Article

Lateral limiting pressure on square pile groups in undrained soil

Article

Lateral limiting pressure on square pile groups in undrained soil

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Abstract

In this paper, the lateral limiting pressure on square pile groups in undrained soil is explored using two−dimensional finite element modelling. A parametric study is conducted to assess the role of pile−soil adhesion, group size and pile spacing on group capacity and corresponding failure mechanisms. Results from the finite element output show that large groups of closely−spaced piles exhibit significant reductions in lateral capacity compared to equivalent single pile values. Significant variations in the load−sharing across the group are also observed, with the corner piles experiencing loads up to 162% above the group average for a 25−pile group. A simplified closed−form design approach is developed using a modified Ramberg−Osgood formulation to predict the lateral group capacity. The proposed approach is shown to provide excellent agreement to the numerical results and a rigorous upper bound prediction of a selection of field data and predictions determined using existing design guidelines.

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... In recent years, the focus of pile design has shifted towards 21 serviceability limit state resulting in the application of non−linear frameworks to pile group analysis 22 (Sheil et al. 2018). Within a non−linear framework, pile settlement is no longer uncoupled from the 23 ultimate capacity and therefore an accurate capacity estimation remains an essential underpinning 24 element of formal pile design calculations (Sheil andMcCabe 2014, 2017). 25 ...
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Full-scale lateral load tests on a group of bored and a group of driven precast piles were carried out as part of a research project for the proposed high-speed rail system in Taiwan. Standard penetration tests, cone penetration tests (CPT), and Marchetti Dilatometer tests (DMT) were performed before the pile installation. The CPT and DMT were also conducted after pile installation. Numerical analyses of the laterally loaded piles were conducted using p-y curves derived from preconstruction and postconstruction DMT and by applying the concept of p multipliers. Comparisons between preconstruction and postconstruction CPT and DMT data and evaluation of the results of computations show that the installation of bored piles softened the surrounding soil, whereas the driven piles caused a densifying effect.
Article
A static lateral load test was performed on a full-scale pile group to determine the resulting pile-soil-pile interaction effects. The 3 X 3 pile group at three-diameter spacing was driven into a profile consisting of soft to medium-stiff clays and silts underlain by sand. The piles were instrumented with inclinometers and strain gages. The load carried by each pile was measured. A single pile test was conducted for comparison. The pile; group deflected over two times more than the single pile under the same average load. Group effects significantly reduced load capacity for all rows relative to single pile behavior. Trailing rows carried less than the leading row, and middle row piles carried the lowest loads. Maximum moments in the group piles were 50-100% higher than in the single pile. P-multipliers were 0.6, 0.38, and 0.43 for the front, middle, and back row piles, respectively. Good agreement between the measured and computed Pile group responses was obtained using the p-multiplier approach. Design curves are presented to estimate p-multipliers over a range of pile spacings.
Article
Pile-supported marine structures are designed for significant amounts of lateral load. In this paper, the influence of parameters like flexural rigidity of pile material, embedment length of pile, and arrangement of piles with respect to the direction of loading on the behavior of laterally loaded pile groups has been studied through an experimental program. The results obtained from lateral load tests carried out on model pile groups arranged at different spacings and embedded in a marine clayey bed are presented and discussed. The results indicate that the lateral load capacity of the pile group depends mainly on the rigidity of pile soil system for different arrangements of piles within a group. This is further substantiated by a simplified finite element analysis bringing in the differences in passive resistance. The group efficiencies under lateral loading obtained from the present investigation are found to be in good agreement with the predictions of earlier researchers.
Article
An isolated single pile and a large-scale test group of 16 prestressed concrete piles spaced at 3 diameters were subjected to a static lateral loading using a fixed-headed production group for reaction. The foundation consisted of sand overlying a partially cemented sand at the Roosevelt Bridge replacement, Stuart, Fla. Ten piles of the test group, six piles of the reaction group, and a single pile were instrumented with strain gauges and inclinometers. The piles were 76 cm(2), and approximately 16.5 m long. Standard penetration tests (SPT), cone penetration tests (CPT), DMT, and PMT in-situ tests were used to establish the soil profile and py curves. Subsequent to testing, the strain gauges and inclinometer data were reduced to ''measured'' p-y curves. The p-y curves developed from SPT correlations and PMT results provided an accurate soil representation. The single pile was subjected to 320 kN, while the pile groups were loaded to about 4,800 kN. The testing results show that the nonlinear characteristics of cracked prestressed concrete piles dominate analyses and data reduction. Consequently, the FLPIER program, with its nonlinear concrete capabilities, could predict properly the ''postcracking'' response. The group interaction was accurately modeled by p-y (actually p, only) multipliers, which were determined as 0.8, 0.7, 0.3, and 0.3 for the leading, middle leading, middle trailing, and trailing rows, respectively, with the overall group p-y multiplier being 0.55.
Article
