Short Piles Research Articles

Experimental investigation of local scour around two submerged short square piles under tandem, side-by-side and staggered arrangements in steady current

This research investigates the effects of the arrangement of two submerged square piles on water flow induced local scour topography at the sand-covered bed in steady current under clear water scour condition. The height of each pile is the same as its boundary length. Experimental tests were conducted for G/D = 1 to 5 under the tandem arrangement and G/D = 1 and 2 under side-by-side (SBS) and staggered arrangements, where G is the gap between the two piles and D is the boundary length of the square piles. Results showed that in the tandem arrangement, the scour of the upstream pile is similar to that of a single pile, but the scour of the downstream pile goes through three stages: scour, backfill and re-scour. The backfill stage is caused by the downstream motion of the sand dunes generated from the upstream pile. In the SBS arrangement, the evolution of scour of each pile is similar to that of a single pile. However, the scour rates at the two inner upstream corners of the piles are slowed down by the sand dune between the gap at G/D = 1. In the staggered arrangement, the maximum scour depth of the downstream pile is greater than that of the upstream pile because the flow is accelerated twice from the corners of the two piles, respectively. The maximum scour depth at the SBS and staggered arrangements at G/D = 1 and 2 are slightly greater than that of a single pile, while the maximum scour depth of the tandem arrangement at G/D = 1 to 5 is similar to that of a single pile.

Uniaxial Compression Behavior of Short Square and Circular RC Piles Constructed with GFRP Bars and Spirals Preconditioned in Simulated Marine Environments

The current experimental investigation assessed the durability of reinforced concrete (RC) piles with glass fiber-reinforced polymer (GFRP) bars and spirals exposed to simulated marine environments. A total of 18 specimens—9 square (300 mm in cross section) and 9 circular (304 mm in diameter)—and short RC piles were prepared and tested under uniaxial compression. For each pile geometry, three specimens were reinforced with pristine GFRP bars as reference piles. The other six piles were reinforced with GFRP bars that had been exposed to marine environments at subtropical regions (22°C) or accelerated aging temperature (60°C) for 12 months, three specimens for each environment. Mechanical property and microstructural analysis tests were carried out to characterize the conditioned/aged GFRP bars. The GFRP-RC piles conditioned at 60°C exhibited similar behavior to their reference counterparts. The current environmental reduction factors for GFRP reinforcing bars stipulated in design codes and guidelines are conservative. A more accurate design equation to calculate the axial capacity of piles should consider the contribution of longitudinal GFRP bars even when exposed to marine environments.

Analysis of Load Transfer Law of Short Pile-Net Composite Foundation for High-Speed Railway

Although pile-net composite foundation has been widely used in the construction of high-speed railway, load transfer characteristics of its structural system during the filling of roadbed are seldom studied, so field studies are conducted in the Gan-Long (Ganzhou-Longyan) high-speed railway DK86 + 998.0–DK87 + 191.2 test section, aiming to explore the bearing characteristics of a short pile-net composite foundation over low to medium compressible soil. The study encompasses a field measurement of Earth pressure and pore water pressure which lasted almost two years, and a systematic analysis of variation law of soil pressure between piles and their tops and that of pore pressure in reinforcement zone and retaining layer in medium and low compressibility soil area. The results suggest that the soil in the test section bears the characteristic of a low water content, low porosity ratio, and high liquid limit, with compression factor being approximately 0.25, and test values of the natural soil pressure and the lateral distribution are close to the theoretical values. Soil pressure at the top of the piles is higher than that between the piles by approximately 2.4 times because of the differences in pile-net rigidity. Besides, the soil pressure of the pile-net composite foundation follows the pattern of “jagged” in the transverse direction of the roadbed. The filling load of the composite foundation soil arch is 80 kPa and the composite foundation reaction coefficient is 6.4 kN/m3 when the filling is stable. The pile-soil stress ratio at the shoulder and the center of the line is 3.2 and 2.8, respectively. The change of the hole pressure at the pile end point is larger than that at the reinforcement area, and the side verification short pile can effectively transmit the additional stress of the upper part to the pile end soil layer.

