Piles In Soft Soils Research Articles

3D Numerical Modeling of Negative Skin Friction Effects on Tapered Piles in Soft Soils

3D Numerical Modeling of Negative Skin Friction Effects on Tapered Piles in Soft Soils

Influence of Settlement on Base Resistance of Long Piles in Soft Soil—Field and Machine Learning Assessments

Understanding the role that settlement can have on the base resistance of piles is a crucial matter in the design and safety control of deep foundations under various buildings and infrastructure, especially for long to super-long piles (60–90 m length) in soft soil. This paper presents a novel assessment of this issue by applying explainable machine learning (ML) techniques to a robust database (1131 datapoints) of fully instrumented pile tests across 37 real-life projects in the Mekong Delta. The analysis of data based on conventional methods shows distinct responses of long piles to rising settlement, as compared to short piles. The base resistance can rapidly develop at a small settlement threshold (0.015–0.03% of pile’s length) and contribute up to 50–55% of the total bearing capacity in short piles, but it slowly rises over a wide range of settlement to only 20–25% in long piles due to considerable loss of settlement impact over the depth. Furthermore, by leveraging the advantages of ML methods, the results significantly enhance our understanding of the settlement–base resistance relationship through explainable computations. The ML-based prediction method is compared with popular practice codes for pile foundations, further attesting to the high accuracy and reliability of the newly established model.

Shake-table test on dynamic response of prestressed high-strength concrete pipe piles under Soil–Structure interaction

This paper presents the results of a shake-table test on a superstructure model supported by a prestressed high-strength concrete (PHC) pipe pile in soft soil. The primary objective is to investigate the dynamic response of the PHC pipe pile in soft soil influenced by soil–structure interaction (SSI). Accordingly, a single PHC pipe pile with iron blocks is constructed and embedded in soft soil. First, the production of the physical model of the PHC pipe pile and experimental details are elucidated. Then, the study focuses on the dynamic response of the soil–pile–superstructure system considering different ground motion types and peak ground accelerations (PGAs). Finally, the inertial and kinematic effects on the dynamic response of the PHC pipe pile are analyzed. The results show that the SSI effect can increase the predominant period of the superstructure. With the SSI effect, the seismic design should consider the adverse effects of long-period and pulse-type ground motions on the pile. The SSI effect caused the rate of increase in the pile bending moment to be gradually higher than the increase in PGA. Moreover, the dynamic response of the PHC pipe pile is mainly dominated by the inertial effect.

Soft computing for determining base resistance of super-long piles in soft soil: A coupled SPBO-XGBoost approach

Prediction of base resistance for long piles is usually challenging because of the complex mobilization of load over the depth. This study hence proposes a novel machine learning (ML) method where the eXtreme Gradient Boosting (XGBoost) algorithm is coupled with the state-of-the-art Student Psychology-Based Optimization method (SPBO) to predict base resistance of piles. A dataset (796 datapoints) from well-instrumented static load tests among various projects in the soft soil region of Ho Chi Minh City is used to develop the model. Five input parameters including the applied load, loading point displacement, axial stiffness, SPT value of the soil beneath the pile toe, and the distance from the loading point to the pile toe are considered. Performance of the coupled SPBO-XGBoost model is comprehensively assessed by comparing it with other optimized XGBoost models including the Teaching-Learning Based Optimization, Bayesian Optimization, and other well-known ML techniques. The established model is used to predict data obtained from independent studies and compared with practice design codes of pile foundation. The results show that the proposed SPBO-XGBoost model outperforms all other models considering the prediction accuracy and reliability. Sensitivity analysis and Partial Dependence Plots are conducted to gain insights into the base resistance mechanism, giving considerable implications to design practice of pile foundation.

Prediction Method of Vertical Ultimate Compressive Bearing Capacity of Single Pile in Soft Soil considering the Influence of Gravity

Considering that the pile foundation is widely used in soft soil, in order to improve the prediction accuracy of the vertical ultimate compressive bearing capacity of a single pile, this paper puts forward a calculation model of the pile side friction resistance in homogeneous soil based on the previous research and further deduces the calculation method of pile body internal force in layered soil under the influence of gravity field. In this research, the transmission of load along the pile body is related to the previous research on the ultimate end resistance, and an analytical calculation for the vertical ultimate compressive capacity of a single pile is proposed. The novelty of the method is that the ultimate bearing capacity is solved from the perspective of force transfer while considering its own gravity, making the results more accurate. In order to verify the reliability of the method, four engineering test piles in the soft soil area of Suzhou, China, were selected, and it is indicated that the results of the static load test and finite element simulation are consistent with the proposed method, proving that the method proposed in this paper for predicting the vertical ultimate compressive bearing capacity of single pile in soft soil area has an excellent effect.

