FIELD STUDY OF GROUP EFFECTS ON THE PULLOUT CAPACITY OF ‘DEEP’ HELICAL PILES IN SAND

2021 ◽  
Author(s):  
Aaron S. Bradshaw ◽  
Lindsay Cullen ◽  
Zachary Miller
Keyword(s):  
Numerical Models ◽  
Ground Surface ◽  
Pile Group ◽  
Load Test ◽  
Load Testing ◽  
Pullout Capacity ◽  
Pile Groups ◽  
Helical Piles ◽  
Single Helix ◽  
Group Effects

This paper presents the results of a field load test program used to investigate group effects on the pullout capacity of single-helix ‘deep’ helical piles/anchors in sand. The high tensile capacity and silent installation of helical piles has given them serious consideration as an alternative to conventional deep foundations and anchors for offshore renewable energy structures. New offshore applications may consider the use of groups of helical piles to resist structural loads. Group interaction effects are known to occur in helical piles but there is a scarcity of field data on groups in sands under tensile loading. This study involved the installation and load testing of single-helix 152-mm diameter round shaft piles and pile groups embedded in sand to depths of 12 and 18 helix diameters below the ground surface. The study was designed to explore the effects of close pile spacing, group configuration (i.e. number of piles), and soil strength as interpreted from Cone Penetration Test (CPT) resistance. The results showed group efficiencies ranging from about 0.6 to 1.0 at a horizontal spacing of 2 to 3 times the helix diameter in sands with friction angles of about 39 to 44 degrees. The data from this study may also be useful for calibration and validation of numerical models for further analysis of helical pile group interactions.

Experimental and Numerical Study of Laterally Loaded Pile Groups with Pile Caps at Variable Elevations

2000 ◽  
Vol 1736 (1) ◽  
pp. 12-18 ◽  
Author(s):  
Michael C. McVay ◽  
Limin Zhang ◽  
Sangjoon Han ◽  
Peter Lai
Keyword(s):  
Numerical Study ◽  
Ground Surface ◽  
Pile Group ◽  
Special Device ◽  
Pile Groups ◽  
Finite Element Program ◽  
Lateral Resistance ◽  
Pile Cap ◽  
Element Program ◽  
Pile Caps

A series of lateral load tests were performed on 3×3 and 4×4 pile groups in loose and medium-dense sands in the centrifuge with their caps located at variable heights to the ground surface. Four cases were considered: Case 1, pile caps located above the ground surface; Case 2, bottom of pile cap in contact with the ground surface; Case 3, top of pile cap at the ground surface elevation; and Case 4, top of pile cap buried one cap thickness below ground surface. All tests with the exception of Case 1 of the 4×4 group had their pile tips located at the same elevation. A special device, which was capable of both driving the piles and raining sand on the group in flight, had to be constructed to perform the tests without stopping the centrifuge (spinning at 45 g). The tests revealed that lowering the pile cap elevation increased the lateral resistance of the pile group anywhere from 50 to 250 percent. The experimental results were subsequently modeled with the bridge foundation-superstructure finite element program FLPIER, which did a good job of predicting all the cases for different load levels without the need for soil–pile cap interaction springs (i.e., p-y springs attached to the cap). The analyses suggest that the increase in lateral resistance with lower cap elevations may be due to the lower center of rotation of the pile group. However, it should be noted that this study was for pile caps embedded in loose sand and not dense sands or at significant depths. The experiments also revealed a slight effect for the case of the pile cap embedded in sand with a footprint wider than the pile row. In that case the size of the passive soil wedge in front of the pile group, and consequently the group’s lateral resistance, increased.

