Model Piles Research Articles

Influence of pile end soil on torsional vibration of pile considering the stress diffusion

This study focuses on the influence of the pile end soil on the torsional vibration of a pile based on a fictitious soil pile model considering stress diffusion. The pile end soil is simulated as a cone-shaped fictitious soil pile whose parameters remain the same as the soil. The dynamic equilibrium equations for the pile–soil system subjected to torsional dynamic loadings are developed and solved to obtain the corresponding analytical solution. Then, comparisons with other solutions are conducted to verify the reliability of the proposed solution. Finally, parametric analysis results are presented based on the proposed solution to portray the influence of the stress diffusion angle, thickness and shear wave velocity of the pile end soil.

Experimental Study on Inner Interface Mechanical Properties of the ESDCM Pile with Steel Core

The mechanical property of the pile-core–cement-soil interface is a crucial factor affecting the shaft capacity of the expanded stiffened deep-cement-mixing (ESDCM) pile. The research on the characteristics of the steel-pipe–cement-soil interface is very limited, and the conventional concrete–cement-soil interface research results cannot provide direct guidance for the engineering application of the steel-pipe–cement-soil combination pile. Hence, in this study, we employed a model pile with a steel-pipe–cement-soil combination. By using a confining pressure transfer test and an inner interface shear test, the influence of confining pressure on the inner interface and shear deformation of the inner interface were investigated. The results demonstrated that the lateral confining pressure has almost no effect on the inner interface due to the encapsulation of the soil-cement column. The interface shear experienced four stages: the steel pipe small deformation, which is the extra stage compared to the common concrete–cement-soil combination form; the whole pipe compression; the brittle failure; and the shear-slip stage. The peak shear stress at the interface is 194 kPa, and the corresponding pile core top displacement and core bottom displacement are 5.9 mm and 5.4 mm, respectively. The inner interface bond coefficient is only 0.052, indicating that even the smooth steel pipe can work closely with the cement-soil at a low bonding coefficient. Further optimization of the steel-pipe–cement-soil interface structure can be an essential means to improve the mechanical properties of the pile. When the upper load is transferred downward, it spreads around through the cement-soil, and as the load increases, the load that can finally be transferred to the deep part accounts for a relatively small amount, only about 7%. This work promotes the understanding of the interface mechanical properties of ESDCM piles and guides the application of an ESDCM pile with a steel core in practical engineering.

Zoning operation of energy piles to alleviate the soil thermal imbalance of ground source heat pump systems

• Zoning operation of energy piles is investigated to alleviate soil thermal imbalance. • Dense heat injection into the central piles can relieve the cold accumulation. • Heat extraction from the outer layer piles can relieve the cold accumulation. • A reasonable strategy is proposed to achieve good system efficiency and reliability. Energy piles have attracted increasing interest for application in ground source heat pumps, because it is environment-friendly, energy-efficient, and without additional drilling cost. However, when there is a large difference between the heating and cooling loads, the system will suffer from a soil thermal imbalance which may further decline the system performance and even cause a system failure. A hybrid ground source heat pump system that integrates auxiliary equipment can solve the problem, however, it needs additional investment and a complicated control strategy. In this paper, the zoning operation of energy piles can effectively improve the temperature recovery ability of soil in the energy pile group and thus alleviate the soil thermal imbalance. Specifically, a heating-dominated residential building in Beijing is selected for a case study, with 144 energy piles arranged in a 12 × 12 layout. An analytical model of the spiral-coil energy pile group with seepage will be adopted, which can consider the groundwater flow, the geometry of spiral coils, and the thermal interaction among different energy piles, achieving high calculation accuracy and fast calculation speed. Based on this analytical energy pile model, a system model will be built to investigate the system performance influenced by different zoning operation strategies. Results show that intensive heat injection into the center of the pile group (Strategy 2 and Strategy 3) or heat extraction from the outer layer of the pile group (Strategy 4) can relieve the cold accumulation. Strategy 2 can relieve the outlet temperature decline from 5.54 °C to 4.46 °C and improve the heating COP from 3.297 to 3.423 compared to the conventional full operation strategy. Although the annual heat pump COP of Strategy 2 is a little lower than that of conventional full operation strategy, Strategy 2 has the shortest unmet heating or cooling time. Therefore, the proposed zoning operation strategy can achieve good system efficiency and excellent system reliability compared to the conventional strategy.

