Pile Groups In Sand Research Articles

Thermal-mechanical behavior of deeply buried pipe energy pile group in sand obtained from model test

One practical and effective method for shallow geothermal development is energy piling. This research presents the deeply buried pipe energy pile (DBP-EP), which has a wide range of potential applications and can collect deeper geothermal heat from the pile toe. This work conducts a model test investigation of the thermal–mechanical behavior of the DBP-EP group in sandy soil because the construction of the former differs from that of the common inside buried pipe energy piles (IBP-EP). The findings indicate that the heat exchanger tube at the pile toe of DBP-EP will be extended outward for heat exchange with the soil, in contrast to IBP-EP, and that the temperature change at the pile toe is greater than that of the whole. The pile cross-section strain decreases gradually from inside to outside along the radial direction. The axial earth pressure change rule around the pile is larger at both ends and small in the middle. For every 1℃ that the inlet temperature raises, the pile top’s final displacement increases by roughly 0.11‰D. At various inlet temperatures, the DBP-EP group heat transfer rate per meter drops by 8% − 23% when compared to the single pile’s. The average axial earth pressure difference surrounding the pile gradually rises when the pile top is not loaded, while the pile side friction difference of the pile group reduces in comparison to that of the single pile. The variations in pile side friction, axial earth pressure surrounding the pile, and pile top displacement of the pile group are reduced when the pile top is loaded because of the dense effect between the pile and the soil. This study contributes to the theoretical understanding of the design and practical implementation of DBP-EP structures.

Numerical investigation of the lateral response of pile groups in sand under local scour conditions

Bridge foundations located in a water flow environment commonly experience scour, which can lead to significant drops in the soil elevation immediately surrounding the foundation. This has significant ramifications for lateral bearing capacity as well as the integrity of the supported superstructure. While pile groups are one of the most foundation systems for bridges, current research on scouring effects has been largely limited to single piles. This paper fills this gap through the use of 3D finite element (FE) analysis, validated using centrifuge tests reported elsewhere in the literature. Results from a parametric analysis is described exploring the effects of the scour hole geometry, defined by the depth and slope angle, on the lateral behavior of pile groups. In particular, the influences on the load–displacement and bending moment and soil resistance distributions with depth for each pile within the group are considered. The results show that scour can have a significant detrimental influence on the lateral response of a pile group. An increase in the length of the pile group is also shown to significantly reduce the sensitivity of the lateral bearing capacity of the group to scour.

Performance of axially loaded defective pile groups in sand: capacity and serviceability evaluation

Performance of axially loaded defective pile groups in sand: capacity and serviceability evaluation

Weakened section detailing for scoured/elevated pile groups in sands toward post-earthquake resilient behavior: Quasi-static tests

Scoured or elevated pile-group foundations in coastal regions may experience noticeable residual deformation after strong earthquakes, leading to the loss of functionality and even collapse of the supported structures. To address this problem, a weakened section detailing, which is characterized by a large cover-thickness across a pile-length beneath the cap, is proposed to release constraints on the pile/pile-cap interface, and thereby reduce the residual deformation and meanwhile mitigate underground pile damage. To demonstrate the effectiveness of this section detailing, a pair of quasi-static tests were designed and conducted on two scaled specimens representing scoured pile-group foundations, one with the weakened section detailing and the other with the conventional one, under laterally cyclic loads that mimic horizontal earthquake loading. Test results are interpreted in terms of (1) structural failure mechanisms including damage modes and ductility capacity, and (2) post-earthquake resilient behavior reflected by residual deformation. Compared with the conventional one, the results well demonstrate the feasibility of the weakened section in reducing residual cap deformation (by as large as 34% and 80% for the translational and rotational deformation, respectively, at the ultimate state), mitigating underground damage, and improving ductility capacity under earthquake conditions, while almost maintaining the compression, shear and bending capacities under normal operational conditions. The test results also indicate a need to enhance the seismic shear capacity of the weakened section.

