Behaviour of embedded model screw anchors in soft clays

150A

REINFORCEMENT:BOLTS & ANCHORS

takes into account sample variability as well as combining images taken at different scales. -from Authors

ferent methods for the solution of applied problems -from Author

Drilling 943230 The quest for borehole stability in the Cusiana Field, Colombia T. Addis, D. Boulter, L. Roca-Ramisa & D. Plumb, Oilfleld Review, 5(2-3), 1993, pp 33-43. The Cnsiana field, in the eastern Andes, was discovered in 1991 and promises to be among the top 50 oil reserves of the world. However, severe difficulties were encountered during the drilling of the discovery wells, due primarily to mechanical stability problems. The field hes on the eastern flank of the Oriental Andes cordillera, an area being actively compressed by the eastward thrust of the Nazca plate and the southeasterly thrust of the Caribbean plate. The article analyses the stress field present in the area, focusing on how a mechanical balance is monitored and achieved, and reviews the latest theories and measurement techniques relevant to this case study. -G.E.Hodgson 943231 Record drilling depth struck in Greenland P. A. Mayewski & others, Eos, 75(10), 1994, pp 113,119,124. Details the achievement of the Greeuland ice sheet project (GISP2) for drilling 3053.4m through ice to reach bedrock. The drill used allowed whole 13.2 cm diameter and up to 6m sections to be removed. Drill instrumentation allowed measurement of 16 parameters including weight, pressure, temperature, inclination, azimuth, rotations per minute and current. A new borehole liquid, n-butyl, which is considered to have minimal health and environmental risk, was used. -R.Gower 943232 Drilling and testing hot, high-pressure wells R. MacAndrew & 6 others, Oilfield Review, 5(2-3), 1993, pp 15-17,20-32. The difficulties encountered, and the procedural modifications required in drilling and testing high-temperature, high-pressure (HTHP) wells are presented. These wells are defined by the UK Department of Energy as wells where the undisturbed bottomhole temperature at prospective reservoir depth or total depth is greater than 150"C, and either the maximum anticipated pore pressure of any porous formation to be drilled exceeds a hydrostatic gradient of 0.8 psi/ft, or l~ressure control equipment with a rated working pressure m excess of 10 000 psi is required. The article discusses three important aspects of HTHP drilling in the UK sector of the Notch Sea Central Graben: drilling safety, casing and cementing, and testing. -G.E.Hodgson

ROCK AND SOIL REINFORCEMENT AND SUPPORT

Bolts and anchors

943234 Behaviour of embedded model screw anchors in soft clays S. N. Rao, Y. V. S. N. Prasad & C. Veeresh, Geotechnique, 43(4), 1993, pp 605-614. In recent years helical anchors have been used extensively in the construction of transmission tower foundations, pipelines and braced excavations. The Paper describes an experimental programme carried out to show the behaviour of multiple helical anchors at different embedment ratios in soft marine clays. The results indicate that the anchor capacity increases with embedment ratio. The uplift capecity at any embedment ratio is explained in terms of the contribution of cohesive resistance between the top and bottom helical plates, the bearing resistance of the top helical plate alone and the shaft adhesion above. -from Authors

943235 Field tests of anchors in clay. I: description R. Dyvik, K. H. Andersen, S. B. Hansen & H. P. Christophersen, Journal of Geotechnical Engineering ASCE, 119(10), 1993, pp 1515-1531. A description of and selected test results for four field model tests are presented. The model tests were designed to simulate the conditions of a suction anchor for a tension-leg platform in soft clay. The intention of these tests was not to produce results that would be extrapolated directly to prototype conditions; instead, they form a basis for a critical evaluation of design procedures for suction anchors (originally developed for offshore gravity-base structures). -from Authors

Machine excavation 943233 A brief review of Soviet theoretical a p p r o a c h e s to dynamic rock failure L. L. Mishnaevsky Jr, International Journal of Rock Mechanics & Mining Sciences, 30(6), 1993, pp 663-668. To develo~p a CAD/CAM model of a machine excavation, mathematxcal models for the rock destruction ]~rocess are needed. It is known that rock destruction under indentation includes such stages as: rock deformation, surface crushin.g, fommtion of destruction nucleus, formation of Hertzxan cone crack, squashing of cone (the rock bounded by a Hertzian cone crack), spalling of rock between the Hertzian crack and the free surface. The review here provides a description of investigations in mathematical modelling of rock destruction for drilling, and the applicability of dif-

943236 Field tests of anchors in clay. II: predictions and interpretation K . H . Andersen, R. Dyvik, K. Schroder, O. E. Hansteen & S. Bysveen, Journal of Geotechnical Engineering ASCE, 119(10), 1993, pp 1532-1549. Four field model tests are used to check procedures proposed for the foundation design of sucuon anchors for offshore tensinn-leg platforms. The test program contained one static and three cyclic tests in a soff clay deposit. The model was loaded in tension with a load inclination of about 10" from the vertical. The cyclic tests were mn with various cyclic load histories, eccentricities, and geometries. The procedures gave predicted values in very ood agreement with the measurements. This was true for oth static and cyclic failure loads and cyclic displacements. The applied calculation procedures are thus well

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