Displacement Piles Research Articles

Foundation Piles-A New Feature for Concrete 3D Printers.

Foundation piles that are made by concrete 3D printers constitute a new alternative way of founding buildings constructed using incremental technology. We are currently observing very rapid development of incremental technology for the construction industry. The systems that are used for 3D printing with the application of construction materials make it possible to form permanent formwork for strip foundations, construct load-bearing walls and partition walls, and prefabricate elements, such as stairs, lintels, and ceilings. 3D printing systems do not offer soil reinforcement by making piles. The paper presents the possibility of making concrete foundation piles in laboratory conditions using a concrete 3D printer. The paper shows the tools and procedure for pile pumping. An experiment for measuring pile bearing capacity is described and an example of a pile deployment model under a foundation is described. The results of the tests and analytical calculations have shown that the displacement piles demonstrate less settlement when compared to the analysed shallow foundation. The authors indicate that it is possible to replace the shallow foundation with a series of piles combined with a printed wall without locally widening it. This type of foundation can be used for the foundation of low-rise buildings, such as detached houses. Estimated calculations have shown that the possibility of making foundation piles by a 3D printer will reduce the cost of making foundations by shortening the time of execution of works and reducing the consumption of construction materials.

DEM investigation of sand response during displacement pile installation

Previous experimental and numerical studies indicate that the stress state of sand at a specific depth changes significantly during the installation of a displacement pile. At a given depth level, the horizontal stress in sand increases as the end of pile approaches and reduces as the pile continues to penetrate and go past the sand element. This horizontal stress reversal, together with the large-strain deformation of the sand at the pile shaft, may cause a reduced accuracy in the calculation of pile capacity. In this paper, the micro-mechanical behaviour of sand developed around pile shaft during the installation of a closed-ended pile was studied using the two-dimensional Discrete Element Method (DEM). Sand assembly was modelled as uncrushable discs, and the closed-ended pile was modelled as a rigid clump which was made of a large number of overlapped discs with a fixed distance. The sand responses in terms of stress, strain and volume changes during the monotonic jacking of the closed-ended pile were investigated. Simulation results revealed micro-mechanical behaviours of the sand in both the interface zone “B” adjacent to the pile shaft and the far field zone “A” away from the pile. It was shown that the sand along the pile shaft at a small normalised distance to pile tip was subjected to a volume reduction as the pile goes past. As the pile drives deeper, the sand at a larger normalised distance to pile tip exhibited dilation. This captured process will give insights to the degradation of shaft friction at a given sand horizon.

Research on the overall bearing behavior characteristics of the all-vertical-piled wharf under horizontal load

Based on the ANSYS model, the simulation analysis of the all-vertical-piled wharf is carried out. It is found that the zero point of the pile displacement of the all-vertical-piled wharf is about 6 times the depth of the pile width (pile diameter) below the mud surface. The difference in pile displacement changes under various working conditions below this position is very small, and the pile displacement above this position is positively correlated with the horizontal load. Through research, the pile displacement curve and load-displacement curve of the all-vertical-piled wharf are constructed, and the method for determining the overall ultimate bearing state of the all-vertical-piled wharf is established. The research results can provide a reference for the study and judgment of the overall bearing safety of the all-vertical-piled wharf under horizontal load.

Model test and analysis of soil displacement of cone-perforated column composite pipe pile under static pressure

In view of the fact that there is relatively little research on soil squeezing effe ct of conical-perforated column composite pipe pile, the lateral displacement and surfa ce uplift of conical-perforated column composite pipe pile after single pile is pressed i nto soil are observed by static pressure pile sinking method, and the change law of soil lateral displacement and surface uplift during pile sinking is analyzed. It is found that the lateral displacement increases with the increase of pipe pile driving depth, and whe n the pipe pile is fully penetrated, the soil lateral displacement ends, and the influence range of soil lateral displacement is 2 days.

