Model Piles Research Articles

Comparison of bearing capacities of model drilled micro piles using DDS and CFA technologies

Drilled piles installed using CFA (Continuous Flight Auger) and DDS (Drilled displacement system) technologies are relatively new construction products in the market of Kazakhstan for the last 15 years, but already today the technology has a significant practical value in the construction of the cities of Astana, Almaty and other regions. This article presents model tests of bored piles installed using Drilled Displacement System (DDS) and Continuous Flight Auger (CFA) technologies on a volumetric bench. For testing we used 1:20 scale, piles diameter was 20 mm, length was 300 mm. Drilling was performed using augers that were prepared in advance through a 3D printer. The load on the model piles was applied in steps of 39 N up to the ultimate load of 391 N. Based on the results of the study, the «settlement-load» plots of the DDS and CFA model piles were obtained, as well as a comparison of the bearing capacity of these piles by static test method. Based on the study, it was found that the DDS piles exhibit good bearing capacity performance compared to the CFA piles. Overall, the results of the study provide valuable information on the performance behavior of DDS and CFA piles, which can be used to optimize their design and installation in different soil types.

Experimental Modelling of Helical Piles Subjected to Axial Loading

In the construction sector, axial loads have traditionally been supported by piles. There hasn't been sufficient comparative study related to the economics and viability aspects of conventional and helical piles up to this point in natural soil condition. The current study was conducted to test the behavior of helical piles subjected to axial loading and the results were compared with the conventional pile counterpart. For this, a total of eighteen experiments were performed with varying number of helical piles either single or multi helical piles in a raft. Helical piles were penetrated into ground, vertical load of 512 kg was applied and the settlements were recorded with the gauges installed. The reduction in settlement was found to increase due to increasing the number of piles, inter distance between the piles and increasing the number of helices. Nine double helical piles were observed to reduce settlement by 80.5% when compared to nine conventional piles. Due to the smaller number of piles needed to support the applied axial load when employing helical piles as opposed to conventional piles, the cost was greatly lowered.

ОСОБЛИВОСТІ РОБОТИ КОРОТКИХ ПАЛЬ ПРИ ПІДСИЛЕННІ ФУНДАМЕНТІВ МІЛКОГО ЗАКЛАДАННЯ ЗА РЕЗУЛЬТАТАМИ ФІЗИЧНОГО МОДЕЛЮВАННЯ

In this work, the results of physical modeling of the strengthening of the foundation of shallow laying by transplanting on piles on small-scale models are analyzed. The redistribution of the load between the elements of the strip foundation reinforced with ready-made (precast) piles of shallow laying was studied. The operation of the existing strip foundation, its reinforcement with piles, the formation of the grid of the newly created pile foundation was simulated, while the relative length of the piles and their step along the row, the nature of the placement of the reinforcement piles (removable or arranged through the body of the foundation), and the density of the sand base were varied. The operation of models of single piles of different lengths and grid without piles as a foundation for shallow laying was also investigated. The nature of inclusion in the work of piles and the newly created grid is determined. The dependences of the load-bearing capacity of the elements of the pile foundation, the degree of realization of this load-bearing capacity when working together in the soil environment, and the relative length and pitch of the piles, and the density of the base soil are given. The specific values of the load-bearing capacity of the reinforcement piles per unit of spent material are determined.
 The obtained results were analyzed regarding the difference between the inclusion of short and long piles in the work of reinforcement with a comparison of all options.

Performance Study of Casing Piles in Expansive Soil Foundations: Model Testing and Analysis

This study investigates the critical behavioral characteristics of pile foundations in expansive soil foundations through a series of model tests, including settlement, axial force, and side frictional resistance. The experiment initially utilized sand, bentonite, and gypsum as the fundamental materials for the preparation and composition research of expansive soil simulant materials. Subsequently, the performance of different types of model piles under various loads and water immersion conditions was analyzed. The results indicate that non-cased piles exhibit typical friction pile behavior, while PVC-cased and steel-cased piles effectively reduce side frictional resistance, resulting in a more uniform distribution of axial force along the pile. After immersion, the model test materials experience expansion, with a faster initial expansion rate and a more gradual later expansion rate. Different types of model piles exhibit different displacement characteristics, and the presence of an outer casing can reduce the uplift of the inner pile. Furthermore, PVC casing demonstrates better performance in handling negative frictional effects. This study provides valuable insights for the design and construction of pile foundations in expansive soil foundations.