Investigation of the vertical responses of 2 × 2 square flexible batter pile groups in sand

The vertical bearing behaviors of the flexible batter pile groups in sand are investigated in this study. A series of model tests are carried out to study the effects of the batter angle (θ) on the vertical bearing capacities (V g) and distributions of internal forces of the pile groups. In addition, finite-element (FE) analysis is performed to explore the vertical bearing behaviors of the pile groups with various configurations, and the vertical bearing mechanism of the batter pile groups is analyzed. Moreover, a design method is proposed for predicting the bearing ratios (β) of the batter pile groups. The results show that the batter pile groups generally can provide higher vertical bearing capacities than the vertical pile groups with the same configuration. The batter angles for providing the greatest vertical stiffness are decreased with the increase of length–diameter ratio (R) and are not affected by the variation of relative density (D r). The predicting results obtained from the design method match well with the model test and FEM results. Some suggestions are proposed for guiding the application of the batter pile groups in practice engineering.

Axial and Lateral Efficiency of Tapered Pile Groups in Sand Using Mathematical and Three-Dimensional Numerical Analyses

AbstractThis study presents a new mathematical equation for calculating the pile group efficiency in cohesionless soil under combined axial and lateral loading conditions, considering the tapering ...

Cyclic Pile-Soil Interaction Effects on Load-Displacement Behavior of Thermal Pile Groups in Sand

Cyclic Pile-Soil Interaction Effects on Load-Displacement Behavior of Thermal Pile Groups in Sand

Settlement of Pile Groups in Sand.(Dept.C)

This article describe the methods for predicting the settlement of the pile groups in sand, and a development was done based on (Vesic 1967) and (Berezantzev 1961) taking into account the stats of soil, relative density, of sand and method of installation. The method was used to predicts the settlement of pile groups for actual pile groups of B high rise tower in Cairo, good agreement between the observed and the predicted settlement recommend the use of this method.

Scour effects on vertical effective stresses and lateral responses of pile groups in sands

For pile-supported structures, scour is a major threat as it removes soils around foundations and causes structural damages. Scour effects on the performance of the pile foundation have been well studied. However, most of these studies are focused on lateral responses of single piles, while very limited research is focused on lateral responses of pile groups. Therefore, prevailing design standards only recommend scour design procedures for single piles. Here, we proposed an improved analytical method (IAM) to analyze laterally loaded pile groups considering various scour-hole dimensions. The IAM was validated against the results of 3D finite element (FE) models calibrated against a full-scale load test. A series of parametric analyses were conducted to investigate the effects of scour-hole depth, scour-hole slope angle, sand relative density, pile spacing, number of piles, and pile group configuration on both post-scour vertical effective stresses and lateral responses of pile groups. Based on the IAM, a simple practical approach called the influence depth method (IDM) was also developed for use in routine design. The feasibility of applying the standard methods for the scoured pile groups was evaluated by comparing them with the 3D FE analyses and the proposed methods (IAM and IDM).

Application of binomial system-based reliability in optimizing resistance factor calibration of redundant pile groups

Recent research has indicated the potential of optimizing the design of pile groups using system-based reliability. Binomial distribution can be used to optimize the design of redundant pile groups. The application of binomial system-reliability is challenged by the need for determining a framework for calculating a key input variable related to the maximum number of defective piles a pile group can have without collapsing under applied loads, m factor. The objective of this research is to develop two robust finite element (FE) based methods to calculate m and utilize these methods in developing a framework for optimizing the calculation of pile resistance factors in redundant pile groups using binomial reliability. The methods were developed, verified, and applied to optimize the calibration of pile resistance factors for gravity loaded pile groups in sand. The resistance factors were optimized for the number of piles in a group, spacing of piles in a group, and the method of designing the pile as opposed to the current code approach of specifying a constant resistance factor for pile design irrespective of the pile group configuration. Analysis results show that resistance factors range from 0.31 to 0.96 for a system target reliability index of 3.0.

