IFCEE 2021: Installation, Testing, and Analysis of Deep Foundations

Piles socketed into rock are frequently utilized to carry large loads from long-span bridges and high-rise buildings into solid ground. The pile design is derived from internal shear and moment magnitudes following code recommendation and numerical predictions. Little experimental data exist to validate code prescriptions and design assumptions for piles embedded in rock. To help alleviate the lack of large-scale test data, the lateral response behavior of three 18-in. diameter, 16 ft long, reinforced concrete piles was evaluated. The pile specimens were embedded in a layer of loose sand and fixed in “rock-sockets,” simulated through high strength concrete. The construction sequence simulated soil-pile interface stress conditions of drilled shafts. The pile reinforcement varied to satisfy the internal reaction forces per (1) code requirements, (2) analytical SSI predictions, and (3) structural demands only. The pile specimens were tested to complete structural failure and excavated thereafter. Internal instrumentation along with crack patterns suggested a combined shear-flexural failure, but do not support the theoretically predicted amplification and de-amplification of shear and moment forces at the boundary, respectively.

A smart cell is a closed-type grout distribution system that is attached to the bottom of a reinforcement cage for drilled shaft foundations and acts in a similar manner to a hydraulic jack in bi-directional static load testing. Control of the grout is maintained during grouting, and a uniform stress is imparted across entire base area simultaneously. The goals of tip post-grouting are to improve the stiffness of the in situ soil, improve the shaft’s nominal axial resistance, and better align the load transfer curves to the project requirements. This paper will present an overview, basic principles, and the design methodology of tip post-grouting using this technique. The construction, tip post-grouting, select results, and general observations from the grouting performed on more than 120 total drilled shafts for Las Marotas vehicular bridge crossing the Paraí River and the Yapacani railway bridge structure crossing the Yapacani River, Bolivia, will also be presented and discussed. The general subsurface conditions for the sedimentary deposits at the two bridge sites consist of highly variable soil deposits, bedding, composition, and engineering characteristics. The diameter of the temporarily cased drilled shafts was either 1,200 mm (4 ft) or 1,500 mm (5 ft), and the length ranged from nearly 15 m (49 ft) to nearly 25 m (82 ft). Most of the drilled shaft foundations for these bridge structures were installed with a post-grouting cell at the bottom of its reinforcement cage to enhance performance and to reduce uncertainty. Using the measurements of the grouting operation, the premobilization of axial resistance and induced load imparted into the drilled shaft and to the soil beneath the base will be discussed.

To reduce the uncertainties regarding the behavior of piles in sandy profiles, an experimental field was developed by the Federal University of Rio Grande do Sul (UFRGS) in Araquari-SC. The experimental campaign included (1) field tests (CPT, SPT, and SDMT), (2) bored and continuous flight auger piles with bentonite and polymer, and (3) static load tests. In this scenario, this research aims to study the variables that intervene in the soil loading transfer mechanism. The subsurface profile was characterized using laboratory tests to obtain critical state angle, for use in the back analysis of the soil pressure coefficient (k_s) from static load tests. Using the beta method (β), the k_s was obtained, to be subsequently compared to the at-rest lateral earth pressure coefficient (k₀). The results showed that, with depth, the value k_s approaches the value of k₀, with a relation of k_s/k₀ close to unity.

Large diameter drilled shafts can meet the criteria for mass concrete, and the South Carolina Department of Transportation (SCDOT) is considering provisions to limit the maximum overall and the maximum temperature differential across these shafts. To meet project specific requirements, a design-build team developed a cooling system consisting of six steel access tubes installed in an approximately 0.4 m (2 ft) diameter circle around the center of nineteen 2.5 m (8 ft 2 in.) diameter drilled shafts. PVC tremie pipe was inserted inside the steel tubes to the bottom of the shafts to convey water from the bottom of the tubes back up to the top of shaft after concreting was complete. Thermal (TIP) wires were installed in these shafts to measure temperatures on 1-ft vertical increments at multiple locations around the perimeter and in the interior of each shaft. The variations in temperature within the shafts due to the cooling system are discussed, and conclusions about the effectiveness of the cooling system to meet project requirements are also presented.

This paper describes the bi-directional static load testing (BDSLT) performed using Super Cells on four sacrificial bored piles and select results obtained therefrom for the Hong Kong–Zhuhai–Macao Bridge project on the Pearl River Delta. The BDSLT device consists of multiple units of pressure cells assembled to conform to the diameter of pile and transfers the force of each cell directly to the shaft without the use of large steel bearing plates. The general subsurface profile where the sacrificial piles were installed, two piles each at two locations, consists of marine silts, alluvial clays and sands, and residual soils, which are underlain by granite. The test piles were tipped into the weathered granite layer, where the BDSLT devices were located about 3.5–5.2 m (11.5–17 ft) above the bottom of each pile. The test piles were instrumented with embedded strain gauges and telltale extensometers along with surface mounted displacement transducers. The results of the static axial load testing were intended to confirm the design assumptions of axial resistance and to evaluate the contractor’s means-and-methods. However, the maximum anticipated test load could not be achieved due to the low side resistance along the pile length above the testing device, especially within the upper layers.

Driven pile foundations are a commonly used deep foundation alternative throughout the U.S. and the world. Over the last ten years or so, design stresses for these pile foundations, particularly steel H-piles and pipe, have been trending higher due to detailed evaluation and understanding of soil/rock conditions and increased confidence in quality control and testing methodologies. Design stresses in steel piles have been routinely approaching and/or exceeding 20 ksi in order to increase the allowable pile loads and enable the driven steel pile industry to compete more efficiently with other deep foundation types such as micro-piles or drilled shafts. The use of higher stresses has now placed more emphasis on obtaining and classifying rock cores, particularly for the larger HP sections, where design loads of 200–300 t or more are now being used. The pile capacity is now controlled by the rock quality and/or the drivability of the pile rather than the limitations on the structural steel design. As a result, larger hydraulic hammers with more efficient energy transfer and bigger load test frames are necessary for successful installation. For other applications, in order to avoid driving to rock, which in some cases can be over 250 ft deep, other types of innovative steel foundations are being used. These steel foundations have not commonly been used in New England. They are trademarked, fabricated, non-traditional pipe pile sections that improve soil resistance to keep pile penetration lengths relatively short with reasonably high design loads that would not normally be obtainable with standard steel or pipe piles. This paper discusses the current trends in New England with regard to more frequent use of high capacity H-piles driven to rock and the emerging use of non-traditional pipe piles driven to shallow depths in sandy soils. Design challenges and case history examples are discussed.