Interaction between a long pile and the multilayered soil body with account for elastic and rheological properties as well as soil stabilization

Introduction. When the footing is embedded in loose clayey soils, buildings may settle down for a long period of time. The projected settlement period is of great importance for the design of foundations designated for such soils. Therefore, the approach to describing the process of foundation settlement must be considered as rheological. This article addresses the setting of and a solution to the problem of interaction between a long pile and surrounding multilayered and underlying soils with account taken of the rheological properties of the surrounding soil body. The creep process is considered with account taken of stabilization.
 Materials and methods. Linear problem setting is considered. The analytical method is employed to present a solution. The rheological stabilization parameter is used to describe the creep process.
 Results. An expression is derived to determine the reduced shear modulus for the multilayered soil body. The relationship between the value of the force applied to the pile toe and the time is derived with regard for the rheological stabilization parameter. Analytical solutions are enforced by graphs in the article. Graphs describing the relationship between pile settlement, the force applied to the toe of the pile, passing through alternating soil layers, and the time are provided for various values of viscosity and the variable parameter of stabilization.
 Conclusion. Solutions, obtained by the co-authors, are used to perform the preliminary identification of displacement of long piles and surrounding multilayered underlying soils. The rate of stress changing underneath the pile toe depends on soil viscosity. The rheological coefficient of stabilization has a major effect on the time of pressure stabilization underneath the pile toe, as well as the time of the pile settlement stabilization. Dependencies, derived in this article, make it possible to project the future settlement pattern.

Full-scale performance testing of bored piles with retaining walls in high cutting slope

This study aims to verify the suitability and reinforcement behavior of newly designed bored piles with retaining walls (BPRWs) for cutting-slope stabilization in the Tibet Plateau. As the first BPRWs prevention works in the alpine and hypoxic areas, full-scale performance testing is conducted of the high cutting slopes along the Lhasa-Nyingchi Railway under construction. Amid the construction processes of slope excavation and BPRWs installation, the overall structural performance, including lateral displacement, bending moment and lateral earth pressure, was determined to evaluate the cutting-slope stability and retaining mechanisms of BPRWs. The monitoring parameter distribution rules were thoroughly analysed. The relationship between the lateral earth pressure and pile displacement was studied, and a soil resistance calculation model was proposed. Finally, the BPRWs suitability was assessed. The results revealed that the retaining behaviour of BPRWs is closely related to the construction process. The displacement rate over time is characterized by alternating peaks and valleys, and the maximum displacement rate and bending moment occurs at the retaining wall pouring stage. The bow-shaped bending moment distribution with the pile depth exhibits low values on both ends and a high value in the middle. The ground reaction coefficient is allometrically attenuated with increasing lateral displacement. The proposed soil resistance model can satisfactorily predict the lateral earth pressure. The BPRWs deformation satisfies the service requirements at the construction and service stages. This case study provides a reinforcement reference for BPRW in alpine and hypoxic areas.

An Investigation of Effect of Distance and Shape of Pile on the Displacement of Gag Pile by 3D FEM Analysis

An Investigation of Effect of Distance and Shape of Pile on the Displacement of Gag Pile by 3D FEM Analysis

Impact of installation on the recovery of the bearing capacity of displacement piles in sensitive clay

Deep foundations are essential for the soft soil deposits that are ubiquitous in the Nordic countries. Precast driven displacement piles are commonly used, due to the ease of installation and their low cost. The stiffness and strength of the clay surrounding the piles will change during and after the pile installation process. This paper presents an effective stress based numerical framework that elaborates the pile set-up and pile ageing mechanisms observed empirically. For the trial case studied, it is demonstrated that the magnitude of the increase in axial bearing capacity over time is strongly linked to the pile installation stage. Furthermore, it is found that classic effective stress based soil mechanics concepts readily describe the observed behaviour.

Numerical Modelling of Displacement Pile Resistance in Sand Ground. Part 1: Soil Physical Model, Calibration of Model Parameters

Accuracy of numerical modelling of ground resistance of the displacement pile highly depends on proper evaluation of its states: prior loading and its changes during the loading. Evaluation of initial ground stage, its subsequent changes caused by pile installation and, finally, evolution of the loaded pile resistance are the modelling stages that require validation with specialized test results performed under controlled laboratory conditions. Selection of the proper physical soil model and its parameters should be also done in accordance with the relevant soil tests results. The first paper briefly introduces testing results of a displacement pile prototype. Tests were conducted in the created sand deposit in the laboratory pit. Determining pile resistance and ground stress-strain distribution in the vicinity of the pile allows selecting the physical model for the soil. Numerical calibration of the parameters for the physical model of the selected soil was performed. The second, following paper will introduce analyses of pile resistance. It involves creation of a discrete model and its parameters, numerical modelling of pile resistance against vertical load. The pile ground resistance modelling applying the physical model of the selected soil includes the following stages: evaluation at rest stage and assessment of residual effects of installation and displacement pile loading resistance. Numerical analyses results were validated with displacement pile prototype testing results.