Displacement analysis of single pile in soft soil with ground load

The pile will have a large lateral displacement in soft soil under the role of heaped load. Based on Biot consolidation theory, combined with a certain highway project, a three-dimensional FEM model was established, the process that the soil lateral load deformation lead to the pile side displacement was simulated. On the ground of the former result, the influence factors for the displacement of pile top and the pile displacement field distribution are analysed. The results shows that, the building load area, load grade and the distance from loading area to pile have a major influence on the pile side displacement. On the other hand, the load on pile top have a very small contribution for stability of anti-side displacement. The buildings nearby the area of pile foundation should be given attention in practical engineering.

Base resistance of super-large and long piles in soft soil: performance of artificial neural network model and field implications

This study aims to examine the performance of artificial neural network (ANN) model based on 1137 datasets of super-large (1.0–2.5 m in equivalent diameter) and long (40.2–99 m) piles collected over 37 real projects in the past 10 years in Mekong Delta. Five key input parameters including the load, the displacement, the Standard Penetration Test value of the base soil, the distance between the loading point and pile toe, and the axial stiffness are identified via assessing the results of field load tests. Key innovations of this study are (i) use of large database to evaluate the effect that random selection of training and testing datasets can have on the predicted outcomes of ANN modelling, (ii) a simple approach using multiple learning rates to enhance training process, (iii) clarification of the role that the selected input factors can play in the base resistance, and (iv) new empirical relationships between the pile load and settlement. The results show that the random selection of training and testing datasets can affect significantly the predicted results, for example, the confidence of prediction can drop under 80% when an average R2 > 0.85 is required. The analysis indicates predominant role of the displacement in governing the base resistance of piles, providing significant implication to practical designs.

Evaluation of passive pile analysis methods using three-dimensional finite element analysis

ABSTRACT Piles in soft soil supporting bridge abutments are often exposed to passive loading induced by adjacent bridge approach embankment. Several methods for analysis of passive piles have been developed, but the international design specifications do not recommend a specific method for the analysis of passive piles. Therefore, the applicability of existing empirical and analytical analysis (conventional) methods is examined by comparing their outputs with those of a validated finite element model (FEM) at various adjacent embankment stress levels, and construction times, soft clay thicknesses, and pile spacing to diameter ratios. Outputs of both conventional methods and FEM show that increasing the embankment stress, thickness of soft clay layer, and pile spacing to diameter ratio results in an increase in the lateral pile displacement, maximum bending moment, and lateral pressure, and vice-versa on increasing embankment construction time. The outputs of the conventional analysis methods are compared to the FEM outputs and are underestimated except for few cases. The conventional analysis methods may yield better predictions at pile diameter-to-spacing ratio equals 3–4 for a soil preloaded prior to pile construction to a degree of consolidation greater than 50%.

Model test of static drilling and rooted energy pile considering over-consolidated behavior of soft soil

In order to study the bearing characteristics of static drilling and rooted energy piles in soft soil with different consolidation states， based on the energy pile model test， the thermal response of the model piles in normal consolidated soil and over-consolidated soil is tested. The results show that the heat diffusion in the soil around the pile decreases with the increase of the distance away from the heat exchange tube （heat source）. The over-consolidation state of the soil layer affects the generation and dissipation of pore water pressure in the soil layer. Compared with the normal consolidated soil， the dissipation rate of the pore pressure in the over-consolidated soil layer is slower. The vertical deformation of the soft soil around the pile first manifests as rebound after the temperature rises， and then becomes settlement. Compared with the normal consolidated soil， the over-consolidated soil rebounds significantly， and the subsequent settlement is smaller. The additional temperature stress of the pile body increases first and then decreases； in the case of over-consolidated soil， the maximum additional temperature stress position of the pile body is higher than that in the case of normal consolidated soil， and the negative friction caused by heating is smaller. The bearing characteristics of statically drilled rooted energy piles are closely related to the over-consolidated state of soft soil， and comprehensive consideration is required in engineering design to ensure operational safety. <fig fig-type="abstract-image" id="F1" orientation="portrait" position="float"><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="SP.J.1249-2022-39-1-93/6E4E2FEE-B986-4675-B4CC-9CA8241BD5AC-F001.jpg"/></fig>