For construction sites with zones of loose soil and the potential for liquefaction during a seismic event, deep foundation elements such as driven piles are often recommended as an economical solution. Typically, the designed deep foundation elements would resist liquefaction by advancing piles to a depth below the liquefiable layer so they obtain the required allowable compressive capacity. However, foundation contractors may have difficulty installing piles successfully to the minimum penetration depth once adjacent piles have been installed. Because of such installation difficulty, specific analyses of the piles during installation may be beneficial to provide a combination of revised pile capacities and review of the susceptibility to liquefaction caused by soil densification from installing the piles. This paper discusses challenges posed by advancing piles with a hydraulic impact hammer, spaced 1.8 m (6 ft) on center, to the minimum-required penetration depth of 19.2 m (63 ft) to obtain the required compressive capacities of 533.8 kN (120 kips) and lateral capacities of 31.1 kN (7 kips). Seventeen of 586 piles were driven to depths between 1.5 and 4.9 m (5 and 16 ft) short of the minimum required penetration depths. This paper will describe an investigation consisting of 10 seismic cone penetration tests (SCPT) to evaluate the increase in relative density within the pile field resulting from pile driving. This paper also will summarize two analyses using the SCPT tests to determine the site’s susceptibility to liquefaction and revisions to the pile capacities as a result of the soil being densified.

This study investigates the soil plugging process of an open-ended pipe pile during the impact driving through model pile tests. A semi-circular model pile with an inner diameter of 34.5 mm was driven to a depth of 500 mm along a transparent front wall of a soil tank. The authors prepared loose and dense soils with alternating colored layers of fine sands and then took photos of the entire pile driving process using a digital camera after each hammer blow. The high-definition images clearly show the effect of initial soil density on the soil plugging behavior of open-ended pipe piles. Detailed image analysis further reveals that the incremental filling ratio (IFR) repeats a trend of intermittent increase and decrease during pile driving, whereas the plug length ratio (PLR) continuously decreases as the pile penetration increases, suggesting that pipe piles may experience repeated transitions from a plugged condition to an unplugged or partially plugged condition during the impact driving process. We also computed vertical strains of the soil plugs during the pile driving process using the obtained images. Our image analyses show that the compression of the soil plug during the pile driving is more pronounced in loose sands than dense sands.

The efficacy of eight pile design methods to calculate capacities of large diameter open-ended pipe piles (LDOEPs) is explored using data made possible by the 2016 release of the U.S. Federal Highway Administration (FHWA) deep foundation load test database. The analyses were performed using APILE Offshore 2019 software by Ensoft Inc. Capacities were predicted using four SPT based methods proposed by (1) FHWA; (2) the U.S. Army Corps of Engineers; (3) American Petroleum Institute (API); and (4) the Lambda method; and four recently adopted CPT based methods proposed by (5) Norwegian Geotechnical Institute (NGI); (6) Imperial College Pile (ICP); (7) University of Western Australia (UWA); and (8) Fugro. Three plugging conditions were considered for each method, and predictions were compared to the interpreted capacities from static load test data using the Original and/or Modified Davisson Criteria per American Association of State Highway and Transportation Officials (AASHTO) recommendations. The study demonstrates that CPT based methods are somewhat superior to SPT methods, but all methods exhibit scatter between measured and predicted capacities with the computed capacity off by a factor of two in many cases. In particular, API and the Revised Lambda methods best predict pile capacity when using SPT data, while the NGI method seemed to be the best among the CPT methods and arguably the best method overall. Seven of the eight methods (all except NGI) better predicted pile capacity considering that the piles are unplugged and ignoring contributions of soil internal friction on the pile inside diameter. FHWA was the least conservative and the worst predictor of LDOEP capacity.

Open-ended pipe piles are often used for both land and offshore structure foundation because of their relatively low driving resistance. During driving, soil enters into the open-ended displacement piles, which is known as soil plugging. This paper addresses an experimental study of the plugging effect on the capacity of open-ended piles driven in sandy soil. A series of tests were conducted in the laboratory on small scale model pipe piles installed in sand with different soil conditions. The effect of pile diameter and soil density on plugging behavior of this kind of pile was evaluated. The laboratory test results show that plug length generally increases as pile diameter increases, and the relative density of soil decreases. The jacking force for pile driving was evaluated from the model tests, which significantly depends on the plugged length as well as soil properties. Furthermore, the effect of penetration speed on soil plugging was evaluated. It was found that the length of the soil plug inside the pile became smaller with the increase of pile penetration speed. A correlation between plug length ratio (PLR) and incremental filling ratio (IFR) is proposed based on the laboratory experiments.

Large diameter open-end piles are increasingly being used in transportation infrastructure projects due to their high load carrying capacity and construction efficiency; however, there is uncertainty in their design and performance. In particular, the development of pile plugging is not well understood and is not necessarily well captured in available static design methods. Many of the commonly used existing design methods were developed for smaller diameter piles, and some are known to overpredict large diameter open-end pile resistance. The Federal Highway Administration recently completed a multi-year research study evaluating the bearing resistance of large diameter open-end piles. As part of the research, the authors evaluated several existing static design methods for prediction of large diameter open-end pile resistance. The evaluation included multiple combinations of design methods and considered multiple combinations of side and base resistance to reflect effects of pile plugging. This paper outlines the evaluation of design methods and identifies trends for suitable methods and their application for large diameter open-end piles.

Augered cast-in-place (ACIP) piles and drilled displacement piles (DDP) are becoming increasingly common, particularly for providing high bearing capacities with relative ease of installation, reduced overall costs, and potential for shortened construction schedule and reduced construction material quantities. The static analysis methods used for these methods’ designs contain uncertainties, particularly for DDP where the surrounding geomaterials are reformed, resulting in increased unit side-shear resistance. Load testing is often performed to assess the side-shear and end-bearing resistances and to evaluate the selected construction method and required pile lengths. Bi-directional static load testing (BDSLT) can be advantageous for determining mobilized side-shear and end-bearing resistances at lower cost compared to conventional top-loading static load tests. A case study is presented where an ACIP pile and a DDP were constructed in close proximity to each other, and both were bi-directionally load tested. The benefits and limitations of each foundation type are addressed. A comparative study of load test results is presented, showing the response of each pile type in similar subsurface conditions. Critical aspects of the test data and their interpretation are reviewed, focusing on fundamental aspects of performing a BDSLT and methods applicable to converting measured strain to calculated internal force for drilled deep foundations. Higher mobilized side-shear resistances were observed for the DDP, which exhibited 50%–100% greater resistance compared to the ACIP pile in dense deposits. However, limitation in the DDP construction method (manifested as relatively shallow drilling-tool refusal) was encountered, limiting the DDP maximum achievable total capacity.

The surface roughness of steel piles may vary considerably, depending on how much exposure they have to the environment during storage or in the field. Although several studies have recognized the importance of roughness on the mobilization of frictional forces, its application to the design of deep foundations in the field requires further research. This paper presents the results of static load tests performed with an instrumented model pile with three different surface roughnesses jacked in a half-cylindrical calibration chamber with digital image correlation (DIC) capabilities. The model piles were tested in tension and compression in dense and medium-dense sand samples prepared by air pluviation. The analysis of the data obtained from local sensors and the images processed with DIC indicate that an increase in the pile surface roughness results in an increase in the average unit shaft resistance and an increase in the displacements and strains in the soil next to the shaft of the pile. Values of K/K₀ accounting the effect of surface roughness are provided for the estimation of the tensile and compressive limit unit shaft resistance of jacked piles in sand.

