Full-scale Pile Load Tests Research Articles

Capacity prediction and design optimization for laterally loaded monopiles in sandy soil using hybrid neural network and sequential quadratic programming

Data driven methods have gained momentum in recent years in solving highly non-linear engineering problems that are challenging to solve using conventional methods. In this paper, we present a hybrid neural network model to predict the lateral response of large-diameter monopiles in multi-layered soil. The hybrid neural network consists of a mixture of convolutional and fully-connected layers, which capture the impacts of the soil profile, the pile geometry, and loading conditions on the lateral load response of monopiles. To train the neural network model, we produced data from high-fidelity three-dimensional (3D) finite element (FE) models that are validated against full-scale pile load tests. To ensure consistent model performance across the entire range of pile capacities considered in the dataset (ranging from approximately 100 kN to 100,000 kN), we utilize the relative error (percentage error) as the criterion for training the model. To achieve this goal, we explored six different combinations of data transformation methods (i.e., natural logarithm and root transformations) and cost functions. Among these models, the model trained with Mean Squared Error (MSE) using natural logarithm transformation yielded the most accurate and consistent predictions of the lateral capacities of monopiles. To demonstrate the strengths of the developed neural network model, it was used as a surrogate model to perform pile design optimization using sequential quadratic programming. In addition, a design example is provided to show how the developed method can be easily implemented.

Experimental Investigation of Helical Pile Performance for Loess Deposits Improvement

Collapsible loess is classified as problematic soil found on most continents. The loess immediately collapses under stresses induced by axial compressive loading or the soil weight when exposed to moisture. In Iran, vast areas of the Golestan province are covered with Aeolian loess deposits. This paper investigates whether the simultaneous effect of inundation and pre-loading in helical pile installation is operative and effective in improving Golestan loess. The effect of installation conditions on loess collapsibility is studied via two main approaches, i.e., field investigations and physical modeling. The experimental studies include the installation of ten single and triple helix piles in the Amirkabir University of Technology Frustum Confining Vessel, i.e., FCV-AUT. Also, ten single and double helix piles with embedment depth of 3 to 6 m and a helix diameter of 250 mm were installed in Golestan province, and full-scale pile static loading tests were performed. The results indicated that the simultaneous application of crowd loading and water pressure during the installation of helical piles results in collapsibility potential reduction due to the soil treatment. Moreover, high or low crowd loads accompanied by water pressure during pile installation bring about similar load-displacement behavior of model piles installed in FCV-AUT and full-scale helical piles. Eventually, it was illustrated that the applied improvement technique is effective on loess soils since it uses the least amount of material, machinery, and equipment while attaining the highest possible bearing capacity ratio regarding sustainability.

Contribution of the standard penetration test SPT to the design of pile foundations in sand– Practical recommendations

The objective of this article is to present original research work results on the contribution of the standard penetration test (SPT) to the design and analysis of pile foundations on the basis of the interpretation of a database of full-scale pile loading tests undertaken in sandy soils, with the aim to provide practical recommendations to the designers. The article encompasses three parts, the first one presents a detailed comparative study of 10 currently used methods of design on the basis of the SPT, assessed according to their predictive capability of the axial bearing capacity, within a database consisting of 46 axial pile loading tests carried out in 27 sites in the United Arab Emirates. The second part presents some experimental findings related to the critical (or creep) vertical load, whereas the third part highlights the concept of the reference pile settlement and its application to the limit state design of pile foundations.

Investigation of the factors affecting the ultimate bearing capacity of bridge piles in limestone with a calibrated 3D FEM

In this study, we investigated the behavior of a pile constructed on limestone rock under axial loading using a numerical approach. A parametric study was performed based on the full-scale pile load test results and the geotechnical reports on the site. Different values of unconfined compressive strength were implemented to investigate the pile’s behavior in relation to skin friction resistance only and the combination of end bearing and skin friction resistance. Additionally, we studied the effects of the length/diameter ratio on the pile’s capacity using nine pile load models. Numerical analysis showed that, in the initial loading stage, the applied load was transferred by skin friction only, until a certain displacement value, after which end bearing resistance shared the transferred load with skin friction resistance. Furthermore, there was a strong correlation between the load values measured using the finite element method and the values predicted from other methods used in the literature.

