PSI - Issue 70

Ashutosh Kumar et al. / Procedia Structural Integrity 70 (2025) 175–182

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domain was adopted. The FEM model had dimensions of 1500 mm (length) × 1500 mm (width) × 1000 mm (depth). The plate anchor measured 150 mm × 150 mm with a thickness of 20 mm and was connected at its center to a mild steel anchor rod with a diameter of 12 mm. A typical test geometry is shown in Fig. 1. It consists of an anchor plate embedded in two-layered soil configurations. The fist configuration comprises loose soil over dense soil, and the second consist of dense soil over loose soil. The thickness of both the soil layers are equal (i.e., h1=h2). The soil layer immediately above the anchor plate is designated as Layer 1 while the soil layer from the top of Layer 1 to the ground surface is designated as Layer 2. The parameters ϒ 1and ϕ 1 represent the unit eight and internal friction angle of Layer 1, respectively, while ϒ 2 and ϕ 2 represent those of Layer 2. The embedment depth is denoted by H, the width of the plate anchor by B, and the uplift load acting on the anchor plate by Q. A finite element mesh was generated using 10-node tetrahedral elements. The reason to choice of 10-node tetrahedral elements in PLAXIS 3D for the present study is that the 10-node tetrahedral elements are second-order (quadratic) elements with three degrees of freedom per node, allowing them to capture complex stress and strain gradients more accurately than lower-order elements (e.g., 4-node tetrahedra). This is critical for modeling the non linear soil-anchor interaction and failure mechanisms in two-layered soil systems, where stress concentrations occur near the plate anchor. Further, the quadratic interpolation functions enable better representation of curved deformation patterns, which is essential for accurately simulating the uplift behaviour of plate anchors under varying embedment depths (e.g., H/B = 1, 2, 3). Soil behavior was modeled with an elastic, perfectly plastic constitutive model. The plate anchor was represented by a plate structural element, assumed to be rigid and non-deformable. To mimic the rough surface of the anchor plate, lateral movement of the plate element was constrained. The anchor rod was simulated using an embedded beam structural element. To introduce interface behaviour between single and two-layered soil configuration, an interface element which is available in PLAXIS 3D library was employed. The interface element is a critical tool for simulating the interaction between soil and structural elements, such as anchor plate, embedded beams, or piles. These zero-thickness elements are placed at contact surfaces to accurately capture relative movements, slippage, friction, or separation. The interface behavior is governed by properties like cohesion, friction angle, tensile strength, and stiffness parameters (normal and shear). A key parameter, the strength reduction factor (Rinter), scales the interface strength relative to the adjacent soil, allowing for partial or perfect interaction modeling. Interface elements are widely used in geotechnical applications, including retaining structures, pile foundations, and tunnel linings, to ensure realistic stress transfer and deformation patterns at soil-structure boundaries. An interface reduction factor of Rinter = 0.70 was applied. The model comprised 12,208 elements and 21,260 nodes, making it suitable for analyzing the horizontal pullout behavior of anchor plates in single-layer and two-layered soil with RD of 75% (dense sand) and 30% (loose sand), respectively. A medium mesh with a coarseness ratio of 0.125, surrounded by a finer mesh, was deemed sufficient for the analysis. The analysis utilized a displacement control approach, in which the plate was subjected to a series of prescribed displacements, and the resulting resistance was measured. The load displacement curve was used to determine the anchor’s capacity, defined as the maximum load at which the curve reaches a plateau. Fig. 2 illustrates the geometry of the PLAXIS 3D model, including the generated mesh, boundary conditions, and interface elements surrounding the plate anchor. Table 1 presents the properties of the anchor plate and anchor rod used in this study.

Fig. 1 A typical test geometry of an anchor plate in two layered soil configurations (NTS)

Fig. 2 Geometry of PLAXIS-3D model