Search

Under various stress paths, the deformation characteristics represented great differences. In this paper, a series of cyclic triaxial tests have been conducted with Fujian standard sand. By comparing the constant deviatoric (CDS) and constant axial stress paths (CAS), the influence mechanism of the cyclic amplitude of the deviatoric stress was discussed. The test results showed that the stress path significantly influenced the volumetric and shear strains. The increasing and decreasing trend in the volumetric strain (ɛv) was consistent with the spherical stress (lnp). Compared with the two stress paths, the slope of the ɛv−lnp curve during the loading and unloading stages was larger under the CAS path. In the CDS path, qc almost did not affect the cumulative volumetric strain, and in the CAS path, the effect was obvious. The shear strain curve was in accordance with the direction of the stress path. As the cyclic number increased, the shear strain gradually accumulated. The shear strain accumulation under the CAS path was larger. The shear strain largely depended on the relative position between the critical state line (CSL) and the stress state of the soil during cyclic loading and unloading. Practical Applications: In practical engineering, the soil will experience various stress paths. For example, in slope or earth–rock dam engineering, where the water level rises and falls repeatedly, the soil often goes through the stress path of constant deviational stress with the cyclic increase and decrease in the spherical stress. In foundation pit engineering, the soil often experiences the stress path of the constant axial stress (CAS) with cyclic loading and unloading of the lateral stress. The stress path greatly influences the deformation and strength of soil. Therefore, the previous two stress paths are compared in this paper to discuss the influence of the cyclic amplitude of deviatoric stress. Under three different consolidation states, the cyclic amplitude of the deviatoric stress significantly influenced the volumetric and shear strains. The shear strain largely depended on the relative position between the critical state line (CSL) and the stress state of the soil during cyclic loading and unloading. Therefore, in practical engineering, if the stress path in the experiment differs from the actual value, the influence of the stress path should be properly considered. The results should be modified according to the degree of influence of each stress condition. [ABSTRACT FROM AUTHOR]

Collapsibility significantly impacts the bearing capacity of pile foundations in loess areas. To improve the load-bearing capacity of piles, the pile-base postgrouting technique is widely used worldwide. However, there are still several related issues to be solved: the impact of loess collapsibility on the bearing capacity; the effectiveness of the pile-base postgrouting technique in enhancing the bearing capacity; and the diffusion pattern of the grout during the grouting process. To investigate these issues, this experiment utilizes a visual static pressure device combined with numerical simulation. According to the experiment, the maximum axial force and neutral point appeared to shift downward after grouting, resulting in a 17.5% increase in the bearing capacity of the pile foundation. Additionally, an increase in grouting pressure leads to a rise in both the number of shear cracks and the diffusion radius. As the permeability of the grout improves, the number of shear cracks and diffusion radii tend to stabilize after an initial increase. These discoveries enable a thorough analysis of the changes in side friction and base resistance of postgrouted piles in collapsible loess. Furthermore, they provide valuable references and guidance for the implementation of the pile-base postgrouting technique in loess areas. [ABSTRACT FROM AUTHOR]

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]

Cracks develop in concrete piles under lateral static loading as the tensile stress exceeds the concrete strength, causing a decrease in the pile's flexural rigidity and influencing the load–deflection behavior. This paper presents a three-dimensional finite-element analysis (FEA) performed by PLAXIS 3D (version 2021) to investigate the impact of concrete cracking on the load–deflection behavior of laterally loaded piles in rock mass. Two FEA models were established to assess the influence of concrete cracking on load–deflection behavior. In the first model, nonlinear rock mass behavior was coupled with linear pile behavior (FEANL), while in the second model, nonlinear rock mass behavior was coupled with nonlinear pile behavior (FEANN). The three-dimensional (3D) FEA models were verified with a full-scale test case study for a deep-water pile foundation. The FEANN yields a more accurate simulation of measured deflection than the FEANL. A single run of the FEANN typically requires an entire day of computational time. Thus, a simplified approach was proposed to minimize the computational time process by incorporating the relationship of the change in pile flexural rigidity versus the bending moment (EI–M) into FEANL. In addition, the available EI–M relationships in the literature, such as the American Concrete Institute (ACI) method and beam theory, were evaluated by the EI–M relationship derived from the FEANN. The beam theory yields a lower estimate of pile flexural rigidity than the ACI method. The predicted deflection obtained through the simplified approach exhibits good agreement with the measured deflection utilizing the EI–M relationship derived from the FEANN. On the other hand, the EI–M relationship obtained from the beam theory overestimates the deflection compared to those obtained from the EI–M relationships of the ACI method and FEANN. [ABSTRACT FROM AUTHOR]

Previous earthquake events indicate that pile foundations in liquefiable soils are vulnerable to damage due to the coupling of inertial and kinematic effects. Inclined piles are widely applied in structures located in liquefiable soils, but few investigations of the coupling of the superstructure–pile inertial and soil–pile kinematic effects have been conducted. To address this gap, this study adopted a three-dimensional (3D) numerical model to investigate the coupling of inertial and kinematic effects in pile foundations with different inclination angles. The pile head bending moment was employed to represent the pile response, while the soil surface displacement and structure acceleration were utilized to quantify the kinematic and inertial effects. The role of the inclination angle on the interactions between inertial and kinematic effects is herein considered for pile groups. In particular, the inertial effect significantly influences the behavior of pile groups with larger inclination angles, whereas the kinematic effect predominates the pile head moment in vertical pile groups. In this paper, the influence of the pile inclination angle, superstructure configuration, and earthquake intensity on the interactions was investigated. The principal findings revealed that the kinematic effect dominates in the vertical pile group irrespective of the properties of the superstructure, while the inertial effect plays a significant role in the response of the inclined pile groups, especially for superstructures with considerable heights. Practical Applications: Inclined piles are vulnerable to damage due to the interaction of inertial and kinematic effects during earthquakes. This study conducted a series of three-dimensional (3D) finite-element simulations to investigate the interaction of inertial and kinematic effects in pile foundations with different inclination angles. The influence of pile inclination angle, superstructure height, and earthquake characteristics was investigated. In current practices, various codes and pseudostatic methods have been adopted to sum a percentage of the inertia-induced bending moment and another percentage of the kinematic-induced bending moment. This study indicates that under certain conditions, the simple summing of the bending moment induced by the inertial and kinematic effects could be inaccurate. The present study identified several factors that influence the interaction of inertial and kinematic effects on piles with different inclination angles. The inclined piles in liquefied soil, especially for supporting tall and heavy superstructure, attention should be given to the influence of inertial effect on the pile head bending moment. [ABSTRACT FROM AUTHOR]

