Force Of Pile Research Articles

Computer simulation and model test study on influence of water immersion degree on wind power generation pile stress

The force of foundation piles in collapsible soil is a complex and important issue. Different degrees of collapsibility will have different effects on the force of foundation piles. In order to analyze and discuss the distribution and change law of the axial force and negative friction resistance of the foundation pile in moe detail, this paper summarized the existing research results on the influence of immersion collapsibility on the development of the axial force and negative friction of the foundation pile, and through model test research, the strain of the loaded foundation pile and the unloaded foundation pile under the same site conditions were measured as the site was wet.The test shows that the degree of collapsibility is positively correlated with the force of foundation piles in collapsible loess site. The presence or absence of a load on the top of the pile has a greater impact on the development process of the pile's force during the immersion of the site; but it has little effect on the distribution of the pile side friction when the site is fully immersed and saturated.

순환자원 활용 말뚝채움재의 실내모형시험을 통한 주면마찰력 비교 연구

Rural multi-purpose buildings needs to ensure their safety against various disasters. Therefore, a pile foundation, which is a foundation type that can transmit the load of the structure to the bedrock layer, has been designed. The pile foundation method is largely divided into driving piles method and pre-bored pile method. Recently, in order to respond to the Noise and Vibration Control Act and related environmental complaints, construction of pile foundation adopts pre-bored pile method. The bearing capacity of the pre-bored pile method is calculated through a load test in situ. However, a disadvantage stems in that it is difficult to measure the ultimate bearing capacity due to field conditions. Therefore, in this study, the skin frictional force of pre-bored pile was measured through a model test in laboratory for each pile filling material. In result, the pile filling material with using circulating resources shows superior skin frictional force than ordinary portland cement. This study also judged that the result can be applied in place of ordinary Portland cement in the field.

Study on the vertical bearing performance of pile across cave and sensitivity of three parameters

A new method was used to study the performance of pile across cave. This paper investigated the vertical bearing characteristics of piles cross caves using centrifugal model tests and a theoretical model of sensitivity. Twelve pile scenarios were selected, the first was a conventional pile, 24 cm long and 2.5 cm in diameter, with no karst cave as a control. In the other eleven scenarios the piles passed through karst caves of four different heights, of four different spans, and three different numbers of caves. The results reveal that increasing the height, span, and number of caves all are negative for vertical ultimate bearing capacity of piles. The axial force and unit shaft resistance of piles are great different. According to the ratios of the tip and shaft resistance, caves change the type of piles. The sensitivity of vertical ultimate bearing capacity to these factors from high to low is height, number, and span of caves. Importantly, the bearing characteristics of piles decrease faster once the height of the prototype karst cave is higher than 9 m, but decreases slowly when the cave’s span is greater than 9 m × 9 m.

A new modified approach to evaluating the installation power of large-diameter helical piles in sand validated by centrifuge and field data

Helical pile (screw pile) is becoming increasingly popular in emerging pile foundation techniques for offshore structures. Its installation parameters (i.e., installation force, torque, and power) are significantly important for design and construction of helical pile foundation. However, there are very limited studies on the installation power of large-diameter multi-helix piles in sand particularly with the consideration of the installation effects of rotary press-in. This paper proposes a new modified method suitable for predicting the installation torque and force of single-helix and multi-helix piles, which involves four aspects of important factors: the installation effect of helical piles, the bidirectional force (i.e., vertical and tangential shear stress) on the side of the central shaft during rotary press-in, the interaction between helices for muti-helix piles, and the vertical installation force (crowd force) effect on torque generation. The proposed and the two existing methods (i.e., Ghaly and Hanna model and Al-Baghdadi model) are used to predict the installation toque and power of helical piles in sand with different relative densities (loose, medium dense, and dense) based on pile geometry characteristics. Predictions from aforementioned three methods are compared with measurements from the centrifugal model tests of various screw piles in sand with the proposed method giving better agreement with the measured data. The calculation from the proposed method also gives closer agreement with field measurements of the double-helix pile than those from existing methods. In addition, it is found that the installation power of helical piles increases nonlinearly with the increase of the relative density of sand (or peak friction angle) and installation force and torque account for about 10% and 90%, respectively, of the total power through the parameter sensitivity analysis.