Analytical solution for vertical vibration of partially embedded large-diameter floating pile

A rigorous analytical model for partially embedded large-diameter floating pile (PLFP) is devised based on a three-dimensional continuum pile and soil model. The analytical solutions to the dynamic response of PLFP are obtained using Fourier transformation and variable separation. Then, the accuracy of the obtained dynamic impedance and velocity is verified by comparing the derived values with existing solutions and the measured data of the experimental model. Finally, parameter analyses of dynamic impedance and velocity response are conducted. The results indicate the following. The use of a one-dimensional pile model to calculate the dynamic impedance of PLFP results in the overestimation of resonance amplitude and frequency. Defect detection is more difficult to implement in a partially embedded pile than in a fully embedded pile. In practice, the suitable position for a signal receiver installed on a pile head during low-strain pile integrity testing is 0.6r0.

Comparative Analysis of Single Pile with Embedded Beam Row and Volume Pile Modeling under Seismic Load

Abstract Indonesia is located between the Eurasian, Pacific, Philippines, and Indo-Australian plates. Various tectonic processes in the world and collisions between large plates and several small plates trigger many earthquakes in Indonesia. This study aimed to evaluate the response of bored piles in the Auditorium Building of Brawijaya University toward seismic loads through analytical and numerical approaches based on finite elements with 2D (embedded beam row) and 3D (volume pile) modeling, where the analysis approach of pile deformation and lateral resistance with numerical methods will depend on idealization of the model used. In addition, the lateral resistance was compared based on combination lateral loads, pile stiffness, and soil stiffness when the values were different. The 2D finite element analysis reduces lateral resistance but overestimated the deflection on the pile surface. This is because in the 2D finite element modeling with an embedded beam row that the friction factor represented by the spring can reduces the stiffness and the pile–soil is tangent, so that there is no slipping against each other. In addition, the 3D finite element analysis with volume pile modeling increases soil stiffness at greater depths and the friction factor (interface) can improve the interaction between the soil and pile.

Model Test Study on the Load-bearing Behaviour of Multi-tooth Piles under Different Bearing Layers

In soft soil or karst areas, several problems exist, such as the poor properties of the pile tip bearing layer or difficulties in cutting the rock. Using multi-tooth piles, end-bearing piles can be turned into friction piles to solve these problems. Through the scale model device, three variables: the bearing layer, tooth length, and tooth number, are designed to experimentally explore the load-bearing behaviour of multi-tooth piles under different bearing layer conditions. The test results show that the model pile has better anti-settlement performance in the sand bearing layer than in the red clay bearing layer. Compared with smooth piles, multi-tooth piles can greatly improve the bearing capacity of pile foundations in bearing layers with poor stiffness. The tooth length and tooth number greatly impact the compressive bearing capacity and the pile-side resistance of the multi-tooth pile, respectively. The concept of roughness is innovatively introduced to quantify the roughness of pile surfaces, which provides an effective method for the subsequent experimental and theoretical research of multi-tooth piles and other similar piles with small cross-section modifications. This study can enrich the research field of small, modified cross-section piles and provide a reference for innovative research on pile foundations.

A new approach for improving lateral performance of pile foundations in seasonally frozen regions

Ground freezing in cold areas can cause brittle damage to deep foundations during seismic loading. This paper presents a novel solution to this problem by replacing local soil around the pile with a temperature-insensitive composite material, namely polyurethane glue-bonded rubber particles-sand mixture (PolyBRUS). Three 1/12 scale reinforced concrete pile foundations embedded in unfrozen, frozen, and frozen with local replacement conditions were prepared, and quasi-static cyclic loading tests were conducted to reveal the adverse effects of seasonal freezing on pile foundations and verify the performance of the proposed solution. The model preparation, including model pile configuration, model construction, sensor configuration, and frozen soil formation, were described in detail. The pile foundation lateral performance data, including failure mode observations, lateral load-displacement hysteresis relations, and moment distributions, were presented. The evolution of secant stiffness and energy dissipation of the pile-soil system with lateral displacement were analyzed and discussed. It was found that the peak lateral load of the model pile in 20 cm-thick seasonal frost is 53% larger than the unfrozen conditions. In contrast, the ultimate displacement in seasonally frozen conditions is 25% less than that in unfrozen conditions. And seasonal freezing can render a pile from ductile to brittle failure. More importantly, the results show that the local replacement with the proposed material can ensure similar lateral behavior for the soil-pile system under both unfrozen and frozen conditions. It is concluded that the proposed local replacement approach offers excellent potential for mitigating the adverse effects of seasonal freezing on the lateral performance of deep foundations in cold regions. In future studies, local replacement zone optimization and large-scale field tests are recommended to further confirm this method's effectiveness and provide design parameters for pilot testing.