The numerical simulation of boundary value problems involving a high number of pile-type structures, such as pile foundation systems of high-rise buildings, represents a standard task in computational geotechnics. Due to their ability to simplify the underlying pile modeling process and decrease the simulation runtime embedded beam formulations (EBFs) have attracted widespread interest from the geotechnical community. State-of-the art EBFs are typically equipped with nonlinear interface constitutive models to capture the soil–structure interaction behavior with reasonable accuracy. However, reliable information concerning the calibration of related parameters is limited, which decreases the confidence in the results obtained with EBFs. The present work addresses this research aspect for the first time, along with a theoretical discussion of inherent simplifications in the numerical description of the soil–structure contact associated with EBFs. The significance of selecting adequate embedded interface constitutive model parameters to ensure EBF predictions with high credibility is demonstrated by means of parametric studies. This has motivated the development of an automatic calibration software, leveraged by particle swarm optimization, that provides guidance in selecting suitable values. The effectiveness of the calibration software is confirmed by back-calculation of different pile problems with default and calibrated parameter sets. Likewise, the results provide insight into crucial factors driving the calibration framework, with a view to increasing its potential for take-up in engineering practice. Potential lines of research in the context of the automatic calibration software are explored throughout this work and may serve as valuable reference in future research. Practical Applications: The design of geotechnical problems involving a high number of pile-type structures, such as pile foundation systems of high-rise buildings or wind turbines, is routinely assisted by finite-element analyses. The computational expense of these simulations is significantly influenced by the pile modeling technique. Due to their exceptional ability to simplify the underlying modeling process and reduce the runtime to an acceptable limit, embedded beam formulations have therefore attracted widespread interest for geotechnical design tasks. As with all soil–structure interaction problems, it is essential in embedded beam formulations to accurately describe the interface behavior between the soil and the structure. This work presents the first attempt to highlight the relevance of this concern and visually describes relevant limitations resulting from an inadequate selection of interface constitutive model parameters. This observation has motivated the development of an automatic calibration software to increase the confidence in the parameter selection. The high potential of this software to increase the credibility of numerical predictions obtained with embedded beam formulations is demonstrated based on pile problems with different soil stratification layers, pile geometries, and pile arrangements. In all cases considered, the results confirm that the numerical fidelity could be significantly increased by employing calibrated parameter sets. [ABSTRACT FROM AUTHOR]

This paper pertains to the finite-element lower bound limit analysis (FELA-LB) of vertical strip anchors embedded in cohesionless and cohesive soils and subjected to static and earthquake forces (using pseudostatic analysis) to estimate the optimal horizontal pullout capacity using nonlinear programming (NLP) technique for isolating the optimal solution. In the developed procedure, a mesh of finite-number triangular elements and assuming a linear stress field that satisfies all the equations of internal equilibrium at all points within the soil medium, elemental interface equilibrium, boundary conditions and no-yield conditions at all the nodal points, has been adopted. In contrast to the use of linear programming (LP), as used in the early phase of the development of FELA of stability problems, in the adopted optimization scheme (NLP), the nonlinear no-yield conditions are incorporated directly, eliminating the necessity of successive linearization of the no-yield constraints. The convergence of the solutions (by varying the number of elements in the soil mesh) and extensibility of the selected stress field (by extending the mesh of elements) has been checked and ensured. The correctness of the estimated lower bound has been checked by comparing the obtained solutions with those reported in the literature. Parametric studies showing the effect of the embedment depth of the vertical anchor, soil properties, and earthquake acceleration on the horizontal pullout capacity of the vertical anchor have also been presented in the paper. Practical Applications: Anchor plates are used in the design and construction of foundation for retaining walls, sheet piles, bulkheads, transmission towers, bridge abutments, and buried pipelines to withstand the horizontal, vertical, or inclined loads. The present study adds to the existing state of art for the design and installation of anchor systems subjected to static and seismic conditions and may improve the performance of such foundation systems. [ABSTRACT FROM AUTHOR]

Aiming at the condition of shield tunnel undercrossing the foundation of a pile group directly, using the settlement and inclination of the pile caps as the evaluation index, the reinforcing effect of the pregrouting of the soil around the pile foundation, the deep hole grouting behind the tunnel segment, and the combination of the two reinforcement methods are analyzed through three-dimensional numerical simulation. A reasonable reinforcement scheme is found and applied to practical engineering. The results show that for the pregrouting reinforcement of the soil around the pile, the optimal reinforcement scheme is to extend 0.5 m around the pile cap in the plane and vertically from the surroundings of the pile cap to 1/3 of the pile length below the bottom of the cap. When deep hole grouting reinforcement is adopted, larger reinforcement range and a certain range of radial reinforcement radius of tunnel section will result in a better effect of reinforcement. The combination of the two schemes is better than the single use of one. The practical application results show that the combined reinforcement scheme can effectively control the influence of shield tunnel excavation on the pile foundation of an elevated waiting hall. [ABSTRACT FROM AUTHOR]

Seismic retrofitting of existing bridges has been in practice for years to meet the stringent seismic requirements set forward by revised design codes. For retrofitting, however, bridge piers are often prioritized while less attention is given to the bridge foundations, which are equally prone to damage under seismic loadings. The current work presents a series of experimental studies in assessing the performance of 2 × 2 pile groups reinforced with micropiles in terms of head-level stiffness and damping under low-to-high levels of static and dynamic loadings, encompassing the influence of loading-induced soil nonlinearity. Practical micropiles inclinations of 0°, 5°, and 10° with respect to the vertical are studied. Experimental results reveal that the head-level stiffnesses of pile groups reinforced with micropiles, contrary to the general expectations, become smaller than the pile group without micropiles at higher levels of applied loading. To elucidate the governing mechanism for such experimentally obtained results, three-dimensional nonlinear finite-element analyses were carried out. Results from the numerical analyses support the experimental results, suggesting that the presence of micropiles may not always increase the head-level stiffness of soil–foundation systems, particularly at higher levels of applied loading where the soil nonlinearity generated at the vicinity of piles and micropiles governs the overall head-level stiffnesses. [ABSTRACT FROM AUTHOR]

The installation of many pile foundations near slopes inevitably exposes them to the influence of the slopes on the stiffness and strength of the soil–pile system, which is a significant issue involving geomechanics and worthy of concern. Therefore, a modified failure wedge model with an optimal base angle is developed to address the impact of slopes on laterally loaded piles in sand, drawing insights from previous experimental results and finite-element analyses. The objective of this model is to provide a more comprehensive and universal analysis of the lateral behavior of piles while considering a limited height slope, compared with previous models applicable in relatively limited cases. In this modified model, factors such as edge distance from the slope crest and slope height are taken into consideration. The proposed theoretical method demonstrates its capability to accurately predict the lateral response of a pile. Based on this method, an analysis is conducted to examine how slope inclination, edge distance from the slope crest, and slope height affect the soil–pile system. [ABSTRACT FROM AUTHOR]

A comprehensive experimental program was performed in order to understand the mechanical behavior of model piles associated with water infiltration in collapsible loess. Real-time measurements were recorded for pile head settlement, pile shaft friction, and pile base resistance, as well as for the soil behavior, including soil settlement, volumetric water content, and soil suction. The experimental results suggest that both the pile head settlement and pile base resistance increased with water infiltration. The linear pile axial force distribution gradually changed to a "D" shape, with the maximum pile axial force occurring in the middle instead of the end stage of water infiltration. Such behavior can be attributed to a reduction in the contribution of soil suction, degradation of the pile–soil interface shear strength, and settlement of the collapsible soil. In addition, a softening model was proposed by modifying the traditional shear displacement method for interpretation of the mechanical behavior of piles in collapsible loess. There was good agreement between our experimental results and those from the literature and the results predicted using the proposed model, suggesting that the model can be used as a tool in the rational design of pile foundations in collapsible soils. [ABSTRACT FROM AUTHOR]