Full drilled displacement piles (DDP) were selected for a project located in central new Jersey and a full-scale static load test was performed to confirm the piles could meet the design requirements. Due to higher than anticipated installation times, it was decided to change to a partial drilled displacement pile (PDDP) option prior to starting production pile installation. PDDP test piles were installed, and drill times reduced significantly. A single PDDP pile was dynamically tested to confirm the alternate pile type met the design capacity. Results of the capacity predictions will be compared to the load test results for both pile types.

This paper investigates the problems associated with micropile installation in weak glacial deposits consisting of low plasticity silts, fine sands, and varved silts with clayey seams. The sensitivity of glacial soils to disturbance resulted in ground instability when casing withdrawal was performed under pressurized grouting. It was found that fluid pressure exerted by self-weight of grout in the borehole was sufficient to trigger instability in the glacial soils. The result was large grout penetration into the surrounding disturbed soils and upward flow of grout along the external face of the casing. Varved silts showed greater resilience against liquefaction due to their relatively cohesive nature compared to more granular materials such as silts and fine sands; however, plastic deformation may result from high grouting pressures that exceed the passive resistance. Grouting pressures locked in the hardened grout around the casing may contribute to high resistance to casing withdrawal. To avoid soil disturbance and locking up of casings, the length of grout column above the soil surface should be minimized and grouting should be performed without pressure.

Until recently, accurate long-term measurement of strain, temperature, corrosion potential, and other variables in concrete deep foundations and in superstructure elements has been difficult and costly. However, advancements in sensor technology and wireless data transmission has both simplified data acquisition, increased reliability, improved accuracy, and reduced costs. These advances now provide long-term measurements, which can be accessed in real time for in-service structures through a cloud-based system. Owners along with other stakeholders can now document and maintain “cradle to grave” records on their structural assets with respect to pre-stress level, post-tensioning level, corrosion, temperature, and several other variables of interest—load transfer from the super structure to the sub structure and effects from scour, sudden impacts, etc. Based on these measurements, design parameters, changes in loading, the effects of possible extreme events, corrosion rates, and other anomalous data can be evaluated in real time. This process allows owners with sufficient time to plan remedial actions which will prevent or at least minimize the risk of catastrophic failure. This paper discusses two case histories of structures constructed in Florida, including the installation of the system, results from the days of monitoring, and its implications for the future.

When piles are designed and constructed in the field, a pilot hole, which is a type of pile driving assistant method that prepares a hole before installing the pile, is often adopted to aid the installation process where the existence of hard or stiff layers is expected. This is to mitigate or prevent damage to the pile during the installation process, as well as to ensure the pile reaches the required minimum tip elevation. A conventional pile driving process can also cause excessive vibration or noise during the installation. With pile driving assistant methods, a pile can be installed with greater ease when being inserted and seated on the bearing layer. Many state agencies have been using similar installation methods even though the names and specifications are different. This study presents a summary on the current guidelines for pile driving assistant methods that use a pilot hole adopted by different states and identifies challenges to improve the reliability and stability of the piles constructed with a pilot hole.

An expander body (EB) is an element consisting of a folded steel sheet with a circular cross section that can be added to a relatively small diameter pile and ground anchor to increase axial resistance. During the injection of pressurized grout, the outer portion of the EB is expanded (inflated) from its original diameter of about 120 mm (4.75 in.) to about 400–800 mm (15.75–31.5 in.), depending on the model and stiffness of the in situ soil surrounding the device. Due to the controlled expansion process, the stress state is improved around the device and can be deduced from the recorded measurements; hence, the available axial resistance for these smaller diameter elements can be increased considerably due to the greater soil stiffness and shear strength around the device as well as to the larger cross-sectional area (i.e., end resistance) and larger surface area. This paper describes the general principles of the EB system as well as the construction, grouting operation, quality control, and select results from static axial compression load tests performed on continuous flight auger (CFA) + EB piles.

The p–y method for analysis of the lateral load transfer of deep foundations has been widely accepted in the geotechnical profession. However, the p–y models typically used are often based on one or several full-scale, instrumented loading tests in a specific soil deposit and may not be appropriate for other deposits that exhibit differences in soil fabric, stress history, or geological deposition. Cost-effective application of the p–y method to design deep foundations in a given geological region should leverage high-quality load transfer data derived from the region of interest. This paper presents the p–y curves for a driven pipe pile, uncased drilled shaft, and cased drilled shaft installed and tested in Willamette Silt. Differences and similarities are identified and then used as the basis to develop a simple hyperbolic p–y curve model set within the ultimate lateral resistance framework of an existing, commonly used p–y curve model. Thereafter, simple scaling relationships are provided to extend the model to account for differences in foundation diameter and for a casing installation and shaft construction method used frequently in Willamette Silt. The accuracy and uncertainty in the model are described, and a parametric comparison of the model is presented to illustrate the range in lateral resistance-lateral displacement response of a deep foundation designed using the proposed p–y curves.

The response of offshore structures to cyclic wind and wave loading is likely to govern critical design elements and ultimately the cost of installation and the structure lifespan. This is especially true for offshore wind and tidal turbines, where the magnitude of cyclic load is in greater proportion to their relatively light weight. A variety of novel foundation types have been proposed for renewable energy developments, but few experimental studies have been conducted examining their response under long term cyclic loading. A system was developed and used to apply hundreds of thousands of load cycles to intermediate-scale model foundations. System details are described for a helical pile application, and consideration is given to typical challenges encountered in long term cyclic axial loading, such as selecting hardware, managing simultaneous instrument measurement and control tasks, monitoring measurement accuracy, managing large data sets, and protecting equipment during unsupervised testing.

Dynamic behaviors of helical piles are of significant interest because such piles can offer an efficient alternative to conventional piling systems to resist static and dynamic loads. However, dynamic properties of helical piles with larger slenderness ratios have not been fully investigated, such as natural frequencies and damping ratios. To investigate dynamic behaviors of soil-helical pile interaction, full-scale vibration tests were performed on a 4.3 m long and double-helix helical pile using a shaker. Three accelerometers were installed on top of the pile, and strain gauges were placed on pile surface at different depths. The shaker was installed on the pile cap. The pile was subjected to harmonic (quadratic) loading of different force intensities acting within a frequency range from 9.8 to 19.5 Hz that covered the resonant frequencies of the tested soil–pile system. Based on the displacement amplitude of the pile at different excitation frequencies during the vibrating tests, the natural frequency of the pile is 15.3 Hz. Experimental p–y curves were developed to estimate the dynamic soil–pile interaction. The equivalent damping ratios vary from 0 to 1 along the pile length and were obtained using the energy dissipation method. The results indicate that the damping ratios decreased with the number of vibration cycles in the upper portion of the pile and increased with the number of vibration cycles in the lower section of the pile due to the soil–pile gap development extending from the soil surface along the upper part of the helical pile.