Bearing capacity of a driven hanging piles with longitudinal grooves on their side surface

The article considers the influence of longitudinal grooves of various geometric shapes on the side surface of factory-made driven reinforced concrete piles on their bearing capacity. Information is given on previously performed experimental studies (laboratory and full-scale testing) of changes in the bearing capacity of piles with grooves. The research was carried out on models of piles in a tray and using driven reinforced concrete full-scale piles in the field. Full-scale piles and models of piles had wedge-shaped and semicircular grooves on the side surface, which were placed on one, two and three sides. Based on experiments, an increase in the bearing capacity of piles with grooves in clay soils has been established. The article also provides a theoretical analysis of the influence of the depth of wedge-shaped and semicircular grooves on the operation of the piles under consideration. By solving the optimization problem, formulas were obtained for calculating the optimal depth of wedge-shaped and semicircular grooves on the side surface of reinforced concrete piles. A comparative analysis of the efficiency of work in clay soils of driven hanging piles with longitudinal grooves of wedge-shaped and semicircular shape is carried out. In conclusion, the main conclusions are formulated based on the results obtained. It is established that the optimal depth of wedge-shaped and semicircular grooves depends on the mechanical characteristics of the soils, the length of the piles, the angle at the top of the groove (for wedge-shaped grooves) and does not depend on the size of the cross-section of the pile and the number of grooves. It was also revealed that the bearing capacity of a pile with grooves of optimal depth always exceeds the bearing capacity of a similar pile without grooves. The article compares the efficiency of piles with wedge-shaped and semicircular grooves.

Machine learning based prediction model for the pile bearing capacity of saline soils in cold regions

The difficulty in determining the bearing capacity of pile foundations in saline soil environments in cold regions can pose a challenge when developing a bearing capacity prediction model. To address this, the study uses data from the construction of the De Xiang Expressway project in Qinghai Province, China, and considers pile length, pile diameter, corrosion depth, and spalling thickness as influential parameters. We combine Python with ABAQUS to build a finite element model of a single pile in a salt marsh environment with random parameters and develop a database for machine learning. We use the kernel ridge regression (KRR) and multilayer perceptron (MLP) algorithms to establish load-bearing capacity prediction models for vertical and horizontal loads, respectively. The SHAP (SHapley Additive exPlanations) method is employed to perform explanatory analysis on the prediction models, providing insight into influential parameter effects on prediction accuracy. The results demonstrate that the database established through the random parameter finite element method is suitable for machine learning. While the KRR model exhibits good performance in predicting vertical load-bearing capacity, the MLP model performs well in predicting horizontal load-bearing capacity. Moreover, the SHAP method effectively explains the importance of influential parameters on the prediction results and enhances the reliability of the prediction models. The vertical bearing capacity of a saline soil pile foundation is more affected by the depth of salt erosion than the thickness of spalling, while the horizontal bearing capacity is more affected by the thickness of spalling than the depth of salt erosion.

Numerical modeling of pile embedded in crushable sand subjected to earthquake loading

Numerical modeling of pile embedded in crushable sand subjected to earthquake loading

Performance Assessment of Pile Models Chemically Grouted by Low-Pressure Injection Laboratory Device for Improving Loose Sand

The complexity and partially defined nature of jet grouting make it hard to predict the performance of grouted piles. So the trials of cement injection at a location with similar soil properties as the erecting site are necessary to assess the performance of the grouted piles. Nevertheless, instead of executing trial-injected piles at the pilot site, which wastes money, time, and effort, the laboratory cement injection devices are essential alternatives for evaluating soil injection ability. This study assesses the performance of a low-pressure laboratory grouting device by improving loose sandy soil injected using binders formed of Silica Fume (SF) as a chemical admixture (10% of Ordinary Portland Cement OPC mass) to different (W/C) water/cement ratios (by mass materials) mixes. Trial grouting processes were executed to optimize the practical ranges of the operating factors of the laboratory device to obtain consistent grouted model pile samples. The paper examined the relations of the binders' W/C ratios with the densities, elasticity modulus (E), and Uniaxial Compression Stress (UCS) of the grouted piles. The investigation results show that as the binder W/C ratio rises, the grouted pile samples' dry density, E, and UCS values decrease. For the binder injected with a W/C ratio of one and 10% SF additive by weight of cement mass, the highest values of the grouted pile for density, E, and UCS were about 2.32 g/cm3, 23 MPa, and 2000 MPa, respectively. The UCS of the grouted pile proved that the binders' W/C ratios and the SF addition have an evident effect on the investigated factors of the grouted piles.