Investigation on determining uplift capacity and failure mechanism of the pile groups in sand

Foundations of some structures such as transmission towers, mooring systems for ocean surface or submerged platforms, tall chimneys, jetty structures are subjected to uplift loading. In such cases, to increase the uplift resistance of piles, pile foundations like anchored piles, batter piles and micro piles are extensively employed depending on in-situ conditions. This paper deals with the contribution of pile surface to the uplift capacity and the failure mechanism obtained for the pile groups in sand, and the main goal of the study is to investigate the effect of the pile surface roughness on the uplift capacity for different spacing ratios between piles. Therefore, the paper presents some findings of a single pile and pile groups embedded in sand under uplift loading. The variables investigated include the pile surface, pile embedment ratio and the spacing ratio between piles. Experiments were conducted to study foregoing parameters, and three-dimensional analyses were performed using the finite element method to illustrate the failure mechanism of pile groups and the interaction between piles for different spacing ratios between piles. The results show that the finite element simulation results indicate good agreement with the experiment results, and all variables significantly affect the uplift capacity of piles.

Implications of Thermal Cyclic Loading on Pile Group Behavior

This study investigated the thermomechanical behavior of thermal pile groups in sand. To analyze the influence of cyclic thermal loading on the stress–strain behavior of piles in a group, pile groups containing four thermal piles installed in dense Toyoura sand were numerically investigated. A concrete pile cap was considered on the piles. Axial mechanical load was applied instantaneously on the pile cap and thermal load was applied along the pile length for six thermal cycles consisting of alternate heating and cooling of the piles. The concrete piles and pile cap were considered to behave in a linear-elastic manner under the mechanical load and thermal load. The soil was assumed to possess elastoplastic behavior and was simulated using the Mohr–Coulomb plasticity model. The effect of mechanical and cyclic thermal load on the pile groups was studied by varying the pile group parameters such as pile spacing (sp), pile diameter (Dp), and thickness of the pile cap (tpc). In all the analyses, the effect of cyclic thermal load was compared in terms of development of axial displacement, axial strains, and axial stresses in the piles. Thermomechanically loaded piles exhibited higher displacements, strains and stresses than did mechanically loaded piles. The results also indicate that the axial load on the piles under cyclic thermal loading was larger for the piles with higher aspect ratio than for the piles with lower aspect ratio. The effect of pile spacing was more pronounced in case of piles with higher aspect ratio. An increased thickness of the pile cap resulted in higher axial load and displacement in the piles. The cyclic thermal load resulted in residual or plastic strains in the piles. The thermomechanical behavior of a pile group is influenced by parameters such as pile spacing, aspect ratio, and pile cap thickness, which should be considered in thermal pile group design for structural stability performance of the pile group.

Scour effects on lateral behavior of pile groups in sands

Scour that removes soils around foundations supporting bridges and marine structures is the major cause for structural failures. Recently, many studies have been conducted to investigate scour effects on lateral behavior of single piles using numerical analyses, laboratory model tests, or centrifuge tests. However, very limited research is focused on scour effects on lateral behavior of pile groups. No simple method is currently available for practicing engineers to analyze pile groups under scour conditions. In this study, a simple and practical method was proposed based on the existing p-y curve theory to facilitate the design of laterally loaded pile groups under scour conditions. Feasibility of the proposed method was examined against 3D finite element (FE) analyses through a series of parametric studies by varying scour-hole dimensions, soil properties, and pile group configurations. The results showed that the proposed method generally produced agreeable results with the 3D FE analyses. Scour-induced lateral capacity loss of pile groups was 10–13% more in dense sands than in loose sands. Pile groups were more susceptible to scour than single piles under the equivalent scour conditions. A pile group with smaller pile spacing and larger pile numbers showed a less loss of lateral capacity due to scour.

Response of pile groups in sand due to lateral cyclic loading

This paper considers data from centrifuge model tests on pile groups in silica sand involving lateral one-way cyclic loading. The influence of cyclic load amplitude, pile spacing within the pile group and number of cycles on the observed response are highlighted. Investigating the contribution of each pile on the lateral capacity shows leading row piles exhibit highest bending moments and attract larger loads due to ‘shadowing’ effects. Cyclic loading results in a subtle change of the load distribution within the pile group, with the load gradually shifting from the leading to the trailing piles as the number of cycles increases. The effect of cyclic loading on the initial stiffness of the p–y curves is more significant; initial stiffness reduces with increasing number of loading cycles at a rate that is higher in the leading row than in the trailing row. The changes in load distribution are quantified using simple analytical equations that may be used in design.