Cavities are common subsurface anomalies that have a significant impact on the bearing capacity of footings. While cavities behave three-dimensionally, in previous studies, the analysis of cavities has been limited to two-dimensional plane-strain analysis because of the time-consuming nature and complexity of three-dimensional modeling. However, this study demonstrates that the bearing capacity factor derived from three-dimensional modeling can be up to 10 times higher than that obtained from plane-strain analysis, highlighting the importance of considering three-dimensional effects. The present paper conducted three-dimensional simulations to investigate the impact of spherical cavity on the failure mechanisms and bearing capacity of footings under undrained conditions. An extensive parametric study was performed to investigate the influential parameters, including footing width to cavity dimension ratio (B/D), cover depth ratio (C/D), overburden factor (γD/Su), and void eccentricity ratio (S/D) for both circular or square footings. The results indicate that increasing the overburden factor and void eccentricity ratio leads to a decrease and increase in the bearing capacity of the footing, respectively. Furthermore, changes in other parameters can either increase or decrease the bearing capacity depending on the characteristics of the cavity (size and location) and footing (size and shape). General solutions for the bearing capacity factor are provided for different variations of the dimensionless parameters. This study also examined various failure mechanisms, including both cavity-independent and cavity-dependent failure mechanisms, associated with circular and square footings and influential parameters. These mechanisms are categorized into three zones for cavity-independent failures and four zones for cavity-dependent failures. The changes in the influential parameters including B/D, S/D, γD/Su, and C/D lead to changes in the type of failure mechanism and the size of the failure zones, while the foundation shape does not have a significant effect on the failure mechanism. Sinkholes and underground cavities annually contribute to infrastructure damage and financial losses. The 1981 incident in Winter Park, Florida, exemplifies the real-world consequences. Previous investigations have been limited to two-dimensional models due to the time-consuming nature and complexity of three-dimensional modeling, but the real-world nature of cavities in three dimensions requires a more comprehensive understanding. This study directly addresses this need by investigating the impact of three-dimensional cavities on the bearing capacity of circular and square building foundations, also known as footings. This study thoroughly investigated the factors influencing the results, encompassing cavity size, depth, soil weight, and off-center position. It extensively explored potential footing failures, providing detailed discussions. Our findings are presented as easy-to-understand maps and charts covering a broad range of potential scenarios. These visual tools can help engineers and researchers accurately estimate the stability of a building's foundation when a cavity is present underneath. In simpler terms, this research has created a handy tool for professionals to predict the potential danger posed by hidden cavities to buildings and infrastructure. This knowledge can then be applied to ensure safer building practices, potentially saving a significant amount of money and preventing accidents in the future. [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]

In excavation engineering, most of the retaining structures are subjected to asymmetrical loads, including in asymmetrical excavation and asymmetrical overloading. However, a theoretical solution to, and deformation-controlling method for, this problem has remained elusive to date. In this work, a semianalytical solution for determining the deformation of retaining structures subjected to asymmetrical loads was derived based on the principle of minimum potential energy. The retaining structures were viewed as flexible, and the overall deformation of the retaining system was evaluated by our proposed theoretical model. This model was verified by comparing it with practical monitoring data. Subsequently, the theoretical solution was applied to analyze the stress and deformation characteristics under the conditions of asymmetrical excavation and asymmetrical overloading, which can be controlled to ensure the safety of a project. Finally, because of the requirement for a small amount of deformation in the foundation pit retaining piles, the earth pressure on the retaining piles is close to the static earth pressure. Reducing the length of the retaining pile on one side had a greater influence on the deformation on that side, but less of an influence on the other side. Thus, the proposed model can be used for optimizing the asymmetrical design of a retaining structure in order to balance the economy and safety of a project. Our design theory can be applied to a variety of engineering projects. A typical case is the Guangzhou Baiyun District Comprehensive Transportation Hub Project in China. The method was used to analyze the status of the subway foundation pit, offering a new design scheme to reduce the design length of the retaining piles, which resulted in great economic benefits in its practical application. The findings provided in this paper can be applied to the engineering of any long, narrow foundation pit that can be simplified into a two-dimensional plane–strain calculation model, being used to realize more accurate deformation control over the foundation pit envelope. The core of this calculation method is that it can accurately describe the magnitude of the earth pressure. The distribution of the earth pressure is worthy of further study. [ABSTRACT FROM AUTHOR]

Although three-dimensional finite-element analysis has been introduced to foundation design for years, simplified computer-based calculations based on the spring analogy of soils and structural elements are also frequently used in many engineering projects. Using coefficients of subgrade reactions and pile stiffness is a straightforward way to design and analyze a piled raft foundation. This paper discusses the determination of the coefficients of pile reactions for embedded piled raft foundations in soft clays subjected to vertically uniform loads through a series of finite-element analyses. The geologic property was assumed to be composed of homogeneous soft clays with the shear-wave velocities varying at 100–140 m/s. The foundations with a square raft ranging from 16 to 36 m and embedment depths of 8 and 12 m were studied. Load intensity approximating 1.5 times the excavated soil pressures was considered where the maximum uniform load was applied to the foundation. The foundation settlements and reactions of the piles were obtained first from a three-dimensional finite-element analysis. For design convenience, the dimensionless pile displacements, pile reactions, and coefficients of pile reactions were developed and presented in plots. The embedment depth-to-raft size ratio, pile slenderness ratio, and pile-to-pile spacing distance-to-pile diameter ratio were examined to find their optimized correlation. Finally, a design example was given to verify the proposed suggestions. We conclude that the proposed method can be an alternative to the piled raft foundation design. [ABSTRACT FROM AUTHOR]

The seismic design of pile foundation–supported structures has gained significant attention in the last few decades; there have been several failures during moderate to severe earthquakes. Seismic soil–pile foundation–structure interaction (SSPSI) was reported as the governing phenomenon behind the failure mechanism of such structures. In this context, in this study an attempt is made to investigate the influence of SSPSI (mainly the inertial part of the interaction) in a pile-supported structural system with variation in dynamic characteristics and the ratio of superstructure stiffness to pile foundation stiffness (Ks/Kp) through physical model experiments using a shake table. The primary aim in this study is to assess the extent of the effect of dynamic soil–structure interaction in a scaled-down pile foundation–supported bridge structure in nonliquefied ground with the help of a simplistic normalized parameter, i.e., Ks/Kp, for different ranges of the period of the superstructure system. The study primarily highlights variation of the normalized lateral period of the whole interaction between the superstructure and pile foundation as a function of the practicable range of Ks/Kp, which may be helpful for designers in predicting the dynamic characteristics of the system as a first step in seismic design. Similarly, the trend of normalized spectral acceleration and displacement response at the superstructure and pile head with respect to Ks/Kp is presented for the prediction of design forces. Finally, an idealized case study prototype design problem is used to verify the outcome of the study and illustrates simplified design steps for pile foundation–supported structures in general. [ABSTRACT FROM AUTHOR]

