Soil Plug Research Articles

First Jack-Up Production Platform in the North Sea

Introduction A jack-up gas production platform by Amoco International Oil Co. was installed in Aug. 1972 in 75 ft of water in the Leman field, British North Sea. It was the first jack-up production platform installed in the North Sea. production platform installed in the North Sea. The main advantage of using the jack-up platform rather than the conventional template-type platform is that all production, storage, and living facilities can be installed, tested, and checked out in the fabrication yard before it is removed for installation. As a result, considerable expensive offshore work is avoided, and more important, much less time is required to commission the production facilities and begin operation. Design Basically, the platform is designed as a flat-bottom, flush-deck barge with vertical sides and raked ends. Between the flat bottom and flush deck, the barge is subdivided into thirty compartments by six athwartships full scantling bulkheads, four longitudinal bulkheads and several division bulkheads. The barge is supported by six caissons 71-in. OD and 195 ft long, each extended through a well in the platform. There are three wells on the port side and three on the starboard. The dead weight of the barge and caissons is 3,070 kips. The dry weight and wet weight of the production facilities are 1,550 kips and 1,840 kips, respectively. The soils encountered in the boring to the maximum penetration explored (203 ft) are primarily fine sand. penetration explored (203 ft) are primarily fine sand. A laterally loaded pile computer program was used to develop soil-resistance caisson-deflection characteristics for the caisson design. The design penetration for the six caissons is 55 ft, with a 20-ft-long grout plug placed on top of the natural soil plug. The design analysis was performed with a staticelastic space frame analysis computer program. Stokes' fifth order wave theory was used to generate the wave forces on the caissons. The maximum lateral deflection of the barge under storm condition is 10 in. The natural period of the platform is computed by the Rayleigh method and is found to be 2.5 seconds, which is much less than the period of the storm wave. Thus the dynamic amplification effect is negligible. The limiting angle of roll of the barge under tow was 9.25 degrees, at which position the stress in the caissons would be equal to 80 percent of yield. The draft of the barge is 5.1 ft. The period of roll of barge under tow was calculated to be 4.8 seconds. Construction The platform, built in Holland during 1971 and 1972, was constructed in three sections - one each in Amsterdam, Sliedrect, and Rijn. The three completed sections were then assembled at DeGroot and Van-Vliet yard at Slikkerveer and then towed to the DeGroot International N.V. Yard at Zwijndrect. JPT P. 323

Ecology and Behavior of Melecta separata callura (Hymenoptera: Anthophoridae)

Melecta separata callura (Cockerell), the primary biotic enemy of Anthophora edwardsii Cresson, behaves similarly to its European congeners, but differently from other North American parasitic melectine and nomadine bees. Features unique to Melecta (s. str.) include: digging through the soil plug of the completed host burrow; opening a small hole in the cap of the cell; ovipositing through this opening and attaching its egg to the roof or upper cell wall; resealing the cell; and replugging the host burrow. The bees spin a cocoon. They pupate in the autumn and overwinter as adults in the cells of their hosts. Melecta was parasitized by Sphaeropthalma unicolor (Cresson) and an undetermined bomblyiid fly. With the exception of a few host associations and flower records, there have been no studies on the ecology and behavior of any North American species of Melecta. Some features of the life history and interrelationships with host species have been worked out for the related Xeromelecta californica (Cresson) by Linsley and MacSwain (1942) and Porter (1951). These studies serve as a useful basis for comparisons between the two genera. In addition, a few studies on the ecology and behavior of European species of Melecta M. armata Panzer by Semichon (1904, 1911, 1922, 1925) and Malyshev (1928) and M. luctuosa Scopoli by Giordani-Soika (1936) provide a basis for intrageneric comparisons. Melecta (Melecta) separata callura (Cockerell) is a parasite of Anthophora edwardsii Cresson. The present study was conducted at a site near Coalinga and is; supplemented by unpublished 1947 observations made at a site near Somersville by Drs. E. G. Linsley, J. W. MacSwain and R. F. Smith. Thorp (1969) has discussed the ecology of the host bee, the habitats of the two sites where M. separata was studied, the temporal and spatial distribution of the two species, and has briefly outlined the ecology of the parasite. The present paper treats in more detail the behavior of the adult females. associated with oviposition, and the feeding behavior and development of the larvae of