Pile Tip Research Articles

A Simple Approach for the Dynamic Analysis of a Circular Tapered Pile under Axial Harmonic Vibration

The tapered pile offers sustainable use of construction materials due to its higher axial and lateral capacity and better performance owing to its geometry. This paper develops a semi-analytical solution of the vertical dynamic impedance of the tapered pile based on the dynamic Winkler theory and transfer matrix method. The accuracy and reliability of the proposed approach are verified by comparing the impedance functions of cylindrical and tapered piles obtained from the analytical solution and finite element analysis. A parametric study is performed to investigate the influence of the taper angle on the vertical dynamic impedance and resonant frequency. The results reveal that the taper angle has a significant influence on the vertical dynamic impedance, while it does not affect the oscillation period of the dynamic impedance and the resonant frequency. Besides, the vibration performance of the tapered pile is better than that of a cylindrical pile with the same volume. For a fixed-volume tapered pile, varying the pile length while keeping the pile tip diameter constant yields a better dynamic impedance than varying the pile tip diameter while keeping the pile length constant. Finally, the vertical displacement amplitude of the tapered pile decreases as the taper angle increases, especially for high-frequency excitation.

Vertical dynamic response of single floating piles in poroelastic soil

This paper presents a closed-form formulation for the time-harmonic response of single floating piles that are embedded in a saturated soil layer of finite thickness. The frictional force of surrounding soil to pile vertical motion is first established, considering the soil layer as homogeneous isotropic poroelastic medium that obeys Biot’s governing equations. The pile and the soil column underlying the pile tip are modelled using one-dimensional rod theory, and then closed-form solution is obtained from the boundary and continuity conditions, instead of numerically solving complicated integral equations that are used in the common boundary integral methods. Finally, we use arithmetic examples to identify the sensitivity of the dynamic pile impedance and of the soil reactions to the main geometrical and material problem parameters.

Preliminary assessment of potential pile tip damage and extrusion buckling

Pile tip damage has become of particular concern for the offshore wind industry due to the extensive use of large-diameter, thin-walled piles for monopiles and jacket structures. The potential for damage has increased in recent developments due to the occurrence of embedded boulders within the seabed sediments (e.g. glacial tills) or partially weathered soft rocks (e.g. limestones, chalk). To assess the risk of pile tip damage, this paper presents a simple schematic approach to estimate: i) whether pile tip damage might occur following impact with embedded boulders; and ii) what soil strength (e.g. as reflected in the cone tip resistance qc) might initiate progressive distortion of an initial minor dent (extrusion buckling). The methodology was developed based on results of centrifuge model tests and large displacement finite element analysis, encompassing: i) undamaged thin-walled piles installed through embedded layers of different sized boulders; and ii) initially ‘pre-dented’ piles driven through homogeneous sand triggering progressive distortion. Numerical analysis was used to develop predictive guidelines for conditions that might cause significant pile tip damage. The guidelines were validated by comparison with results from model tests and also through well documented field cases where extrusion buckling occurred. The paper provides guidance for choosing the critical parameters involved in the calculation processes to enable direct application in design, allowing assessment of whether more detailed investigation and analysis should be undertaken.

Field test study on soil squeezing effect of H-type prestressed concrete revetment pile

The pretensioned H-type prestressed concrete revetment pile is a new product specially developed for the protection of coastal dykes in rivers and lakes. Its cross section is H-shaped, and the H-type revetment pile is also a soil squeezing pile. The excess pore pressure and soil displacement caused by the soil squeezing effect of H-shaped piles are deeply analyzed. The influence range of excess pore water pressure is 14~15d, and the excess pore water pressure completely dissipates after 6d. The farther the vertical distance from the pile tip is, the less obvious the horizontal displacement is. In a row of piles. In the process, it will cause repeated uplift and settlement; However, after the erection, the law of vertical deformation is reflected in the near settlement and the far uplift.

