Search

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]

Building and ground settlement due to construction dewatering is a well-studied topic. However, most previous investigations have not considered the barrier effect of an adjacent underground structure on the drawdowns and resulting settlements. In this study, the barrier effect and its influence during construction dewatering for a metro station foundation pit is investigated. There are five aquifers at the foundation pit site, and a row of buildings supported on pile foundations, which act as an underground barrier to flow, is present on one side of the pit. On the other sides, there are no deep underground structures to impede groundwater flow. Field monitoring of the groundwater level drawdown, diaphragm wall movement, and ground and building settlements on both sides of the pit was carried out during dewatering. The results indicate that on the side with the pile foundations, the groundwater level drawdown, ground settlement, differential settlement, and angular distortion of building incurred by dewatering were relatively greater, but the diaphragm wall movements were relatively smaller. The effect of preexisting barriers should be considered in the assessment of construction dewatering-induced drawdowns, soil settlements, and building movements. [ABSTRACT FROM AUTHOR]

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

Enhancing the dynamic properties of expansive soils using cementitious materials has attracted the attention of many researchers over the past few decades. Supplementary cementitious materials (SCMs) can be used as partial substitutes for cement owing to their pozzolanic activity that further improves the mechanical performance of cement-stabilized soils upon curing. In this study, the effect of cement and zeolite incorporation on the mechanical behavior of expansive clay was quantified using the pressure wave velocity (Vp) indicator obtained from ultrasonic pulse velocity tests performed at different curing times. Furthermore, a polynomial model was developed to establish the relationship between Vp and zeolite replacement levels at specific curing times and cement contents. The results show that a polynomial function captured the decreasing trend of Vp upon the increase in zeolite at curing times below 14 days. Additionally, the developed equation explained the upward trend of Vp owing to the pozzolanic activity of zeolite at later curing times with an accuracy of over 92%. The coefficients of the polynomial model also increased with the increment of the cement percentage which conformed to the consecutive rise in Vp. Ultimately, the polynomial coefficients were expressed in terms of cement content and curing time using the Volterra series. Using this model, the optimum percentage of cement replaced with zeolite (Zopt), the efficiency of using Zopt instead of cement, and the percentage of zeolite replacement to achieve equivalent Vp of cemented clay samples (ZC) were estimated. The findings of this study contribute to promoting geotechnical sustainability by replacing cement with zeolite that has a considerably lower environmental footprint. Clay is a type of soil that can be found in many construction projects. For instance, many roads and buildings' foundations are constructed on clay soils. To ensure the necessary strength of the clay under the main structure, the soil should often be stabilized using adhesive construction materials such as cement. Interestingly, a portion of the cement could be replaced with other minerals not only to improve engineering performance but also to promote sustainability by lowering cement consumption. In this study, the effect of zeolite as a partial replacement for cement on the strength of clay soils was experimentally evaluated. The effect of various design parameters, such as cement replacement level and curing time, on the stability of clays was investigated using an advanced technique called the ultrasonic pulse velocity (UPV) test. Furthermore, a simple mathematical model was proposed based on the experimental results to help engineers design the stabilization plan and timely decide about the next steps of the construction process. [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]

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]

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]

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

Pile foundations supporting high-rise buildings are generally subject to cyclic loading because of dynamic loading. The corrosion of steel materials in pile foundations is another major concern, especially for piles in a marine environment. In this study, a series of cyclic and static loading tests on model piles made of fiber-reinforced polymer (FRP) and seawater–sea sand concrete (SSC) and ended in a rock socket were reported. Three structural configurations (FRP tube–confined, FRP rebar cage–reinforced, and centered FRP rebar–reinforced) were adopted for the model piles. Strain along the depth of the piles was measured using fiber Bragg grating (FBG) optic sensors and an advanced distributed optical sensing technique known as optical frequency domain reflectometry (OFDR). Strain distribution, axial cyclic stiffness, and shaft friction mobilization of the piles under static and different modes of axial cyclic loading were analyzed and explored in detail. The test results indicated that the FRP tube–confined model pile showed higher confinement and cyclic capacity and lower stiffness degradation, leading to relatively more stable behavior. A high level of cyclic loading can cause microcracks to form and grow within the pile material, thereby decreasing pile stiffness. The strain profile of all the piles along the depth appeared to follow a similar trend, and fluctuations at certain points led to failure. Cyclic stiffness showed gains initially when cyclic load conditions were below a certain threshold level but degraded when loading was increased beyond it. Moreover, shaft resistance gradually increased with cycles, causing higher mobilization in the upper portion of the socket. The experimental results have provided the first systematic study on the performance of the FRP-SSC composite model piles ended in rock sockets under axial cyclic and static loadings. This will contribute to development of a potential predictive method for pile settlement and capacity for the better design of rock-socketed piles. [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]

