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The prevailing design methodology for foundation pit support structures conventionally treats the pit cross section as a two-dimensional plane, facilitating the computation of soil and water pressures acting upon the retaining structure. Regrettably, this conventional approach tends to overlook the critical corner effect, particularly when the foundation pit is in proximity to a subway tunnel, where the nuanced nature of this corner effect remains indeterminate. Consequently, this research is directed toward an in-depth investigation of a deep foundation pit contiguous to a subway tunnel. A systematic evaluation and optimization of the corner effect pertaining to the deep foundation pit are undertaken through a combination of comprehensive field monitoring and simulation methodologies. The results show that a substantial mitigation in the deformation of the supporting structure, settlements of the ground surface and adjacent buildings, as well as the displacement of the subway tunnel, were achieved through a consideration of the corner effect. Notably, the ameliorative impact of adjacent buildings on the corner effect is observed. Further scrutiny reveals that the supporting structure within a distance of 12 m from the pit corner is most susceptible to the corner effect, as evidenced by a plane strain ratio (PSR) falling below 0.8. Beyond a spatial threshold of 20 m, the PSR attains a value of 1.0, indicative of a negligible corner effect and the foundation pit section existing in a plane strain state. The adjustment of pile length or diameter based on the PSR emerges as a viable strategy that can realize the construction cost optimization on the premise of ensuring the stability of the foundation pit. The impact of pile diameter variation is paramount, corresponding to a reduction in the range of PSR values below 0.8 from 12 m to 9.8 m. The corner effect is significantly diminished. [ABSTRACT FROM AUTHOR]

Records of pile lengths are not available for several hundred high-mast light towers (HMLTs) throughout the state of Minnesota. The foundation systems, typically steel H-piles or concrete-filled steel pipe piles connected to a triangular concrete pile cap, risk overturning in the event of peak wind loadings if the foundation piles are not sufficiently deep to provide the designed uplift capacity. Without prior knowledge of the in situ pile lengths, an expensive tower foundation retrofit or replacement effort would need to be undertaken. However, the development of a nondestructive screening tool to determine the in situ pile length—compared with replacing or retrofitting all towers with unknown foundation geometries—would potentially provide significant cost savings. The main goal of the research is the development of nondestructive evaluation testing techniques for determining in situ pile lengths using steady-state vibration and hammer-impact seismic testing. The foundation testing protocol involves (1) a preliminary site investigation to determine the shallow subsurface geometry and orientation of the foundation pile cap, (2) the use of seismic cone penetrometer (SCP) attached to a cone penetration test rig to capture the induced steady-state and impact waveforms, and (3) data-driven analysis of field testing results to determine the pile lengths. [ABSTRACT FROM AUTHOR]

Excavation of foundation pits can cause deformation and differential settlement to nearby pipe gallery structures, potentially resulting in significant issues such as seepage and structural damage. Based on a deep foundation pit construction project for a residential building plot adjacent to the Wuhan-Jiujiang utility tunnel, a three-dimensional finite element analysis model with cement-soil mixed wall (SMW) and trench cutting remixing deep wall (TRD)-drilled pile is established to study the impact of the excavation process on the utility tunnel. The results indicate that as the foundation pit excavation depth increases, the lateral deformation of the drilled pile support structure shows an initial increase followed by a subsequent decrease, and the maximum lateral deformation occurs at the point approximately one-third from the bottom of the foundation pit. Besides, the surface settlement exhibits an initial increase, followed by a subsequent decrease and eventual stabilization. The deformation of the utility tunnel structure causing by excavation is always within specified limit of 15 mm. Compared to the structure before excavation, the maximum values of axial force, shear force, and bending moment of the utility tunnel increases by 0.09%, 0.14%, and 4.88%, respectively. The stress variation is small, which satisfies the safety requirements for its usage, the feasibility of the TRD-drilled pile support structure is demonstrated. This study can serve as a reference for safety assessment of comparable engineering projects. [ABSTRACT FROM AUTHOR]

Many instances of severe damage to pile foundations and pile-supported infrastructures have been caused by liquefaction-induced lateral spreading during major earthquakes, particularly in coastal areas. The current study conducted a series of shaking table experiments to determine the differences between the responses of a free- and a fixed-head group pile under lateral spreading in the presence of finned and circular protection piles. The results indicated that the maximum bending moment tolerated by nonprotected free-head piles was more than that by fixed-head piles. Also, reductions in bending moments were more significant in free-head piles in the presence of protection piles than in fixed-head piles. The bending moments of front and rear piles under restricted pile head conditions were reduced by about 31% and 21%, respectively, when finned piles were used as protection piles, while they were 34% and 42%, respectively, under free-head conditions. Furthermore, modification factors of recommended lateral pressure distribution along a pile per the current design code were determined for the protected and nonprotected free- and fixed-head pile groups of the current study and it was observed that this modification factor (CL) was highly dependent on the location of piles in a group, pile head conditions, and the presence of protection piles in the lateral spreading analysis. [ABSTRACT FROM AUTHOR]