Slope effect on dynamic p–y backbone curve in dry sand

This study aims to evaluate the slope effect on the dynamic p–y backbone curve, which is a worldwide simplified tool in the seismic design of pile foundations. Data of dynamic centrifuge tests on single and group piles in sloping sandy ground were adopted to derive soil resistance and pile displacement. Meanwhile, the free-field soil displacement was computed by performing three-dimensional numerical simulations of centrifuge models excluding the pile-supported structure. Dynamic p–y loops of soil resistance and pile displacement relative to the free-field soil displacement showed an irregular shape with the occurrence of large residual displacement. The soil resistance mobilized at the free-head pile was smaller than that at the fixed-head pile because of the difference in the phase responses. An empirical factor was introduced to account for the slope effect on the dynamic p–y backbone curve, which was formed by fitting peak points of the dynamic p–y loops with a hyperbolic function. Pseudo-static analyses applying the suggested dynamic p–y backbone curve showed good agreement with the centrifuge test data.

Centrifuge modelling on monotonic and cyclic lateral behaviour of monopiles in kaolin clay

This paper details a programme of centrifuge tests (100g) on the monotonic and cyclic lateral behaviour of large-diameter semi-rigid monopiles in kaolin clay. Piles of different diameters were used, with a maximum prototype value of 5·9 m. The pile–soil interaction was investigated in terms of the overall load–displacement behaviour, distribution of bending moment and pile deflection, p–y curves and excess pore pressure response. For monotonic loading, procedures were developed to fit the monotonic p–y curves obtained from different pile and soil properties using a hyperbolic tangent model. In addition, an explicit model was derived to assess the development of excess pore pressure within the surficial soil, which was found to approach the vertical effective soil stress at large displacement. For cyclic loading, the accumulation of lateral pile displacement could be accompanied by either increase or decrease in soil resistance, which strongly depends on the loading rate. Strong correlation between the development of peak soil resistance and a dimensionless velocity group was obtained, and was supported by the measured excess pore pressure. Under undrained conditions, the peak soil resistance decreases almost linearly with the accumulation of excess pore pressure.

The P-y Response of Laterally Loaded Flexible Piles in Residual Soil

This paper describes the main features related to lateral displacements with depth after successive lateral loading–unloading cycles applied to the top of reinforced-concrete flexible bored piles embedded in naturally bonded residual soil. The bored piles under study have a cylindrical shape, with 0.40-m in diameter and 8.0-m in length. Both bored piles types (P1 and P2) include an embedded steel pipe section in their center as longitudinal steel reinforcements: pile type P1 has another 16 steel rods as steel reinforcement to concrete while pile type P2 has no further steel reinforcement. Pile type P1 has three times as much stiffness (EI) and four and a half times the plastic moment (My) than pile type P2. A similar load–displacement performance was observed at initial loads as for small displacements of both piles. At this initial loading stage, the response of the reinforced concrete piles is a function of the soil characteristics and of a linear elastic pile deformation. During this stage, piles can even be understood as probes for evaluating soil reactions. For larger horizontal displacements, after the concrete section starts undergoing large deformations, approaching the ultimate bending moment, pile behavior and consequently the load–displacement relation starts to diverge for both piles. For pile P1 the values of relevant lateral displacements are extended to about 2.5-m in depth, while for pile P2 lateral displacements are mostly constrained to about 2.0-m in depth. Measurements of horizontal displacements of pile P1 against depth recorded with a slope indicator show that, after unloading, lateral loads at distinct stages (small and near failure loads), exhibits a much higher elastic phase of the system response. An analytical fitting model of soil reaction is proposed based on the measured displacements from slope indicator. The integration of a continuous model proposed for the soil reaction agrees fairly well with the measured displacements up to moments close to plastic limit. Results of load–displacement show that the stiffer pile (P1) was able to mobilize twice as much lateral load compared to pile P2 for a service limit displacement of about 20 mm. The paper shows results that enable the isolation of the structural variable through real scale pile load tests, thus granting understanding of its importance and enabling its quantitative visualization in examples of piles embedded in residual soil sites.

