Geometrical effects on the load transfer mechanism of pile groups: three-dimensional numerical analysis

2018 ◽  
Vol 55 (5) ◽  
pp. 749-757 ◽  
Author(s):  
Yaru Lv ◽  
Dongdong Zhang
Keyword(s):  
Load Transfer ◽  
Three Dimensional ◽  
Bending Moment ◽  
Pile Group ◽  
Transfer Mechanism ◽  
Single Pile ◽  
Pile Groups ◽  
Load Transfer Mechanism ◽  
Side Resistance ◽  
Geometrical Effects

This paper investigates geometrical effects on the load transfer mechanism of off-ground capped pile groups subjected to vertical load by four three-dimensional numerical simulations, including a circular single pile, an X-shaped cross-sectional concrete (XCC) single pile, a 4 × 4 circular pile group, and a 4 × 4 XCC pile group. The ultimate bearing capacities of the XCC and circular piles within pile groups are approximately 0.86 and 0.74 times that of the XCC and circular single piles, respectively. The group efficiency of the XCC pile group is mainly improved by its side resistance. Comparing the XCC pile group to the circular pile group, the increment in side resistance is almost larger than the increment in pile perimeter, indicating that the pile geometry alters the load transfer mechanism via stress concentration and lateral stress arching. A nonuniform load distribution on piles within a capped pile group causes a bending moment along the pile shafts. The bending moment of XCC piles is smaller than that of circular piles because the raft stiffness of an XCC pile group is increased by its larger circumscribing pile diameter.

scholarly journals Single Pile Settlement and Load Transfer Mechanism due to Excavation in Silty Clay

2018 ◽  
Vol 8 (1) ◽  
pp. 2485-2492 ◽  
Author(s):  
M. A. Soomro ◽  
K. F. Memon ◽  
M. A. Soomro ◽  
A. Memon ◽  
M. A. Keerio
Keyword(s):  
Load Transfer ◽  
Bending Moment ◽  
Small Strain ◽  
Transfer Mechanism ◽  
Ground Movement ◽  
Major Influence ◽  
Silty Clay ◽  
Single Pile ◽  
Load Transfer Mechanism ◽  
Pile Settlement

In densely built areas, development of underground transportation system often involves excavations for basement construction and cut-and-cover tunnels which are sometimes inevitable to be constructed adjacent to existing piled foundations. In order to gain new insights into single pile responses (i.e. settlement and load transfer mechanism) to an adjacent excavation in saturated silty clay, a three-dimensional coupled- consolidation numerical analysis is conducted in this study. An advanced hypoplasticity (clay) constitutive model with small-strain stiffness was adopted. A linear increase in pile settlement was observed due to excavation-induced stress release. This is because part of the pile is placed within the boundaries of a major influence zone due to excavation-induced ground movement. Based on a settlement criterion, apparent loss of pile‘s capacity is 14%. A maximum bending moment of about 350 kNm is induced in the pile with the maximum deflection of 28 mm. In addition, mobilisation of shear strength at the pile-soil interface was found to be a key factor governing pile-soil-excavation interaction. During excavation, a downward load-transfer mechanism in the piles can be identified.

scholarly journals 3D Centrifuge Modeling of the Effect of Twin Tunneling to an Existing Pile Group

2017 ◽  
Vol 7 (5) ◽  
pp. 2030-2040
Author(s):  
M. A. Soomro ◽  
M. A. Keerio ◽  
M. A. Soomro ◽  
D. K. Bangwar
Keyword(s):  
Axial Force ◽  
Urban Areas ◽  
Load Transfer ◽  
Three Dimensional ◽  
Bending Moment ◽  
Pile Group ◽  
Centrifuge Modeling ◽  
Pile Groups ◽  
Moment Capacity ◽  
Centrifuge Tests

In densely built urban areas, it is inevitable that tunnels will be constructed near existing pile groups. The bearing capacity of a pile group depends on shear stress along the soil-pile interface and normal stress underneath the pile toe while the two would be adversely affected by the unloading process of tunneling. Although extensive studies have been conducted to investigate the effects of tunnel construction on existing single piles, the influence of twin tunnel advancement on an existing pile group is merely reported in the literature. In this study, a series of three-dimensional centrifuge tests were carried out to investigate the response of an existing pile group under working load subjected to twin tunneling at various locations in dry Toyoura sand. In each twin tunneling test, the first tunnel is constructed near the mid-depth of the pile shaft, while the second tunnel is subsequently constructed either next to, below or right underneath the pile toe (Tests G_ST, G_SB and G_SU, respectively). Among the three tests, the 2nd tunnel excavated near the pile toe (Test G_ST) results in the smallest settlement but the largest transverse tilting (0.2%) of pile group. Significant bending moment was induced at the pile head (1.4 times of its bending moment capacity) due to the 2nd tunnel T. On the contrary, tunneling right underneath the toe of pile (i.e., Test G_SU) results in the smallest tilting but largest settlement of the pile group (4.6% of pile diameter) and incremental mobilisation of shaft resistance (13%). Due to stress release by the twin tunneling, the axial force taken by the front piles close to tunnels was reduced and partially transferred to the rear piles. This load transfer can increase the axial force in rear piles by 24%.

