Negative Skin Friction Research Articles

New Method and Application of Negative Friction Resistance Monitoring for PHC Pipe Pile

The theoretical calculation of PHC pipe pile negative friction resistance is difficult to obtain valuable results due to many complex factors involved, such as soil properties, consolidation conditions and actual working environment, so the field monitoring is the only feasible method. The pile negative friction resistance can be got by pre-buried sensors inside the pile to monitor the changes of stress and strain of shaft. However, for PHC pipe pile, the sensors can not be embedded and protected effectively in the process of pile manufacturing, which makes the negative friction resistance of PHC pipe pile become a very thorny problem. Based on the improved field monitoring method and data analysis of sliding micrometer technology, a new method was introduced into the PHC pipe pile negative skin friction resistance testing in this paper. We can got not only the PHC pipe pile negative friction resistance, distribution range and neutral point position with different load or time, but also the strain distribution, axial force distribution, skin friction resistance and toe resistance distribution of pile, etc. The practical engineering application shows that the new method is very effective to monitor PHC pipe pile negative friction resistance and very beneficial to further research on formation mechanism and theoretical calculation of negative friction resistance of PHC pipe pile.

Field Measurement and Analysis of Residual Stress in Bored Piles

AbstractResidual stress exists in piles before load transferring from the upper structure to the pile head. The resulting mechanism of residual stress distribution in piles after unloading and the influencing factors are analyzed and compared with those of pile foundations with negative skin friction conditions. An instrumented bored pile was measured after a vertical compressive static loading test to obtain the distribution of residual stress and deformation. The results indicate that (1) the distribution of residual stress in the pile is similar to that in a pile foundation with negative skin friction on the piles due to the soil-constrained piles fully springing back, which is equivalent to prestress exerted by the surrounding soil on the pile; (2) compared with negative skin friction, the shaft resistance induced by residual stress is smaller, and the residual stress does not affect the settlement of the pile foundation; (3) the magnitude of residual stress is closely related to the pile size, proper...

Large-scale tests of pile-supported earth platform with and without geogrid

In recent years, concrete piles, such as cast-in-place piles and precast concrete piles, have been increasingly used to support superstructures and embankments when they are constructed on soft soils. On the top of pile head elevation, a certain thick granular cushion including geosynthetic reinforcement is usually installed to transfer more external load onto the piles through soil arching effect and membrane effect. This technique involving the use of rigid piles, gravel cushion and geosynthetics is usually referred to as geosynthetic-reinforced and pile-supported earth platform. This paper presents two well-instrumented large-scale tests of pile-supported earth platform with and without geogrid reinforcement. The performance of the pile-supported platform with geogrid and its load transfer behavior were investigated and compared with those for the test without geogrid. The validation of the EBGEO (2010) calculation was performed based on the test results. The test results indicate that under lower applied load, the loads carried by the piles in the test with geogrid were close to those in the test without goegrid, while with an increase in external load the loads carried by piles in the test with geogrid increased faster than those in the test without geogrid. The negative skin friction for the test with geogrid was smaller than that for the test without geogrid. Based on the contours of earth pressures on foundation base the maximum earth pressures were distributed along the edge of central cap in the test with geogrid. The minimum earth pressures were on midway subsoil between two caps in both tests. Based on the test results, the efficacy for the test with geogrid was 2.5% greater than that for the test without geogrid at the end of loading. The efficacies predicted by the EBGEO (2010) calculation agreed well with the measured efficacies.

A simplified approach for negative skin friction calculation of special-shaped pile considering pile-soil interaction under surcharge

A simplified approach was proposed to analyze the negative skin friction calculation of special-shaped pile considering pile-soil interaction under surcharge. Based on the concentric cylinder shearing theory, considering the changes of pile shape (such as, taper angle and diameters of pile base, etc.), the load-transfer of special-shaped pile was built. The accuracy of the developed simplified approach was verified by numerical simulation model with the same condition. Then, the influence factors, such as, taper angles, the diameter of pile base, surcharge, and pile-soil interface parameters were analyzed and discussed. The results show that the developed simplified approach can calculate NSF of special-shaped pile under surcharge effectively. A limited parametric study indicates that in many practical situations special-shaped piles (such as belled wedge pile shown in this work) offer a design option that is more economical than traditional uniform cross-section piles.

