39 40 This paper presents an experimental and analytical study to investigate the effect of shape on the 41 pullout capacity of shallow horizontal plate anchors in sand. Novel dynamically penetrating plate 42 anchor concepts have been proposed by various groups for use in the offshore energy sector. These 43 anchor concepts will likely have shapes that are not common, and analysis of uplift capacity may 44 be needed for design. Most of the research on the capacity of shallow horizontal anchors has 45 focused on square, rectangular, or circular shapes. Physical and analytical modeling was used to 46 study the normalized capacity (i.e. breakout factor) of square, circular, triangular, and kite shaped 47 plate anchors. The 1g physical model results indicated that the circular shape anchor had the 48 highest capacity, and was 50% to 70% higher than the square that had the lowest capacity. The 49 2 triangle and kite shapes had capacities that were between the circle and square shapes. A non-50 associated flow limit equilibrium analytical model predicted breakout factors for the four different 51 anchor shapes that were within about 15% of the measured values on average. The results suggest 52 that the analytical modeling approach could be extended to horizontal plate anchors of any shape. 53

This paper addresses scaling issues related to small-scale 1-g model tests on plate anchors in sand under drained loading conditions. Previous centrifuge studies from the literature have suggested that the results of conventional 1-g model testing are inaccurate because of scale effects. Other studies have suggested, however, that scaling errors can be reduced in 1-g model tests if the results are presented in dimensionless form and the constitutive response of the model soil is representative of the prototype behavior. There are no experimental studies in the literature that have tested the validity of this approach for plate anchors. A simple 1-g scaling framework was developed for vertically loaded, horizontal plate anchors.Small-scale 1-g model tests were performed on square plate anchors in dry sand, and combined with existing centrifuge and 1-g model test data from the literature to test the scaling approach for both capacity and deformation. The 1-g model tests provided a reasonable representation of the full-scale prototype behavior when the scaling approach was applied.

In recent times, interest in dynamically installed foundation systems for deep-sea construction has increased; however, these foundation systems are still under development and need quantification of various soil parameters with different perspectives. For the design of dynamically installed foundations, it is essential to assess the strain-rate effect on very soft soils. The T-bar has been widely used to characterize soft offshore sediments, such as silt and clay, and there is extensive existing literature on the interpretation of test results. Strain-rate dependence has not previously been fully examined for T-bar tests in very soft clay at very high rates of penetration. This paper examines this aspect using a physical model test. A 65-cm-thick kaolin clay bed was formed using vacuum consolidation. A T-bar was driven into the clay bed at rates that varied from 0.1 cm/s to 60 cm/s. The tests revealed that the resistance factor increased by 9 % for every 10-fold increase in the penetration rate for the material tested in this research.

The Geotechnics Sub-Committee of the American Society of Civil Engineers (ASCE) Coasts, Oceans, Ports, and Rivers Institute (COPRI) Marine Renewable Energy (MRE) Committee is preparing a guide document for marine renewable energy foundations. That guide would use standard design codes for fixed foundations and mooring anchors in API RP 2GEO and DNV.The static method of computing axial pile capacity described in API RP 2GEO (2011) is generally used to compute ultimate compressive and tensile capacities of pipe piles driven to a given penetration. Lateral soil resistance -pile deflection (p-y) data for clays and sands are usually developed using procedures proposed by Matlock (1970) andMurchison (1983), respectively, and outlined in API RP 2GEO (2011). Marine energy foundations are unique in several ways. Axial pile capacity computations are usually based on a reasonable lower bound, in contrast to the soil resistance to driving, which is based on a reasonable upper bound. For structures supporting wind turbines, however, underestimating (or overestimating) the soil stiffness could require a change in turbine operation and a loss of power production. Although the classical API method is recognized as an appropriately conservative design method for offshore pile foundations, a prediction method is more well suited for structures supporting wind turbines, such as the CPT-based methods for predicting pile capacity in granular soils presented in API RP 2GEO (2011). If a prediction method is used to compute the soil resistance to driving, the evaluation of pile drivability may be overly conservative. Ageing in both clay and sand should also be taken into account. Wind turbines are often supported on large diameter monopiles. The applicability of the p-y data for such large diameter piles needs to be verified. Finally, marine renewable energy generated by in-stream hydrokinetics, ocean thermal energy conversion, and wave energy converters may be floating devices usually anchored to the seafloor. There are uncertainties in the design and installation of these anchors, which become critical for large sustained tensile loads that may degrade due to creep and cyclic loading.

The objective of this paper is to address the applicability of using API RP 2GEO (2011) for the design of wind turbine monopile foundations in normally to moderately overconsolidated clays. The study involved three-dimensional numerical modeling using the finite-element method, one-g laboratory model testing, and analysis of field test results. The following conclusions concerning the use of Matlock (1970) soft clay p-y curves for the design of large-diameter monopile foundations are drawn: Numerical modeling and model-scale testing with rigid piles of different diameters indicate that the form of the Matlock (1970) p-y curves, in which the lateral displacement is normalized by pile diameter and lateral soil resistance is normalized by the ultimate resistance, appropriately captures the effect of pile diameter.Field and model testing indicate that the Matlock (1970) p-y models consistently overestimate the lateral displacements at the pile head when used to analyze laterally loaded piles in normally to moderately overconsolidated clays.An approximate version of the Jeanjean (2009) p-y model, in which the Matlock (1970) p-y curves are scaled by p-multipliers calculated at various depths, generally provides a reasonable match to measured lateral displacements at the pile head when a relatively large strain at one-half the undrained shear strength is assumed, i.e., ?50 = 0.02. This result applies both to small scale model tests in kaolinite and large-scale field tests in high-plasticity clay.Model tests show that cyclic loading causes the stiffness of the lateral pile-soil response to degrade by 20 to 30 percent. The amount of degradation is dependent on the displacement amplitude and the number of cycles. All of the degradation happens within 100 cycles, after which the stiffness is reasonably constant.Model tests show that the ultimate lateral capacity of the pile is not significantly affected by the previous cyclic loading.