Force Of Pile Research Articles

Mechanical Responses of Slurry Shield Underpassing Existing Bridge Piles in Upper-Soft and Lower-Hard Composite Strata

With the development of urban metro systems, shield tunnels that pass through existing bridge pile foundations have become an inevitable engineering problem. Therefore, ensuring the stability of the strata and existing bridge piles during tunnel construction is a common goal in engineering practice. Currently, research on the mechanical responses of strata and existing piles under different conditions of upper-soft and lower-hard composite strata during shield tunneling has not been conducted extensively. This paper presents a numerical simulation of a shield tunnel passing through an existing bridge pile foundation in upper-soft and lower-hard composite strata. Subsequently, the surface subsidence and mechanical responses of a single pile were analyzed and evaluated. Additional stresses generated in the soil by existing bridge piles and the selection of grouting pressure were considered to optimize the driving pressure of the slurry shield. Allowable values were proposed to evaluate the construction disturbances caused by the tunnel excavation. The results show that the disturbance to the soil and existing piles is significantly influenced by the hard-rock height ratio, and the surface subsidence increases when the hard-rock height ratio decreases. The displacement and internal force of a single pile are significantly influenced by the load applied to the pile. This study demonstrates the changes in the mechanical responses of a single pile during shield tunnel boring, and provides in-depth insights into the deformation control caused by shield underpassing structures in upper-soft and lower-hard composite strata.

3D Finite Element Analysis of Seismic Response of Rigid Pile Composite Foundation with Microprobe Group.

In order to study the seismic performance of the rigid pile composite foundation, a three-dimensional finite element analysis of the seismic response of the rigid pile composite foundation with microprobe group was proposed. The three-dimensional finite element method is used to analyze the dynamic response law of pile group rigid pile composite foundation under the action of the earthquake, especially the internal force response of the pile body. It is worth noting that when the internal force response of pile decreases significantly, the maximum internal force of the whole pile is also significantly smaller than the maximum internal force of pile foundation. However, when the pile body is located on a layered foundation and the modulus of adjacent soil layers differs greatly, the earthquake action will cause the pile body to generate a large internal force. The seismic performance of the rigid pile composite foundation is feasible, and it can be extended and applied to the similar seismic performance test of other composite foundations.

Overturning progressive collapse mechanism and control methods of excavations retained by cantilever piles

Deep excavation accidents occur frequently, including overturning progressive collapse (OPC) caused by local over-excavation or other reasons. However, limited research has been presented on the mechanism, evaluation index and control methods of such progressive failure. Therefore, based on an overturning collapse accident of an excavation retained by double-row piles, this paper uses the finite difference method (FDM) to study the OPC mechanism. The influence of local over-excavation on the internal force, displacement and stability of double-row piles was analyzed. To evaluate the risk of OPC, the anti-overturning stability value (ASV) and modified overturning stability index (MOSI) were proposed as evaluation indexes of overturning displacement and overturning stability. The results show that overturning collapse in the local over-excavation area (LOA) developed to adjacent retaining structures through the loading effect of the soil arch in the active zone, the unloading effect of the soil in the passive zone and the load transfer effect of the capping beam. The ASV can be used to predict the scale of retaining piles that will experience additional displacement caused by local over-excavation. Compared with the traditional overturning stability index (OSI) and the ASV, the MOSI can better reflect the occurrence of OPC and its scale. A capping beam cannot reduce the risk of progressive failure but will increase the risk and degree of OPC, which is different from the progressive bending collapse of cantilever excavations. Therefore, when calculating the overturning stability of retaining structures without considering the load transfer effect of the capping beam, the scale of the OPC outside the LOA will be severely underestimated. Extending the retaining piles and reinforcing the soil in the passive zone in the LOA can control the development of OPC, but the two measures have their own limitations and should be selected according to specific project conditions.