3D numerical analysis of pile response due to soil movements induced by an adjacent deep excavation

Purpose This paper aims to investigate single pile and pile group responses due to deep braced excavation-induced soil movement in soft clay overlying dense sand. The analysis focuses first on the response of vertical single pile in terms of induced bending moment, lateral deflection, induced axial force, skin resistance distribution and pile settlement. To better understand the single pile behaviour, a parametric study was carried out. To provide further insights about the response of pile group system, different pile group configurations were considered. Design/methodology/approach Using the explicit finite element code PLAXIS 3 D, a full three-dimensional numerical analysis is carried out to investigate pile responses when performing an adjacent deep braced excavation. The numerical model was validated based on the results of a centrifuge test. The relevance of the 3 D model is also judged by comparison with the 2 D plane strain model using the PLAXIS 2 D code. Findings The results obtained allowed a thorough understanding of the pile response and the soil–pile–structure interactions phenomenon. The findings reveal that the deep excavation may cause appreciable bending moments, lateral deflections and axial forces in nearby piles. The parametric study showed that the pile responses are strongly influenced by the excavation depth, relative pile location, sand density, excavation support system and pile length. It also showed that the response of a pile within a group depends on its location in relation to the other piles of the pile group, its distance from the retaining wall and the number of piles in the group. Originality/value Unlike previous studies which investigated the problem in homogeneous geological context (sand or clay), in this paper, the pile response was thoroughly studied in a multi-layered soil using 3 D numerical simulation. To take into account the small-strain nonlinear behaviour of the soil, the Hardening soil model with small-strain stiffness was used in this analysis. For a preliminary design, this numerical study can serve as a practical basis for similar projects.

The role of parameters of foundation structures in the formation of a stress-strain state of the foundations of the building

Requirements for the reliability and cost-effectiveness of rational foundation structures determine the performance of calculations taking into account the interaction of the loadbearing structures of the building with the soil base. Computer modeling makes it possible to perform such calculations and obtain the stress-strain state of the structures of the building and the soil base.
 Numerical modeling of the interaction of a building with a soil massif makes it possible to study the influence of all components of the system "soil base - foundation - building". At the same time, during numerical modeling it is possible to consider different options for the location of elements in the plan, different geometric dimensions of the elements and their properties. The results of the interaction calculations of the building with the soil base make it possible to choose the best option for foundation structures, which is cost-effective and ensures reliable operation of the building.
 In this study, the search for rational parameters of the foundation structures of the building was performed by numerical modeling of the joint work of the elements of the system "soil base - foundation - building". The study was performed on the example of a 16-storey frame building.
 A study of the influence of the parameters of the pile foundation on the stress-strain state of the foundation structures and bearing elements of the frame of the building:
 -The influence of the piles location in the plan is considered. The process of redistribution of forces in piles depending on the amount and location within the contour of the building is investigated. Deformation assessment is performed.
 -The optimal pile length has been searched. The relationship between the length of piles and deformations, their load-bearing capacity and quantity has been studied. The distribution of piles according to the coefficient of use of their bearing capacity has been obtained.
 -A study of the influence of the stiffness of the foundation pile cap on the redistribution of stresses and strains in the structures of the building. The relationship between the thickness of the pile cap and the percentage of reinforcement elements of the frame of the building has been obtained.
 It is confirmed by the results of the research that the use of numerical modeling of the interaction of the pile foundation with the soil base allows to obtain a quantitative assessment of the stress-strain state. It becomes possible to search for rational parameters at the design stage of foundation structures.