This summary discusses the article "Installation Effects and Behavior of a Driven Prestressed High-Strength Concrete Nodular Pile in Deep Saturated Soft Clay" by Jian-lin Yu, Jia-jin Zhou, Ri-hong Zhang, and Xiao-nan Gong. The authors conducted a full-scale experimental study to investigate the behavioral characteristics of a driven prestressed high-strength concrete (PHC) nodular pile in deep-saturated soft clay. They compared the installation effects and shaft frictional resistance of the nodular pile to a similar nonnodular pile. The study found that nodular piles had higher load-bearing capacity and improved shaft resistance compared to nonnodular piles. The authors also discussed the influence of pile installation on the surrounding soil and provided information on pile spacing and pore-water pressure. [Extracted from the article]

In this study, the uplift load-carrying capacity of micropiles was investigated, focusing on the effect of various installation conditions including installation angle (θ), spacing (S), and group configuration. For this purpose, a series of uplift model load tests was conducted using single micropiles (SMP) and group micropiles (GMP). The uplift load capacity of both SMP and GMP increased with θ up to 30° but decreased for a higher installation angle of θ = 45°. Micropile spacing had less effect on the uplift load capacity for GMP. The uplift loadcarrying mechanism of inclined micropiles is proposed based on decomposed axial and lateral loads and resistance components. Based on the proposed load-carrying mechanism, axial and lateral load capacity ratios were proposed and adopted to formulate the uplift load-capacity equation for inclined micropiles. For GMP, the group-effect factor was proposed based on the reduction effect of group micropiles on the overall uplift load capacity. Full-scale uplift load tests were conducted to check the validity of the proposed method. Both SMP and GMP were constructed and tested. It was observed that the estimated results using the proposed method were in good agreement with the measured results. [ABSTRACT FROM AUTHOR]

The combined pile-raft foundation (CPRF) has been widely recognized as economic and rational foundation for high-rise buildings when subjected to vertical loading because of its effectiveness in load sharing by both raft and pile components. This results in smaller total and differential settlements with a reduced number of piles as compared with group piles. Until recently, the behavior of CPRF when subjected to lateral and real earthquake loading conditions in addition to vertical loads has not been well understood as a result of the complexities involved in the interaction of the pile, soil, and raft under such loading considerations. In the present study, an attempt has been made to investigate the behavior of CPRF with the use of centrifuge testing and a numerical model under pseudostatic and dynamic loading conditions carried out with finite-element software. After successful validation of the present CPRF model with both centrifuge and numerical model results, the same model was used for further study under El-Centro 1979, Loma Prieta 1989, Bhuj 2001 and Sikkim 2011 real earthquake pseudostatic loading and real acceleration-time history. The maximum displacement and bending moment were observed at the pile head, which is attributable to the rigid fixity of the piles with the raft. The crossover point in the bending moment profile was observed at shallow depths for all cases of loading. The occurrence of the resonance condition that yielded maximum horizontal displacement of the CPRF as a result of one of the input motions is also highlighted in the present study. The difference in the response of soil just below the raft of the CPRF and at the far field indicated that near-field and far-field ground motions were not in tandem. A case study on an existing CPRF of Messeturm Tower, Frankfurt am Main, Germany, is also presented. The existing CPRF of Messeturm Tower was modeled and analyzed under static and pseudostatic loading conditions. Obtained results show good correlation with the static field-measured results. Results in terms of bending moment in piles, total settlements, and normalized lateral displacement (u/D) are reported. The present findings are useful because they provide broader understanding of the response of the CPRF under pseudostatic and dynamic loading conditions. [ABSTRACT FROM AUTHOR]

Piles have been used to transfer superstructure (bridges, buildings, etc.) loads to deeper competent bearing strata to minimize settlements. Accurate predictions of design settlements of vertically loaded piles under working load are a critical issue in the design of pile foundations. Numerous comprehensive trials, built on a regression-based predictive formula that produces the axial settlement using elastic shortening as the input variable, were performed in this study, and a simple relationship was established between the elastic shortening of piles and the measured design settlements of 93 full-scale pile load tests installed in variable bearing materials. The calculated axial settlements of piles from the proposed method in this study were compared to the measured axial settlements of the piles. Accuracy and validity of the proposed method were verified through conventional statistical analysis in terms of mean of bias (λm) and coefficient of variation (μ). The proposed method yielded values of λm =1.06 and μ =0.15. [ABSTRACT FROM AUTHOR]

The present research intends to study the effects of the seismic soil-pile-structure interaction (SSPSI) on the dynamic response of buildings with various heights by conducting a series of shaking table tests on 5-, 10-story, and 15-story model structures. Two types of foundations for each case are investigated, including (1) a fixed-base structure, representing the situation excluding the soil-structure interaction; and (2) a structure supported by an end-bearing pile foundation in soft soil. An advanced laminar soil container has been designed that uses three-dimensional numerical modeling to minimize the boundary effects and to simulate free-field motion during the shaking table tests. Four real earthquake events, including Kobe 1995, Northridge 1994, El Centro 1940, and Hachinohe 1968, are imposed to each model. According to the experimental measurements, it is observed that the SSPSI amplifies the maximum lateral deflections and in turn interstory drifts of the structures supported by end-bearing pile foundations in comparison with the fixed-base structures. The rocking component plays an important role in increasing the lateral deflection of the superstructures, which can shift the performance level of the structures to near collapse or even collapse levels and as a result should be assessed precisely in the seismic design of buildings resting on soft soils. [ABSTRACT FROM AUTHOR]

