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Currently, bored piles are commonly designed based on saturated soil mechanics with an assumed drained condition, even though in most cases the loess is unsaturated. Upon water infiltration, the matric suction reduction and matric suction reduction-induced soil collapse deformation could cause significant changes to the pile load transfer mechanisms. In order to investigate the mechanical behaviors of bored piles in collapsible loess subjected to water infiltration, a large-scale model test was performed. The testing results indicated that the continuous pile settlement observed before the wetting front proceeded to the pile base, and the corresponding changes in the pile load transfer mechanism were mainly attributed to the changes in the magnitude and direction of pile shaft friction. While as the loess beneath the pile base was gradually saturated, the reduction in pile base stiffness further accelerated the pile settlement until the sum of pile base resistance and pile shaft friction failed to balance the service load applied on the pile head. Considering the influences of loess collapsible deformation, as well as the contribution of matric suction to the mobilization of pile shaft friction and pile base resistance, the traditional load transfer method was modified to extend its application to bored piles in unsaturated collapsible loess subjected to water infiltration. The relatively good agreement between testing and predicting results indicated that the modified load transfer method could be a powerful tool in the design and bearing behaviors evaluation of bored piles in collapsible loess. [ABSTRACT FROM AUTHOR]

Full-scale axial load tests were performed on five screw injection piles founded in medium-dense to dense sand at a site in Delft, the Netherlands. Each pile was instrumented with distributed fiber-optic sensors along its full length, giving detailed insights into the shaft and base response under compression loading. The paper focuses on the pile base response and combines the test results with a newly compiled database of instrumented load tests on screw displacement piles in sand. Given the range of screw displacement piles on the market, the influence of different installation methods and pile geometries on the base resistance can be assessed through the database. In summary, the analysis showed that all screw displacement pile types tended to mobilize base capacities similar to bored or nondisplacement piles. Despite high variability in the database, no significant trend with pile geometry, such as length or diameter, was evident. [ABSTRACT FROM AUTHOR]

In the random field model's consideration of the spatial variability of soil, soil properties at different locations play different roles in the reliability analysis of the foundation. Investigating the importance distribution of the random field through reliability sensitivity analysis (RSA) is beneficial for understanding how the random field affects the reliability of the foundation. However, many existing RSA methods for the random field model are deficient in terms of efficiency, accuracy, and applicability under complex engineering conditions. Consequently, this study proposes an efficient RSA method for the random field model based on the Karhunen–Loève (KL) expansion method and the first-order reliability method (FORM) to identify the important random field domain in foundation engineering. In the proposed method, the mean reliability sensitivity index (MRSI) is extended to a random field model of continuous form to characterize the importance distribution of the random field. The MRSI is analytically derived based on the results of the KL expansion method and the FORM without additional limit state function (LSF) calculations. Subsequently, the important random field domain, in which the variation of the mean of the soil property contributes significantly to the reliability index, is identified based on the MRSI. Last, two foundation engineering examples that consider the cross-correlated random fields of cohesion and friction angle, including strip footing on single-layer soil and pile in multiple-layer soil, were used to verify the proposed method. The results showed that an important random field domain with a small area dominates the variation of the reliability index of a foundation, and important random field domain area increases with autocorrelation distance (ACD). This innovative identification method holds great engineering significance, because it allows geotechnical practitioners to gain a comprehensive understanding of the failure modes and foundation treatment areas of foundations in spatially varying soil. In the random field model's consideration of the spatial variability of soil, soil properties at different locations play different roles in the reliability analysis of the foundation. Investigating the importance distribution of the random field through RSA is beneficial for understanding how the random field affects the reliability of the foundation. However, many existing RSA methods for the random field model are deficient in terms of efficiency, accuracy, and applicability under complex engineering conditions. Consequently, this study proposes an efficient RSA method for the random field model to identify the important random field domain, in which the variation of the mean of the soil property contributes significantly to the reliability index. Two foundation engineering examples that consider the cross-correlated random fields of cohesion and friction angle, including strip footing on single-layer soil and pile in multiple-layer soil, were used to verify the proposed method. The results showed that the innovative identification will allow geotechnical practitioners to gain a comprehensive understanding of the failure modes and foundation treatment areas of foundations in spatially varying soil. [ABSTRACT FROM AUTHOR]