In this study, we instrument the foundations and towers for two onshore shallow wind turbine generators (WTGs) to evaluate foundation response, quantify in-service loads, and assess the assumptions behind WTG foundation design calculations. Measurements of pressure at the soil–foundation interface, soil strain just below foundation level, and tower moments over long periods provide insights into the operational moments experienced by the tower and the load transfer mechanisms to the foundation system. The results of this study have implications for design practices in three distinct ways: (1) the assessment of rotational stiffness calculation assumptions, (2) the evaluation of pressure distribution used in the bearing capacity formulation, and (3) the estimation of tower loads used in the tower and anchor bolt design. Our observations show that the induced overturning moments correlate well with incipient wind speeds and directions and the associated soil pressure and strain responses. The overturning moments and the response parameters relate linearly within the spectrum of measured magnitudes. However, the pressure distribution across the foundation footprint does not monotonically increase or decrease with distance from the neutral axis of the foundation base (e.g., the pressure sensed at the foundation's center close to the foundation is between 1.5 and 2 times greater than the pressures sensed at the edges). In addition, the measured soil strain as a function of cyclic moments shows that the in-service cyclic shear strains are less than 1.4 × 10−5 (i.e., two orders of magnitude smaller than the assumed design strain level). Finally, the spectrum of cyclic moments follows a semilog trend, thus indicating that operational and nonoperational loads dominate the fatigue load spectrum. Our study suggests that adequately designed WTG foundations on competent fine-grained soil result in very low operational soil shear stresses and strains, which might indicate that the current design practices are too conservative in nature. Field measurements establish load spectrums for cyclic fatigue loads for the long-term operational conditions of WTGs. [ABSTRACT FROM AUTHOR]

Piled embankments are becoming widely used to cope with engineering problems (e.g., excessive settlements, bearing failure) caused by soft soil subgrade to maintain the safety and stability of the constructed facilities. This study focused on an international motor-racing circuit currently under construction, where the underlying soft soil substratum characterized by a high void ratio and compressibility may largely influence the long-term performance of the project. Pretensioned high-strength concrete (PHC) pile-supported embankment is designed to improve this project, and its effectiveness remains to be studied. In addition, this study specifically focused on negative skin friction (NSF) and neutral plane (NP) position development, which significantly influence the bearing capacity of the pile foundation and have not been fully understood. As such, two large-scale field tests were performed on the PHC pile-supported embankments to monitor the settlement of piles and the surrounding soils. According to the monitored layered settlements, the NP development with time was quantitatively analyzed, and NP gradually moved up toward the pile top during soil consolidation. Comparison between the measurements of two test sites with and without geogrid reinforcement indicated that geogrids could not only alleviate total and differential settlements of the foundation but also contribute to the shallower final NP position. A numerical model, whose effectiveness was validated by comparing with the field measurements, was established to predict the complete variation of NP positions and explore the effects of various influencing factors through a parametric study. This study enhances the comprehension of NSF and NP development in pile foundations and provides valuable guidance for this motor-racing circuit and other related projects in the future. [ABSTRACT FROM AUTHOR]

The capsule expansion technique (CET) is a novel active measure to control the deformation of subsurface structures induced by underground engineering construction. CET has been applied to tunnel deformation control, but its application in pile foundations is rarely reported. In this paper, a field trial and three-dimensional coupled consolidation finite-element analysis were performed to study the interaction of capsule–soil–pile and control efficiency of CET. Field trial results verify the feasibility of CET in controlling pile horizontal deformation, and the control efficiency is 60% higher than that of Tube-a-Manchette grouting with 40%. Numerical back analyses indicate that the pile maximum displacement increases almost linearly with the expansion diameter, while the control efficiency of CET hardly changes. The total stress of the soil in front of the pile is significantly reduced by 20.3% due to the dissipation of excess pore-water pressure, resulting in the reverse displacement of the pile. High excess pore pressure induced by CET would cause the soil to bear additional stress after dissipating, leading to the reverse displacement of the soil and further diminishing the control efficiency. Moreover, control efficiency can be improved by reducing the surrounding excess pore-water pressure induced by expansion and increasing the excess pore-water pressure at the back side of the pile. [ABSTRACT FROM AUTHOR]

Field load tests are carried out on a single pile and piled-raft foundation (PRF) consisting of a 2 × 2 pile group with consideration of the time effect. The piles along with the raft in the PRF have been instrumented with load cells and strain gauges. Gradual compressive loading has been applied to the PRF with an increment of 10% up to the estimated safe load capacity. Settlement corresponding to the safe load is monitored for 4 months. The settlement of the PRF, axial load carried by piles, shaft friction along the pile length, moments in the raft, and load sharing ratio between piles and raft for each increment of loading are observed with respect to time. A nonlinear analysis is suggested to scrutinize the behavior of vertically loaded rigid PRFs in layered soil medium (present approach). Considering the theory of the interaction factor, an approximate procedure is implemented to analyze the nonlinearity of pile groups with a rigid raft. Additionally, the nonlinear response of piles using hyperbolic functions is presented (alternative hyperbolic function approach). A simplified method for the calculation of the flexibility matrix considering the time effect is also suggested (present time-based approach). The analyses are validated with the field results and available literature. Parametric studies have been performed to calculate the immediate and time-dependent settlements of the PRF by varying the length to diameter ratio of the pile, spacing to diameter ratio of the pile, and pile group configuration using the present approach and present time-based approach. Immediate settlements corresponding to the safe load by the present approach and alternative hyperbolic function approach are approximately 8.18% and 6.48% less than the measured settlement. [ABSTRACT FROM AUTHOR]

Energy piles, as an environmentally friendly means to exploit renewable energy, have attracted the attention of global researchers over the past years. Traditional heat exchanger configurations (1-U-shape, 1-W-shape, and multi-U-shape in series or parallel) have been utilized. Traditional 1-U-shape is limited by pile length, short heat transfer path, and low total heat transfer rate. Traditional 1-W-shape heat exchange tubes will cause thermal interference. Moreover, the heat exchange rate per unit tube length is not high for multi-U-shape in series or parallel. Therefore, this paper presents an efficient pile foundation heat exchanger configuration, i.e., deep penetration 1-U-shape configuration. Through a numerical study, energy pile groups with deep penetration 1-U-shape heat exchangers are investigated under continuous operation mode and intermittent operation mode. The temperature change of the piles and soil under intermittent operation mode is analyzed. Thermal performances (e.g., outlet water temperature and heat transfer efficiency) are compared under the two operation modes. Four typical monitoring points under the two operation modes are compared, and the difference in temperature variation is obtained to study the influence on the temperature field of the piles and soil. Results show that in summer mode, the temperature of the pile under intermittent operation mode presents restorability while the temperature of the soil increases gradually. Intermittent operation mode yields a lower temperature of outlet water temperature than continuous operation mode does, and therefore intermittent operation mode is recommended. [ABSTRACT FROM AUTHOR]

