Displacement Piles Research Articles

Analysis of Horizontal Pile Displacement Caused by Pit Excavation

Analysis of Horizontal Pile Displacement Caused by Pit Excavation

A Nonlinear Prediction Model of Antislide Pile Top Displacement Based on MIC‐SVR for Jurassic Landslides

In this study, a nonlinear prediction model of antislide pile top displacement is proposed. Based on the quantitative analysis of the rock mass structure characteristics of the soft and hard interbedded sliding bed in the Jurassic strata, the post‐thrust force and geometric characteristics of the top of antislide pile displacement, and bending moment, the main controlling factors affecting the displacement of the top of antislide pile were determined by maximal information coefficient (MIC). Through orthogonal experiment design and 3DEC numerical experiment, a database of main controlling factors (sliding bedrock inclination, thrust size, embedded depth, and pile section size) of pile top displacement was established and a nonlinear prediction model of the displacement of the top of antislide pile based on the main controlling factors was proposed. Finally, two engineering examples were used to validate the performance of this model, with the comparisons of four prediction methods (SVR, MIC‐SVR, LSTM, and ELMAN). The results show that the MIC‐SVR model has a practical reference value for the prediction of the displacement of the top of an antislide pile in the Jurassic landslide in the Three Gorges Reservoir Area.

A new modified method of predicting load-settlement behavior for large-diameter helical piles in sand considering nonlinear degradation of soil stiffness

With respect to the design of helical pile foundations, reliable prediction of pile settlement is necessary to ensure appropriate structural and serviceability performance. At present, most research into the load-settlement response is focused on the regular displacement piles (precast/cast-in-place driven displacement piles) while there is little research on the prediction of the load-settlement curve of helical piles in sand. This paper presents a new modified method taking Randolph’s analytical pile solution as the theoretical framework with the consideration of the nonlinear soil stiffness degradation corresponding to different loads and settlements. The proposed method for helical piles is verified by centrifuge tests of 9 helical piles in three types of sand (loose, medium dense and dense sand) and 4 helical piles in two field test cases with better agreement with test results compared with the existing method for driven piles. Also, the influence of different parameters of pile and soil on the load-settlement curve of single-blade piles is analyzed. Highlights A novel empirical formula is proposed to analyze the nonlinear behavior of the load-displacement curve of a single-helix pile based on the back-analysis method. The load-settlement curves predicted from the new modified method is in reasonably good agreement with measured ones from both centrifuge and field tests. The calculated load-settlement curves of 4 helical piles in 2 field tests from the new modified method are in significantly better agreement with those from exisiting method for driven piles in sand.

Numerical Modelling of Various Aspects of Pipe Pile Static Load Test

Due to the development of dedicated software and the computing capabilities of modern computers, the application of numerical methods to analyse more complex geotechnical problems is becoming increasingly common. However, there are still some areas which, due to the lack of unambiguous solutions, require a more thorough examination, e.g., the numerical simulations of displacement pile behaviour in soil. Difficulties in obtaining the convergence of simulations with the results of static load tests are mainly caused by problems with proper modelling of the pile installation process. Based on the numerical models developed so far, a new process of static load test modelling has been proposed, which includes the influence of pile installation on the soil in its vicinity and modelling of contact between steel pile and the soil. Although the presented method is not new, this is relevant and important for practitioners that may want to improve the design of displacement piles. The results of the numerical calculations were verified by comparing them with the results of pipe pile field tests carried out in a natural scale on the test field in Southern Poland.

Monopile responses to monotonic and cyclic loading in undrained sand using 3D FE with SANISAND-MSu

Monopile response under undrained conditions in sand is gaining increasing interests owing to the recent development of offshore wind farms in seismic regions. Pore pressure evolution in liquefiable soil can significantly reduce the strength and stiffness of the soil which in turn affects the structural dynamic response. Several numerical models have been developed in the last two decades to enhance understanding of the mechanism of monopile–soil interaction with the existence of pore water pressure. In this study, the effects of geometry and static vertical load on monopile lateral response were studied using three-dimensional finite element methods that consider the existence of lateral cyclic load-induced pore water pressure. To achieve reliable simulation results of pore pressure development and pile displacement accumulation during cyclic loading, the simple anisotropic sand model with memory surface for undrained cyclic behavior of sand was adopted. For piles with the same diameter, a accumulated pile head displacement during lateral cyclic loading decreased linearly with increasing pile embedded length but increased with increasing eccentricity. Static vertical load had minor effects on pile cyclic lateral response. The distributions of mean effective stress and pore water pressure in the soil domain were presented. The pile reaction curve (cyclic soil reaction against pile defection) of the monopile was extracted. The numerical results aim to provide reference for optimized engineering design procedures.

