Pile Load Tests Research Articles

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.

Dual performance of novel steel pipe heat exchangers equipped in cast-in-place energy pile

Pile foundations support superstructures by transferring structural loads into the ground, where rocks or hard ground formations exist. Energy piles additionally utilize geothermal energy for heating and cooling buildings via embedded heat exchange pipes. However, when constructing energy piles, additional budgets are required for materials and labor to install conventional high-density polyethylene (HDPE) heat exchange pipes. The applicability of cast-in-place energy piles equipped with novel steel pipe heat exchangers (SPHXs) is investigated herein as substitutes for deformed rebars to reinforce concrete. Energy piles encasing SPHXs are expected to fulfill multiple functions of supporting structural loads and operating as heat exchangers without requiring additional heat exchange pipes. Two cast-in-place energy piles encasing SPHXs of different diameters were constructed in a test bed. Then, pile load tests (i.e., dynamic load test and lateral load test) were conducted to estimate the bearing capacities of these energy piles. Consequently, both energy piles secured safety factors greater than 2.0, and the allowable lateral loads were sufficient, indicating acceptable structural capacities as pile foundations. In addition, a thermal performance test (TPT) was performed on the selected energy pile, and the result was compared with that of a conventional cast-in-place energy pile to assess the heat exchange capacity of the energy pile with SPHXs. The thermal performance of the cast-in-place energy pile considered herein was 30% greater than that of the conventional energy pile of similar scale, which shows the applicability of the proposed energy piles.

Assessment of ultimate load of drilled shaft socketed in rocks based on pile load tests

To investigate the settlement characteristics of drilled shaft socketed into igneous, metamorphic, or sedimentary rock, experimental results of the pile load tests were thoroughly collected in 20 different locations, clearly tabulated, and extensively compared with the standards for assessment of ultimate load. Total and elastic settlement patterns of drill shaft were completely dependent on the socketed pile length, the imposed load, the pile diameter, and the shear stress in bedrock, whereas residual settlement did not depend on the factors. It was also observed that the trends of total, residual, and elastic settlements were independent on bedrock types. Comparison between the experimental data and the standards shows that the total and residual settlements of large drilled shaft socketed in bedrock were too high to determine the ultimate load, and the reasonable amount of total or residual settlement measured from pile load test is proposed to assess the ultimate load capacity of drilled shaft socketed in bedrock.

The test effect evaluation of distributed optical fiber sensing technology applied to stress test of bored pile

The application of distributed optical fiber sensing technology to stress test of bored pile is a kind of line measurement method developed in recent years. It has the advantages of more measuring points and stronger anti-interference, but its test effect is rarely compared with other methods in practical engineering. In order to evaluate the test effect of distributed optical fiber sensing technology, the optical fiber and sliding micrometer tube were embedded at the same time during the construction of test pile, and then the static load test of pile was carried out to compare the test results of the two. The test results show that the strain distribution of the pile obtained by the distributed optical fiber sensing technology and the sliding micrometer method are the same, and the maximum strain difference between them is about 100 με. The distributed optical fiber sensing technology can better reflect the detailed deformation of the pile.

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.

Features of static pile load test

Pile foundations are commonly used in engineering practice to transfer the loads from heavy structures such as high-rise buildings to competent soil strata. In this manner, such complications as unfavorable geological conditions, compressible soil layers, and high levels of groundwater are avoided. Different types of piles are used in construction work. The specific type of pile used depends on the type of loading, the foundation soil, and the location of the groundwater table. The technical progress of large, bored piles and the continuous improvements of construction procedures and piling equipment today have created new possibilities. This paper describes a series of pile load tests that were performed in the capital city of Nur-Sultan, Kazakhstan. The control equipment, technological features are important for detailed information about the process of testing and the associated results make them more accurate and reliable. Keywords: pile, static test, load, equipment, soil

Performance monitoring of offshore PHC pipe pile using BOFDA-based distributed fiber optic sensing system

Brillouin Optical Frequency Domain Analysis (BOFDA) is a distributed fiber optic sensing (DFOS) technique that has unique advantages for performance monitoring of piles. However, the complicated production process and harsh operating environment of offshore PHC pipe piles make it difficult to apply this method to pile load testing. In this study, sensing cables were successfully pre-installed into an offshore PHC pipe pile directly for the first time and the BOFDA technique was used for in-situ monitoring of the pile under axial load. High-resolution strain and internal force distributions along the pile were obtained by the BOFDA sensing system. A finite element analysis incorporating the Degradation and Hardening Hyperbolic Model (DHHM) was carried out to evaluate and predict the performance of the pile, which provides an improved insight into the offshore pile-soil interaction mechanism.