Experimental Investigation of Single Model Pile and Pile Group Behavior in Saturated and Unsaturated Sand

AbstractThe research focus of this paper is directed to investigate the behavior of a single model pile and pile groups in sand under both saturated and unsaturated conditions. Forty different mode...

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.

Axial Resistance of Nondisplacement Pile Groups in Sand

When subjected to axial loading, the response of a pile in a pile group is different from that of an isolated single pile, all other factors being the same. Three-dimensional finite-element analyses were performed to study the response to vertical loads of nondisplacement pile groups in sand. The analyses were done with an advanced bounding-surface-plasticity constitutive model. The mechanical response of soil elements at various locations between the group piles was thoroughly investigated to reveal the underlying pile–soil–pile interaction mechanisms. Pile group efficiency was found to be a function of the pile head settlement, number of piles in the group, pile-to-pile spacing, and relative density of the sand. The effect of cap–soil contact on the pile group resistance development was also studied. For small pile groups, the group efficiency is close to or greater than 1 at settlement levels likely to be of interest in design.

Thermo-mechanical behaviour of floating energy pile groups in sand

This paper presents the experimental results of small-scale model tests of an instrumented floating energy pile group in which the piles were embedded in dry medium-dense sand and subjected to the seasonal temperature pattern of the city of Nanjing in China. The study also included a model test to assess the effect of including nonthermal piles on the thermo-mechanical behaviour of the floating energy pile group. For comparison, a model test of a single floating energy pile embedded in the same soil and subjected to a similar temperature pattern was also conducted. The results show that the thermo-mechanical behaviour of an energy pile group is different from that of a single energy pile in terms of the thermally induced change in axial pile stress and the displacement of the pile top and tip. This difference in behaviour could be explained by the higher lateral confining pressure expected on a single pile than on a pile in a group due to pile interaction effects, which could lead to different end restraint boundary conditions. We conclude that the thermo-mechanical behaviour of an energy pile is controlled mainly by the end restraint boundary conditions.

Physical modeling of behaviors of cast-in-place concrete piled raft compared to free-standing pile group in sand

Similar to free-standing pile groups, piled raft foundations are conventionally designed in which the piles carry the total load of structure and the raft bearing capacity is not taken into account. Numerous studies indicated that this method is too conservative. Only when the pile cap is elevated from the ground level, the raft bearing contribution can be neglected. In a piled raft foundation, pile–soil–raft interaction is complicated. Although several numerical studies have been carried out to analyze the behaviors of piled raft foundations, very few experimental studies are reported in the literature. The available laboratory studies mainly focused on steel piles. The present study aims to compare the behaviors of piled raft foundations with free-standing pile groups in sand, using laboratory physical models. Cast-in-place concrete piles and concrete raft are used for the tests. The tests are conducted on single pile, single pile in pile group, unpiled raft, free-standing pile group and piled raft foundation. We examine the effects of the number of piles, the pile installation method and the interaction between different components of foundation. The results indicate that the ultimate bearing capacity of the piled raft foundation is considerably higher than that of the free-standing pile group with the same number of piles. With installation of the single pile in the group, the pile bearing capacity and stiffness increase. Installation of the piles beneath the raft decreases the bearing capacity of the raft. When the raft bearing capacity is not included in the design process, the allowable bearing capacity of the piled raft is underestimated by more than 200%. This deviation intensifies with increasing spacing of the piles.

Static behaviour of 3x3 pile group in sand under lateral loading

This paper presents the static lateral load behaviour of single pile in comparison with 3x3 pile group in sand. The piled raft system is modelled using PLAXIS3D. Parametric studies of varying length to diameter (L/D) and spacing of piles in a group and diameter of piles (S/D) have been performed. The behaviour of group piles in terms of static lateral load capacity and group efficiency has been discussed.