Bearing Characteristics of Diaphragm Wall Foundation under Vertical and Combined Load

To investigate the bearing characteristics of diaphragm wall foundation under combined load, the results from elasto-plastic analyses of 3D finite element models (FEM) were presented in this study. The vertical load of the diaphragm wall foundation is borne by inner and outer side resistance, resistance of soil core and the end of wall, respectively. Moreover, the sum of end resistance and soil core resistance accounts for about 75% of the vertical load. The mobilization mechanism and distribution of side resistance of the foundation were also analyzed. It is clarified that the mobilization characteristics of inner and outer side resistance of the wall are completely opposite. Due to the combined load, the horizontal load has an amplification effect on the settlement of the foundation. Additionally, the calculation methods of the Eight-component Winkler spring model and rigid pile displacement were used for determining the vertical load-bearing capacity and the overturning stability. A comparison between results from the FEM and the theoretical calculation methods showed that the results of the numerical simulation properly coincided with that of the displacement solution of theoretical model. The conclusions obtained by the above methods all indicate that the foundation has the characteristics of overall overturning failure under the combined load.

Identification of residual force in static load tests on instrumented screw displacement piles

Abstract Occurrence of the so-called residual force of an unknown value significantly disturbs interpretation of static load tests performed on piles equipped with additional measuring instruments. Screw displacement piles are the piling technology in which the residual force phenomenon is very common. Its formation mechanism is closely related to the installation method of this type of piles, which initiates generation of negative pile skin friction without any additional external factors. Knowledge of the value and distribution of a residual force (trapped in a pile shaft before starting the load test) is a necessary condition for the proper interpretation of instrumented pile test results. In this article, a clear and easy-to-use method of residual force identification, based on the analysis of shaft deformations recorded during pile unloading is presented. The method was successfully verified on two pile examples and proved to be effective and practical.

Vibro piles performance prediction using result of CPT

Abstract Vibro piles belong to the group of full displacement piles with an expanded base, characterised by a very high load capacity, especially in non-cohesive soils. The problem is to adopt a reliable method for the determination of full load–settlement (Q–s) curve. A frequent difficulty is the determination of the load capacity limit based on the static load test because the course of the load–settlement curve is of a linear nature. This publication presents the empirical method. It allows direct prediction of a full axially loaded pile settlement curve based on the values of qc cone resistance obtained in cone penetration test (CPT). The advantage offered by this procedure is the accuracy of the obtained limit values in relation to the actual load-bearing capacity as compared to other methods based on soil parameters obtained in in situ testing. An additional advantage is the Q–s characteristics, which enable designing for intermediate values, allowing for the criterion of minimal or equal settlements. The shape of analytical curves was compared with static pile load test (SPLT) curves. This comparison showed large convergences between the analytical and measured curves.

Discussion of “Evaluation of installation effects on set-up of field displacement piles in sand”

Discussion of “Evaluation of installation effects on set-up of field displacement piles in sand”

Analysis of Dynamic p-y Curve Characteristics According to Mode Shape of Structure Using Shaking Table Tests

In the seismic design of pile foundations, a p-y curve representing the nonlinear behavior of the ground considering the dynamic load of the earthquake is required. Recently, p-y curve analyses reflecting the soil-structure interaction have been conducted, but studies on multilayer structures have not been investigated extensively. In this study, the p-y curve characteristics were analyzed, considering the influence of the ground-structure interaction based on the mode shape of the structure (no structure, single-story structure, and three-story structure) through shake table tests. It was found that (1) the bending moment and pile displacement increased with input acceleration, and (2) the maximum soil resistance and pile displacement occurred at the natural frequencies of each structure were observed. In addition, the bending moment, soil resistance, and p-y curve slope were higher in the single-story structure than in the three-story structure. The findings indicate that the seismic design simulated for a single-story structure is conservative.

