Pile Tip Research Articles

Research on the bearing performance of HSCA high-strength preloaded expansion piles in calcareous sand foundation.

With the rapid development of infrastructure construction on oceanic reefs, calcareous sand, as the primary medium of these reefs, exhibits unique physical and mechanical properties such as high void ratio, low strength, and susceptibility to particle breakage. These characteristics reduce the bearing capacity and stability of pile foundations in calcareous sand foundations. This study investigates the bearing characteristics of high-strength preloaded expansion piles in calcareous sand foundations, taking into account the influence of HSCA high-performance expansion agent dosage through a series of indoor model tests and in-situ tests. The research delves into the load-settlement curves of expansion piles, the distribution of axial force and side resistance of piles, and the effects of Calcareous sand compaction and reinforcement around the piles. The results indicate that adding the HSCA high-performance expansion agent results in compaction preloading of the Calcareous sand around the pile, significantly increasing the expansion stress on the pile side, thereby enhancing the resistance on both the pile side and pile tip. When the expansion agent dosage is 20%, the ultimate bearing capacity can be increased by 56%, and the ultimate side resistance by 63%. The Coulomb strength theory of non-cohesive soil is employed to accurately calibrate the incremental side resistance of the expansion section. A prediction model for the bearing capacity of the expansion pile is established by combining the side resistance prediction model with the ultimate side resistance load-sharing ratio. The research outcomes provide important guidance for the optimization, design, and construction of high-strength preloaded expansion piles in calcareous sand foundations.

The bearing characteristics of a single pile in a heterogeneous layered foundation

Based on a project in Lanzhou city, Gansu province, China, the bearing and internal force characteristics of two piles of different lengths under vertical load were tested and analysed using Brillouin optical frequency-domain analysis and an anchor pile static load test. The results showed that the longer pile had higher vertical bearing capacity and greater elastic working range, but the axial forces of the long and short piles showed the same trend. It was also found that the lateral friction resistance of the soil layer around the pile plays a role earlier than the pile tip resistance, and the lateral friction resistance of the upper soil layer plays a role earlier than the lower soil layer. The increasing amplitude of lateral friction resistance in different soil layers was also found to differ. The settlement of the short pile top was mostly caused by displacement of the pile bottom and the pile tip resistance was more affected by pile tip sediments. The relationship between pile end resistance and displacement under the influence of sediments can be analysed by a threefold line model.

Bearing behaviors of rock-socketed piles in layered dynamically compacted soil-rock mixtures: A case study

After layered dynamic compaction (DC) treatment in a mountainous area with deep backfill in Chongqing, China, a series of pile tests and analyses were conducted to evaluate the vertical bearing capacity of rock-socketed piles and to investigate their mechanical characteristic and load-bearing behavior. Static pile load tests (SPLT) were carried out on three types of rock-socketed piles with different diameters (800 mm, 1000 mm, and 1200 mm). Based on the test data of pile reinforcement stress, the pile axial force, frictional resistance, and load-sharing ratio were calculated and analyzed. The results indicate that load-settlement curves of static load tests for all piles change progressively, and the S-lgt curves are relatively straight lines without obvious downward bending. The pile axial force exhibits the characteristics of “large at the top and small at the bottom”, resulting in stress concentration at the pile top, especially prominent in longer piles (lengths of 33.2–37.1 m). Additionally, the overall frictional resistance increases with the increase of pile top load. In shorter piles (lengths of 16.5–22.6 m), the frictional resistance presents a C-type curve with depth, while in longer piles, it presents an S-type curve distribution. Comparatively, the test pile bears the upper load mainly by the side friction resistance, which is more prominent in the longer pile. With the increase of pile top load, the load-sharing ratio of side friction decreases and the load-sharing ratio of pile tip resistance increases.