The neutral plane solution has been widely used to estimate downdrag settlements and drag loads mobilized in piles in consolidating soil profiles. Pile settlement is typically assumed equal to soil settlement at the neutral plane depth corresponding to effective stress conditions at the end of consolidation. This paper demonstrates that, in general, pile settlement is not equal to soil settlement at the neutral plane depth; rather, it is the relative velocity between the pile and soil that is zero at the neutral plane depth. A beam on nonlinear Winkler foundation (BNWF) solution, in which the shaft friction capacity is proportional to effective stress, is utilized to demonstrate that pile settlement is not equal to soil settlement at the neutral plane depth, because the neutral plane depth evolves as consolidation progresses. The BNWF solution also shows that pile settlement depends on drainage conditions, with more settlement occurring when consolidation occurs first near the top of the consolidating soil layer, and less settlement occurring when consolidation initiates at the bottom. A modified neutral plane solution that is amenable to hand calculation is formulated to account for the evolution of neutral plane depth on pile settlement. Finally, the proposed BNWF and modified neutral plane solutions are compared with measurements of downdrag settlement from a centrifuge test program. The proposed methods produced more accurate estimates of pile settlement than the traditional neutral plane solution. [ABSTRACT FROM AUTHOR]

This engineering educational module on the behavior of piles in soft clays during earthquake loading sought to introduce engineering as a viable career to eighth graders and teach students how geotechnical engineers design foundations in marginal soils to minimize damage to infrastructure during earthquakes. This module could also be used at various educational levels, from elementary to middle and high school, as well as at the undergraduate level, with appropriate modifications. A 5-h module was created to simulate the real-world behavior of piles in soft clays during earthquake loading and visually show the improvement in how these same piles behave after being stabilized with a deep-soil-mixing technique. In this module, soft soil was simulated using Jell-O, piles were simulated using Slim Jims, and soil stabilization was simulated using peanut butter, marshmallows, or cheese. Each student group had to design a stabilization procedure to improve the behavior of the piles. The students competed to see who could design a stabilized pile with the least amount of deflection for the least amount of money. An abbreviated module was also administered to a group of middle-school science and mathematics teachers. The students' and teachers' learning and perceptions were assessed by administering pre- and post-assessment questions, which were matched. [ABSTRACT FROM AUTHOR]

Meshfree method is one of the numerical methods that typically use higher-order approximate functions and a weighted-residual approach to formulate the shape functions that are independent of the grids. In this paper, a series of computational modeling were conducted using the meshfree local Petrov-Galerkin (MLPG) method to evaluate the bearing capacity and response behavior of extended-length piles. The computational program codes and boundary conditions were generated based on the elastic-plastic behavior of the surrounding soil, reinforcements, and the noncontinuous interfaces between the piles and the soil. Compared to the traditional finite-element method (FEM), the MLPG exhibited higher accuracy in the results and indicated that the optimal length of the pile is directly related to the stiffness of the soil, i.e., the stiffer the soil, the longer the allowable pile length. Overall, the MLPG meshfree method was found to be a reliable and potentially promising numerical method for studying the bearing behavior of pile foundations. [ABSTRACT FROM AUTHOR]

There is currently a lack of established calculation methods for the geotechnical design of heat exchanger piles, although the technology is experiencing a fast expansion. Instead of quantifying the effects of temperature changes on the static behavior of heat exchanger piles, the common geotechnical practice is to apply a large overall security factor. This is done to be on the side of safety with respect to thermal effects. The few existing in situ experiments show that applying a thermal load induces a significant change in the stress-strain state of a pile. This paper presents a geotechnical numerical analysis method based on the load-transfer approach that assesses the main effects of temperature changes on pile behavior. The method is validated on the basis of in situ measurements of the loads and deformations experienced by heat exchanger test piles. The occurrence of critical design situations is further discussed. Some conclusions are formulated on concrete failure and the full mobilization of the pile shaft friction and base resistance during the operation of the heat exchange system. [ABSTRACT FROM AUTHOR]

Pile-soil interaction in an expansive soil foundation has been primarily analyzed by an analytical solution in our previous study. As a complementary work, this paper briefly reviews the derivation process in more detail and extends the capability of the solution in dealing with the pile-soil interaction issue under various conditions. The results show that (1) increasing pile length is able to effectively decrease the upward pile movements, but meanwhile, the tensile stresses along the pile shaft increase as well; (2) a critical pile diameter exists (d≈0.04L); (3) when the diameter is less than this value, the upward pile movements can be reasonably reduced, but for the pile with a larger diameter, it has little effect on reducing the upward pile movements, and as irrigation proceeds, both the displacements and tensile stresses increase and both tend to be much less sensitive to the water's incoming over time; and (4) a critical applied pressure for preventing the upward pile movements that is induced by soil's swelling pressure is found to be 2.5 times of the maximum tensile stress of the free pile only under swelling pressure in expansive soil foundation. [ABSTRACT FROM AUTHOR]

