IFCEE 2018: Installation, Testing, and Analysis of Deep Foundations

When conducting probabilistic analyses using service limit state design for deep foundations, modeling and simulating load transfer data are essential. Before the research presented herein, no quantified uncertainty of load transfer for drilled shafts in shales (cohesive intermediate geomaterials) was available nor were there methodologies for incorporating and simulating the variability and uncertainties of a load transfer model for probabilistic analyses. This paper features a study where load transfer data were analyzed to find the best fit model that reflects data and their variability and uncertainty. The load transfer data are side and tip resistance of individual drilled shafts founded in shales. Intensive nonlinear regression analyses were performed using constant standard deviation and constant coefficient of variation assumptions with four different functional models and two approaches to carry out the analyses. Accordingly, two methods to simulate the load transfer data using Monte Carlo simulation are proposed, which incorporate the uncertainty of the models in probabilistic analyses. Recommendation was made to use non-weighted least square regression and collective approach of analysis to analyze the load transfer data. Quantified variability of the load transfer data, as well as the method to simulate the load transfer data, is now available for probabilistic analysis for service limit state of drilled shafts in shales.

Methods of utilizing data collected from pile top force-time and velocity-time records during impact hammer driving have been used to estimate the static capacity of piles for many years. These methods have been successful but still suffer from questions regarding uniqueness and soil characterization. The method proposed in this paper uses a two-dimension axisymmetric finite element model of the driven pile system coupled with a dimensionless soil model to reduce the number of parameters to be analyzed. These parameters are then applied to the soil in designated layers to determine the characteristics of a soil profile, using a polytope method for signal matching purposes. A static analysis is then performed on the system to estimate the static capacity by a designated method of static load test interpretation. An example from actual data is presented. The performance of the model shows reasonable correlation and opens up the possibility of further research.

This paper presents results of a numerical study of the lateral response of berthing structures by considering soil-structure interaction. Most marine terminals are equipped with a deep water berthing facility. The vessels berth to dedicated breasting dolphins and are restrained by mooring dolphins. These structures comprised of a large cap and supporting piles and are normally subjected to large lateral loads compared to their masses, which present complex analysis and design challenges to engineers. In order to gain a better understanding of soil-pile interaction of such structures under lateral loading, a numerical investigation which combines the differential equations for beam-column with finite difference and discrete methods has been conducted using GROUP software. Interest is focused on the p-y curves, and lateral deflection and bending moment of the piles in berthing structures. A group of drilled shaft piers with rigid cap representing a breasting dolphin are analyzed laterally using theoretical p-y curves generated by software as well as experimental p-y curves produced using the method of pressuremeter tests (PMT). Parametric study including dredging effect, permanent steel casing, and pile head boundary condition are also presented, and parameters influencing the overall structure response are identified and discussed. The results demonstrate good agreement between two analyses associated with theoretical and experimental p-y curves.

Small diameter segmental jacked pipe piles are one option for underpinning lightly to heavily loaded structures to reduce settlement and even restore the structure to near original condition. In most cases, short sections of steel pipe are jacked into the ground through poor soils to achieve the desired load capacity from end bearing on a firm layer. The mass of the structure is used as the reaction to jacking. A study was conducted to evaluate the influence of end configuration on the installation jacking force and load behavior on jacked segmental pipe piles in a stiff overconsolidated clay. Four different configurations of the pipe end were tested: two closed ends (flush and oversized plate) and two open ends (no end plate and oversized ring). Plugging measurements were made of the open end piles during installation. Compression tests were conducted one day after installation to determine short-term axial capacity. The results show that the pile plugging of open end piles occurs very quickly and that substantial side resistance can develop for flush end pipes. Results of the site characterization, pile installation forces, and load tests are presented.

Soil along the walls of bored piles or drilled shafts in clay may undergo changes from in situ conditions as a result of the construction process. Stress relief from unloading, softening from water accumulation in the open hole, disturbance from drilling tools, and water migration from the grout or concrete may affect the behavior of the clay at the interface between the grout/concrete and the soil and the development of side resistance. An increase in water content and decrease in shear strength may occur if the soil absorbs water from the grout or concrete. A series of laboratory tests were conducted to determine the degree of moisture migration on the water content and shear strength of clay from portland cement grout. The results demonstrate that the changes in the clay behavior may depend on: initial state of clay (liquidity index), w/c ratio of grout, time, and head of fluid (grout pressure). Results of the lab tests illustrate the degree of influence of these variables on changes in water content and shear strength of the clay. The implications on undrained (total stress) design of bored piles and drilled shafts in clay are discussed.

Geoengineering profession has witnessed continuous advancement in the application of cone penetrometer test (CPT) data for the analysis of deep foundations. Numerous methods based on scaling systems between CPT data and the pile capacity have been advanced. Rational methods founded on the CPT-based estimates of geoengineering parameters are also available for use in various analytical formulations. There are areas still demanding significant refinement. Diverse data sets of pile load tests and CPTs have played a key role in implementing this approach. The applicability of each method is limited for soil and pile typology. Pile capacity is not an agreed single value also. Each method requires one of the numerous criteria to define capacity value on the pile load-displacement curves. For most part, the manner in which CPT-based pile designs were advanced shows a certain degree of randomness. Furthermore, CPT readings are recorded in short-term at a high strain rate of loading. This differs significantly from the pile resistance in long-term involving setup or increased capacity overtime. This important yet missing component in pile-CPT correlations leads to uneconomical designs. These and other related issues are discussed in detail, and recommendations are made to steer future research on the topic.

During the past 15 years, drilled pier and CFA pile foundations have largely supplanted driven piles for the support of heavy structures on the Island of Oahu in Hawaii. These drilled foundations derive the majority of their support from side shear in coral reef formations, which consist of weak, fossiliferous calcareous limestone interbedded with coral detritus and lagoonal deposits. This paper summarizes the results of ten instrumented load tests performed on CFA piles and drilled piers ranging in size from 460 to 1,200 mm in diameter. The results of these tests are evaluated relative to ultimate support values and strain required for the development of side shear load transfer. Conclusions are presented relative to the contribution of construction installation methodologies for the various foundations tested. Based upon the results of the experience gained from these load tests, recommendations are presented for design side shear parameters for drilled pile and pier foundations installed in similar geologic formations.

An approximate semi-analytical method is developed to obtain the dynamic response of laterally loaded end-bearing piles embedded in a homogeneous soil. In the analysis, the soil is modeled as a three-dimensional viscoelastic continuum, and the pile as an elastic Timoshenko beam with solid circular cross-section. The Timoshenko beam theory is used to include the effects of shear deformation and rotatory inertia of the pile cross-section that might be important for short stubby piles and for piles subjected to high frequency loading. In the analysis, the horizontal soil displacements are expressed as products of separable functions, and the extended Hamilton’s principle in conjunction with the calculus of variations is used to obtain two sets of coupled differential equations governing pile and soil motions, along with the relevant boundary conditions. The coupled equations are solved analytically and numerically following an iterative algorithm. The pile differential equations and boundary conditions can be simplified to obtain the Euler-Bernoulli beam theory representing the pile behavior. Complex dynamic pile-head impedances are obtained from the present analysis using the two beam theories.

Lack of well-defined approaches to characterize soft rocks and the lack of methods for designing driven piles pertaining to soft rocks often lead to some challenges during design and construction. The design of piles in soft rocks are currently performed using static analysis methods, which were originally developed for soils. Understanding the current limitation of design of piles in soft rocks, a research is being conducted by the authors to firstly develop an electronic database containing the information on subsurface, pile, hammer, driving, dynamic, and static load tests of piles driven in soft rocks obtained from the Wyoming Department of Transportation. The database facilitates storage of quality data required for static and dynamic analysis and can be easily retrieved for future development of resistance factors for load and resistance factor design (LRFD) in soft rocks. Pile resistances estimated using static analysis and wave equation analysis program (WEAP) have been compared with those determined using case pile wave analysis program (CAPWAP). Performance has been assessed using statistical parameters, such as resistance bias (ratio of measured to estimated pile resistance) and COV, which will be used for developing resistance factors for different static methods and WEAP. Results showed that the static analysis methods were largely conservative and inconsistent in estimating the total resistances of steel H-piles driven in soft rocks. Although WEAP overestimated almost 60% of the total test piles, the mean estimation was extremely close to the measured pile resistance with a relatively low coefficient of variation (COV). The reliability of the design on soft rocks can be improved by the performing pile dynamic tests with CAPWAP analyses on greater number of piles.