This paper focuses on the effect of frozen soil thawing on the pull-out capacity of a helical pile in fine-grained soils. Helical piles are increasingly popular in cold regions because of their ease of installation and minimization of the impact of frost heave. However, any temperature changes caused by a warming subsurface may adversely affect pile capacity. In this paper, helical piles installed in frozen soil layers are investigated to elucidate the changes in capacity due to thawing. A numerical model describing the load-displacement and capacity response of helical piles in frozen and thawed soils is successfully validated by comparison to previous results from two field-scale pull-out (tension) experiments. The results indicate that the pile uplift capacity decreases significantly with soil thawing due to decreases in soil undrained strength and stiffness, resulting from increasing pore pressures. The results from this study will contribute towards future development of design guidelines for helical piles in cold regions for sustainable infrastructure and resilient communities.

The multiline ring anchor (MRA) was devised as a cost-effective means for securing floating offshore wind turbines (FOWTs) to the seabed. FOWTs occurring in arrays create the possibility for attaching mooring lines from multiple units to a single anchor. Additionally, the deep embedment of the MRA into relatively strong soil permits high load capacity to be achievable with a small and lighter anchor, thereby reducing anchor material, transport, and installation costs. However, since the MRA is shorter than a conventional caisson, features such as wing plates and keying flaps are needed to achieve parity in load capacity with a caisson having a comparable diameter. Preliminary studies show that attaching wing plates to MRA in soft clay is highly effective in enhancing its horizontal load capacity, but only marginally effective in improving vertical load capacity. This motivated the current study investigating the use of keying flaps to further enhance vertical load capacity. Two-dimensional finite element analyses were conducted to understand how keying flaps impact the failure mechanism of the stiffeners and provide reliable evaluations of the uplift resistance of the MRA. The results show that the thickness of the stiffener, flap length, and flap angle can affect the failure mechanism and bearing factors. For the optimal design of the stiffener, a comparative study was carried out to compare the effects of keying flaps and thickness of the stiffener. The studies show that introducing keying flaps can have comparable load capacity with thicker stiffeners and that it can be an economical solution for achieving high vertical load capacity while containing material and fabrication costs.

Rock-socketed caisson design is governed by the side resistance and end bearing of the rock. In Philadelphia and many other regions, upper limits are set on the allowable design based on presumptive values together with unconfined compressive strength test results on intact rock specimens. When locally assigned upper limits are applied to the Wissahickon mica schist in Philadelphia, the length of the rock socket would be as long as 10 m (33 ft) under the maximum design load of 88,520 kN (19,900 kips) for a 49-story building. In order to optimize the socket design, an Osterberg cell load test of a rock-socketed caisson was planned and successfully completed during the design phase. As a result, a significant reduction was achieved in the rock socket lengths by increasing the allowable side resistance from 0.9 to 1.4 MPa (10 to 15 tsf) and the end bearing from 4.8 to 12.5 MPa (50 to 130 tsf). This case study illustrates the importance of understanding the unique aspects of the site geology such as degree of weathering, top of rock, and metamorphic texture variations, in terms of local presumptive strengths, and how that justified performing a very expensive test even though the outcome could not be guaranteed. It also highlights the importance of foliation or schistosity and fracture dip angle in characterizing the rock mass and their influence on the unconfined compressive strength of the rock cores. Without such an understanding, making the case for the load test would have proved very difficult during design.

This case history summarizes the foundation design of an 11-story hotel that was constructed above and around an existing transit headhouse structure in the South Boston Seaport District. The hotel was designed to span over the headhouse structure at the third-floor level and be supported on a line of exterior columns at the eastern end of the building. This paper discusses how unique site and design challenges were considered and solved for the foundation design and construction. These challenges included protecting existing and adjacent structures, overcoming buried obstructions, and supporting high vertical and shear loads. Multiple foundation systems were evaluated. Deep, driven steel H-piles were ultimately selected to support new building column loads; however, along the eastern side of the headhouse, significant shear loads were imposed on the foundations. To resist these loads, the authors designed a “composite” foundation element consisting of end-bearing H-piles encased within a circular concrete section.

Bio-inspired design is increasingly popular in a variety of disciplines. Tree roots provide an anchorage system that is significantly more efficient than typical engineered systems. Trees are capable of withstanding substantial axial and lateral loads, with root structures that have improved throughout time. In comparison, engineered piling systems require the foundation to extend deeper in order to support comparable loads to those experienced by trees. This study explores the effect of lateral roots on trees’ bearing and uplift capacity to identify best practices for bio-inspired foundation design. The tree–soil interaction during loading is investigated using a transparent soil representing sand, made of fused quartz and a mixture of mineral oils having a matched refractive index. Load deformation response was obtained during loading. Soil movements were obtained by tracking fused quartz particle movements illuminated by laser light. Successive images were analyzed using digital image correlation to obtain displacement and strain fields.

Major bridges in areas of high seismicity are often supported on deep pile foundations. During an earthquake, ground shaking is not uniform in the entire soil domain supporting a bridge and its foundations. Ground motions may be different at each support and at various depths along each pile. In particular, site response effects alter the seismic waves as they propagate upward, leading to depth-varying motions. This raises the question of what motions are the most appropriate for use in evaluating the seismic response of a pile-supported bridge. In this study, excitations caused by depth-varying motions are investigated by performing analysis of kinematic pile-soil interaction. Depth-varying free field motions are computed along the length of the piles and used as inputs through soil springs into foundation models. The resulting “kinematic motion” is computed at the pile cap, which gives an indication of the effective earthquake excitation imparted to the bridge. Results are presented from major bridge projects covering a range of pile types and ground conditions. In terms of their computed response spectra, the kinematic motions are often found to be lower than the free field ground motions at the mudline or ground surface. As a result, seismic design demands may be reduced by implementing kinematic or depth-varying motions in global bridge model analysis, as opposed to following the ground surface response spectrum approach used in standard practice. Significant reductions in demands are found particularly for bridges on stiff pile foundations at sites with soft upper soils underlain by denser materials.

In this paper, we present results of rigorous numerical analyses of small and large non-displacement pile groups subjected to axial loads. The finite-element (FE) analyses were performed using a realistic two-surface-plasticity constitutive model for sand implemented in ABAQUS. The model closely captures the stress-strain response of sand under various loading paths. The model mesh was carefully prepared such that the thickness of the shear bands formed in the FE simulations matched those observed in calibration chamber experiments complemented by image analyses. The load-settlement responses of 2×2 and 4×4 pile groups in medium-dense and dense sands were compared. The overall group efficiency for these pile groups ranged from 0.93 to 1.12 for settlement levels ranging from 30 to 50 mm. However, the efficiency of the individual piles depended on the location of the pile in the group, settlement level, and sand density. A summary table of efficiencies for the individual piles in the group and the pile groups are provided for design of non-displacement pile groups in sand.