Theoretical investigation of the resistance effect of embedded isolation piles on tunneling-induced lateral ground movements

This paper presents an isolation pile–soil lateral interaction model that considers not only the relative linear sliding at the pile-soil interface but also the pile group–soil interaction. The model allows for the calculation of the pile–soil interaction force using the elastic continuum method combined with the displacement compatibility relationship at the pile–soil interface, thus enabling the total lateral ground displacement to be obtained. The proposed method is validated by comparisons with the elastic foundation method (EFM) and the boundary element method (BEM). The advantages of the proposed method in calculating the lateral ground deformation resisted by isolation piles are demonstrated. The mechanical mechanism of the isolation pile’s lateral resistance effect on ground deformation can be summarized as follows: the combination of positive and negative resistance effects drives the lateral ground displacements along the depth direction from the original inhomogeneity caused by the tunnel excavation to a relatively homogeneous state. The soil parameters including Poisson’s ratio, internal friction angle and ground volume loss; the isolation pile parameters including the distance of the tunnel axis from the pile axis, the pile length, the buried depth of the pile top and the relative pile bending stiffness; and isolation pile–soil interface parameters including relative pile shaft–soil stiffness and relative pile tip–soil stiffness all exert a significant influence on the lateral resistance effect of the isolation pile. In light of that the resistance effects at different depths below the surface are not uniform, it is of the utmost importance to assess the resistance performance of the isolation pile in accordance with the location and lateral deformation requirements of the protected structure in actual engineering.

Analysis of the End-Bearing Capacity of Piles in Sand Under Limited Region Failure by a Mixed Zero-Extension Line Method

The failure zone around the pile tip varies greatly with the different failure patterns considered in research on the end-bearing capacity of piles. In an effort to improve the consideration of the size of the failure zone, a new failure pattern is proposed in the estimation of the end-bearing capacity of driven piles in sand and the failure zone is determined by zero-extension line (ZEL). Considering a failure zone limited below the pile end plane and an equivalent frictional contact condition with the equivalent frictional strength fully mobilized at the failure zone boundary, a more realistic prediction of the end-bearing capacity of piles is achieved. Reasonable values of parameters are obtained through parameter and numerical analysis. It is found that the failure zone is roughly within the range of 40° from the vertical direction. Comparison between the ultimate toe capacity predicted by the proposed method, a method directly using cone penetration test (CPT) data, and a method based on characteristic theory shows that the mixed zero-extension line method considering limited region failure has a better consistency with experimental data.

Insights from the numerical analysis of axially loaded piles in liquefiable soils

Axially loaded piles in liquefiable soils can undergo severe settlement due to an earthquake event. During shaking, the settlement is caused by the decreased shaft and tip capacity from excess pore pressures (ue) generated around the pile. Post shaking, soil settlement from the reconsolidation of liquefied soil surrounding the pile results in the development of additional load (known as drag load), causing downdrag settlement of the pile. Estimating the axial load distribution and pile settlement is essential for designing and evaluating the performance of axially loaded piles in liquefiable soils. In practice, a simplified neutral plane solution method is used, where the liquefied soils are modeled as a consolidating layer without considering the effect of ue generation/dissipation. A TzQzLiq analysis models the load and settlement response of axially loaded piles in liquefiable soils by accounting for the effect of excess pore pressure (ue) generation/dissipation on the shaft and tip capacity. This paper presents the deficiencies of the simplified neutral plane method in predicting the drag load as well as the downdrag settlement by comparing it with the TzQzLiq analysis validated with hypergravity model tests. The results show that the drag load and the downdrag settlement predicted by the neutral plane method might be over- or under-estimated depending on the pile load, the rate of ue dissipation, and the soil settlement. For the cases studied, it was found that most of the pile settlement occurs during shaking due to the decrease in the pile's tip resistance from the development of ue in the soil surrounding it. While large drag loads develop during reconsolidation, the resulting downdrag settlement is small. While the neutral plane method generally predicted a downdrag settlement comparable to that of the TzQzLiq analysis, it overpredicted drag load and could not predict co-seismic settlement. Finally, the study advocates for the development and use of a displacement-based procedure (accounting for all the mechanisms occurring during and after an earthquake event) such as based on TzQzLiq analysis in accurately evaluating the performance of the pile (i.e., the pile settlement and the maximum load), thus providing an overall safe, efficient, and optimized design.

