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In this study, the pressure-cast-in-situ pile with spray-expanded frustum (PPSF) was proposed to increase pile bearing capacity, reduce pile settlement, and improve construction speed. The construction process of the PPSF composed of pile body, ribbed plate, and expanded body with double frustum was introduced. To capture the PPSF response, field static load tests on three PPSFs installed with string wire stress gauges were carried out. The ultimate bearing capacity (UBC) of a single PPSF was obtained, and the distribution of axial force, skin friction, and end force were analyzed using the measured results. Following the assumption that the strength of pile–soil interface elements was statistically described by the probability density function of the Rayleigh distribution, the load transfer models of PPSF were established based on the disturbed state concept (DSC) theory. The research results showed that there is a compression effect between the expanded body of the PPSF and the surrounding soil, which can effectively improve the bearing capacity of the PPSF. Considering the concrete consumption per unit volume, the UBC of PPSF is 66% more than that of the cast-in-situ bored pile. According to the results of measured and fitted relationships, the load transfer models of PPSF can be well described using the DSC theory and the Rayleigh distribution. [ABSTRACT FROM AUTHOR]

A large amount of excavation waste soil will be produced during highway construction, which will lead to environmental pollution and construction site occupation. To make full use of the excavation waste soil, hydraulic pile-forming equipment with a maximum pressure of 200 t is developed based on the principle of building clean transportation infrastructure. In addition, a precast pile with modified waste soil (PPMS) is proposed to achieve the large-scale consumption of the excavation waste soil. The PPMS has the advantages of regular shape, reliable quality, and stable bearing capacity. The relevant production standards and construction processes are proposed in this paper. The static pressure test analysis of the PPMS and lime–soil compaction pile was performed to verify the feasibility of the PPMS in reinforcing soft foundations. The test results show that the bearing capacity of a single PPMS could reach 600 kN. Under the upper load of 400 kPa, the settlement of the PPMS-reinforced soft foundation is 30% smaller than that of the lime–soil compaction pile. The PPMS has the advantages of high bearing capacity and economic and environmental protection, which is suitable for reinforcing soft foundations. [ABSTRACT FROM AUTHOR]

To capture the influence of temperature variation of pile–soil interface on the response of a single energy pile, numerical simulation and theoretical analysis were adopted in this paper. The temperature variation mechanism of a single energy pile was clarified using numerical simulation, and the temperature variation model of the pile–soil interface was established. Considering the influence of temperature variation on the conventional load transfer model of the pile–soil interface, the improved hyperbolic functions were proposed, and the parameters related to the improved load transfer model were determined. To predict the response of a single energy pile considering the temperature variation of the pile–soil interface, an iterative algorithm was developed using load transfer methods. Comparisons of the load-settlement response of three well-documented cases between the present computation results and the results derived from other methods were made to verify the reliability of the calculation method. Furthermore, a parameter analysis was carried out to assess the influence of soil properties and the parameters related to the load transfer models on the thermomechanical response of a single energy pile. [ABSTRACT FROM AUTHOR]

A simple analytical approach for nonlinear analysis of the load-displacement response of a single pile is presented. Two models are adopted in the proposed approach. One model uses a softening nonlinear relationship to simulate the degradation behavior between the unit skin friction and the pile-soil relative displacement developed in the pile-soil interface, and the other model adopts a bilinear load-displacement relationship to capture the pile-end response. Based on the two proposed models, a highly effective computer program has been developed for nonlinear analysis of the load- settlement behavior of a single pile. Comparisons are made between the present method, other analytical methods, and a well-documented field experimental pile loading case. The results of the comparisons indicate that the proposed method is generally in good agreement with field-observed behavior and the calculated results derived from other approaches. A parametric study is conducted to assess the influence of the parameters related to the proposed model on the load- displacement response of a single pile. Key words: pile, softening model, bilinear model, ultimate unit skin friction, end resistance, settlement. Cet article presente une approche analytique simple pour l'analyse non lineaire du comportement en charge-deplacement d'un pieu unique. Deux modeles sont adoptes dans l'approche proposee. Un modele utilise une relation d'adoucissement non lineaire pour simuler le comportement en degradation entre la friction superficielle unitaire et le deplacement relatif pieu-sol developpe a l'interface pieu-sol; tandis que l'autre modele adopte une relation bilineaire de charge- deplacement pour illustrer le comportement de l'extremite du pieu. A partir de ces deux modeles proposes, un programme informatique tres efficace a ete developpe pour l'analyse non lineaire du comportement en charge-tassement d'un pieu unique. Des comparaisons sont faites entre la methode presentee, d' autres methodes analytiques et un cas bien documente d'un pieu experimental sur le terrain. Les resultats des comparaisons indiquent que la methode proposee concorde generalement bien avec le comportement observe sur le terrain et avec les resultats calcules avec les autres approches. Une etude parametrique est realisee pour evaluer l'influence de parametres relies au modele propose sur le comportement en charge-deplacement d'un pieu unique. Mots-cles: pieu, modele d'adoucissement, modele bilineaire, friction superficielle unitaire ultime, resistance a l'extremite, tassement. [Traduit par la Redaction], Introduction Much effort has been made to develop theoretical methods to analyze the behavior of single piles and pile groups. Many of these various numerical methods fall into five main [...]