Seismic structure-soil-structure interaction between two different adjacent piled bridges founded in nonlinear soil

ABSTRACT This paper evaluates the influence of structure-soil-structure interaction (SSSI) on the seismic behaviour of two adjacent bridges with different superstructure masses. The bridges are supported by groups of piles implanted in nonlinear clay. A thorough detailed parametric numerical analysis has been carried focusing on the effect of the superstructure mass ratios (200%, and 300%), inter-bridge spacing, and the position the two bridges towards each other and towards the seismic loading direction. An extensive series of numerical analyses have been carried out using a full three-dimensional finite-difference FLAC software. The responses of adjacent bridges have changed remarkably due to (SSSI) effect. The results showed a significant positive effect of the superstructure mass ratio of (300%) by a considerable drop of acceleration up to (96.39%) and a notable reduction of the internal forces of the grand bridge piles up to (75.9%). This implies the properly planned configurations of adjacent structures and attentive selection of their properties could be employed efficiently to control the effects of structure–soil–structure interaction, whereas inter-bridge spacing has a rather slight effect on the superstructure acceleration and the pile’s internal forces. In contrast, the positioning of the bridges has revealed a sensible influence on their seismic behaviour.

Design and Performance of Concrete Pile Strengthened with Lengthened Steel-Tube Core: Model Tests and Numerical Simulations

In order to solve the problem of insufficient bearing capacity of existing concrete piles, a type of concrete pile with an additional lengthened strengthening core is designed, by inserting the steel tube through guiding hole and pouring core concrete. To reveal the mechanical performance of the reinforced piles, scale model tests and finite element simulations were performed. The results showed that both the vertical and horizontal bearing capacity increase with the length of the stiffening core. The axial force of the enhanced core is also smaller than conventional concrete piles, and the extended core can share the axial force of the foundation pile to improve the stress distribution of the pile body. These findings point toward a useful and general method for increasing the load capacity of existing concrete piles.

Model Test of Jacked Pile Penetration Process Considering Influence of Pile Diameter

In order to investigate the influence of different diameters on pile end resistance, pile side resistance, pile axial force and pile force transmission law of jacked pile penetration, two pairs of embedded sensitized microfiber grating sensors were installed by slotting the pile body. The pile-jacking process of static-pressing viscous foundation soil with different diameters of closed-tube model piles was successfully monitored. The test results show that the pile pressure, pile end resistance and pile side resistance of the two test piles increase linearly with the increase of pile depth. When the pile jacks, the final pressure of the test pile TP1 is higher than that of the test pile. TP2 is 31% higher, pile end resistance is 18% higher, and total side resistance is 57% higher. The results show that increasing the pile diameter can significantly increase the pile side resistance; under different penetration depths, the pile side resistance is from top to end. Continuously exerted, the axial force of the pile body decreases with the depth of the pile and the slope of the distribution curve of the axial forcegradually decreases. At the maximum penetration depth, the axial force of the pile TP1 is 18% larger than that of the test pile TP2; As the depth increases, the unit side resistance at the same penetration depth gradually decreases, that is, the side resistance has a “degradation effect”; at the end of the pile jacking, the percentage of the pile end resistance to the pile force exceeds 50%, that is, the pile end resistance bears most of the load. This research can be used as a reference for the study of pile driving mechanism in clayey and layered clayey soils.

Bearing and uplift capacities of under-reamed piles in soft clay underlaid by stiff clay using lower-bound finite element limit analysis

Ensuring a safe foundation design in soft clay is always a challenging task to engineers. In the present study, the effectiveness of under-reamed piles in soft clay underlaid by stiff clay is numerically studied using the lower-bound finite element limit analysis (LB FELA). The bearing and uplift capacities of under-reamed piles are estimated through non-dimensional factors Ncul and Fcul, respectively. These factors increased remarkably and marginally compared to Ncul and Fcul of the piles without bulbs when the bulb is placed in stiff and soft clay, respectively. For a given ratio of undrained cohesion of stiff to soft clay (c2/c1), the factors Ncul and Fcul moderately increased with the increase in the length-to-shaft-diameter ratio (Lu/D) and adhesion factors in soft clay (αs1) and stiff clay (αs2). The variation of radial stress along the pile-soil interface, distribution of axial force in the under-reamed piles, and state of plastic shear failure in the soil are also studied under axial compression and tension. The results of this study are expected to be useful for the estimation of the bearing and uplift capacities of under-reamed piles in uniform clay and soft clay underlaid by stiff clay.