High strain dynamic testing (HSDT) has been used successfully as part of or the sole means of loading test programs on both driven pile and drilled foundations. Signal matching analysis of pile top force and velocity measurements allows for modeling of soil resistance and its distribution along the pile, determining not only the total static resistance, but also the end bearing component. While the estimation of total static resistance has been proven reliable with multiple published correlation studies performed, the accurate estimation of shaft resistance versus end bearing is limited. This limitation is caused by the lack of resolution of the measurements and relatedly the difficulty of distinguishing between the end bearing and shaft resistance near the pile bottom. This ability is further complicated on drilled foundations due to the non-uniform nature of these foundation types. The best available means of improving the accuracy of the calculated end bearing–shaft resistance distribution is making additional measurements of force and velocity near the toe. The analysis of these data requires a multi-level signal matching approach. This paper describes measurement and analysis techniques, which were developed for the purpose of improving the resistance distribution predictions of HSDT. Three case studies are presented, where pile top and pile toe measurements in combination were taken on various foundation types, which allowed for a more refined prediction of end-bearing through a multi-level analysis of the data at the pile toe and pile top. Limitations of this approach are also discussed.

Underreamed piles are cast-in-place drilled shafts that have one or more bulbs added to the straight shaft to increase their axial capacity. The underreams are typically formed by using a belling tool and filling the cavity with plain concrete. This study explores the mechanisms that contribute to the gain in capacity of underreamed piles relative to their straight counterparts. Soil-structure interaction of underreamed piles is explored using a synthetic transparent soil made of fused quartz and a mixture of mineral oils with matched refractive indices. The effect of the number of underreams and the distance between them, as well as the ratio between the diameters of the underreams and the straight shaft, were explored. Several underreamed pile configurations were 3D printed in-house. Load deformation response was obtained during uplift and compressive loading. Soil movements were obtained by tracking the successive movements of the speckle pattern resulting from the interaction of a laser light sheet and the fused quartz. Successive images were analyzed using digital image correlation (DIC) to obtain the resulting, displacement, and strain fields. The study aims to provide guidance on designing more efficient underreams for these structures.

In 2017, the 57-year-old Eisenhower Bridge over the Mississippi River in Red Wing, Minnesota, was replaced by a new bridge with a longer span and taller, wider approach embankments. The north abutment embankment grade was raised over 20 ft; the new north abutment is supported by H-piles in an area of thick, soft alluvial deposits. The added embankment loading was expected to compress layers of underlying soft soils and result in undesirable downdrag conditions. The pile structural integrity was evaluated, and a nominal dragload of 350 t was estimated during the design phase, which was within the established structural limit. To evaluate actual downdrag response and compare measured values with predictions, four HP 14×117 steel piles were instrumented with a series of strain gauges. Two piles were located within the bridge footprint, and two were located outside the footing within the approach embankment fill. For performance comparison, two instrumented piles were driven to the top of bedrock with the aid of PDA, and two instrumented piles were driven to an elevation 5 ft above bedrock. A group of earth pressure cells was placed around the piles to measure overburden stress relative to pile strain. As of 2020, the bridge is complete, and the embankment fill had been in place for more than 2 years. An assessment of the pile strain profile indicates that negative skin friction progressively increased, then gradually stabilized during various stages of the construction. Maximum compressive force in the piles was around 300 t, and embankment fill overburden stress was 2 tsf. The neutral plane location became increasingly distinct at a position about 30%–50% of the pile length from the toe.

A spreadsheet program, t-zMich, which analyzes load transfer from a pile to cohesionless soil, is presented. The program is an interactive tool which provides real-time graphical presentations of input data and analysis results. Users provide soil stratigraphic information, soil properties by layer, groundwater conditions, pile types and dimensions, installation method, and elastic properties of the pile. The program runs an iterative procedure to calculate displacements and load takeout along the length of the pile. Hyperbolic interface shear stress versus displacement (t–z) curves model the displacement–dependent load transfer from pile to soil by side friction. A hyperbolic equation also models pile end bearing. The paper presents arguments for the use of hyperbolic models in t–z analyses. Visual output is produced in the form of pile load versus settlement curves. Users observe the loads taken out by side friction and end bearing. This paper describes the iterative procedure and guides the reader through the program’s features.

Offshore wind turbines (OWTs) are subjected to long-term cyclic loading during their service life. Long-term cyclic axial loads cause changes in the soil-pile interface properties (i.e., strength and stiffness). To investigate these effects, a cyclic interface shear test (CIST) device was developed by the research team. The CIST device allows for directly measuring the shear stress–vertical displacement response (static and post-cyclic t–z curves). Furthermore, the automated CIST device allows for investigating the effects of cyclic loading characteristics (i.e., pattern, amplitude, frequency, and number of cycles) on the soil-pile interface properties, especially interface shear resistance. In addition, the CIST system allows for conducting interface shear tests with two control modes: pressure control (constant load on the interface) and a pressure control with displacement monitoring (control of plates radial displacement before shearing), which is equivalent to constant normal displacement/volume confinement condition. Moreover, the CIST test setup allows for performing scaled 1 g pile tests subjected to long-term cyclic axial loading and allows for the use of instrumentation within the soil and at the interface (such as pore pressure sensors). This study presents the first phase of this research and presents preliminary test results. In this study, 3D printed smooth plates simulating conventional steel piles were used and the soil-plate interface was subjected to cyclic loading. The soil used in the experimental program is a normally consolidated kaolinite clay mixed with sand to reduce consolidation time. In this paper, a short description of the new device is provided and the results from a series of displacement-controlled one-way cyclic interface preliminary tests on cohesive soil–smooth plates interface are summarized and compared to a reference baseline static interface test (no cycles). The preliminary tests presented in this paper show that a contractive behavior was observed at the interface during the application of loading cycles and the interface shear resistance increased with the number of cycles. This increase ranged from 40% to 75% when compared to the static interface shear resistance (no cycles).

In situ test-based pile design methods are often used to estimate the ultimate capacity of closed-ended pipe piles (CEPs). Among these, methods based on the cone penetration test (CPT) prove to be the most accurate. However, in soil profiles with high gravel contents (e.g., >20%), these CPT-based methods tend to overestimate pile capacity. In this paper, we present the results of an instrumented static load test (SLT) performed on a 17.7 m (58 ft) long CEP with an outer diameter of 610 mm (24 in.) driven in a soil profile with gravelly sand layers. We compare the shaft and base resistance components measured from the SLT with estimates from three widely used CPT-based pile design methods. We also review additional cases of high-quality SLTs performed in gravelly soil profiles to provide context for the observations from the current SLT. Depending on the gravel content of the layers in the soil profile, predictions from CPT-based design methods tend to overestimate the ultimate pile capacity by a factor ranging from 1.2 to 2.6.