This study examines the capacity of single piles subjected to cyclic axial tension or compression load in the loess area under in situ compaction degree and extruding conditions. Four cyclic tension and compression loading tests, and two conventional tension and compression tests on single piles were carried out at a typical loess site of the Loess Plateau region of Northwest China's Shaanxi Province. A series of pretest preparations, including site leveling, steel cage production, pile formation, and soil compaction, are performed. The axial displacement of pile top, pile axial force, and frictional force of the pile side of a single pile measured in the test process were analyzed. The cyclic tension or compression load–displacement curves of the piles in loess, under the in situ compaction degree condition, show the load results in an influence of the movement trend that cannot be ignored. There is no overlap between the compression-unloading curve and tension-unloading curve. This phenomenon indicates that the cyclic loading accelerates the destruction of the pile foundation. Under an extruding condition, the difference between the maximum deformation and the minimum deformation is 2.412 mm, which is 60% of the ultimate deformation of a conventional single pile. The lateral friction of the pile shows multipeak distribution along the pile body, and the attenuation range of lateral friction strength at the pile tip is more than 50% in the failure stage. [ABSTRACT FROM AUTHOR]

At present, the reliability analysis and design method of vertically loaded piles embedded in spatially variable soils is difficult to be applied in practical engineering due to the huge computation effort required. To improve computational efficiency, this paper proposes a new method called the FORM–KL–LTM, which integrates the advantages of the first-order reliability method (FORM), the Karhunen–Loève (KL) expansion method, and the load transfer method (LTM). The main framework of the FORM–KL–LTM is the FORM, which is used to perform reliability analysis for the pile. The KL expansion method is adopted to carry out random discretization to generate the discrete soil parameters required by each iterative computation of the reliability index using the FORM, and the LTM is employed to evaluate the nonlinear load–settlement behavior of the pile head and to compute the values of limit state functions required by the FORM. The proposed method is computationally efficient because the number of random variables is controlled by the limit number of KL expansion terms. Based on the FORM–KL–LTM, a reliability sensitivity analysis method is proposed, which can compute the sensitivity index for measuring the relative sensitivity of the reliability index with respect to soil properties. Furthermore, a procedure for the reliability-based design (RBD) of piles embedded in spatially variable soils is established for the design of pile geometry, and a design ratio is defined to select the controlling limit state in the RBD of pile for both the ultimate limit state and the serviceable limit state. The procedure, accuracy, and efficiency of the proposed methods are demonstrated by providing an example of the reliability analysis and design of a vertically load pile in spatially variable soils. The spatial variability of soil has been recognized as an important source of uncertainty of the bearing performance of the pile, and therefore, it should be considered in the reliability analysis and design of a pile foundation. However, the methods used in the current literature, such as the discretization of a random field, the calculation of load–displacement curves, and the reliability analysis of a pile foundation, require a huge computation effort. Low computational efficiency is highly disadvantageous to designers, which makes the reliability analysis and design method by considering a soil's spatial variability difficult to be widely applied to practical engineering. Therefore, this study proposes a new method called the FORM–KL–LTM to perform the reliability analysis and design of vertically loaded piles in spatially variable soils. This method greatly reduces the number of random variables and simulations of the performance function, thus improving the computational efficiency. Based on the FORM–KL–LTM, a reliability sensitivity analysis method is proposed to carry out a sensitivity analysis of soil parameters on the reliability of a pile foundation. Moreover, this paper defines the design ratios for discussing which limit state mainly controls the failure state of the pile foundation under different soil properties and pile geometry. [ABSTRACT FROM AUTHOR]

Ground fissure is the most common geological catastrophe phenomenon in Xi'an, posing a major security threat to the currently developing urban cloud rail transit system. In this paper, a 3D-FEM calculation model is established to study the influence of the intersection angles between the hidden ground fissure and the cloud rail on the deformation and failure characteristics of the structure. The findings indicate that the pile foundation is under tension in the main deformation area of the hanging wall of the ground fissure, and the negative friction zone (NFZ) appears below the neutral point (buried depth 18 m for intersection angle 30°). The pile foundation is under compression in the footwall, and the pressure it bears is less than the tensile force sustained by the hanging wall pile, and the NFZ is above the middle point. The NFZ of the pile foundation in the hanging wall and footwall increases as the intersection angle decreases. The pile foundation mainly undergoes vertical settlement, and the horizontal displacement is relatively small. The 3D movement of the pile foundation results in settlement and inclination of the superstructure of the cloud rail simply supported beam bridge, such as the pier and track beam. Therefore, the cloud rail bridge should span the ground fissure at a large angle as far as possible, and 3D adjustable support should be adopted to adjust the offset of the track beam caused by the ground fissure. [ABSTRACT FROM AUTHOR]

Existing projects indicate that a large number of pile boreholes formed via cement fly ash gravel (CFG) pile construction in soft soil could produce a borehole group effect in the absence of timely backfilling. The borehole group effect could cause ground settlement and threaten the safety of adjacent buildings, tunnels, and pipelines. However, the mechanism of the borehole group effect, causing serious deformation in surrounding soil, has seldom been studied, and there exists no simple simulation method to predict the borehole group effect. In this study, a case involving CFG pile boreholes in a soft soil area causing a significant settlement of surrounding buildings was introduced. Based on this case, a centrifuge test was designed to simulate the influence of a single borehole and multiple boreholes on the surrounding soft soil. The mechanism of the borehole group effect was investigated via centrifuge tests and the finite-element method. In the case of a single borehole, a horizontal circumferential stress arch and vertical stress transfer arch were formed in the soil, which effectively limited the shrinking deformation of the borehole wall. In the case of a large number of boreholes with a small spacing, the horizontal and vertical stress arches around the boreholes affected and weakened each other. As a result, the shrinking deformation of the borehole group was greater than that of the single borehole. In other words, the borehole group effect was found to cause serious deformation in the surrounding soil. To overcome the difficulty in the simulation of a large number of pile boreholes in engineering, the borehole-type conversion and multihole merging method was proposed. The simulation results indicated that the simplified method was reasonable. [ABSTRACT FROM AUTHOR]

This study proposed an analytical approach for predicting the end-bearing capacity of driven piles that are subjected to axial loads in saturated and unsaturated soils. This is a generalized approach in which the stress characteristic method is employed successfully for both saturated and unsaturated soils. An iterative technique computer code was developed for the proposed analytical approach extending the finite difference method to develop solutions with the aid of MATLAB (version 2019a) that provides graphical output to visualize the results. The results from the proposed approach were compared against measurements for 13 pile load tests that include 11 in saturated soils and 2 in unsaturated soils, with good agreement. In addition, numerical analyses were performed using ABAQUS (version 6.14) to simulate the driven pile penetration and pile loading by employing the arbitrary Lagrangian–Eulerian adaptive mesh methods. The comparisons between the numerical predictions and measurements from a published model pile test suggested that the ultimate bearing capacity is well predicted by the finite-element model in comparison to the proposed analytical method. However, the proposed analytical method was simple for use in engineering practice applications to estimate the end-bearing capacity of pile foundations in both saturated and unsaturated soils. [ABSTRACT FROM AUTHOR]