Load and resistance factor design (LRFD) is the predominant design method utilized today for reinforced concrete and structural steel, and is the primary focus of the AASHTO LRFD bridge design specifications. Historically, micropile design has been performed mainly with allowable stress design (ASD) methodologies, and most of the micropile design manuals and specifications in existence prior to 2008 were based on ASD. In light of this history of ASD design methodologies, and in spite of the widespread use of LRFD in general structural design disciplines, there have been a number of questions and a great deal of confusion regarding the proper use and implementation of LRFD design methodologies for micropiles. The author, as part of a DFI/ADSC Joint Micropile Committee initiative, developed a presentation in response to these questions and issues which covers the fundamentals of LRFD as it applies to micropiles, and provides an illuminating comparison with ASD methodology. This paper is a formalized and updated snapshot of the current state of practice of LRFD for micropile design based on the most current information and design codes relevant to micropiles. It will describe the fundamentals of load and resistance factor design (LRFD), demonstrate micropile design concepts utilizing LRFD, compare the results with historical ASD design, point out the limitations of current LRFD practice relative to micropiles, and finally, make some observations and recommendations for the path forward with regard to proper implementation of LRFD as a true reliability based design methodology for the design of micropiles.

Results of numerical models to simulate torpedo anchor installation in soils are presented. An explicit dynamics finite element hydrocode was used to model installation of a torpedo anchor in a sandy soil deposit. The constitutive model used consisted of an equation of state to model compaction and wave propagation, along with a rate independent frictional strength model to simulate the frictional soil response. An arbitrary Lagrangian-Eulerian formulation was used to model the soil medium, along with a gap interaction algorithm and a strain penalty model to accommodate large mesh distortions during torpedo installation. Model validation was carried out by comparison against laboratory results of torpedo embedment in synthetic transparent soil models. Constitutive parameters were derived from uniaxial and triaxial tests on transparent soils. Comparison of the results showed that the simulations are capable of capturing the salient features of soil kinematics during torpedo anchor installation.

This paper presents the results from a pile load testing program for a bridge construction project at Chalmette, Louisiana. The load testing includes three 66-in. spun-cast post tensioned open-ended (O.E.) cylinder piles and one 30-in. square prestressed concrete (PSC) pile driven at four different locations along the bridge site. Both cone penetration tests (CPT) and soil borings/laboratory testing were used to characterize the subsurface soil conditions. All test piles (TP) were instrumented with strain gauges to measure the load distribution along the length of the TPs and to measure the side and tip resistances, separately. Static load test (SLT) was performed only on the PSC pile and statnamic load tests (SNLT) were conducted on both pile types. Design parameters such as the total stress adhesion factor, α, and the effective stress coefficient, β, were back-calculated. The α values ranged from 0.41 to 0.86, and the β values ranged from 0.13 to 0.29. The load test results showed that SNLT overestimated the tip resistance as compared to dynamic and static load tests.

The lateral resistance of pile groups is greatly affected by the pile spacing. The presence of neighboring piles at close spacings results in a reduction in the lateral capacity of each pile in the group due to the greater interaction between the piles. In this study, the effect of pile spacing on the static lateral behavior of two pile group configurations (vertical and battered piles) is investigated using finite element (FE) modeling. A total of six three-dimensional FE models were developed in Abaqus version 6.12 for 4 × 4 vertical and battered pile groups at three pile spacings (3D, 5D, 7D), where D is the pile width. The nonlinear pile group behavior was accounted for using elastoplastic constitutive models and pile-soil interface model. The influence of spacing on pile group efficiency, internal axial load in the piles, and p-multipliers is discussed. The results showed that the battered pile group had larger group efficiency (70–90%) than the vertical pile group (40–80%) at all pile spacings. The vertical pile group had a significant boost in pile group efficiency (28%) when the spacing increased from 3D to 5D, while it was 14% in the battered pile group. The internal axial load decreased only in two pile rows in both pile groups with increased pile spacing. The p-multipliers increased with increased pile spacing in both pile groups, in which the rate was highest in the middle and trailing rows.

This study explores the use of state-of-the-art data analytics techniques for predicting the axial load capacity of piles. A support vector machine algorithm was developed. About 213 load tests obtained from FHWA’s deep foundation load test database (DFLTD) version 2 were used to evaluate the performance of the developed approach against the FHWA design method. The scope was limited to impact-driven, un-tapered, steel, and concrete piles, loaded in compression, using a static load test. The results of the predictive analysis show an improvement over the capacities obtained by the FHWA pile design method. Perhaps more remarkably, the predictive model outperformed the FHWA pile design method by relying only on seven readily available features as compared to a laborious and error-prone design methodology. This study demonstrates the potential of machine learning in geotechnical engineering as an alternative to conventional design approaches. The methodology is also demonstrated with an online capacity computation tool.

The original strong-rock (SR) p-y curves for rock-socketed shafts exhibit a brittle response where the post-peak resistance drops to approximately zero. This brittle response could result in a progressive failure of the rock p-y curves which, in turn, results in excessive pile lengths. This paper proposes a modification to the strong-rock (SR) p-y curves where the post-peak residual strength is equal to 20% of the ultimate resistance (0.2*p_ult). This residual resistance is proposed based on the assumption that the lateral resistance of cracked rock (after the peak point) should not be smaller than the lateral resistance of heavily weathered rock estimated from the weak-rock (WR) and Liang et al. p-y curves. The effectiveness of the modified SR curves is evaluated against the results of a lateral load test. The modified SR curves are compared against back-calculated p-y curves from the lateral load test.

Foundation reinforcement using micropiles can enhance the bearing capacity of foundations and reducing the settlement of structures in building remodeling with vertical extension. However, in the process of vertical extension following foundation reinforcement, the allowable bearing capacity of the existing piles is still likely to be exceeded due to the additional load. This study presents a preloading method used to carry a partial load from the existing piles and to mobilize skin friction along the reinforcing piles in advance to ensure that the carried load on the existing piles does not exceed the pile’s allowable bearing capacity. Two cases, foundation underpinning without preloading and with preloading, were compared using FEM analysis with PLAXIS 3D. The analysis results showed that the preloading method using jacking equipment had a significant influence on mobilizing the skin friction along the reinforcing pile and reducing the carried load on the head of the existing piles.

Young coastal sedimentary deposits are not ideal for a large iron ore stockpile shed, particularly a building more than 800 m long and about 33 m high that contains sensitive mechanical reclaimers and conveyor systems. This paper will review the site conditions encountered near Corpus Christi, Texas, and discuss how the foundation engineers adapted building foundation design as more detailed geotechnical challenges became evident after contract award. Controlling deformations while understanding and managing risk to accommodate mechanical systems and overall plant operations was of paramount import to the entire team from owner to foundation contractor and engineer. Although there was significant risk with the geotechnical conditions, schedule dictated that the building be erected on time. This paper focuses on the site evaluation and risk management in the building foundation design. A companion paper will discuss ground improvement and monitoring performed after the building was erected.