Incremental load transfer analysis of an energy pile under arbitrary mechanical and thermal loads

This paper describes a new incremental approach to simulate the axial load–displacement response of energy piles. A load transfer approach is used to model the interaction of pile with surrounding soil, the underlying layers, and the superstructure. Interface springs are nonlinear–hyperbolic and Masing’s rule applies to model their hysteresis behaviour. Mechanical and thermal loads are incrementally applied to the pile using an iterative finite difference method. This strategy makes it possible for both mechanical and thermal loads to have arbitrary time histories during analysis. The self-weight of the energy pile can also be considered. The simulation results are found to compare favourably with published experimental results from field and laboratory testing of three energy piles. The effects of amplitudes of mechanical load and temperature change as well as those of the stiffness of the pile extremities on the thermomechanical response of the pile and the position of the null point are evaluated and discussed. The simulations show that the thermal-induced axial force due to a unique temperature change was greater for an energy pile under lower amounts of mechanical load. It is found that the effect of the end restraining condition on the response of the energy piles is more considerable during the heating processes than during the cooling processes. More restrained pile–superstructure connection also results in more thermal-induced axial force in the energy pile. The null point is always located closer to the stiffer extremity of the energy pile.

Lateral dynamic response of pile group embedded in unsaturated soil

A mathematical formulation is proposed for the analysis of a pile group embedded in unsaturated soil subjected to horizontal time-harmonic vibration. The unsaturated soil is governed by the motion theory of three-phase poroelastic medium, and the piles with fixed connection to cap are modeled as Timoshenko beam models. By introducing Helmholtz decomposition to the governing equations, the resistance and attenuation function of displacement of the surrounding soil are theoretically derived. Then, the impedances of pile group in frequency domain are evaluated by utilizing the superposition approach based on the dynamic interaction factors. The internal forces of piles induced by both kinematic effects arising from the adjacent pile motion and inertial effect from pile cap, as well as the degree of contribution of the two effects have been investigated. The accuracy of the proposed method was validated by its comparison with a benchmark solution for the corresponding single phase medium problem. A comprehensive parametric study is performed to depict the effects of saturation, permeability, and pile group arrangement, and indicating that the saturation and permeability exert considerable effects on the nearly saturated condition, by contrast, the unsaturated case is much less affected.

Internal Force of the Anti-slide Pile in Soil Based on the Deep Beam Model

According to the deep beam model, the bury conditions, the geometry characteristics and the load condition, we established a load transfer model based on the tie rod arch and an internal force model for the loaded and anchored segments of the anti-slide pile. Then, we analyzed the shear, bending shear and local compressive failures of the pile, caused by the equivalent concentrated thrust force, the lateral frictional force, active earth pressure, and passive earth pressure, etc. With the laboratory results of the deep beam model, the relation between the shear span ratio and the tie rod arch was presented. According to the mechanical balance conditions of the cantilever beam, we obtained the power function curve of the tie rod arch and the influence factors. Subsequently, we established the equations of the horizontal displacement and the deflection angle at the bearing segment by superposing the load and the displacement of the strip nodes. According to the deformation characteristics of the Timoshenko deep beam element, the equations of the horizontal displacement and the deflection angle at the anchored segment were proposed. With the established calculation model and the material mechanics, the displacement, shear force and bending moment curves at the loaded and anchored segment of the anti-slide pile were proposed. Finally, the case study indicates that the displacement and the internal forces are nonlinear in the pile. The results obtained using the preliminary beam are larger than the numerical results, which is the smallest results than the other two methods.