A Review on the Behaviour of Combined Stone Columns and Pile Foundations in Soft Soils when Placed under Rigid Raft Foundation

In the last few decades, it has been observed that raft foundations are very commonly used as a foundation solution for moderate to high rise structures either by resting on stone columns or on piles in soft soils. It is believed that, combining stone columns and piles in one foundation system is the more suitable foundation for medium rise structures. The combined foundation system provides a superior and more economical alternative to pile, and a more attractive alternative to stone columns in respect to ground improvement. This paper presents the review of existing studies reported in the literature in the last two decades about the behaviour of stone columns under raft foundations and piled raft foundation in soft soil, notably the failure mechanism and the bearing capacity. Also, a limited work from the literature concerning the performance of combined (pile/stone columns) foundation system in soft soil is comprised. Furthermore, very extensive ongoing research work regarding the investigation and study on the performance of combined (pile/stone columns) foundation system in soft soils is discussed. The main goals and methodology to study the performance of the combined (pile/stone columns) foundation systems in soft soil are also addressed.

Influence of lowering groundwater level on the behavior of pile in soft soil

The article presents the results of numerical analysis of the development of negative skin friction forces of a single pile by lowering the level of the groundwater ta-ble in soft clay soils. The analysis is conducted with a three-dimensional model (3D) us-ing the ABAQUS software package. Results from the present work are found to be in congruent with the available published results. Moreover, the influence of lowering of the groundwater table in distribution of negative skin friction and axial forces on the pile as well as the maximum relative displacement between the soil and pile at various stages has been observed. The compression of the pile material is also taken into con-sideration in the study. Based on the results of the current numerical analysis, an equa-tion has been proposed for estimating the additional load on the pile, which is caused by negative frictional forces.

Centrifuge modelling of a tetrapod jacket foundation under lateral cyclic and monotonic loading in soft soil

The tetrapod jacket foundation is one of the most common types of foundations used for offshore structures. Although the static bearing capacity of the jacket foundation is important, a safe design must be taken into consideration for accumulative deformation and stiffness degradation during cycling. To address this, a set of centrifuge model tests of a tetrapod jacket foundation subjected to cyclic and monotonic loading was conducted in kaolin. The test results mainly reveal (i) the influence of loading history on the lateral bearing capacity of the jacket foundation; (ii) the evolution of accumulative deformation of the jacket foundation during cycling; (iii) the stiffness degradation of soil–pile interaction under cyclic loading. Comparing typical “lateral soil resistance”–“pile lateral displacement” (p–y) curve approaches with test results, a hyperbolic tangent p–y curve method is adopted to calculate the soil–pile interaction of the jacket foundation. The values of the p-multipliers of leading-row and trailing-row piles in soft soils are clearly lower than that in sands. Finally, a cyclic p–y curve method related to cycles and embedded depths is developed for the jacket foundation in the hope of providing guidance for the design of the jacket foundation in soft soil.

Field study of monotonic and cyclic lateral behaviour of piles in soft soils improved with and without vacuum preloading

Project Oufei is the largest individual reclamation project in Wenzhou city, China, and the main infrastructure consists of seawalls, sluices and separation dikes. These infrastructures face repeated horizontal forces from wind and waves; thus, it is essential to evaluate the lateral bearing of single pile used for sluice gates. This paper presents a case study on lateral monotonic and cyclic behaviour of bored piles in soft soils. Four instrumented piles were loaded monotonically and cyclically to assess the contribution of soil improvement by vacuum preloading with prefabricated vertical drains. The test results show that the ultimate horizontal capacities were 200 kPa and 100 kPa for piles in the treated zone and untreated zone, respectively, under monotonic loading and up to 220 kPa and 120 kPa for piles in the treated zone and untreated zone, respectively, under cyclic loading, indicating that the ultimate horizontal capacity of piles in the treated zone can meet the design requirement of 130 kPa. Moreover, soil improvement decreased the maximum bending moment of the bored piles and enhanced the pile head stiffness, and the influence depth of soil improvement is up to 10 m. This indicates that soil improvement by vacuum preloading with prefabricated vertical drains is effective and can be used for lateral loading in reclamation project.