A multitude of geotechnical applications such as foundations, retaining walls, and slopes have been analyzed through the use of limit equilibrium methods (LEM) based on soil mechanics or plastic equilibrium theory. The most commonly used LEM methods for foundations utilize a shear surface based on the assumption of an ideal stiff material, but have found widespread application to softer soils not meeting the assumed criteria. These shear surfaces can be observed through foundation displacements and soil deformations in the field or the lab, however full development and observation of the shear surface typically requires failure to occur and instrumentation to be installed into the soil. The instrumentation, however, can cause variations in the soil behavior or not capture the correct deformations within the soil if their stiffness differs from the surrounding soil mass and only give deformations at discrete locations. In order to overcome these limitations, the failure surfaces of suction caisson foundations with an aspect ratio of 1 were examined non-intrusively through the use of a transparent soft clay surrogate under monotonic vertical compression and uplift loading. In the soft clay, a partial formation of the commonly assumed three-zone LEM failure mechanism was observed.

Deep and large diameter drilled shafts use mostly bundles of Grade 60 (415 MPa) reinforcing bars as longitudinal reinforcement with rebar splices to make it longer. Lower grade steel requires large number of bars which result in rebar congestion and difficulty in placing concrete. This leads to increased labor cost for fabrication and installation. By utilizing larger size and higher strength threadbar, the congestion of rebar can be reduced significantly and bundling of bars can be avoided. The lap splices are replaced with simple threaded couplers and end hooks are replaced with end terminators. Threadbar conforms to ASTM A615-15 and can be epoxy coated if required for corrosion protection. This paper describes an attractive value engineering of replacing Grade 60 (415 MPa) bundle of rebars with larger diameter Grade 75 (515 MPa), Grade 80 (550 MPa), and Grade 100 (690 MPa) threaded bars and threaded couplers in some specific drilled shaft projects in the United States.

The load resistance factor design (LRFD) method for drilled shafts specifies that the service load multiplied by a load factor typically greater than 1.0, be less than or at most equal to, the sum of the nominal (ultimate) end-bearing and side shear resistances, each multiplied by a respective resistance factor less than 1.0. Some designers are reluctant to design combined end-bearing and side shear drilled shafts, referencing the known larger displacement required to mobilize peak end bearing than side shear. The authors have developed a modified LRFD method that combines the nominal (ultimate) side shear from empirical methods with the maximum allowable end-bearing derived from in situ pressuremeter testing (PMT). The creep pressure (p_f) from the pressuremeter may be taken as the maximum allowable end-bearing value, and is typically greater than can be justified from SPT or other empirical methods. For the cases presented, settlements calculated using the creep pressure in dense strata or intermediate geomaterials were typically on the order of ½-in. or less, which is much closer to the ¼-in. maximum deflection often cited as required to mobilize peak side shear resistance.

Relaxation is commonly described as the relative reduction in pile capacity as a function of time. This paper presents a possible mechanism for the development of dilation induced relaxation of driven piles in cohesionless soils, and presents field data collected from two construction sites where relaxation was recorded. Recommendations for detection of dilative zones during the subsurface investigation program, as well as methods to address the issue during preliminary design (i.e., test pile length estimates based on static analysis methods) and final design during construction (i.e., production pile length determination typically based on dynamic testing methods) are also included.

Building information modeling (BIM) has been immensely used in both research and practical purposes of construction field. The accuracy of details in BIM is also continuously enhanced through these endeavors. However, main application area of BIM is typically limited to superstructure issues, yet the application to substructure problem is highly uncommon. In this study, the possibility of using BIM for underground case is explored based on a case in Peoria County, IL. To do so, boring logs are composed from various locations within the county and used to identify the soil characteristics. The preliminary model gives 3D visualization of the modeled area and still carries all of the original information from the boring logs. Adding more boring logs can be easily done by using the spreadsheet format of the logs. Also, the model can be transferred to the IFC format, which enables 4D and 5D BIM analyses possible in the future works.

Monopile foundation have been widely used for offshore wind projects. With growing size of offshore wind turbines and their deeper water depth, stronger foundations are needed. The hybrid monopile foundation, which combines a monopile with a friction wheel, is investigated in this study. A series of centrifuge tests was performed on foundation models under cyclic loadings in sandy soil. The tests were conducted on a monopile, a monopile with solid wheel, and a monopile with crashed stone wheel. The cyclic responses of the three models are described. Accumulated lateral displacements and lateral stiffnesses are investigated: the lateral displacement increases continuously with cycles but at a lower rate, and the stiffness tends to be larger during the cycles. The hybrid monopile foundation shows a better lateral capacity comparing to the original monopile foundation. The theoretical analyses of monopile foundations were introduced and compared with the experimental results. The results are aiming to optimize the design of offshore wind foundation and provide better in-service behaviors.

Offshore wind turbines are generally subjected to large lateral-moment loadings induced by wave, wind, and ice. Friction wheel foundation, which is a mono-pile with a friction wheel near the seabed, has been proposed and proved by previous studies to effectively increase the stiffness and bearing capacity of the mono-pile under later-moment loading. In this paper, a new design of friction wheel filled with gravel was studied by numerical modeling. Numerical models of friction wheel foundations were established, as well as the mono-pile foundations. The load-displacement curves are validated by centrifuge tests. The stress and strain distributions along the mono-pile and friction wheel are depicted to discuss the mechanism of load transfer and the resistance contribution that the wheel makes. To optimize the design, several numerical models were built to carry out a parametric study regarding the annulus size between the outer ring and the inner ring and the height of the gravel wheel. The results can be applied to future design of the friction wheel foundations and predict the performance of this hybrid foundation under lateral-moment loading condition in offshore wind engineering.

This paper presents a geomechanical assessment of the effects of reservoir-induced deformations during production and injection operations on the bearing capacity of offshore piles. Injection/extraction of fluids deep into/from reservoirs results in spatiotemporal deformations of the reservoir rock, which translate into seabed movements. This can impact the performance of offshore foundations specifically in an event of a hurricane. A numerical model is developed in this study to replicate a driven pile from the EC368A platform. The model is calibrated versus real data from literature. Next, the geomechanical response of the overburden to injection and production flow is incorporated in the model in a novel manner. Finally, the pile’s ultimate bearing capacity is assessed for three cases: trivial subsurface deformations, injection-induced deformations, and production-induced deformations. Results confirm the proposed hypothesis that reservoir-induced deformations can notably affect pile’s performance, and thus should be incorporated in the design of offshore platforms.

Pile foundations supporting bridge abutments are often driven inside corrugated metal pipe sleeves (CMS) which extend through the approach fill to reduce downdrag or for construction expediency. The annular space between the pile and the sleeve is typically filled with uncompacted pea gravel. Designers often assume that the lateral resistance of the pile within the sleeve will be minimal; however, no test results are available to confirm this assumption. To investigate the lateral resistance of piles driven within CMS, a full-scale lateral load test was performed. The test pile configuration included a 32.4 cm (12.75 in.) pipe pile within a 60 cm (24 in.) CMS with uncompacted pea gravel filling the annular space. Results indicate that after small pile displacements, the lateral pile resistance was similar to that provided by an individual pipe pile and was even greater at larger displacements. As the pile displaced laterally, the gravel within the annular space became engaged and displaced the CMS into the compacted fill. Back-analyses indicate that the ultimate lateral pile resistance for this case can be approximated by treating the pipe-gravel-CMS as a composite pile having an EI equal to the pipe pile but with a diameter equal to the CMS.

Seismic performance of piles in improved ground can be crucially affected by soil degradation, gap formation, and energy dissipation through material and radiation damping. In this paper, we investigated these mechanisms using centrifuge modeling of the response of a single pile to a seismic excitation. We represented the interaction forces between the pile and the soil system using discrete interaction elements distributed along the pile. The resisting force generated in each element consisted of a hysteretic component and a radiation damping component. The hysteretic force was formulated by the Extended Bouc-Wen (EBW) model and the key parameters of the model were calibrated. The simulated soil reactions were validated against their counterparts derived from the curve-fitted measured bending moments. The simulated soil reaction for the soft clay followed the trends and captured the peaks for most parts of the excitation. For the improved clay, however, the interaction element was unable to capture the significant hardening that occurred around the peak of the excitation. Contribution of the radiation damping in the simulated soft clay reaction was found to be much more significant than that of the improved soil.