Field study on axial behavior of instrumented post-grouted steel pipe micropiles in tropical lateritic soil

This paper presents a field study on the axial behavior of new configuration of steel pipe micropiles in tropical lateritic soil. The micropiles were installed following a two-step grouting process with high injection pressures at a new experimental site located at the University of Campinas (Unicamp). The main innovation of the micropiles relies on the use of high-strength steel pipes as a drilling tool, casing protection, structural component and injection device. Full-scale pile loading tests were performed under compression and tension loads to investigate the axial behavior of the micropiles. The micropiles were instrumented along the shaft with electrical extensometers, and they were monitored during the progress of the loading tests. The load–movement responses, elastic moduli, axial load transfer mechanism, and unit bond stress relating to the micropiles and their interactions with the tropical soil were measured and evaluated. The bearing capacity of the post-grouted micropiles was considerably improved by the proposed post-grouting technique. The ultimate load capacity of the grouted steel pipe micropile under a compression load is approximately the same under a tension load. The average ultimate bond strength was 99 kPa and 100 kPa for the micropile under compression and tension, respectively. The distribution of unit bond stress along the shaft of the micropile under compressive and tensile load presented a post-peak softening behavior. The average ultimate grout-to-ground strength at the soil–micropile interface was 2.4 and 1.7 times greater than other nongrouted and non-injected piles installed in the same soil conditions at Unicamp.

Bearing capacity assessment of bored piles equipped with expander body systems using the mechanics of unsaturated soils

Bearing capacity of single piles are occasionally predicted using the renowned theoretical methods (α and β methods). These methods are based on laboratory tests, which can be time-consuming, but also applicable in foundation engineering practice for unsaturated soils. Full-scale pile load tests were carried out on bored piles equipped with Expander Body Systems in the Federal District of Brazil, known for its unsaturated, collapsible and porous soil. This paper has the aim to assess the applicability of the β method, considering the contribution of soil matric suction, in order to estimate the bearing capacity of these piles subjected to uplift and compression loads in unsaturated soils. Based on the experimental results, it is indicated that the use of the β method considering the matric suction, can be a useful tool for bearing capacity estimation of bored piles equipped with Expander Body Systems in unsaturated soils.

Experimental and theoretical studies of laterally loaded single piles in slopes

In this study, a series of small-scale laboratory model tests and numerical simulations was performed to investigate the lateral behavior of a single pile embedded in slopes and in horizontal ground. In the model tests, small-scale model piles were fitted with strain gauges around their surface at various depths, while the lateral deflections at the pile head were measured by dial gauges. A total of four sets of model pile tests was conducted with piles installed in model slopes of 0°, 30°, 45°, and 60°. The changes in pile head deflections and their bending moments with changes in pile location and the embedded length of the piles were analyzed by the finite element method (FEM). Subsequently, a new p-y curve (p denotes the soil resistance and y denotes the pile deflection) for a steep clay slope was developed based on those finite element analysis results, taking into account the influences of the declination of the slope and the position of the pile in the slope. The numerical results agree very well with those from a scale model pile load test and other full-scale pile load tests reported in the literature.

