Shaft Resistance Of Piles Research Articles

A thermo-hydro-mechanical model for energy piles under cyclic thermal loading

This paper introduces a thermo-hydro-mechanical finite element model for energy piles subjected to cyclic thermal loading. We address four particular features pertaining to the physics of energy piles: three-dimensionality, embedded heat exchangers, soil constitutive modeling and pile–soil interface. The model is designed to capture the strong coupling between all important physical and thermomechanical processes occurring in a concrete pile embedding U-tubes heat exchangers and surrounded by a saturated soil mass. It encompasses solid and fluid compressibility, fluid and heat flow, thermoplastic deformation of soil, buoyancy, phase change, volume change, pore expansion, melting point depression, cryogenic suction and permeability reduction due to ice formation. The model is distinct from existing energy pile models in at least two features: (1) it can simulate the detailed convection-conduction heat flow in the heat exchanger and the associated unsymmetrical thermal interactions with concrete and soil mass; and (2) it can simulate cyclic freezing and thawing in the system and the associated changes in physical and mechanical properties of the soil mass that likely lead to thermoplasticity and deterioration of pile shaft resistance. The performance of the model is demonstrated through a numerical experiment addressing all its features.

The Effect of Targeted Field Investigation on the Reliability of Axially Loaded Piles: A Random Field Approach

This work deals with the effect of targeted field investigation on the reliability of axially loaded piles, aiming at an optimal serviceability and ultimate limit state design. This is done in a Random Finite Element Method (RFEM) framework properly considering sampling in the analysis; the RFEM method combines finite element analysis with the random field theory. In this respect, the freely available program called RPILE1D has been modified by the authors as to consider sampling of both soil and pile properties. In each RFEM realization, failure is considered to have occurred when the calculated shaft resistance of pile considering spatially uniform properties (average of sampled values from the soil and pile random fields) is greater than the respective “actual” one considering spatially random properties for both soil and pile. The necessary numerical demonstration of the proposed methodology is done by considering two sampling strategies: a) sampling from a single point and b) sampling from a domain, both along the pile, whilst the various parameters governing the statistical uncertainty of the problem are examined; 5383 different cases were considered in total. As shown, a targeted field investigation may minimize or even eliminate the statistical error inserted in the design. The error is quantified by the difference in the probability of failure comparing different sampling scenarios. Another main finding is that the optimal horizontal sampling location occurs where the pile is going to be constructed. In addition, it is shown that the benefit of a targeted field investigation is much greater than the benefit gained using characteristic soil property values.

Impact of pile roughness on shaft resistance in sand

The impact of pile roughness on shaft resistance was studied using centrifuge modelling. Two types of piles with different roughness were jacked in flight at 100g in dense and medium dense Fontainebleau NE34 sands. An experimental method was used to infer the pile shaft and tip capacities. For the piles tested in this study, an increase in pile roughness and sand density increased the shaft resistance significantly. Pile roughness was also found to affect the ratio of the tension to compression shaft resistances. The experimental results obtained were compared with those obtained using the Imperial College pile (ICP) method for different angles of friction. The variation in friction angle according to pile roughness and sand density showed that the ICP method provides a good estimate of pile shaft resistance.

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.

Design and Calculation Method for Composite Foundation Using Large-diameter Rigid Piles in Pebble Bearing Soil

In the composite foundation using rigid piles, large pile-soil stress ratio often results in insufficient exploitation of bearing capacity of soil among piles. The rigid piles bear most of the vertical loads which makes the stress mechanism similar to that of pile foundation and fails to save cost. Based on the test and study of pile shaft resistance and tip resistance in the composite foundation using large-diameter rigid piles in pebble bearing soil and the stress monitoring of pile top and soil among piles, the pattern of variation in pile-soil stress ratio of composite foundation using large-diameter rigid piles was achieved. Furthermore, according to field test, use of cushion would lower the stress in rigid piles and exert bearing capacity of soil among piles which leaded to higher bearing capacity of composite foundation and smaller differential settlement. In contrast to “Technical Code for Ground Treatment of Buildings” (JGJ79-2012), a new design and calculation method for composite foundation using large-diameter rigid piles in pebble bearing soil was proposed based on the results from field test, numerical simulation and theoretical analysis. This improved and practical method has fully considered the potential bearing capacity of soil among piles and has been verified through practical engineering cases.