Probabilistic method for the size design of energy piles considering the uncertainty in soil parameters

Energy piles have attracted increasing attention as profitable solutions for the utilization of shallow geothermal energy. Although various complex geotechnical design models of energy piles have been proposed, a simplified sizing method that considers the uncertainty propagation in the soil is required. In this study, a Monte Carlo Simulation-based method was proposed for the size design of energy piles considering the uncertainty of parameters in the soil, such as thermal conductivity and friction angle. The small-sample analysis method of Markov chain Monte Carlo simulation combined with the Bayesian theoretical framework was developed to generate equivalent samples. Subsequently, the thermal response function and thermomechanical load transfer methods were employed to address the failure probability of the energy pile in the serviceability limit state and ultimate limit state. In addition, a case study was presented to illustrate the implementation of the proposed probabilistic sizing method. The analysis results of the case study confirm the necessity of modeling the soil uncertainty in the energy pile size design.

Durability life prediction and horizontal bearing characteristics of CFRP composite piles in marine environments

In this paper, the durability life and horizontal bearing characteristics of carbon fiber reinforced polymers (CFRP) composite piles in marine environments are studied. The durability life of CFRP composite piles is divided into the initial corrosion stage of reinforcement and the crack propagation stage of concrete protection layer. The chloride diffusion model and Monte Carlo simulation method are used to predict the initial corrosion time of CFRP composite piles. Based on the thick-walled cylinder theory, the critical corrosion depth of the reinforced steel corresponding to the cracking of concrete protective layer is deduced. The durability life prediction model of crack propagation stage is established. The flexural stiffness reduction factor of CFRP composite piles with different replacement ratios is obtained by conducting the model pile bending tests. The attenuation law of bending stiffness and horizontal bearing characteristics of CFRP composite piles in marine environments are analyzed. The results show that the higher the replacement ratio of CFRP bar, the slower the reduction rate of flexural stiffness of CFRP composite pile is. Under the same buried depth, the pile bending moment and shear force of CFRP composite piles decrease with the increase of CFRP reinforcement replacement ratio. The horizontal displacement of CFRP composite piles increases with the increase of CFRP reinforcement replacement ratio.

Model and field tests of drilled displacement system piles

Drilled Displacement System (DDS) and Continuous Flight Auger (CFA) piles are two popular techniques used for building pile foundations that offer advantages over traditional pile systems, including improved load-carrying capacity, reduced installation time, and less spoil generation. This article presents laboratory-scaled model tests conducted on model piles installed using the Drilled Displacement System (DDS) and Continuous Flight Auger (CFA) technologies on a test tank setup filled with soil. Model piles considering a scaling factor of 1/20 with a diameter of 20 mm and a length of 300 mm were adopted for the study. Static loading is applied to the model piles and the corresponding displacements are measured during each loading phase. The results of the analysis were compared for load-settlement curves and ultimate bearing capacity estimates for both DDS and CFA piles. Based on the study, the DDS piles were observed to perform well in terms of load-carrying capacity compared to the CFA piles. Further, full-scale field tests under static load conditions were carried out on DDS-drilled piles of diameter 400 mm and length 6 m. The load-settlement response from the field test shows good agreement with the model tests. Overall, the results of the study provide valuable insights into the behavior and performance of DDS piles that can be used to optimize their design and installation in different soil types.