Determination of the impact of pile modeling methods on the distribution of forces in the pile foundation

The effect of the pile and the soil environment modeling method on the distribution of forces in the pile foundation and its deformation was studied and analyzed.
 Based on the obtained results, the difference in the distribution of forces in piles and the difference in the settlement of the pile foundation was demonstrated. A comparison is drawn between the models, in which elements of the scheme such as "base" and "foundation" were made using different methods. The zones where the peak forces are the largest and the smallest were marked.
 The structural scheme and geological conditions are based on the existing project, as well as engineering and geological investigations.
 The finite element model of the building consists of a base, underground, and above-ground structures. A linear-elastic model with the following soil parameters was used to simulate the work of the base: E – modulus of elasticity; V – Poisson's ratio; as well as the elastoplastic Mohr-Coulomb model, in which the soil is defined by the following parameters: E – modulus of elasticity; V– Poisson's ratio; c – cohesion; φ is the friction angle. The calculation was performed with the help of the LIRA-SAPR 2017 software complex.
 In order to improve the accuracy of the calculation of the results, the identification of the parameters of the base was carried out, where the results of in-situ test piles for static indentation were used as the initial data. The soil parameters, which were obtained in the result of identification, were applied to the model of the soil environment in the calculation scheme. As a result, it is possible to assess the influence of the identification parameters on the change in the stress-strained state (SSS) of the foundation structures as well as compare the forces values in piles and the deformation of the foundation before and after the identification.
 With the development of technologies and software complexes, the number and variability of calculation methods were increasing, as well as the variety of calculation models. Each calculation model is unique and created with a certain goal – to make the calculation results closer to the real work of foundation structures. It is necessary to make the most effective and rational modeling method to achieve the goals set, as well as to obtain a quick and accurate result.

Dynamic Response Analysis of Pile Group Foundation of Super-Giant Sewage Treatment Structure on Hydraulic Fill Foundation

In this study, a 3D numerical model, considering the dynamic interaction between soil, pile foundation, and super structure, and the parameter analysis of internal force response of pile group foundation under differences seismic intensity, was established based on the Bangladesh sewage treatment plant project to investigate the dynamic response of pile group foundation of liquid-containing structures. The results show that the internal force of pile gradually increases with time, and the horizontal dynamic displacement peak value appears earlier under different seismic wave responses and seismic intensity. With the increase of seismic time history, the variation degree of dynamic impedance with frequency and impedance peak will increase. The pile group effect and single pile bearing capacity of foundation in hydraulic fill fine sand and silty clay were verified. By comparing numerical simulation and theoretical calculation, the results show that the pile group foundation exerts the soil squeezing effect after pile construction is completed, and the dynamic elastic modulus of the soil layer can be increased. Simultaneously, the soil layer will have a better integral stiffness. The pile group effect coefficient obtained by the solid perimeter method is most consistent with the numerical simulation method.

Research on hydrodynamics of foundation structure of offshore wind turbine under typhoon-wave-current coupling

Offshore wind turbine is facing with extremely complicated climatic environment. The accurate prediction of wave movement caused by strong typhoons and its action on foundation of wind turbine are crucial. To disclose hydrodynamic characteristics of foundation structure of wind turbine under typhoon-wave-current coupling effect on the sea, a 10 MW super-large offshore wind turbine in Wailuo Wind Farm, Guangdong was chosen as a research object and a real-time meso-scale WRF-SWAN-FVCOM (W-S-F) coupling simulation platform was constructed by using Model Coupling Toolkit The spatial-temporal evolution of typhoon-wave-current in the offshore wind farm was simulated when a super typhoon “Rammasun” passed through. Next, the hydrodynamic load distribution characteristics of single pile foundation of wind turbine were analyzed by combining the meso-micro scale nested method. Extreme load model of foundation piles under different wave phases was proposed. Results demonstrated that the constructed W-S-F platform increased the simulation precision of typhoon path by 42.51% than single WRF model. The horizontal wave force of the foundation pile reached the negative and positive peaks at phases T0 and T4 under typhoon-wave-current coupling, and it presented symmetric distribution circumferentially around the 180° angle of wave attack. The phase T4 was the most adverse phase for the strength design of single pile foundation of offshore wind turbine. At the bottom of foundation, the maximum shear reached the 7.68 × 106 magnitude and the maximum bending moment reached the 5.2 × 108 magnitude.