Performance and behaviour of prebored and precast pile with floating pile tip based on A full-scale field static axial load test

This study investigates the load transfer mechanism of a Prebored and Precast pile (PP pile), constructed installed in accordance with the rules applicable to the Hyper-Straight pile method (HS pile), in clay soils. While the HS pile method, developed in Japan, typically results in high bearing capacity piles in various soil types, its performance in clay soils remains understudied. Our research focuses on a unique configuration where the pile tip “floats” within a soil–cement mixing (SCM) column near the bottom of the borehole, a condition that significantly influences the system’s performance.We conducted a full-scale axial static load test on a 500 mm diameter and 140 mm thickness straight shaft precast prestressed concrete spun pile. The pile was instrumented with vibrating wire strain gauges (VWSG) and displacement measuring devices (tell-tales), embedded 15 m deep in a 750 mm diameter SCM column (15.75 m long). The pile tip was positioned 75 cm above the bottom of the borehole, creating a floating condition within the SCM material. Both the pile and the surrounding SCM were instrumented to provide comprehensive data on the system’s behavior.The test involved two loading–unloading cycles. The 1st Cycle reached a maximum load of 3627 kN, resulting in a 75.52 mm pile head settlement. The 2nd Cycle achieved a maximum load of 4181 kN, leading to a 118.04 mm pile head settlement. In the 1st Cycle, we observed upward movement of the SCM material around the shaft after the pile skin friction reached its maximum capacity. Stress at the pile tip exceeded the unconfined compressive strength of the SCM material, indicating potential local shear failure.Contrary to expectations based on HS pile performance in other soil types, the ultimate bearing capacity of our pile was determined to be 2000 kN, comprising 545 kN from skin friction and 1455 kN from end bearing. This result aligns more closely with the behavior of conventional bored pile rather than the “hyper” capacity typically associated with HS pile. Consequently, we classify our pile as a “prebored and precast pile,” like systems used in China and Korea.Our study concludes that the strength of the SCM material and the pile tip location significantly influence the pile’s bearing capacity in clay soils. These findings highlight the critical impact of soil type on the performance of piles constructed using the HS method. The observed behavior suggests that current design methods for HS pile may overestimate capacity in clay conditions, emphasizing the importance of soil-specific analysis and testing.This research contributes to the understanding of PP pile behavior in clay soils, providing valuable insights for geotechnical engineers. It underscores the need for refined prediction models and design methods specific to these soil conditions, paving the way for more accurate and reliable foundation designs in regions with predominant clay soils.

Study on the Diffusion Law of Grouting Slurry at the Pile Tip of Bored Piles in Gravel Pebble Layers

The post-construction improvement technology of bored pile tips has been widely used in the construction of gravel pebble layers, but the diffusion law of the grouting slurry remains to be revealed. To study the diffusion law of the grouting slurry at the tip of bored piles in gravel pebble layers, an equivalent relationship between the seepage continuity equation and the mass diffusion continuity equation was established based on an in-depth comparative analysis; further relying on the Diluted Species Transport Module in Porous Media of Comsol Multiphysics, a three-dimensional numerical model of slurry diffusion was established to systematically study the impact of key factors such as different porosities, grouting times, grouting pressures, slurry diffusion coefficients, and the ratio of vertical to horizontal slurry diffusion coefficients on the diffusion radius of the slurry. The calculation results show that with the continuation of grouting, the increase in porosity, grouting pressure, and slurry diffusion coefficient, or the decrease in the ratio of vertical to horizontal slurry diffusion coefficients, the diffusion range of the slurry increases accordingly. Furthermore, comparatively speaking, the impact of porosity is the smallest, while the impact of the slurry diffusion coefficient is the greatest. The research findings reflect the diffusion trend of the slurry in the gravel pebble layer, which has guiding significance for the quality control of the actual design and construction of grouting.

Penetration mechanism of open-ended pipe piles under jacking and driving methods

Different pile penetration methods will cause different pile penetration results. Therefore, it is very necessary to study the pile penetration mechanism under different pile penetration methods. In this paper, numerical simulations using the discrete element method (DEM) are carried out to investigate the meso-scopic mechanism of pipe pile penetration under jacking and driving methods. The mechanism is comprehensively compared and analyzed in terms of particle movement, changes in the force chain, displacement changes, resistance of penetration pile, soil lateral stress and soil vertical stress. Results show that the height of the soil plug in the jacked pile is lower than that in the driven pile. The degree of contact force chain at the bottom of the soil plug in the driven pile is slightly higher than that at the bottom of the soil plug in the pile of the jacked pile. The total resistance of the driven pile greater than that of the jacked pile. Within a certain distance below the pile tip, the jacked pile affects the vertical stresses of the soil in this area to a greater extent than the driven pile. Then, parametric sensitivity analysis is performed, which captures the effects of the penetration velocity in the jacking method and the hammering frequency in the driving method. This study can provide a reference for the selection of the penetration method of pipe piles in actual projects.