Jointed rock mass is inherently heterogeneous because of the presence of discontinuities. The discontinuities may occur in the form of joints, faults, and fissures. The variability of engineering properties of jointed rock mass depends on geometrical shapes due to past geological processes. The spatial arrangement, surface roughness, number, length, orientation, and inter-connectivity of discontinuities may play a significant role in an accurate prediction of jointed rock mass strength. The jointed rock mass strength is pivotal for the safe and economical design of strip foundations in rock engineering. The reliability method used in this work provides a more rational approach over the conventional factor of safety approach by accounting for the variability of properties of the jointed rock mass. A reliability based optimization of foundations built on jointed rocks with two discontinuity sets is presented to compute the optimum value of the allowable bearing capacity of strip footings. The discontinuity strength model along with the modified Bell approach is adopted to determine the ultimate bearing capacity. Reliability analysis is conducted by treating uniaxial compressive strength of intact rock, discontinuity cohesion, discontinuity orientation, joint spacing, rock material frictional angle, and discontinuity frictional angle as random variables. The effects of orientation on the allowable bearing capacity are presented for the target probability of failure of 0.13%.

All construction projects have certain risk components associated with them. Effectively identifying and managing the various risks in any project are critical to a successful outcome. Deep foundations can represent a significant portion of the total project risk. The risk factors associated with deep foundations include safety, quality, foundation performance, cost, and schedule. There are many innovative foundation testing methods available that can help to mitigate these risks. This paper will discuss how foundation testing solutions can help lower the risks by accelerating the construction schedule, assessing the quality and capacity of the foundation, and thus eliminating some of the unknowns and reducing the overall cost to the project. These solutions will be discussed in detail along with selected case histories showing how innovative testing methods are used to reduce project risk.

Sustainable infrastructure emerges when environmental, economic, and social factors find common ground during the infrastructure lifecycle, resulting in an efficient and accelerated construction without compromise in quality. Resilient infrastructure is able to recover to full designed functional capacity after extreme natural or man-made events. Optimum sustainability is achieved through (1) reduced wastage of global construction materials and (2) data-driven maintenance procedures based on need, instead of periodic maintenance based on past practice—there is a transformation from maintenance on a schedule to maintenance on demand. Can we measure resiliency and sustainability? The answer is yes. Are there case studies that show that resiliency and sustainability are achievable together and measurable in infrastructure? The answer again is yes, with the use of embedded sensors and wireless communications.Modern technologies such as embedded sensors and wireless communications have rapidly advanced, becoming ubiquitous in many a human endeavor. As these technologies mature, stakeholders are learning to apply them to bridge structures, creating smart transportation infrastructure. Data are collected wirelessly over an IoT-based cloud architecture to facilitate monitoring real-time and/or on as-need basis. This enables communications between various elements of smart infrastructure even beyond the transportation industry, enabling quantification of resiliency and sustainability. This paper discusses the concepts and a case study of recent deep foundation projects in Florida involving smart infrastructure that achieved resiliency and sustainability.

The basic design studies for the First Line of the Bogotà Metro propose the execution of approximately 270,000 mL of drilled shafts. The cost of performing these drilled shafts represents 15% of the total cost of the project. The results of load tests on piles reported in the city, although limited in terms of quantity, have shown that the actual load capacity of the piles can exceed the expected values in the designs. With the objective of optimizing the dimensions of the foundations, nine field loading tests on real scale piles were executed. The proposed tests contemplated the installation of hydraulic elements inside each pile (Osterberg cells) to induce actions capable of failing the pile and that allowed to register the mobilization of resistance along the shaft and the tip by means of the instrumentation of the induced deformations on the pile. This paper presents the results and interpretation from the static, axial, and bi-directional load tests carried out using hydraulic jacks (e.g., Osterberg “O-cell” cells) on deep foundations distributed along the corridor and the relevant construction aspects of the tests.

Sonic echo (SE) measurements are commonly used for integrity testing of deep foundations and to determine the length of unknown foundations. The rod wave (unconstrained compression wave) velocity of the pile is an important parameter that is directly used to calculate the length of the pile or the distance to a pile defect. Often, it is not possible to measure the rod wave velocity, so assumed values are used, which creates uncertainty in length determination and defect location. It has been observed that SE measurements performed with short-duration impulse sources generate narrow-band, high frequency noise. Finite element simulations using ABAQUS show that this high frequency noise results from resonance in the radial direction of the pile and is a function of rod wave velocity, Poisson’s ratio, and the geometry of the pile. In this study, it is shown that measurements of the frequency and particle velocities of this radially propagating wave during SE testing allow for determination of the rod wave velocity and Poisson’s ratio of the pile without the need for additional velocity measurements or use of assumed values. Results from numerical simulations and experimental validation are presented.

The use of applied geophysics in geotechnical engineering is steadily increasing. Electrical resistivity is a common near-surface geophysical method that has traditionally been used for site characterization in large projects. More recently, there has been a rise in its potential use for locating and/or examining infrastructure. One potential use for electrical resistivity is to “see” deep foundations; specifically, to identify defects during construction, evaluate existing structures for re-use, or determine the dimensions of unknown foundations. Electrical resistivity has been successful with large foundations (>1 m diameter) but the method fails at long, slender elements like singular driven piles. The limitations of imaging the foundations are in the data post processing. Most geophysical inversion schemes solve the forward problem using the finite element method (FEM), which cannot capture small heterogeneities without over discretization of the element mesh. Additionally, the FEM inversion schemes have the propensity to smooth inverted ERT images and create near surface mathematical artefacts, making the final images inaccurate representations of the true electrical resistivity distribution of the subsurface. This paper presents an alternative solution using the analytic element method (AEM). An advantage of AEM over FEM is its ability to directly solve electrostatic interface conditions across discontinuities (such as a concrete pile) without needing a finely discretized mesh at these interfaces. This paper presents two examples comparing the FEM with the AEM using electrical resistivity: a steel H-pile and a reinforced concrete pile driven in sand. The FEM solutions show that the foundation cannot be discerned from the background soil. The pile elements are more accurately represented in the AEM models where sharp interfaces are easily seen. The next step in this research will be to incorporate the AEM in an electrical resistivity inversion to fully realize the capabilities of the AEM and capture a true representation of the subsurface electrical resistivity distribution. This has the potential to expand the use of electrical resistivity for examining deep foundations.

One of the key challenges of drilled shaft non-destructive testing (NDT) is the quality of the acquired data, which is related to the survey configuration. In the specific case of crosshole tomography (CT), relatively small spacing is used between sources and receivers in the access tubes. Even with such an extensive data acquisition program, CT can fail to detect defects that are large enough to negatively affect foundation performance. Full waveform inversion (FWI) is a high-resolution tomographic technique that can potentially address this issue. Instead of relying on first arrival times in a ray-based analysis, FWI attempts to simulate wave propagation within the drilled shaft and match the entirety of the signals acquired during crosshole testing. This approach improves resolution at the expense of higher computational costs. However, FWI might not necessarily require such extensive instrumentation for satisfactory performance. Therefore, it is beneficial to evaluate possible survey configurations that can optimize data acquisition and increase the practicality of FWI for drilled shaft structural integrity testing. In this study, it is proposed that a sequential optimal experimental design (SOED) approach can provide insights into potential optimal survey configurations. The outcomes are presented as a benefit-cost curve that allows one to select an appropriate number of crosshole sources based on available resources. The principles of SOED are first described, followed by a discussion of its performance when used to evaluate optimal survey configuration. 2D FWI is then performed using different survey configurations on numerical models of drilled shafts with known defects. The results highlight an increase in the number of crosshole sources, which directly increases the computational efforts but does not continually lead to appreciable improvements in the inverted images and subsequent interpretation of defect geometry and location.

