A non-associative macroelement model for vertical plate anchors in clay

Abstract

This work proposes a new plastic hardening, non-associative macro-element model to predict the behaviour of anchors in clay for floating offshore structures during keying and up to the peak load. Building on available models for anchors, a non-associated plastic potential is introduced to improve prediction of anchor trajectory and loss of embedment at peak conditions for a large range of padeye offsets and different pull-out directions. The proposed model also includes a displacement-hardening rule to simulate the force and displacement mobilisation at the early stages of the keying process. The model is challenged and validated against different sets of numerical and centrifuge data. This extensive validation process revealed that two of the four newly introduced model parameters assume a constant value for the range of simulated cases. This suggests that only two of the newly introduced parameters may need to be calibrated for the use of the proposed macro-element model in practice.

A Cyclic Macro-Element Framework for Consolidation-Dependent Three-Dimensional Capacity of Plate Anchors

“…This paper proposed a new macro-element modelling framework aiming to capture the cyclic behaviour of plate anchors and the evolution of the cyclic capacity related to changes in soil strength, as triggered by processes of pore water pressure generation and/or consolidation during loading. The modelling framework combined a macro-element model for the anchor [27] with a one-dimensional model of undrained shearing and consolidation for a soil element, representative of the whole soil mass around the anchor. The onedimensional model of undrained shearing and consolidation for the soil element is based on the critical state and bounding surface concepts in order to accurately capture pore water pressure generation and dissipation during both consolidation and shearing mechanisms.…”

“…The kinematics of the anchor are given by a previously published macro-element model [27]. A schematic view of the surfaces adopted in this macro-element model is presented in Figure 3 in a simplified two-dimensional representation, but it should be reminded that the model is formulated in a three-dimensional loading space (H, V, M).…”

“…The monotonic uplift of such anchor has been already considered by Peccin da Silva et al [26], who used the macro-element model for the plate anchor but neglected the evolution of pore pressure generation and soil strength during loading. Peccin da Silva et al [27] also provided a detailed account for the determination and/or calibration procedure of the anchor macro-element model parameters and the same values are used here, as summarised in Table 2. It should be emphasised that while 10 parameters are employed, the values of the bearing capacity factors (N v , N h and N m ) and shape parameters of the loading surface f (m, n and q) can be assumed based on the previous literature (e.g., [4,28,30,42]).…”

“…It should be emphasised that while 10 parameters are employed, the values of the bearing capacity factors (N v , N h and N m ) and shape parameters of the loading surface f (m, n and q) can be assumed based on the previous literature (e.g., [4,28,30,42]). Peccin da Silva et al [27] demonstrated that two of the plastic potential parameters (ξ and χ) typically assume the same value, while the parameters ω and R 0 can be calibrated from a monotonic load displacement curve of an anchor. In absence of specific soil data for this idealised loading geometry and scenario, the same soil parameters identified in scenario 1 are employed.…”

“…This paper presents a new strategy to account for changes in pore water pressures and effective stresses in the soil when employing a macro-element modelling approach. The modelling framework expands a previously developed macro-element model for the plate anchors [26,27] and combines it with a simple one-dimensional model of shearing and consolidation for a representative soil element around the anchor. The representative soil element tracks the effects of pore pressure generation and changes in effective stress on the soil strength, which in turn governs the anchor capacity in the macro-element model.…”