Effect of Densification on the Random Field Model Parameters of Liquefiable Soil and their Use in Estimating Spatially-Distributed Liquefaction-Induced Settlement

Densification-type ground improvement has gained wide acceptance as an effective technique to improve the static and cyclic strength and seismic performance of liquefiable soils. However, there has been little attempt to quantify the degree of change in certain measures of soil spatial variability following densification. This study uses the random field model (RFM) framework to quantify changes in the trend, inherent variability, and the autocorrelation of soil following various densification-based ground improvement methods using case history data. Ground improvement technologies investigated include driven displacement piles, vibro-replacement (i.e., stone columns), and deep dynamic compaction. Vertical RFM parameters are shown to change significantly following densification, with reductions in the coefficient of inherent variability, and increases in the scale of fluctuation, the latter of which appears related to the initial relative density. One case history is used to illustrate the utility of the RFM framework to link spatial variability of the post-shaking settlements to the results of a geostatistical model of the subsurface, including the three-dimensional distribution of CPT measurements and fines content. It is shown that the spatial distribution of differential surface settlements is correlated to those spatially-varying subsurface characteristics that are known to lead to larger liquefaction-induced settlement. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman,serif;}

Comparison Study on the Performance of a Novel and Traditional Energy Piles by Laboratory Tests

Phase change material (PCM) is a substance that can absorb or release sufficient latent heat at phase transition. By encapsulating phase change paraffin in hollow steel balls in the concrete, an energy pile with PCM was innovatively produced to improve energy efficiency for the ground heat pumping system. Laboratory tests were carried out on both PCM energy pile and traditional concrete pile to evaluate the thermo mechanical performance. Two piles were heated and cooled through inside tubes at a constant flow rate. The laboratory tests on the two piles were symmetrical for the two horizontal directions in geometry, and heat transfer process follows conservation laws of energy. The temperature response of the pile and soil, internal strain, pile displacement, pore pressure, and soil pressure under heating-cooling cycles were examined. Compared with the traditional concrete pile, the PCM energy pile can effectively reduce the surrounding soil temperature. The use of PCM in the pile can improve the capacity of heat storage and make the pile more effective in heat exchange. Non-uniform thermal strain and accumulations of heat and irrecoverable displacement were observed in the repeated heating-cooling process. The study can provide references for the practical implication of PCM energy piles.

Effect of model scale on helical piles response established from shake table tests

This paper investigates the effect of model scale on seismic response of prototype helical pile (HP) groups employing finite element modelling approach verified by the results of single gravity shaking table models of piles installed in dry and saturated sands. The prototype shaking test configuration was established from model shake table tests by adopting a set of similarity and dimensional laws. The results demonstrated that the scaled models exhibited generally similar responses. The HPs' response in the saturated sand bed was dominated by the rocking behaviour, while the flexural behaviour dominated the response in the dry tests. In addition, the HPs' lateral response followed the lateral soil uniform deformation in the dry tests, while they did not follow the nonuniform soil deformation in the saturated tests. However, the prototype models' axial and lateral responses were different from the results of the shaking table scale. The HP exhibited less scaled lateral deformation, bending moments, and settlement in the prototype models than those at the shaking table scale in the dry and saturated tests. Meanwhile, the prototype helices’ stress was higher than the shaking table helices in the saturated tests and less than them in the dry tests. A set of scaling factors was suggested for extrapolating the soil and HP responses from 1 g shake table model tests. Based on the obtained results, the soil and HP responses may be extrapolated from 1 g shake table model tests employing the following scaling factors: soil displacement increase factor, SDIF = 0.8n in the saturated tests, and SDIF = 0.6n in the dry tests, while the pile displacement increase factor, PDIF = 0.7n in the saturated test and 0.5n in the dry test.

