A Large Deformation Finite Element Study On Failure Mechanism And Bearing Capacity Of Torpedo Anchor

With the rapid economic development at home and abroad,the demand for oil and natural gas resources continues to increase.The depletion of land resources has been unable to meet the current consumption,thus forcing the development of offshore oil and natural gas to gradually develop from shallow to deep water areas.The torpedo anchor is the most promising and developmental deep sea anchor foundation in the deep sea anchoring system.Its installation overcomes the shortcomings of the traditional anchor foundation relying on water depth.It is completed by its own weight without any external force,and it is cost-effective,simple manufacturing process,and installation.The advantages of high efficiency and economy,and excellent anchoring performance are widely used in the field of deep-sea engineering.At present,most studies on the failure mechanism and penetration depth of torpedo anchor foundation are confined to homogeneous soil during the penetration and installation stage of torpedo anchor,but the sea-bed is affected by many uncertain factors with obvious spatial variability and autocorrelation.In the traditional deterministic geotechnical engineering analysis,the uncertainty of the nature of the soil is often ignored,which leads to a large deviation in the estimated depth of the torpedo anchor foundation.In this paper,under the framework of Monte Carlo simulation,the large deformation finite element method and random field theory are combined,and the coupled Euler-Lagrange finite element calculation method is used to simulate the dynamic penetration process of the torpedo anchor foundation.Whilst the installed torpedo anchors in offshore practice are often characterized with off-verticality,the effect of inclination on the anchor pull-out capacity has seemingly received little attention in the research literature.This paper presents a numerical study on the pullout capacities and failure envelopes of inclined embedded torpedo anchors subjected to combined vertical and horizontal loading.Using Coupled Eulerian–Lagrangian finite element method,effects of load inclination,azimuthal angle of pull-out plane and anchor inclination were sequentially evaluated.It was found the most critical pull-out plane is the one that coincides with anchor plane towards the anchor inclination direction.Its corresponding failure envelope,which can be well fitted by a closed form expression,gives the conservative estimation of anchor pull-out capacities.The comprehensive parametric investigation indicated this conservative failure envelope is mainly affected by anchor inclination and soil's strength gradient.A series of tables with fitting constant values appropriate for different strength and inclination conditions were furnished.On these bases,a simple design procedure was developed for estimating the ultimate pull-out capacities of inclined embedded torpedo anchors.The outcomes of this work are likely of helping for engineers to factor the anchor inclination into the design practice of torpedo anchors.