parametric studies were conducted using the proposed solution to explore the effects of rock properties and pile dimensions.

Particle size effects on the axial pull-out and push-in behaviour of roots

For smaller plant roots in coarse-grained soils, large relative size of soil particles compared to roots can affect their axial resistance. Even for the larger roots of trees, particle size effects may be important, e.g. when testing 1:N scale models of tree uprooting in a geotechnical centrifuge. In this study the distinct element method (DEM) was used to investigate this problem. The sinker root of a centrifuge model tree root system under axial loading was analysed, with its simulated behaviour compared with finite element method (FEM) simulations, where the soil was modelled as a continuum and hence did not incorporate particle size effects. Both were validated against laboratory tests. Considering the same prototype size and soil particle size distribution, different scale factors/g-levels were applied to model roots, hence varying the ratio of root diameter (dr\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{\\rm r}$$\\end{document}) to mean particle size (D50\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${D}_{50}$$\\end{document}). Even at the lower dr/D50\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${d}_{\\rm r}/{D}_{50}$$\\end{document} values investigated (6–21), particle size effects on end-bearing capacity were negligible upon push-in of the root. In contrast, effects on shaft resistance (for pull-out) were significant and were interpreted by a simplified analytical model developed in this study using a combination of cavity expansion and root-particle size ratio. The absolute size of the root analogues considered was also representative of small diameter roots present in other plant species at 1:1 scale, making the analytical model also applicable to crop-lodging problems and for defining input parameters for analyses of nature-based solutions (NBS) using vegetation (e.g. for slope stabilisation).

Prediction of the End-Bearing Capacity of Axially Loaded Piles in Saturated and Unsaturated Soils Based on the Stress Characteristics Method

This study proposed an analytical approach for predicting the end-bearing capacity of driven piles that are subjected to axial loads in saturated and unsaturated soils. This is a generalized approach in which the stress characteristic method is employed successfully for both saturated and unsaturated soils. An iterative technique computer code was developed for the proposed analytical approach extending the finite difference method to develop solutions with the aid of MATLAB (version 2019a) that provides graphical output to visualize the results. The results from the proposed approach were compared against measurements for 13 pile load tests that include 11 in saturated soils and 2 in unsaturated soils, with good agreement. In addition, numerical analyses were performed using ABAQUS (version 6.14) to simulate the driven pile penetration and pile loading by employing the arbitrary Lagrangian–Eulerian adaptive mesh methods. The comparisons between the numerical predictions and measurements from a published model pile test suggested that the ultimate bearing capacity is well predicted by the finite-element model in comparison to the proposed analytical method. However, the proposed analytical method was simple for use in engineering practice applications to estimate the end-bearing capacity of pile foundations in both saturated and unsaturated soils.

Applicability analyses on the end-bearing capacity of gravity installed anchors in clay

As an efficient solution for deepwater moorings, gravity installed anchors (GIAs) have many attractive attributes and play a remarkable role in various deepwater applications. The end-bearing capacity factor offers an efficient method to evaluate GIA end bearing under complex conditions involving multiple factors. It can also assess total anchor bearing capacity. Based on numerous large deformation finite element (LDFE) analyses, two formulas have been developed to calculate the end-bearing capacity factors for GIAs in clay under quasi-static or dynamic conditions. Through rigorous statistical analysis, it is demonstrated that the formulas provide accurate predictions of the end-bearing capacity for various GIAs, particularly those with loading characteristics similar to OMNI-Max anchors, i.e., the padeye location and the loading angle. The contribution of the end bearing to the overall bearing capacity of GIAs is analyzed under various loading conditions. Furthermore, a comparative study proves that the formula accounting for the loading rate effect can be degenerated to evaluate the end-bearing capacity factor of the anchors under quasi-static conditions. The results provide a comprehensive understanding of the end bearing and offer an efficient solution for determining the total bearing capacity of various GIAs in clay under complex conditions. These findings contribute to the advancement of design and performance assessment of GIAs, enhancing their reliability and effectiveness in applications.