The results presented in this paper were obtained from a large testing program that was conducted to evaluate the post-liquefaction axial load capacities of three drilled shaft and three driven pile foundations constructed at the Turrell Arkansas testing site (TATS), located within the New Madrid Seismic Zone. An increase of side and toe resistances, significant ground and driven piles and drilled shafts top settlements were observed following blasting. This increase and settlements were attributed to the increase of effective stress as the excess porewater pressure dissipated. The liquefaction-induced dragloads that developed, at the neutral plane ranged from 200 to 650 kN. The load and settlement distribution curves for each installed foundation during the application of load to the top of each foundation and after blasting are also discussed. The induced dragloads represented more than 5 and 10% of the total resistance of the drilled shaft and driven pile foundations, respectively.

A common practice for evaluation of liquefaction risk in pile groups relies upon the simplified procedure using SPT N₆₀ values. However, there have been few documented instances where the densification caused by driving displacement piles in groups has been taken into account for reduction in liquefaction risk. This paper presents a collection of field data obtained prior to and after driving piles in granular soil that demonstrates a significant increase in N values. The increase is most pronounced within groups of piles spaced at 4 pile diameters or less and the increase extends beyond the limits of a group, but to a lesser degree. Using the collected data, this paper presents a method that estimates the increase in N values for loose to medium dense sands as a consequence of pile driving. The method is based on theoretical considerations with empirical validation. The method can be used to provide an improved evaluation of liquefaction risk in pile groups, as shown by an example.

Pile foundations in liquefiable soils need to be checked for the bending moments due to the liquefaction induced stresses to arrest the plastic hinge formation. Recent studies reveal that the bending moments in the pile are significantly higher during the partial liquefaction stage (excess pore water pressure ratio <1.0) than at the fully liquefied condition. This study proposes a method to estimate the pile bending moments during partial liquefaction. Advanced multi-stage cyclic triaxial tests are conducted on sandy soil to understand the partial liquefaction behavior. The test results are then utilized to model the soil pile interaction in partially liquefiable soils following the beams on nonlinear Winkler foundation (BNWF) approach. The method is based on mobilized strength design concept. The developed numerical model is analyzed using the traditional lateral soil springs along with the proposed springs. It is understood from this study that the bending response of pile foundations in partially liquefiable soils can be effectively estimated with the proposed methodology compared to the existing models.

Side resistance factors and tip resistance factors were calibrated for use in service limit state (SLS) designs of side friction shafts and end bearing shafts in shales. The SLS design procedure utilizes the t-z method and adopts the factored strength approach to account for variability and uncertainty in the design and associated input parameters. The variability and uncertainty considered for calibration of the resistance factors were derived from full-scale load tests performed on drilled shafts embedded in shales in the central United States. Monte-Carlo simulations were used to calibrate the resistance factors. The range for side resistance factors is 0.05–0.2, and the range for tip resistance factors is 0.1–0.5, depending upon shale uniaxial compressive strength coefficient of variation, normalized loads, and probability of failure. Under the same conditions, side resistance factors are smaller than tip resistance factors. The obtained resistance factors are substantially low but reasonably reflect the collective variability and uncertainty presented in the design of drilled shafts in shales.

This paper presents the details and preliminary results of full-scale lateral load tests on driven piles in Bangkok clay. Steel piles of moderate size were instrumented with strain gauges at various locations along the length. Field load tests were carried out to large pile displacements. Based on the framework of elastic beam on foundation, the strain gauge outputs were employed to determine pile bending moments, deflections, and external soil reactions. The experimental pile responses were compared to the numerical predictions of the computer program LPILE. It was found that the numerical model predicted unrealistically stiff load-deflection behavior. The reason was likely the use of Matlock p – y model for soft clay which significantly overestimated the experimental p – y relationships of Bangkok clay particularly near the ground surface.

Bi-directional load testing is widely used to test drilled shafts, which can conveniently provide both side and tip resistance. However, extrapolation of the side and tip resistance movement curve is often required to determine the equivalent top-down load-settlement curve. It is prone to extrapolation errors due to limited movement in one or both directions. As a result, the calibrated resistance factors based on the extrapolated curves are affected by the extrapolation errors. In this study, eight bi-directional load tests, all performed on drilled shafts, were selected from Louisiana and Mississippi which has reported maximum equivalent top down settlement close to or larger than 5% of shaft diameter. For each load test, baseline extrapolations of the complete top and bottom movement curves using hyperbolic functions were performed to determine top-down load-settlement curve. Statistical error analysis of extrapolation was performed on truncated top and bottom movement curves to determine variation caused by incomplete settlement data. Statistical distribution of the bias errors due to extrapolation was analyzed using histogram plots. One-inch and 5%B failure criteria were used to determine ultimate resistance. The error associated with calibrated resistance factors due to selected extrapolation scenarios was quantified.

Helical piles are used frequently in western Canada to support transmission line towers due to their high tensile capacities and their ease of installation in difficult soil conditions such as soft clays or organic materials. There are several studies documenting their performance under lateral loads. However, most of the available studies are for single piles. The use of group of piles to support the foundations of transmission line towers is very common. Depending on the type of tower (i.e., tangent, light angle, heavy angle, or dead end) and loading conditions, groups of two to five piles are frequently used. In the present study, two pile groups, each of them with two piles, were presented. The paper documents the pile configuration and installation details of pile groups. The pile groups were installed into very stiff clay till so that one pile was vertical and the trailing pile was inclined at batter angle of either 20 or 30°. Soil stratifications and groundwater conditions were also summarized. Lateral load tests were performed using ASTM standard ASTM D3966 (ASTM 2013) for lateral load tests and the results were summarized in the paper. The results of the load tests were compared to a theoretical model using nonlinear p-y curves for lateral loading and t-z curves for axial loading. Based on the results of this study, it was found that a group of two helical piles can develop considerable resistance to lateral loads and that the lateral resistances of the pile group are highly dependent on the batter angle.

About eight 1:50 scale-model open-ended pile driving tests investigated the development of soil plugging. Scale test piles represent full scale 0.322 m (1 ft) and 0.635 m (2 ft) diameter piles, 20 m (66 ft) and 30 m (98 ft) long, driven into a medium sand of two densities. Pile driving hammer and drop height were scaled in addition to pile diameter, length, and soil grain size. The pile driving record and visual observations of localized down drag corresponded with anticipated full-scale behavior. Evaluation of plug length ratios and incremental filling ratios show the expected independence of plug length development on overall pile length. Soil density and pile diameter influenced plug length development. A dimensionless normalizing ratio based on driven length, nominal grain size, and inside and outside pipe diameters effectively normalizes the data. Soil density alone influences the relationship between the dimensionless normalizing ratio and plug length ratio. Scale-model testing provides a viable, if simplified, method for exploring soil plugging in open-ended pipe piles.

In this study, the performance of a non-displacement auger cast-in-place (ACIP) piles in sand under compressive and tensile loading was investigated by performing a field load test. In this full-scale load test study, ACIP piles were installed in layered sand, with loose sand [minimum Texas cone penetrometer (TCP) blow count of 7] in the top 4 m with very dense sand (maximum TCP blow count of 95) in the bottom layer 7 m below ground. The load test was performed on a 760 mm (30 in.) diameter fully instrumented ACIP pile with eight 450 mm (18 in.) diameter reaction piles. The test pile utilized a load cell and multiple pile top dial gages to measure applied load and settlement during the load test. Also, vibrating-wire sister bar strain gauges with thermocouples were attached along the length of the test pile and selected reaction piles. The design load for the test pile was 816 kN (92 t) and the test pile was loaded to 2,840 kN (320 t) before unloading. Using the Vipulanandan ACIP pile model, the ultimate capacity was predicted to be 4,545 kN (512 t), more than five times the design capacity. Skin friction-displacement relationships for the test pile in compression and reaction piles in tension were developed with depth representing the loose to very dense sand. The maximum skin friction measured in the very dense sand was 210 kPa (2.2 tsf) in compression and 57.3 kPa (0.6 tsf) in tension. The measured skin friction in the ACIP test pile in compression was more than 50% higher than the TxDOT design standard for drilled shafts in high blow count dense sands.