Field testing study on jacked pile penetration characteristics in laminated clay based on FBG sensing technology

In order to analyze the change of static pressure pile characteristics in silt and silty clay with the penetration depth, two PHC pipe piles were penetrated in the field in the actual project, and the research was based on the full section test technology and FBG test technology. The results show that the pile pressure increases with the increase of the pile penetration depth; The change of pile tip resistance is affected by the soil layer hardness; When the pile tip is in the transition stage, the pile tip resistance increases significantly; In the process of pile penetration, the hardness and brittleness of the soil layer will be affected by the pile penetration, and the different soil layers will have different effects on the pile tip resistance of the two piles; When the pile goes deep into the soil, the pile side resistance will change slowly, but it will usually increase. This fluctuation is related to the difference of the soft and hard layers of the soil layer, and will also be subject to performance constraints; The pile end resistance ratio in hard soil will be smaller than that in soft soil, which will further affect the load sharing ratio of the test pile. The test results can provide support for practical engineering technology.

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.

Effects of soil unloading and grouting on the vertical bearing mechanism for compressive piles

The present study conducts a series of model cast-in-place piles tests to analyze the vertical bearing characteristics and the grout returned diffusion mechanism along the pile shaft of tip post-grouting piles with different grouting and pile shaft soil unloading conditions. The model test results show that the pile tip post-grouting technology can improve the weak difference in the bearing characteristics and axial force distribution of the pile foundation caused by pile shaft soil unloading. The pile shaft resistance can be improved by the returned grout in the pile shaft. The pile shaft resistance will mainly bear the pile top load when the pile top load and the grouting volume are relatively small, and the pile tip resistance will mainly bear the pile top load with the increases of the pile top load and the grouting volume. The grouting return height increases with the increase in pile shaft soil unloading degree, and the analyzed values of the grouting returned height based on the pile bearing characteristic results are close to the measured values. The grouting diffusion mechanism of the cement on the pile tip and pile shaft soil during the pile tip post-grouting process is revealed.

Simple house foundation models in potential landslide area (case study: Bojong Koneng Village, Babakan Madang Sub-District, Bogor District)

Bogor Regency is a land area that has varied geomorphological conditions, mostly in the form of plateaus, hills and mountains with constituent rocks dominated by volcanic eruptions. This study was conducted to determine the topographic and geotechnical conditions at the Bojong Koneng location to determine the prediction of landslide areas, obtain the foundation planning criteria for simple houses in vulnerable areas, and design a foundation model suitable for simple houses in erosion-prone areas based on field survey in Curug Village, Bojong Koneng Village, Babakan Madang, Bogor Regency, West Java With a slope ranging from 10°-25° sloping to the north which is a soft black clay layer with the slope of the layer in the direction of the slope. In the existing slope model without Strauss piles, the safe slope stability factor (SF) is only around 1.02, so the slope is not fully declared safe. The installation of Strauss piles fondation theoretically helpbaas to improve slope stability for hard soil conditions at a relatively shallow depth from the ground surface or in this study at a depth of 5.20 meters. The SF value at the tip of the strauss pile is only attached to the hard soil layer, almost approaching the condition of the strauss pile penetrating 1.00 m deep hard soil. However, when viewed from the sliding plane of the Strauss pile fondation tip which is only attached to the hard soil layer, it behaves like a pile so this needs to be avoided in planning.

Laboratory investigations on the thermo-mechanical behaviour of an energy pile group operated in heat release mode

Compared to the single energy pile, the thermo-mechanical behavior of pile group become more complicated due to mutual influences of different piles. A model test device of pile group with 2 × 2 layout was built to study the thermo-mechanical characteristics of pile group with different number of energy piles, inlet temperatures and connection forms of buried pipes. The results show that compared to single energy pile, the energy pile group mode will lead to the decrease of heat exchange performance and the increase of pile tip soil pressure and pile head displacement. But, the side friction and axial force of pile will decrease as a result of pile group effect. Meanwhile, increasing the inlet temperature can enhance heat exchange characteristics of pile group, but it will also result in the increase of the soil temperature, pile head displacement, pile tip soil pressure, pile shaft axial force and pile side friction. Additionally, reducing the number of energy piles in pile group can improve the heat exchange rate per unit pile depth, but the total heat transfer amount of energy pile group will decrease. With the increase of the number of energy pile in pile group, the temperature change and pile head displacement of the pile increase, but the pile side friction and pile body axial force decrease. Under current experimental conditions, the pile head displacement and pile body axial force in parallel connection mode are larger than those in series connection modes, and the pile body excess temperature is the smallest in parallel mode of four energy piles and the largest in series mode of four energy piles. For the series connection mode, the heat exchange performance, pile body excess temperature, pile head displacement and pile body axial force gradually decrease along the series direction due to the decrease of temperature change.