A three-dimensional collapse mechanism is described for analysis of the ultimate strength of laterally loaded piles under undrained conditions. The analysis is based on the upper-bound method of plasticity theory. The mechanism combines a deforming conical soil wedge in the near surface with plane strain deformation at depth. Four optimization parameters are employed, which define the geometrical extent and spatial variation of the Soil deformation. The mechanism is capable of rationally accounting for many complexities such as strength nonhomogeneity, soil-pile adhesion. and suction on the back of the pile. Lateral force and pile top moment loading can both be accommodated. Parameter studies showing the effects of these features are presented along with comparisons of model predictions with recent centrifuge test results. An empirical prediction equation is fit to analytical results for typical soil conditions to provide a more convenient form of the analysis method. The empirical fit is demonstrated for cases of linearly increasing strength and for two-layered soil systems.
Article
The coupled bridge foundation-superstructure finite-element code FLPIER was employed to predict the lateral response of the single piles and 3 X 3 to 7 X 3 pile groups founded in both loose and medium dense sands. The p-multiplier factors suggested by McVay et al. for laterally loaded pile groups with multiple pile rows were implemented for the predictions. The soil parameters were obtained through a back-analysis procedure based on single pile test results. The latter, as well as the numerical predictions of both the single and group tests, are presented. It was found that the numerical code FLPIER did an excellent job of predicting the response of both the single piles and the 3 x 3 to 7 x 3 pile groups. The latter involved the predictions of lateral load versus lateral deflection of the group, the shears and bending moments developed in the individual piles, and the distributions of-the lateral loads in each pile row, which were all in good agreement with the measured results.
Article
A non-linear three-dimensional finite element procedur is developed and applied for the analysis of pile group foundations. The numerical procedure allows for elastic, non-linear elastic and elastic-plastic hardening behaviour of sand. In order to include the interaction effects involving relative slip and debonding, the thin-layer interface element is used. The predictions for displacements and loads obtained from the numerical procedure are compared with laboratory model test results of a pile group. Displacements, stresses and forces distribution in various components of the pile group are also examined. Furthermore, the effects of the non-linear soil response and relative motions at the interface are indentified and discussed.
Article
The OpenSees finite element framework was used to simulate the response of 3×3 and 4×3 pile groups founded in loose and medium dense sands. Several numerical static pushover tests were conducted to investigate the interaction effects for pile groups. The results were then compared with those from centrifuge study. It is shown that our simulations can predict the behaviour of pile groups with good accuracy. Special attention was given to the three dimensional distribution of bending moment. It was found that bending moment develops in the plane perpendicular to the loading direction. In addition, bending moment data from simulations was used to derive p–y curves for individual piles, which were used to illustrate different behaviour of individual piles in the same group. Copyright © 2003 John Wiley & Sons, Ltd.
Article
Using the results from three full-scale lateral pile group load tests with spacing ranging from 3.3 to 5.65, computer analyses were performed to back-calculate p-multipliers. The p-multipliers, which account for reduced resistance due to pile-soil-pile interaction, increased as pile spacing increased from 3.3 to 5.65 diameters. Extrapolation of the test results suggests that group reduction effects can be neglected for spacings greater than about 6.5 for leading row piles and 7 to 8 diameters for trailing row piles. Based on analysis of the full-scale test results, pile behavior can be grouped into three general categories, namely: (a) first or front row piles, (b) second row piles and (c) third and higher row piles. P-multiplier versus normalized pile spacing curves were developed for each category. The proposed curves yield p-multipliers which are higher than those previously recommended by AASHTO (2000), the US Army (1993) and the US Navy (1982) based on limited test data, but lower values than those proposed by Reese et al (1996) and Reese and Van Impe (2001). The response (load vs. deflection, maximum moment vs. load, and bending moment vs. depth) for each row of the pile groups computed using GROUP (Reese et al, 1996) and Florida Pier (Hoit et al, 1997) generally correlated very well with measurements from the full-scale tests when the p-multipliers developed from this test program were employed.
Article
A series of static lateral load tests were conducted on a group of fifteen piles arranged in a 3x5 pattern. The piles were placed at a center-to-center spacing of 3.92 pile diameters. A single isolated pile was also tested for comparison to the group response. The subsurface profile consisted of cohesive layers of soft to medium consistency underlain by interbedded layers of sands and fine-grained soils. The piles were instrumented to measure pile-head deflection, rotation, and load, as well as strain versus pile depth. The average load resisted by each group pile was lower than the load resisted by the single pile at the same deflection. The lead row resisted loads similar to a single pile with the second row and third and subsequent rows resisting successively smaller loads. Maximum bending moments in the trailing row piles were larger and occurred at greater depths than the lead row piles. Group effects became more pronounced at larger deflection levels due to increased overlap of the shear zones that resisted the lateral motion of the piles thereby reducing the soil resistance. LPILE Plus version 4.0 (Reese et al., 2000) was used to model the single pile test. The initial input soil parameters were adjusted to obtain a good match between the measured and computed results. This refined soil profile was then used to model the pile group in GROUP version 4.0 (Reese et al., 2000). User-defined p-multipliers were adjusted to match the measured and calculated results. For deflections up to 38 mm, p-multipliers were 1.0, 0.87, 0.64, 0.81, and 0.70 for Rows 1 to 5, respectively. For larger deflections, the p-multipliers decreased to an average value of 1.0, 0.81, 0.59, 0.71, and 0.59. Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2004. Includes bibliographical references (p. 215-220).
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Kimura, M., Adachi, T., Kamei, H. and Zhang, F., 1995. 3D Finite Element Analyses of the 277 Ultimate Behavior of Laterally Loaded Cast−in−place Concrete Piles. 15 th 278 International Conference of Numerical Models in Geomechanics, Davos, 279
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