Pile Load Test Data Research Articles

Prediction of pile bearing capacity using support vector machine

This paper examines the potential of support vector machine (SVM) in prediction of bearing capacity of pile from pile load test data. In this study, SVM uses regression technique by introducing ε-insensitive loss function. The data from a pile load test has been used to build the SVM model. SVM uses penetration depth ratio (<i>l/d</i>), mean normal stress (σ_<i>m</i>), and no of blows (<i>n</i>) as input parameters. The output of SVM model is bearing capacity (<i>Q</i>) of pile. Sensitivity analysis of the develop SVM model shows that <i>l/d</i> has the most significant effect on <i>Q</i>. An equation has been also developed for the prediction of bearing capacity of pile. This study shows that SVM approach give an alternative tools to geotechnical engineers for the determination of bearing capacity of pile.

Calibrating Resistance Factors of Single Bored Piles Based on Incomplete Load Test Results

This paper addresses a problem often encountered in calibrating resistance factors for the ultimate capacities of piles based on load test databases. In practice, many pile load tests are not conducted to failure but only to a multiple (e.g., 2) of the design load. This leads to a difficult situation of incomplete information: for these test results, the ultimate bearing capacities of the test piles are unknown. How can these test results still be used to calibrate resistance factors of piles? A full probabilistic framework is proposed in this research to resolve this problem. A local pile test database of Taipei (Taiwan) is presented for demonstration. The analysis results show that the inclusion of the incomplete pile load test data enhances the stability of the calibrated resistance factors. For a target reliability index of 3, the calibrated resistance factor is in the range of 0.4–0.66 for two design models adopted in the current Taiwan design code. Moreover, it is found that the safety factor adopte...

Role of Linear Elasticity in Pile Group Analysis and Load Test Interpretation

This paper compares linear-elastic and nonlinear pile group analysis methods through settlement analyses of hypothetical scenarios and real case studies, and elaborates on the implications for interpretation of pile load test data. Comparisons between linear-elastic and nonlinear methods justify the proposition that pile-to-pile interaction is dominated by linear elasticity, characterized by the small-strain soil stiffness. As the size of a pile group increases, nonlinearity in individual pile behavior becomes overwhelmed by the interaction effects. In such cases, similar estimates will be achieved by both linear and nonlinear methods if the soil modulus is derived from the initial tangent, rather than some secant stiffness, assessed from the load test data. The study clarifies the capabilities and limitations of linear elasticity in pile group analysis and provides guidance on pile test interpretation for analysis of pile group response.

Reliability-Based Code Calibration for Axial Ultimate Bearing Capacities of Single Bored Piles in Taipei Basin

ABSTRACTIn Taipei, many pile proof load tests were not conducted to failures but only to a multiple (e.g., 2) of the design load. This leads a difficulty of incomplete information: For these test results, the ultimate bearing capacities of the test piles are unknown. This paper addresses the issue of calibrating resistance factors of piles for the axial ultimate bearing capacities based on the incomplete information from these tests. A simplified probabilistic method is proposed to resolve this issue. A local pile test database of Taipei is presented, and the analysis results show that the inclusion of the incomplete pile load test data helps in calibrating the resistance factors. Moreover, it is found that the calibrated resistance factors for the axial ultimate bearing capacities are consistent to the safety factors that are adopted in the current Taiwan design code. This paper also addresses another important issue for the pile design in Taipei: the end bearing capacity in the sandstone layer is very uncertain. A maximum likelihood method is taken to identify the best estimate for this end bearing capacity. The conclusion of this paper may be useful for reliability-based designs for the axial ultimate bearing capacities of single bored piles in the Taipei region.

Load Transfer Characteristics of Socketed Piles in Mumbai Region

This report uses load-transfer approach for analyzing the load-displacement response of piles socketed in weathered rocks typically found in Mumbai region. The field information used in the load-transfer analysis is obtained from conventional site investigations and does not necessitate elaborate tests. The load transfer behaviour of each stratum is expressed as a non-linear function. Empirical relations are used to express rock mass modulus and limiting values of unit side and base resistance in terms of unconfined compressive strength of intact socket material, which implicitly take into account the site-specific conditions. More than twenty pile load test data were back-analyzed before generalizing the governing parameters applicable to this region. This report demonstrates a wide range of applications of load transfer approach which includes the load-displacement behaviour and separation of elastic and net pile displacements.