Experimental study of the effects of the void located at the pile tip on the load capacity of rock-socketed piles

To address the design challenge of the rock-socketed piles posed by the void located below the pile tip, the physical laboratory model tests were designed and performed to simulate rock socketed piles using similar materials. The study investigates the behavior of the single pile under axial loading with the void located at varying distances from the pile tip. Through multi-level load tests, the variations of unit pile side friction, pile tip resistance, pile axial force and pile settlement are obtained for different positions of the void from the pile tip, as well as after grouting. Its comparison to the rock-socketed pile without void is performed as a reference to quantify the reduction in its bearing capacity. The results are presented in the form of graphs for different void positions and its grouting shows the influence on pile bearing capacity and emphasizes the importance of its detailed cautious investigation and introduction in the analysis. The 2D finite element modeling of the model pile-the void based on ABAQUS is performed to further investigate the influence of the void below pile tip on the bearing capacity of model pile, applying the Mohr Coulomb model as the constitutive model of rock mass behavior. The critical distance of the void below the pile tip is determined.

Mechanical Properties of Adjacent Pile Bases in Collapsible Loess under Metro Depot

Metro transit construction has begun to develop rapidly in northwest China because of the acceleration of urbanization. Accordingly, metro depots are also regarded as an essential auxiliary facility for stopping, operation, and maintenance of trains. Meanwhile, many commercial buildings are constructed over metro depots to improve the utilization rate of land due to the increasingly scarce urban land resources, known as transit-oriented development (TOD). These buildings have a large covered area and transfer concentrated loads to the bases. Therefore, pile bases under metro depots have the bearing characteristics of undertaking large concentrated loads, while lesser loads are placed on the soil between the adjacent pile bases. Additionally, the main ground in northwest China is collapsible loess, so the collapsibility should also be considered. Based on the above background, this research performed static loading tests with and without immersion in a reduced scale of adjacent pile bases under a metro depot in Xi’an. The remolding process of natural loess could destroy its structure and the anisotropy of natural loess could also affect the test results. Therefore, four kinds of artificial collapsible loess with different mass ratios of barite powder, kaolin, river sand, cement, industrial salt, and calcium oxide were made by the free-drop method. This method could make the artificial loess simulate the structure of natural loess reasonably. Then, the artificial loess with the most similar properties to intact loess was selected by comparison. Finally, static loading tests with this artificial loess were implemented. The results showed that the ultimate bearing capacity was 4.5 kN. At the same time, the axial force decreased along depth, since the pile shaft friction was positive, and the load sharing ratio of pile tip force increased to 0.58 when the load exceeded 4.5 kN in the situation without immersion; the settlement of pile bases increased significantly after immersion, while the negative shaft friction occurred at the depth of −8 cm~−35 cm, and the load sharing ratio of pile tip force reached 0.92.

Grout Diffusion Mechanism along the Pile Shaft during the Process of Pile Tip Post-Grouting in Sand

Pile tip post-grouting technology has been widely adopted in pile foundations to improve its bearing characteristics. Grouting in the pile tip leads to the grouting cement spreading along the pile body to a certain extent. To better understand the grout diffusion mechanism along the pile body returned, a total of 45 groups of laboratory model tests were carried out on sand, with different grouting pressures, grout volumes, and soil stress histories taken into account. By comparing the characteristics of the grouted bulbs, the grout diffusion mechanism along the pile body returned was revealed. Combined with the test results, a simplified model to describe the grout diffusion pattern and the corresponding grouting mode of grouting cement along the pile body returned during the process of pile tip post-grouting was proposed. This model can comprehensively reflect the grout diffusion characteristics along the pile body, with different grouting conditions and soil stress histories taken into account.