Study on Bearing Mechanism of Long-Short-Pile Composite Foundation under Rigid Foundation

Long-short composite pile is a widely used ground improvement technique. This study presents the results of finite difference analyzes using FLAC3D software to investigate the load-bearing and bearing mechanism of long-short pile composite foundation under rigid foundation. The pile-soil load-sharing ratio and stress ratio, axial force distribution in the piles, and pile side friction resistance distribution characteristics are also studied. The results showed that due to negative skin friction of pile in composite foundation soil functions are fully utilized. On the other hand, the load distribution between piles and subsoil is significantly affected by the cushion.

Experimental analysis on settlement controlling of geogrid-reinforced pile-supported embankments on collapsible loess in high-speed railway

Centrifugal model tests were performed to investigate the effectiveness of settlement control using geogrid-reinforced pile-supported embankments for high-speed railways on collapsible loess. First, the acceptability of using remoulded loess to simulate the behaviour of undisturbed collapsible loess in wetting test was examined in centrifuge tests. Then, the settlement of geogrid-reinforced pile-supported embankments under different conditions was investigated using remoulded loess. Experiments results showed that the collapse deformation process of remoulded and undisturbed collapsible loess can be divided into three stages with respect to time. The settlement of embankment built on collapsible loess foundation without improvement does not meet the post-construction settlement constraint for embankment of ballast track high-speed railways. Use of rigid piles, with or without caps, can significantly reduce embankment settlement and the rate of post-construction settlement. It was also observed that the negative skin friction developed in the piles varies with pile spacing and the pile configurations.

Research on Negative Skin Friction on Pile by a Simple Model Experiment

Accompanied by the substantive construction of domestic ports, the negative skin friction on pile becomes a common problem. In order to provide references for the related experiment research in the future, the designs of model experiments reported in the literatures were emphatically analyzed and compared. Compared to conventional pile model test, the model test on negative skin friction on pile needs to apply load on soil surface and it is difficult to simulate large surcharge by conventional test methods. An experimental scheme which could produce large surcharge load by conventional test conditions is given in this paper. Pile stress, displacement of pile top and layered settlement of soil was tested under different surcharge level. The depth of neutral point and the group effect of NSF are discussed.

Discussion of “Shielding Piles from Downdrag in Consolidating Ground” by S. Y. Lam, C. W. W. Ng, and H. G. Poulos

Discussion of “Shielding Piles from Downdrag in Consolidating Ground” by S. Y. Lam, C. W. W. Ng, and H. G. Poulos

Response of Single Piles in Marine Deposits to Negative Skin Friction from Long-term Field Monitoring

The behavior of single piles subjected to negative skin friction in soft soil was conducted by analyzing the results from full-scale long-term field measurements and three-dimensional (3D) numerical analyses. A skin friction coefficient (α and β coefficients) of the instrumented piles is back-calculated at different degrees of consolidation (U) of soft marine clay. Back-calculated β-values ranged from 0.15 to 0.35 for clay, and from 0.30 to 0.55 for sand, respectively. In addition, back-calculated α-values ranged from 0.1 to 0.3 for coated pile, and from 0.2 to 0.8 for uncoated pile when undrained shear strength of the soft clay was about 30–60 kPa, respectively. Moreover, this study describes behavior of a pile based on full-coupled 3D finite element (FE) analysis. The appropriate parametric studies needed for verifying the pile-soil interaction with consolidation are presented in this paper. Compared to the results from the measurements, it is shown that the computed results are capable of predicting the pile-soil behavior under consolidation. The major parameters that influence the pile behavior are discussed for different soil-pile conditions.