Study on Behavior and Bearing Capacity Computation Method of Shallow Rock-Socketed Short Piles Based on the Self-Balanced Loading Test

The self-balanced loading test is a state-of-art pile testing method, but its suitability to pile bearing capacity determination in transformer substation engineering in mountainous and hilly areas is not yet clear. In this study, a two-dimensional axisymmetric numerical model is established by the PLAXIS software to simulate the behavior and bearing mechanism of shallow rock-socketed short piles based on the self-balanced loading test. The model is first validated by simulating the field tests of two adjacent piles under self-balanced loading. Then the influence factors of the load-displacement curves of piles are analyzed. Thereafter, the mechanical mechanism of the self-balanced loading tests is simulated and compared with the conventional static loading tests. It is observed that the rock modulus, rock-socketed depth of piles, and burial depth of the Osterberg Cell affect the load-displacement significantly, but the cohesion of the rocks affects little. Moreover, compared with the conventional static loading tests, the shear stress of the pile-soil interface distributes less uniformly under self-balanced loading conditions. On this basis, a bearing capacity computation method of shallow rock-socketed short piles based on the self-balanced loading test is proposed.

Numerical study on stress paths in grounds reinforced with long and short CFG piles during adjacent rigid retaining wall movement

Abstract Ensuring the safety of existing structures is an important issue when planning and executing adjacent new foundation pit excavations. Hence, understanding the stress state conditions experienced by the soil element behind a retaining wall at a given location during different excavation stages has been a key observational modelling aspect of the performance of excavations. By establishing and carrying out sophisticated soil–structure interaction analyses, stress paths render clarity on soil deformation mechanism. On the other hand, column-type soft ground treatment has recently got exceeding attention and practical implementation. So, the soil stress–strain response to excavation-induced disturbances needs to be known as well. To this end, this paper discusses the stress change and redistribution phenomena in a treated ground based on 3D numerical analyses. The simulation was verified against results from a 1 g indoor experimental test conducted on composite foundation reinforced with long and short cement–fly ash–gravel (CFG) pile adjacent to a moving rigid retaining wall. It was observed that the stress path for each monitoring point in the shallow depth undergoes a process of stress unloading at various dropping amounts of principal stress components in a complex manner. The closer the soil element is to the wall, the more it experiences a change in principal stress components as the wall movement progresses; also, the induced stress disturbance weakens significantly as the observation point becomes farther away from the wall. Accordingly, the overall vertical load-sharing percentage of the upper soil reduces proportionally.

Analysis of Features of Long and Short Pile Composite Foundation in High-Rise Buildings

Analysis of Features of Long and Short Pile Composite Foundation in High-Rise Buildings

Numerical analysis of piled rafts with short bored piles

Abstract Numerical analysis of the behavior of piled rafts seated on uniform soil with low bearing capacity has been important to support the project design. The calibration of the numerical model with instrumented load test allows usage of the results, in given conditions, in the foundation design of small and medium-sized buildings built on soils with the same mechanical properties analyzed in this paper. In this context, this paper evaluates numerical models, which allow to consider the influence of short bored piles connected to the raft. The models are also assessed using piled rafts concepts. From the results obtained, the load supported by the total shaft resistance is significant for the case of bored piles, and this load is from 14% to 30% higher in the case more flexible or thinner raft. Inserting piles in the rafts reduces settlement and increases overall stiffness. Such effects are amplified in piles with higher slenderness ratios (L/d).

Improved Performance of Raft Foundation Using Detached Pile Columns in Loose Subsoil Conditions

Piles act as settlement reducers in case of connected piled‐raft foundation and hence decrease the settlements of the raft. The design concept of the connected piled‐raft foundations is to lessen the number of piles and utilize the bearing capacity of the system piled raft. Due to significant straining actions at the pile head‐raft connection, an alternative technique is proposed to disconnect the piles from the raft. A granular layer (cushion) beneath the raft is incorporated. The disconnection has a beneficial effect on reducing axial load compared to connected piles. For small piled rafts, nonconnected piled rafts show less stiffness than connected piled rafts, and the soil is highly stressed and shows greater raft settlement. In the case of the large piled raft, nonconnected piled rafts show greater settlement efficiency. Cushion stiffness was realized to be more substantial for a nonconnected piled raft with shorter piles than one with longer piles. The results show that the load transfer mechanism in a nonconnected piled raft is mainly governed by the thickness and stiffness of the cushion layer and by the stiffness of the subsoil.