Corrosion is important in the design, maintenance, and preservation of bridge steel pile foundation systems. It is an inevitable phenomenon when steel is exposed to the environment, as metals tend to return to their lower energy state. While the corrosion rate of steel is predictable for atmospheric exposures, it is highly variable and difficult to predict for steel buried underground because of the high variability of soils. Applying a protective sacrificial layer is a common protection method to prevent corrosion. This study aims to evaluate the efficiency of a galvanized and painted galvanized steel bridge pile for achieving a 100-year service life and to economically compare them for using piles without a coating. To meet this objective, 21 steel coupon samples and nine 30 cm pile samples with galvanized coating, painted-galvanized coating, and no coating were tested in a cyclic corrosion test chamber to investigate the efficiency of each coating. The test was conducted for 600 days simulating a 100-year service life. Results from the experimental test revealed that galvanized and painted-galvanized coating methods show remarkable performance in protecting the piles against corrosion, and both methods can protect the piles from corrosion for 100 years. Further evaluation showed that, while the cost to increase the pile size was determined to be less than the premium for galvanizing or galvanizing and painting the piles for the bridge in this study, a cost–benefit evaluation for each protection measure is suggested, knowing that costs can vary widely depending on specific project requirements, location, market prices, etc. [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]

The design of rock-socketed pile foundations requires careful consideration of critical construction aspects such as the socket roughness and smear for accurately estimating the shaft load capacity. Despite the effect of smear being investigated extensively over the years, previous studies are limited in accurately characterizing the effect of smear on the shaft response. This paper presents a comprehensive investigation on the load-bearing mechanisms of model smeared rock-socketed piles with different smear fabrics (configurations) at the pile-rock interface. These model piles were loaded into synthetic soft rocks while being intermittently subjected to three-dimensional (3D) X-ray computed tomography (CT) imaging. Interpretations from the X-ray CT images were correlated with the pile-head load-displacement behavior to gain insights into the load transfer attributes between the pile, smear, and rock. The various interactions between these components were deduced by monitoring the micromechanics at the pile-rock interface through shaft energy utilization, interface void volume, smear volume, and sand density mapping. Based on the observations, it was inferred that the load transfer between the smear and the rock is primarily dependent on the percentage and position of smear occupancy at the interface. Results indicated that for the partially smeared interfaces, the interface mechanics are a combination of smeared and clean shafts with the residual resistances dependent upon the combined compression of smear and rock debris at the interface. Moreover, it was observed that the continuous presence of smear for more than half area of the leading faces of the pile asperities results in the smeared regions of the pile taking precedence over the unsmeared regions in governing the load-carrying capacity of the shaft. The discussions presented in this study can provide a strong base to further study the smear effect, subsequently aiding in enhancing the existing design guidelines to economically construct piles in soft rock. [ABSTRACT FROM AUTHOR]