Torsional load arising from horizontal load eccentricity has a significant effect on the ultimate horizontal load carrying capacity of tripod bucket foundations in clay. In this paper, the effect of torsional load on the failure mechanism and ultimate horizontal capacity of tripod bucket foundations in undrained clay was studied using 3D finite-element analyses. Three single buckets were connected to form a rigid tripod bucket foundation system. Two different shear strength profiles, that is, uniform and linearly increasing with depth were considered. A detailed parametric study was conducted by varying the bucket spacing and embedment depth to explore the effects of different governing parameters. All the analyses were carried out for smooth and rough interface conditions. The influence of torsion on horizontal capacity is presented in the form of combined horizontal-torsional (H-T) failure envelopes. Reductions in ultimate horizontal capacity with increasing load eccentricity were quantified for the ease of practice. Finally, an expression for estimating combined H-T capacity is provided as a function of normalized spacing and embedment. Additional analyses were also performed to evaluate the effect of moment arising from vertical eccentricity on the combined H-T capacity. [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]

The performance of batter-piled raft systems during seismic events continues to be a major concern. In response, a series of shaking table tests, including vertical and nonvertical configurations, were conducted, and the effects of superstructure frequency and pile angle on the seismic performance of the models were examined under a wide range of accelerations (0.2–0.7 g). Smaller bending moments, horizontal displacements, and rotations were captured for the nonvertical models, so the application of batter piles is reliable under seismic conditions. The maximum bending moment in the vertical models was recorded to be 8 times greater than in the batter piles at the lowest level of ground motion. Thus, the performance of the system was more sensitive to the frequency of the superstructure for vertical piles. [ABSTRACT FROM AUTHOR]

An increasing number of concrete faces rockfill dams (CFRDs) are being built on deep alluvium foundations. Understanding the behavior of CFRDs that are built on alluvial foundations is critical to the performance assessment and design optimization of these dams. This paper aims to quantitatively study the influence of alluvial foundations on CFRD behavior and discusses the corresponding treatment measures. Four parameters are proposed to describe the distribution characteristics of alluvium foundations. The parameters are related to the mechanical properties of an alluvium foundation, which have practical physical meaning. A series of numerical calculations are performed on the behavior of CFRDs with different alluvium characterization parameters based on a case history. The influence of an alluvium foundation distribution on CFRD behavior is quantitatively analyzed according to the numerical calculations and measured data from case histories. Corresponding treatment measures or suggestions for the dam or foundation are discussed. The findings could offer reliable insights into CFRD behavior on alluvium foundations and provide an engineering analogy or reference for the planning, design, and construction of CFRDs. [ABSTRACT FROM AUTHOR]

This paper presents a new method for the nonlinear analysis of rafts resting on multilayered heterogeneous soils using the Vlasov model. The finite-element and the finite-difference methods are employed to solve the governing differential equations for the flexure of the raft and the displacement within the supporting soil mass, respectively. The soil heterogeneity in the vertical direction or in the horizontal directions within each soil layer is considered, and the soil nonlinearity is taken into account through the reduction of the soil shear modulus as a function of strains within the supporting soil mass. Through a comprehensive comparative study, it is found that the present method is validated as reasonable by field measurements and is in good agreement with nonlinear three-dimensional finite-element analysis and other existing analysis methods. A study is carried out to investigate the effect of soil layering, soil nonlinearity, and soil heterogeneity in the vertical direction and in horizontal directions on the raft behavior. It is concluded that neglecting the real conditions of the supporting soils (e.g., soil layering, soil nonlinearity, and soil heterogeneities in the vertical or in horizontal directions) in the analysis of the soil–raft interaction leads to an unrealistic prediction of the raft behavior. [ABSTRACT FROM AUTHOR]

Piled raft foundations (PRFs) below stepped high-rise towers are often subjected to nonuniform triangular-shaped loads with eccentricities. In this study, 20 rectangular piled rafts with different pile configurations and orientations, embedded in medium-dense sandy soil, are analyzed using three-dimensional nonlinear finite-element (FE) analysis in which the critical state–based Clay and Sand Model (CASM) is used as the soil constitutive model. Different triangularly distributed loads with and without eccentricities are considered in addition to uniformly distributed loads. A systematic parametric study is performed by varying the different design parameters based on which the PRF behavior is systematically investigated in terms of multiple performance parameters such as maximum settlement, differential settlement, angular distortion, tilt, and load distribution between the raft and the piles and between the individual piles. It is observed that the pile diameter, number of piles, and raft plan area control the differential settlement, angular distortion, and tilt the most. Based on the insights gained from the parametric study, a design optimization exercise is performed, in which the most optimal pile configuration is selected based on the criteria of allowable settlement and angular distortion with additional considerations for tilt, load distribution, and the volume of concrete required. [ABSTRACT FROM AUTHOR]

A hand-calculation method for estimation of nonlinear load–settlement response of piled raft foundations (PRFs) embedded in sandy soils is developed using three-dimensional finite-element (FE) analysis in which the elastoplastic constitutive behavior of the soil is modeled using the unified Clay And Sand Model (CASM). Three types of PRFs with rectangular, strip, and circular rafts and with a variety of pile dimensions and arrangements are considered in the study. The PRFs are assumed to be embedded in five different sands (Ottawa sand, Erksak sand, Sacramento sand, Portaway sand, and Decomposed Granite sand) with different elastic properties, critical state parameters, and relative densities. Systematic parametric studies are performed to develop equations for the estimation of the average nonlinear settlement of PRFs. The maximum and differential settlements are also estimated from the average settlement. The proposed equations require the relative density, elastic constants, and critical state friction angle of sand, and the piled raft geometry and properties as inputs. The settlement equations are applicable to PRFs of sizes similar to those considered in the study and can be used by practitioners for quick, initial estimation of PRF settlement as part of design calculations. [ABSTRACT FROM AUTHOR]

Issue 1 The authors employed three-dimensional (3D) finite-element software Plaxis 3D ([1]) to model a ring foundation in a cohesive soil, where a quarter of the problem domain (i.e., a 90° sector of the domain) was discretized. The authors employed the commercial finite-element software, namely, Plaxis 3D, to determine the ultimate bearing capacity of ring foundations in cohesive soils. In particular, for both cases of rough and smooth foundations, Eq. (10) of the original paper cannot make a realistic prediction in terms of the change of undrained bearing capacity when the I k i value varies from 1 to 10. Rather, Eq. (10) of the original paper generates almost constant undrained bearing capacity with all I k i values for each interface condition (i.e., rough I q SB ult sb i 363 kPa and smooth case I q SB ult sb i 93 kPa). [Extracted from the article]