Chiaia station is one of the art stations of Line 6 of the Naples underground network; it was constructed in a 50-m-deep excavation, a few meters from historic buildings and 4.5 m from the main façade of a sixteenth-century Basilica. The excavation, carried out partially in loose to medium dense sands overlying the soft rock formation of Neapolitan Yellow Tuff (NYT), was supported by a retaining wall made of contiguous bored piles braced with internal struts and prestressed ground anchors. The excavation sequence was quite complex due to archeological findings and to the presence of anthropic cavities used over the centuries to quarry NYT blocks. One of the key goals of the design was to limit movements around the shaft to prevent damage in the historical buildings. Long-term monitoring data obtained during nearly 9 years confirm the success of the overall construction process. A rather complex three-dimensional (3D) finite-element model with constitutive relationships for both the upper sandy layers and the soft rock is presented in the paper; this model was adopted to back-analyze the data from the monitoring and explore the influence of some of the key features of the case study. The role of the building bending and shear stiffness, of the soft rock stiffness, and of further apparently minor issues—such as the seepage and the ground anchors' prestress—were investigated and discussed with the support of the model calculations. Observed settlements at the end of the excavation were in the range 10–15 mm, and in the long term they increased by 20%–50% to as much as 20 mm. The deflection ratios were very small, in the range 0.05‰–0.15‰ , and no visible damages to the buildings were recorded. These values were reproduced by the finite-element model only after the introduction of the relevant building stiffness. [ABSTRACT FROM AUTHOR]

Existing simplified procedures for evaluating soil liquefaction potential or for estimating excess pore pressures during earthquakes are typically based on undrained cyclic tests performed on saturated soil samples under controlled loading and boundary conditions. Under such conditions, the effect of excess pore pressure (ue) dissipation and redistribution to neighboring soil layers cannot be accounted for. Existing simplified procedures treat liquefiable layers as isolated soil layers without any boundary conditions even if dense and loose layers are very thin, permeable, and adjacent to each other. However, redistribution is likely to increase and decrease ue in the neighboring dense and loose layers respectively. Until now, no procedure short of fully coupled numerical analysis is available to estimate the importance of redistribution. This paper presents an approximate analytical procedure for assessing the effects of ue redistribution in (1) soil layers that would have liquefied if they were undrained, and (2) soil layers that would have not liquefied even if undrained. It is found that a layer that is initially assumed liquefied under undrained conditions might not even liquefy accounting for the ue redistribution to neighboring layers. On the other hand, a layer initially assumed to not liquefy can develop significant ue and can even liquefy due to pore pressure migration from the neighboring layers. Thus, accounting for redistributed ue is important for liquefaction consequence assessment quantification, particularly in systems that span the depth of these effects like deep foundations. Migration of u toward the tip of a pile can reduce its capacity, even if the tip is embedded in a dense sand layer. On the other hand, if redistribution can result in the reduction of ue in initially assumed liquefied layers, risks associated with liquefaction might be avoided. A criterion is also developed to evaluate the thicknesses of a layer below which redistribution could prevent liquefaction even if the layer is deemed liquefied according to the existing liquefaction-triggering procedures. Finally, the proposed procedure is illustrated by application to selected shaking events of centrifuge tests involving liquefaction of layered soil profiles. The predictions from the procedure matched the centrifuge test results reasonably. [ABSTRACT FROM AUTHOR]