Determination of Embedded Depth of Soldier Piles in Pile-Anchor Supporting System in Granite Residual Soil Area

Reasonable depth of pile embedment is one of the key factors for the success of deep foundation pit projects. This paper has taken a deep foundation pit project in a granite residual soil area in Shenzhen as an example and used physical model tests to study the deformation law of the piles and the surrounding soil during the excavation of the deep foundation pit, revealing the variation law of earth pressure in time and space in the pit and then verified it by numerical simulation. The influence of the embedded depth of the pile on the deformation and earth pressure of the deep foundation pit is then explicitly discussed. The study shows that the embedded depth has a significant effect on the deformation and earth pressure distribution of the foundation pit. The earth pressure in front of the pile tends to approach the passive earth pressure as the embedment depth decreases, while the earth pressure behind the pile is in between the Rankine active earth pressure and the static soil pressure; the settlement value and settlement range of the surrounding soil are doubled. The pile displacement increases as the maximum displacement point rises. The maximum displacement of the pile body was used as the basis for determining the instability of the foundation pit. The optimum embedded depth is obtained when the depth of embedment of the pile is 0.22 H (H is the excavation depth of the foundation pit).

Driven cast-in-situ pile capacity: insights from dynamic and static load testing

Driven cast-in-situ (DCIS) piles are classified as large displacement piles. However, the use of an oversized driving shoe introduces additional complexities influencing shaft resistance mobilisation, over and above those applicable to preformed displacement piles. Therefore, several design codes restrict the magnitude of shaft resistance in DCIS pile design. In this paper, a series of dynamic load tests was performed on the temporary steel driving tubes during DCIS pile installation at three UK sites. The instrumented piles were subsequently subjected to maintained compression load tests to failure. The mobilised shear stresses inferred from the dynamic tests during driving were two to five times smaller than those on the as-constructed piles during maintained load testing. This was attributed to soil loosening along the tube shaft arising from the oversized base shoe. These radial stress reductions appear to be reversible by the freshly cast concrete fluid pressures, which provide lower-bound estimates of radial total stress inferred from the measured shear stresses during static loading. This recovery in shaft resistance is not recognised in some European design practices, resulting in conservative design lengths. Whilst the shaft resistance of DCIS piles was underpredicted by the dynamic load tests, reasonable estimates of base resistance were obtained.

Dynamic response of timber pile ground improvement: 3D numerical simulations

Driven timber displacement piles are being increasingly used to densify and reinforce soils against earthquake-induced ground deformations. However, the role of timber piles to reinforce the soils and redistribute cyclic stresses to timber piles has not been established, despite their excellent flexural properties. This study presents a series of dynamic 3D, linear-elastic, numerical simulations set with the unit cell framework to evaluate the role of the tapered timber pile and design variables such as pile length, spacing and relative density on the amplification and stress redistribution possible with this ground improvement technique. The simulations indicate that the depth-dependent shear strain and shear stress redistribution variously depend on the pile length, spacing, relative density, and input motion frequency. Further, the previously-accepted shear strain compatibility assumption developed for stone columns served to greatly overestimate the magnitude in cyclic shear stress reduction. Due to the tapered pile geometry and the depth-varying soil properties implemented, the accuracy of a recently proposed approach to estimate shear stress redistribution to account for column flexure was found to depend on the flexibility of the composite soil-pile system: longer, more flexible piles and lower relative density were predicted more accurately than shorter, stiffer timber piles with higher relative density. In general, the average shear strain ratio between the improved and unimproved soil is most sensitive to pile length, moderately sensitive to relative density, and least sensitive to pile spacing, and the average ratio of shear stress reduction coefficients is most sensitive to pile spacing, moderately sensitive to pile length, and is least sensitive to relative density.

The Application of Improved Genetic Algorithm to the Back Analysis of Foundation Pit Construction

The improved genetic algorithm is combined into the foundation pit finite element method. On the basis of the measured lateral displacement data on site, the parameters of the foundation soils were obtained by the back analysis. Then the lateral deformation of the surrounding soil was analyzed on the condition of each different step under the foundation pit excavation according to the inversion parameters, and the calculation and analysis of lateral displacement of cement-soil pile with anchorage retaining structure was did. The results reveal that the calculated value is agreed with to the measured value, which indicates that the improved genetic algorithm is efficient to the related constructions.