Laboratory tests were carried out on model rafts, single piles, and piled rafts made from aluminum and instrumented with strain gauges and deflection gauges. The foundations were installed in dry sand contained in a rigid tank. Maintained loads were applied to each foundation until failure was closely approached. Parallel to the tests, analyses were performed using PLAXIS™ 3D program and empirical methods in order to assess the accuracy of the various analysis methods by comparing the measured and predicted behavior of the foundations. The results confirmed that the efficiency of the piled rafts increased with increasing pile-pile spacing and approached unity at a spacing equivalent to 8D (D = pile diameter). The data obtained from the shaft strain gauges provided valuable insight into the load-transfer characteristics, and subsequently, proved that the capacity of a piled raft is significantly enhanced by intense interaction between the raft and the supporting soil.

The ability to drill safely and efficiently in all types of overburden (both natural and placed) and rock is fundamental to contractors providing specialty geotechnical engineering techniques. Such techniques include grouting, soil nailing, anchoring, micropiling, and freezing, as well as installing geotechnical instrumentation. Manufacturers of drilling equipment and systems must be very aggressive and innovative in a fiercely competitive economic environment, and a constant stream of developments are forthcoming. However, these developments may arrive at a pace bewildering for the non-specialist, who may not be aware of their significance or potential. The authors have therefore developed this state of the art paper with the intention of providing an overview of small hole drilling equipment and systems, as available in the U.S. as of 2017. Particular attention is paid to newer developments in DTH (down-the-hole) drilling for rock, and to casing underreaming systems, and rotary vibratory drilling for overburden.

Bridge foundation design has progressed towards larger diameter and longer drilled shafts in recent years, pushing the practical limits of construction. Load testing can lead to reliable foundation performance with shorter piles, helping to reduce cost and mitigate construction issues associated with unnecessarily long piles. A case study of an Osterberg load test program on a 10-ft (3-m) diameter 140-ft (43-m) long drilled shaft is presented. Results from the load test are used to determine final pile lengths for the project. A reduction of about 25 ft (7.6 m) or more is achieved per pile compared with lengths determined using conventional methods, providing cost savings, and improved constructability. Relatively simple numerical modeling tools are demonstrated to provide useful information during design and construction. Beam-spring models with side resistance (t-z) and end bearing (q-z) springs developed based on the load test illustrate the overall pile capacity within a displacement-based design framework. Axis-symmetric finite element (FE) models are calibrated using load test data and extended to address top-down loading and effects of potential anomalies on the pile capacity.

The Spring Villa test site is a national geotechnical experimentation site located near Opelika, Alabama and managed by Auburn University. The test site is located at the southern end of the Piedmont geologic province and is underlain by residual silts and sands which grade with depth into partially weathered rock. The site has been extensively characterized through borings, penetration tests, and geophysical tests. Several types of deep foundations (e.g., pipe piles, H-piles, and drilled shafts) have previously been installed at the site and many have been load tested. This combination of characterization and foundation data makes the Spring Villa site, a unique location to test new characterization methods and develop correlations to load test data in residual soils. Recent and ongoing work at the site includes examination of non-destructive testing methods for deep foundations and lateral load testing of pile bents. Despite the large amount of testing previously performed at the site, no comprehensive database exists showing the locations of these individual tests. This paper will present a new publicly available GIS database meant to address this issue by compiling the data from the various sources into a single location. The history and geology of the Spring Villa test site are briefly described. Results from previous characterization efforts are discussed along with a description of the various types of deep foundation that have been installed and tested at the site. The complied data should make it possible for future researchers to better utilize the site to develop and test methods for evaluating deep foundations in residual soils.

A sacrificial pile bent was laterally load tested in the weak direction to structural failure at the Auburn University National Geotechnical Experimentation Site. This test was conducted as part of a larger effort to determine the load path due to weak axis loading of a pile bent. The test bent consisted of 4 HP 12 × 53 piles installed at 8 ft center to center spacing with the outer two piles battered at 1.5:12. The free length was, on average 9 ft. The bent was topped with a 3 × 3 ft reinforced concrete cap. The bents were loaded to failure by pulling them against an existing 3 × 3 pipe pile group. The H piles were instrumented with strain gages along the free length and an inclinometer tube. This paper documents the load test setup and program and presents results of the test.

With the recent proliferation in the use of augered cast-in-place (ACIP) piles in Hawaii, there is still concern about the ability to install ACIP piles in difficult ground conditions, such as older alluvium containing abundant cobbles and boulders and into medium hard to hard basalt rock formations. The Waipahu project involved the installation of 24-in. (600-mm) diameter ACIP piles extending through up to 85 ft (26 m) of very soft organic soils and bearing in very stiff to hard older alluvium, reaching a maximum depth of up to 125 ft (38 m) below the ground. In addition, two instrumented bi-directional load tests were conducted and the measured side resistance values were used to re-evaluate the design of the ACIP piles. The net effect of the increased downdrag load but higher skin friction values in the older alluvium resulted in overall shorter ACIP piles for the project. The foundation drilling contractor utilized unconventional methods to efficiently drill through the older alluvium to the design tip elevations of the production piles. Thermal integrity profiling (TIP) testing was conducted on each production pile to provide the project owner with a higher degree of assurance that the foundations were constructed as intended. Care should be taken when estimating the total grout quantity of the ACIP piles as this value directly influences the results of the TIP analysis.

The evaluation of the bedrock present in San Francisco, known as the Franciscan Complex, can be an integral part of the design of the drilled shafts because the rock socket accounts for a significant amount of the load capacity. Franciscan Complex comprises a mix, or “mélange”, of predominantly sedimentary sandstone and shale that has undergone extensive faulting and shearing related directly to plate tectonics. This faulting and shearing action results in a chaotic mixture of materials, many of which have been broken down and weakened by shearing. The Franciscan Complex is especially unique in its irregularity across San Francisco, even within the footprint of a single building site (such as the case with the Oceanwide Center project). This paper will present the challenges in predicting unit side resistance in the Franciscan Complex using: (1) conventional equations like those presented in AASHTO (2008) and FHWA (2010) based on RQD; (2) using alternative equations incorporating GSI instead of RQD; and (3) using the Hoek-Brown strength criterion in finite-element modeling. All of these methods will then be compared to the results of bi-directional load test data collected at the project site with a discussion about the best methods to estimate drilled shaft capacity in Franciscan Complex mélange. In addition, a brief discussion of base resistance developed in the shafts is included herein.

The present paper discusses dynamic pile load testing (DLT) experiences in Costa Rica, specifically the results from three case studies, performed by the authors. These cases are the Caldera Grain Pier, the Moin Oil Terminal and a bridge over Tarcoles river at Chucas hydroelectric project. In every case, DLT was relevant to define criteria, follow-up driving conditions, estimate set-up, and confirm pile capacity. On two of those projects, static pile load tests (SLT) were also carried out, in parallel, thus allowing comparisons between DLT and SLT results. For every case study, results are presented and compared, furthermore, conclusions and lessons learned are drawn. The final perception is that DLT is a unique technique that can accurately predict the capacity of a pile, if used properly. Comparison with SLT results was key to draw the latter conclusion given the good correlation between SLT and DLT results.

The presence of temporary casing between freshly placed concrete and surrounding limestone formations may inadvertently leave crumbled debris upon casing extraction that may lead to side shear reduction. The primary objective of this work was to quantify how different methods of installation and extraction of temporary casings affect the side shear resistance on small scale limestone sockets. About 29 miniature shaft specimens were cast in six different simulated limestone beds ranging in strengths from 65 to 885 psi. Three casing installation/extraction methods were used: rotated with coarse cutting teeth, rotated with fine cutting teeth, and driven. At least one of the sockets in each bed was selected to be an uncased control, in which the casing was extracted and all debris were cleaned out prior to concreting. Results showed that the presence of casing caused loss in capacity. Weaker, more voided limestone was less affected than stronger, more contiguous material.