Digital Evaluation of Vertical Compressive Bearing Capacity for Jet Grouting Pile-Mini Steel Pipe Pile Composite Foundation

The jet grouting pile-mini steel pipe pile in soft soil area is composed of the jet grouting pile and the mini steel pipe pile. Through the analysis of the stress mode of the composite foundation under the overall compression of the pile top, the hypothetical diagram and calculation equation of the interfacial friction resistance distribution of the composite foundation are put forward. Thus, the calculation equation of the axial force of the mini steel pipe pile and the jet grouting pile is deduced, and the axial force distribution diagram of the mini steel pipe pile and the jet grouting pile in the composite foundation is defined. The vertical compression composite foundation in the field was selected for bearing capacity test and calculation and comparative analysis, and the relative error was 3%. Therefore, the stress mode and calculation method of the jet grouting pile-mini steel pipe pile proposed in this paper can meet the needs of engineering design and popularization and application of the composite foundation.

Design of Axially Loaded Piles in Consolidating Soils

The present design method in various codes for axially loaded piles embedded in consolidating soil is not satisfactory. It is too conservative in calculating the maximum pile force. Furthermore, the additional pile settlement due to the consolidation is neglected in ascertaining whether the requirements of allowable settlement have been met. This is because the behavior of such piles is not well understood. A new step-by-step design method based on the combination of results of extensive parametric studies of an elastoplastic load transfer model incorporating pile–soil slip reported previously is presented. In contrast to the iterative procedure required by some existing methods to determine the neutral plane location, these design charts can be used to determine the pile top settlement, neutral plane location, and maximum pile load directly. Further saving in the design of pile foundation is obtained with the concept of a compensating-pile foundation.

A Machine Learning Study on Internal Force Characteristics of the Anti-Slide Pile Based on the DOFS-BOTDA Monitoring Technology.

Long-term monitoring of constructed anti-slide piles can help in understanding the processes by which anti-slide piles are subjected to the thrust of landslides. This paper examined the landslide control project of Badong No. 3 High School. The internal force of an anti-slide pile subjected to long-term action of landslide thrust was studied by Distributed Optical Fiber Sensing (DOFS) technology. The BP neural network was used for model training on the monitored strain values and the calculated bending moment values. The results show the following: (1) The monitoring results of the sensor fibers reflect the actual situation more accurately than steel rebar meters do and can locate the position of the sliding zone more accurately. (2) The bending moments distributed along the anti-slide pile have staged characteristics under the long-term action of landslide thrust. Three stages can be summarized according to the development trend of the bending moment values. These three stages can be divided into two change periods of landslide thrust. (3) The model produced by the BP neural network training can predict the bending moment values. In this paper, the sensing fibers monitoring over a long time interval provides a basis for long-term performance analysis of anti-slide piles and stability evaluation of landslides. Using the BP neural network for training relevant data can provide directions for future engineering monitoring. More novel methods can be devised and utilized that will be both accurate and convenient.

Experimental and numerical analysis of the under-reamed piled ring foundation

The experimental and numerical analysis of the under-reamed piled ring foundation (with/without RDFS cushion) supported by soft clay was carried out. Total 34 model tests were performed to understand the effect of the under-reams and randomly distributed fibre reinforced sand (RDFS) cushion on the parameters like pile length, centre to centre spacing between under-reams, differential settlement, axial force in the under-ream pile and load sharing mechanism. Results have indicated that in comparison to the straight piles, under-reams at the bottom of piles significantly increases the load carrying capacity and reduce the differential settlement of the piled ring foundation. Load improvement factor for under-reamed piled ring foundation with RDFS cushion was noticeably higher, and settlement reduction ratio was lower than that without RDFS cushion. RDFS cushion increases the percentage of the load taken by the ring raft in the under-reamed piled ring foundation. The inner edge of the ring raft settled more than that outer edge and the centre. And the differential settlement of the under-reamed piled foundation with/without RDFS increased with the increase in the pile length and reduction in spacing between under-reams.