Experimental study on load sharing characteristics of long-short CFG pile composite foundation adjacent to rigid retaining wall rotating about its base

Practicing geoengineers and researchers generally consider the load sharing behavior in multi-type pile composite foundation as an important design aspect. On the other hand, due to urbanization, such foundation system in cities will inevitably appear next to supported excavation. This paper discusses the result from relatively large-scale indoor experiment conducted to investigate the load sharing behavior of loaded long-short CFG pile composite foundation behind a neighboring rigid retaining wall undergoing rotation around the bottom. It was found that with progression of wall movement, the hidden load from soil displacement was borne by the piles with marked reduction in soil load sharing. At the end of wall rotation, the percentage of long piles’ head load increment needed to arrive at a new static equilibrium was about 12.57~32.22% while the end bearing increased by more than 97%. The consequences on the short piles, however, were manifested with an increasing pile head (13.42%) and toe (28.9%) load for the pile far from the wall whereas the closest one experienced a certain increment up to 15×10-4rad wall rotation and finally the head load and end bearing decreased to 8.28% and 12.63%, respectively. The 3D numerical back analysis conducted using FE software ABAQUS yielded the pile – soil stress ratio lower than the value obtained from the experiment but provided great insight into pile settlement characteristics during wall rotation.

Features of pile groups from short piles according to numerical modeling

There are many controversial issues when designing a new pile foundation. One of them is the difference between short piles and long piles. Research in the position, the load, which is a pile foundation, is partly transferred to the grid, and partly - on the pile and does not always have the possibility of a finger in the pile foundation corresponds to the failure of a single pile.The nature of this redistribution significantly depends on the length of the pile, especially it depends on the work of the group with a short finger. On such a day, the issue of creating a reliable calculation model of a sound basis that provides a sufficient correspondence between the results of the calculation and the work of natural piles - is still one of the problems of foundation construction. The use of pile bearing capacity resources is one of the best ways to achieve savings when setting up pile foundations. Previous studies have shown that when working with a pile group with short piles, the group works as a continuous soil-pile massif. By confirming this hypothesis, it would be possible to reduce the number of piles within the dimensions of the grille without significant loss of bearing capacity of the pile group.Complex numerical studies of the calculated model of the columnar pile foundation with the help of Plaxis software package depending on the geometric parameters (length and number of piles) were carried out. The pitch and number of piles were varied at constant grid sizes. Variants of short and long piles, as well as soil environment from sandy and clay soils are considered. The stages of realization of bearing capacity of piles and grid in the composition of the pile foundation for piles of different lengths were analyzed.The efficiency of using short piles in comparison with long piles is estimated. It has been determined that short piles in the bush work more efficiently than long ones. In the case of short piles, in order to save materials, you can reduce the number of piles in the group while maintaining the size of the grille with a slight loss of load-bearing capacity.

Parametric study of short open-ended unplugged pipe piles for lowlands based on Winkler approach

Parametric study of short open-ended unplugged pipe piles for lowlands based on Winkler approach

Seismic behaviour of piles in non-liquefiable and liquefiable soil

This paper investigates the nonlinear soil–pile–structure interaction employing three-dimensional nonlinear finite element models verified with the results of large-scale shaking table tests of model pile groups-superstructure systems. The responses of piles in both liquefiable and non-liquefiable soil sites to ground motion with varying intensities were evaluated considering both kinematic and inertial interaction. The calculated piles and soil responses agreed well with the responses measured during the shaking events. The numerical models correctly predicted the different pile deformation modes that were exhibited in the experiments. The finite element analysis was then employed to perform a parametric study to evaluate the kinematic and inertial effects on the piles' response, considering different ground motion Intensity and piles characteristics. It was found that the bending moment of piles in the liquefiable site increases significantly, compared to the non-liquefiable site, due to the loss of lateral support of the liquified soil, and the maximum bending moment occurs at the interface between the loose and dense sand layers. The inertial interaction contributes the most to the bending moments at the pile top and the interface between the top clay and liquefied loose sand layers. For piles with a larger diameter, the bending moment due to kinematic interaction increases significantly, and the bending moment distribution corresponds to short (rigid) pile behaviour. In addition, the piles at the saturated site displace laterally as a rigid body during strong ground motions because the pile base loses the lateral support due to the soil liquefaction. Finally, the kinematic interaction effect becomes more significant for piles with higher elastic modulus.