Field behavior of pre-bored grouted planted nodular pile embedded in deep clayey soil

This paper presents the results of field tests performed to investigate the behavior of pre-bored grouted planted nodular (PGPN) pile embedded in deep clayey soil. The test piles were all instrumented to measure the shaft and tip resistance and to determine the load transfer along the pile shaft. The test results show that the displacement necessary to fully mobilize the shaft resistance of PGPN pile is in the range of 1.83–3.32% D (D is pile diameter), and that the ultimate skin frictions of grout–soil interface of different soil layers are larger than the conventional proposed ultimate skin frictions for non-displacement piles. Furthermore, the pile tip resistance accounts for about 16% of the total applied pile head load corresponding to a pile head displacement of 0.1 D, and the pile tip resistance continues to increase after tip displacement reaches 5% of pile tip diameter.

Interactions between energy piles caused by temperature

A new simplified method is proposed to estimate the zero point of displacement variation, assuming that the pile shaft and end resistance are in the elastic stage. The additional pile axial force was calculated by using the proposed method. The temperature distribution among surrounding soils was estimated by using the finite-line-source model. The temperature distribution obtained by the proposed method was compared with that obtained by the finite-element model, and a good agreement was obtained. A method for estimating the interaction caused by heating between energy piles is proposed, and a comparison between the calculated results obtained by the proposed method and those obtained using Abaqus software on energy piles was done to verify the accuracy of the proposed method. It is shown that reasonable predictions about interaction between energy piles can be made without expensive and time-consuming analyses by means of the method proposed in this paper.

Experimental Investigation on Efficiency Factor of Pile Groups Regarding Distance of Piles

There are a lot of the parameters which affect pile group behavior in soil. One of these factors is the distance of piles from each other. The impact of distance on pile groups in sand has been investigated through some researches, whereas most of them have not represented an exact estimation according to the continuous change of the distance in sand. Moreover, most of previous investigations have considered two piles as a perfect group. Since two-pile group has the least interaction effect among piles, it cannot suitably demonstrate the influence of spacing. In this lecture, several 4-pile groups modeled with different spacing were subjected to axial loading in laboratory. The pile groups were free-head with length to diameter ratio of 13.5. The piles are designed in a way which the shaft resistance of piles can be completely mobilized through the test. Then, the bearing capacities of pile groups are measured and compared with the single pile's resistance in order to calculate the efficiency coefficient of the groups. It is revealed that the distance is noticeably effective in efficiency factor and this effectiveness, non-linearly decreases by increase of spacing. The results show that the efficiency coefficient is changing between almost 1 and 1.4.

Effect of Steel Casing on Vertical Bearing Characteristics of Steel Tube-Reinforced Concrete Piles in Loess Area

This study aims at investigating the effect of steel casing on vertical bearing characteristics of steel tube-reinforced concrete piles in loess area by centrifugal model test. Five piles were selected, one of them was a conventional reinforced concrete pile which was 35 cm in length and 2.5 cm in diameter as a contrast pile, and the length of steel casing for the remaining four steel tube-reinforced concrete piles was 8 cm, 12 cm, 16 cm, and 20 cm respectively. The results show that the axial force, unit skin friction, tip resistance, and shaft resistance of steel tube-reinforced concrete piles with different steel casing lengths were different from conventional reinforced concrete pile. Additionally, the ultimate bearing capacity of steel tube-reinforced concrete piles was compared with a conventional reinforced concrete pile. Moreover, advantages of steel casing in pile foundation engineering were summarized. The results of this study can provide reference for vertical bearing characteristics of steel tube-reinforced concrete piles in loess area.

Investigation of Thermal Loading Effects on Shaft Resistance of Energy Pile Using Laboratory-Scale Model

AbstractCyclic temperature changes in an energy pile generate cyclic thermal expansive and contractive strains along the interface, which may impact both the serviceability and the ultimate pile re...

Time-lapsed shear-wave velocity (Vs) tomographic images and stress in sand surrounding displacement pile during setup

This study reports model pile tests designed to characterize the underlying mechanisms of driven pile setup in dry sand by means of stress measurement with the tactile pressure sensors and spatio-temporal, shear-wave velocity (Vs) distributions using an automated high-speed tomographic imaging system. The pile-load test results demonstrate a distinct increase in the pile shaft resistance after pile setup. The measured stress and Vs in the soil surrounding the pile suggest the increase in the radial effective stress during pile loading [Formula: see text], as a result of the aging-induced stiffness increase, is the dominant mechanism of pile setup. The spatio-temporal evolution of Vs distributions reveals that during initial aging (before pile installation), Vs is similar at any distance to the pile shaft and exhibits a similar aging rate S0 in terms of stiffness increases. After pile installation, the soil exhibits a higher aging rate S1. In addition, the ratio S1/S0 decreases with increasing distance from the pile shaft. A lower initial Vs and a higher aging rate S1 are also observed for the measurements at the three sensing layers of different depths, suggesting that more soils disturbed by pile installation tend to recover at a relative higher aging rate.