Study on Negative Skin Friction of Pile Groups Considering Coupled Effect of Surface Load and Soil Consolidation

2009 ◽  
Author(s):  
Gang-qiang Kong ◽  
Qing Yang ◽  
Mao-tian Luan
Keyword(s):  
Skin Friction ◽  
Influence Factors ◽  
Pile Group ◽  
Engineering Practice ◽  
Surface Load ◽  
Soil Consolidation ◽  
Test Results ◽  
Pile Groups ◽  
Negative Skin Friction ◽  
Group Effects

The study was performed based on an analysis of model test results of 3×3 pile group and confirmed the reliability and accuracy of determining negative skin friction (NSF) using numerical modeling of fluid-soild interaction. A 3D numerical model with surface load and soil consolidation was established using FLAC3D, which focused on the mechanism of NSF and its influence factors such as friction of pile-soil interface, spacing of pile and time of consolidation. The results obtained under different cases in an engineering practice were finally compared with measured and empirical data, showing that it is necessary to consider surface load and soil consolidation when dealing with NSF. The results also indicated the analysis with surface load and soil consolidation could simulate the developing process of NSF and produce a more accurate outcome — closer to measured data. The NSF increases rapidly at beginning and then slowly down, finally stabilized at a constant as soil consolidation progresses. Due to pile group effects, the piles at the centre had a smaller downdrag and settlement than those at corner or at edges; pile group effects became more obvious when pile spacing decreased.

scholarly journals Numerical simulation of concrete pile groups' response bored in cemented sand deposit under axial static load testing

2019 ◽  
Vol 92 ◽  
pp. 16011
Author(s):  
Mehdi Aghayarzadeh ◽  
Hadi Khabbaz
Keyword(s):  
Numerical Simulation ◽  
Static Load ◽  
Direct Method ◽  
Pile Group ◽  
Foundation Engineering ◽  
Load Testing ◽  
Pile Groups ◽  
Cemented Sand ◽  
Non Linear ◽  
Static Load Testing

For a safe foundation to perform as desired, the ultimate strength of each pile must fulfil both structural and geotechnical requirements. Pile load testing is considered as a direct method of determining the ultimate bearing capacity of a pile. Pile groups are commonly used in foundation engineering and due to the difficulties and cost of full-scale load tests, most pile group tests are scaled down regardless of whether performed in the field or laboratory. In this paper, it is aimed to simulate the behaviour of concrete bored pile groups under axial static load testing using PLAXIS 3D software and to compare the obtained results with measured curves in an experimental study introduced in the literature. In numerical simulation, to account for the stiffness variation existing inside the pile group and to achieve a reasonable correlation between measured and predicted load-settlement curves three different analyses, including linear elastic, completely non-linear, and a combination of non-linear and linear analyses were performed. The results indicate that the combined non-linear and linear analysis seems a suitable analysis for pile group behaviour prediction.

Flexibility coefficients and interaction factors for pile group analysis

1986 ◽  
Vol 23 (4) ◽  
pp. 441-450 ◽  
Author(s):  
Bahaa El Sharnouby ◽  
Milos Novak
Keyword(s):  
Load Distribution ◽  
Group Analysis ◽  
Vertical Plane ◽  
Ground Surface ◽  
Pile Group ◽  
Lateral Loads ◽  
Pile Groups ◽  
Group Evaluation ◽  
Interaction Factors ◽  
Single Piles

Flexibility coefficients of single piles and interaction factors established for groups of two piles are presented to facilitate analysis of arbitrary pile groups exposed to static horizontal loads. Such an analysis may yield pile group flexibility, stiffness, deflection, and distribution of loads on individual piles. The data given are complete in that they include horizontal translation, rotation in the vertical plane, and cross effects between the two, making it possible to establish complete stiffness and flexibility matrices of pile groups provided with either rigid caps or arbitrarily flexible caps. Homogeneous, parabolic, and linear (Gibson's) soil profiles are considered and the piles may have a free length sticking above the ground surface. The methods of group evaluation based on superposition of interaction factors are reviewed and compared and numerical examples are given. Key words: piles, pile groups, lateral loads, flexibility, stiffness, load distribution.

scholarly journals FLOATING RAFT-PILE FOUNDATIONS ANALYSIS USING NUMERICAL SIMULATION