In the summer of 2014, the Minnesota Department of Transportation (MnDOT) began construction work on Bridge 10004 to elevate MN Highway 101 above the existing embankment grade eliminating seasonal flood closures. Thirty-inch diameter piles were used at many of the pile-bent piers to accommodate lateral load requirements associated with relatively long exposed lengths of piling. The axial compression loads were not particularly large, resulting in relatively few piles per pier. During construction, the 30-in. diameter piling was not demonstrating satisfactory capacity at planned toe elevations. Piles were driven considerably deeper than anticipated, with significant impacts on time and cost. Progressive pier construction made any longer-term pile re-strikes for capacity verification difficult. A static load test, modified from an earlier concept pre-design load test program, was conducted at Pier 8 and the data used to evaluate the situation. The test pile was instrumented with internal strain gages, which continue to be monitored several years into bridge service. Design, construction, performance, and load test performance are discussed.

A closed-ended, steel, pipe pile was densely instrumented with a combination of vibrating-wire strain gauges and electrical-resistance strain gauges at Purdue University. The instrumented pile was driven into a multi-layered soil profile in Indiana, U.S. Static and dynamic pile load tests were carefully performed on the test pile. The results of these tests allowed us to learn how shaft and base resistances were mobilized when the test driven pile was subjected to axial loads. The load-settlement response, load-transfer curves, unit shaft resistance distribution with depth, and base resistance are presented in the paper. The static bearing capacity of the pile was estimated using five modern CPT-based pile design methods; the performance of these methods was assessed through layer-by-layer comparisons with the static load test results.

Like many other types of deep foundations, the behavior of helical piles and anchors may depend on the quality of the installation. Poor quality installation generally produces poor performance. Installation monitoring of helical piles and anchors is essential on all projects and can assist the engineer in evaluating and validating axial capacity. The installation monitoring of helical piles and anchors should be required on projects by the engineer and should be included in contract specifications as a routine part of the use of helical piles and anchors. The methodology is analogous to monitoring of other deep foundations. Key parameters for monitoring installation of helical piles and anchors include incremental torque, advance (number of rotations per unit of advance), and advance speed or rpms. Methods currently being used in the field are described and examples from several sites are presented illustrating typical results from installation monitoring and the impact of poor quality installation on behavior.

Typically, impact hammer selection must consider drivability, testing requirements (assuming the same hammer is used for high strain dynamic testing), and the potential for pile damage, especially where piles are installed into dense or hard strata. Criteria for minimum, preferred and maximum hammer size required for pile installation, testing, and damage mitigation will be reviewed and summarized. Maximum driving stresses and the effect of pile cross section relative dimensions will be discussed. The paper will provide suggested guidelines for a preliminary screening tool for selecting an impact hammer to safely install and test steel pipe and H-piles, and illustrate this through a brief case study. A companion paper will examine in depth a recent case history where an H-pile was damaged during installation and testing, make use of the screening tool and advanced pile driving simulation software to show how the pile damage could have been predicted.

Drilled shafts are increasingly selected for deep foundation support. To satisfy the design intent, the as-built shaft shape, shaft vertical alignment, shaft base cleanliness, cage alignment, concrete cover, and concrete integrity are all important. Several quality control methods are available to check these design considerations. Many current quality control test methods are time consuming, do not provide quantitative information, do not address all design considerations, or cannot be performed until the shaft has cured for several days. There have been several recent advances in drilled shaft quality control instrumentation. These recent advances in drilled shaft quality control methods offer owners, engineers, and contractors innovative and powerful tools for quality control and quality assurance of drilled shafts. This paper addresses recent advances in quality control methods for drilled shafts and presents field data from recent projects where these technologies have been used for evaluation.

For years, the Alabama Department of Transportation (ALDOT) has been collecting dynamic testing data during pile installation and restrikes to estimate the pile axial resistance of driven piles at the end-of-initial-driving (EOID) as well as at various time periods after EOID. Traditionally, this dynamic testing information is analyzed using a signal matching software CAPWAP designed to provide more accurate results of the axial resistances of the installed piles. The CAPWAP signal matching software can be time-consuming and requires a trained engineer to perform the analysis. A new, faster version of the CAPWAP software, called iCAP, is now available that performs the signal matching analysis of the dynamic data automatically, i.e., without operator interaction. The iCAP software calculates the pile bearing capacity without relying on an assumed soil damping factor and, therefore, can be used to determine the Jc damping factor for the simplified case method. The ALDOT provided acquired dynamic testing data for 25 test piles installed throughout the state of Alabama for analysis to determine the feasibility and reliability of using the iCAP signal matching software for pile driving projects. A comparison of the signal matching analysis of 74 unique blows of both concrete and H-Pile pile testing data is performed to determine the accuracy and reliability of the iCAP results compared to the CAPWAP results. The results show a reliable comparison between the iCAP and CAPWAP analysis for all piles in various soil types within the state of Alabama.

Thermal integrity profiling (TIP) is a relatively new non-destructive test (NDT) method which can be used to assess the integrity of cast-in-place deep foundations by using the heat of hydration to assess the quality. The heat generated during curing is directly related to the cement content and shaft geometry and is therefore a useful indicator of anomalies. The temperature can be measured at a discreet time with an infrared probe lowered slowly into the shaft through a conduit, or continuously by data loggers attached to thermal wires embedded within the concrete or placed within water filled tubes. Two case studies are presented demonstrating the methods of TIP and their observed effectiveness for determining anomalies in drilled shafts. Based on the case studies, in the authors’ experience, thermal wires embedded within the concrete collects data with the most accurate representation of the integrity of the drilled shaft, and is the preferred method of the three for most applications.

As more existing structures need to be reevaluated, repaired or expanded, the demand of use of a low strain integrity testing (LST) to determine/corroborate the existing pile/shaft length and integrity under existing structures has also increased. When applying LST to the piles under existing structures, multiple downward travelling waves will superpose with the upward traveling waves (reflection from defects and the toe). This makes the data interpretation very difficult when only one acceleration measurement is obtained. Two acceleration measurements were introduced about 20 years ago as an extension to LST and significantly improve the reliability of application of LST to piles under existing structures. However, due to the complexity of testing conditions, lack of clear guidelines, and experience, this technique has not been frequently applied. After discussing the background of this method, this paper presents case studies and recommendations on the application of this technique.

Shaft base cleanliness is a widely discussed topic regarding quality control and quality assurance of the drilled shafts. Several existing tools and approaches have been proposed and published to assess the shaft base cleanliness. In the drilled shaft construction industry, in situations where the stability of the soil material is questionable, and the groundwater table is shallow, the wet construction method approach is primarily used. In this method, slurry is placed into the hole to maintain stability in the excavation (i.e., drilled hole) and to impede the intrusion of groundwater into the excavation. During the drilling process, cuttings, debris, and sediments are accumulated at the bottom of the hole which can impact the performance of the deep foundation element. The bottom of the drilled hole is typically cleaned using an airlift system and/or cleaning buckets to ensure the drilled shafts base cleanliness. After this process is completed, the conditions at the drilled shaft’s base can be quantitatively assessed using shaft base inspection devices. This paper presents results of a side-by-side comparison of mini-SID and shaft quantitative inspection device (SQUID) tests performed for seven drilled shafts installed in intermediate geomaterial. The effort associated with data collection, debris definition, and measurements are presented and discussed in detail.

Foundation reuse for bridge replacement projects is an attractive and economical option in many cases but also presents significant challenges. One of these challenges is the need to characterize the length and condition of existing bridge foundation elements. Geophysical and non-destructive evaluation measurements play a critical role in this aspect of bridge foundation reuse. The focus of this paper is on the use of the continuous wavelet transform (CWT) approach for interpreting sonic echo (SE) measurements. Measurements were performed on concrete piles from a 50-year old bridge that is being replaced. The SE data were collected and interpreted using conventional time domain arrival picks and the CWT method, using both amplitude and phase information. After testing, the piles were exhumed and ground truth measurements of length, condition, and seismic velocity were performed. The results from the CWT yielded consistent results with conventional methods. In some cases, the CWT allowed for interpretation that could not be made using conventional methods.