Full-scale field test study of bearing characteristics of post-grouting pile for offshore wind turbines

Full-scale load tests were conducted on a combined steel pipe and bored pile foundation used for offshore wind turbine in Fuqing Xinghua Bay. Due to the complex geological conditions of the project, lengthening the bored pile will cause it to exceed the steel pipe pile so much that there are construction risks such as collapsed holes, hence, combined tip-and-side post-grouting was used to improve the bearing characteristics of the pile foundations. The results of double-level O-cell bi-direction tests before and after grouting on test pile SZ32 are reported. Comparing the test results before and after grouting shows that post grouting can significantly enhance the bearing capacity of the pile foundations. Furthermore, the relative displacement required to mobilize the shaft resistance of the test pile is significantly reduced by the post grouting craftwork. Additionally, the core samples obtained from the coring tests showed that the cement grout was distributed from 0.5 D below the pile tip to 5.3 D above the pile tip, respectively. Finally, the results could be applied to similar foundation design used in offshore wind turbine.

Load-bearing Behavior of Offshore Rock Socketed Monopile Foundation Regarding Different Rock Mass Classification

With the increasing electricity demand in China, wind power has been heavily developed in recent years. It is important to stabilize the wind turbine foundations in rock bedded near the sea area while installation. Based on different rock classification standards (GB 50218 and GSI), this paper numerically analyzed the load capacity of rock socketed monopile. When the rock class is high (class III and above), under effective socketed depth, the rock-socket effect is important, and the pile tip deflection is nearly 0, which could be considered as a clamping constraint. In this case, even if the rock quality around the pile tip decreases a little or becomes a little weakened, the pile deformation and internal force will not change a lot. However, when the rock mass class is lower than IV, the pile tip load capacity will largely decrease. The definition of rock mass parameters is also important when analyzing rock socketed monopile. In conclusion, it is suggested to take GB 50218 as a reference. BQ engineering rock mass classification and its corresponding rock mass parameters could be applied. Also, the M-C model is suggested to be used for some related work.

Seismic response and nonlinear characteristics of pile‐soil springs in structures supported by pile group in granular soil on sloping bedrock

AbstractIn places prone to earthquakes, piles need to be designed to resist seismic damage. However, the characteristics of the soil significantly impact the seismic resistance of piles. Accordingly, in this study, shaking table tests and three‐dimensional finite element analyses were conducted to investigate the seismic response and nonlinear characteristics of pile‐soil springs of a structure supported by a pile group in granular soil on a sloping bedrock. The analytical experiments and simulation were conducted on a group of nine piles arranged in the shape of a square. The results showed that the constraint condition at the pile tip influenced the bending moment response of piles during large input motion, such as that observed during earthquakes. Furthermore, the pile location, direction of pile displacement, and depth was found to affect the influence of the sloping bedrock on the pile soil springs.

Application of the modified Hoek-Brown criterion in the analysis of the ultimate bearing capacity at the tip of a pile in inclined rocks

To calculate the ultimate bearing capacity at the tip of a pile in inclined and highly fractured rocks (GSI≤ 25), the exponent “a” is incorporated in the resolution approach to generalize the formulation of the original Hoek-Brown failure criterion. This exponent, with values close to 0.5 for good geomechanical qualities of the rock mass, has significantly higher values for GSI less than 25. An analytical formulation was developed that allows a suitable understanding of the geomechanical behavior. Thus, different exponent “a” and tensile strength coefficient will lead to the development of different failure modes of piles. Presented here are the mathematical equations obtained to resolve the bearing capacity and the charts used to determine the bearing capacity factor based on the slope angle of the rock and the exponent “a”. In addition, it is demonstrated that to get the same ultimate bearing capacity at the pile tip, the pile embedment ratio increased with an increasing rate as the exponent a of modified Hoek-Brown increased. Through this research it is shown that the modified Hoek-Brown criterion can be applied to highly fractured media of rock mass efficiently to estimate the bearing capacity of piles in inclined slope.