The Environmental Effects Induced by a Metro Shield Tunnel Side-Crossing on Adjacent Pile Foundations and Its Impact Partition

With the advantages of fast construction speed and small disturbance to stratum, shield tunneling is becoming the preferred construction scheme for metro construction. However, if the disturbance of stratum cannot be clearly understood, it will affect the safety of adjacent underground structures and aboveground buildings. Based on the construction of the interval tunnel between Shizishan station and Chuanshi station of Chengdu metro line 7 project, this paper proposed a simplified calculation method to analyze the impact of shield excavation on adjacent pile foundation. A two-stage method of modified Peck formula and Winkler elastic foundation model was used to investigate the additional displacement and internal force of pile. A three-dimensional numerical model validated with the field test data was performed to compare with the theoretical results. The impact factors and their impact degree were discussed. The results show that the additional displacement and internal force are at a reasonable and acceptable level. The permanent pile foundation should adopt the small diameter pile as far as possible. When the small diameter pile foundation cannot meet the stress requirements, the design scheme of the pile group should be adopted. The area around shield tunnel is divided into strong impact area of pile foundation (S ≤ 0.75 D), slight impact area (0.75 D ≤ S ≤ 1.5 D), and no impact area (S > 1.5 D). The pile researched in this paper (S = 0.83 D) is in the slight impact area.

Study on the optimization of pile group foundation under oblique load

With the development of economy and science and technology in China, pile group foundation is widely used in various constructions to meet the complex engineering conditions. Pile foundation is often affected by inclined load (i.e. horizontal load and vertical load). The behavior of pile under inclined load is much more complex than that under single load. In engineering, the vertical component and the horizontal component of the pile top are often calculated separately, and then modified. This method is only suitable for small deformation, which is different from the actual situation. In this paper, taking the four pile foundation as an example, through the rotation of the cushion cap (the column does not rotate) and the column eccentricity, the force of the foundation pile can be relatively uniform. At the same time, the design calculation of the group pile foundation under the oblique load can be approximately equivalent to the design calculation of the group pile foundation under the single vertical load. When the force distribution on the pile top is relatively uniform under the same inclined load, the eccentricity of the column has a linear relationship with the depth of the cap. Through ABAQUS numerical simulation analysis, the correctness of the above understanding is verified.

Vertical Load Transfer Behavior of Composite Foundation and Its Responses to Adjacent Excavation: Centrifuge Model Test

Abstract In urban construction, more and more foundation pit excavations are adjacent to existing buildings with composite foundations. Therefore, it is necessary to study the interaction between foundation piles and supporting structures. In this article, a centrifuge model test has been carried out to study the vertical load transfer behavior of composite foundation with rigid piles and its responses to adjacent excavation. The test model was designed based on a real excavation project adjacent to an existing composite foundation. The sand pluviation method was used to build the foundation model. An in-flight excavation method and a loading device for multilevel uniform surface load were used in the test. Finally, the variations of induced axial force, pile skin friction, and pile-soil stress ratio along with the depth were investigated. Some useful conclusions can be drawn as follows: (1) the negative skin friction in the upper part of piles, induced by the overlaying load, increases first and then decreases along with the depth; (2) pile-soil stress ratio decreases along with the depth under initial loads, while it increases first and then decreases when the load is larger; (3) pile-soil stress ratio always increases with loads in the same depth, indicating that mobilized skin friction of piles is continuously developed; and (4) more significant changes of the axial force, skin friction, and pile-soil stress ratio of composite foundation piles are observed in the shallow soil and for the later excavation stage. Therefore, the deformation of the foundation pit should be strictly controlled during the later excavation stages.

