Response of Laterally Loaded Large-Diameter Bored Pile Groups

Many high-rise buildings, bridges, and transmission towers are constructed on steep slopes in Hong Kong and are supported by large-diameter piles. These structures may be subjected to large lateral loads, such as those caused by typhoons, earthquakes, and high-speed vehicles. The margin of safety of the slope may decrease as a result of stresses transferred from the piles to the slope. To minimize the transfer of lateral load from the buildings to the shallow depths of the slope, an annulus of compressible material (sleeving) is sometimes formed between the piles and the adjacent soils. In this paper, a three-dimensional analysis is carried out to investigate the effects of unsleeved and sleeved single piles and pile groups on the stability of a cut slope. Mechanisms of load transfer from the piles to the slope are studied. The stability of the slope is evaluated using the strength reduction technique. The evolution of slope failure is examined and the factors of safety for both initiation of instability and global failure of the slope are identified from the numerical analyses. The sleeving technique is found to be capable of significantly reducing the stresses in the shallow depths of the slope in front of the piles, thus improving the local stability of the slope, but offers limited benefit with respect to global stability.Key words: laterally loaded pile and pile group, sleeving, slope stability, three-dimensional analysis, load transfer mechanism, factor of safety.

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Cyclic Loading of Piles Using the P-Y Method

DFI Journal The Journal of the Deep Foundations Institute ◽

10.37308/dfijnl.20190529.204 ◽

2019 ◽

Vol 13 (2) ◽

Author(s):

Matt Bristow

Keyword(s):

Cyclic Loading ◽

Soil Depth ◽

Large Diameter ◽

Reference Conditions ◽

Numerical Procedure ◽

New Method ◽

Shear Stresses ◽

Applied Loading ◽

Cyclic Degradation ◽

Laterally Loaded

A new analytical method is presented to determine the effects of cyclic loading on laterally loaded piles. The method uses a new numerical procedure to quantify the effects of the cyclic loading at each soil depth and convert that to a set of cyclic p-y modifiers. The reduced foundation stiffness associated with the cyclic loading can be determined, including the residual static capacity and an estimate of the accumulated displacement. The new method introduces the concept of cyclic degradation damage, which is defined as sum of the cyclic degradation that is occurring at each soil depth. Cyclic degradation calculations are based on the shear stresses in the soil. Consequently, anything that causes the shear stresses to change (e.g. pile length, pile diameter, applied loading, etc.) will automatically be included in the calculation of cyclic p-y modifiers. The method has been validated by comparing the cyclic p-y curves produced using the new method with established cyclic p-y curves derived from fielding testing. The new method has also been used to investigate what happens to the cyclic p-y modifiers as one moves away from the reference conditions used to determine the established cyclic p-y curves in API RP2A (2000). The new method shows that every application (e.g. combination of cyclic loading, pile properties, and soil characteristics) has its own unique set of cyclic p-y curves, though most p-y curves fit within an upper and lower bound range. Examples are provided for large diameter monopiles.

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Development of Simulation Based p-Multipliers for Laterally Loaded Pile Groups in Granular Soil Using 3D Nonlinear Finite Element Model

Applied Sciences ◽

10.3390/app11010026 ◽

2020 ◽

Vol 11 (1) ◽

pp. 26

Author(s):

Muhammad Bilal Adeel ◽

Muhammad Asad Jan ◽

Muhammad Aaqib ◽

Duhee Park

Keyword(s):

Finite Element ◽

Element Model ◽

Design Guidelines ◽

American Petroleum Institute ◽

Winkler Foundation ◽

Group Effect ◽

Pile Groups ◽

Element Analysis ◽

Laterally Loaded Pile ◽

Laterally Loaded

The behavior of laterally loaded pile groups is usually accessed by beam-on-nonlinear-Winkler-foundation (BNWF) approach employing various forms of empirically derived p-y curves and p-multipliers. Averaged p-multiplier for a particular pile group is termed as the group effect parameter. In practice, the p-y curve presented by the American Petroleum Institute (API) is most often utilized for piles in granular soils, although its shortcomings are recognized. In this study, we performed 3D finite element analysis to develop p-multipliers and group effect parameters for 3 × 3 to 5 × 5 vertically squared pile groups. The effect of the ratio of spacing to pile diameter (S/D), number of group piles, varying friction angle (φ), and pile fixity conditions on p-multipliers and group effect parameters are evaluated and quantified. Based on the simulation outcomes, a new functional form to calculate p-multipliers is proposed for pile groups. Extensive comparisons with the experimental measurements reveal that the calculated p-multipliers and group effect parameters are within the recorded range. Comparisons with two design guidelines which do not account for the pile fixity condition demonstrate that they overestimate the p-multipliers for fixed-head condition.

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