Effect of Solidified Depth on the Vertical Compressive Bearing Characteristics of the Soil Continuously Solidified Pile Group Foundation

To meet the ultra-high bearing capacity design requirements of pile foundations under geological conditions without a good holding layer, we invented a new type of group pile foundation with the soil continuously solidified between piles (hereinafter referred to as the SCS group pile foundation). Considering the solidified depth as a key influencing factor, the vertical ultimate compressive bearing capacity, load transfer law, and damage pattern of the soil around the continuously solidified group pile foundation were investigated using an indoor half-model test. The results revealed that the setting of the continuously solidified part has a significant effect on its compressive bearing characteristics. The ultimate compressive bearing capacity of the SCS group pile foundation was increased by four to nine times compared with the traditional group pile foundation. When the pile spacing is 4–6D (D = pile diameter), designing a continuously solidified depth greater than 14D is recommended. Except for the solidified depths of 2D and 18D, the lateral resistances of the other model piles first increase and then decrease with increasing depth. The maximum values were located at the continuously solidified part and were obviously larger than those of the other pile sections. The maximum pile lateral frictional resistance was provided at the maximum depth of the continuously solidified part. After setting up the continuously solidified part, none of the bearing capacity of the pile ends exceeded 5%. The bearing capacity of the SCS group pile foundation was mainly shared by the continuously solidified part and the pile lateral frictional resistance. For the same pile spacing, the high strain damage zone of the soil at the bottom of the continuously solidified 2D–14D foundation was “abacus bead”; when the burial depth of the continuously solidified part reached 18D, the foundation soil exhibited “inverted bowl” damage.

Material point method simulations of displacement pile and CPT penetration in sand considering the effects of grain breakage

Full displacement installation dramatically alters the stress and strain fields applying around piles and Cone Penetrometer (CPT) probes at sand sites. Calibration chamber tests have indicated that severe particle crushing occurs near to the pile or cone tips and a distinct shear zone may develop that leaves crushed sand adhering to the pile or cone shaft. It is therefore important to investigate how particle breakage affects the stress and deformation fields developed as this process occurs. In this study, installation by monotonic jacking of conically tipped model piles or CPT probes into silica sand is simulated by material point method (MPM) analyses. A thermodynamically consistent model which considers competing grain crushing and dilation is employed to model the sand behavior, while an MPM approach is adopted to cater for the large deformations involved in the penetration process. Particle crushing is predicted beneath the pile tip and around the pile shaft. The numerical results are compared to directly related instrumented pile calibration chamber tests. The numerical results show that the computed stress and displacement fields match key aspects of the experimental results well, especially in reproducing the volumetric compression observed experimentally. The results confirm that combining MPM with suitably sophisticated constitutive models creates new capabilities for analyzing large-deformation problems.

Correction: A dynamic p–y model for piles embedded in cohesionless soils

Correction: A dynamic p–y model for piles embedded in cohesionless soils

Soil plug behaviour of open-ended model piles jacked in cohesionless soil

ABSTRACT The objective of this study is to investigate the behaviour of soil plugging of open-ended pipe piles under various soil and pile conditions. Extensive laboratory tests were conducted on small-scale model pipe piles installed in sand with varying soil conditions. The diameter of the pile, soil density, rate of penetration and the degree of saturation all influenced the soil plugging behaviour. The laboratory test results indicated that the length of the soil plug typically increases as the diameter of the pile increases and the relative density of the soil decreases. Additionally, the plug length decreases as the matric suction value increases. The jacking force was found highly dependent on the plugged length and particle properties of the soil. The effect of penetration speed on soil plugging and load settlement behaviour were also investigated. Finally, a correlation has been developed between the plug length ratio (PLR) and the incremental filling ratio (IFR).