Effect of slope with overburden layer on the bearing behavior of large-diameter rock-socketed piles

Pile foundation is a typical form of bridge foundation and viaduct, and large-diameter rock-socketed piles are typically adopted in bridges with long span or high piers. To investigate the effect of a mountain slope with a deep overburden layer on the bearing characteristics of large-diameter rock-socketed piles, four centrifuge model tests of single piles on different slopes (0o, 15o, 30o and 45o) were carried out to investigate the effect of slope on the bearing characteristics of piles. In addition, three pile group tests with different slope (0o, 30o and 45o) were also performed to explore the effect of slope on the bearing characteristics of the pile group. The results of the single pile tests indicate that the slope with a deep overburden layer not only accelerates the drag force of the pile with the increasing slope, but also causes the bending moment to move down owing to the increase in the unsymmetrical pressure around the pile. As the slope increases from 0o to 45o, the drag force of the pile is significantly enlarged and the axial force of the pile reduces to beyond 12%. The position of the maximum bending moment of the pile shifts downward, while the magnitude becomes larger. Meanwhile, the slope results in the reduction in the shaft resistance of the pile, and the maximum value at the front side of the pile is 3.98% less than at its rear side at a 45o slope. The load-sharing ratio of the tip resistance of the pile is increased from 5.49% to 12.02%. The results of the pile group tests show that the increase in the slope enhances the uneven distribution of the pile top reaction and yields a larger bending moment and different settlements on the pile cap, which might cause safety issues to bridge structures.

Calculation of displacements and internal forces of anchored retaining piles.

Pile-anchor retaining structures are widely used in excavation engineering. The evaluation of lateral displacements, the internal forces of piles are extremely important for the performance of the structure. Most of the existing methods are empirical, semiempirical or FEM methods, while analytic calculation methods for this evaluation are rare. This paper presents an analytic method to calculate the displacements and internal forces of anchored retaining piles based on the existing design code. In the calculation method, the singular function is applied to evaluate the effect of segmented loading on the deflection of a beam with a nonuniform cross section. The load concentration function, expressed by the singular function, can describe the segmented load and be integrated without a complicated procedure for determining the integral constants. The method is applied to a structure in Wenzhou, China, and the calculation results are compared to the field measurement results. This method is only valid for pre-failure predictions.

Influences on Antislide Piles Used for Slope Reinforcement: Numerical Simulation Based on the Soil Arching Effect

This study explores the pile-soil interaction mechanism and the optimal use of antislide piles for slope reinforcement based on finite difference numerical modelling. The force and displacement principles of slopes and antislide piles are analysed. The influences of various factors are investigated, such as postpile filling parameters, pile embedding methods, and pile cross-sectional shapes. Numerical modelling is used to determine the optimal layouts of antislide piles for push and traction landslides. The findings indicate that the cohesive force of the fill has a greater influence on the piles and slope than the friction angle and is the primary control factor. Fully buried antislide piles provide a better antisliding effect than semiburied ones. With fully buried piles, the best controlling effect is obtained when the ratio of the length of the pile’s free section to the height of the sliding body is approximately 4/5. Moreover, stepped-cross-section piles provide better slope reinforcement than those with rectangular, T-shaped, or trapezoidal cross-sections. In practical applications, end-bearing arches can be utilized as the primary control structures, with friction arches used for secondary control to improve the soil arching effect as much as possible, thereby enhancing the stability of the piles and slope. To control landslides of various thrust forms, antislide piles should be set in the active section, the core sliding section, or both, as required. This paper provides guidance for improving the design of antislide piles.

Analysis of defective prestressed pipe piles residual bearing capacity and treatment measures

Due to poor geologic conditions, unreasonable design principles, or construction method, many quality defects often occur during prestressed pipe piles’ field construction, which will greatly influence pipe piles’ normal service or result in engineering accident. To acquire some treatment measures of the defective pipe piles, we have carried out some theoretical researches on this type of pipe pile. First, the types of defective prestressed pipe piles were summarized. Then, we explored the force and deformation characteristics of the defective pipe piles and brought forward the relationship between pile-top displacement and residual bearing capacity. Finally, we offered some treatment measures for the defective pipe piles. The results show that the main performance of the defective prestressed pipe piles includes pile deviation, incline, and breakage. The residual bearing capacity of the incline pipe piles is less than half of the designed bearing capacity, and the top displacement of the incline pipe pile is positively correlated with the square of the sliding depth. Some treatment measures such as foundation adjustment, adding piles, splicing pile, and filling core can improve defective pipe piles. The research results can provide some references for similar engineering.