James D. Murff

Behavior of Suction Embedded Plate Anchors during Keying Process

Suction embedded plate anchors (SEPLAs) allow for accurate positioning, thus providing an attractive alternative to traditional drag embedment anchors. This paper presents an analytical model for predicting the behavior of SEPLAs during the keying process, with a specific focus on predicting the loss of embedment depth as the anchor rotates from its initial vertical position to its target orientation perpendicular to the direction of loading. The soil is idealized as an incompressible, rigid-plastic material obeying an associated-flow rule. A generalized plastic limit analysis is employed to estimate the trajectories and corresponding capacities of SEPLAs under different loading conditions. The effects of soil resistance on the shank and anchor interaction with the anchor chain are also considered in the model. The SEPLA design commonly features a hinged flap; the effect of the flap is examined theoretically by comparing the solutions for the SEPLA with and without flap. Predicted solutions are shown in r...

Undrained Capacity of Plate Anchors under General Loading

Under general conditions of loading, a plate anchor is subjected to six degrees of freedom of loading, three force components and three moment components. Prediction of the anchor performance under general conditions of loading requires realistic estimates of the anchor pullout capacity for each individual load component as well as the interaction effects when these loads are applied in combination. This paper presents an analysis of plate anchor capacity under these general conditions of loading. The study considers a range of plate width-to-length ratios ranging from 1:1 to 2:1. The anchor capacity estimates and interaction relationships were developed based on finite-element studies and upper bound plastic limit analyses. Interaction relationships developed from the numerical and analytical studies were fitted to a simple six degrees-of-freedom yield locus equation.

An Expert Panel Review of Geotechnical Site Investigation Regulations and Current Industry State of Practice

The paper describes a joint industry project (JIP) conducted to provide an independent review of the current Bureau of Safety and Environmental Enforcement (BSEE) regulations and the American Petroleum Institute (API) standards (including their historical development). The main objective of the JIP was to make recommendations for improving industry’s state-ofpractice including revising regulations as needed to reflect the best methods for conducting deepwater geotechnical investigations. The study provides a careful review of all regulations applicable to an integrated site investigation required for the foundation design of a permanent floating production system. A panel of experts in offshore geotechnical engineering was assembled to obtain their technical guidance for defining the most appropriate work scope for an offshore geotechnical investigation for a permanently moored production system. The study describes the progress that has been made in site investigation technology (continuous sampling and insitu testing methods) and interpretation of the data since the regulations were initially published. The study also discusses how the current regulations should be interpreted in light of these recent advancements, as applied to the foundation design of suction piles, plate anchors, or driven piles. The expert panel also recommended revising the regulatory text to ensure that best field practices and sound engineering design principles can be employed when designing foundations to be safe and accomplish their intended purpose. The major benefit of the revised regulatory text is avoiding ambiguity between regulators and practicing geotechnical engineers as to what constitutes best practices for conducting a deepwater integrated site investigation. Introduction On December 27, 2001, the Minerals Management Service (MMS) published amended requirements in the Federal Register (30 CFR 250) to address the design of Floating Production Systems (FPSs). The purpose was to incorporate into their regulations a body of industry standards pertaining to FPSs so that system designers would know what is acceptable. Instead of writing their own standards, MMS determined that it would be most efficient and provide the highest level of expertise to the regulatory process if they incorporated the American Petroleum Institute (API) standards. In recent years, practicing geotechnical engineers working on deepwater offshore projects worldwide have found that establishing the scope of an offshore site investigation is often difficult. The difficulty lies in the ambiguity in the regulations leading to a lack of consensus among regulators, certified verification authorities (CVAs), and practicing geotechnical engineers as to requirements for conducting site investigations for deepwater projects. Since the new requirements (30 CFR 250) were published over a decade ago, the practice of conducting deepwater site investigations has dramatically improved. Today, high quality, digital geophysical data is routinely acquired very efficiently with an Autonomous Underwater Vehicle (AUV). The suite of data such as swath-bathymetry, sub-bottom profiles, and sidescan sonar imagery can be interpreted and mapped to provide a clear 3D picture of the seafloor and subsurface geologic/sediment conditions. More innovative site investigation methods have been developed for obtaining large diameter continuous samples (Jumbo Piston Core JPC), performing continuous cone penetration test (CPT) soundings and combining these data with the geophysical survey data into an integrated geologic/geotechnical model.