Interactions between adjacent piled-raft foundations may induce additional settlement and cause the tilt of the structure. This case study investigates the long-term performance of a large piled-raft foundation system supporting high and heavy alumina solution storage tanks based on field measurements and three-dimensional (3D) numerical simulations. To properly consider the interactions among rafts, piles, and soils; the elastoplastic behavior of clayey and sandy soils; and the consolidation behavior of soil after construction, a 3D finite-difference code was utilized for the numerical modeling. Two undrained mechanical analyses were conducted to simulate the installation of foundations/tanks and the filling of alumina solution into the tanks, while two coupled hydromechanical analyses were performed to model the period between the two undrained stages and the stage after tank filling, respectively. The predictive capability of the numerical model was checked by comparing the simulation results first with single pile load test data and then with in situ settlement measurements at different locations of the piled-raft foundations. The long-term behavior of the piled-raft foundations was further investigated by analyzing various aspects including the axial force variation along the pile at different locations, the time-settlement relation at monitoring locations, the vertical effective stress increment and displacement of soil, and the differential settlement between monitoring locations. Based on the simulations, the tilt of the platform was mainly due to the superposition of additional stresses near the centerline of the two rows of piled-raft foundations. Finally, parametric studies were conducted to investigate the interactions among the piled-raft foundations at different pile length configurations. The results show that by properly increasing the length of the piles near the centerline of the two rows of piled-raft foundations, the differential settlement of the platforms can be mitigated. [ABSTRACT FROM AUTHOR]

Design codes vary in their recommendations for the end-bearing response for bored piles founded in sand, both for the ultimate design value and the response at small settlements. The ultimate end-bearing resistance may be expressed either in terms of bearing factors Nq relative to the in situ vertical effective stress, with the Nq value varying with the friction angle of the sand, or as a factor applied to in situ test data, such as the standard penetration test blow count or the tip resistance qc. Numerical studies have led to proposed ratios of design end-bearing pressure to qc at specific settlement ratios, such as 5% and 10% of the pile diameter. The work presented here used numerical analysis to evaluate the full pile base response from initial stiffness to ultimate end-bearing resistance at a settlement ratio of 10% of the pile diameter. The resulting base responses are suitable for implementation in beam column analyses and have been validated by comparison with published design guidelines and with data from a full-scale instrumented pile load test. [ABSTRACT FROM AUTHOR]

Energy piles are a consolidated underground heat exchanger alternative to traditional boreholes in ground source heat pump (GSHP) systems. Previous works focused on assessing the differences between piles and boreholes, but few assessed small piles in operational conditions. Moreover, most of these studies centered around cylindrical concrete piles, overlooking short screw piles. Using in-situ testing, established analytical methods, and advanced three dimensional (3D) finite element model simulations, this work assesses three thermal response tests (TRT) executed in different energy pile structures, one being a unique group of eight short energy screw piles connected in series, located in the same site in Melbourne, Australia. Detailed numerical analysis provided reliable soil and structure thermal parameter predictions and detailed computations allowed the study of thermal effects for the energy screw piles steel components. The results show limited impact of the steel components on effective thermal conductivity, but a reduction in thermal resistivity that may provide a speedier thermal exchange in short term GSHP operation. In addition, the more traditional TRT rigs and analytical interpretation provided reasonable results for the pile group in series, and show a similar performance to a borehole heat exchanger of similar pipe length; however, the short piles engage only the upper soil layers, with potentially lower thermal conductivity. TRT in single short screw piles require careful consideration, because common rigs may be unable to cater for the required low fluid flow rates and heating power. Thus, for the cases assessed herein, the pile group TRT proved to be more reliable than individual pile testing, due to their short length. [ABSTRACT FROM AUTHOR]

This paper demonstrates the influence of pile head freedom on the thermomechanical performance of a belled pile. Field tests on the belled pile response to a cooling–heating cycle and incremental structural construction are carried out. The temperature changes, axial strain profiles, and pressures at the pile toe are recorded through the buried instruments. The variation in the degrees of freedom, tensile forces, and inferred pile head settlements along the pile depth for different test procedures are analyzed using the measured data. The degree of freedom close to the pile head calculated from strain rates decreases with the structure mass with a gradient of −2.8×10−5/kN. The reducing effect of the incremental superstructure on pile freedom decreases along with the orientation of the pile depth. Compared with the inferred thermal displacement of the pile without an applied structural load, the values decrease by about 10% when the pile was subjected to incremental floors, and an elastic recoverable characteristic response to cooling–heating-recovery phases is observed. Compared with the equal-diameter pile, the belled pile showed a significant constraint close to the toe. Mechanical loads can decrease the cracking risk because of a possible tensile force under cooling conditions. [ABSTRACT FROM AUTHOR]