Shaft resistance of pre-bored precast piles in Shanghai clay

Pre-bored precast piles with an enlarged base (PPEB piles) have been increasingly used in China over the past 5 years. However, the distributions of the shaft and toe resistance of the pile are still unclear. In order to reveal the ultimate bearing capacity and load transfer mechanism of PPEB piles in clay, three full-scale ultimate static loading tests were carried out in Shanghai. The test piles were instrumented with vibrating wire strain gauges to enable accurate measurement of the local shaft resistance along the pile shaft during the loading tests. The tests results revealed that about 75% of the pile bearing capacity was provided by shaft resistance when the ultimate load was applied and the majority of the shaft resistance was mobilised along the lower part of the test piles. After load testing, the soils around the test piles were excavated to evaluate the reliability and constructability of PPEB piles. The applicability of conventional methods (α-method and β-method) in estimating shaft resistance was assessed. In comparison with instrumented bored piles, the local shaft resistance of the PPEB piles in the lower stiff clays was significantly higher.

A Numerical Study on Installation Effects and Long-Term Shaft Resistance of Pre-Bored Piles in Cohesive Soils

Pre-boring is a technique widely used to facilitate large displacement pile driving in hard/dense soils, but usually at the expense of reducing the long-term shaft resistance of the pile. In the US, it is a routine practice for large displacement pile to be driven through dense cohesive soils with the ultimate capacity of pre-bored piles usually being determined based on empiricism and local experience. Understanding and quantifying the impacts of pre-boring installation on pile capacity can greatly help geotechnical design engineers to understand the interactions among the factors of pre-boring, pile size, soil conditions, and so forth and to improve the design and construction qualities of pile foundations in hard/dense soils. Due to the high cost and time involved with field instrumentation and testing on pre-bored piles, a numerical analysis study was funded by the Louisiana Department of Transportation and Development (DOTD) as a first step to exploring the impacts of pre-bore size on the long-term shaft resistance reduction of piles. This study was conducted using a practical finite element model that integrates the entire process from pile installation through subsequent consolidation to pile loading. The long-term shaft resistance was then examined after full consolidation by applying a vertical shear displacement on the soil element adjacent to the pile until the ultimate state was reached. Based on the numerical simulations, a set of reduction factor curves were then developed for a typical Louisiana soil stratum, which may provide guidelines for better design and construction of pre-bored piles in Louisiana.

Assessment of the Shear Strength of Pile-to-Soil Interfaces Based on Pile Surface Topography Using Laser Scanning.

This article presents in situ research on the side surface of continuous flight auger (CFA) foundation piles using a three-dimensional (3D) laser scanner (Leica ScanStation C10) in order to evaluate the morphology assessment of pile concrete surfaces in various geotechnical layers. Terrestrial laser scanning describes the 3D geometry of the construction with high spatial resolution and accuracy. A total of six areas were selected from the acquired point cloud for which a two-step approach for removing the form was applied. In the first step, the reference surface was fitted using the least squares method, and then, cylindrical projection of the surface was performed. In the second step, an operator of removal of the multi-plane form was applied. For each sample, height parameters (Sq, Ssk, Sku, Sp, Sv, Sz, Sa) and functional volume parameters (Vmp, Vmc, Vvc, Vvv) according to the standard ISO 25178-2:2012 were determined. Significant differences in the values of surface height and functional volume parameters were observed for each geotechnical layer where piles were formed. Because the piles remain embedded in the ground, in situ tests of the side surface of piles are rarely performed and taken into account in the assessment of pile bearing capacity. The study of surface topography is a crucial stage in the assessment of the shear strength at the interface between a concrete pile and the soil layer. The obtained concrete morphology assessments are applicable during the determination of the skin friction factor in the analytical or numerical estimation of pile shaft resistance. The proposed procedure of morphology evaluation may improve the fidelity of the assumed friction factor between the concrete and soil and increase the reliability of direct shear experiments.