Combined piled raft foundation (CPRF) is an effective solution for supporting high-rise constructions. The traditional design philosophy of CPRF does not consider the capacity of foundation based on combined vertical (V), horizontal (H), and moment (M) load. However, V-M-H load acts on the CPRF system concurrently due to the action of wind, wave, earth pressure, and earthquake loading in addition to gravity loading. In this context, the present investigation deals with the effect of combined V-M-H load interaction on the behavior of CPRF in sand and clay, respectively. The response of CPRF under combined loading is obtained using a 3D finite element analysis. First, validation of the numerical model is performed considering the model test results conducted in Agartala sand and another based on the available field test result of Messeturm Tower in Frankfurt clay obtained from the literature. Further, failure and design envelopes for the validated CPRF system are developed considering V-M-H load in both sand and clay deposits attributing a variety of influential system parameters. Simplified expressions for design lateral and moment capacities are proposed based on multiple linear regression analysis. Finally, the implication in design based on the findings of the present study is illustrated using a prototype case study structure. [ABSTRACT FROM AUTHOR]

Drainage techniques can be employed to reduce damage of pile rafts in liquefiable ground by decreasing the build-up of excess pore water pressure and maintaining soil stiffness during earthquakes. This paper aims to evaluate the impact of drainage wells on the seismic response of floating piled rafts in fully saturated ground. In practice, floating piles are commonly employed as underpinning elements beneath the raft foundations to reduce undesirable settlement of the raft. Centrifuge experiments were performed on 2 × 2 piled raft foundations with and without drainage wells in mildly sloping ground. Two types of ground involving a uniform sand layer and a uniform sand layer with a superficial gravel layer were reconstructed, whereas the piles were floating within the liquefiable sand. The models were fully instrumented and sine waves were introduced to the models' base at the 80 g centrifugal acceleration. Records of the transducers demonstrate that the drainage wells system significantly decrease the settlement of foundation, dissipation time under dynamic loading by forming closer drainage routes, and excess pore water pressure ratio. In contrary, presence of drainage systems significantly increases the rafts acceleration response, and the bending moment and the axial force of the piles. Results of the piled raft systems in the presence and absence of the drainage wells and the superficial gravel layer are compared with together and also compared with the far-field in terms of the acceleration response, permanent settlement, and excess pore water pressure. [ABSTRACT FROM AUTHOR]

Recently, few nuclear facilities have been proposed on soil sites worldwide. Controlling the overall and differential settlement is a difficult task for a nuclear structure that rests on a soil site. Under these circumstances, a combined piled–raft foundation (CPRF) provides the required level of performance with a significant cost saving compared with a pile foundation. The combined system involves complexities in the interactions between the soil–pile–raft and superstructure system. The literature focuses on simulating the interactions between pile, soil, and raft. Until recently, the behavior of a CPRF that supported a heavy and massive structure had not been well studied and understood. A combined three-dimensional (3D) model of soil–pile–raft–superstructure systems will be developed in this study that considers the soil and interface nonlinearity along with the complex superstructure geometry. The modeling approach for the piled raft system will be validated using the standard benchmark problem and field case histories. Various aspects of a CPRF for a typical nuclear building (NB) will be investigated, such as the effect of the depth of soil medium, comparison of the behavior of the raft foundation, pile foundation, and CPRF, contact pressure distribution, pile behavior, soil behavior; and various performance indicators. The presented systematic procedure to configure the CPRF system could be useful in similar practical applications. This study indicated that the stiffening of the superstructure and sequential construction has a beneficial effect on the combined system. The findings of this study could be useful to frame the general guidelines for the economical design of CPRF systems. [ABSTRACT FROM AUTHOR]

A new simplified approach based on the pseudostatic method of analysis is proposed to investigate the response of a combined pile–raft foundation (CPRF) and a group pile considering the complex interaction. In this method, the raft is considered as a plate supported by group of piles and soil, where piles are modeled as Euler beam elements resting on elastic Winkler foundation and the raft is divided into square grids attached with horizontal springs. The reliability of the proposed method is verified by laboratory testing results and those of Plaxis3D simulations for a 4-piled raft system. Good agreement between the laboratory results, numerical simulations, and the proposed method is demonstrated, showing the potential applicability of the new simplified method. [ABSTRACT FROM AUTHOR]

This study investigates the influence of soil–structure interaction (SSI) on period and damping of steel moment-resisting frame buildings supported by shallow footings on dry sand deposits. A series of impact hammer tests were conducted on a 3-story and a 6-story model steel frame for this purpose. Different base conditions (e.g., loose and dense sand beds, surface and embedded footings, heavily loaded and lightly loaded footings) were considered to gain a complete understanding of inertial SSI effects. Experimental results were compared with FEMA provisions as well as with analytical results obtained from a finite-element model. The period and damping amplifications are more prominent in the case of the 3-story building than in that of the 6-story building, indicating more sensitivity of short and stiff buildings to SSI over the taller ones. For a heavily loaded 3-story building on loose sand, the period and damping amplifications are 21 and 330%, respectively. Although the analytical results match well with those of the experiment, FEMA provisions tend to overestimate the responses, especially for the 6-story building. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to establish a complete analytical solution concerning the linear pressure distribution under rigid rectangular spread footings. An eccentricity diagram is developed to map the unique footing deformations and compression zones in each one of five distinct regions. For each region, the linear soil pressure, neutral axis position, and pressure values at the four corners are expressed in closed forms. The accuracy and consistency of the explicit expressions are verified by presenting several special boundary cases, whereas the physical interpretation is brought out by analyzing the eccentricity diagram. A generic nomogram providing the maximum soil pressure is also formed to promote efficient structural footing design. The developed analytical formulas for responses and resultants enable algorithmic implications without iterations and offer high computational efficiency. Proper examples, generated via developed computer software, exhibit how the theoretical content of this article is applied in practice. The software enables three-dimensional (3D) viewing of the deformed and undeformed physical and mathematical model of the structure, allowing detailed visual inspection of the results. [ABSTRACT FROM AUTHOR]

This paper proposes an efficient hybrid approach for analysis of the responses of piled-raft foundations subjected to coupled loads (combination of vertical loads, horizontal loads, and moments) in layered soils. The proposed method comprehensively accounts for pile-pile, pile-soil surface, soil surface-pile, and soil surface-soil surface interactions. Moreover, to capture the influence of embedment and active/passive effects of piles, a modified Vesic's subgrade modulus for embedded piles and passive piles was adopted. To avoid a large number of time-consuming integration processes, the shear displacement method and elastic foundation beam method were employed to calculate the vertical and horizontal responses of a single pile, respectively, and the results were then extended for the pile group. The results calculated with the proposed method for piled-raft foundations in layered soils were found to have good agreement with those obtained from the more rigorous finite-element methods (FEMs) and elastic theory method in layered soils. It was found that the proposed procedure can accurately predict the responses of piled-raft foundations under complex loads in layered soils. [ABSTRACT FROM AUTHOR]

