Pile Load Test Results Research Articles

Prediction of Pile Axial Bearing Capacity Using Artificial Neural Network and Random Forest

Axial bearing capacity of piles is the most important parameter in pile foundation design. In this paper, artificial neural network (ANN) and random forest (RF) algorithms were utilized to predict the ultimate axial bearing capacity of driven piles. An unprecedented database containing 2314 driven pile static load test reports were gathered, including the pile diameter, length of pile segments, natural ground elevation, pile top elevation, guide pile segment stop driving elevation, pile tip elevation, average standard penetration test (SPT) value along the embedded length of pile, and average SPT blow counts at the tip of pile as input variables, whereas the ultimate load on pile top was considered as output variable. The dataset was divided into the training (70%) and testing (30%) parts for the construction and validation phases, respectively. Various error criteria, namely mean absolute error (MAE), root mean squared error (RMSE), and the coefficient of determination (R2) were used to evaluate the performance of RF and ANN algorithms. In addition, the predicted results of pile load tests were compared with five empirical equations derived from the literature and with classical multi-variable regression. The results showed that RF outperformed ANN and other methods. Sensitivity analysis was conducted to reveal that the average SPT value and pile tip elevation were the most important factors in predicting the axial bearing capacity of piles.

Back analysis of tensile test drilled shafts and barrettes

ABSTRACT This paper presents a method to interpret the tensile test results for a concrete pile when the concrete is stressed beyond its tensile limit, which results in anomalies in the strain gage data that is collected during active load testing. Two drilled shafts and two barrettes are studied using the proposed method. Any pile loads that are computed using strain data and which are greater than the specific applied load are discarded because these results are physically impossible. A Spline function is then used to fit the remaining valid data for pile load along the depth. Using the fitted Spline function and assuming that the behavior at the pile/soil interface can be modeled as a hyperbolic model, a back-analysis method is used to determine the parameters for the model. The software, SHAFT is used to compare the results for the back analysis and the measured gage data. It is found that the back-analysis method that is used in this study gives a reasonable interpretation of the pile loading test results, such as the t-z curves, using the pile force and a depth fitting function.

Nonlinear solutions for laterally loaded piles

A nonlinear analysis framework for laterally loaded piles is presented that is as accurate as equivalent three-dimensional nonlinear finite element analysis, but computationally one order of magnitude faster. The nonlinear behavior of sands and clays are account for by using hyperbolic modulus–reduction relationships. These nonlinear–elastic constitutive models are used to calculate the reduced modulus at different points in the soil based on the soil strains induced by lateral pile displacement. The reduced modulus at different points in the soil domain are spatially integrated to calculate the reduced soil resistance parameters associated with the differential equation governing the lateral pile displacement. The differential equations governing the lateral displacements of pile and soil under equilibrium are obtained by applying the principle of virtual work to a continuum-based pile–soil system. These coupled differential equations are solved using the one-dimensional finite difference method following an iterative algorithm. The accuracy of the analysis is verified against equivalent three-dimensional nonlinear finite element analysis, and the validity of the analysis in predicting the field response is checked by comparisons with multiple pile load test results. Parametric studies are performed to gain insights into the lateral pile response.

Experimental study on bearing behaviour of different uplift piles

Based on pile load test results of uplift bored piles for a deep-embedded underground transformer substation, the uplift behaviour of enlarged toe pile and shaft post-grouting bored piles have been studied. The loading transfer characteristics and uplift capacity improvement mechanism for the two different type uplift piles have been investigated. The research shows that post-grouting can significantly improve bored pile uplift bearing capacity. After pile shaft grouting, the interface condition between pile and soil is improved, the friction resistance of pile side is increased obviously, and the uplift bearing capacity is improved. For long uplift pile, the uplift resistance of shaft grouting bored pile is better than that of enlarged toe pile.