Monitoring of an instrumented geosynthetic-reinforced piled embankment with a triangular pile configuration

ABSTRACT A comprehensive monitoring programme was undertaken at a geosynthetic-reinforced piled embankment over soft ground to better understand its time-dependent performance. The programme involved continuous monitoring of earth pressure, axial force in piles, settlement of structural elements, lateral movement of subsoil, and geogrid tensile strain of the instrumented system. Earth pressure measurements evidenced the mobilization of soil arching; pile efficacies were derived from established analytical methods and assessed against observed data for piles with circular cap configuration arranged in a triangular pattern, with the Concentric Arches model giving the best predictions. The development of axial load in piles can be properly captured by a regression equation with analytical approach. Penetration and compression behaviours of structural elements were evaluated by settlement measurement on piles and soils at ground level relative to pile toe or substratum. The proposed approach in obtaining tensile force of geogrid was verified with the measured differential-settlement data.

Dynamic Lateral Response of the Partially-Embedded Single Piles in Layered Soil

Scouring can reduce the strength and rigidity of the pile–soil system and become one of the major causes for the failure of the structure of the partially-embedded single pile. The stratification of the soil fields has a significant influence on the internal force and deformation of laterally-loaded piles. A dynamic model of the laterally-loaded single pile in layered soil is established employing Hamilton’s principle based on the modified Vlasov foundation model. Then, the finite difference method is used to obtain the numerical matrix containing the control equations of the single pile to achieve accurate modeling of the soil–structure interaction (SSI) system affected by scouring, so as to solve the natural frequencies of the single pile. Green’s function method obtains the analytical solution of the forced vibration of the single pile. The effects of scouring and the layered soil on the dynamic response of the single pile are studied by numerical calculation and parameter analysis. It is shown that the dynamic model of the partially-embedded single pile in layered soil based on the modified Vlasov foundation model can accurately predict the dynamic characteristics of pile foundation affected by scouring. As the scouring degree intensifies, the first-order natural frequencies of the single pile in layered soil decrease significantly. The subgrade reaction coefficient of each layer of soil in the modified Vlasov foundation model decreases, and the shear coefficient increases. The first-order natural frequencies of the single pile at each scour level increase with the increase in the thickness of the underlying soil. When the elastic modulus of the first layer of soil is increased by one time, the first-order natural frequencies of the single pile are increased by about 20%.

Kinematic response of single vertical and batter piles to bidirectional ground motions in liquefiable soil

Kinematic responses of single fixed head vertical and batter piles in liquefiable soil under bidirectional ground motions have been studied with fully-coupled three-dimensional nonlinear dynamic analyses. Pressure dependent multi-yield constitutive model has been adopted for modeling the liquefiable sand behavior. The variable permeability of saturated sand during the process of liquefaction process has also been considered. The analyses are carried out for combinations of bidirectional earthquake loading conditions. For this, combination of longitudinal and transverse ground motions as well as combination of longitudinal and vertical motions are considered. The responses of the soil-pile systems under liquefying ground conditions, subjected to these bidirectional ground motions, are compared with the unidirectional loading conditions. Further, the effect of sloping ground on the response of the piles under bidirectional ground motions is also investigated. The developed sectional forces in both vertical and batter piles are lesser under bidirectional motions in comparison to unidirectional ground motion in both level and sloping grounds. However, the pile displacement is more in case of sloping ground under bidirectional ground motions comparing to unidirectional motion.