Characteristics of Pile Models Injected by Low-Pressure-Injection Laboratory Setup for Chemical Improving Loose Sandy Soil

The jet grouting method for soil improvement is a novel geotechnical alternative for enhancing problematic soils where traditional foundation designs cannot provide sustainable solutions. The paper methodology was based on improving loose fine sandy soil using silica fume as a chemical additive added (with 10 percent of the cement weight) to the water and Portland cement mixes with different W/C ratios to produce pile models injected by a low-pressure injection laboratory setup that was designed and locally manufactured for this purpose. The setup design was inspired by previous research works, where its performance was validated by systematically performing unconfined compression tests (UCTs) on samples of the laboratory-injected pile models. Based on the UCTs results, high determination coefficient (R2) mathematical models were developed that related the W/C ratios of the injected mixtures to the basic parameters (cohesion, friction angle, and elasticity modulus) of the grouted pile models, validating the laboratory setup injection efficiency.

Research on interactive experience design of tram charging pile based on user perspective—Taking Quanzhou Normal University as an example

This research takes the target user experience and interaction optimization as the core, AEIOU, ELITO, weight matrix analysis model as the research basis, Quanzhou Normal University charging pile online operation model as the research object, adds quantitative design research scheme analysis, builds a new interaction model, comprehensively covers each contact and crowd status, behavior, etc. in the charging step, makes a comprehensive analysis, and puts forward key issues in different emotional points The significance and purpose, and the design goals and ideas are given in order to find new design opportunities for the interactive design of the charging pile.

Experimental Investigation of Helical Pile Performance for Loess Deposits Improvement

Collapsible loess is classified as problematic soil found on most continents. The loess immediately collapses under stresses induced by axial compressive loading or the soil weight when exposed to moisture. In Iran, vast areas of the Golestan province are covered with Aeolian loess deposits. This paper investigates whether the simultaneous effect of inundation and pre-loading in helical pile installation is operative and effective in improving Golestan loess. The effect of installation conditions on loess collapsibility is studied via two main approaches, i.e., field investigations and physical modeling. The experimental studies include the installation of ten single and triple helix piles in the Amirkabir University of Technology Frustum Confining Vessel, i.e., FCV-AUT. Also, ten single and double helix piles with embedment depth of 3 to 6 m and a helix diameter of 250 mm were installed in Golestan province, and full-scale pile static loading tests were performed. The results indicated that the simultaneous application of crowd loading and water pressure during the installation of helical piles results in collapsibility potential reduction due to the soil treatment. Moreover, high or low crowd loads accompanied by water pressure during pile installation bring about similar load-displacement behavior of model piles installed in FCV-AUT and full-scale helical piles. Eventually, it was illustrated that the applied improvement technique is effective on loess soils since it uses the least amount of material, machinery, and equipment while attaining the highest possible bearing capacity ratio regarding sustainability.

Study of negative friction forces in laboratory conditions

The article laboratory studies are presented to determine the magnitude of negative friction forces on the lateral surface of model piles and the patterns of action of negative friction forces in the spectrum of factors influencing the magnitude of these forces are identified.

Soil-structure pile foundation interaction model due to lateral loading

Experimental research on piles, by models and physical tests on a laboratory scale, using materials and sizes that are different from the prototypes. The model is designed, treated, and interpreted the results of observing the response based on similarity using Model theory, but the soil sample cannot be modeled with model theory, giving rise to doubts similarity of the research. This study was conducted to examine the effect of pile-soil interaction on several views of the elastic modulus of the soil due to lateral loads. Laboratory model pile foundations are laterally loaded, on soil samples in a test box. The deflection of the pile foundation is analyzed based on the use of linear, layered, and non-linear modulus of elasticity. A non-linear simulation of the Winkler model with a spring along the depth of the pile was carried out to calibrate the horizontal deflection of the laboratory experimental model. The results showed that the Winkler model's modulus of elasticity was approximately 40% of the pile length, and the non-linear difference between the Winkler and laboratory models was 10.77%, comparisons can be conclusive about the need for similar research on lateral loading of laboratory model piles. The analysis also noted that the surface deflection was determined by winkler’s model elastic modulus analysis with an excess of about 12% to 14% in the first 10% of the pile length.

