Development Of Negative Skin Friction Research Articles

Semi-numerical analysis of negative skin friction on permeable pile due to consolidation induced by piling

A semi-numerical approach is proposed to estimate the dissipation of excess pore water pressure and the development of negative skin friction at the normal impervious pile and the permeable pile after piling. An impeded drainage boundary associated with the opening ratio and opening size is introduced to simulate the drainage condition at the soil-permeable pile interface. In the proposed mathematical framework, analytical approaches are adopted to solve the linear equations, and numerical techniques are utilized to address the nonlinear problems so that the adaptivity and efficiency of the mathematical framework can be well balanced. Through comparisons with the field tests, the model tests, and the theoretical answers, the correctness and rationality of the proposed method are validated. Through a parametric study, the key design parameters of the permeable pile are investigated, and the following design tips are obtained: 1. The opening ratio plays the most important role in the drainage efficiency of the permeable pile; 2. Increasing the number of openings is preferred rather than increasing the size of openings, especially when the opening ratio is determined.

Semi-analytical solution for negative skin friction development on deep foundations in coastal reclamation areas

This paper derives a semi-analytical solution to predict the development of negative skin friction, caused by the consolidation of newly filled soil, on piles in the reclamation area. The simulation of the whole consolidation process of the filled soil is realized by coupling the one-dimensional consolidation model before the pile driving with the two-dimensional consolidation model after the pile driving. The negative skin friction generated at the pile shaft during the consolidation is calculated by accounting the pile-soil interactions with the introduction of the load-transfer method. To address the dramatic changes of the pore water pressure at the initial drainage stage in the classic Terzaghi drainage boundary, the continuous drainage boundary is implemented. A semi-analytical solution to the developed model is derived and subsequently validated through the comparisons with the field tests and finite element method (FEM). A comprehensive parametric study is also conducted to demonstrate the effects of the pile installation time, the surcharge load, the consolidation time before or after piling, and the pile head load on the development of negative skin friction. The negative skin friction was found to be vastly different for piles installed immediately after landfilling and those installed close to full consolidation. To optimize construction period while reducing the negative friction on piles, the pile is better to be driven after the time t=90%TvH2Cv1. It is also observed that the surcharge load on the ground could significantly enhance the stiffness and ultimate capacity of the soil, and the workload subjected at the pile head can transfer the “negative” skin friction into the positive shearing resistance.

Numerical investigation of pile-head load effects on the negative skin friction development of a single pile in consolidating ground

This study conducted parametric analyses to investigate the influence of structural loading (pile-head loading) on the development of negative skin friction in friction single piles and friction-end-bearing single piles in consolidating ground. Numerical effective stress-based mechanical-flow analysis models were built in ABAQUS software. The appropriateness of the modeling approach was verified by applying it to simulate a field model test described in the literature. For small surcharges, pile-head loading considerably reduces the depth of the neutral plane and therefore drag load for the friction pile. Under the same pile-head loads, the reduction in total drag load for the friction-end-bearing pile is smaller than that for the friction pile. However, when the friction-end-bearing pile is subjected to larger pile-head loads, the degree of total drag load reduction is comparable to that of the friction pile. Considerable pile-head displacement occurs under the combined action of pile-head and surcharge loadings. In contrast to the friction pile, the friction-end-bearing pile, because of the greater stiffness and strength of its bearing stratum, exhibits a significant reduction in negative skin friction, no bearing failure, and a smaller pile-head displacement when it is subjected to large pile-head loading.

Influence of dredger fill self-consolidation on development of negative skin friction of piles

With the rapid development of land reclamation, a great amount of buildings are constructed on degree fill. Negative skin friction (NSF) caused by the self-consolidation of dredger fill has a significant influence on the stability of construction. Therefore, centrifuge model tests were conducted to investigate the influence of dredger fills thickness, pile top load, and piles radius on the self-consolidation of dredger fills, piles settlement, and NSF. The results show that pile top load is the main factor controlling the settlement of piles, and the settlement of piles increases with an increase of pile top load. Thickness of dredger fills has significant influence on its self-consolidation. Shaft friction increases with an increase of depth, and the increase rate is much higher when the dredger fills is thicker. Fitting formulas for maximal settlement of piles, maximal NSF, and neutral plane location in the dredger fill were also acquired, providing significant reference to practical engineering.

Analysis of Negative Skin-Friction on Single Piles by One-Dimensional Consolidation Model Test

The computer program pile negative skin friction (PileNSF) was developed by the authors to predict the bearing capacity of a pile embedded in a consolidating ground due to surcharge loading. The program uses a one-dimensional analytical soil-pile model, which was formulated based on the nonlinear load-transfer method and Mikasa’s generalized one-dimensional consolidation theory. To investigate the development of negative skin friction on single piles, as well as to validate the computer program (PileNSF), a laboratory model test was performed in this study. The clay layer was subjected to increasing surcharge loads to simulate actual field conditions. Results showed that as excess pore pressure decreases and as surcharge load increases, the dragload and downdrag on pile increases. The measured values of soil settlement, excess pore water pressure, and axial force on pile were compared with the predicted values obtained from the computer program. The results of the computer program (PileNSF) showed to be in good agreement with the measured data. Therefore, negative skin friction on single piles can be effectively predicted using the computer program, PileNSF, provided that reasonable parameters are used in the analysis. After validating the program, a parametric study was carried out to study the influence of various pile design parameters on negative skin friction.