Analysis of pile end bearing capacity in Holocene interlayered silty deposits based on CPT soil behavior type index

The existing correlations between pile and cone penetration test (CPT) results often lack versatility for silty geomaterials, as they were primarily developed for clays or sands. To establish meaningful correlations, it is essential to understand the geology of the environment under examination. The CPT and its derived parameters, including the Soil Behavior Type (SBT) index, have proven to provide reliable soil information, particularly in the field of pile foundation engineering. This paper presents the findings and interpretations from several pile load tests conducted alongside field cone penetration tests on a Holocene saline interlayered silty formation, a distinct condition encountered in practice. Various CPT-based pile design methods were employed to evaluate pile capacity based on CPT results. As observed, predictions for pile shaft resistance in this geological formation remained consistent across all methods, while notable variations emerged in estimating pile end bearing. This was inferred to be a result of limited research on pile end bearing capacity in the literature, leading to proposals of broad ranges for pile influence zone and toe coefficient values, as well as various CPT tip resistance averaging techniques across different methods. Consequently, to improve accuracy, modifications based on site-specific test data may be necessary. Drawing from the assessments, effective modifications involved considering the SBT index near the pile tip. Subsequently, the current study introduces a new region-specific adjustment to the widely recognized Enhanced Unicone method based on the SBT index, resulting in a more accurate estimate of pile end bearing in such interlayered silty contexts, with less scatter compared to other available approaches.

Evaluation of side and tip resistances for barrette piles using CYCU/Barrette/Side&Tip/64

This study focuses on evaluating the side and tip resistances for barrette piles under compression loading. An extensive dataset from field load tests, designated as CYCU/Barrette/Side&Tip/64, was utilized for analysis. These data were categorized into drained and undrained soils, based on the predominant soil conditions along the pile shaft. In contrast, tip resistance depended on the soil (drained or undrained) or rock condition at the pile tip. Eight interpretation methods were employed to evaluate the measured side and tip resistances of each load test. The predicted side resistance was calculated using the classical α and β methods developed for more common piles such as drilled shafts. For the prediction of tip resistance, end-bearing capacity models for a drilled shaft resting on soil or socketed in rock are considered. Subsequently, a comparison was made between the measured and predicted capacities. Based on these analyses, it was observed that the measured side resistance is the main contributor to the overall capacity of barrette piles. The percentage of measured side resistance ranges from around 80% to 90%. In addition, the predicted side resistance calculated using the α and β methods is smaller than the measured side resistance interpreted using the L2 criterion. To reduce this prediction bias, the adhesion factor (α) and stress factors (K/Ko) for barrette piles were adjusted. For the tip resistance, the trend is opposite – predicted values are larger than the measured values for barrette piles resting on soil or socketed in rock. Another approach to correct for prediction bias called the generalized model factor is presented.

Mechanical mechanism of soft soil foundation improved by geosynthetic-reinforced pile-supported technology based on field experiment

Geosynthetic-reinforced pile-supported (GRPS) technology is an effective method for improving soft soil foundations. Conducting field tests is crucial for accurately assessing the mechanical behavior of GRPS technology. Based on the fourth expansion project at Pudong Airport, field tests were conducted to investigate the effects of GRPS technology on soft-foundation treatment. Specifically, the tests examined the changes in the pile and soil settlement, pore water pressure, and pile and soil stress. The results showed that the settlement of the GRPS foundation mainly occurred during the loading period, accounting for approximately 65% of the total foundation settlement. Increasing the pile modulus and reducing the pile spacing decreased the total foundation settlement. The filling load was mainly transferred to the piles through the soil arching effect, resulting in a large excess pore water pressure in the soil layer near the pile tip. In addition, when the filling height was low, the load transfer relied predominantly on the tensile membrane effect of the geogrid, which was more pronounced near the piles. However, as the filling height increased, the soil arching effect surpassed the tensile membrane effect and played a key role in load transfer.

Field test on application of tip grouting in enlarged head cast-in-place bored pile

Pile tip grouting is an important technique for improving the bearing capacity of cast-in-place bored piles. This paper presents a field experimental study on the effects of tip post-grouting in an enlarged head cast-in-place bored pile. The bearing data of the pile before and after the grouting were obtained through two load tests. The settling rod method was used to monitor the settlement at three critical sections, including the pile bottom during loading, while the method of rebar stress gauge was employed to monitor the strain of the pile shaft. The study results indicate that post-grouting at the pile tip significantly enhanced the bearing capacity of the pile and helped control the settlement at the pile top. A comparison between the measured and calculated settlement values at critical sections demonstrates the applicability of the settlement rod method and strain gauge method. Post-grouting at the pile toe effectively improved the side friction of the pile, resulting in smaller axial forces in the lower part of the grouted pile under equivalent loads.