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

Hurricane and tsunami events can generate extreme water flows in nearshore regions of the United States with catastrophic consequences to coastal structures. Field records have shown that light-frame wood structures exhibit high vulnerability to wave-induced forces due to their light construction characteristics, which feature flexible connections and slender pile foundation systems. Previous research has studied the behavior of these structures under wave action, but most studies used rigid body modeling, which is shown in this study to be insufficient for capturing the force demand on these structures. Using a fluid-structure interaction (FSI) framework, this research investigated the structural and soil flexibility effects in the interaction between elevated light-frame wood structures and water flows. Study variables included the flexibility of timber-to-timber connections, soil type, pile embedment, wavelength, and wave amplitude. The study concluded that structural and soil responses to water flows can introduce strong coupled motions. Neglecting this coupling effect may underestimate the force demand on the light-frame wood structures by more than 40%. Accounting for both structural and soil flexibilities is necessary to accurately quantify the wave force demand of these structures. [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]

Brittle failures were observed in pile foundations during past earthquakes due to seasonally frozen ground. This paper introduces a new geosynthetic material derived from waste tires, i.e., polyurethane-bonded rubber particles and sand, termed PolyBRuS, for application around deep foundations to improve their seismic performance in cold regions. Cyclic triaxial tests were carried out at various temperatures, confining pressures, and freeze–thaw cycles to assess the cold-weather dynamic characteristics of PolyBRuS. The results show that the material behaves as a nonlinear viscoelastic material at an axial strain of less than 1%. Its dynamic elastic modulus rises after freezing and continues to increase as temperature drops, but it is much less sensitive to confining pressures and freeze–thaw cycles; its damping ratio rises significantly with increasing axial strains and decreasing subfreezing temperatures and declines moderately with increasing freeze–thaw cycles. Compared with natural soils, its dynamic elastic modulus is similar to those of unfrozen fine-grained soils and is much less sensitive to subfreezing temperatures; its damping ratio is comparable to that of fine-grained unfrozen soils and is substantially higher than frozen soils at subfreezing temperatures. These characteristics make this material an excellent candidate to replace local soil around deep foundations for vibration reduction and seismic hazard mitigation in cold regions. [ABSTRACT FROM AUTHOR]

Composite plate shear walls/concrete-filled (C-PSW/CFs), also known as SpeedCore systems, are a relatively new structural member in American codes and standards. Prior research has focused primarily on C-PSW/CF walls with either flange/closure plates or filled composite members as boundary elements. Walls without boundary elements have also been studied, but they are no longer permitted by the American Institute of Steel Construction (AISC 341-22). The reason is that composite walls without boundary elements do not provide adequate ductility for seismic design. This paper presents the results of experimental and numerical studies conducted to evaluate the cyclic lateral load behavior of C-PSW/CFs using hot-rolled structural steel members as boundary elements. The steel web plates of the C-PSW/CF specimens were connected to each other using threaded tie bars with double nut connections. Composite interaction between the steel and concrete infill was achieved using the tie bars and additional shear studs welded to the boundary elements. The composite walls were embedded and anchored to reinforced concrete foundation blocks using welded deformed bar anchors. The experimental investigations focused on the cyclic lateral load-drift responses including test observations and limit states, moment-rotation response of the plastic hinge and the section moment-curvature relationship, overall lateral stiffness, strength, and displacement ductility. The experimental results show that the specimens exceeded their nominal flexural capacities calculated using the plastic stress distribution method or fiber-based section modeling using measured material properties. The specimens had plastic hinge rotation capacity greater than 0.028 rad. and displacement ductility ratio greater than 5.2. Detailed 3D nonlinear inelastic finite element models and simpler fiber-based macro models of the tested specimens were developed and benchmarked using experimental results. The detailed 3D finite element models can reasonably simulate the global and local behavior of the specimens, and are recommended for conducting further parametric studies of composite wall design details. Simpler fiber-based macro models can efficiently simulate the cyclic lateral load behavior of the specimens, and are recommended for modeling C-PSW/CFs while simulating the behavior of multi-story building structures. [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]