The behavior of pile foundations subjected to horizontal loading is typically evaluated using horizontal load tests. Although load tests are valuable to understand site-specific soil-structure interaction phenomena, validated predictive methods are also useful during the design phase. In this study, the results from horizontal load tests are compared with methods which predict the horizontal bearing capacity of piles using in situ measurements of soil behavior. Specifically, several horizontal load tests were performed in order to evaluate the behavior of two 12-m long Strauss piles and four bored piles with similar length, all installed in a lateritic soil profile. Two prediction methods were evaluated using p-y curves computed from the results of Marchetti's dilatometer test (DMT) results. The predictive methods using the p-y curves from the DMT showed good agreement with the behavior observed in the pile loading test. [ABSTRACT FROM AUTHOR]

Tapered piles in comparison to cylindrical piles can be beneficial in terms of the load capacity. In this paper, estimation of the load capacity for tapered piles using cone penetration test (CPT) resistance was investigated. Fourteen calibration chamber load tests using different pile types and six CPTs were conducted under various soil conditions. From the calibration chamber test results, the total, base, and shaft load capacities were analyzed in terms of soil conditions and taper angle. To evaluate CPT-based load capacity of tapered piles, normalized base and shaft resistances were obtained from normalized unit load-settlement curves. Based on the normalized base and shaft resistances, design equations that can be used to evaluate the base and shaft resistances of tapered piles were proposed. The proposed method is valid for sands of medium to dense conditions, while it may result in unconservative predictions for loose sands. To check the accuracy of the proposed method, field load tests using both cylindrical and tapered piles were conducted and compared with the predictions using the proposed method. A simplified approach using an equivalent cylindrical pile was also investigated and compared. [ABSTRACT FROM AUTHOR]

The capacity of a pile-soil system can be obtained by pushover analysis using the beam-on-nonlinear-Winkler foundation model. When the pile section enters the plastic state, the plastic hinge method is usually adopted to model its postyielding flexural behavior. The propagation of the plastic zone in a pile can be traced using a series of plastic hinges distributed along the pile that is embedded in the soil. This study proposes a proper model for arranging the distributed plastic hinges along the depths of the pile that are prone to yielding. A modified definition of plastic curvature is proposed herein in order to correctly simulate the nonlinear flexural behavior of a pile. Examples are presented to show the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

The existence of large magnitude stresses at the tip of a bearing pile is a well known phenomenon leading to crushing of soil grains and thus affecting pile behavior. Classical foundation design calculations which assume that the soil fails in shear and neglect volume change can be safely used where stress levels or particle strengths prevent crushing, however in the case of weak grains or high foundation stresses consideration should be given to the effects of grain crushing and the resulting volumetric compression. Model pile tests have been carried out in two skeletal carbonate sands and a standard silica sand with the aim of examining the variation of skin friction and end bearing capacities with degree of penetration. The mobilization of the strength of crushable soils requires a much higher strain level while at the same time the end bearing pressure on the model piles exceeded 10 MPa inducing considerable particle breakage. The peak skin friction for all sands occurred at a settlement normalized by pile diameter, S/D, of less than 0.1. At this point the carbonate sands generally had lower skin friction values than the silica sand. Further displacement caused a rapid decrease in skin friction for all three materials. At higher lateral stresses the less crushable Toyoura silica sand generated higher skin frictions. Samples of Chiibishi sand were sectioned and photographed. It was observed that a spherical plastic zone was formed at the base of the pile which expanded with increasing S/D and a degraded layer of broken particles developed around the pile as S/D increased. Large values of the Marsal particle breakage factor were restricted to a zone extending outwards to one pile radius. An end bearing capacity modification factor has been proposed to adapt the conventional bearing capacity equation for soil crushability. This modification factor is a function of soil compressibility and degree of penetration. The factor was shown to decrease with increasing soil compressibility and increase with normalized penetration S/D. [ABSTRACT FROM AUTHOR]

Underground tunnels are considered to be a vital infrastructure component in most cities around the world. Careful planning is always necessary to ensure minimum impact on nearby surface and subsurface structures. This study describes the experimental investigation carried out to examine the effect of existing piles installed in cohesive soil and extended to bedrock on the circumferential stresses developing in a newly constructed tunnel supported by a flexible lining system. A small scale testing facility was designed and built to simulate the process of tunnel excavation and lining installation in the close vicinity of preinstalled model piles. Lining stresses were measured for different separation distances between the lining and the existing piles Consistent decrease in the lining load was observed when the piles are located within a distance of one tunnel diameter from the tunnel. The results presented in this study indicated that measuring the lining response near existing pile foundations may be used to evaluate the extent of the interaction between the lining and the surrounding piles. [ABSTRACT FROM AUTHOR]

Pile foundations located within consolidating ground are commonly subjected to negative skin friction (NSF) and failures of pile foundations related to dragload (compressive force) and downdrag (pile settlement) have been reported in the literature. This paper reports the results of four centrifuge model tests, which were undertaken to achieve two objectives: first, to investigate the response of a single pile subjected to NSF with different pile tip location with respect to the end-bearing stratum layer; and second, to study the behavior of floating piles subjected to NSF with and without shielding by sacrificing piles. In addition, three-dimensional numerical analyses of the centrifuge model tests were carried out with elastoplastic slip considered at the pile-soil interface. The measured maximum β value at unprotected single end-bearing and floating pile was similar and slightly smaller than 0.3. On the contrary, smaller β values of 0.1 and 0.2 were mobilized at the shielded center piles for pile spacings of 5.0 d and 6.0 d, respectively. The measured maximum dragload of the center pile in the group at 5.0 d and 6.0 d spacing was only 53% and 75% of the measured maximum dragload of an isolated single pile, respectively. Correspondingly, the measured downdrag of the center pile was reduced to about 57% and 80% of the isolated single pile. Based on the numerical analyses, it is revealed that sacrificing piles “hang up” the soil between the piles in the group and, thus, the vertical effective stress in the soil so reduced, as is the horizontal effective stress acting on the center pile. This “hang-up” effect reduces with an increase in pile spacing. For a given pile spacing, shielding effect on dragload is larger than that on downdrag. [ABSTRACT FROM AUTHOR]