Determination of the Pile Stiffness Matrix Based on the Pile Load Test Results and the Effect of Pile Interaction

Determination of the Pile Stiffness Matrix Based on the Pile Load Test Results and the Effect of Pile Interaction

Lateral dynamic load tests of offshore piles based using the m-method

The static load test method is currently the standard horizontal bearing capacity test for offshore foundation piles. The static load test method requires extensive testing time, high equipment cost, and uses equipment sensitive to environmental conditions. As offshore wind power piles increase in diameter, the static load test method becomes increasingly cumbersome to use. In this contribution, a single pile model test under the action of static force and impact was carried out. Based on the m-method, the dynamic and static transformation relationship of m value in the test was explored, and a new lateral dynamic load test method for offshore piles is proposed. The new method employs the in-situ ship impact impulse test method. The m-value dynamic-static ratio (m value under dynamic force/m value under static force) exhibits a quadratic parabolic distribution relative to horizontal displacement and external load. The m value under impact can be converted into the equivalent static m value, which can be used to analyze the pile-soil interaction and evaluate the pile horizontal bearing capacity.

Static Load Test Imperfections Influence on Continuous Q-S Curves

The static load test is the most reliable method of indicating the actual pile bearing capacity. Within the pile load increments, the settlement is measured and set of points Q-s (load – settlement) is plotted. The ways of executing the pile load test and their interpretation are far from optimal and have many different approaches. Usually, the pile test does not allow evaluating the bearing capacities within the measured range and extrapolation of the results within the Q-S curves is necessary. None of the present interpretation models includes the influence of imperfections in the pile load test. The paper presents the results of calculations with the model that takes into account the occurrence of imperfections during the test execution. The analysis is based on the modified Meyer-Kowalow curve model, proposed by Meyer and Wasiluk, and on the field test obtained on many construction sites for piles in different technologies, few of them loaded up to the failure. The model considered in the paper allows extracting statistical imperfections in the collected set of points. Imperfections should be understood as mechanical changes of the pile and pile-soil interaction. All phenomena are gathered within one imperfection. The imperfections are due to changing soil and pile skin when the soil body bends according to the Kirchhoff’s principle. Calculations indicate the influence of imperfections on the pile limit load and other parameters of the Q-s curves according to the basic model that exists. Performed analysis based on approximately 65 piles defines three main groups, first with a relatively small influence of imperfections, second with changes of the limit load for the entire pile and the pile toe without the large change of pile character (ratio of skin friction and pile toe resistance) and the third with a significant change in limit loads and pile bearing capacity components ratio (skin and toe). Values measured during the pile load test can be corrected within extract imperfections. Presented model in many cases determines more critical values for designers than basic models suggest.

Cross hole sonic test results for analysis of pile load test

Quality of concrete for pile can be checked using Cross-hole Sonic Logging (CSL) Test. A processing method wide-band CSL data is presented herein. First Time Arrival (FTA) is an important consideration. In pile capacity analysis or CSL analysis, it is assumed that pile cross section is uniform with uniform value of elastic modulus of concrete but in real practice both are non-uniform. The procedure identifies the location accuracy and further characterizes the features of the defect. FTA is used to find out the location of the distress in the pile. This method identifies the exact location of any void or defect inside the rebar cage of a drilled shaft. This method provides a significant improvement to current techniques used in quality control during construction of bridges. In this present paper, the analysis has been carried out based on uniform and non-uniform values of pile cross section and E value of concrete. Cross hole sonic and pile load test using O-Cell were carried out on same pile at 7 and 28 days of concreting. Same pipes were used for base grout after cross hole sonic test. These results were used to analyze O-cell test results based on a case study and presented in this paper. The distribution of skin frication and skin friction force has also been presented herein with both uniform and non-uniform cross section and E values of concrete. Based on the field test results and analysis a simplified methodology, has been proposed in this paper, for development of Equivalent Top Down Loading with consideration of elastic shortening of pile and surrounding soil for both cases i.e., uniform and non-uniform E values and pile cross sections.

