The vertical loaded plate anchor is a typical foundation of offshore floating production and storage facilities. An important issue is to evaluate the stability and the bearing capacity of the anchor subjected to static and cyclic loads for designers. Model tests of the vertical loaded plate anchor were conducted to study the deformation time history of the anchor subjected to a combination of static and cyclic loads in this paper. The bearing capacity of anchors was evaluated based on the deformation criterion. According to model test results, the decrease of the bearing capacity of vertical loaded plate anchor subjected to cyclic load is less than 20% compared to the static bearing capacity if the number of cycles to failure is less than 1000. In order to analyze the deformation time history of anchors, a visco-elastoplastic constitutive model is introduced. Parameters of the model associated with the model test stratum were determined by unconsolidated undrained cyclic triaxial tests. The deformation time histories associated with model tests were numerical simulated using finite element method based on the visco-elastoplastic constitutive model. Calculating and model test deformation time histories were compared, which showed that they were basically agreement. Therefore, the stability and the bearing capacity of a vertical loaded plate can be evaluated based on deformation time history of anchors.
The vertical loaded plate anchor (VLA) is a foundation of offshore floating production and storage facilities, which is subjected to working load (static load) and cyclic load due to wave (DNV, 2005). Sediments in the deep water are generally very soft clays with high water contents (Randolph, 2012). An important issue is to evaluate the bearing capacity for VLA in soft clays subjected to static and cyclic loads.
The pseudo static method (Andersen et. al. 1988, Wang et. al. 2011, 2015a, 2015b) can be used to evaluate the bearing capacity of VLA. But deformation of VLA can not be analyzed using these methods. An alternative approach to evaluate the cyclic stability is to analyze deformation procedures of VLA subjected to cyclic loads by numerical simulation. The approach determines not only the deformation-time history but also the bearing capacity based on the deformation criterion. The finite element method based on incremental constitutive models is the usual numerical simulation. Some existing methods were developed based on the incremental elastoplastic models (Cheng et al 2016, Pablo 2014). But the calculation amount associated with these methods is huge. Another alternative approach is to develop explicit analysis methods based on the visco-elastic theory (Hardin et al 1972, Wang et al 2013) and the creep theory (Hyde et al. 1976, Cathie 1982). For the approach, the stress strain response of soils is not traced in detail but is described using the visco-elastic relationship for each stress cycle. The cyclic accumulative strain is considered as the creep under the static deviatoric stress prior to cyclic stress and the relationship between the cyclic accumulative strain rate and the deviatoric stress is determined based on the creep theory. Some explicit numerical methods were also developed to analyze accumulative deformation of foundations in sands under long-term cyclic loading with low amplitude (Niemunis et al 2005, Martin et al. 2009, Franc et al 2010). It is necessary to further research how to use explicit methods to evaluate stability of anchor foundation in soft clays under cyclic loading with high amplitude.