2011 ◽  
Vol 7 (2) ◽  
pp. 40
Author(s):  
Helmy Darjanto
Keyword(s):  
Numerical Simulation ◽  
Pile Foundation ◽  
Load Transfer ◽  
Numerical Models ◽  
Pile Group ◽  
Vertical Displacement ◽  
Constitutive Law ◽  
Pile Foundations ◽  
Pile Groups ◽  
Foundation Soil

The numerical simulation of raft-pile foundations subjected to vertical load is presented in this paper. For comparison study, numerical models of single raft and pile groups are completed. The numerical models are adopting the elastic constitutive law for the materials. The stresses and vertical displacement of the models are observed. The behaviour of the raft-pile foundation compared to the pile-group is then investigated. The results using the same external load show that the raft-pile foundation has smallest displacement compared to the others. In terms of stresses, the raft shows contribution of the load transfer to the underneath soil as well as the piles. Moreover, the behaviour of the raft-pile system appears to be a combination of the pile-group and the single raft. In order to estimate the bearing capacity of the raft-pile system, it is suggested that the contribution of the raft should be included in addition of the piles’. Keywords: raft-pile foundation, soil-structure interaction, floating foundation

scholarly journals Pile group settlement analysis on the basis of Static Load Test

2019 ◽  
Vol 97 ◽  
pp. 04031 ◽  
Author(s):  
Nikola Dudek
Keyword(s):  
Pile Group ◽  
Load Test ◽  
Static Load Test ◽  
Pile Groups ◽  
Stiffness Modulus ◽  
Test Load ◽  
Bored Pile ◽  
Driven Pile ◽  
Settlement Analysis ◽  
Element Method

Settlement of large pile groups is most often estimated by the Alternative Foundation Method. However, this method has some limitations related to assumed uniformity of pile loads. A very big problem is also related to estimating the stiffness of subgrade loaded by a group of piles. Similar problems arise when piled foundation is numerically modelled in Finite Element Method or Boundary Element Method programmes. The results obtained are highly dependent on the input data, especially on characteristics describing soil subgrade stiffness and strength and moduli at pile – soil contact. The paper presents an example of using the results of trial static calculations for the pile made using a technology not identical with that ultimately implemented for the project. The subgrade stiffness modulus was determined with Inverse Analysis using bored pile test load. The results attained were used for further calculations (forecast) the settlement of prefabricated driven pile (a single one) and then to estimate of pile group settlement under full load from bridge structure abutment.

scholarly journals LOAD-SETTLEMENT BEHAVIOUR OF MODEL PILE GROUPS IN SAND UNDER VERTICAL LOAD

2017 ◽  
Vol 23 (8) ◽  
pp. 1148-1163 ◽  
Author(s):  
Mauricio Martines SALES ◽  
Monica PREZZI ◽  
Rodrigo SALGADO ◽  
Yoon Seok CHOI ◽  
Jintae LEE
Keyword(s):  
Pile Group ◽  
Single Pile ◽  
Load Testing ◽  
Driven Piles ◽  
Pile Groups ◽  
Pile Installation ◽  
Model Pile ◽  
Group Configuration ◽  
Settlement Behaviour ◽  
Good Agreement

Model pile load testing is effective to study the load-settlement behaviour of pile foundations given the con­trolled environment in which the testing is done. This paper reports a testing program in a large calibration chamber involving individual piles and pile groups installed in sand samples of three different densities. Tests on both nondis­placement and driven piles are evaluated to assess the influence of the pile installation process on pile load-settlement response. A method is proposed to predict the load-settlement response of a pile group based on the response of a single pile. The method is shown to produce estimates that are in good agreement with measurements. The influence of pile group configuration, pile spacing, soil density and method of pile installation is discussed.

scholarly journals Experimental testing of a full-scale of group efficiency in multiple soil layers