Dynamic analysis of laterally loaded pile groups in sand and clay

2002 ◽  
Vol 39 (6) ◽  
pp. 1358-1383 ◽  
Author(s):  
Yasser E Mostafa ◽  
M Hesham El Naggar
Keyword(s):  
Dynamic Loading ◽  
Dynamic Load ◽  
Load Transfer ◽  
Pile Group ◽  
Nonlinear Behaviour ◽  
Single Pile ◽  
Offshore Platforms ◽  
Group Effect ◽  
Pile Groups ◽  
Pile Head

Pile foundations supporting bridge piers, offshore platforms, and marine structures are required to resist not only static loading but also lateral dynamic loading. The static p–y curves are widely used to relate pile deflections to nonlinear soil reactions. The p-multiplier concept is used to account for the group effect by relating the load transfer curves of a pile in a group to the load transfer curves of a single pile. Some studies have examined the validity of the p-multiplier concept for the static and cyclic loading cases. However, the concept of the p-multiplier has not yet been considered for the dynamic loading case, and hence it is undertaken in the current study. An analysis of the dynamic lateral response of pile groups is described. The proposed analysis incorporates the static p–y curve approach and the plane strain assumptions to represent the soil reactions within the framework of a Winkler model. The model accounts for the nonlinear behaviour of the soil, the energy dissipation through the soil, and the pile group effect. The model was validated by analyzing the response of pile groups subjected to lateral Statnamic loading and comparing the results with field measured values. An intensive parametric study was performed employing the proposed analysis, and the results were used to establish dynamic soil reactions for single piles and pile groups for different types of sand and clay under harmonic loading with varying frequencies applied at the pile head. "Dynamic" p-multipliers were established to relate the dynamic load transfer curves of a pile in a group to the dynamic load transfer curves for a single pile. The dynamic p-multipliers were found to vary with the spacing between piles, soil type, peak amplitude of loading, and the angle between the line connecting any two piles and the direction of loading. The study indicated the effect of pile material and geometry, pile installation method, and pile head conditions on the p-multipliers. The calculated p-multipliers compared well with p-multipliers back-calculated from full scale field tests.Key words: lateral, transient loading, nonlinear, pile–soil–pile interaction, p–y curves, Statnamic.

Load transfer mechanism in pile group due to single tunnel advancement in stiff clay

2015 ◽  
Vol 45 ◽  
pp. 63-72 ◽  
Author(s):  
Mukhtiar Ali Soomro ◽  
Yi Hong ◽  
Charles Wang Wai Ng ◽  
Hu Lu ◽  
Siyuan Peng
Keyword(s):  
Load Transfer ◽  
Pile Group ◽  
Transfer Mechanism ◽  
Load Transfer Mechanism ◽  
Stiff Clay

scholarly journals Large-scale model tests of a single pile and two-pile groups for an offshore platform in sand

2021 ◽  
Author(s):  
Aligi Foglia ◽  
Khalid Abdel-Rahman ◽  
Elmar Wisotzki ◽  
Tulio Quiroz ◽  
Martin Achmus
Keyword(s):  
Large Scale ◽  
Load Transfer ◽  
Pile Group ◽  
Scale Model ◽  
Single Pile ◽  
Pile Groups ◽  
Group Efficiency ◽  
Large Scale Model ◽  
Load Tests ◽  
The Given

Estimating pile group efficiency for open-ended steel piles in small group arrangements is a challenging task for designers. This paper reports on the large-scale experimental campaign performed for the BorWin gamma offshore converter platform, which involved single piles and two-pile group systems on a scale of 1:10. The experimental works included installation, dynamic end-of-driving tests, dynamic restrike tests, and static load tests of a single pile and a pair of two-pile groups in densely compacted, artificially prepared homogeneous sand. The CPT profiles and the blow counts confirmed that the foundation systems are comparable to each other. The experimental results of the single pile system were compared with conventional design methods. Such comparison indicated that CPT-based methods and load-transfer methods are applicable at the considered model scale. The bearing capacity prediction obtained via the CAPWAP method is conservative with respect to the static capacity. A consistent setup effect can be detected by analyzing the complete dynamic loading session. The pile group efficiency for the given foundation system was found to be less than 1.0 at both very small and very large soil strains, while it equaled 1.0 at failure.

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