Deep foundation applications, such as foundations for jacket structures and reaction piles, may benefit from larger shaft resistances during tensile compared with compressive loading. A suitable analog for designing surfaces whose load transfer depends on the direction of loading is the skin of snakes. Snake scales reduce friction when they move forward (i.e., caudal direction) and increase friction when they move backward (i.e., cranial direction). A series of centrifuge load tests were conducted on instrumented piles in medium-dense sand to investigate the load transfer behavior of piles with snakeskin-inspired surfaces. Load tests were performed on three bioinspired piles, a reference rough pile, and a reference smooth pile at two embedment depths each. The results present distributions of axial load and shear stresses along the pile length and head load–displacement and local shear stress–displacement relationships. During both installation and pullout, the cranial shaft friction mobilized similar shear stress magnitudes and shear resistance distribution with depth to that of the rough pile, while similarities were observed between the caudal shaft friction and that of the smooth pile. The results show that the bioinspired piles mobilize directionally-dependent shaft capacities, where the ratio of capacities during cranial pullout to caudal installation was measured to be 1.6 to 2.1, as evidenced by the computed β coefficients. Variations in relative density in the centrifuge models were quantified by means of cone penetration test (CPT) soundings, and the pile test results were corrected for potential scaling effects to obtain β coefficients that are more representative of field conditions. [ABSTRACT FROM AUTHOR]

Five dynamic, large-scale centrifuge tests on pile-supported wharves were used to investigate the time- and depth-dependent nature of kinematic and inertial demands on the deep foundations during earthquake loading. The wharf structures in the physical experiments were subjected to a suite of recorded ground motions and imposed superstructure inertial demands on the piles. Partial to full liquefaction in loose sand resulted in slope deformations of varying magnitudes that imposed kinematic demands on the piles. It was found that the wharf inertia and soil displacements were always in phase during the critical cycle when bending moments were at their maximum values. The test results were analyzed to provide the relative contributions of peak inertial loads and peak soil displacements during critical cycles, and the data revealed the depth dependency of these factors. The results of this study are used in a companion paper to provide recommendations for the design of pile-supported wharves subjected to foundation deformations. [ABSTRACT FROM AUTHOR]

Jetted and grouted precast piles (JGPPs) are a newly developed urban-friendly deep foundation technique that employs water jetting for pile penetration and pressure grouting to enhance the axial and torsional resistance of precast piles. Previous experimental studies of JGPPs in a large test chamber setup have revealed that they can withstand very high axial loads; however, validation of the same in a typical field scenario was needed. This paper presents the pioneering study of the full-scale axial response of JGPPs in cohesionless soil condition. The study showed that JGPPs exhibit high skin and tip resistances under axial top-down loading. The paper also proposes a direct method to predict the ultimate skin resistance of JGPPs using the pressuremeter test results. The experimental results were compared with the values estimated using both the proposed and existing methods. [ABSTRACT FROM AUTHOR]

Time-dependent response of piled raft foundations (PRFs) in saturated, normally consolidated and moderately overconsolidated clayey soils under the single-drainage condition is investigated using three-dimensional, elastoplastic finite-element (FE) analysis with the modified cam clay (MCC) soil constitutive model. Four different types of clay (Boston Blue Clay, San Francisco Bay Mud, London Clay, and Shanghai Clay) with different values of overconsolidation ratio (OCR) (OCR=1 , 2, and 5) and 20 different configurations of rectangular PRFs are considered for the study. The settlement response and load sharing of PRFs are investigated. Regression analyses are performed with the FE analysis results to obtain fitted equations for immediate settlement, primary consolidation settlement, and degree of consolidation of PRFs. These equations are applicable to PRFs with cast in situ bored piles similar in size to those considered in this study. The proposed equations can be used to estimate time-dependent PRF settlement in normally consolidated and moderately overconsolidated clay as part of preliminary design calculations. [ABSTRACT FROM AUTHOR]