The subject shaft was part of a large infrastructure project involving the construction of six new stations, additional tracks to accommodate to increase capacity of ridership (50,000 passenger trips per day increase), and electrifying the trains from the current diesel system. The work extends along the existing tracks for approximately 7 miles (11.26 km) between several communities and ends at a private university. The large diameter drilled shafts [7–8 ft (2.13–2.44 m) in diameter and up to 125 ft (38.1 m) in depth] support a new elevated train viaduct structure. The shafts were installed with slurry methods. The subsequent thermal integrity profile (TIP) test performed after a particular shaft was concreted revealed a potential design concrete cover issue (less than required) at a depth between 60 and 72 ft (18.3 and 21.9 m) from working grade. Several remediation measures were evaluated including jet columns to generate the required cover and replacing the exposed rebar by drilling and grouting replacement bars into the shaft. An engineering analysis was performed to confirm the shaft could perform structurally without any remediation efforts. Finally, corrosion analysis was performed to ensure the durability of the shaft was not compromised during the shaft’s service life.

The South Carolina Ports Authority (SCPA) is currently building the Hugh K. Leatherman Terminal (HLT). The terminal is built on historic marsh, dredge spoils, and even an abandoned Navy airfield runway, where post-construction settlement is anticipated up to 12 in. (305 mm) over 25 years. The associated downdrag forces anticipated to act on the driven piles supporting site structures were a driving factor in pile length calculations planned at the site. Since these piles were designed using a traditional design approach, Insight Group in coordination with SCPA recommended an alternate design approach, referred to as “Neutral Plane Method,” in an effort to minimize cost and improve constructability. High strain dynamic test results in conjunction with neutral plane analyses were used to develop production pile driving criterion for each structure. As a result, production pile length reductions ranged from 6 ft (1.8 m) to 27 ft (8.2 m). PDA testing and neutral plane analysis results for one representative building are presented, illustrating cost savings and improved constructability.

Driven piles have been commonly used as a suitable deep foundation alternative to the soil conditions in Central Florida. Pile driving is a complex dynamic soil-structure interaction problem that induces vibrations and settlements in the surrounding soils. Numerical models need to be capable of accurately simulating pile dynamics so that the response of soil during the pile installation can be properly assessed. In this paper, numerical analyses were conducted using the finite element platform PLAXIS 2D to compare different modeling approaches used in the technical literature (i.e., continuous versus discontinuous) for the pile driving process. A parametric study was performed to elucidate the role of plastic zones in the process of pile penetration. The constitutive soil model used was the hardening soil model enhanced with small strains (i.e., HS small). Subsurface conditions were determined using laboratory and field-testing data collected from a project site. Input parameters were estimated from subsurface exploration data and processed using GRLWEAP, which is a wave equation analysis program. The concept of a plastic zone with reduced stiffness and strength was introduced around the pile to model the continuous process of pile installation. Based on the results, a continuous pile driving approach matched well with field measurements and provided better insight into the pile-dynamic behavior than a discontinuous modeling approach based on a single blow at various depths. The continuous and discontinuous numerical modeling approaches are compared and discussed associated with pile penetration and velocities at the top of the pile.

Highway bridges are critical structures with little tolerance to movement. Consequently, bridges are typically supported on pile foundations to limit the settlement. Approach embankments are prone to settle more than the bridge, especially when embankment is founded on cohesive soil layers. Such consolidation induced settlement generates negative skin friction on the pile foundation—a phenomenon known as downdrag. Downdrag reduces pile capacity and diminishes its ability to limit vertical movement. This paper presents a comparison of two methods available to design for practitioners, the analytical method and the finite element method, in estimating settlements of deep foundations subjected to the downdrag phenomenon. The behavior of soil layers is modeled in a two-dimensional nonlinear finite element analysis using commercial software package PLAXIS2D. A sensitivity analysis is performed on selected input parameters to determine their significance and impact on the convergence. This paper is expected to be of benefit to researchers and practitioners in the field of geotechnical engineering by presenting a correction to the plain strain assumption.

The unpiled raft foundation may not provide safe and economical design for highly compressible subsoil strata. The effectiveness of rafts is improved by the addition of piles as settlement reducers. However, the load distribution in piled raft is such that axial stress and bending moments are carried by the piles with minimum contribution from raft and subsoil. To mobilize the strength of subsoil in the load transfer mechanism, the concept of disconnected composite piled raft with cushion was considered. The present study aims at understanding the behavior of disconnected composite piled raft with cushion using 3D FEM analysis, by considering pile and raft as linearly elastic and non-associated Mohr–Coulomb elasto-plastic behavior for cushion and subsoil. In this study, the raft and piles were disconnected using a layer of granular material referred to as a cushion (load transfer platform). This cushion layer helped in the redistribution of the axial stress ratio amongst piles and subsoil as compared to the connected piled raft and unpiled raft. The results indicated that the bending moment, axial force, and settlements of disconnected composite piled raft were substantially modified by the cushion thickness under varying vertical pressure.

Pressure injected footings (PIFs), or Franki piles, were a popular foundation option 50 years ago and are similar to rammed aggregate piers of today. Installation methods varied, but PIF creation generally involved ramming of a bulb of compacted concrete inside of a pipe to a certain depth. Once the desired depth was achieved, a “bulb” was often created by expelling the concrete plug and ramming additional concrete through the pipe. Besides creating a larger bearing area, the compaction effort involved in bulb creation densified the soil below. After bulb creation, the pipe was withdrawn as concrete was compacted in successive lifts to the surface. In some instances, the casing remained and in others, a rebar cage was installed, and normal slump concrete was then poured to the surface. Though these types of foundation elements are generally no longer used, they are often found in older buildings whose foundations are being reused for building repurposing and/or renovation. However, a methodology to account for their contribution to foundation capacity is lacking. Neglecting their support is often too conservative and not warranted; thus, a proper understanding of their behavior and how they interact with new foundation elements, such as micropiles, is critical for a safe, economic, and effective design. In this paper, a methodology is presented for the three-dimensional finite element (FE) modeling of PIFs and the compacted soil below the bulb. A model is presented and calibrated to a full-scale load test. Engineers can use the methodology presented in this paper to derive an understanding of the contribution of PIFs to foundation support and their interaction with new foundation elements during design.

In this study, a series of finite element analyses were carried out to study the effect of multiple hazards on a single drilled shaft in unsaturated sandy soil. The geotechnical design of the drilled shaft was carried out for proportionate axial load induced by a three-story building and lateral load induced by the 1940 El-Centro earthquake on a single shaft by using analytical methods and LPILE software. Then, finite element code, PLAXIS 2D with UBC-3D PLM constitutive model, was used to develop a plane strain model and analyzed by applying hydrological load from the 1979 Tropical Storm Claudette for various durations and earthquake at the end of each duration. The effect of hydrological load on the displacement of the drilled shaft was studied. Also, local liquefaction was observed near the drilled shaft at the ground surface, which caused heaving of the sand and vertical displacement of the drilled shaft.