Experimental Program of Indoor Model Research about Single Pile Negative Friction

This article aims to study the influence of negative skin friction resistance of waterishlogged pile foundation, through indoor scale model test of pile foundation in the loess areas. The program involved in the model similar than design, the model groove design, the selection of test materials, the design of the ground soil, the layout of measuring points and the research of load method in the test. Through the experimental study on the reduced scale model, we can deepen the understanding of the action mechanism of negative skin friction resistance of the pile, which could guide the engineering practice and design.

진동타입말뚝의 해석기법 개발 및 평가

진동타입기에 의해 시공되는 말뚝의 해석을 위한 해석기법을 개발하고 해석기법의 신뢰성을 평가해보기 위해 시스템변수를 달리하여 해석을 수행하였다. 말뚝의 동적 주면마찰 하중전이곡선을 결정짓는 부주면마찰력의 크기는 정적 연직하중이 작용하지 않는 경우에 대한 해석을 통해 시행착오적으로 구할 수 있을 것으로 생각된다. 진동타입기에 의해 시공되는 말뚝의 연직변위량은 정적 연직하중의 크기에 비례하는 결과를 보였다. 진동타입시 말뚝의 가속도는 부주면 마찰력 및 정적 연직하중과는 무관하며 기진력의 크기에 의존함을 알 수 있었다. 정적 연직하중의 증가에 따른 말뚝주면 하중전이곡선의 변화양상을 비교해 볼 때 진폭은 거의 일정하나 곡선이 전체적으로 상향으로 이동함을 알 수 있었다. 말뚝선단 하중전이곡선에 대하여 최대 하중값은 부주면 마찰력 및 정적 연직하중의 크기와 무관하게 일정함을 알 수 있었다. Technique for analyzing a pile installed by vibratory pile driver was developed and analyses were performed with varying system variables in order to evaluate reliability of the developed technique. Negative skin friction which defines dynamic skin load transfer curve seems to be obtained by trial and error method for the situation without static vertical load. Vertical displacment of the pile was proportional to the static vertical load. It can be seen acceleration of the pile was dependent on excitation force regardless of the negative skin friction and the static vertical load. Comparing the shapes of skin load transfer curves with static vertical load, amplitudes of the curves were nearly the same but it can be seen that the curves shift to upward. Maximum values of the toe load transfer curves were constant regardless of the negative skin friction and the static vertical load.

Fully Coupled Consolidation Analysis of Shear Strength Mobilization and Dragload of a Pile Subject to Negative Skin Friction

Mobilization of negative skin friction (NSF) along a pile shaft increases the axial load (dragload) and pile head settlement (downdrag) of the pile, which may exceed the structural capacity of the pile and violate its serviceability performance, respectively. Therefore, the dragload estimation is essential for a pile embedded into a settling ground, where NSF is very likely to occur. This paper presents the results of a series of fully coupled consolidation numerical parametric studies of a pile embedded into a consolidating ground. The investigation focuses on the influences of pile geometry, ground compressibility, and loading condition on pile responses. The soil compressibility and time to apply the pile head load are found to have little influence on the degree of skin-friction mobilization in the long term. The long-term neutral plane (NP) lies within the 60–70% range of the pile embedded length when the pile head load is absent. The presence of a head load shifts NP upward, and the amount of upshift increases with decreasing pile diameter and length. A simple design chart is proposed to estimate the skin-friction distribution in the long term in cases where the pile head load is absent. Finally, an illustrative example is provided to demonstrate how the chart is used and performs. The study offers practicing engineers a simple and quick approach to estimating the dragload of a pile subject to NSF.