Agreeing on the nominal resistance (aka. capacity) derived from any load-settlement curve requires the use of an interpretation criterion. Few of the currently available criteria have been originally designed for drilled foundations despite the increasing use of such piles for supporting infrastructure projects. The performance of 16 interpretation criteria used in current geotechnical practice was assessed using a database of 194 load tests conducted on drilled shafts. Their performance was evaluated in terms of: (1) applicability; (2) correlation among each other; and (3) the effect of drilled shaft diameter, length, and soil type. Eight of the 16 methods could not be reliably used. Capacities interpreted from the remaining eight were consistent but resulted in excessive settlement in a few cases. Performance was also evaluated in terms of serviceability. A new criterion is proposed, where the nominal resistance is defined as the load corresponding to the smallest of (1) a settlement equal to the elastic compression of a free-standing column plus 0.75 in. (20 mm); (2) the load at plunging or strain-softening; or (3) settlement corresponding to 5% of the pile diameter, unless modified by the structural engineer of record. The proposed method showed good correlation with several established criteria while including a built-in serviceability safeguard against excessive settlement. [ABSTRACT FROM AUTHOR]

The rigid inclusion technique has been used worldwide to reinforce soft soil for road and railway embankments and deep building foundations. This technique is studied through field tests and physical and numerical models. Most studies focus on embankments or slabs on soils reinforced with rigid inclusions. Previous research based on numerical modeling demonstrated that the load-transfer mechanisms for a rigid slab differ from those for an embankment. Here, a simplified physical model was developed to assess the load-transfer mechanism between the inclusion head and the load-transfer platform (LTP) under a rigid slab. This research focused on the use of an alternative material for the LTP, which is a compacted soil with or without cement. When the reinforced soil contribution is neglected, the LTP weight and applied load are transmitted completely to the inclusion cap (load-transfer efficiency of 100%). As the LTP material stiffness increases, the settlement magnitude decreases considerably. The experiments demonstrated that the applied load was transferred to the inclusion head through an inverted truncated load-transfer cone (LTC) over the inclusion; the external angle depended on the LTP material strength in accordance with Coulomb's theory. The principal stress state at the base of the LTC also was determined. Equations are proposed to determine LTP thickness and inclusion spacing. [ABSTRACT FROM AUTHOR]

This study presents 3M, an analytical method to estimate the skin friction of bored piles in sands. It is based on the fundamental mechanic behavior of sands and keeps track of the major mechanisms occurring in the soil close to the pile during loading. These include the development of a shear band, its potential expansion as induced by soil dilatancy, and the ensuing increment of horizontal stresses owing to the restraining effect of surrounding soils. The resulting analytical equations are easy to apply and insert in a worksheet. The procedure to evaluate the shear band expansion is calibrated against results of direct shear tests at constant normal load, whereas the increment of horizontal stresses is evaluated by the closed-form solution for the expansion of a cylindrical cavity into a dilatant elastic-perfectly plastic medium. The effectiveness of the 3M method in predicting shaft friction has been checked against numerical results, centrifuge, and full scale pile load tests. Nevertheless, prior to use in design practice, preliminary validation is required with more well-documented experimental data from load tests on instrumented bored piles. [ABSTRACT FROM AUTHOR]

Drag Load and Position of the Neutral Plane The writers agree with the discusser that loads applied to the structural design of controlled-modulus columns are similar to conventional foundations, including downdrag. Applied stress in the foundation soils, and thus depth of the neutral plane, are influenced by the available soil-column interface side friction, spacing of the columns, and fill height. "Installation effects of controlled modulus column ground improvement piles on surrounding soil.". [Extracted from the article]