Inspection of the geologic materials under the base of drilled shaft excavations is usually conducted to increase confidence in the anticipated base resistance, particularly, when the drilled shaft will rely significantly on rock sockets for its capacity. Current efforts rely on the use of probes inside corings at the bottom of the excavation. These assessments are qualitative, indirect, and spatially limited. A non-destructive testing (NDT) tool that provides information on the geometry and mechanical properties of the geologic materials under the drilled shaft excavation would potentially address these limitations. In this study, an NDT system that relies on full waveform tomography of stress wave data is examined for this purpose. FWI extracts as much information as possible from the recorded stress wave data by simulating wave propagation within the domain and matching the observed and simulated sets of waveforms in an iterative optimization scheme. In a series of numerical simulations, anomalous features were placed within a domain that represents competent base materials for a drilled shaft excavation. A source–receiver array at the bottom of the excavation was used to acquire waveforms for processing. Recommendations are provided on the selection of an appropriate FWI workflow given the constraints of this application. Finally, the results highlighted that an FWI NDT approach can accurately evaluate the spatial extent of any anomalous conditions and the contrasts in their mechanical properties relative to the surrounding bedrock.

Analytical models available in the literature that predict transient heat flow in soils around ground source heat pump systems (GSHPs) mostly simplify the condition and consider constant heating rate. However, in practical application, inlet fluid temperature (thermal loading) changes with time, and therefore, heat flux along the depth varies over time. Therefore, in this study, we developed an analytical model based on a solid cylindrical source model for analyzing transient heat flow in soils surrounding an energy pile by considering a time-dependent heat flux. Heat conduction equation is solved in two-dimensional axisymmetric condition. A time-dependent heat source term can enhance the previous analytical solution (e.g., a solid cylindrical model) for practical applications. In order to solve the heat transfer equation, Green’s function and imaging methods are utilized. Results indicate that soil thermal response close to an energy pile significantly changes while considering a temporal variation of the heating rate.

This study focuses on refining the solution used to calculate the heat transfer in a novel, self-operating geothermal energy pile based on the principle of a thermo-syphon. This new type of energy pile, formed by pressurizing a hollow helical pile with carbon dioxide (CO₂) to form a heat pipe, is highly efficient, which could be an important alternative of existing energy pile. Specifically, this new type of energy pile utilizes spontaneous liquid–vapor phase change and natural convection inside the pile to transfer heat from the pile tip and the head. By isolating the pile from the soil and analyzing it as an independent heat transfer unit, the pile seems to have equivalent thermal conductivity that is thousand times of common metals. A simplified closed-form solution has been developed to estimate the heat transfer rate as well as equivalent thermal conductivity, which links the geometry of the energy pile with its thermal efficiency. This simplified solution could be used as a preliminary approach to assess such an energy pile system, but it has great room for improvement since the derivation used a number of assumptions. This study refines the simplified solution by replacing some of the assumptions with mathematical quantifying components and leads to more accurate heat transfer estimates.

Geothermal deep foundations (energy piles) are used for heating and cooling of buildings. The intermittent operation of the ground source heat pumps (GSHP) connected to energy pile subjects the soil–pile interface and the surrounding soil to cyclic temperature changes affecting soil–pile interaction and shaft resistance of the pile. To evaluate the effects of cyclic thermal loading on the soil–pile interface properties and effect of temperature cycles on pore water pressure, a fully automated modified thermal-borehole shear test (Modified-TBST) device was utilized to perform tests in saturated normally consolidated clayey soil. In addition to directly measuring the shear stress-vertical displacement curves (t–z curves), the soil temperature at different locations and the pore water pressure were monitored. The fully automated Modified-TBST device uses two concrete plates to simulate the pile surface with temperature and expansion/contraction controls. A series of tests were conducted to evaluate the effects of intermittent operation times for temperature change (ΔT = 10°C) and temperature cycles (N = 10 heating cycles). It was observed that the operation time of the GSHPs connected to energy piles has significant effects on thermally induced pore water pressure when installed in saturated clayey soil.

The operation of the ground source heat pumps (GSHPs) coupled with energy piles subjects the foundation and the surrounding soil to temperature changes and cycles, which affect the thermo-mechanical behavior of energy piles. The majority of the research presented in the literature focuses on the effects of temperature change on axial serviceability and resistance of energy piles. However, studies evaluating the effects of temperature change and cycles on the behavior of energy piles subjected to lateral loading are scarce. The behavior of soils surrounding energy piles is affected by temperature changes and cycles, soil volumetric change, thermally induced pore water pressure, and thermally induced water flow. Hence, it is anticipated that the thermo-mechanical soil-structure interaction of laterally loaded energy piles is affected by similar factors. This paper aims to assess the behavior of laterally loaded model energy piles subjected to thermal loading. An instrumented aluminum energy pile with diameter of 51 mm and an embedded length of 0.41 m installed in saturated moderately overconsolidated clayey soil was utilized in this study. The pile was instrumented with strain gauges and temperature sensors, and the surrounding soil was instrumented with temperature and pore water pressure sensors. The mechanical and thermal responses of a heating and a baseline (no temperature change) test are analyzed and compared in the current study. The experimental results indicate that the operation of the GSHPs connected to energy piles affects the soil strength and the soil-pile interaction behavior when the pile is subjected to lateral loading.

Currently, soil structure interaction in energy piles has not been understood thoroughly. One of the important underlying features is the effect of tip and head restraints on displacement, strain, and stress in energy piles. This study has investigated thermo-mechanical response of energy piles subjected to different end restraints by using recently found analytical solutions, thus providing a fundamental, rational, and mechanics-based understanding. End restraints are found to have a substantial effect on thermo-mechanical response of energy piles, especially on thermal axial displacement and axial stress in the pile. Head restraint imposed by interaction of an energy pile with the superstructure led to a decrease in the magnitude of head displacement and increase in axial stress, while decreasing the axial strain. The impact of head restraint was more pronounced in end bearing than in fully floating energy piles.

Soil structure interaction in energy piles has not yet been understood comprehensively. One of the important underlying issues is the location of a zero-displacement point, known as the null point. This study investigates how the location of a combined null point in fully floating energy piles is affected by relative magnitudes of thermal and mechanical loads. Analytical solutions are used to address four different loading scenarios including compressive and tensile loads, and heating and cooling. It was found that the location of the combined null point coincides with the location of the maximum magnitude of the axial stress induced by thermo-mechanical load. Furthermore, while a thermal null point is always present in fully floating energy piles, the combined null point is absent in the case of a small magnitude of thermal load as compared to the mechanical load. With increase in the relative magnitude of thermal load as compared to the mechanical load, the combined null point emerges at different locations for different load combinations. In all cases, it subsequently moves towards the mid-length of the pile with increase in the relative magnitude of thermal load.