Shake table experiments are conducted to assess the potential of the polymer injection technique as a liquefaction countermeasure. A large 2.9 m high (10 ft) laminar soil container on a 3.9×1.85 m (13×6 ft) shake table is employed. Mitigation of liquefaction-induced settlement for a shallow foundation is explored. In a series of two shake table experiments, the system response is studied first without (baseline) and subsequently with polymer injected into the liquefiable stratum. Each test is densely instrumented to provide insights into the dynamic response of the soil and foundation system. Furthermore, cone penetration tests (CPTs) are performed pre- and postinjection to assess the extent of soil improvement. Strong base excitation is imparted by the shake table, resulting in liquefaction and excessive foundation settlement in the original baseline test. In the second test, with the polymer injection countermeasure, a significant reduction is observed in the tendency for liquefaction and the resulting foundation settlement. After this test, careful excavation provided additional insights into the polymer's configuration within the deposit, increasing overall soil relative density, confinement and creating solidified paths for the shallow foundation load toward the lower, more competent stratum. As such, these mechanisms have the potential to allow for: (1) an increase in soil resistance to liquefaction, and (2) a significant reduction in settlement of overlying shallow foundations. [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 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]

The serviceability limit of the foundation system plays an important role in the safe long-term performance of a building. Under governing load cases in service life, the building foundation system should satisfy the serviceability limit state, i.e., total and differential settlement criteria. This study investigated the distress of a building through foundation performance assessment incorporating the soil–foundation–structure interaction (SFSI) effects. A spatially variable soil model [zonewise, obtained from field observation and electrical resistivity tomography (ERT) study] was used to obtain the settlement of the foundation system. Engineering properties of the subsurface were estimated from the collected soil samples and field tests. ERT result shows the variability of the subsurface layer. A three-dimensional finite-element model of soil, foundations, and structures was developed to estimate the settlement demand of the foundation and structures. The numerical model includes the geometric variability of all the foundations of the building and subsurface variability. Settlement and bearing capacity demand of the foundations were estimated and compared with the standard provisions. Results obtained show that the building foundation system satisfies the serviceability limit of the foundation system under total settlement criteria. However, the differential settlement of the system exceeds the required limit despite considering the SFSI effects, and is one of the major causes of distress to the building. The main contributions of this study also include establishing the spatial variability of the soil layer through ERT and correlating it with the crack zone in the building. [ABSTRACT FROM AUTHOR]

This document is a closure to a case study on ground subsidence caused by the drying effect of Australian native eucalypts. The study highlights the potential for clay soil shrinkage and subsequent damage to structures such as residential buildings, road pavements, and pipelines. Recommendations for addressing the drying effects of trees on nearby buildings vary by country, with the Australian standard AS 2870 providing guidelines for designing footings near trees. The closure also addresses potential queries from practitioners, including the age of the trees, the construction date of the netball court, and the impact of cutting tree roots during barrier construction. The writers express gratitude to Dr. Vishnu Diyaljee for their insights and thank the discusser for their valuable questions and additional insights. [Extracted from the article]

This article discusses a case study on the effects of ground subsidence caused by the drying effect of a group of Australian native Eucalyptus trees near a netball court. The study demonstrates the impact of evapotranspiration on the cracking of the court and highlights the importance of monitoring sap flow from trees to understand water movement. The article also compares the recommendations for tree placement near infrastructure in Canada and Australia, emphasizing the need for geotechnical engineers to consider the influence of trees on foundation distress. The study suggests the use of root barriers and collaboration with agriculturists to mitigate tree-induced suction and prevent settlement issues. The article concludes by calling for a reevaluation of the Canadian Foundation Engineering Manual to address the influence of trees on foundation behavior. [Extracted from the article]