Based on disturbed state concept (DSC) theory, this paper reports an analysis of the progressive failure mechanism of a pile–soil system from a new perspective. Assuming that the strengths of the pile–soil interface elements and the soil elements at the pile end follow an exponential distribution, the load transfer models of skin friction and end resistance based on DSC theory are established, and the significance and value method of the parameters in the models are clarified. The analysis of the relevant parameters shows that the proposed DSC load transfer models can simulate the nonlinear hardening or softening behavior of skin friction and end resistance. Based on the proposed DSC load transfer models, a simple and efficient iterative calculation method for the analysis of the bearing behavior of a single pile is established. It is demonstrated from case studies that, compared with calculated results using other methods, the load–settlement curves at the pile head obtained from the method proposed in this paper are in better agreement with the measured values, and could reflect the skin friction and end resistance softening characteristics of the tested piles in a more realistic manner. Furthermore, a parametric study is carried out to analyze the influence of the relevant model parameters on the response of a single pile. [ABSTRACT FROM AUTHOR]

To get an accurate bearing capacity of a postgrouting pile, the range of grout diffusion should be considered in practice. Considering the time-dependent behavior of power-law cement grout viscosity, calculation methods are proposed to determine the diffusion radius and the climbing height of the grout. Moreover, an iterative calculation method is established to compute the climbing height of the grout along a single pile embedded in layered soils. Four cases reported in the literature are used to demonstrate the effectiveness and accuracy of the proposed calculation methods. The calculation results show that the computed grout diffusion radius and climbing height of the grout are in good agreement with the measured value. For practical purposes, to get an accurate prediction on the bearing capacity of postgrouting pile, the time-dependent behavior of grout viscosity should be considered. [ABSTRACT FROM AUTHOR]

The uniform arrangement of pile groups widely used in practice often causes obvious differential settlement of pile foundations. To decrease differential settlement of pile groups, individual piles nonuniformly arranged can be adopted. This paper presents a model test study on the bearing capacity of pile foundations under different pile arrangements. A versatile full-automatic loading system and data acquisition and analysis systems of the model test were developed. Using the model test setup, the response of a single pile subjected to axial load was clarified, and the reinforcing effect between an axially loaded pile and a load-free pile was then analyzed. Furthermore, model tests were carried out to assess the behavior of the pile groups composed of individual piles with variable length and diameter. For practical purposes, some suggestions on the nonuniformly arranged individual piles within pile groups were given to decrease differential settlement among each individual pile and make maximum use of the bearing capacity of each individual pile. [ABSTRACT FROM AUTHOR]

To make full use of skin friction of soils around pile, this paper presents a novel pile composed of ribbed plates, an expanded body with double frustum, and a pile body, named as the pressure-cast-in-situ pile with spray-expanded frustum. A multifunction auger drill is used to form the expanded body by spraying cement slurry rotationally at a given depth, pouring superfluid concrete, and vibrating and squeezing pile body. The ribbed plates are completed by spraying cement slurry fixedly with a hollow drill pipe. Due to the improvement of skin friction of the expanded pile body, the novel pile will get a large bearing capacity. Moreover, due to the squeezing effect of superfluid concrete during the pile construction, the soils around pile can be compacted, which also leads to an obvious increase in bearing capacity of the novel pile. The application of the proposed technique of the novel pile is verified by using static loading tests on three novel piles and one traditional cast-in-situ pile. Comparisons of the four test piles demonstrate that the ultimate bearing capacity of the novel pile increases by more than 45% under the condition of the same concrete consumption per unit volume. For practical purposes, the pressure-cast-in-situ pile with spray-expanded frustum is worthy of promotion due to the advantages of high bearing capacity and significant economic benefits. [ABSTRACT FROM AUTHOR]