Numerous cone penetration test (CPT)-based methods exist for calculation of the axial pile capacity in sands, but no clear guidance is presently available to assist designers in the selection of the most appropriate method. To assist in this regard, this paper examines the predictive performance of a range of pile design methods against a newly compiled database of static load tests on driven piles in siliceous sands with adjacent CPT profiles. Seven driven pile design methods are considered, including the conventional American Petroleum Institute (API) approach, simplified CPT alpha methods, and four new CPT-based methods, which are now presented in the commentary of the 22nd edition of the API recommendations. Mean and standard deviation database statistics for the design methods are presented for the entire 77 pile database, as well as for smaller subset databases separated by pile material (steel and concrete), end condition (open versus closed), and direction of loading (tension versus compression). Certain methods are seen to exhibit bias toward length, relative density, cone tip resistance, and pile end condition. Other methods do not exhibit any apparent bias (even though their formulations differ significantly) due to the limited size of the database subsets and the large number of factors known to influence pile capacity in sand. The database statistics for the best performing methods are substantially better than those for the API approach and the simplified alpha methods. Improved predictive reliability will emerge with an extension of the database and the inclusion of additional important controlling factors affecting capacity. [ABSTRACT FROM AUTHOR]

A study to evaluate corrosion rates was conducted using pile foundations abandoned during the reconstruction of I-15 through Salt Lake Valley, Utah. Corrosion rates were measured for 20 piles extracted from five sites after service lives of 34–38 years. Measurements were made of soil index properties, resistivity, pH, cation/anion concentrations, and water table elevation. The critical zone for corrosion was typically located within the groundwater fluctuation zone; but correlations with soil properties were generally poor. Despite low resistivity, average corrosion rates for pile caps in native soil were typically between 2 and 9 μm/year with a maximum of 19 μm/year and did not pose any structural integrity problems. Nevertheless, for abutment piles where chloride concentration was very high, the average pile corrosion rate increased to 13 μm/year within the embankment and the maximum corrosion rate was 48 μm/year in the underlying native soil. Based on data from this and previous studies, equations were developed to predict maximum corrosion loss for piles in nonaggressive soil as a function of time. [ABSTRACT FROM AUTHOR]

The principal objective of this study is the development and calibration of a macroelement model for soil-pile interaction under simultaneously applied lateral and vertical loads. Herein, we focus on cast-in-drilled-hole single piles that are partially or fully embedded in soil, which are frequently used as support structures in highway construction. The model is calibrated and verified using primarily three-dimensional finite-element simulations and, whenever possible, with experimental data obtained from open literature. These data indicate that lateral loads significantly affect the vertical response of single piles, whereas the converse coupling is negligible. The proposed macroelement model is capable of mimicking this phenomenon. As such, it is a computationally efficient alternative to finite-element analyses, and is feasible to be utilized in practical applications. [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]

Micropiles are applied in foundation rehabilitation projects to enhance the pullout capacity of the existing foundation system and minimize the vertical deflection of the structures. Consequently, the methods to calculate the pullout load–displacement behavior are important for the design of micropiles used for such rehabilitation projects. Production pullout load tests were performed on approximately 120 micropiles used for seismic retrofitting of the 580/980/24 freeway interchange in Oakland, Calif. These micropiles were required to satisfy the serviceability design capacity at a maximum deflection of 1.27 cm(0.5 in.), in addition to the ultimate design capacity. Because the existing structures varied in height and loading, micropiles of different pullout capacities were designed. In this paper, the measured data are using a closed-form “t–z” method to develop probability distribution functions for the model parameters. As the back-calculated model parameters are assumed to be random variables, the Monte Carlo simulation process is employed to develop a series of load–displacement curves. A method for determining the probability of micropile failure at the service limit state is developed using the results of the simulations. The method is utilized to obtain resistance factors that can be applied to LRFD based service limit- state design. [ABSTRACT FROM AUTHOR]

This note studies settlement ratio, Rs, of pile groups in sandy soils, defined as the ratio of the settlement of a pile group to that of a single pile at the same average load per pile. 31 cases of field pile-group load tests and the corresponding field single-pile load tests were collected for this study. More than one-half of the cases consist of 3-diameter spaced, 9-pile groups. Based on the field test data, statistical analyses of Rs at different load levels were conducted for pile groups with cap-ground contact (PGCs) and pile groups with freestanding caps (PGFs), respectively. The mean of Rs decreases with the load level for both PGCs and PGFs, whereas the coefficient of variation of Rs increases with the load level. The influence of cap-ground contact on Rs does not appear to be significant based on a comparison of the mean Rs values of these PGCs and PGFs. In addition, a comparative study on Rs and group resistance ratio Rr, which is defined as the ratio of the average resistance of a pile in a group to that of a single pile at the same settlement, was conducted to clarify possible misunderstanding between Rs and pile group efficiency factor η for driven pile groups in sandy soils. The value of Rs compares settlement at the working load and is often larger than unity. The value of η compares failure loads, which occur at different settlements for pile groups and their respective single piles. η is usually larger than unity due to soil densification and additional contributions from the cap-ground contact for PGCs. [ABSTRACT FROM AUTHOR]