Two-dimensional Analysis of the Group Interaction Effects Between End-bearing Piles Embedded in a Rock Mass

This research is a two-dimensional analysis of the interaction effect in a group of piles socketed in a rock mass when studying the end-bearing capacity of the group. This problem was extensively studied for deep foundations in soils, but very little is published about foundations in rock. The study was conducted in 2D to establish the basis and criteria to analyze the problem, as well as understand the main factors and failure mechanisms involved when several piles work together in a foundation. The factors included in the analysis are, among others: the parameters of the rock mass, the pile embedment, and the pile separation. The research highlights shaft resistance as one of the key factors in the interaction. It proves that neglecting shaft resistance changes the interaction influence and the failure mechanism which may not be on the safe side. The research includes an analysis of the failure modes of different pile configurations using the discontinuity layout optimization (DLO) method, by taking advantage of the method’s ability to show the wedge configuration at the failure. The minimum and maximum efficiencies are characterized in terms of the pile separation values, thereby proposing a procedure to obtain the absolute minimum efficiency of the group. A second procedure is also presented for the approximate prediction of the bearing capacity of the pile tip, for a group with a particular number of piles and properties, by considering the contribution of the corner piles and the intermediate piles.

Discussion on pile axial load test methods and their applicability in cold regions

The measurement of pile axial load is of great significance to determining pile foundation design parameters such as skin friction and end bearing capacity and analyzing load transfer mechanisms. Affected by the temperature and ice content of frozen ground, the interface contact relationship between pile foundation and frozen soil is complicated, making pile axial load measurements more uncertain than that in non-frozen ground. Therefore, it is necessary to gain an in-depth understanding of the current pile axial load test methods. Four methods are systematically reviewed: vibrating wire sensors, strain gauges, sliding micrometers, and optical fiber strain sensors. At the same time, the applicability of the four test methods in frozen soil regions is discussed in detail. The first two methods are mature and commonly used. The sliding micrometer is only suitable for short-term measurement. While the Fiber Bragg grating (FBG) strain gauge meets the monitoring requirements, the Brillouin optical time-domain reflectometer (BOTDR) needs further verification. This paper aims to provide a technical reference for selecting and applying different methods in the pile axial load test for the stability study and bearing capacity assessment of pile foundations in cold regions.

End bearing capacity of a single incompletely end-supported pile based on the rigid plastic finite element method with non-linear strength property against confining stress

An Incompletely End Supported Pile (IESP) is a pile in a soft soil layer underlain by a hard soil layer that does not reach the bottom hard layer in practice. This study estimates the end bearing capacity of IESP by using an inhouse Rigid Plastic FEM code (RPFEM), considering shear strength non-linearity of soil against confining pressure, and soil-foundation interaction. The effect of the distance between the pile tip and the bottom hard soil layer (d/B) on the end-bearing capacity of IESP was mainly investigated for three types of soil: cohesive soils, cohesionless soils and intermediate soils. Also, theratio (r) of the end bearing capacity of the pile when it reaches the bottom hard layer to that of the pile when the bottom layer has no influence was was considered. By considering the shear strength non-linearity, the end bearing capacity was accurately estimated. The estimations were consistent with previous analytical, experimental and numerical solutions. It is found that the end bearing capacity inversely decreases with the distance d/B and becomes constant around d/B = 3. Based on the results, a formula for estimating the end bearing capacity of IESP is proposed. Comparisons with methods in existing literature confirmed the reliability of the proposed equation.

A Machine Learning-Based Method for Predicting End-Bearing Capacity of Rock-Socketed Shafts

A Machine Learning-Based Method for Predicting End-Bearing Capacity of Rock-Socketed Shafts

A Three-Dimensional (3D) Semi-analytical Solution for the Ultimate End-Bearing Capacity of Rock-Socketed Shafts

A Three-Dimensional (3D) Semi-analytical Solution for the Ultimate End-Bearing Capacity of Rock-Socketed Shafts

The pullout capacity of OMNI-Max anchors in clay

Being an impressive representative of gravity installed anchors (GIAs), the OMNI-Max anchor has many attractive attributes and becomes more and more a conspicuous role in recent deepwater applications. However, the pullout capacity property of OMNI-Max anchors has not been well understood due to their three-dimensional structure and the loading way in variational seabed conditions. Full knowledge of the pullout capacity property is beneficial to understand not only the working performance but also the comprehensive kinematic behaviors of OMNI-Max anchors in the seabed. The present work aims to investigate the complicated pullout capacity property of OMNI-Max anchors in clay under multiple factors, including the anchor embedment depth, the anchor orientation, the bearing area, the loading angle, and the soil strength. Large deformation finite element analyses are performed using the coupled Eulerian-Lagrangian (CEL) technique. Numerous cases of multiple factors are designed and analyzed to acquire the effects of different influential parameters. An explicit expression of the end-bearing capacity factor of OMNI-Max anchors is finally formulated in terms of multiple factors, whose effectiveness and applicability are validated by orthogonal tests and available published data. This expression can be simply utilized to evaluate the pullout capacity of OMNI-Max anchors under complicated conditions.