A new development of ANFIS–GMDH optimized by PSO to predict pile bearing capacity based on experimental datasets

Prediction of ultimate pile bearing capacity with the aid of field experimental results through artificial intelligence (AI) techniques is one of the most significant and complicated problem in pile analysis and design. The aim of this research is to develop a new AI predictive models for predicting pile bearing capacity. The first predictive model was developed based on the combination of adaptive neuro-fuzzy inference system (ANFIS) and group method of data handling (GMDH) structure optimized by particle swarm optimization (PSO) algorithm called as ANFIS–GMDH–PSO model; the second model introduced as fuzzy polynomial neural network type group method of data handling (FPNN–GMDH) model. A database consists of different piles property and soil characteristics, collected from literature including CPT and pile loading test results which applied for training and testing process of developed models. Also a common artificial neural network (ANN) model was applied as a reference model for comparing and verifying among hybrid developed models for prediction. The modelling results indicated that improved ANFIS–GMDH model achieved relatively higher performance compared to ANN and FPNN–GMDH models in terms of accuracy and reliability level based on standard statistical performance indices such as coefficient of correlation (R), mean square error, root mean square error and error standard deviation values.

Reliability-Based Calibration of Resistance Factors in LRFD Method for Driven Pile Foundations on Inshore Regions of Iran

This paper presents the improvement of load and resistance factor design (LRFD) method for axially loaded driven piles in Iran. The LRFD method has been well developed and successfully implemented in geotechnical engineering, especially in the design of pile foundations in different parts of the world. To extend the use of this method in Iran, it is necessary to use the results of reliable local pile load tests and construction records to calibrate LRFD resistance factors regionally. To this end, we first collected a comprehensive database of static and dynamic load tests which have been performed on driven piles in fine-grained soils across Iran. Based on this database, we calculated the resistance factors for different design methods using three different methods of reliability analysis (FORM, FOSM, and MCS) and for two levels of reliability (βT = 2.33 and 3). Finally, we used these calculations together with experience and engineering judgment to propose resistance factors for the National Building Code of Iran.

Time-lapsed shear-wave velocity (Vs) tomographic images and stress in sand surrounding displacement pile during setup

This study reports model pile tests designed to characterize the underlying mechanisms of driven pile setup in dry sand by means of stress measurement with the tactile pressure sensors and spatio-temporal, shear-wave velocity (Vs) distributions using an automated high-speed tomographic imaging system. The pile-load test results demonstrate a distinct increase in the pile shaft resistance after pile setup. The measured stress and Vs in the soil surrounding the pile suggest the increase in the radial effective stress during pile loading [Formula: see text], as a result of the aging-induced stiffness increase, is the dominant mechanism of pile setup. The spatio-temporal evolution of Vs distributions reveals that during initial aging (before pile installation), Vs is similar at any distance to the pile shaft and exhibits a similar aging rate S0 in terms of stiffness increases. After pile installation, the soil exhibits a higher aging rate S1. In addition, the ratio S1/S0 decreases with increasing distance from the pile shaft. A lower initial Vs and a higher aging rate S1 are also observed for the measurements at the three sensing layers of different depths, suggesting that more soils disturbed by pile installation tend to recover at a relative higher aging rate.

A review of piling industry practices in Dubai, UAE: proposed UCS-based correlations

There is limited published information available on design guidance and performance of deep pile foundations in Dubai, UAE. In response to this situation, the piling industry tends to be over-conservative when designing foundation systems for buildings and infrastructure. Consultants, pile testing experts and the Dubai Creative Clusters Authority decided to collaborate with a common goal: share information with the industry and make pile design recommendations to help colleagues prevent the large-scale over-engineering of pile foundations currently ongoing in the Emirate of Dubai. A total of over 200 pile load test results, from which 91 are preliminary pile load tests, were available to the authors to conduct the study presented in this paper. The interpretation of the available information combined with finite-element back-analyses enabled the authors to propose Dubai-specific relationships between the rock’s unconfined compressive strength and the pile’s ultimate skin friction resistance. Relationships between the rock’s unconfined compressive strength and its elastic modulus are also proposed.