Interaction between a long pile and multi-layer underlying soils

Introduction. The majority of construction sites feature complex geotechnical conditions, as they have alternating soil layers, including loose soils. A pile foundation is the principal type of foundations constructed on these sites. This article encompasses a problem statement and a solution to the problem of interaction between a long pile and multilayer underlying soils.
 Materials and methods. The problem is explored in linear and nonlinear settings. The S.P. Timoshenko elastoplastic model is analyzed to describe nonlinear shear deformations. Analytical and numerical methods are employed to present the solution. The results of the analytical solution are compared with the results of the elastic problem obtained using the Plaxis 3D software package.
 Results. An equation designated for determining the reduced shear modulus of the multilayer soil mass is obtained. Analytical solutions are supported by the graphical solution obtained using Mathcad software. Numerical solutions are obtained using the Plaxis 3D software package. The diagrams describing the dependence of the settlement of the pile, that passes through alternating soil layers, on the load are provided. The diagrams, describing the dependence between the force, applied to the pile toe, and the pile radius in case of a variable load applied to the pile head and variable pile length are provided.
 Conclusions. The resulting dependence, needed to determine the reduced shear modulus of the multi-layer soil mass, demonstrates good convergence with numerical methods in the elastic setting. These solutions can be used to pre-determine the displacement of a long pile surrounded with the underlying multi-layer soil mass. The selection of an optimal correlation between the pile length and the pile diameter allows for the most effective use of the bearing capacity of the pile.

A Comprehensive Study of Franki pile with the other pile models Embedded within cohesionless soils

Frankie pile is classified as a large displacement pile cast in place with a concrete mixture. This paper dealt with the laboratory work to produce a model of the Franki pile similar to the full-scale production process in the field to investigate its behaviour and make a comparison study with the other familiar types of piles models (precast concrete pile, closed-ended steel pipe pile, and bored pile with the same surface and cross-sectional area). The investigation occurred within dry sandy soil with two different relative densities (30 and 60) % will be denoted as (S1) and (S2) respectively. Axial compressive piles load tests were performed for embedded piles models in sandy soils at relative densities of 30% and 60%. Several interpretations have been used to estimate the ultimate capacity of pile models from the results of pile load tests. It was found that the Davisson, De Beer, Fuller and Hoy, and Tangent Methods gives an approximate acceptable result for all typical pile load tests, so average values of theses methods were adopted for comparisons. It was observed that the ultimate bearing load value at a Franki pile was greater than the other types of piles models in both densities. The for precast concrete pile, 2.98 for close ended pipe pile and 5.5 for bored piles for low relative density. While for high relative density the bearing ratio of Franki pile over other pile models were 0.94 for precast concrete pile, 2.26 for pipe pile model and 3.16 for bored pile model. During this study, it was found that a Franki pile was more effective in weak granular soils.

Shaking Table Tests on a New Antislide Pile under Earthquakes

A retaining form of a shock-absorbing antislide pile is proposed for slope engineering. A flexible material (shock-absorption layer) is filled in front of an ordinary antislide pile, which is used to absorb a large amount of seismic energy, thereby decreasing the transmission of seismic energy to the antislide pile. The flexible material thus reduces the seismic response, hence improving the aseismic capacity of the antislide pile. To verify the seismic performance of the shock-absorbing antislide pile, a shaking table contrast test was conducted and the results were compared with those from an ordinary antislide pile. The test results show that the flexible material absorbs a portion of the seismic deformation of the slip mass, decreasing the final displacement of the shock-absorbing antislide pile compared to that of the ordinary antislide pile, thereby reducing the sensitivity of the pile body to the displacement. Under the same conditions, the acceleration response of the slope body at the same height is lower for the shock-absorbing antislide pile than that for the ordinary pile, with the seismic performance of the former being superior to that of the latter. Furthermore, the shock-absorbing antislide pile is similar to the ordinary pile in terms of the dynamic earth pressure distribution form of the pile shaft; however, its value is relatively smaller, and the former exhibits better dynamic stress performance than the latter. The test results should prove useful for aseismic design of slopes.

Post Buckling Behavior of Slender Piles Partially Embedded in Sand Soil under Axial Load

Pile instability due to buckling is considered to be one of the most important causes of superstructures failures especially in bridges and wind turbines. The mechanism of load-transfer of partially embedded piles in sand subjected to axial load to surrounded soil and the corresponding deformation are important aspects of pile design. In the present research, an experimental model was developed to measure the lateral displacement of piles subjected to axial loads. The experimental results indicated that the post buckling load of partially embedded pile was enhanced up to five times of the buckling load of free case. Two proposed formulas based on the laboratory experiments were induced to determine post buckling load of the partially embedded pile. The predicted buckling capacity of piles was compared to the experimental buckling load, which showed a good agreement.