Typically, impact hammer selection must consider drivability, testing requirements (assuming the same hammer is used for dynamic load testing), and the potential for pile damage, especially where piles are installed into dense or hard strata. There are various guidelines regarding the maximum allowable driving stresses and the maximum recommended driving energy of the impact hammer to avoid damaging steel pipe piles and H-piles during installation under such conditions. In a companion paper, these guidelines were reviewed to develop a preliminary screening tool for selecting an impact hammer to safely install and test steel pipe and H-piles. This paper will examine a case history where an H-pile was damaged during installation. The paper will review the hammer selection against this screening tool and how the pile damage could have been predicted using the screening tool in conjunction with sophisticated simulation and analysis software. The paper will also demonstrate the importance of interpreting the results of a pile driving simulation properly to ensure a reliable prediction of the actual pile driving conditions.

Ultrasonic calipering of bored pile excavations allows for assessment of pile excavation shape. In a typical application, the device is lowered into the excavation in incremental depths. At each depth, a 360° sweep of the excavation wall is performed. A circle is fitted to the data points using a non-linear least-squares technique to approximate the cross-sectional profile of the pile for verticality, perimeter area, and volume calculations. To determine pile verticality, one profile ring is selected as the datum ring. The geometric centers of the datum ring and all other profile rings are compared. A center offset is computed for the divergence of each profile ring center point from the datum ring center point. “Encroachment” is also assessed as the portion of the excavation wall which would encroach into the perfectly vertical projection of the datum ring to the depth in question. Verticality is computed as either the maximum encroachment or center offset divided by change in depth, and may be expressed as an angle, a percentage, or as a deviation: depth ratio. Typical practice for specifying required verticality is the simple ratio of deviation:depth, which does not take into account the diameter of the pile. Thus, a specified 1:100 tolerance allows for a deviation of 300 mm at a depth of 30 m, regardless if the pile diameter is 600 mm or 3,000 mm. For the former, this deviation represents 50% (a full radius) of allowable deviation, creating a vertical projection into which a rebar cage cannot be lowered without scraping the side wall, and/or a column support with a large built-in eccentric load. For the latter, it represents a 10% of diameter deviation, which is much less significant in terms of functionality, whether this is bearing capacity (axial pile) or creating a moisture barrier (secant wall). To overcome this, a normalized verticality calculation is presented. Rather than simply taking the ratio of deviation to depth, the compound ratio (deviation/diameter):(depth/length) is proposed.

The focus of this research is the assessment rock strength in real time during drilled shaft installations. This is achieved through measurements of specific energy which requires five drilling parameters to be continuously monitored and recorded during shaft construction. In a recent investigation conducted by the Florida Department of Transportation, real time measurements of specific energy were used to assess both the quality and length of rock sockets. It was found that the specific energy required to excavate a shaft was directly correlated to the compressive, tensile, and shear strength of the drilled rock. Furthermore, the specific energy obtained from monitoring clearly defined the spatial variability, both horizontally and vertically, within each socketed rock mass. Based on these findings, a new method of estimating shaft capacity was developed in terms of specific energy that can be used as a quality control measure for every drilled shaft installed on a site.

Bentonite slurry is recognized to degrade side shear of drilled shafts with time, but there is no scientific rationale to expect the same from polymer slurry. The objective of this work was to examine the differences in side shear behavior as a function of exposure time to both types of drilling slurry. Thirty two 1/10th scale drilled shafts were constructed using both polymer and bentonite slurry where open excavation exposure times ranged from near 0 to 96 h. Pull-out test results showed that polymer constructed shaft capacity was consistently larger than the bentonite ones. While the majority of the reduction in side shear from bentonite exposure occurred before 4 h, the polymer shafts did not show appreciable effects of time dependency. The measured side shear in all shafts was larger than predicted design values.

The recently developed instrumented Becker penetration test (iBPT) when configured as a reusable test pile provides direct measurements of strain and acceleration at up to five locations along the drill string. This paper describes details of the test system, measurements, and presents representative results from an iBPT sounding performed at a predominantly fine sand site where indicator test piles were previously installed. The ability of the iBPT system to estimate equivalent SPT N₆₀ values at the site is first demonstrated. Representative iBPT pile driving analysis (PDA) measurements obtained from the multiple modules at the base and along the shaft during field driving is then presented. Finally, a new multistage signal matching approach for estimating the distribution of resistance along the pile, and pile ultimate capacity is demonstrated using individual iBPT module dynamic measurements.

Geotechnical engineers have been active in evaluating certain geo-structures in an effort to reduce their associated environmental impacts. However, there is a lack of understanding of how different design methods for the same type of geo-structure can affect the environment. Drilled shafts and driven piles can be designed in many different ways, and the selection of a valid design method entirely depends on the designer’s preference. In this study, single drilled shafts and driven piles are designed for theoretical sand profiles using eight different design methods, and a life cycle assessment (LCA) is conducted to evaluate the environmental impacts of the designs. In a sustainable perspective, it is important to realize that the decisions made in engineering projects can potentially impose substantial and long-term impacts on the environment. As geotechnical engineers, careful selection of design methods and decision-making throughout geotechnical projects can possibly reduce those environmental impacts.

The use of energy piles is gaining acceptance as a sustainable method of resource management and conservation. Energy piles are structural foundations that act as thermal exchangers designed and executed to reduce the energy required for heating and cooling demands. Published work on energy piles shows that in granular and very stiff, moderately to highly overconsolidated clayey soils, thermal effects on the mechanical properties of the soils may be neglected. However, heating may induce flow of water around the pile and could affect the skin friction and the adhesion between the pile and the surrounding soil. This issue has not been fully investigated in the literature. The main objective of this paper is to investigate the impact of utilizing energy piles in slightly overconsolidated clay by conducting laboratory-scale pile load tests on identical “ordinary” and “energy” model piles. The energy model piles are fitted with small diameter copper pipe loops that function as the transport medium through which temperature-regulated water is circulated. Results indicate that the adhesion between the pile and the clay was reduced by about 15 to 20% in energy piles that were subjected to three cycles of heating and cooling when compared to the adhesion of an identical control pile.

Geothermal piles are being used to serve dual-purpose: transfer the structural load to the ground and act as heat exchanger elements to harvest and reject heat from and to the ground. Thermal loading can change the mechanical performance and bearing capacity of the geothermal piles during heating and cooling cycles. Therefore, the thermo-mechanical responses of the geothermal piles should be comprehensively studied. In this paper, the thermo-mechanical performance of a geothermal pile was analyzed using a 3D finite difference model in FLAC. The energy pile tests performed at Lambeth College, London were simulated using the developed numerical model. Comparison of both thermal strain and thermo-mechanical strain along the depth of the geothermal pile during both heating and cooling cycles confirms that the numerical model can accurately simulate the thermo-mechanical performance of energy piles. The validated model have been used to study the effects of soil properties and thermal operation periods (both short-term, after 10 days, and long-term, after 2 months) on the response of the geothermal pile. Results showed that increasing the soil stiffness induces lower strains and higher stresses along the pile. Increasing soil elastic modulus by 10 times results in 5% reduction in the minimum axial strain in the geothermal pile. It is also important to note that the position of the null point depends on the stiffness of the soil and pile. Results indicated that the null point moves upward by increasing the soil stiffness.