Bending Resistance of Polylactic Acid Absorbable Root Canal Pile after Repairing Residual Roots

As we all know, tooth growth is very important for children. Whether it is the growth of new teeth or the loss of deciduous teeth, the residual roots of deciduous teeth will affect the physiological replacement of permanent teeth, and the repair of non-absorbable retention posts will also participate. Therefore, the purpose of this article is to explore the polylactic acid can absorb the bending resistance of the root canal pile after repairing the residual root. The method adopted in this paper is to randomly select 24 isolated mandibular premolars to ensure the morphological similarity of the sample as much as possible. After routine root canal treatment and filling, the crown is removed, and the sample is divided into 3 groups on average.. Respectively, polylactic acid absorbable root canal post, fiberglass post and composite resin short post retention, to perform post-core resin crown repair. Subsequently, the electronic universal material testing machine and formula were used to calculate the bending resistance of each material in the fracture mode, and then LSD two-sided inspection was used for comprehensive comparison. Corresponding conclusions are drawn through data comparison. The research results show that the bending strength of the polylactic acid absorbable root canal pile group is 1031.44±359.78N, the bending strength of the glass fiber pile group is 1121.34±193.50N, and the composite resin short pile The group was 1581.36±677.20N, and the differences were statistically significant (P<0.05). The three groups of samples in the experiment are all favorable tooth creases. Therefore, it can be concluded from the experimental results that the bending resistance of the polylactic acid absorbable root canal pile after restoring the residual root is lower than that of the composite resin short pile, which can also meet the clinical needs.

Simulating the model for consolidation of short bored pile in pure friction soil media

In this paper, the analysis of a numerical study for consolidation analysis of short bored pile subjected to axial loads is presented. An analysis of short-bored pile is performed using finite element analysis software Abaqus CAE with the base of procured experimental data in sand media and a comparative analysis on Ansys FEA. Three models in combination of pile and footing system were developed by the application of incremental axial load for which the displacement upon each load was analyzed taking in consideration the stresses and strains. A parametric study was conducted to study the effect of load on and it’s observed displacement on the pile with or without footing. A close correlation is found between the results obtained by the FE models and the Experimental Model solution. The results indicates that the load bearing capacity of pile–footing system increases drastically when both acts together instead of acting individually.

Simulating the model for consolidation of short bored pile in pure friction soil media

Simulating the model for consolidation of short bored pile in pure friction soil media

Numerical Analysis on the Load Sharing Performance of Long-Short CFG Pile Composite Foundation Subjected to Rotation of Adjacent Retaining Wall

The stress and displacement boundary conditions of excavation retaining structures affect the deformation mechanism and movement of the retained soil mass. The soil movement disturbs the load sharing performance and structural integrity of cement-fly ash-gravel (CFG) pile composite foundations existing in the vicinity, which merits considerable research work. This article presents results from 3D finite element analyses performed to study the influence of retaining wall rotation on the load sharing characteristics of adjacent CFG pile composite foundation comprising long and short piles. To verify the numerical model, a relatively large-scale 1 g physical model test was conducted. It is revealed that to arrive at a new static equilibrium during progression of wall rotation, the percentage load sharing ratios of the long and short piles change increasingly while the load proportion carried by the upper soil reduces remarkably. The percentage load sharing characteristics of CFG pile composite foundation are more affected in immediate proximity to the wall than those located at far distance. For the foundation having 3 × 3 long and short piles placed at 3.0–15.0 m away from the wall, the location resulted in a reduction of soil bearing capacity ranging between 1.4 and 7.5% of the total imposed load while the corresponding increase in the % load borne by the long and short pile range was 0.83–4.15 and 0.59–3.36%, respectively. For the other parameters considered in this article viz. pile spacing, subsoil stiffness, cushion stiffness and thickness, and applied working load, the increment in % load sharing of the long and short pile range was 3.45–4.15, 1.3–5.79, 1.48–3.36, 4.15–4.79, and 3.67–4.15% and 3.36–4.67, 1.43–4.99, 1.48–3.36, 3.36–3.64, and 1.38–3.36% of the imposed load, respectively. Moreover, the long piles’ load sharing proportion was higher than that of short piles, and peripheral piles received larger load proportion.