Nonlinear Response of Single Piles in Sand Subjected to Lateral Loads using khmax Approach

This paper presents results of analysis of full-scale pile load test data of 14 piles embedded in either loose or medium dense sands. The analysis was performed using two methods, p–y curve approach and a more recently developed khmax approach. Comparison of the results obtained using both the methods is also presented. A step-by-step analysis procedure is presented for predicting lateral load deflection response of single piles in sand using the khmax approach. The results presented show that the khmax approach has promise over the p–y curve approach because of its simplicity and the fact that it provides upper- and lower-bound curves, which are valuable guides to making engineering decisions. For loose sands, a new range of khmax values is recommended to better predict the lateral load–deflection response of single piles.

Comparing CPT and pile base resistance in sand

The comprehensive database of load tests on closed-ended piles in sand has been re-examined to study the relationship between CPT resistance, qc, and ultimate base capacity, qb. The aim is to establish the origin of low reported values of qb/qc which contrast with continuum models that suggest qb = qc for steady deep penetration. Partial embedment of the pile tip into a hard layer underlying weak material has been accounted for by weighting qc. Partial mobilisation has been accounted for by defining failure according to a plunging criterion. When these two mechanisms are considered, the resulting values of qb/qc have a mean value of 0·90 and show no trend with pile diameter. The remaining slight underprediction of the ‘continuum’ model (qb = qc) could be attributed to the underestimation of plunging load in pile tests for which steady penetration is not reached. This exercise makes two contributions: first, it is suggested that any reduction of qc when estimating the end bearing capacity of closed-ended piles in sand should be linked to partial embedment and partial mobilisation, rather than absolute diameter; second, the dearth of high-quality pile load test data in the public domain is highlighted.

Comparing CPT and pile base resistance in sand

The comprehensive database of load tests on closed-ended piles in sand has been re-examined to study the relationship between CPT resistance, qc, and ultimate base capacity, qb. The aim is to establish the origin of low reported values of qb/qc which contrast with continuum models that suggest qb = qc for steady deep penetration. Partial embedment of the pile tip into a hard layer underlying weak material has been accounted for by weighting qc. Partial mobilisation has been accounted for by defining failure according to a plunging criterion. When these two mechanisms are considered, the resulting values of qb/qc have a mean value of 0·90 and show no trend with pile diameter. The remaining slight underprediction of the ‘continuum’ model (qb = qc) could be attributed to the underestimation of plunging load in pile tests for which steady penetration is not reached. This exercise makes two contributions: first, it is suggested that any reduction of qc when estimating the end bearing capacity of closed-ended piles in sand should be linked to partial embedment and partial mobilisation, rather than absolute diameter; second, the dearth of high-quality pile load test data in the public domain is highlighted.

Evaluating accuracy for two empirical methods in predicting settlement of drilled shafts

Several theoretical, empirical and semi-empirical methods are available in the literature to predict settlement of drilled shafts in sandy soils. In the Arabian Gulf countries, specifically in the United Arab Emirates, equations and procedure from the rest of the world are being used in analysis and design of drilled shafts without proper validation. It is the aim of this study to assess the applicability and evaluate the accuracy of two well known, and commonly used methods for pile prediction in the United Arab Emirates (UAE), namely Vesic (1977) and Poulos (1979), via comparison with data from field pile load tests conducted on shafts drilled in the region. Some of these tests were conducted for the purpose of this study, while others were made available through the courtesy of International Piling Contractors who are active in the region (e.g. Bauer International and Swiss Borings). Pile load test data were analyzed to back-calculate the model parameters related to settlement under different loading stages. Geological data and soil properties were obtained from studies conducted at the relevant sites. An effort is made to correlate soil properties with the prediction models. Statistical analysis is conducted to assess the accuracy of the results obtained from the two methods at different stages of loading via those obtained from pile load tests. Moreover, a detailed parametric study is conducted to assess the effect of the related parameters on the predicted pile settlement and the estimated settlement at different stages of loading. The study concluded with a recommendation of the most appropriate models and procedures to be followed for predicting the settlement of drilled shafts in the UAE, together with useful charts and correlation relations. Results showed that settlement values predicted by Vesic (1977) and Poulos (1979) overestimates the true values.

Performance of Axially Loaded Pipe Piles in Sand

This paper summarizes the parameters that influence the axial capacity of pipe piles driven into sands. The parameters that affect pile behavior are for convenience divided into four categories: (1) Soil characteristics; (2) pile characteristics; (3) method of pile installation; and (4) type of loading. When possible, the influence that these parameters have on the capacity is quantified. In addition, the paper describes supporting evidence from pile load test data, small‐scale laboratory tests, and in situ cone probings that has been used to justify limiting values for unit shaft and toe resistances. The use of limiting values has significant economic impact on long piles, especially those used for offshore applications. This information is, therefore, evaluated and critiqued to place the use of limiting values in proper perspective. The results of this paper are based on a synthesis of literature on (1) pile load test data on piles in sand, (2) data from cone penetrometer tests in sands, and (3) information on the stress‐strain and strength behavior of sand.