Research on the Soil-Plugging Effect on Small-Diameter Jacked Piles through In Situ Testing and DEM Simulation

Small-diameter jacked piles are widely used in civil engineering. The formation and development of the soil-plugging effect and surface frictional behavior of jacked piles have a high impact on the construction process and pile quality. Clarifying the developmental pattern of the soil-plugging effect and the change law of frictional force forms the premise of scientific construction and construction quality. Firstly, we carried out two groups of in situ tests on the small-diameter jacked piles, recording the relationship between penetration depth and resistance force. Then, the discrete element method (DEM) was used to analyze the mechanical behavior of the small-diameter jacked piles during the construction process. The particle flow code (PFC) 2D was used to carry out the DEM simulation. The research results show that pile resistance exhibited an irregular development trend as the construction process proceeded. There is a sudden change in pile resistance when the pile tip reaches the interface of certain soil layers. Both tests revealed the same phenomenon, yet both occurred at different depths. The DEM analysis showed that plug sliding was the main reason for the above phenomenon. The difference in strength and stiffness of adjacent soil layers causes the soil plug to slide, leading to a sudden change in pile resistance. When the upper layer is soft and the layer below is hard, this phenomenon is especially obvious. This also leads to a difference in the location of the sudden change in pile resistance between the two groups of tests. The research results of this paper can be helpful for revealing the relationship between the soil-plugging effect of small-diameter jacked piles and the development of pile resistance and also provides a reference for relevant engineering construction and design.

New approach for predicting the load-displacement curve of axially loaded piles in sand

A relationship to predict the load-displacement curve for axially loaded piles in sandy soil is presented by using the tri-linear softening model to describe the shaft load-displacement relationships, as well as a bi-linear model is adopted to characterize the unit end resistance-displacement reaction in the region of the pile's tip soil. Subsequently, an analytical mathematical approach to a single pile-surrounding soil interaction relation is provided as a nonlinear analysis to obtain the load-displacement curves. The mechanical response of piles under compression loading was analysed, and thus, an analytical method is developed to establish a solution for the entire compression process of the piles. A combination of the prementioned models with the pile response under compression loading was employed to establish a fully analytical approach. Furthermore, additional analytical approaches and field-tested pile loading history cases were utilized to prove the degree of exactness of the suggested method by comparing the experimental load-displacement curves with the ones founded by the proposed theoretical method in this work. The results of this study illustrate that the proposed method could be considered as an analytical mathematical technique for utilizing both the tri-linear softening model and the bi-linear elastic-plastic model for the purpose of predicting the load-displacement curves of the axially loaded pile with a 98% degree of accuracy compared to field load tests results.

Interpreting CAPWAP results for driven piles with corrections for setup and residual loads

Evaluation of pile capacity using dynamic testing and Case Pile Wave Analysis Program (CAPWAP) analysis has been shown to provide reasonable measurements of capacity and separates the shaft and tip resistance. It is a common method for verifying pile capacities; however, consideration of setup and presence of residual loads at the time of testing are necessary for interpreting the resistance distribution. A test pile program was conducted that included dynamic testing of piles at the end of initial driving and early restrikes to measure the rate of setup. The piles were instrumented to measure residual stresses. The shaft resistance and tip stiffness were interpreted from analyzing multiple blows and corrected for residual stresses. The results from CAPWAP were compared to measurements from static load tests. It was found that correcting CAPWAP results for residual loads resulted in better interpretation of the rate of setup and resistance distribution. Analyzing successive blows with CAPWAP provided an improved estimate of the tip load–movement curve by extrapolating the increase in tip capacity with penetration. The results demonstrate the importance of correcting CAPWAP results for residual stresses to gain a better understanding of the pile capacity, resistance distribution, and tip stiffness for design purposes.