This paper proposes a semianalytical solution to analyze the long-term settlement of a single pile embedded in fractional derivative viscoelastic soils under time-dependent loading. In this paper, a three-dimensional (3D) fractional derivative viscoelastic model will be introduced to describe the rheological behavior of soils around the pile. Based on the shear deformation compatibility between the pile and soils, the semianalytical solution will be strictly derived using the correspondence principle and the Laplace transform technique. Three well-documented cases will be used to verify the correctness and reliability of the proposed semianalytical solution, all of which show a very close agreement. Furthermore, worked examples that include instantaneous and ramp loadings will be carried out to capture the influence of six dimensionless parameters, that is, a, b, c, d, κ, and α, on the long-term settlement of a single pile. The results indicate that: the dimensionless settlement for fractional derivative viscoelastic models is larger in the early stage and smaller in the later stage than those for conventional viscoelastic models; the dimensionless settlement capacity of the pile is controlled by the parameters a and d, and the dimensionless settlement rate is controlled by the parameters b and α, which means the selection of these four parameters has a great influence on the long-term settlement; and the parameter c causes little variation in the results. [ABSTRACT FROM AUTHOR]

Excavation beneath an existing building to add a new basement is an effective mean to expand underground space that caters to the increased need of space in urban areas. Because piles serve as load-bearing structures in high-rise buildings, excavation inevitably changes the bearing capacity of the existing piles and affects the safety of aboveground structures. This paper presents a series of experimental tests in a calibration chamber designed to clarify the effect of excavation on the performance of existing loaded piles. Excavation tests as well as pile load tests at the ground level and at the formation level of excavation were involved in capturing the effect of excavation on the capacity, stiffness, and load transfer of loaded piles. Test results showed that the reduction of pile capacity due to excavation is proportional to the magnitude of confinement of the area to be excavated. Constructing a new basement beneath an existing basement may result in a larger reduction of pile capacity when comparing that conducted at the ground surface. Unlike the nonloaded pile subjected to excavation, tensile force is not observed along the loaded pile shaft in the present test series. The results also indicated that the stress relief induced by excavation may be instrumental in the stiffness efficiency of the pile group. [ABSTRACT FROM AUTHOR]

A uniform arrangement of individual piles is commonly adopted in the conventional pile group foundation, and basin-shaped settlement is often observed in practice. Large differential settlement of pile groups will decrease the use-safety requirements of building, even cause the whole-building tilt or collapse. To reduce differential settlement among individual piles, non-uniformly arranged pile groups can be adopted. This paper presents a finite element analysis on the response of pile groups with different layouts of individual piles in pile groups. Using the user-defined subroutine FRIC as the secondary development platform, a softening model of skin friction and a hyperbolic model of end resistance are introduced into the contact pair calculation of ABAQUS software. As to the response analysis of a single pile, the reliability of the proposed secondary development method of ABAQUS software is verified using an iterative computer program. The reinforcing effects of individual piles is then analyzed using the present finite element analysis. Furthermore, the response of non-uniformly arranged pile groups, e.g., individual piles with variable length and individual piles with variable diameter, is analyzed using the proposed numerical analysis method. Some suggestions on the layout of individual piles are proposed to reduce differential settlement and make full use of the bearing capacity of individual piles in pile groups for practical purposes. [ABSTRACT FROM AUTHOR]

This paper gives a set of time-dependent displacement solutions for the case of a vertical concentrated force acting in the interior of fractional derivative viscoelastic soils. First, a three-dimensional fractional derivative viscoelastic model is introduced to describe the creep behavior of soils. Then based on the well-known Mindlin's elastic solutions and the correspondence principle from static elasticity to quasi-static viscoelasticity, the proposed precise solutions are systematically obtained in the Laplace transform domain. Subsequently, the proposed displacement solutions are validated against three previously published solutions, and all of the comparisons show a good agreement. Finally, parametric study and discussion are given, to analyze in detail the influence of parameters on the solutions. It is indicated that the displacements for fractional derivative viscoelastic models are smaller in the early stage and larger in the later stage than those for conventional viscoelastic models, and the proposed displacement solutions are more general. [ABSTRACT FROM AUTHOR]