Numerical analysis of passive pile groups in offshore soft deposits
Introduction
Passive pile loading is generally triggered by pile displacement less than surrounding soil displacement and is a common geo-frontier for pile foundations, as well as active pile loading which is related to external loads (e.g., wind, waves, current, ice, traffic, ship impact, and mooring forces). In Korea, its evaluation is significantly associated with general problems in the planning, design, construction, and maintenance of pile foundations constructed in offshore soft deposits. Simultaneously, these could lead to more significant remedial costs than onshore pile foundations. As Korean government’s land development has subsequently impacted on offshore reclamation since the 1990s, more consideration has been given to soil–structure interaction problems associated with passive pile loading. It is mainly attributed to Korean representative offshore deposits which are composed of an over 30 m normally consolidated soft clay, with a strength that varies linearly with depth.
Much work has been carried out on group piles under active loading [10], [11], [18], [27]. A relatively less work has been done on the passive pile loading, with the initial works [14], [22], [31] focusing on the performance of in-situ pile structures which is limited to site-specific characteristics. Due to the introduction of sophisticated technology, the focus of many works has tended to be on both centrifuge and numerical modeling since the Springman’s work [29], [30]. Numerical studies into the response of passive pile loading fall into two categories, based on a 2-D plain strain FE approach which are corresponded to a series of centrifuge tests [4], [12], [13], [30], [31] or field tests [15] and a 3-D FE approach with focus on piles within the slope [8], [9] or piles subjected to lateral soil movements [5], [23]. Most of the studies mentioned above have been carried out on the assumption of small strain theory. It is fortunate that the results of 3-D FE analysis on single pile was reported by Miao et al. [21], however, in view of excessive pile–soil displacements, little has been done on the basis of large strain theory, which is taken into account in the paper.
Also, no attempt has been made to investigate the behavior of two-row pile groups with fixed pile tips in soft clay deposits with up to 30 m depth, which are typical types frequently encountered in the Korean offshore environment. Focusing on this type of pile structure, accordingly, this paper describes the results of numerical investigation into short- and long-term passive pile loadings. For this work, 2-D elastoplastic-consolidation coupled FEM analyses were conducted on the basis of large strain mode using an updated Lagrangian formulation, which is favorably verified in cases of both centrifuge tests and field tests. From a parametric study with some of the idealizations, it is shown that passive pile loading is mainly influenced by soil profile, pile head boundary condition, magnitude of surcharge load, and average degree of consolidation. From the viewpoint of the passive pile loading in construction (short-term) and consolidation (long-term) phases, simple table is presented as an initial framework for more detailed pile design.
Section snippets
Large strain analysis
The theory of large strain analysis used in the present study is briefly summarized into three parts. When large strain theory is included in a finite element analysis package, firstly it is necessary to include additional terms in the structure stiffness matrix to model the effects of large structural distortions on the finite element equations. Secondly, it is essential to involve a procedure to model correctly the stress changes developed by the finite material rotations. This particular
Parametric study
Based on 2-D plane strain large strain finite element approach, a parametric study was performed on a hypothetical 1.0 m diameter and 30 m length pile foundation constructed on normally consolidated soft clay layer frequently encountered in the southeast region of Korean peninsular. As shown in Fig. 8 and Table 4, this study examines the effects of major factors in passive pile loading, such as soil profile (only clay layer, clay–sand layer, sand–clay–sand layer), pile head boundary condition
Numerical investigation of passive pile loading
In this study, numerical investigation of passive pile loading (i.e., the magnitude and profile of passive loading acting on the piles) was conducted on the basis of one assumption: The profile of passive pile loading is equal to the profile of subgrade reaction which is closely related to the distribution of relative pile–soil displacement. In this investigation, corresponding 2-D large strain coupled FE analyses (Fig. 12) to the parametric study were performed, directly applying the passive
Concluding remarks
The main objective of this study is to investigate numerically time-related passive pile loading with respect to two-row pile groups with fixed pile tips, which are constructed on three potential soil profiles encountered in Korean offshore deposits. For this work, elastoplastic-consolidation coupled large strain finite element analyses were performed on the 2-D plane strain model. The simulation techniques were favorably validated in two cases of centrifuge tests and two field cases. In spite
References (31)
- et al.
3-D Finite element modeling of pile groups adjacent to surcharge loads
Comput Geotech
(1996) - et al.
Behavior of piled bridge abutments on soft ground: a design method proposal based on 2-D elastoplastic-consolidation coupled FEM
Comput Geotech
(2004) Applied analyses in geotechnics
(2000)Finite element procedures
(1995)General solutions of the equations of elasticity and consolidation for porous material
J Appl Mech
(1956)- Bransby MF. Piled foundations adjacent to surcharge loads. PhD dissertation, University of Cambridge;...
- Brinkgreve RBJ. Selection of soil models and parameters for geotechnical engineering. In: Yamanuro JA, Kaliakin VN,...
- Brinkgreve RBJ, Broere W, Waterman D. PLAXIS 2D – version 8. Professional version, Netherlands: PLAXIS BV;...
- Chaui F, Magnan JP, Mestat P, Delmat P. Three-dimensional analysis of the behavior of piles in unstable slopes. In:...
- Chen LF. The effect of lateral soil movements on pile foundation. PhD dissertation, University of Sydney;...
Response evaluation of horizontally loaded fixed-head pile groups using 3-D nonlinear analysis
Int J Numer Anal Methods Geomech
Influence of pile cap flexibility on cap-pile-soil system
Int J Offshore Polar Eng
Full-height piled bridge abutments constructed on soft clay
Geotechnique
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