2019 ◽  
Vol 13 (3) ◽  
pp. 135-142
Author(s):  
Le Thiet Trung ◽  
Duong Diep Thuy ◽  
Pham Viet Anh
Keyword(s):  
Load Transfer ◽  
Experimental Testing ◽  
Pile Group ◽  
Load Testing ◽  
Group Effect ◽  
Pile Groups ◽  
In Situ Tests ◽  
Group Efficiency ◽  
Pile Group Effect

Results of in-situ tests showed that the performance of single isolated piles and individual piles within a group is largely different. When piles are arranged in a group, the interaction between piles and the foundation depends on the pile arrangement and the pile group effect. To date, studies on the pile group effect in Vietnam have been limited to reduced-scale laboratory testing or static load testing where piles are installed into homogeneous sandy or clayey foundation. This paper presents in situ tests which were performed on both single piles and pile groups, loaded to failure, with the aim of studying the pile group effect of piles embedded in multi-layered foundation. Strain gauges were installed along the shaft of 10 m long steel pipe piles, with a diameter of 143 mm. The influence of loose sand layers on the group effect in case of friction piles was evaluated. The experimental results indicated that the influence of sand layers was evident, and the group factor was calculated to be 1.237. Keywords: group efficiency; pile groups; axial capacity; load transfer.

Dynamic Response of Pile Groups under Vertical Forces in Saturated Soil

2011 ◽  
Vol 261-263 ◽  
pp. 1499-1504
Author(s):  
Yuan Yi Zhao ◽  
Zhou Hong Tao
Keyword(s):  
Permeability Coefficient ◽  
Near Field ◽  
Ground Surface ◽  
Pile Group ◽  
Dynamic Force ◽  
Pile Groups ◽  
Propagation Equation ◽  
Soil System ◽  
Different Types ◽  
Ground Surface Movement

Based on Biot’s wave propagation equation and boundary conditions, this paper builds up pile group and soil system used for calculation in 3 dimension models, though mass conservative and motion equation. The results of ground surface movement are obtained under the effect of vertical dynamic force though Newmark direct integration. Compared with the measured results, the numerical outcomes conform accurately. The calculating results show that vibration of ground surface can be affected by several parameters such as soils’ possion ratio, permeability coefficient, different types of pile groups and so on. Different factors have different effects on ground’s surface vibration in both far field and near field.

Effects of dead loads on the lateral response of battered pile groups

2002 ◽  
Vol 39 (3) ◽  
pp. 561-575 ◽  
Author(s):  
L M Zhang ◽  
M C McVay ◽  
S J Han ◽  
P W Lai ◽  
R Gardner
Keyword(s):  
Pile Group ◽  
Lateral Load ◽  
Load Test ◽  
Vertical Load ◽  
Pile Groups ◽  
Dead Load ◽  
Vertical Loading ◽  
Lateral Resistance ◽  
Tension And Compression ◽  
Load Tests

The effects of vertical load on the lateral resistance of single piles were initially reviewed to facilitate the interpretation of the test results of pile groups. Then, 18 different lateral load tests were carried out in the centrifuge on the 3 × 3 and the 4 × 4 fixed-head battered pile groups to investigate the effects of vertical load on the group lateral resistance. Vertical dead loads ranging from approximately 20 to 80% of the vertical ultimate group capacity Puv were applied. Based on these tests, the effects of vertical dead load on the lateral resistance of the battered pile groups are found to depend on pile arrangement, pile inclination, and soil density. The lateral resistances of the 3 × 3 pile groups do not appear to vary considerably with the vertical dead loads in the range of the vertical loads studied. For the 4 × 4 pile groups however, the lateral resistances at vertical loads of approximately 50 and 80% Puv may be 26-29% and even 40% higher than that at the 20% Puv dead load. It may be inferred that designs based on standard lateral load tests with small vertical dead loads would be on the safe side. Three mechanisms for vertical load effects are discussed in terms of axial tension and compression failures, influence of pile inclination, and initial subgrade reaction caused by vertical loading. Preliminary numerical analyses are also performed to simulate the responses of some of the battered pile groups.Key words: pile group, battered pile, lateral resistance, load test, pile-soil interaction, centrifuge test.

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