Full-Scale Well Instrumented Large Diameter Bored Pile Load Test in Multi Layered Soil: A Case Study of Damietta Port New Grain Silos Project

A Large diameter bored pile with diameter of 1.00 m and length of 34.00 m has been implemented in multi layered soil. The pile was tested under three axially loading and unloading cycles, in order to determine the load settlement curve and assess the ultimate pile capacity. Extensive investigation was carried out to obtain reliable soil properties at the examined pile location, through in situ and laboratory soil tests. Twelve strain gauges were fixed on pile steel reinforcement bars at top of each soil layer level. Moreover, four dial gauges were set up at pile head. Also, three telltales were extended to three different levels inside the pile. The pile load test field measurements are presented in the form of load settlement and load distribution curves for different loading steps. In addition, the pile ultimate capacity is calculated using different codes criterions and compared with the loading test results. Large diameter bored pile, Settlement, Pile load distribution, Pile installation, Instrumentation, Full scale pile load test, Pile behavior.

ANN-based empirical modelling of pile behaviour under static compressive loading

Artificial neural networks have been widely used over the past two decades to successfully develop empirical models for a variety of geotechnical problems. In this paper, an empirical model based on the product-unit neural network (PUNN) is developed to predict the load-deformation behaviour of piles based SPT values of the supporting soil. Other parameters used as inputs include particle grading, pile geometry, method of installation as well as the elastic modulus of the pile material. The model is trained using full-scale pile loading tests data retrieved from FHWA deep foundations database. From the results obtained, it is observed that the proposed model gives a better simulation of pile load-deformation curves compared to the Fleming’s hyperbolic model and t-z approach.

Analysis of rock-socketed piles loaded in axial compression in Mumbai region based on load transfer characteristics

Existing methods consider the intact rock properties for the analysis of rock-socketed piles. In the present analysis, a new method is proposed incorporating rock mechanics principles to study the load-settlement response of rock-socketed piles of Mumbai region using load transfer technique. As a rock-socketed pile is supported by the rock mass, it would be more realistic to consider rock mass properties in lieu of intact rock properties. The database of sixty cases depicting response of varying pile diameters is analysed and presented in this paper. Further, a full-scale pile load test case conducted in Mumbai region using O-Cell technology is analysed to study the performance of the proposed model. The method is capable of separating the contribution of skin friction from the weathered stratum and socket material and the point resistance.

Study on pile ultimate capacity criteria and CPT-based direct methods

Due to the variety of current Cone Penetration Test (CPT)-based methods of estimating the pile bearing capacity, for optimum design, it is necessary to evaluate the performance of such methods in various geotechnical conditions. Geotechnical databases including piling and in situ testing records have been recognised as useful tools for analysis, design and economical construction. In order to evaluate current CPT-based pile bearing capacity methods, AUT-CPT and Pile database has been compiled including 450 full scale pile load tests and CPT sounding records. This database consists of different pile types with a relatively wide range of geometries and various soil conditions. Forty-three records of piles driven in sand deposits were then employed to evaluate effects of ultimate capacity interpretation criteria from load displacement diagrams. The Brinch Hansen 80% criterion and the load at the displacement of 10% of the pile diameter were compared to estimated capacities from 10 CPT-based design methods currently used in practice. The Brinch Hansen 80% criterion and the load at the displacement of 10% of the pile diameter lead to reasonable results, the Brinch Hansen 80% criterion showed less scatter. For evaluating the accuracy and the precision of CPT-based methods, the results were compared to estimated capacities. Methods with the best performance are introduced. Generally, comparisons indicate that the CPT-based methods mainly predict the pile capacity with reasonable accuracy.

New Simple Approach to Prediction of Axial Settlement of Single Piles under Design Load

AbstractPiles have been used to transfer superstructure (bridges, buildings, etc.) loads to deeper competent bearing strata to minimize settlements. Accurate predictions of design settlements of vertically loaded piles under working load are a critical issue in the design of pile foundations. Numerous comprehensive trials, built on a regression-based predictive formula that produces the axial settlement using elastic shortening as the input variable, were performed in this study, and a simple relationship was established between the elastic shortening of piles and the measured design settlements of 93 full-scale pile load tests installed in variable bearing materials. The calculated axial settlements of piles from the proposed method in this study were compared to the measured axial settlements of the piles. Accuracy and validity of the proposed method were verified through conventional statistical analysis in terms of mean of bias (λm) and coefficient of variation (μ). The proposed method yielded values ...