Comparison of Single and Group Bored Piles Settlement Based on Field Test and Theoretical Methods

Bored piles settlement behavior under vertical loaded is the main factor that affects the design requirements of single or group of piles in soft soils. The estimation of bored pile settlement is a complicated problem because it depends upon many factors which may include ground conditions, validation of bored pile design method through testing and validation of theoretical or numerical prediction of the settlement value. In this study, a prototype single and bored pile group model of arrangement (1*1, 1*2 and 2*2) for total length to diameter ratios (L/D) is 13.33 and clear spacing three times of diameter, subjected to vertical axial loads. The bored piles model used for the test was 2000 mm in length, and 150 mm in diameter has been constructed in soft clayey soils. Furthermore, different theoretical methods have been used for the estimation of bored pile settlement, such as Poulos and Vesic's methods and then their comparison with the pile load test data based on the quick pile load test as presented in (ASTM-D1143, 2007). In general, the theoretical method for estimation the bored pile settlement by Poulos and Vesic's gives higher value of the settlement for the single and group bored pile compared to the pile settlement results obtained from field pile load test data. Therefore, it is not recommended to be used for soft clayey soils. On the other hand, Hansen’s 90% and Butler and Hoy’s results may be considered reliable interpretation method to compute the settlement of single and group bored pile.&#x0D;

Model tests on the bearing capacity of precast open-ended micro pipe piles in soft soil

Laboratory 1g model tests were carried out to study the bearing capacity and load transfer mechanisms of precast open-ended micro pipe piles in soft soil. The single pile, 2 × 2 and 3 × 3 pile groups were designed and tested under vertical compression, uplift and horizontal loads, respectively. A steep fall pattern occurred in the load–displacement curves of piles under vertical compression and uplift loads. The measured soil plug length and axial force indicated that the piles could be considered as fully plugged friction piles under vertical compression load. The pile groups behaved in a non-integral failure mode under vertical uplift load and a conical wedge failure mode under horizontal load. At the early loading stages under vertical compression and uplift loads, the pile shaft resistance of the upper part tended to be fully mobilised earlier than that of the lower part. At the later loading stages, the pile shaft resistance of the upper part decreased, whereas the shaft resistance of the lower part still showed a little increase. The maximum bending moment of the pile occurred at a depth of about 10Dp under horizontal load.

Study on Buckling Behavior of Tapered Friction Piles in Soft Soils with Linear Shaft Friction

The buckling instability of long slender piles in soft soils is a key consideration in geoengineering design. By considering both the linear shaft friction and linear lateral stiffness of the soft soil, the buckling behaviors of a tapered friction pile embedded in heterogeneous soil are extensively studied. This study establishes and validates an analytical model to formulate the equilibrium equations and boundary conditions and then numerically solves the boundary value problem to obtain the critical buckling load and buckling shape by using software Matlab. The effects of boundary conditions, tapered ratio, stiffness ratio, friction ratio, lateral stiffness, and shaft friction on the buckling behavior of the friction pile are extensively explored. This study demonstrates that the buckling load decreases with the increase of friction ratio of the linear shaft friction. There exists an optimal tapered ratio corresponding to the maximum dimensionless buckling load in the tapered friction pile with linear shaft friction. The result means that the linear shaft friction should be considered in designing the tapered friction piles in heterogeneous soils. The results also have potential applications in the fields of growing of tree roots in soils, moving of slender rods in viscous fluids, penetrating of fine rods in soft elastomers, etc.

Vertical and Lateral Bearing Capacity of FRP Composite Sheet Piles in Soft Soil

Fiber‐reinforced polymer (FRP) composite sheet piles are usually favored for slope and river‐retaining structures due to their construction and environmental efficiency. Their applications, however, have been hindered by the lack of understanding of the bearing capacity. This paper studies the vertical and lateral bearing capacity of FRP composite sheet piles through three full‐scale tests conducted in Haiyan, a soft soil site in the Yangtze River Delta of China. In the three tests, we measured the vertical bearing capacity of the FRP composite sheet piles, the bearing capacity of the composite foundation, and the lateral capacity of the FRP composite sheet piles, respectively. The test results show that the Q‐S (load on the top of the pile versus settlement) curve of the FRP composite sheet piles exhibits a steep fall while that of the composite foundation is relatively flat. Moreover, the ultimate bearing capacity of the FRP composite sheet piles is measured to reach 23.8 kN while that of the composite foundation increases by 47.1 %, reaching 35.0 kN. It shows that the FRP composite sheet piles under the composite foundation have a favorable bearing performance. Finally, the final horizontal displacement of the FRP composite sheet pile in the reinforced area with anchoring the sheet pile is smaller than the final horizontal displacement in the nonreinforced area, indicating that the horizontal bearing capacity can be significantly improved by anchoring the sheet pile.