This paper describes the development and application of design charts for piled embankment designs. It outlines the computational approach adopted, the geotechnical profiles used, and the application of the design procedure using the charts. The soil profile used for the charts is representative of a Malaysian soft clay profile, involving a more or less normally consolidated soil, with a strength and stiffness that varies linearly with depth. Such a profile is typical of the ground conditions in a variety of countries in the Southeast Asian region. The design charts address the issues of pile capacity, settlement due to embankment load, settlement due to a temporary piling construction platform, and lateral response of piles near the edge of the embankment. The charts consider variations in ground conditions, embankment height, pile length, and pile spacing. An illustrative example is given to demonstrate the use of the charts. [ABSTRACT FROM AUTHOR]

This paper presents the field performance evaluation of an integral abutment bridge constructed in Massachusetts that was monitored for a period of three years. Emphasis is primarily made on observed seasonal and yearly behavior. Although the bridge abutments were constructed without any skew, differences have been observed in performance between the north and south abutments and are attributed to differences in construction conditions. Longitudinal displacement and rotation fully characterize the abutment deformation response. Fundamental parameters that control the response of the bridge (longitudinal restraint, pile moments) are evaluated through the use of simple mechanical models. The use of simple models allows estimation of bridge parameters for use in more involved finite element models. Data collected during the monitoring period indicate that current design procedures used for integral abutment bridges in Massachusetts are conservative. [ABSTRACT FROM AUTHOR]

An attempt is made to establish an analytically based estimate of the influence zone surrounding the tip of a loaded pile in sand. In the framework of the cavity expansion theory and a confined local failure mechanism, explicit expressions are derived in which the sizes of the upward and downward influence zones are properly linked with the angle of shearing resistance, the stiffness, the volumetric strain, and the mean effective stress of the sand at the pile tip. Based on a series of parametric analyses, the mean range of the influence zone is suggested. For piles in clean sand, the influence zone above the pile tip is between 1.5 and 2.5D and the zone below the tip ranges from 3.5 to 5.5D, where D is pile diameter. For piles in more compressible silty sand, the influence zone extends between 0.5 and 1.5D above the pile tip and between 1.5 and 3D below the tip. Because of its analytical nature, the present study may provide a meaningful insight into the current empirical interpretations. [ABSTRACT FROM AUTHOR]

A series of static cyclic lateral load tests were performed on a full-scale 4×3 pile group driven into a cohesive soil profile. Twelve 324-mm steel pipe piles were attached to a concrete pile cap 5.18×3.05 m in plan and 1.12 m in height. Pile–soil–pile interaction and passive earth pressure provided lateral resistance. Seven lateral load tests were conducted in total; four tests with backfill compacted in front of the pile cap; two tests without backfill; and one test with a narrow trench between the pile cap and backfill soil. The formation of gaps around the piles at larger deflections reduced the pile–soil–pile interaction resulting in a degraded linear load versus deflection response that was very similar for the two tests without backfill and the trenched test. A typical nonlinear backbone curve was observed for the backfill tests. However, for deflections greater than 5 mm, the load-deflection behavior significantly changed from a concave down shape for the first cycle to a concave up shape for the second and subsequent cycles. The concave up shape continued to degrade with additional cycles past the second and typically became relatively constant after five to seven cycles. A gap formed between the backfill soil and the pile cap, which contributed to the load-deflection degradation. Crack patterns and sliding surfaces were consistent with that predicted by the log spiral theory. The results from this study indicate that passive resistance contributes considerably to the lateral resistance. However, with cyclic loading the passive force degrades significantly for deflections greater than 0.5% of the pile cap height. [ABSTRACT FROM AUTHOR]

This paper identifies some of the causes of imperfections in real pile foundations and then examines their possible effects on pile behavior. The imperfections considered arise from two main sources, natural imperfections caused by the geological circumstances and imperfections related to the construction of the piles. In each case, single piles are considered first, and then pile groups are addressed separately. Case histories are presented to illustrate the effects on pile performance which are predicted by theoretical analyses. The analyses with which these examinations are carried out will still inevitably involve some degree of idealization, but at least attempt to incorporate the key “nonideal” aspects. The paper also discusses the particular problems involved in investigating and analyzing underperforming pile foundations and reviews some methods by which the consequences of imperfections may be overcome or ameliorated. [ABSTRACT FROM AUTHOR]

Much of the reported research on the dynamic analysis of pile foundations assumes linear behavior of soil that may not be valid for strong excitations. In this paper, material nonlinearity of the soil caused by plasticity and work hardening is considered in the dynamic analysis of pile foundations. An advanced plasticity based soil model, HiSS, is incorporated in a finite element technique. To simulate radiation effects, proper boundary conditions are used. The model and algorithm are verified with analytical results that are available for elastic and elastoplastic soil models. Analyses are carried out for free-field response and pile head response of end-bearing single piles. Both harmonic and transient excitations are considered in the analyses. Effects of frequency of excitation and stiffness of soil are investigated. It was found that the nonlinearity of soil has significant effects on the pile response for lower and moderate frequencies of excitations (a0<0.6) while at higher frequencies its effects are not as significant. [ABSTRACT FROM AUTHOR]