The load-displacement responses of laterally loaded, single bored piles in weathered granite soil are investigated using field model tests and numerical analyses. Field model tests were conducted to simulate the loading conditions of foundations for offshore structures subjected to large overturning moments with small lateral loads. The results of numerical analyses from existing methods were compared with experimental data to assess their suitability to predict lateral load capacities. These comparisons revealed the following reasons for underestimating the lateral load capacities of piles in weathered granite soil in practice: cohesion component of soil, friction between pile and soil, volume expansion characteristics of soil, and the underestimation of ultimate lateral soil resistances of curves. Parametric studies were used to determine the influence of the previously described factors on the lateral load capacities of piles and confirmed the importance of the appropriate estimation of these factors and their reflection in the design of engineering practices. [ABSTRACT FROM AUTHOR]

In this research, centrifuge model pile-load tests were carried out to failure to investigate the behavior of large-diameter bored pile groups with defects. The model piles represented cast-in-place concrete piles 2.0 m in diameter and 15 m in length. Two series of static loading tests were performed. The first series of tests simulated the performance of a pile founded on rock and a pile with a soft toe. The second series of tests simulated the performance of three 2×2 pile groups: One reference group without defects, one group containing soft toes, and one group with two shorter piles not founded on rock. The presence of soft toes and shorter piles in the defective pile groups considerably reduced the pile group stiffness and capacity. As the defective piles were less stiff than the piles without defects, the settlements of the individual piles in the two defective pile groups were different. As a result, the applied load was largely shared by the piles without defects, and the defective pile groups tilted significantly. The rotation of the defective pile groups caused large bending moments to develop in the group piles and the pile caps. When the applied load was large, bending failure mechanisms were induced even though the applied load was vertical and concentric. The test results confirm findings from numerical analyses in the literature. [ABSTRACT FROM AUTHOR]

Quality assurance (QA) tests, such as integrity tests, are routinely conducted to ensure the safety of pile foundations. QA tests provide additional information and result in changes in estimated reliability of pile foundations. This paper aims to formalize a procedure to quantitatively evaluate the impact of routine QA tests on the reliability of pile foundations. Three cases of reliability analyses based on interface coring of large-diameter bored piles are studied; namely, no toe debris detected, toe debris detected without repair, and toe debris detected and repaired. The prior information of the occurrence probability and thickness of toe debris is established based on a practice survey and accumulated QA data. The Bayesian approach is then applied to update the occurrence probability and the mean toe debris thickness based on outcomes of on-site QA tests and remedial actions taken after these QA tests. Subsequently, the reliability of the piles can be updated. The updated reliability can be significantly higher than that before the QA tests. The degree of reliability improvement depends on the pile specifics, the outcomes from the QA tests, and the remedial actions taken after the QA tests. [ABSTRACT FROM AUTHOR]

Defects present in a pile may not be encountered during a cross-hole sonic logging (CSL) test. Even when defects are indeed encountered, they may not always be detected. This paper proposes a probabilistic analysis procedure for evaluating the reliability of CSL, thereby providing a theoretical supplement to existing experimental evaluations of CSL. The reliability of this integrity testing method is represented by the inspection probability, which is expressed as the product of the encountered probability and the detection probability. Mathematical models to calculate the encountered probability are formulated and a detection probability model is suggested based on existing CSL test data. Several examples are presented to illustrate the proposed procedure. The results indicate that there exists a minimum detectable defect size below which the defect cannot be inspected. For a given number of access tubes, the minimum detectable defect size, as a percentage of the pile cross-sectional area, decreases with the pile diameter. The encountered probability can be taken as an index to determine the required number of access tubes. When the target encountered probability is specified as 0.95, three and four access tubes will be sufficient to encounter defects larger than 15 and 5% of the pile cross-sectional area, respectively. [ABSTRACT FROM AUTHOR]