Model Test on Negative Skin Friction for Super-Long Pile under Surcharge Load Considering Time Effect

Super-long pile bridges and high-rise buildings are commonly used in the form of pile foundation. In the flood area, due mainly silt stratum, as well as the decline in groundwater mound pile under the conditions set out in the consolidation, there will be a negative pile skin friction and negative friction obvious time effect, which bearing capacity of the pile has a great influence. Current research on negative friction for super-long pile considering time effect is relatively little. In the model box, on the base of the super-long pile silt model test, set out in a pile mound under consolidation, soil testing flour gradually over time preloading consolidation settlement, pile-soil relative displacement, so as to arrive negative friction pile variation with time, tip resistance variation with time from the pile-axial force curve deduce the location of the neutral point and changes in circumstances, the pile foundation engineering practice has a certain significance.

Numerical study of a new belled wedge pile type under different loading modes

A new pile type with tapered pile body and an enlarged pile tip, referred herein as belled wedge pile, has been developed to improve both side resistance and tip resistance of pile when compared to the conventional tapered or belled cross-section piles. The new pile shape, due to wedge shape, can also reduce the development of negative skin friction when the surrounding soils are deforming under the applied surcharge loads. The construction method, quality assurance and quality control of the belled wedge piles are described. A numerical modelling technique using FLAC3D is used to perform numerical simulations to gain insight on the load carrying capacity and the load transfer behaviour of the belled wedge piles, in comparison to other pile shapes including the conventional belled piles, the tapered piles and uniform cross-section circular piles. The comparison study of the performance of these four pile shapes under compression loads, uplift loads and surcharge loads indicates that the belled wedge pile would possess the best load carrying capability and would be subjected to less downdrag among the four pile shapes evaluated. A parametric study using the established numerical modelling technique reveals the effects of various influence factors, such as the relative stiffness between the pile and the surrounding soils, taper angle, the diameter of the enlarged pile tip and stiffness ratio between the bearing soil and the overburden soil. In addition, performance of belled wedge pile within a group is evaluated in terms of the influence of pile position and pile spacing. The numerical parametric study results reveal that belled wedge pile is one of the cost-effective pile systems, which can improve vertical load carrying capacities under both compression and uplift loads and reduce the amount of negative skin friction developed due to the surcharge loads at the ground surface.

Numerical Modeling of Piles in Collapsible Soil Subjected to Inundation

Collapsible soil exhibits considerable strength when it is dry, but when it is inundated, it loses its strength and experiences significant volume reduction. Foundations on collapsible soils subjected to inundation may experience sudden settlement without any increase in the in situ stress level. Pile foundations are often used to penetrate layers of collapsible soil to transfer the load to a lower, stronger soil layer. Nevertheless, because of indentation, these piles may experience negative skin friction, which may lead to significant reduction in the pile capacity, or perhaps separation of the pile from its cap. In the literature, although several theories can be found dealing with the design of pile foundations and the prediction of negative skin friction on these piles, little to none was found to estimate the negative skin friction because of the sudden collapse of the surrounding soils. This is mainly because of the difficulties associated in modeling collapsible soil experimentally or numerically. This paper presents a numerical model, which is capable of incorporating the effects of inundation of collapsible soil, and the negative skin friction on axially loaded vertical piles. The model uses the theories of the unsaturated soil and soil-water characteristic curve to estimate the effect of soil suction because of progressive inundation. The procedure takes place by estimating the change in the soil properties and the irrecoverable soil-volume change during inundation. The paper also presents the results of laboratory tests conducted on a single pile driven in collapsible soil subjected to inundation. The measured values of the negative skin friction compared well with the predicted values from the numerical model presented. The pile design guideline is also presented to assist designers in predicting negative skin friction because of inundation. Furthermore, the theory developed can be used to evaluate the condition of an existing pile foundation driven in collapsible soil and to establish the remedies needed to avoid catastrophic failure.