This paper presents results from a full-scale lateral load test on a 0.6 m cast-in-steel-shell (CISS) pile in sand liquefied by controlled blasting. Lateral loads were applied by a hydraulic actuator to simulate seismic inertial forces. The CISS pile was instrumented to provide the data necessary for back calculating lateral soil resistance and displacement. Details of the pile instrumentation and testing procedure are described. The back-calculated soil resistance and displacement are presented as p–y curves and compared to static sand p–y curves. Results from three simplified analyses are presented, where liquefied soil resistance was accounted for by modifying standard static p–y curves, and compared to measured test results. Limitations of the simplified methods are discussed. Test results show the blast induced liquefied sand did not provide resistance to lateral pile movement at displacements up to 50 mm. At displacements of sufficient magnitude, a phase transformation in the sand occurred resulting in a reduction in pore water pressure, and increased lateral soil resistance. The shape of the back-calculated p–y curves for liquefied sand is significantly different from the shape of standard p–y curves. As a result, the modified standard p–y curves do not adequately model the liquefied soil response. Consequently, results from simplified analyses vary from conservative to non-conservative as displacement levels increase. [ABSTRACT FROM AUTHOR]

Results of a three dimensional (3D) guided wave evaluation of the stress waves generated by the impulse response method show that the conventional interpretation technique based on 1D wave propagation theory is essentially a special application of the first branch of longitudinal wave modes with frequency components up to several thousand hertz. To extend the frequency range and incorporate special wave characteristics of higher modes so that the integrity of an embedded pile can be evaluated in a more thorough manner, a frequency-controlled method capable of exciting waveforms with higher and selective frequency components is introduced to nondestructively evaluate prototype concrete piles. Experimental results on a prototype pile are analyzed by processing the responding signals in the joint time–frequency domain, then comparing the processed waveforms with the theoretically computed results. These results show that the mode attributes of the experimentally excited waves are consistent with the results of theoretical evaluations. Based on this finding, this guided wave approach can be applied to evaluate the integrity of a drill shaft with appropriately determined parameters of the soil–pile system. [ABSTRACT FROM AUTHOR]

A lateral load test was performed on a full-scale pile group to evaluate pile–soil–pile interaction effects. The 3×3 pile group at 3.3 pile diameter spacing was driven opened ended into a profile consisting of loose to medium dense sand underlain by clay. The load carried by each pile was measured and strain gages were attached to determine bending moment. A single pile test was conducted for comparison. Group effects significantly reduced lateral resistance for all rows relative to single pile behavior. Trailing rows carried less load than the leading row. In contrast to tests in clay, lateral resistance was also consistently lower for middle piles within each row. Backcalculated p-multipliers were 0.8 for the front row and 0.4 for the trailing row piles which is consistent with results from previous centrifuge tests and full-scale tests where different installation methods were used. Good agreement between measured and computed pile group response was obtained using the p-multiplier approach. Based on centrifuge and full-scale tests in sands, design curves are presented to estimate p-multipliers over a range of pile spacings. The computer program SWM was able to match the measured group response without the use of p-multipliers. [ABSTRACT FROM AUTHOR]

Lateral load test was performed on a full-scale pile group following blast-induced liquefaction to evaluate pile–soil–pile interaction effects. The 3×3 pile group at 3.3 pile diameter spacing was driven into loose to medium dense sand. A single pile test was conducted for comparison. In contrast to preliquefaction tests, group interaction effects were insignificant after liquefaction. The lateral resistance of each pile in the group was similar and about the same as that for the single pile test. p–y curves were developed based on the bending moment versus depth data for Ru values of 95%. While the slope of p–y curves for nonliquefied sand typically decreases with continued deflection, the slope of the backcalculated p–y curves for liquefied sand increases with deflection. This phenomenon appears to be connected with load-induced dilation and a decrease in excess pore pressure locally around the pile. The p–y curves stiffened with depth and as the excess pore pressure ratio decreased. Equations were developed for p–y curves in liquefied sand which also account for the effect of variations in pile diameter. [ABSTRACT FROM AUTHOR]

Proof pile load tests are an important means to cope with uncertainties in the design and construction of pile foundations. In this paper, a systematic method to incorporate the results of proof load tests not conducted to failure into the design of pile foundations is developed. In addition, illustrative acceptance criteria for driven piles based on proof load tests are proposed for use in a reliability-based design. Finally, modifications to conventional proof test procedures are studied so that the value derived from proof tests can be maximized. Whether or not a proof test is conducted to failure, its results can be used to update the probability distribution of the pile capacity using the method proposed in this paper. Hence, contributions of the proof test can be included in foundation design in a logical manner by considering several load test parameters such as the number of tests, the test load, the factor of safety, and test results. This adds value to proof load tests and warrants improvements in the procedures for acceptance of pile foundations using proof load tests. A larger test load for proof tests, say 1.5 times the predicted pile capacity, is recommended since it will yield more information about the capacity statistics and thus allow for more economical designs. [ABSTRACT FROM AUTHOR]