Low-Strain Damage Imaging Detection Experiment for Model Pile Integrity Based on HHT

Low-Strain Damage Imaging Detection Experiment for Model Pile Integrity Based on HHT

Experimental modeling of a single pile in liquefiable soil under the effect of coupled static-dynamic loads

Experimental modeling of a single pile in liquefiable soil under the effect of coupled static-dynamic loads

Uplift Load Carrying Capacity of Cylindrical and Belled Pile in Cohesive soil Bed

Foundation of some structures like transmission towers, mooring systems for ocean surface or submerged platforms, tall chimneys, jetty structures etc. are subjected to uplift loads. Literature reflects that scholars have conducted pull out field prototype and model test and failure pattern of soil is studied for belled piles in loess soil and cohesionless soil. In this research work, the authors have carried out 36 tests on single pile and pile groups and uplift load carrying capacity is obtained by experimental investigation of single pile, triangular pattern (2x1) and square pattern (2x2) using the model piles of cylindrical and belled shaped in cohesive soil of soft consistency. The piles are having 20 mm shaft diameter and varying L/d ratio of 6, 8,10,15,18 and 20 for both cylindrical pile and belled pile. Belled portion is cast in belled pile with an angle of 70° with horizontal and having base diameter of 60 mm and height 55 mm. Spacing between two piles in various pile group was kept three times the piles shaft diameter (3d) in all experiments. Based on the experimental results as the L/d ratio increases uplift load carrying capacity increases. Uplift load carrying capacity of single pile, triangular pile group and square pile group of belled pile is 410%, 280% and 240% more than cylindrical piles. Uplift load carrying capacity of triangular pile group and square pile group increases by 182% and 273% for cylindrical pile and 104% and 141% for belled pile in comparison with single pile. Failure pattern of soil is obtained from experiments performed on belled pile and by using this failure pattern, theoretical uplift load carrying of belled pile is obtained.Uplift load carrying capacity.

Physical model study of pile type effect on long-term settlement of geosynthetic-reinforced pile-supported embankment under traffic loading

In coastal area, the long-term settlement of high-way embankment is seriously concerned. Geosynthetic-reinforced pile-supported (GRPS) embankments have been widely adopted for the construction over soft soils to solve the large settlement problem. However, the long-term performance of GRPS embankment under traffic loadings is not fully understood. In this study, a series of physical model tests were conducted. Different pile types (rigid pile, rigid-flexible pile, flexible pile) and geosynthetic layers (single-layer and double-layer) were comparatively investigated. Two stages of long-term cyclic loadings were applied to simulate the traffic loadings. Based on the results, it is found that the model test with rigid pile has the least settlement, whereas the model test with flexible pile experiences the largest settlement when subjected to both 1 Hz and 2 Hz cyclic loadings. In the view of long-term settlement control, the rigid pile is the best choice for the GRPS system. The applied cyclic loadings have the lowest effect for the pile strain distribution in rigid pile model but much higher effects in both flexible pile and the rigid-flexible pile models, which demonstrates that the traffic loading after the construction of GRPS embankments may leads to unneglected stress redistributions. The findings of this study would provide the reference to consider the traffic loading effects on different pile types of GRPS embankment.

THE RESULTS OF LABORATORY STUDIES OF THE OPERATION OF MODELS OF PYRAMIDAL-PRISMATIC PILES ON THE EFFECT OF VERTICAL PULLING LOAD IN CLAY SOIL

This paper presents the results of laboratory tests of models of pyramidal-prismatic piles on the effect of vertical pulling load. The experiments were carried out in clay soil. It is established that models of pyramidal-prismatic piles, depending on the size of the pyramidal section, can have both greater and lesser resistance compared to prismatic and pyramidal (control) piles. Thus, it was found that the resistance of pyramidal-prismatic piles to the pulling load is 1.19-1.80 times higher than the resistance of a model of a prismatic pile with a cross-section size of 20×20 mm. Compared with the model of a prismatic pile with a cross-section size of 30 ×30 mm and with the model of a pyramidal pile (with a cross-section size of 30×30 mm at the top and 20×20 mm at the bottom), the models of pyramidal-prismatic piles have less resistance (by 6-45%). An increase in the size of the upper section of the pyramidal part of the PPP has a more significant effect on increasing their resistance to pulling out than an increase in the length of their pyramidal section. Correlations have been established that can be used for a preliminary assessment of the resistance of pyramidal-prismatic piles to the pulling load relative to the resistance of traditional (prismatic and pyramidal) piles.