Behaviour of piles in consolidating soil

ABSTRACTThe development of negative skin friction on circular piles in a consolidating layered soil is investigated by an elasto-plastic load transfer theory which accounts for slippage of the soil. The elastic load transfer theory is premised on the compatibility condition that the vertical displacement of the ‘pile’ is equal to the summation of the vertical displacement of the layered soil due to the consolidation of the upper soil layer and the vertical displacement in the ‘soil layers’ along the pile’s centroidal axis caused by a system of pile-soil interactive forces. Slippage of the soil is accounted for by imposing the shear strength of the clay layer as the limit of the pile-soil interface shear stress. The saturated upper clay is consolidating under a uniform surcharge in accordance with Terzaghi’s one-dimensional consolidation theory. The validity of the proposed solution is confirmed by comparison with field measurements. Extensive parametric studies with regard to the effect of pile-soil slip on pile behaviour are presented.

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.

The pressure distribution along stone columns in soft clay under consolidation and foundation loading

The mechanism whereby foundation loading is transmitted through the column has received little attention from researchers. This paper reports on some interesting findings obtained from a laboratory-based model study in respect of this issue. The model tests were carried out on samples of soft clay, 300 mm in diameter and 400 mm high. The samples were reinforced with fully penetrating stone columns, of three different diameters, made of crushed basalt. Four pressure cells were located along each stone column. The 60 mm diameter footing used in the model was supported on a clay bed reinforced with a stone column and subjected to foundation loading under drained conditions. The results show that the dissipation of excess pore water pressure developed during the initial application of total stresses, when the foundation was subjected to no loading, generated considerable stresses within the column, and that this was directly attributable to the development of negative skin friction. The pressure distributions in the column during foundation loading showed some complex behaviour.

Development of negative skin friction on single piles: uncoupled analysis based on nonlinear consolidation theory with finite strain and the load-transfer method

The development of negative skin friction (NSF) on single piles is investigated based on an uncoupled method of analysis with the Mikasa (1963) generalized nonlinear consolidation theory in terms of finite strain and the nonlinear load-transfer method. Predicted results are compared with results based on the conventional linear consolidation theory with infinitesimal strains. It is found that predicted development of dragload using the conventional consolidation theory is slightly greater and conservative compared to that using the nonlinear consolidation theory based on effective stress (β method). Effective stress predictions using the conventional theory are larger due to the faster dissipation of excess pore pressures, with the assumption of constant coefficient of consolidation and permeability. However, since the relative displacements required to mobilize the ultimate skin friction are small, and piles are usually installed near the final stages of soil consolidation, the differences in the predictions for the development of dragload on piles between the two consolidation theories are overshadowed. Using the uncoupled model for pile NSF, it is therefore found that the most significant factor for the estimation of dragload and downdrag is the proper selection of the β value rather than the consolidation theory used.

Load transfer from a raft to a pile with an interposed layer

The load transfer mechanisms between a pile and a raft with an interposed granular layer have been studied by means of centrifuge physical model tests. The tests were carried out with an instrumented single model pile in two configurations: in direct contact with the raft and separated from the raft by a coarse granular layer. As the model tests show, a granular layer beneath a raft changes the pile shaft behaviour significantly compared with that exhibited by a pile in contact; it allows downward relative raft–pile and soil–pile displacement and the consequent development of negative skin friction around the upper pile shaft perimeter. Hence, the raft load is partially transferred to the pile through the pile head and partially through the negative skin friction of the upper shaft. The contact pile reduces the raft stress on the soil, and then a piled raft stiffness results that is close to that of a free-standing pile up to yield load and close to that of an unpiled raft after the yield load has been reached; the non-contact pile increases the piled raft stiffness over the whole investigated settlement range with respect to the unpiled raft.

Influences of soil consolidation and pile load on the development of negative skin friction of a pile

Negative skin friction (NSF) along a pile caused by soil consolidation is of great concern to engineers. The development of NSF is time-dependent because soil consolidation is also time-dependent. In this paper, a numerical solution is provided for the development of negative skin friction of a pile in nonlinear consolidated soil under different loads on a pile top. A hyperbolic interface model is also developed. This model considers the development of shear strength during soil consolidation and loading–unloading scenarios at the pile–soil interface. One-dimensional nonlinear consolidation theory is invoked to estimate the soil settlement and shear strength. The distributions of NSF and the axial force along the pile are obtained using the differential quadrature method (DQM). The influences of soil consolidation and different pile loads on the negative skin friction of a pile are discussed.