ASSESSING THE INCREASE IN BEARING CAPACITY OF BORED PILES IN SANDY SOIL USING EXPANSIVE ADDITIVES

The pile foundation is usually designed to exceed the weak soil to the strong stratum. There is very close relation between the pile capacity and surrounding soil conditions. In cohesionless soil, the bored pile is effecting surround soil by loosening deposits through a combination of pile volume replacement and exist of pile case used for installation of bored pile. In this study, the improvement of the weak soil that surrounds the pile and observing the effect of improvement on pile increase the skin friction of the bored pile capacity for bored pile carried out. This study conducts research into the use of expansive additives in concrete bored piles. The aim of this project was to investigate how Na2Co3 as an additive in concrete can increase the shaft resistance of a bored pile. Several tests were conducted on concrete single piles with a variation of length to the diameter ratios and different percentages of soda ash additives. All tests were made in dry, sandy soil at loosening state. All tests showed that the shaft capacity could be increased using expansive additives due to increase the volume of the pile or enlargement of pile volume during concrete setting; it was also concluded that the shorter expansive piles could be able to achieve the same pile capacity as a longer conventional pile. This would lead to reductions on the volume of concrete poured, the amount of steel reinforcement used and the amount of soil excavated. Therefore, construction costs can be decreased and construction times can be shortened.

Discussion of “Effect of Surface Roughness on the Shaft Resistance of Displacement Model Piles in Sand” by Ruben D. Tovar-Valencia, Ayda Galvis-Castro, Rodrigo Salgado, and Monica Prezzi

Discussion of “Effect of Surface Roughness on the Shaft Resistance of Displacement Model Piles in Sand” by Ruben D. Tovar-Valencia, Ayda Galvis-Castro, Rodrigo Salgado, and Monica Prezzi

Closure to “Effect of Surface Roughness on the Shaft Resistance of Displacement Model Piles in Sand” by Ruben D. Tovar-Valencia, Ayda Galvis-Castro, Rodrigo Salgado, and Monica Prezzi

Closure to “Effect of Surface Roughness on the Shaft Resistance of Displacement Model Piles in Sand” by Ruben D. Tovar-Valencia, Ayda Galvis-Castro, Rodrigo Salgado, and Monica Prezzi

Shaft Resistance of Piles under Horizontal Force and Overturning Moment

Shaft Resistance of Piles under Horizontal Force and Overturning Moment

Field Performance of Open-Ended Prestressed High-Strength Concrete Pipe Piles Jacked into Clay.

The behavior of open-ended pipe piles is different from that of closed-ended pipe piles due to the soil plugging effect. In this study, a series of field tests were conducted to investigate the behavior of open-ended prestressed high-strength concrete (PHC) pipe piles installed into clay. Two open-ended PHC pipe piles were instrumented with Fiber Bragg Grating (FBG) sensors and jacked into clay for subsequent static loading tests. Soil plug length of the test piles was continuously measured during installation, allowing for calculation of the incremental filling ratio. The recorded data in static loading test were reported and analyzed. The distribution of residual forces after installation and the effect on the bearing capacity were also discussed in detail. The test piles were observed to be in partially plugged condition during installation. The measured ultimate shaft resistance and total resistance of the test piles were 639 and 1180 kN, respectively. The residual forces locked in the test piles after installation significantly affected the evaluation of the axial forces, and thus the shaft and end resistances. It tended to underestimate the end resistances and overestimate the shaft resistances if the residual forces were not considered in the loading test. However, the residual forces did not affect the total bearing capacity of open-ended PHC pipe piles in this study.

Thermally-activated piles and pile groups under monotonic and cyclic thermal loading–A review

A number of full- and small-scale physical tests, and numerical studies examining the behaviour of thermally-activated piles have now been published. Collating studies involving monotonic and cyclic heating or cooling of isolated piles and pile groups, this article examines the reported results of the pile-soil interactions in terms of the pile head displacement and maximum internal stress changes during thermal loading, which are key for the design of thermally-activated piles.The results from the various studies largely confirm the complementarity of stress change and pile movement, and support the use of the bounds defined by a perfectly restrained pile and an unrestrained pile. The latter bound is unlikely to apply to all pile groups however, and more work is required in order to fully understand the limits of the former when applied to groups.Two aspects of cyclic thermal loading of T-A pile foundations have been highlighted; namely, that (i) once operational a T-A foundation will take some time to establish a new dynamic equilibrium reflecting the changing seasonal thermal boundary conditions and (ii) thermal ratcheting is most likely to occur when the pile shaft resistance is largely or fully mobilised by external loads, prior to thermal cycles being applied. It seems that these two effects are sometimes conflated and further investigation is needed in order to better understand their long-term effect.