Numerical Simulation Analysis of Deep Foundation Pit Engineering Based on HS-Small Constitutive Modell

Numerical simulation has become one of the most important means of foundation pit engineering analysis, but there is a lack of numerical simulation of deep foundation pit engineering examples under the condition of adjacent buildings in Xi ’ an. In this paper, MIDAS GTS NX software is used to simulate the deep foundation pit engineering of Xi ’ an International Conference Center Phase II by using the Hardening Soil-Small constitutive model which is more suitable for foundation pit engineering. Combined with the measured data, the study on the characteristics of building settlement, the characteristics of surrounding surface settlement, the deformation characteristics of foundation pit retaining structure, the soil pressure at pile side and the variation characteristics of pile internal force is conducted under the condition of stepwise excavation-reduction of groundwater level of foundation pit. The results show that the top displacement of the retaining structure and surface settlement near the building are larger than those without load. The building settlement and surface settlement rate present the characteristics of medium-term slowdown. The lateral earth pressure and internal force of pile show different trends in free section and anchorage section, affected by building load. The simulation results of the constitutive parameters of HHS numerical simulation determined by parameter inversion are in good agreement with the measured data, which verifies the reliability of HHS constitutive model in the numerical simulation of foundation pit engineering in Xi ’ an area, and provides reference for the numerical simulation of similar engineering cases in relevant areas.

Experimental Investigation of the Impact of Necking Position on Pile Capacity Assisted with Transparent Soil Technology

Necking in different positions of a pile body has a significant influence on the bearing performance of a single pile. The transparent soil model experiment was adopted to investigate the impacts of necking positions on the vertical bearing capacity of a single pile and the soil deformation around the pile, and subsequently, the causes of the variation of bearing capacity were analyzed. The results show that the existence of necking does not change the bearing behavior of single pile as pile friction resistance. The bearing capacity of piles decreased by 8.21% and increased by 7.30% when the necking is located in the shallow and middle pile body, respectively, while it did not change significantly when the defects were in the deep part of the pile. The necking position has a significant effect on the deformation and deformation range of soil. The soils at the top, side, and near the end of a pile were mainly influenced by shallow necking, middle necking, and deep necking, respectively. The soils at the location of necking had apparent settlement phenomenon as the piles subsided. The soils at shallow necking’s locations were relatively loose, which reduced the side friction force of piles and finally resulted in a reduction of bearing capacity of a single pile. With the increase of the load, the soil around piles gradually developed penetration phenomenon (large deformation), while the soil at the end of pile moved up against pile settlement, which made the necking soil in the middle denser. The loss of side friction resistance was less than the resistance from the necking, which gave birth to an increase in the bearing capacity of a single pile. It was finally found that the side friction resistance and the resistance caused by necking were the main factors governing the bearing capacity of necking single piles.

Interaction between a subsoil and group of piles joined with a raft

Most pile-slab foundations are designed without taking into account the contribution of growth. Although it is well known that the grille plays an important role in overall load-bearing capacity. In such structures, the overall subsidence of the foundation is likely to be small due to the installation of more piles than necessary. However, from an economic point of view, it is desirable that the foundation be designed in such a way that the subsidence is limited to an acceptable level, but taking into account the bearing capacity of growth.
 The main problem is a work of pile’s group taking into account interaction between piles through a soil base is considered. During the interaction there are additional stresses in the inter-pile space, there is an effect of "compression" of the piles by the soil from the loads transmitted to neighboring piles.
 This paper presents the results of a study of the joint work of piles and grilles under the action of static load using numerical simulations. The study used a group of piles (5 pcs.) With a diameter of 420 mm and a length of 10 m, combined with a grid. Fine sand of medium density was used as the basis of the pile foundation.
 Numerical modeling was performed using an ideal elastic-plastic model with the Coulomb-Mohr strength criterion.
 The work of piles at different distances between piles (1.5-2.5 m) and grating thickness 300 was compared; 500mm.
 The interaction of piles and growth-verification with the surrounding soil mass is analyzed. At the lower end of the pile, in the area of contact of the pile with the ground there is a complex stress-strain state. The pitch, diameter, length of the piles, as well as the rigidity of the grille have a significant effect on this stress-strain state. Taking into account the influence of these factors is necessary to determine the patterns of distribution of external loads between the piles and the grille.
 Irregular settling of the group was revealed
 piles joined by a grid. The central and extreme piles are included in the work in different ways.
 It is established that the inclusion of the pile grid in the work depends on its stiffness, as well as the axial distance between the piles.
 It is investigated that when the distance between the piles changes, the redistribution of forces in the growth piles and piles changes.