3D Finite Element Analysis of Negative Skin Friction (NSF) Behaviors in Pile Groups with Cap

The pile-soil interactions are constrained by the pile cap in pile groups with cap, while mutually independent in pile groups without cap. The mechanism of changing of NSF in pile groups with cap are analyzed briefly. The NSF behaviors of pile groups with cap under the condition of groundwater level lowering are analyzed by three-dimensional finite element method. The analysis shows that the NSF of pile groups with cap is generally similar to that of a single pile: as the working loads on cap increasing, the neutral point moves up, additional settlement increases and the downdrag decreases, though there are differences between piles in different positions. The constraints of settlement of piles in various positions by the cap are significant when the working load is not large, so that the neutral point of piles are almost coincident. As the working load increasing, the deformation of the cap increases and the neutral point of piles become more various, lowest for the corner pile, second for the perimeter pile and highest for the interior pile. The NSF of each pile in pile groups with cap mobilizes differently along the depth. It is mobilized most fully for the corner pile, second for the perimeter pile and least for the interior pile.

Physical and numerical modeling of drag load development on a model end-bearing pile

A centrifuge model study is carried out to investigate the behavior of pile subject to negative skin friction induced by pile installation, ground water drawdown and surcharge loading. A single end-bearing pile is examined as the induced negative skin friction would induce the most severe stress on the pile structural material as compared to friction piles. In addition, the behavior of the pile under simultaneous negative skin friction and dead/live loads is examined. To facilitate detailed interpretations of the test results, the model setup is extensively instrumented and involves elaborate test control schemes. To further examine the phenomenon of negative skin friction on an end-bearing pile, finite element analyses were conducted. The numerical analysis is first validated against the centrifuge test data and subsequently extended to examine the effects of pile slenderness ratio, surcharge intensity and pile-soil stiffness ratio on the degree of mobilization of negative skin friction induced on the pile. Finally experimental and numerical studies are conducted to examine the effect of applied transient live load on pile subject to negative skin friction.

Numerical analysis of negative skin friction on piles in soft clay

Negative skin friction is considered one of the problems in the design of piled foundations in soft soil. The negative skin friction induces an additional compressive force on the pile called the dragload as well as, an additional pile movement called the downdrag. Ignoring the effect of negative skin friction in the design of piles leads to structural, and serviceability problems. The dragload depends on various factors such as, pile characteristics (method of installation, material, and surface treatment), soil properties (shear strength and compressibility), pile–soil relative movement, and degree of consolidation.In this paper, an axisymmetric finite element model was used to simulate, and analyze the pile–soil interaction problem of negative skin friction. The soft soil was simulated by the double hardening soil model, and the pile was described by a linear elastic model. A field case study for two instrumented end bearing driven pipe precast concrete piles in Bangkok soft clay was back analyzed. The various approaches to model the pile element, and load configurations were analyzed, and compared. An extensive parametric study was carried out to investigate the effect of different factors on the dragload value, neutral plane location, slip length, and pile movement.

Briefing: Serviceability of piles with negative skin friction

This briefing presents an approximate but simple approach to serviceability design of piles with negative skin friction. The method allows the capacity required in the underlying stable soil to be estimated directly from the allowable pile head settlement, soil settlement profile and distribution of shaft stress in the settling soil layer. The method is compared with another approach previously proposed in 2008.

New Load Transfer Hyperbolic Model for Pile-Soil Interface and Negative Skin Friction on Single Piles Embedded in Soft Soils

A proper load transfer model describing the pile and surrounding soil interaction is important for accurately predicting the behavior of piles. In this paper, a new load transfer hyperbolic model for the pile-soil interface is developed based on soil-structure interface tests reported in the literature, which consider the characteristics of increasing initial shear stiffness, the development of shear strength at the pile-soil interface, the loading, step by step loading, unloading, and reverse loading shearing behavior of the pile-soil interface with consolidation. The proposed model was validated by the close agreement between the computed results and published case histories. Further studies based on the proposed model considering negative skin friction on single piles under pile head load and/or surcharge were subsequently conducted. It was found that the pile-soil interface undergoes complicated shearing, and the depth of the neutral plane (NP) and the skin friction along the pile shaft vary during consolidation. The magnitude of the pile head load and pile installation time has a significant impact on the depth of the NP and the dragload. Pile capacity was shown to decrease with consolidation.