Development of negative skin friction on driven piles in soft Bangkok clay: Discussion

pled finite-element analysis presented in the paper. Also, (7) The current finite-element analysis incorporated a the short-term pull-out tests contributed to the determinarigid-elastic model for the end-bearing stratum (Table 2b tion of normalized skin friction a in [ I ] (pp. 396-397 and of the authors' paper) and was not based on the Cam-clay Table 1). theory. (4) The topmost soil layer shows slight overconsolida(8) Detailed descriptions of the numerical analysis are ti011 due to crusting. As a result, it is expected that the given by Wong (1991). The boundary effects of the finiteM value for the topmost soil layer would be greater than element mesh did not contribute significantly to the negative the underlying soft clay layer. The Cam-clay parameters skin friction analysis. As mentioned earlier, the results were were determined by triaxial stress path tests conducted on mainly sensitive to the interface behaviour. The finite-element samples recovered from various depths. The values given mesh shown in Fig. 13 of the authors' paper is drawn to in Table 2 are consistent with previous studies carried out for scale, where the thin interface elements closest to the pile surBangkok subsoils. As explained earlier, as a result of disface were 0.1 m in thickness. The adjacent elements increase turbance (softening), the shear modulus at the soil-pile interin thickness radially outwards. As the height of the embankface is smaller than that of the surrounding undisturbed soil. ment was only 2.0 m, its construction was assumed to be This is not an inconsistency, but rather a feature in the rapid (instantaneous) for the purpose of analysis. numerical model. ( 5 ) The authors apologize for a misprint. The unit weight of concrete should be 2.5 t/m3 and not 1.5 t/m3. Wong, Y.K. 1991. Numerical simulation of negative skin fric(6) The negative skin friction analysis is mainly sensition on driven piles. M.Eng. thesis, Asian Institute of tive to the soil-pile interface behaviour rather than to the Technology, Thailand. effects of the embankment boundaries. Therefore, the error introduced by the axisymmetric finite-element idealization was considered to be small in the numerical model.

Development of negative skin friction on driven piles in soft Bangkok clay: Reply

Development of negative skin friction on driven piles in soft Bangkok clay: Reply

Development of negative skin friction on driven piles in soft Bangkok clay: Reply

This paper describes the results of short-term pullout tests and long-term full-scale measurements of negative skin friction on driven piles in Bangkok subsoils. Two instrumented cylindrical (hollow) prestressed concrete piles were fully equipped with two independent load-measurement systems, load cells, and telltale rods. Pore pressures and ground movements in the vicinity of the piles were monitored throughout the period of investigation. The effect of bitumen coating on negative skin friction was also studied. The long-term behaviour of driven piles was compared with the estimated values obtained from short-term pullout tests and soil strength data. It was found that the negative skin friction can be predicted well by the effective stress approach using values of β between 0.1 and 0.2. The load–settlement and load–transfer behaviour were numerically modelled to acquire a more comprehensive understanding of negative skin friction developed on driven piles. A settlement-controlled concept is also introdu...

Development of negative skin friction on driven piles in soft Bangkok clay : Indraratna, B; Balasubramaniam, A S; Phamvan, P; Wong, Y K Can Geotech JV29, N3, June 1992, P393–404

Development of negative skin friction on driven piles in soft Bangkok clay : Indraratna, B; Balasubramaniam, A S; Phamvan, P; Wong, Y K Can Geotech JV29, N3, June 1992, P393–404

Development of negative skin friction on driven piles in soft Bangkok clay

This paper describes the results of short-term pullout tests and long-term full-scale measurements of negative skin friction on driven piles in Bangkok subsoils. Two instrumented cylindrical (hollow) prestressed concrete piles were fully equipped with two independent load-measurement systems, load cells, and telltale rods. Pore pressures and ground movements in the vicinity of the piles were monitored throughout the period of investigation. The effect of bitumen coating on negative skin friction was also studied. The long-term behaviour of driven piles was compared with the estimated values obtained from short-term pullout tests and soil strength data. It was found that the negative skin friction can be predicted well by the effective stress approach using values of β between 0.1 and 0.2. The load–settlement and load–transfer behaviour were numerically modelled to acquire a more comprehensive understanding of negative skin friction developed on driven piles. A settlement-controlled concept is also introduced for piles subjected to negative skin friction, on the basis of these findings. Key words : consolidation, downdrag, driven pile, embankment, finite elements, pore pressures, pullout, settlements, soft clay.

Performance of Precast Driven Piles in Marine Clay

The research reported is concerned with the behavior of precast reinforced concrete piles driven through soft marine clay and founded in residual soil and weathered rock of sedimentary origin; to study the load‐transfer behavior of such piles, strain gages installed along the pile shafts were monitored frequently during the static loading tests and at regular intervals during and after the construction of the superstructure. Piezometers were installed in proximity to one of the piles. The dissipation of excess pore water pressures indicated that setup in the marine clay was highly significant. Hence, pile capacities calculated using wave‐equation models based on stress‐wave measurements during initial pile driving gave consistently lower values than those of static loading tests one week later. Long‐term instrument readings indicated development of negative skin friction when the piles were in service. The downdrag increased with time, and this additional loading should be accounted for in the pile design as part of the service load on the pile.