Pile foundation is a popular type of deep foundation technique used to transfer superstructure load into subsoil and bearing layers. In these cases, we want to approximate pile behaviour to be able to analyze deformations and forces of the superstructure and also obtain a first indication of axial and/or lateral loads on the piles.The problem of analyzing and designing deep foundations is relevant to many civil engineering structures, because we are commonly and frequently constructing buildings on soft soils. A typical situation may be the analysis of a superstructure that is (partly) founded on piles, such as a pile-raft foundation or a quay wall. In a lot of cases, there is a need to model piles in a 2D (plane strain) model.
The case study involves a circular concrete pile with the dimen-.While it is possible to create a half-pile in the pile designer, it is not possible to create a quarter of a pile. Pile modeling is primarily a 3D problemThe numerical modelling is conducted by the commercial FEM program PLAXIS. This could be a challenging task for the designer in the case of complex pile-soil interaction or in situations involving a consolidation process.
Figure 1: 3D model of a simple pile raftdone using commercial packages PLAXIS 2D v8.6 and PLAXIS 3D, 2013. This will guarantee the most accurate representation of the physical problem, especially regarding soil-structure interaction. Ideally, the piles themselves will be represented by volume elements.
Model Pile In Plaxis 2D How To Efficiently Deal
In this approach, the pile is represented by beam elements, while soil–pile interaction along the pile shaft and at the pile tip is described by special interface elements that are constructed based on node-to-node, non-linear coupling springs.The generation of linear beam elements gives the opportunity to simulate piles as structural elements with specified material properties. The embedded beam is particularly useful in cases of large numbers of piles to be accounted for in a PLAXIS 3D model. This feature was developed to simulate the behavior of piles in a simplified way. Piles as embedded beams, or how to efficiently deal with many pilesThe embedded beam is a special feature in PLAXIS 3D. A large number of piles would have to be considered and the increasing number of elements (as the number of piles to be modeled increased) might become simply impractical at some point.
The PLAXIS 3D calculation kernel automatically takes care of finding intersection loci between beam pile element and soil element faces, introducing at these points so-called “virtual” nodes where relative displacement between soil mesh nodes and pile nodes can be computed. Both pile lines and soil volume could be meshed independently. Another clear advantage of using PLAXIS embedded beam elements is that the generation of the coupling springs (for soil–pile interaction) does not require mesh node connectivity between the lines supporting the pile/beam elements and the surrounding soil volume.
PLAXIS 2D with embedded beam row Figure 8: Pile model in PLAXIS 2D versus pile model in PLAXIS 3D (a) Lateral displacement b) Bending moment Figure 9: Pile model comparison - PLAXIS 2D versus PLAXIS 3DThe post Model Piles in PLAXIS appeared first on Civil Engineering Knowledge Base. Thus, it implicitly requires that any 2D embedded beam would represent a continuously spaced set of piles in the out-of-plane direction with a pile-to-pile spacing value not too large compared to the pile diameter, such that an average soil displacement as provided by the 2D soil mesh between piles would remain an acceptable assumption.When the assumption of continuously spaced piles is satisfied, the PLAXIS 2D model shows very good agreement with equivalent 3D models, but at a fraction of the computational cost. The 2D nature of the plane strain analysis does not allow for the consideration of a singular buried entity (that could only be considered in a 3D model). Figure 6: Axisymmetric model of an axially loaded pile in PLAXIS 2DThe embedded beam feature presented earlier is also available for 2D plane strain situations but can only be used for the analysis of pile rows (rows extending in the out-of-modeling-plane direction). Such models are very cost-effective, computationally speaking, but can only be used in the case of axial loading, as any consideration of lateral loading would not fulfill the axisymmetric conditions and would therefore require a proper 3D model. Figure 5: Available results for embedded beams in PLAXIS 3D And what about 2D?In the framework of a PLAXIS 2D analysis, it is possible to analyze axially loaded piles by assuming axisymmetric conditions.
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