Study on the mechanism of stone column pile formation

This study focuses on the construction mechanism of stone column piles at an iron ore base in China. A theoretical model that describes the stone column pile formation process during sinking was proposed. The calculation formula for the air pressure required to open the pile tip valve during the pile formation process was derived according to the physical and mechanical parameters of the stratum, stone material parameters, and relevant dimensions of the pile tip valve. This ensured that the pile diameter satisfied the design requirements by successfully opening the pile tip valve. The required air pressure values for different pile lengths in the field were calculated based on this theoretical model, and they were found to be consistent with the actual field conditions. These results can serve as a reference for engineering projects.

Research on welding seam tracking algorithm for automatic welding process of X-shaped tip of concrete piles using laser distance sensor

AbstractThe manufacturing of the X-shaped tip of prestressed centrifugal concrete piles is nowadays done half automatically by combining the manual worker and the automatic welding robot. To make this welding process full automatically, the welding seam tracking algorithm is considered. There are many types of sensors that can be used to detect the welding seam such as vision sensor, laser vision sensor, arc sensor, or touch sensor. Each type of sensor has its advantages and disadvantages. In this paper, an algorithm for welding seam tracking using laser distance sensor is proposed. Firstly, the fundamental mathematics theory of the algorithm is presented. Next, the positioning table system supports the procedure is designed and manufactured. The object of this research is the fillet joint because of the characteristics of the X-shaped tip of the concrete piles. This paper proposes a new method to determine the welding trajectory of the tip using laser distance sensor. After that, the experimental results are received to verify the proposed idea. Finally, the improved proposal of the algorithm is considered to increase the accuracy of the suggested algorithm.

Technical challenges and innovations in existing pile extraction and associated borehole backfilling in Japan

This paper critically evaluates and proposes innovative approaches to address the technical challenges associated with extracting existing piles and backfilling the associated boreholes, specifically in the context of Japan. Japan's rapid post-war economic growth has resulted in an infrastructure that is now aging, necessitating the demolition and subsequent reuse of structures. The prevalent use of pile foundations in soft soil conditions in Japan presents unique challenges following demolition, including differential settlement and complications for future construction on the same site. Current practices in Japan for pile removal are outdated and rely heavily on field experience without the support of standardized guidelines, leading to unresolved issues in improving the removal process. This paper provides an in-depth review of the status of technological advances in pile extraction and removal, as well as the development of backfill materials, with a focus on Japan's unique geological, demographic, and urban development factors. It highlights the risks associated with the traditional wire rope method and presents an innovative pile tip gripping and lifting method that aims to improve safety and efficiency by minimizing friction and preventing accidents. It also discusses the critical role of backfill treatment in preventing subsidence and outlines the performance requirements for fill materials, emphasizing the need for materials that provide uniform strength, prevent material segregation, and resist groundwater infiltration. Specifically, the paper discusses the development of cement-based fillers for borehole backfilling in Japan and demonstrates the effectiveness of sodium carbonate and thickeners in improving the physical and rheological properties of cement slurries. Finally, the paper emphasizes the urgent need for innovative technologies and methodologies for pile extraction, removal, and borehole backfilling in the Japanese context, highlighting their importance in ensuring safe, sustainable, and efficient land use in urban areas while addressing environmental concerns and stakeholder interests in land transactions and construction projects.

Rigorous Solution for the Kinematic Response of Single Disconnected Piles Subjected to Vertically Incident P-Waves

A rigorous solution for the kinematic response of the disconnected piles under vertically incident P-waves is presented. A new soil–pile column model is proposed with two fictitious soil columns as the extensions of the shaft along the pile top and tip. The discontinuity of the pile at the two ends is modeled using the Heaviside function to simulate the continuity of the soil–pile column. The total displacement of the soil is divided into the free-field and scattered components. The displacement of the soil–pile system is calculated in terms of the method of separation of variables and the soil–pile interaction. A parametric study indicates that for the disconnected pile, the displacement at the pile top increases significantly with the increase of the cushion thickness, and its effect on the scattered field is weak. The axial force of the disconnected pile decreases gradually with the increase of the cushion thickness. The displacement and axial force of the disconnected pile are significantly influenced by the slenderness ratio of the pile.