The piled raft is a geotechnical composite construction, consisting of the three elements piles, raft, and soil, which is applied for the foundation of tall buildings in an increasing number. In a parametric study, 259 different piled raft configurations have been analyzed by means of three-dimensional elastoplastic finite element analyses. In the study, the pile positions, the pile number, the pile length, and the raft-soil stiffness ratio as well as the load distribution on the raft has been varied. In the scope of this paper, the results of the parametric study are presented and design strategies for an optimized design of piled rafts subjected to nonuniform vertical loading are discussed. [ABSTRACT FROM AUTHOR]

Presents results of full-scale lateral load tests of one single pile and three pile groups in Hong Kong, China. Use of pile foundations; Pile deflection versus depth; Discussion on ultimate lateral load capacity.

Analyzes the ultimate limit state (ULS) performance characteristics of the platform pile foundations. ULS of foundation system; Sources of bias in pile capacities; Pile loading characterizations; Evaluation of pile capacities in Bay of Campeche soils; Pile lateral and axial loading capacities; Reliability implications; Conclusions.

An analysis of pile axial and lateral response to transient dynamic loading is presented allowing for nonlinear soil behavior, the discontinuity conditions at the pile-soil interface, and energy dissipation through radiation damping and soil hysteresis. In addition, the effect of neighboring piles is taken into account for piles in a group. This analysis is used to derive the stiffness of foundation piles of fixed offshore towers. The effect of foundation nonlinearity and pile-soil-pile interaction on the dynamic characteristics of the tower is investigated. It was found that the tower's dynamic characteristics are greatly influenced by the foundation nonlinearity and the pile-soil-pile interaction. [ABSTRACT FROM AUTHOR]

The article presents information on a study on the settlement ratio of pile groups in sandy soils from field load tests. It informs that from an analysis of loading tests on more than 30 pile groups it was found that the mean value of settlement ratio decreases as the average load per pile in the group increases. It is stated that the stiffness factor for aluminum pipe piles is an order of magnitude less than for the groups of solid reinforced concrete piles and steel pipe piles. It is maintained that in foundation engineering practice, piles are usually much longer, stiffer, and have greater failure loads than is the case for many of the piles in the study.

A review of the article "Shielding Piles from Downdrag in Consolidating Ground," by S.Y. Lam, C.W.W. Ng, and H.G. Poulos, which appeared in the periodical Journal of Geotechnical and Geoenvironmental Engineering on June 2013, is presented.

The authors focused on responses to a previous article they had written on understanding the mechanisms involved in pile behavior in foundations. They commented on the sites where the research was conducted, which was reclaimed land with an altered water-table. They stated that it was considered acceptable to assume the soil profile beneath the water table at these sites would be saturated and that pore-water pressure would distribute hydrostatically. They mentioned the residual soil was decomposed granite formed by the weathering of parent rock, and that this soil type exists widely in Hong Kong, China, and in Japan and Malaysia. They stated the soil was in essence sandy and permeable. They talked about the measurement of axial stress after jacking some of the piles.

This article presents an experimental study on the shaft resistance of driven piles in sand, a topic of interest in foundation design. It is informed that the axial capacity of piles driven into sand has been identified as an area of great uncertainty in foundation design. This is due to the fact that the physical process involved in driving piles into sand is extremely complicated. It is well known that the behavior of sand is influenced by a number of factors including two important ones: relative density and stress level. It is further opined that the state-dependent behavior of sand implies that caution should be exerted in the interpretation and extrapolation of experimental results obtained at different test scales and, particularly, better interpretation of test results could be achieved by using the state parameter that simultaneously accounts for the relative density and confining pressure.

Discusses a research on moment-carrying capacity of short pile foundations in cohensionless soil. Comparison of the experimental results of the study and the different methods proposed by the discusser; Equations for the moment at ground level. INSET: Closure, by Edward A. Dickin and Ramli bin Nazir.

Discusses the ultimate bearing capacity of a pile not tested to failure as stated in the paper by Shenbaga R. Kaniraj. Why the pile load test was conducted; Determinants of the design working load; Conditions for the test pile to be accepted. INSET: Closure by Shenbaga R. Kaniraj.

A fully instrumented experiment was conducted to investigate the soil-structure interaction of single short, stiff laterally loaded piles. A hollow steel pipe pile with a diameter of 102 mm, a thickness of 6.4 mm, and a length of 1.524 m was installed in well-graded sand and subjected to increasing lateral load. The pile and surrounding soil were fully instrumented using advanced sensors, including flexible shape acceleration arrays, thin tactile pressure sheets, and in-soil null pressure sensors. The sensors attached to the pile were used to develop the compressive soil-pile interaction pressures and the lateral displacement along the pile length. The tactile pressure sheet sensors provided the soil-pile interaction compressive pressures on the circumference of the pile at a specific depth and along the length of the pile. The measured soil-pile interaction compressive pressures combined with the measured lateral displacement along the pile length were used to develop the soil-pile interaction force-displacement relationships ( curves) using direct measurements. In addition, the in-soil null pressure sensor measurements were used to develop the distribution of horizontal stress changes around the pile as the lateral pile displacement increased. When appropriate, the measured results were compared with data and methods available in the literature. [ABSTRACT FROM AUTHOR]