The damage caused by seismic shaking and liquefaction-induced permanent ground deformation has conventionally been assessed as two separate problems often by different engineers. However, the two problems are inherently linked, since ground shaking causes liquefaction, and liquefaction-induced soil softening affects ground shaking. Modelling both problems within a single numerical model is complex for both the engineer and the software, and most finite element software only have the capabilities to address one of them. To improve the estimates of the seismic performance of buildings on liquefiable soil, a new sub-structuring approach is proposed called the macro-mechanism approach. This approach allows the soil-liquefaction-foundation-structure interaction to be considered in a series of sub-models accounting for the major nonlinear mechanisms of the system at a macro level. The proposed approach was implemented in the open-source finite element software OpenSees and then applied to a case study of a building where significant liquefaction- and shaking-induced damage was observed after the 1999 Mw 7.4 Kocaeli Earthquake. The case study building was also simulated using two different commercial software programs, the finite difference software FLAC, and the finite element software PLAXIS, by two different research teams. A comparison between the results from the macro-mechanism approach compared to full numerical models shows that the macro-mechanism approach can capture the extent of the foundation deformation and provide more realistic estimates of the building damage than full approaches since the FLAC and PLAXIS models consider elastic elements for the building. [ABSTRACT FROM AUTHOR]

Excavation-induced ground movements can have a detrimental influence on adjacent structures and services. These complex soil–structure interactions are affected by a range of factors such as ground conditions, excavation sequence, and the characteristics of the structures. Considerable prior research has been concerned with understanding the ground response during excavation and in evaluating the potential damage to adjacent facilities. A number of case histories have been reported worldwide. Finite-element analysis can be effective in providing insight into the response of the ground and adjacent structures during the entire construction process. Previous studies have shown that observed excavation behavior (e.g., ground movements and retaining wall deformations) can be captured reasonably well in finite-element analysis, provided that certain key modeling aspects are appropriately addressed. This paper extends a previous deep excavation case study in greenfield conditions (i.e., without adjacent buildings and utilities included in the analysis), focusing particularly on the excavation-induced settlements of nearby buildings and buried pipelines. Sensitivity analyses have been conducted to investigate the effects of several aspects on the computed settlements of buildings and pipelines, such as (1) building weight, (2) building stiffness, (3) building foundation type, (4) ground improvement measures, and (5) geometries and material properties of pipelines. Conclusions are drawn for future applications. [ABSTRACT FROM AUTHOR]

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]

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

An innovative yet extremely simple approach to reduce the seismic vulnerability of existing buildings on shallow foundations is to remove the lateral contact between the embedded foundation and the surrounding soil. This paper compares the dynamic response of two identical one-degree-of-freedom reduced-scale model sway frames tested in a geotechnical centrifuge. One of the models was founded on fully embedded shallow strip footings, whereas the foundations of the other were disconnected from the soil laterally. Both models were constructed in dry medium density sand whose strength and small strain shear stiffness profiles were obtained by cone penetration and air hammer tests carried out in flight. Various tools were used to monitor the displacements and accelerations both in the structure and in the soil, including micro-electro-mechanical systems (MEMS) accelerometers, piezoelectric accelerometers, LVDTs, and a high-frequency camera. The experimental results demonstrate that the lateral disconnection of the foundation from the adjacent soil significantly reduces the foundation translational and rotational stiffness, which results in a larger predominant period of the structure and a reduction of the absolute floor accelerations obtained for different sinusoidal input signals. The lateral disconnection also mitigates floor drift and story shear forces. The trade-off is the lower radiative damping observed for the laterally disconnected foundation, which results in a larger number of post-earthquake oscillations of the structure. [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]

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

Soft soil foundations are often encountered in engineering construction. To make the foundation meet the engineering strength and deformation requirements, the soft soil foundation must be treated. Based on bucket foundation and silt solidification technology, the new grid composite foundation is proposed. The strength improvement mechanism of the new type foundation was analyzed according to the Mohr-Coulomb strength theory, and numerical simulations are used to carry out research on the bearing characteristics of the grid composite foundation. By carrying out load simulations for the grid foundation with different foundation widths, the failure modes corresponding to different B/L were analyzed. With overall consideration of the side length of a solidifying grid, the foundation width, and the undrained shear strength of the soil mass, the calculation method for the bearing capacity of the grid composite foundation has been proposed. Moreover, a wall strength check is carried out according to the maximum pull stress of the solidified wall. In the field test, the results of the finite element simulation and the field test are in good agreement, further verifying the feasibility of the grid structure foundation. Thus, a theoretical reference for engineering design is provided. [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]