There has been a growing recognition around the world to use geothermal energy. Rejecting or harvesting to and from the ground results in temperature changes of the soil. The geotechnical properties of sand and clay vary under different environmental temperature. Temperature increment induces volumetric changes and also alters fluid properties (e.g., groundwater) in the soil skeleton. These variations might increase or decrease the soil strength and soil intrinsic permeability. Although several researches have been performed to study the effects of temperature on sand and clay soils; the exact thermo-physical behavior of soils need to be investigated. This paper presents the effect of temperature variation on sand behavior (intrinsic permeability and void ratio). The modified triaxial apparatus with automated heating control system was designed to control the temperature of the cell and the specimen in the range of 5 to 90°C. The device can be used to do mechanical consolidation and shear strength tests at different temperatures to compare the stress-strain behavior of the soil under temperatures. Triaxial permeameter cell is also used to study the variation of soil hydraulic conductivity and soil intrinsic permeability with temperature. Results obtained from the experimental tests confirm that soil hydraulic conductivity increases with temperature. However, interestingly soil intrinsic permeability shows reverse behavior with temperature. This reduction in soil intrinsic permeability with temperature is a result of changes in void ratio of the soil skeleton due to thermal loading.

The goal of this paper is to present the effect of heating and cooling thermal loads on the load-displacement response of heat exchanger piles in granular soils. Two-dimensional discrete element simulations were utilized to determine the changes in the shaft and toe resistances due to heating and cooling loads. The considered heat exchanger pile is 0.3 m in diameter and 20 m in length and it was installed in a homogeneous sand layer with particles ranging in size between 2.2 and 3.6 mm. The pile was divided into 5 m segments with a representative 0.5 m pile strip for each pile segment. For each modeled pile element, the vertical and lateral soil pressures were initially applied then model was left to stabilize. The strips were, then, displaced at a constant displacement rate of 10 mm/s. while measuring the developed shaft and toe resistances. The model was validated against the behavior of a reference pile without temperature changes. Upon validation, the analysis was repeated at temperatures mimicking heating and cooling conditions around heat exchanger piles. The results of the analyses performed in this study showed that the load-displacement curves for heat exchanger piles in granular soils are temperature-independent.

Heat exchanger or energy piles are dual purpose foundations that transfer superstructure loads to the ground while simultaneously exchanging thermal energy with the subsurface. To advance understanding of a soil structure interaction in energy piles computational modeling of an actual end bearing heat exchanger pile was carried out in the present study. Specifically, the main goal was to elucidate effects of the site stratigraphy on the axial displacements, strains, and stresses. This was accomplished by considering the actual layered soil profile comprising four different layers underlain by the bedrock and three hypothetical profiles, each of which consisted of a single soil underlain by the bedrock. All computational predictions were compared with the available relevant experimental data. By comparing the responses for different stratigraphy scenarios, it was found that the response of the layered system clearly reveals the presence of different individual soil layers.

Energy piles support structural loads and exchange heat with surrounding soils using closed-loop ground source heat pump (GSHP) systems. A GSHP connected to an energy pile operates in cycles where it functions for a period of time (running time) then stops for another period of time (stoppage time). This intermittent operation of the GSHP subjects the piles and surrounding soil to changes in temperature and to temperature cycles introducing challenges to foundation design. The research presented in this paper focuses on evaluating the effects of thermal cycles on the soil temperature and soil-pile interaction. In order to investigate these effects, an instrumented concrete energy pile with diameter of 101.6 mm and length of 1.383 m was subjected to different thermal cycles and tested under pull-out loading at the soil-structure interaction (SSI) facility at Lehigh University. In this paper, results from two pile tests are presented. Axial pull-out response of a pile subjected to five thermal cycles was compared to the response of a pile subjected to pull-out loading at room temperature. It was observed that the pile subjected to thermal cycles had an ultimate shaft resistance that is 28% greater than that of the pile tested at room temperature.

Compressed air energy storage (CAES) technology has recently re-emerged due to ever-increasing energy demand. In particular, a pipe pile, where the compressed air could be stored inside the pile using a surplus energy during off-peak hours and released later for electricity generation, (hereafter referred to as “CAES pile”) has been lately receiving attentions. To continue pursuing the idea of using pile foundation system as an energy storage vessel, the effect of pile-soil interactions during internal pressurization on foundation stability needs to be investigated. This paper investigates the behavior of a closed-ended steel pipe pile subjected to the internal pressure using axisymmetric finite element analysis. Special emphases are placed on the investigation of (1) pile head movement; and (2) developments of a longitudinal stress in pile under the pressurization. Results from the numerical analyses indicate that the magnitudes of the structural load applied at the pile head before pressurization play a major role in the mechanical behavior of the CAES pile. It is further observed that the changes in pile head displacements due to the internal pressurization are not significant and the longitudinal stress developed in the CAES pile does not exceed the yield strength of the material.

Energy foundation is promising to allow harvesting geothermal energy while fulfilling its role in supporting structural loads. The environmental responsiveness also means new operational factors beyond the conventional structural loads need to be considered, i.e., the change of soil-foundation interactions resulting from thermal expansion/contraction cycles as well as dry/wet cycles associated with the geothermal heat exchanger. These are the resultants of the coupled thermo-mechanical processes driven by the cyclic thermal boundary conditions. This paper describes a computational model that holistically simulates the soil-structure interactions of geothermal foundation where the non-isothermal geothermal heat exchanger pipe flow is taken into account. The soil-pile foundation interactions are described by interface model that describes the variations of boundary frictional resistance with temperature conditions. The model predicts the variations of soil-pile interactions as well as the thermal conditions inside the pile foundation. It also allows analyzing the non-uniform deformation and the resultant bending moment of energy foundation during operation. The results are compared with documented case studies. Besides, thermo-mechanical behaviors of energy foundations with three types of geothermal heat exchanger pipe patterns (U shape, W shape, and spiral shape) are discussed. The calibrated model will provide a useful tool to improve the existing design methods for energy pile foundations.

The effect of granular bulk density on local scour around an oblong pier under clear-water conditions is studied. A total of four open channel flume tests were conducted, in which the sediment beds were prepared at different relative states of compaction. Uniform Ottawa sand was used for all cases. Flow conditions, i.e., flow velocity and depth, were maintained the same for all cases to isolate the bulk density effect. Time evolution of the maximum scour depth and the scoured bed morphology were compared among all cases. For tests on sediment beds of the lowest and highest density, three miniature pressure transducers were installed at various depths within the bed upstream of pier nose to monitor the pore pressure response. Experimental results indicate that the erosive resistance of the sand bed is a slightly decreasing function of bulk density. The possible underlying mechanism, responsible for such different scour behaviors between test cases, is also discussed.

Scour is a natural phenomenon caused by erosion or removal of riverbed or riverbank materials around bridge foundations by stream power. Under a given flood condition, the scour resistance of soil is one of the key factors that influence the scour process and the maximum scour depth. Scour does not occur when the flow velocity is lower than the critical scour velocity of the soil, or when the scour resistance in the soil is higher than the erosive load by streamflow. A preliminary design of apparatus to evaluate the scour behavior of soil sample is proposed in this study. The test can be carried out on soils samples both in laboratory and field conditions. A slender central blender near the soil surface is used to produce the erosive flow field. The rotation speed of the blade can be adjusted to reach the balance between flow structure and sediments. The plot of erosion rate and rotation speed provides the result of a scour resistance test. This device and testing method provide an easy way to measure the soil erosion resistance that can be used to predict the scour rate and depth around bridge foundation.

Geothermal energy is a renewable, sustainable, clean (i.e., zero carbon emission), and directly used an energy source that has been successfully used for bridge and pavement deicing. However, existing geothermal bridge/pavement deicing designs mostly rely on hydronic loops, which are embedded within concrete decks during bridge construction phase and are considered as internal heating. This paper presents a numerical feasibility study of an external geothermal heated bridge deck design in which the hydronic loops are attached to the bottom of the bridge deck and encapsulated in a layer of geofoam. A series of parametric analyses are performed to investigate the external heating process in comparisons to internal heating. These analyses contain various ambient temperatures, inlet temperatures, wind speeds, and flow velocities. The results demonstrate that external heating can heat the bridge deck to above freezing temperatures in mild winter weather compared to internal heating. Limitations of both heating systems are also evaluated since both systems would be unfeasible for extreme environmental conditions such as high wind speeds (more than 8.94 m/s) and lower ambient temperatures (lower than −2°C).