Response characteristic of crane-wharf interaction system: Numerical simulation and global sensitivity analysis

Crane, an important platform to carry and move cargo in the ports, can evidently affect the overall response of pile-supported wharf system. In many earlier analytical studies, the crane was simply represented by a lumped mass. Such modeling is unable to realistically replicate the salient response characteristics of crane-wharf interaction system. To investigate such interaction effects, a three-dimensional (3D) finite element (FE) model of a typical crane-wharf system is developed. As such, the static/dynamic response of pile-supported wharf with/without crane are systematically studied and directly compared. In addition, global sensitivity analysis is conducted to explore the effects of input parameter uncertainties on global response of crane-wharf system. From the computed results, it is shown that: (1) both the static and dynamic response are considerably dependent on the crane-wharf structure as an integral global system; (2) the bending moment and displacement of pile are more sensitive to the friction angle of soil stratum near pile tip; and (3) the interaction effect among various uncertainty parameters becomes more significant with consideration of crane. Overall, the 3D FE analysis technique and the derived insights provide a useful reference and guidance for evaluation of similar crane-wharf interaction system under static/dynamic loading conditions.

Analysis of particle corner-breakage effect on pile penetration in coral sand: model tests and DEM simulations

Although particle corner breakage has been proved to be the primary mode of particle breakage for coral sand, current studies of pile penetration have continued to present the particle fracture breakage mode, causing the mechanism of pile behaviours in coral sand to remain unclear. This study investigates the particle corner-breakage effect on pile penetration in coral sand at both the macro- and microscales via indoor pile penetration model testing and three-dimensional discrete element method (DEM) simulations. According to the study findings, DEM simulations revealed that particle corner breakage has a more obvious soil contraction effect than fracture breakage. Thus, this study is the first to explain the particular turn of the pile skin friction in coral sand by the dual effects of breakable corners. Next, relationships between the particle breakage mode and the controversial breakage zone around pile tips have been accomplished. Moreover, the decrease in effective contacts and the change in soil skeleton have been proved to be essential factors behind the narrower penetration-affected width in breakable corner grains. The study suggests that neglecting the particle corner-breakage effect can lead to a hidden danger affecting engineering safety in angular granular soil.

Dynamic Responses of Embedded Rock Pile Groups due to Rock Burst considering Coupled Pile-to-Pile Interaction

Abstract This note presents an analytical solution to investigate the dynamic behavior of pile groups of embedded rock due to rock burst, which takes into account the interaction between piles. The energy generated by the rock burst propagates through the soil in the form of stress waves. It is transmitted to the pile foundation through the interaction between the soil around the pile and the pile. For rock-socketed piles, the condition of pile tip fixing is considered. The horizontal dynamic response calculation model of the pile group is established, and the analytical forms of the pile group stiffness and pile group interaction factor are obtained. In addition, the effect of saturated soil parameters on the dynamic response of pile groups are discussed.

Analytical Solutions for Thermomechanical Soil–Structure Interaction in Single Semifloating Energy Piles Embedded in a Layered Soil Profile

Analytical solutions for axial displacement, strain, and stress in a single semifloating energy pile embedded in a layered soil profile subjected to thermal and mechanical loads were derived. An analytical solution for the location of zero displacement, also known as a null point, was derived for a pile subjected to thermal load. It was shown that the location of the thermal null point corresponds to the location of the maximum magnitude of thermal axial stress. It also was shown that the location of the null point moves toward the pile tip as the stiffness of the bedrock below the pile tip increases. The analytical solutions were validated against in situ full-scale energy pile tests. The solutions along with the validation process delineated the load transfer mechanism in energy piles subjected to thermal, mechanical and combined thermomechanical loads embedded in a four-layer soil profile. Flowcharts delineating the procedures for obtaining the analytical solutions for a single energy pile embedded in an arbitrary number of layers, and subjected to thermal and mechanical loads are provided. Although the continuity of stresses and displacements at the interface of different soil layers is maintained, displacement, strain, and stress diagrams exhibit a lack of smoothness, the amount of which depends on the difference in the stiffness of these layers. In summary, the presented solutions provide a rational, mechanics-based framework for advancing the understanding of thermomechanical response of energy piles that not only is essential for analysis and design, but ultimately contributes to a wider use of energy piles and increased sustainability of civil engineering infrastructure.