Influence of helix bending deflection on the load transfer mechanism of screw piles in sand: Experimental and numerical investigations

This study investigates the load transfer mechanism that includes the effect of helix bending deflection on end-bearing capacity, distribution of ground pressure under the helix and soil deformation around the screw pile. The helix to shaft diameter ratio of 2.5 and 2.8 with a strong helix and a weak helix were used. The model ground was prepared with fine sand at 80% of relative density. To investigate the load transfer mechanism, the experimental tests were modelled in a 3D finite element code. A good agreement between the experimental and numerical approaches was found. The numerical analyses showed that large influence zone exists under screw pile with strong helix, which resulted in higher mobilized soil shear strength that contributed to higher end-bearing capacity. In the case of strong helix, uniform pattern of pressure distribution was observed under the central shaft and the helix. Similar pattern of pressure distribution under the central shaft was observed in weak helix case but the pattern of pressure distribution under the helix changed from uniform to triangular to trapezoidal at various stages during the load test. The normalized end-bearing capacity decreased linearly with the increase in normalized helix bending deflection in both approaches, i.e. experimental and numerical.

Liquefaction-induced settlement of the pile group under vertical and horizontal ground motions

End-bearing piles have been widely used to resist earthquake-induced settlement of buildings in sand deposits. However, the earthquake can generate the excess water pressure in saturated sand deposits and thus reduce both the friction resistance and end-bearing capacity of piles, further resulting in the pile settlement which may not be sustained by the superstructure. In this study, a fully coupled dynamic effective-stress finite element procedure is used to investigate the effects of the frequency content of input motion and the amplitude of both horizontal and vertical components of input motion on the settlement of the pile group in saturated sand deposits. A modified generalized plasticity model is employed to characterize the dynamic behavior of various density of sands. The effect of the soil permeability on the seismic response of the pile-soil system is investigated. The results indicate that the relatively distant earthquake cause more severe liquefaction at the sand deposit than the nearby earthquake and thus induces more settlement of the pile group under otherwise identical conditions. Moreover, the vertical ground motion could significantly increase the coseismic liquefaction-induced settlement of the pile group (ρE) and should be taken into account in engineering design. A simplified practical method based on the load-transfer methodology is proposed to estimate the ρE for the pile group with the cap above the ground.

Cavity Expansion–Contraction-Based Method for Tunnel–Soil–Pile Interaction in a Unified Clay and Sand Model: Drained Analysis

This paper proposes an analytical method based on drained solutions of cavity expansion and contraction in a unified clay and sand model to investigate tunnel–soil–pile interactions. Cavity expansion analyses are used to evaluate the effects of pile installation on ground stresses and to determine pile end-bearing capacity and the distribution of shaft friction. Cavity contraction methods were adopted to replicate the tunnel convergence–confinement response using the singularity and image method for ground loss and ovalization of a shallow tunnel in a semi-infinite medium. A 2D model was developed that evaluates changes in mean stress and specific volume during pile installation and tunnel excavation. Outcomes from the developed analytical approach are compared against data from centrifuge tests in silica sand; results demonstrate that trends in pile load capacity degradation, mobilized safety factor, and tunneling-induced pile settlement can be satisfactorily predicted for the case of a tunnel excavated beneath a pile with a constant service load. Criteria based on pile capacity, safety factor, and settlement are proposed that can be used to determine a critical tunnel volume loss or evaluate pile safety level. The paper contributes to the understanding of tunnel–soil–structure interaction mechanisms and provides an efficient means of conducting a preliminary risk assessment of tunnel–pile interaction.

End Bearing Capacity Factor for Annular Foundations Embedded in Clay Considering the Effect of the Adhesion Factor

New limit analysis solutions for the end bearing capacity of annular foundations in clay with linearly increasing shear strength are presented in the paper. The strength profile of clay corresponds to a typical case of a normally consolidated clay in deep water, where the strength at the ground surface is defined as zero and increases linearly with the depth. The annular foundation has internal and external radii and is embedded in clay, where the adhesion factor representing the strength at the soil-structure interface is also taken into account. Using the lower and upper bound finite element limit analysis, the end bearing capacity factor of this problem can be obtained based on three considered dimensionless parameters, which are the ratio between the internal radius and the external radius, the embedded depth ratio, and the adhesion factor. The collapse mechanisms of annular foundations in clay are also examined and discussed in the paper to portray the effects of the radius ratio, the depth ratio, and the adhesion factor.