The move of offshore oil and gas development into deepwater has required that the mooring systems for floating drilling and production platforms/vessels shift from catenary mooring systems to taut-leg mooring systems, requiring the need for a low cost deepwater anchor that can withstand major uplift mooring forces and be designed and easily installed to the design penetration with a high degree of reliability.Many deepwater anchor concepts have been proposed to meet the above requirements in recent years. The four most widely known concepts are discussed in this paper to represent the entire range of concepts in terms of operating principles. The selected anchor concepts discussed herein include two relatively proven anchor concepts, the suction caisson and the vertical loaded (drag embedment plate) anchor (VLA), and two developmental anchor concepts, the SEPLA (Suction Embedded Plate Anchor) and the Torpedo/Deep Penetrating Anchor (DPA).Each anchor type considered in this paper has a different level of technology maturity. The suction caisson is presently the preferred anchor for taut-leg mooring systems for permanent facilities and is probably the most mature in terms of installation experience and prediction of holding capacity, but there are economic issues associated with the fabrication and installation of suction caisson anchors due to their large size. The VLA is probably second in the overall level of maturity from the standpoint of prediction of holding capacity and installation confidence, but there are installation issues and limitations associated with the size, number, and hence cost of marine vessels required to drag the anchors to design penetration, to key the anchors, and to proof load the anchors. The SEPLA and Torpedo/DPA anchors trail in level of maturity and require the most technological development to attain a mature state of practice in the future. This paper will review these four anchors that show the greatest opportunity to serve the needs for deepwater mooring and describe the state of practice in terms of design and installation reliability. The objective of this paper is to discuss the uncertainties (areas requiring further development) of each anchor, the advantages and disadvantages, and to offer the authors' opinions of future technology development direction and focus.The general conclusions regarding future development of the practice of deepwater anchors are as follows:• Torpedo/DPA anchors appear to be the most promising option for improvement in cost reduction and simplifying installation • Future research activities are recommended for Torpedo/DPA anchors in the following order of priority: 1. analytical penetration studies, 2. analytical studies to determine the optimum number, size, and configuration of fins, 3. small and full scale field testing to measure penetration and holding capacity in various soil profiles and optimize installation procedures, and 4. design method verification and documentation.

The empirical procedures for offshore foundations design are directly influenced by the shear strength values selected for analyses.There is generally a large amount of scatter in measured undrained shear strength data from offshore borings because of various types of laboratory tests and sample disturbance. A comparison of strength data obtained on samples of cohesive soils from the Gulf of Mexico taken with a 2.25-in.-OD thin-wall tube percussion sampler and a 3.0-in.-OD thin-wall push sampler confirms that (1) the strength results for 3.0-in. push samples give the highest and most representative values with less scatter, (2) the unconsolidated-undrained triaxial compression test gives the best measure of undrained shear strength for cohesive soils, and (3) strengths interpreted from SHANSEP on push samples correlate well with conventional laboratory and in situ strength data.

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This paper will show on the basis of hindcast wave equation analysis that soil-pile set-up for large diameter driven pipe piles in clay is faster than what the current state-of-practice utilizes for design. Results of hindcast wave equation analyses utilizing observed blowcounts and hammer energy records from two deepwater sites, one in West Africa and the other one in the Gulf of Mexico, are presented to support this conclusion. For offshore structures, this increase in the rate of soil-pile set-up reduces foundation/anchor costs or reduces the waiting time until topsides can be set on the structure or mooring lines can be hooked up to anchors. Hindcast wave equation analyses were performed utilizing the observed blowcount and hammer energy information from two deepwater West Africa and Gulf of Mexico locations where pile driving was stopped and then restarted after a few days. This is a trial and error method of analysis where the soil resistance to driving (SRD) was varied until a good match was obtained between the observed blowcount at the startup of driving and the reported hammer energy using the GRLWEAP wave equation program. The set-up time for the piles ranged from about one to twelve (12) days and the piles ranged from 2134 mm to 2743 mm diameter open-ended pipe piles. The soils generally consisted of normally to slightly overconsolidated highly plastic clays. For the purpose of computing pile set-up, the ultimate pile capacity was computed using the API RP 2A (2000) guidelines. Results show that 60 to 80 percent of the ultimate pile capacity is mobilized in about 7 days, and the extrapolation of the set-up model suggests that the set-up is almost complete in about 60 days.