Improved calculation of the rigidity of double-row piles and double-beam composite support and displacement analysis under different soil properties

As a new type of cantilever-type supporting structure, the double-row pile supporting combination system can improve the overall rigidity to maintain the safety and stability of the side of the foundation pit. The case of a double-row pile foundation pit support project in the Wanquan District of Zhangjiakou is taken as an example. Based on the existing double-row pile crown beam stiffness coefficient calculation method, the effect coefficient of the crown beam and the coupling beam is introduced to optimize and improve the effect of the coupling beam and the crown beam. The results show that (1) in the calculation of the double-row pile structure, the common lateral restraint effect of the crown beam and the connecting beam on the double-row supporting piles should be considered, and the rigid connection of the crown beam and the connecting beam should be taken as a whole to improve the rigidity coefficient of the double beam lateral support of a rectangular double-row pile. (2) The combined stiffness of the double-beam combined support system has a greater impact on the displacement of the pile top, and the displacement under a combined stiffness of 40-50 MN/m are close to the observed value. The calculated length of the crown beam and the introduced crown beam and connecting beam effect coefficient have a great influence on the combined stiffness of the double-beam composite support system. The combined stiffness decreases with the increase of the calculated length, and increases with the decrease of the effect coefficient. (3) The lateral support stiffness of the double-row piles under the double-beam composite support system is affected by the difference between the vertical and lateral displacements of the front and rear piles. The maximum lateral displacement of the front and rear piles is affected by the friction angle of the soil, the cohesion and the proportional coefficient of the horizontal resistance of the soil. Changing the tensile strength will not affect the displacement and deformation of the double-row piles. There is a displacement inflection point below the buried depth of the foundation pit and within the scope of the pile bottom. The displacement at the inflection point is equal under different friction angles and different cohesive forces.

Influence of cap beam restraint condition on the lateral deformation behavior of large-scale bored piles

The restrained force at the pile cap plays an important role in assessing the stability of bored piles. The constraining force of the cap beam is difficult to calculate due to spatial variability in soil properties, nonlinear soil behavior, and measurement errors. Based on theoretical analysis and field measurements this study proposes an analytical model combining Bayesian theorem and Markov Chain Monte Carlo Simulations (MCMCS) to quantify the restrained force of a pile cap beam. A simplified mechanical model of the constrained effect of the cap beam is established and verified by the results of field measurements. Based on a field excavated slope project, a Bayesian updating modeling approach is established by combing prior information, empirical knowledge, field instrumentation results, and site investigations to calculate the constrained effects of the cap beam. To verify its effectiveness, the model is combined with a finite element model, taking into account the uncertainties of soil moduli and measurement errors. The modeling takes into account the spatial variability and strain dependence of Young’s modulus. By comparisons, it can be found that the predicted displacements of the support pile are in good agreement with the field measurements. The results show that a Bayesian back updating approach can reduce the impact of uncertainty that can guide geotechnical engineering design and construction of similar projects.

The effect of thermal consolidation on bearing characteristics of static drilling rooted energy pile

Static drilling rooted energy pile is a new type of energy pile technology recently developed and promoted in soft soil areas. This technology has the advantages of green, low-carbon and good heat exchange effect. But its related basic theoretical research is still lacking. Therefore, the physical model of the static drilling rooted energy pile is deduced. The thermal consolidation settlement process of the soil around the pile is analyzed firstly based on one-dimensional thermal consolidation theory. And, the load transfer method is combined to derive the pile circumference under the coupling effect of load and temperature variation. The governing equations for frictional resistance and pile deformation are deduced and solved with numerical programs. Then an actual engineering case with static drilling rooted energy pile in soft soil area is calculated and analyzed. The results show that the temperature increase of the surrounding soil increases the relative displacement of pile and soil, which resulting in a decrease in the upper side friction resistance and an increase in the lower side friction resistance; and this effect will be enlarged during the cooling stage. The maximum axial addition stress caused by the temperature variation reaches 75.4% of the stress by load, so the influence of temperature changes on the bearing capacity of the pile foundation cannot be ignored. The research laid a theoretical foundation for the analysis and popularization of the static drilling rooted energy pile in coastal soft area.