Analysis of the static load test results referred to limit the bearing capacity of a pile

In the paper the authors used results of static load tests of piles that have been conducted in a full range of loads in order to verify the analytically calculated parameters obtained for a continuous load-settlement curve. For a description of continuous static load test curve of a pile the authors have used Meyer-Kowalow method (M-K method). The result of a static load test is a load-settlement set {N i, si } which is the background for further calculations of M-K curve parameters. Calculations that are presented in the paper were carried out using an original computer program and the authors compared M-K curve parameters, specifically limit the bearing capacity of a pile calculated and measured values obtained from the static load test performed in a full range of load. The research was done in order to determine the optimal method of calculating bearing capacity of pile based on static load test which later can be practically used in the M-K method to obtain full range continuous Q-s curve. Results obtained during the analysis performed by the authors show that the values of the limit bearing capacity of a pile can be calculated with sufficient for practical use accuracy from different parts of the data set, as an example using just the chosen part of the set. The research conducted by the authors points the fact that the limit bearing capacity which is the most important parameter determining safety, can be effectively obtained for different M-K curves using least squares method, even in cases when static load tests were not performed in a full load range. After determining M-K curve parameters it can later be used for further analysis of the pile-soil interactions.

Cone penetration test-based load-transfer formulations for driven piles in sand

This paper presents the development of load-transfer curves that can be used to estimate the displacement under axial load of driven piles in sand. The maximum skin friction and end-bearing stress are obtained from new ISO 19901-4 cone penetration test (CPT)-based formulations, which were calibrated using a high-quality database of static pile load tests compiled for this purpose. The load–displacement responses measured in the 71 static load tests in this database are used to derive CPT-based non-linear load-transfer curves. It is shown that good estimations of pile displacements can be obtained using CPT data and the normalised formats of shaft and base load-transfer functions provided in the American Petroleum Institute and ISO 19901-4 recommendations.

Rock Anchors for Static Pile Load Testing: Considerations and Case Studies

It is common practice in India to install rock anchors around test pile in order to obtain reaction for static load tests wherever competent rock is encountered at reasonable depths. Rock anchor design and installation require adequate attention as it is dependent on several parameters and checks. Authors have performed several static load tests across India with rock anchors up to test load of around 2000tons and also in various rock formations such as Basalt, Breccia, Tuff, Granite, Sandstone, etc. Competent rock levels also have been seen to be varied to great extent such as around 20 m from ground surface and such long free lengths offer several challenges including extension of strands equal to or more than ram stroke. Typically, for rock anchors in soft rocks, computed fixed length may be more than 10 m, and BS code 8081:1989 limits the fixed length to 10 m. In order to assess the rock anchor behavior for such condition where fixed length was more than 10 m, an effort was made to test the anchors to its full capacity and corresponding experience will also be summarized in the paper in the form of case history. This paper addresses rock anchor design philosophy including several checks required for appropriate rock anchor design, approaches for rock anchor design in soft rock, author’s experience of rock anchor design and installation with various rock types across India, along with case studies. Paper will also highlight benefits and limitations associated with installation of inclined anchors for crown girder assembly.

Comparison of ultimate bearing capacity based on empirical method, interpretation of loading pile test and finite element

Civil Engineers in designing the ultimate brearing capacity of the pile usually uses several empirical methods. Then usually the loading pile test will be conducted to confirm the ultimate carrying capcity in the field. Based on conditions that often occurs in the field, an empirical method of research is carried out to find out which method is closest to results of the field test. So that in designing the ultimate bearing capacity of the deep foundation will be closer to the field conditions. The empirical methods used in this case are the method of Bazara and Luciano Decourt, while the interpretation pf filed results uses the methods of Chin, Mazurkiewiz and Lastiasih. Based on the results of empirical methods and interpretation of the ultimate bearing capacity of the field test, the results of the pile loading test will be analysed using finite element. The result of this research shows Finite Elemet method, Luciono Decourt and Lastiasih are the closest produce produce ultimate bearing capacity with loading pile test until failure.

Influence of raft rigidity for piled rafts resting on stratified subsoil

ABSTRACT Raft rigidity is one of the governing factors that control the performance of piled rafts; it influences the interactions of the raft with the piles and the soil. By employing extensive three-dimensional Finite Element Analyses, the effects of raft stiffness on the absolute and differential settlements of piled rafts were investigated with the aim of achieving optimal design with limited number of piles. An appropriate constitutive model was applied to simulate the soil behavior, whose parameters were calibrated using pile load test measurements. While raft thickness is found to have minor effects on the settlements of piled rafts with closely spaced piles, a range of raft-soil stiffness ratios between 0.03 and 0.08 are found to minimize settlements for the case of widely spaced piles. Rigid rafts with raft-soil-stiffness ratios higher than 0.1 are recommended to be avoided for not enhancing the performance of the foundation.