Development of partial factor design method on bearing capacity of pile foundations for Japanese Specifications for Highway Bridges

ABSTRACTThis paper shows the development of a partial factor design method on the bearing capacity of pile foundations for Japanese Specifications for Highway Bridges. Firstly, estimation design equations on the bearing capacities of pile foundations are improved by analysis of pile load test results and uncertainties in the bearing capacities are evaluated. Secondly, the reliabilities of pile foundations designed by the former specifications are evaluated based on reliability analysis considering the uncertainties in the bearing capacities and coefficients of subgrade reaction. Finally, a partial factor design method is developed based on the target reliability index obtained based on the conventional pile installation method by the pile installation methods. The factors are different for each pile installation method.

A Method for Predicting Pile Capacity Using Cone Penetration Test Data

The massive construction in poor lands has encouraged engineers to use deep foundations in order to transfer superstructure loads to the subsoil. Since soil excavation, sampling, and laboratory testing as a part of site investigation are relatively difficult, in-situ tests such as cone penetration test (CPT) as a very informative test may be recommended. The CPT has been widely used in engineering as a part of site investigation, and its data has been used to determine the axial capacity of piles. In this paper, the prediction capability of three empirical widely famous old methods used to predict the axial pile capacity based on CPT data is evaluated by using field data obtained from direct field pile loading tests. In this evaluation, the direct pile load test results are used as measured data. Three popular famous statistical evaluation methods namely the best-fitted line, geometric mean, and geometric standard deviation have been used. The evaluation results indicate that generally although predicting methods based on CPT data have been widely used to determine the axial bearing capacity of piles, they need to be upgraded for the economic and relatively accurate design of piles. According to the statistical studies carried out in the current research, among three old empirical methods, although the Nottingham and Schmertmann Method (1975, 1978) (NSM) [7, 8] has the best agreement with test results, it is felt that the method needs to be upgraded. The modification of NSM has been done in the current paper using a comprehensive database.

Accuracy of pile capacity assessment on the basis of piling reports

Current assessment of foundation pile bearing capacity during driving may considerably improve operational reliability in terms of loads to be transferred. It also enables proper design and trial examinations by focusing attention on piles with atypical driving characteristics. The paper presents the method applicable to assess the bearing capacity of prefabricated driven piles and provides analysis of likelihood of this assessment by the example of numerous prefabricated piles documented by piling reports and results of static pile load tests to the extent allowing to determining the limit bearing capacity. The results attained could be the basis to determine respective safety factors in pile design based on driving resistance analysis.

Pile bearing analysis based upon ultimate values of toe and skin resistance as well as their mobilization with settlement

The main task of pile foundation is the reduction of settlement and ensure the safety of the building. These two factors are in strongly relationship. In practice pile load capacity is calculated based on ultimate resistances including factor of safety. The load-settlement relationship is non-linear, so it would can happen that despite the applied load (several times smaller than ultimate pile load capacity), the settlement exceeds the allowable value, and in consequently it might cause damage of the structure. In the paper the method of determining ultimate resistances and mobilization of these resistances with settlement was presented based on the static pile load test results. The proposed method can be applied in pile load capacity verification.

Pile load test of jacked open-ended prestressed high-strength concrete pipe pile in clay

The performance of open-ended piles can be different from that of closed piles due to the effect of soil plugging. This paper presents the results of a large-scale field pile load test conducted on an open-ended pile in clay under static compressive loads. A prestressed high-strength concrete pipe pile with an outer diameter of 400 mm and a wall thickness of 75 mm was instrumented with strain sensors and installed in a marine deposit for static load testing. The measured load-transfer data during pile installation and the pile load test results are reported and analysed. The data show that the pile was in a partially plugged condition during jacking and behaved in a fully plugged mode in the static load test. The measured ultimate shaft resistance and total resistance of the test pile were 659 and 1180 kN, respectively, which were smaller than the values calculated using a previously proposed method. The back-calculated α and β values (as used in the α and β methods) for axial pile capacity in marine deposits were 0·42 and 0·56, respectively.