Limitations of the Danish driving formula for short piles

Dynamic formulae are a widely used expedient for the control of driven piles to ensure load capacity. These formulae have considerable limitations when used in the prediction of the load capacity on their own, but are very useful in the control of a piling when combined with other tests. This technical note presents an evaluation of the Danish Formula for 54 precast concrete piles, comparing its results with High Strain Dynamic Tests (HSDTs), Static Load Tests (SLTs) and predictions by a semi-empirical static method (Aoki & Velloso, 1975). The data used in the comparison come from three works in the city of Rio de Janeiro, Brazil. All piles were driven with free-fall hammers and in one particular work the piles were relatively short. The predictions of the Danish Formula were evaluated in relation to the pile length/diameter ratio. It was concluded that for short piles - with lengths less than 30 times the diameter - this formula indicates bearing capacities higher than the actual ones. A correction for a safe use of the Danish Formula for short piles is suggested.

Experimental Study on the Pile-Soil Synergistic Mechanism of Composite Foundation with Rigid Long and Short Piles

The rigid long-short-pile composite foundation has been increasingly used as an effective and low-cost reinforcement method. The pile-soil interaction in this foundation type is more complicated than that in the equal-length pile composite foundation. In this study, several physical model tests were conducted to investigate the pile-soil synergistic mechanism of the rigid long-short-pile composite foundation. A comparative analysis was conducted of the static load test data of single-pile and long-short pile composite foundations to assess the load-bearing characteristics and stiffness evolution of the composite foundation and pile-soil unit. The result indicated a positive correlation between the pile length and the overall bearing capacity of the single-pile composite foundation. The overall stiffness of the four-pile composite foundation was lower than that of the single-pile composite foundation due to an increase in the areas of the soil stress and the pull-down effect caused by multiple piles. The long pile exerted a greater influence on the overall settlement than the short pile. In addition, the correction coefficients were obtained to determine the pile-soil stiffness of the four-pile composite foundation based on that of the single-pile composite foundation, providing a theoretical reference for the optimal design of composite foundations.

Behavior of Single Micropile Under Different Lateral Load Rates

This paper displays an empirical work of a micropile inserted in the dry river sand with different length to diameter (L/D) ratios (13, 15, 27, 42, and 50). The experimental work is executed on the models of micropile to imitate the side force motion, acting on the micropile head to explain the micropile conduct due to the different side force rates. Forty-five models are tested (eighteen models for short pile, eighteen model for long pile and nine models for intermediate) embedded in different relative densities of sandy soil. The results illustrate that for the same relative density, the lateral load is decreased when the moving rate increasing from (3.37 to 3.97 then 4.59 mm/min), that means frequency (0.55 to 0.65 then 0.75 Hz), respectively. At the same moving rate of horizontal loading, the value of lateral load increased with the increase of horizontal displacement until reach to the 12mm at the end of the test. The duration of the test decreased with the increase of moving rate and the maximum duration of the test recorded for micropile model has (L/D) of 50 with 75% relative density when the moving rate of lateral load is 3.37 mm/min. Also, it is found that the duration of the test increases when the relative density increased at the same moving rate.

Geotechnical and Structural stochastic analysis of piled solar farm foundations

Development of large scale solar farms supported by large numbers of short piles has created new challenges for engineers to address. Solar arrays are highly flexible structures and the piles can be designed to move to enable more cost effective design. The structural reliability of the above-ground pile can be assessed and probabilities of failure for different section sizes calculated. Economic analysis incorporating capital cost and whole-of-life maintenance cost can be performed to work out whether adopting smaller section sizes provide the best cost outcome.Assessment of pile movements using Monte-Carlo calculations, unsaturated soil mechanics and updating material parameters with suction have been performed. The results show that soil movements are typically larger than pile movements and that soil can slip past the pile with no pile movement when the limiting conditions occur. The results also highlight that the largest soil and pile movements occur infrequently as a result of extreme wetting or drying conditions.Structural reliability analyses showed that correlating wind speed and direction results in a lower probability of failure than if wind load is considered to be uncorrelated with wind direction. The outcomes of the assessment were sensitive to the adopted probabilistic model for pile durability.The main limitation of the analyses is that there is limited information in the literature relating to the types of probability distributions and their input parameters. This adds uncertainty to the stochastic analysis.