A high-accuracy substructure method in the time domain for simulating pile-soil dynamic interaction in horizontal vibration

An accurate and efficient substructure method in the time domain is developed to simulate pile-soil dynamic interaction during horizontal vibration. The present method considers the equilibrium of a linear elastic soil in both the radial and circumferential directions to account for three-dimensional wave scattering, and considers the end bearing pile as a one-dimensional rod. First, an analytical expression for the soil resistance to a horizontal vibration pile in the frequency-domain is obtained. From this, an exact dynamic stiffness relationship between the soil resistance and the pile displacement is constructed at the pile-soil interface. Further, the dynamic stiffness relationship in the frequency domain is transformed into a high-order approximation in the time domain. Then, this high-order approximation is equivalent to a mechanical model system consisting of mass, dashpot and spring elements. Finally, the effectiveness of the present method is verified and the effects of the dynamic stiffness of the soil on the dynamic responses of the pile are investigated.

Estimation of bending moment and pile displacement for soil-pile-quay wall system subjected to liquefaction induced lateral spreading

The liquefaction-induced lateral spreading has been responsible for severe damages on the pile foundation during major earthquakes. Therefore, the seismic response of soil-pile-quay wall systems in liquefiable soils still needs further investigations. In this paper, a three-dimensional (3D) nonlinear dynamic finite element (FE) analyses are used and developed for the coupled dynamic soil-water system considering the soil, pile, and quay wall interaction. The numerical analysis efficiency was verified by the data of a large-scale (1 g) shaking table experiment. A parametric study was also investigated on the model to clarify the effect of each parameter, such as pile stiffness, pile diameter, and pile length, under various peak ground acceleration. On this basis, the results obtained indicate the three factors have significant effects on bending moment and pile displacement. Furthermore, it is observed that the depth of liquefaction changes as the peak ground acceleration changes. Based on the dimensionless soil-pile interaction parameter, a simplified method is provided for predicting the maximum bending moment and the maximum pile displacement of the pile group subjected to liquefaction induced-lateral spreading.

Damage Evolution of Concrete Piles Mixed with Admixtures in Marine Corrosion and Freeze-Thaw Environment

Marine corrosion and freeze-thaw environment will bring serious damage to marine concrete structures, leading to affect the safety and service life of structures. With the help of artificial climate and environment simulation laboratory, the variation of the compression strength and elastic modulus of concrete with the number of freeze-thaw cycles and corrosion time under the corrosion and freeze-thaw environment is studied. The results show that both of them firstly increase and then decrease with corrosion time. When the corrosion time is 270 d and the freeze-thaw time is 90 times, the strength of concrete decreases by 13% and the elastic modulus decreases by 5%. Then, based on the theory of damage mechanics, the damage evolution and constitutive model of concrete under the marine corrosion and freeze-thaw environment are established. Compared with the experimental results, it is found that the model can well describe the damage evolution characteristics of concrete under marine corrosion and freeze-thaw environment. Finally, a numerical model is established on the basis of elastic modulus and strength degradation model of concrete under marine corrosion and freeze-thaw environment. Elevated pile caps of concrete pile component are taken as an example to analyze the process of damage, and the change rules of displacement, deformation, and damage of concrete pile are obtained.

Dynamic responses of an end-bearing pile subjected to horizontal earthquakes considering water-pile-soil interactions

An analytical solution is developed to investigate the seismic responses of end-bearing piles considering water-pile-soil interactions. The pile is assumed to have a linear viscoelastic and circular cross-section. The soil and water are modelled as linear viscoelastic media and linear acoustic media, respectively. The seismic responses of the free-field soil displacement under horizontal earthquakes are first given. Neglecting water-soil interactions, analytical expressions for the impedance of the soil and water media are further derived. The pile displacements induced by horizontal earthquakes are then obtained based on the continuity conditions of the pile with soil and water. The present solution is compared with the substructure method to verify the rationality of the present analytical solution. Parametric analyses are finally conducted to investigate the effects of the water, soil, and pile parameters on the seismic responses of the pile. The results indicate that it is necessary to consider the water-pile-soil interaction in the design of piles installed in offshore areas.