Lateral Response and Failure Mechanisms of Rigid Piles in Soft Soils Under Geosynthetic-Reinforced Embankment

Previous studies regarding geosynthetic-reinforced pile-supported (GRPS) embankments over soft soils have mainly focused on load transfer mechanisms and design approaches. However, little attention was given to the lateral performance of rigid piles in GRPS embankment systems. This paper presents the results of 3D finite element analyses to examine and compare the lateral response and failure mechanisms of floating and end-bearing piles in soft soils under geosynthetic reinforced embankments. The effects of geosynthetic reinforcement and pile length on the stability of the embankments are also investigated. The results indicate that the induced lateral responses in the piles are distinctly different for floating and end-bearing piles. Failure of the floating pile is primarily caused by the inclination of the pile. However, for end-bearing piles, bending failure is clearly established as the principal mode of failure. The benefit of the geosynthetic layers in improving the stability of piled embankments is not particularly apparent. Moreover, the increase in pile length is significant in enhancing the stability of GRPS embankments. Specifically, when the normalized pile length varies from 0.75 to 1.15, the critical height of embankment increases from 6.2 to 11.8 m. However, the effect of pile length becomes negligible when the normalized pile length exceeds 1.15. The lateral movement and failure modes of GRPS embankments are strongly dependent on pile length. Therefore, it is essential to consider this aspect when analyzing the stability of the GRPS embankment.

Two-dimensional physical modelling of soil displacements above trapdoors

Geosynthetic reinforcement has been increasingly used over voids or piles in soft soil to support embankments and minimise differential settlement. Due to differential settlement, soil arching is formed and less pressure is applied onto the reinforcement. This problem is often simulated using trapdoor tests. The reinforcement effect on displacement and soil arching has not been fully understood. In real applications, multiple voids or multiple spans of piles exist under embankments. The effects of multiple voids or spans of piles on displacement and soil arching have not been well investigated. This paper reports a series of two-dimensional trapdoor tests conducted to investigate soil displacements above single and double trapdoors without or with reinforcement. Analogical soil, made of aluminium bars, was used as embankment fill. Paper was used as reinforcement. Two different embankment heights were investigated. The experimental tests showed that both embankment height and reinforcement reduced the vertical displacement on the top of the embankment, and higher embankment caused more soil failure at the edge of the stationary support but reduced the vertical stress on the reinforcement. The maximum tensile strain happened at the edges of the trapdoor. Trapdoors spaced at twice the trapdoor width did not cause much interaction between each other.

Numerical Study on Buckling of End-Bearing Piles in Soft Soil Subjected to Axial Loads

End bearing piles are commonly used as an efficient foundation system for supporting structures built on soft soils. Although, soft soils can provide some confinement to the pile not to be treated as an Euler column, the excessive large lateral movement may cause the soil to fail under axial loads before reaching the buckling load. Moreover, the buckling resistance of end bearing piles under loading–unloading conditions may be influenced since residual stresses in the structural elements of the piles and the surrounding soil exist even after removing the load. In addition, buckling of end bearing piles under extreme loading conditions of loading–unloading nature may result in residual stresses in the structural elements of the piles and the surrounding soil even after removing the load. In this paper, a 3-D numerical model utilizing the finite difference method was developed to study buckling behavior of end bearing piles. First the model’s calculated buckling load was verified against the theoretical solution for an idealized Euler’s case. Then, a comprehensive parametric study was performed to understand the effect of both the soil stiffness and the flexural stiffness of the pile on the behavior of buckled end bearing piles under both loading and unloading conditions. The results showed that both the lateral stiffness of the supporting soil as well as the flexural stiffness of the pile have a significant impact on the buckling length and hence the buckling load. The flexural stiffness of the pile should match (be relatively close) the stiffness of the soil in order to avoid high values of lateral displacement of the pile’s axis.