Empirical Shaft Resistance of Driven Piles Penetrating Weak Rock

In this paper, an empirical relationship between the Unconfined Compressive Strength (UCS) of intact rock and the unit shaft resistance of piles penetrating rock is investigated. A growing number of civil engineering projects are utilizing steel piles driven into rock where a significant portion of the pile capacity is derived from the shaft resistance. Despite the growing number of projects utilizing the technology, little to no guidance is offered in the literature as to how the shaft resistance is to be calculated for such piles. A database has been created for driven piles that penetrate bedrock. The database consists of 42 pile load tests of which a majority are steel H-piles. The friction fatigue model is applied to seven of the pile load tests for which sufficient UCS data exists in order to develop an empirical relation. The focus of this paper is on case histories that include driven pipe piles with at least 2 m penetration into rock.

Field tests of micro screw anchor piles under different loading conditions at three soil sites

Micro screw anchor piles are ideal as the foundation of solar power plants and have been widely used in recent years. In this study, test apparatuses for the uplift loading test, compression test, and lateral loading test of the micro screw anchor pile were designed. Comprehensive field tests (totally 72 piles) for six types of micro screw anchor pile were conducted in clayey, loess, and sandy sites, and some conclusions can be drawn as follows. (1) The typical ranges of bearing capacity in three soil sites with the micro screw anchor pile were obtained under uplift, compressive, and lateral loading conditions; the lateral bearing capacity varied over a small range (8.1 to 11.7 kN) for various site conditions and pile configurations and was much smaller than the uplift and compressive bearing capacities. (2) The screw anchor pile with more helical blades had better performance under uplift, compressive, and lateral loading conditions; increasing the embedded depth of blade substantially enhanced the uplift and compressive bearing capacities but only slightly influenced the lateral bearing capacity. (3) The clayey site had larger uplift and compressive bearing capacities than the loess and sandy sites; the uplift bearing capacity was larger than the compressive bearing capacity in clay but smaller than the compressive bearing capacity in sand. (4) The classic cylindrical shear method was improved by taking into account the shaft resistance above and below the blade(s), which can better predict the uplift and compressive bearing capacities; as for the lateral bearing capacity, a simple but practical prediction method was also proposed. This study will contribute to a better understanding of the failure mechanism and bearing capacity of micro screw anchor piles. The site information and test results are promising to provide data for further analytical and numerical works.

A new hyperbolic variation method for settlement analysis of axially loaded single friction piles

This study describes a new hyperbolic method based on load transfer method for settlement analysis of axially loaded single friction piles. The new method is obtained by examining 14 pile load tests. The examined test piles were loaded until the piles were failed, and they were chosen from friction piles having variable diameters from 0.6 to 2.0 m and located in different geographical regions. Twelve of these test piles were circular bored piles, and two of them were barrette piles. According to the proposed hyperbolic method, the load–settlement graph is divided into two parts, and the relationship between load and settlement is defined by using two different hyperbolic variations each corresponding to one of the parts. Results of the settlement analysis of the four test piles obtained from the new proposed method and the four from the different methods based on load transfer method are presented comparatively with each other and with the pile load test results. The results of the pile settlement analysis and those of the pile load tests demonstrate that the new hyperbolic method yields accurate results for the most bored friction piles. The load settlement plots obtained by the new method match appropriately with measured values. On the other hand, the results of the barrette piles obtained from the hyperbolic method do not show the proper fit like those of the bored piles, when they are compared to those of the other methods based on the load transfer method.

Comparison of Single and Group Jet Grout Columns Settlement Based on Field Test and Theoretical Methods

The settlement evaluation for the jet grouted columns (JGC) in soft soils is a problematic matter, because it is influenced by the number of aspects such as soil type, effect mixture between soil and grouting materials, nozzle energy, jet grouting, water flow rate, rotation and lifting speed. Most methods of design the jet-grouting column based on experience. In this study, a prototype single and group jet grouting models (single, 1*2, and 2*2) with the total length and diameter were (2000 and 150 mm) respectively and clear spacing (3D) has been constructed in soft clay and subjected to vertical axial loads. Furthermore, different theoretical methods have been used for the estimation of (JGC) settlement. Pile load settlement analysis of the jet grout columns showed that the average settlement values were (0.41, 0.663, and 1.5 mm) for the single, group (1*2) and group (2*2) jet grouted columns respectively. While, in the theoretical methods give a higher value of the settlement (2.0, 3.48, and 5.24 mm) for the single, group (1*2) and group (2*2) jet grouted columns compared with the settlement results acquired from field pile load test data. Therefore, it is not recommended to be used for soft clay. On the other hand, Fuller and Hoy’s, Hansen’s 90%, and Butler and Hoy’s results may be considered faithful interpretation methods for the single and group (1*2 and 2*2) (JGC).