Stone columns are a popular formof ground improvement that can be applied to a variety of foundation solutions involving soft soil deposits. Many design methods are based on an assumption that columns with a length-to-diameter ratio greater than 4 bulge uniformly along their length. This mode of deformation is not valid for small groups of columns in which interaction between individual columns and the footing gives rise to more complex behavior. The deformational behavior of stone columns at serviceability limit state is of utmost importance, because settlement rather than bearing capacity criteria are generally more onerous in soft soils. The results of some high-quality laboratory studies have been informative in this respect, but the extrapolation of results from small-scale tests comes with the caveats associated with single-gravity laboratory testing. The FEM, in combination with advanced constitutive models, can provide a link between the deformational behavior and settlement performance of discrete column groups at working stress levels. A series of analyses was conducted to examine the influence of key design parameters such as column length, spacing, and the number of columns. The influence of a stiff crust was also examined, because the reference soil profile adopted for these analyses was that of the well-characterized Bothkennar test site. The following three modes of deformation were identified by examining the distribution of stress and strain within columns and the surrounding soil: individual punching, block punching, and bulging. Individual and block punching developed in short or closely spaced columns, whereas block punching was more prevalent in larger groups. Bulging develops in long, widely spaced columns and generally occurs at the point of lowest lateral restraint. In addition, novel parameters referred to as compression and punching ratios were developed to validate the in-depth analysis and identify the principal design parameters that influence the behavior of small groups of stone columns. The results indicate that the mode of deformation is governed by column spacing and length rather than the number of columns. This finding is important, because it indicates that settlement design methods that are developed for large groups of columns are applicable to discrete groups at similar spacings and lengths. It was also observed that the influence of the stiff crust forces bulging to occur deeper and might have led authors in the past to suggest the existence of a critical length. [ABSTRACT FROM AUTHOR]

Model testing for soft soil foundations with and without a prefabricated vertical drain (PVD) was performed to assess the consolidation and long-term performance of PVDs. Surface settlements and excess pore-water pressures at different depths were monitored throughout the applied multistage loading. Classical methods with improved solutions that considered variations in the discharge capacity and non-Darcian flow were applied via a back-analysis of the consolidation results. Parameters related to the smear effect and well resistance were discussed in these solutions. It was found that the foundation improved with PVD had an approximately 20% increase in the total degree of consolidation compared with untreated soft soil foundations; the well resistance of the PVD system not only existed but it also changed over time; the average discharge capacity in the model test under multistage loading condition was far less than the reported value; and the advanced solutions, especially the solution that considered the varied discharge capacity (with qw0 = 3 cm³/s and Aw = 4.12 × 10-6 1/s), gained a better fitting result than the classical solution. [ABSTRACT FROM AUTHOR]

In the present paper, the response of cylindrical storage tank foundation resting on stone column-reinforced ground has been studied considering the separation between the bottomraft and ground under liftoff condition. The bottomraft of the tank is idealized by a circular plate. The stone column-reinforced ground ismodeled as a tensionless foundation. Soft foundation soil and granular fill are idealized as a spring-dashpot element and Pasternak shear layer, respectively. Stone columns are modeled as stiff nonlinear springs. The stone columns are converted into equivalent concentric rings with one stone column at the center to simulate the axisymmetric condition for the analysis. The governing differential equations are derived fromthe classical theory of thin plate and solved using the finite-difference technique. A parametric study is performed to investigate the differences between the response of tensionless and conventional elastic foundation systems. It is observed that tensionless foundation idealization is essential to analyze the liftoff and avoid erroneous design of the raft for the cylindrical storage tank. Recommendations are also suggested to avoid possible liftoff. [ABSTRACT FROM AUTHOR]

Monopiles are the most commonly used foundation type for offshore wind turbine (OWT) structures and are characterized by relatively large geometric dimensions, compared with offshore pile foundations typically used in the oil and gas industries. To date, there are no established technical guidelines tailored for the design and analysis of OWT monopiles. This paper first identifies various intrinsic drawbacks involved with the existing design and analysis methodologies as applied to OWT monopiles. Next, a comprehensive experimental program of 1g repeated lateral load tests, performed on a scaled rigid monopile installed in dry sand beds, is presented to investigate its behavior under various loading scenarios. The experimental results provide insights into the various blurry issues in the existing literature related to monopile behavior under long-term repeated lateral loading. Lateral soil resistance profiles were determined from the measured pile bending strain data and found to be markedly dependent on the degree of the polynomial function used for curve-fitting of the bending strain data. Finally, an experimental model is presented for estimation of the pile's accumulated rotation, which takes into account various basic characteristics of the applied lateral load cycles. [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]

A newly built roller-compacted concrete gravity dam is located on the Yalongjiang River in southwest China. Complex geological conditions greatly puzzled the designers of the project. There are abundant joints within the riverbed that form the double- inclined wedge foundation. This is a typical mode of instability of concrete gravity dams. The equal-K method, which falls into the category of conventional limit-equilibrium methods, is provided in the design codes of gravity dams to evaluate the stability of a dam against sliding along deep failure surfaces. The factor of safety calculated by the equal-K method is determined by the angle of the force acting on the interface of the two inclined wedges, denoted by φ, which is unspecified in the design codes. On the basis of Sarma's assumption, this study proposes an algorithm for the determination of ∅, which needs only slight improvement of the algorithm in the existing codes. The justification of the proposed procedure is demonstrated by showing that the results from the proposed procedure are very close to those from a rigorous limit-equilibrium method in which all equilibrium conditions are satisfied. [ABSTRACT FROM AUTHOR]

Evaluation of the uplift capacity of plate anchors in saturated clay is an important aspect in the design of offshore foundation systems of various structures. In most of the literature reviewed, simple constitutive models such as Tresca or Mohr-Coulomb (MC) have been used in evaluating the plates' pullout capacity. There exists a need to study the pullout capacity of anchors using other advanced soil models and explore differences in computed behavior. In addition to the MC model, two other constitutive models are used herein to represent the soil behavior. These are Modified Cam-Clay and Soft Soil models. A series of finite-element analyses are performed using the three constitutive models. Undrained effective stress analyses are conducted to study the response of both strip and circular plate anchors in saturated soils. The capacities of plate anchors are assessed through the application of the displacement control approach. The effective stress parameters are correlated with the undrained shear strength, and Nc (dimensionless breakout factor) values from the three constitutive models are presented and compared with the lower bound solution, as well as with the data obtained from similar studies and experimental data available in the literature. Differences resulting from the characteristics of the three constitutive models are examined and discussed. [ABSTRACT FROM AUTHOR]

Growing urbanization is leading to more structures being constructed close to each other, resulting in substantial interaction between their foundations. Although the interaction between two shallow foundations and between piles in a pile group has been studied by several researchers, the effects of interaction between shallow and deep foundations are not very well understood or studied. Not much published literature is available for practicing engineers to analyze and design shallow and deep foundations that are constructed adjacent to each other. The second author of this paper was recently involved in a project in which a structure designed to be supported on drilled shafts was supposed to be constructed adjacent to another structure designed to be supported on a large mat foundation with high floor load. Although the authors have performed a detailed parametric study using finite-element techniques to better understand stress distributions and develop a simplified method to analyze this type of problem, this paper is only focused on estimating lateral stresses on the shafts and their lateral load analysis. A stress bulb for lateral stresses under a uniformly loaded square foundation is proposed, which is a significant tool for practicing engineers to understand lateral stress distribution below a uniformly loaded square area and estimate lateral stresses on nearby deep foundations. [ABSTRACT FROM AUTHOR]