Comparison of field loading test results of bored piles with bearing capacity analysis based on various standards

AbstractICA Construction (Ictas ‐ Astaldi JV) is the general contractor of the WHSD ring road project in St. Petersburg and Section 7 & 8 of M11 Motorway project, which will be the toll highway between St. Petersburg and Moscow. WHSD ring road that has been constructed by ICA Construction passes through nearshore and offshore areas on viaducts and there are also two cable stayed bridges on the alignment. As a part of M11 motorway project, several bridges have been constructed overpassing various rivers. Since, all these structures have deep foundation systems, several axial pile loading tests have been performed on both projects. Soil in the vicinity of St. Petersburg consists of soft to medium dense silty, partially sandy clay layers at top levels. These layers are followed by Cambrian aged hard clay layers. In Russian Federation and some Eastern European countries, bored pile design is based on SNIP norms. In norms like AASHTO or Eurocode, pile bearing capacity calculations consider both contribution of the tip resistance and skin friction. On the contrary, in SNIP norms contribution of the skin friction to pile bearing capacity is very limited. Therefore, piles are generally extended to deep bearing layers. For piles where large axial bearing capacities are required, base enlargement is applied. In this paper, axial pile bearing capacities in the scope of the above mentioned projects are calculated based on SNIP, AASHTO LRFD and Eurocode 7, respectively and the calculated values are compared with the pile bearing capacities obtained from field tests. Total number of axial pile load tests gives the possibility to make a statistical comparison. Results of axial pile load tests have revealed that especially the bearing capacities calculated in accordance with SNIP norms underestimates bearing capacities of bored piles erected in clayey soils.

Nonlinear Regression Analysis for Side Resistance of Socketed Piles in Rock Formations of Dubai Area

Pile capacity installed in Dubai rock formation is calculated based primarily on socket shaft resistance. During preliminary design, socket resistance is estimated by using correlations with rock strength that do not reflect the behavior of Dubai rock formations as well as construction practices. Consequently, large discrepancy is often noticed between predicted pile capacity and that determined from the results of pile load tests. In this study, a new predictive model is developed for socket shaft resistance of piles constructed in rock formations of Dubai area. Five (5) instrumented piles of different diameters and socket lengths ranging from 10 to 15 m are tested. The proposed model takes into account the compressive strength of the rock in addition to the pile movement at the top of socket to predict its side resistance. The average side resistance of the socket predicted using the proposed model compared well with the results of load transfer along the sockets of the test piles. In addition, the developed model is compared with published models from other regions to illustrate the area specific nature of correlations and factors that affect their generality are highlighted.

Bearing capacity and failure behaviors of floating stiffened deep cement mixing columns under axial load

This research aims to clarify and gain an insight into the impact of the length of the stiffened core and the strength of the deep cement mixing (DCM) socket on the behaviors of floating stiffened deep cement mixing (SDCM) columns. The observed behaviors include the axial ultimate bearing capacity, settlement and failure mode. The study begins by conducting a series of physical model tests as a preliminary investigation. The results reveal that the strength of the DCM socket can be reduced to a certain value by inserting a sufficiently long reinforced core to achieve the highest possible load-carrying capacity, indicating an optimum length of the stiffened core for a specific DCM socket strength. For a parametric study on the actual scale condition, full-scale load tests on a floating DCM and an SDCM column with eucalyptus wood as a core in the thick soft clay layer area were carried out to provide a reference case. The extended numerical analysis results suggest that the modes of failure depend on the length of the stiffened core and the strength of the DCM socket. The results from the numerical parametric study were used to establish a guideline chart for suggesting the appropriate length of the core in accordance with the strength of the DCM socket of the floating SDCM columns. The field pile load test results also confirm that core materials with a lower strength and stiffness, such as eucalyptus wood, could potentially be used as a reinforced core.