Oblique tensile tests on model anchor piles in calcareous sand deposits

Offshore anchor piles are extensively used as moor-floating structures in harsh environments that experience oblique tensile loads and the mechanical response is complex. This study investigated the effect of oblique tensile loads on the response of anchor piles in calcareous sand through a series of model tests and the standard penetration tests (SPT) to obtained bearing capacity equations. Eight model piles were installed into the calcareous sand bed with relative densities (Dr) of 53%, 75% and were loaded with different load inclination angles (α). The test results showed that the load-displacement curves were nonlinear and that dense sand could effectively control deformation and improve the bearing capacity. The critical load inclination, corresponding to the maximum load capacity for a given pile under tension loading, was around 30° and was larger than that for the terrestrial sand (5°∼10°), which may have been caused by particle breakage. The bending stress of the anchor pile was 2∼8 times the axial stress. In dense sand (Dr = 75%), the bending moment reaches its maximum around the critical angle (30°), indicating a the strong interaction between the pile and calcareous sand. The ultimate tensile load of anchor piles is a function of load inclination angle and ultimate capacity of uplift and horizontal piles.

Non-destructive method for evaluating local integrity of model piles using electromagnetic waves

The objective of this study is to suggest a more accurate integrity estimation method in drilled shafts using electromagnetic waves propagating through transmission lines. Model piles, whose dimensions were 3.0 m in length, 0.2 m in height, and 0.2 m in width, were prepared. In the center of model piles along the length, the rebar and transmission line with 0, 1, 2, or 3 connectors were installed. In the middle of model piles, defect segments with length of 1.0 m were prepared The defect segments were filled with air, sands with different water contents, and water. The experimental results show that the velocity of the electromagnetic waves are dependent on the properties of the medium surrounding the transmission line. Although defects were detected in the transmission line without the connector, the location and size of defect were not clearly identified. However, for the transmission line with connectors, the location and size of sound and defect segments were more clearly identified using the velocity of electromagnetic waves determined between the connectors. This study suggests that transmission line with connectors may be effectively used for a more accurate evaluation of the integrity of drilled shafts.

Predicting monotonic lateral load-displacement behavior of offshore flexible piles in saturated MCC soils: An application of the cavity expansion theory

This paper proposes an application of the cavity expansion theory to predict the load-displacement response of monotonically laterally loaded piles and the effective stress distribution of saturated modified Cam-clay (MCC) soil surrounding the pile. This approach incorporates geometric relationship, equilibrium equation, and boundary conditions to derive governing equations. These equations are subsequently solved to obtain monotonic p-y curves, which encompass the elastic, elastoplastic, and critical processes. To determine the load-displacement behavior and effective stress distribution of the soil, the proposed approach combines the deflection equilibrium differential equation with the finite-difference method. The accuracy and effectiveness of the approach are validated through a comparison with a Finite Element Method (FEM) simulation. Parametric studies are also presented to investigate the effects of overconsolidation ratio, in-situ coefficient, and mean effective stress. The validity and capacity of the proposed model are further demonstrated using model pile tests. The results affirm that this approach can well predict the monotonic load-displacement response of the pile and effectively captures important phenomena observed in pile tests.

Study of Load Calculation Models for Anti-Sliding Short Piles Using Finite Difference Method

Anti-sliding short piles, a novel technique for slope stabilization, have been applied in engineering practices. Nonetheless, a mature structural calculation theory for these piles is still lacking. In this paper, the study presents an internal force solution model for anti-sliding short piles using the finite difference method. By extending the Euler–Bernoulli beam theory and defining boundary conditions, this study develops a set of finite difference equations for computing the structural forces of anti-sliding short piles. Furthermore, this study conducted laboratory model tests on soil landslide cases reinforced with anti-sliding short piles. By comparing the internal forces and deformations of these piles, the test validates the proposed calculation model for anti-sliding short piles. The results suggest that treating the load-bearing and embedded sections as a unified entity during the calculation process, instead of applying continuity conditions separately at the sliding surface as performed in traditional methods, simplifies the complex solving procedure. Moreover, under identical loading conditions, the displacement, bending moment, and shear force data obtained through the finite difference method closely coincide with the measurements from the model tests, confirming the reliability of the anti-sliding short pile calculation model. Additionally, this study demonstrates that reducing the spacing between nodes along the entire anti-sliding short pile, i.e., decreasing the value of the differential segment length ‘h’, results in more precise computational outcomes. This research offers valuable insights and references for sustainable solutions in the realm of geological disaster prevention and control.