A field test scrutiny on bearing mechanism of super-long bored piles in deep fine silty sand layers

A field test study on bearing mechanism of super-long bored piles in deep fine silty sand layers is performed based on static load testing system of tension-compression anchorage method in actual project. To this end, the load transfer mechanism is scrutinized by analyzing the development and distribution of axial force and shaft resistance of super-long bored piles in deep fine silty sand layers. The results reveal that the load-settlement curve of piles with 20 mm sediment at the bottom demonstrates a steep downward trend, and that of piles with 5 mm sediment at the bottom shows a retard downward trend. Under the action of ultimate load, more than 28% of the settlement on the pile top results from the elastic compression of the pile body. The axial force of piles lessens progressively along the depth direction; however, the decreasing rate varies in different soil layers. Additionally, the shaft resistance in the middle and upper parts of the pile body takes effect before the shaft resistance in lower part of the pile body, which would slightly soften. This study may provide a solid basis for the design, construction, and bearing capacity determination of super-long bored piles in deep silty sand layers.

Assessing the effect of governing parameters of bearing capacity determination of small piled rafts on clay soil

In the present study, a small piled raft foundation has been simulated numerically through PLAXIS 3-D software. The objective of this study was to investigate the effect of governing parameters such as pile length, pile spacing, pile diameter, and number of piles on the settlement and load-bearing behavior of piled raft, so as to achieve the optimum design for small piled raft configurations. An optimized design of a piled raft is defined as a design with allowable center and differential settlements and satisfactory bearing behavior for a given raft geometry and loading. The results indicated that, with increase in pile length, pile spacing, pile diameter, and number of piles, both the center settlement ratio and differential settlement ratio decreased. The load-bearing capacity of piled raft increased with increase in pile length, pile spacing, pile diameter, and number of piles. Furthermore, the percentage load carried by the piles increased as the pile length, pile spacing, pile diameter, and number of piles increased. The bending moment and shear force in corner pile are noted to be more, and they decreased towards the center pile. With increase in pile length, the maximum raft bending moment decreased, whereas the maximum shear force in the raft increased. Further, with increase in pile spacing, pile diameter, and number of piles, the maximum bending moment and maximum shear force in the raft increased. The optimum parameters for the piled raft foundation can be selected efficiently with the consideration of maximum bending moment and maximum shear force while designing the piled raft foundation. Thus, the results of this study can be used as guidelines for achieving optimum design for small piled raft foundation.

Design optimization analysis of pile foundation parameters for widening bridge in cold region

Relying on Yunliang River Bridge of Beijing-Harbin expressway reconstruction and expansion project, the pile-soil interaction model is established by using ABAQUS. Based on the sensitivity analysis of the vertical deformation, cross-bridge deformation and additional bending moment of the old pile under different design parameters such as pile diameter and pile length, the influence of different design parameters of the new pile foundation on the additional internal force and deformation of the old pile is studied, which provides a theoretical basis for the construction of bridge pile foundation in cold areas.

Thermo-Hydro-Mechanical Numerical Analysis of Energy Pile in Saturated Clay

In order to study the mechanical properties of energy piles under long-term heat injection-heat extraction cycle loading conditions, the influence of temperature on the mechanical properties of foundation soils needs to be considered. The subroutine of an elastic-plastic constitutive model of soil considering the influence of temperature is developed in Abaqus. Finally, the changes of additional pile top displacement, lateral friction resistance and axial force of energy pile under long-term heat injection-pumping cyclic loading under different loads and different soil parameters under the same load are discussed. The results show that: (1) The soil around the pile is subjected to plastic deformation due to the expansion and contraction of the pile. The higher the load on the pile top is, the greater the additional temperature settlement generated at the pile top is. (2) Under 0.5PU load, the increase of OCR, swelling index or permeability coefficient of foundation soil will cause the decrease of additional settlement of pile top. And the additional side friction and axial force, plastic parameters or soil permeability coefficient increases will produce greater additional side friction and axial force. This study has certain significance for the long-term use of energy piles.