Elastic‐Creep Analysis of Laterally Loaded Piles

A simple one‐dimensional finite element procedure is used to analyze lateral piles in clayey soils. The analysis included a creep law for the soil based on a probabilistic model and allows for stress‐dependent creep. A field problem is analyzed taking into account the variation in the soil properties with depth. The numerical predictions are compared with field pile load test data and the creep deflections are found to increase nonlinearly with the applied loads. The depth variation of the soil properties is found to be important in the prediction of deflections of a pile‐soil system.

Role of Load Tests in Friction Pile Design

In situ measurements of stresses and pore pressures on a model pile shaft, the Piezo‐Lateral Stress (PLS) cell, are combined with theoretical analyses to reconstruct the conditions of a large‐scale pile load test at a site in Empire, LA. Results show that the mode of penetration of open‐ended piles has an important effect on the performance of pile shafts. Pile plugging during driving retards the rates of soil consolidation and the gain in shaft capacity after installation. The Empire experience is used to identify important factors affecting shaft‐soil interaction which require control and/or evaluation during pile load tests. Methods of enhancing the value of pile load test data in the future are recommended.

Pile Group Analysis: A Study of Two Methods

A brief outline is given of the basis of analysis used in two computer programs, PIGLET and DEFPIG, for analysis of pile group response. A comparison of the capabilities of each program is presented and then a parametric study is made of a six‐pile group to illustrate the similarities and differences between the two programs. Two series of field tests on groups of piles are then analysed by DEFPIG and PIGLET, and it is shown that the predictions from each are consistent and in generally good agreement with the field data. The comparisons suggest that each program may be used with confidence for practical problems, particularly in conjunction with single pile load test data.

A design approach for pile foundations in permafrost

A design philosophy for piles in ice and ice-rich permafrost is proposed, whereby the pile settlements over the design life of the structure are retained within acceptable limits.The secondary creep law for ice is reviewed and the relationships between secondary creep rate, stress, and temperature are obtained using existing creep test data from many different sources. An analysis is performed which relates the steady pile settlement rate to the pile shaft stress and the constant ground temperature.A review of the pile load test data available in the literature is carried out, and the results are compared with the theoretical predictions provided by the pile settlement analysis. Reasonable agreement is obtained between prediction and observation, and it is thought that the analysis presented here provides a conservative (safe) bound on the observed results.The analysis is extended to account for the compression of the pile shaft, varying ground temperature profiles, stress readjustment along the pile shaft, and the end bearing capacity of the pile.The analysis presented here provides a rational basis for pile design in permafrost and, in addition, explains many of the phenomena likely to be observed in the behavior of piles under sustained loading.

Settlement of Building on Pile Foundation in Sand

Displacement type compacted concrete piles (pressure-injected Franki type) were driven into the upper portion of a medium dense sand stratum for the foundation of a 19-story reinforced concrete building. Results of pile load tests and actual building settlements were recorded over a 2 yr. period. The settlement ranged from 1.6 in (4.0 cm) to 3.3 in. (8.4 cm), the average group settlement being approx. 2.5 in. (6.4 cm). These field measurements are compared with settlement predictions computed using: (1) classical elasticity theory which greatly overestimates the actual settlement of a single pile; (2) recent extensions of elasticity theory which provide reasonable results for both single pile and pile group settlement behavior; and (3) empirical curves which require pile load test data to give average group settlement and compare favorably with the field measured values.

Pile Driving Experiences at Port Everglades

Foundations for steam power plant comprising two 240,000 kw units; soil investigations, difficulties encountered in driving of piles, and pile settlements; settlements resulted from consolidation of underlying strata attributable to vibrations developed by pile driving; pile-load test data and comparative driving with air hammer and rated equivalent diesel hammer are presented.

Pile Driving Experiences at Port Everglades

Foundations for steam power plant comprising two 240,000 kw units; soil investigations, difficulties encountered in driving of piles, and pile settlements; settlements resulted from consolidation of underlying strata attributable to vibrations developed by pile driving; pile-load test data and comparative driving with air hammer and rated equivalent diesel hammer are presented.