Lateral Dynamic Response of Helical Pile in Viscoelastic Foundation Considering Shear Deformation

Helical piles are a new type of pile that has good application prospects, and researchers have carried out an in-depth investigation into their vertical uplift and compressive bearing capacity. However, there is relatively little research on the dynamic bearing characteristics of helical piles. Therefore, the lateral vibration of a helical pile embedded in the viscoelastic foundation is systematically studied in this article. Utilizing the equivalent stiffness method to transform a helical pile into a cylindrical pile of special diameter, the lateral vibration model of the helical pile considering shear deformation is established based on the Winkler foundation model and the Timoshenko beam theory. The analytical solutions for the lateral dynamic displacement, bending moment, and shear force of the helical pile are strictly derived, and the rationality of the present solutions is also verified by comparing them with existing solutions. Based on the present solutions, a parametric study is carried out to investigate the influence of the pile and soil properties on the lateral dynamic response of the helical pile. It is found that the load excitation frequency and pile–soil stiffness ratio have a significant influence on the lateral dynamic displacement, bending moment, and shear force of the helical pile with space and time response.

Experimental Study on Post-Grouting Pile Vertical Bearing Performance Considering Different Grouting Methods and Parameters in Cohesive Soil

The selection of grouting methods and parameters significantly affects the improvement in the pile-bearing capacity of cast-in-place bored piles. This study proposes a comprehensive set of test methods for constructing model piles, performing grouting at the pile tip and pile side. A series of single-pile grouting and static load tests were conducted using these test methods. The results reveal that pile-side grouting is more effective in controlling pile settlement compared to tip grouting. Furthermore, tip-side-combined grouting exhibits superior reinforcement effects compared to the other two grouting methods. After grouting, a grout bubble is formed at the outlet, consisting of a compact diffusion zone internally and a split diffusion zone externally. Additionally, a vertical diffusion of grout occurs along the pile body, establishing a lateral friction resistance enhancement region. Within this region, the lateral friction resistance of the pile shows a negative correlation with the distance from the grouting outlet. The test results emphasize the significance of grouting volume and its impact on the bearing capacity, settlement control, lateral friction resistance, and grout bubble size in grouted piles, while the influence of variation in grouting pressure in a small range on bearing characteristics is not significantly apparent.

Analysis of the effect of multiple thermal-cold cycles on the bearing performance of phase change energy piles

As a famous underground heat transfer structure, energy piles have been widely used in geothermal energy development. However, the effect of the cyclic temperature field on the ultimate load capacity of a single pile is substantial. In this study, model piles were poured using a phase change energy storage concrete based on Gum Arabic with polyethylene glycol 600. An indoor modeling test was designed to compare the phase change energy pile (GPEP) with the traditional energy pile (TEP). The ultimate bearing capacity of a single pile is obtained through theoretical formulas and static load tests to compare the bearing performance superiority of GPEP over TEP comprehensively. The response mechanism of GPEP to temperature changes was determined by evaluating the temperature change of the pile body, shear strength, water content of the soil facing the pile, thermally induced frictional resistance, and pressure exerted by the soil facing the pile. The results indicate that the single piles of GPEP increased the ultimate bearing capacity by 13.04 % (theoretical formula) and 13.70 % (static load test) compared to TEP. Due to the energy storage properties, phase change materials effectively restrict the temperature-drag response of energy piles. This study serves as a valuable reference for the practical engineering implementation of GPEP.

Cyclic p-y curve model of piles subjected to two-way load considering the collapse and densification of sand

A cyclic p−y curve model is proposed to study the lateral response of piles in sand under two-way cyclic loads such as wind and wave. The collapse and densification of the soil around the pile caused by the repeated formation of the gap between the pile and soil during the cyclic loading are considered in the proposed model. Based on the nonlinear strain wedge model, the cyclic p−y curve is preliminarily constructed considering the friction characteristics. A collapse and recompression model of sand is established to account for the variation of the relative density of the caved soil and the characteristics of the pile-soil gap. The densification of sand caused by recompression is evaluated using the stiffness hardening index model. The cyclic p−y curve is modified by considering the collapse and densification of sand and its rationality is verified by comparing the results of calculation and centrifugal model test. Furthermore, the strengthening by the caved soil, the characteristics of the cyclic p−y curve, and the soil resistance are analyzed.