Evaluating pile installation and subsequent thixotropic and consolidation effects on setup by numerical simulation for full-scale pile load tests

During pile installation, stresses and void ratios in the surrounding soils change significantly, creating large displacements, large strains, soil disturbance, and development of excess pore-water pressures. The surrounding disturbed soil tends to regain its strength with time due to both consolidation and thixotropic effects. In this paper, the pile installation process and subsequent consolidation, thixotropy, and load tests conducted at different times after end of driving (EOD) were modeled for test piles at the Bayou Laccassine Bridge site, Louisiana. In the finite element (FE) model, the pile was considered as an elastic material and the anisotropic modified Cam-clay model (AMCCM) was used to describe the behavior of the surrounding clayey soils. Pile installation was modeled by applying prescribed radial and vertical displacements on the nodes at the soil–pile interface (volumetric cavity expansion), followed by vertical deformation to activate the soil–pile interface friction and simulate static load tests. The thixotropic effect was incorporated by applying a time-dependent reduction parameter, β, which affects both interface friction and material properties. Results from the FE numerical simulation include the development of excess pore-water pressure during pile installation and its dissipation with time, the increase in effective lateral stress at the pile–soil interface, changes in stress state of the surrounding soil, and setup attributed to both the soil consolidation and thixotropy at different times. FE results are compared with measured values obtained from full-scale instrumented pile load tests, which show good agreement between measured and FE-predicted results.

3M Analytical Method: Evaluation of Shaft Friction of Bored Piles in Sands

AbstractThis study presents 3M, an analytical method to estimate the skin friction of bored piles in sands. It is based on the fundamental mechanic behavior of sands and keeps track of the major mechanisms occurring in the soil close to the pile during loading. These include the development of a shear band, its potential expansion as induced by soil dilatancy, and the ensuing increment of horizontal stresses owing to the restraining effect of surrounding soils. The resulting analytical equations are easy to apply and insert in a worksheet. The procedure to evaluate the shear band expansion is calibrated against results of direct shear tests at constant normal load, whereas the increment of horizontal stresses is evaluated by the closed-form solution for the expansion of a cylindrical cavity into a dilatant elastic–perfectly plastic medium. The effectiveness of the 3M method in predicting shaft friction has been checked against numerical results, centrifuge, and full scale pile load tests. Nevertheless, pr...

Field and Theoretical Study of the Response of Super-Long Bored Pile Subjected to Compressive Load

In this article, two full-scale pile loading tests were conducted to observe the field performance of the super-long bored piles, and a simplified approach for nonlinear analysis of the load-displacement behavior of a single pile was presented. The field tests on piles indicates that, under the maximum test load, more than 70% of the pile top settlement is caused by the compression of pile shaft. For practical purposes, the pile top settlement can be reduced through improving the pile shaft strength. When the load reaches the maximum test load, the proportion of the load carried by the pile tip is approximately 30%. The super-long pile is functioning as an end-bearing friction pile. The skin friction at shallow depth is fully mobilized and decreases from a peak value with increasing load. However, the skin friction of deeper soil is not fully developed due to less relative displacement. Furthermore, a BoxLucas1 model is used to capture the relationship between unit skin friction and pile-soil relative displacement, whereas a hyperbolic model is used to describe the relationship between toe stress and pile base displacement. Based on the BoxLucas1 model and the hyperbolic model, a load transfer method is used to clarify the response of a single pile, and a computational flow chart is developed. The efficiency and accuracy of the present method is verified using the field tests on piles. The proposed simple analytical approach is economical and efficient, resulting in savings in time and cost.