Simulation of bearing capacity of bored piles

This study focuses on how one can possibly predict the ultimate load for the piles that did not reach failure. This challenge was acquired through Chin- Konder method by which, the estimated settlement that correspond to failure load is well defined. Hence, this research aims to make a comparative study between the results of pile load tests carried out in Al-Basrah sewage treatment plant project, and those results induced from the numerical analysis in term of ultimate pile capacity. Consequently, it may give a clear idea on the ability of numerical simulation in getting close to the actual behavior of piles. In the current study, a numerical study using Plaxis 3D Foundation program has been performed on bored piles by the assistance of site investigations of soil. Mohr- Coulomb and linear elastic models were adopted in the simulation for soil and pile respectively. Ten bored piles were used in this analysis under different values of loading. The diameter and length of pile are 0.6m and 24m respectively. The test results indicate that, an excellent agreement has been found as a response of pile capacity between the field and numerical studies. Also, ideal load- settlement curves were created using Chin- Konder method to predict the failure load of bored piles. Also, the results have demonstrated that, the pile capacity obtained from the simulation process is larger about 51% than that design load estimated before the design of piles. This may present a priority to use the finite element method to be accounted as an effective approach in the primary analysis.

Study of pile behavior by improvement of confining soils using frustum confining vessel

A physical modeling apparatus made at Amirkabir University of Technology (FCV-AUT), called Frustum Con ning Vessel, is employed to determine the eff ects of soil improvement on piles performance. The FCV-AUT is capable of linearly modeling the existing overburden stresses in the eld. Three types of Babolsar sand with relative densities between 20% and 70% were examined in these tests. Results of compression and tensileload tests on seven piles, with the embedment length to diameter ratio (D/B) of 9, were used to evaluate the e ects of soil improvement methods of soil densi cation as well as postgrouting on the piles performance. The results show that the increased bearing capacity by soil compaction from loose to medium state is greater than that of the medium to dense state. This increase has been observed to be a function of pile construction methods and pile tip conditions. Also, tip and/or side post-grouting enhanced the performance of boredand concrete precast piles by increasing soil-pile interaction and its bearing capacity. The results of pile load tests carried out on the FCV-AUT have been observed to be well-aligned with the static bearing capacity calculations based on the API method.

Numerical Analysis of Small-Scale Model Pile in Unsaturated Clayey Soil

Pile load tests and numerical analysis of a small-scale model pile in unsaturated clayey soil are presented in this paper. A small-scale model pile was simulated to bear a static axial loading in unsaturated soil using finite element method. All parameters used in the finite element method were obtained in laboratory tests, including the direct shear test, interface direct shear test, and filter paper method. The numerical analysis results were compared with the pile load test results. The results show that the general trend of pile load and pile head settlement relationship obtained by the numerical analysis shows a good consistence with the pile load test results. With increasing water content of the soil, the matric suction, dilatancy angle and shear strength decrease, and consequently the ultimate bearing capacity of pile decreases.

Performance evaluation of nature-inspired algorithms for the design of bored pile foundation by artificial neural networks

The bored pile foundations are gaining popularity in construction industry because of ease in construction, low noise and vibrations. The load-carrying capacity of bored pile foundations is dependent upon soil–structure interaction. This being a three-dimensional problem is further complicated due to large variations in soil properties. Also, modeling of soil is difficult because of its nonlinear and anisotropic nature. For such cases, the artificial neural network (ANN) and nature-inspired optimization techniques have been found to be highly suitable to attain acceptable levels of accuracy. In the present study, two ANNs have been trained for determination of unit skin friction and unit end bearing capacity from soil properties. The training data for ANNs have been obtained from finite element analysis of pile foundations for 4809 different soil types. A dataset of 50 field pile loading test results is used to check the performance of the developed artificial neural networks. To enhance the accuracy of the developed ANNs, two correlation factors have been determined by applying four popular nature-inspired optimization algorithms: particle swarm optimization (PSO), fire flies, cuckoo search and bacterial foraging. In order to rank these optimization algorithms, parametric and nonparametric statistical analysis has been carried out. The results of optimization algorithms have been compared to find the most suitable solution for this multi-dimensional problem which has a large number of nonlinear equality constraints. The effectiveness and suitability of the nature-inspired algorithms for the presented problem have been demonstrated by computing correlation coefficients with field pile loading test results and then with the total execution time taken by each algorithm. The results of comparison show that PSO is the best performer for such constrained problems.