Load–settlement modeling of axially loaded steel driven piles using CPT-based recurrent neural networks

The design of pile foundations requires good estimations of the pile load-carrying capacity and the settlement. Designs for bearing capacity and settlement have been traditionally carried out separately. However, soil resistance and settlement are influenced by each other, and thus, the design of pile foundations should consider the bearing capacity and the settlement together. This requires that the full load–settlement response of the piles be accurately predicted. However, it is well known that the actual load–settlement response of pile foundations can only be obtained through load tests carried out in-situ, which are expensive and time-consuming. In this technical note, recurrent neural networks (RNNs) were used to develop a prediction model that can resemble the load–settlement response of steel driven piles subjected to axial loading. The developed RNN model was calibrated and validated using several in-situ full-scale pile load tests, as well as cone penetration test (CPT) data. The results indicate that the developed RNN model has the ability to reliably predict the load–settlement response of axially loaded steel driven piles, and thus, can be used by geotechnical engineers for routine design practice.

Closure to “Pile Setup in Cohesive Soil. I: Experimental Investigation” by Kam W. Ng, Matthew Roling, Sherif S. AbdelSalam, Muhannad T. Suleiman, and Sri Sritharan

Closure to “Pile Setup in Cohesive Soil. I: Experimental Investigation” by Kam W. Ng, Matthew Roling, Sherif S. AbdelSalam, Muhannad T. Suleiman, and Sri Sritharan

Axial compressive capacity of helical piles from field tests and numerical study

The compressive capacity of helical piles in sand and clay is investigated by means of field testing and numerical modeling. The numerical models are conducted using the computer program ABAQUS and are calibrated and verified using full-scale load testing data. The calibration was accomplished by using reasonable assumptions regarding soil–pile interaction and soil parameters reported from the literature. The model was verified by comparing its predictions with observed load–displacement curves obtained from full-scale pile load tests. The verified numerical model was used to perform a parametric study considering different pile configurations and soil parameters to evaluate the compressive capacity and load-transfer mechanism of helical piles. The compressive capacity obtained from the numerical models is compared with that obtained from existing theoretical methods for calculating the capacity. It is found that the predictions of theoretical equations for piles in cohesionless soil vary largely depending on the choice of bearing capacity factors and proper failure criteria. The interaction of closely spaced helices on the capacity of a helical pile is also evaluated. A bearing capacity reduction factor, R, and helix efficiency factor, EH, are proposed to evaluate the compressive capacity of helical piles in cohesionless soil considering an industry-acceptable ultimate load criterion corresponding to settlement equal to 5% of helix diameter, D.

Load–Settlement Modeling of Axially Loaded Drilled Shafts Using CPT-Based Recurrent Neural Networks

AbstractThe design of pile foundations requires good estimation of the pile load-carrying capacity and settlement. Design for bearing capacity and design for settlement have been traditionally carried out separately. However, soil resistance and settlement are influenced by each other, and the design of pile foundations should thus consider the bearing capacity and settlement inseparably. This requires the full load–settlement response of piles to be well predicted. However, it is well known that the actual load–settlement response of pile foundations can be obtained only by load tests carried out in situ, which are expensive and time-consuming. In this paper, recurrent neural networks (RNNs) were used to develop a prediction model that can resemble the full load–settlement response of drilled shafts (bored piles) subjected to axial loading. The developed RNN model was calibrated and validated using several in situ full-scale pile load tests, as well as cone penetration test (CPT) data. The results indica...

Three-dimensional analyses of concrete piles in clayey soils

The behaviour of solid circular concrete piles in clayey soils under a combination of lateral and vertical loading was investigated by numerical analysis. Piles with different lengths were considered, and ultimate lateral bearing capacity was calculated. The model was verified on the basis of data obtained from a previously published full-scale pile load test. The effect of axial loading on the ultimate lateral bearing capacity has been previously investigated in only a few studies. In this paper, particular attention was devoted to the influence of axial loading on lateral bearing capacity. In addition, a comparison between Flac three-dimensional results and both Allpile and Broms approaches was performed.