GB849724A - Anchoring method and apparatus - Google Patents

Abstract

849,724. Ground-anchors. CALIFORNIA RESEARCH CORPORATION. June 24, 1959 [June 30, 1958(2)], No. 21739/59. Class 45. [Also in Group XXI] An anchor assembly comprises a long casing 78 having means 126 for the introduction of cementing material and a flexible tensile element 80 extending substantially the whole length of the casing and projecting from the top thereof, the lower parts of the element 80 being bonded by the cementing material to the casing, whilst the upper parts are maintained free from bond by a sleeve 104 so that axial forces on the element 80 may produce relative axial movements between the upper parts of the element 80 and the casing 78. The anchor is particularly intended for moorings or for locating off-shore drilling platform structures, and in these cases, the upper part of the assembly, after cementing, is bent over by a laterally applied force on the element 80, the bend being in the direction of the force when in use. In Fig. 2, a drilling barge is moored above the proposed site of the anchor, and a bore 56 is made by a drill string which is guided down lines 44, 46 attached to a weighted template 42 carrying a guide funnel 54. The anchor assembly is guided down the lines 44, 46 by arms 66 into the well bore, the anchor line 60 passing through the rotary table 58 and being held therein by slips 68 when further lengths are to be added. The element 80, as shown, consists of four cables 84, 86, 88, 90 which are splayed out at different levels towards the lower parts of the casing 78, and held by spiders 132, 136, 138, 140 which are clamped to the cables. The lower spider 140 is secured to the bottom of the casing and has openings 144 for passage of the cementing material. The sleeve 104 is filled with a non-adhering material 106, e.g. a bituminous substance, heavy lubricant, packed sand or a plastic polymer. The element may be inserted in the casing before submerging, or after the casing has been run into the bore. Grout is pumped through the pipe 72 into and through the easing, and into the space between the casing and the walls of the bore hole, a hole 127 permitting the escape of air. The pipe 72 is disconnected and the template 42 lifted up, the arms 66 being connected to the nachor assembly by pins which shear when the template is raised. A side pull on the line 60 is then applied to bend over the casing, so that the operational pull on the line is axial relatively to the top of the casing which during the bending becomes buried in the sea-bed. If the sea-bed is of resistant material it is broken up by drilling or explosive, to allow the casing to become buried and to ensure that the curve of bending is smooth and tangential to the vertical lower parts of the casing. The cementing material on the outside of the bend 186, Fig. 8 (not shown), becomes broken, but on the inside is under compression. The cable arrangement 80 may be replaced by a chain. The bending of the anchors may be effected in opposed pairs, e.g. one anchor on each side of a drilling structure, by connecting the ends of the anchor lines 60 to a pair of winch drums on a barge, which are driven in synchronism. The element 80 is looped over a shackle pin 96 connected to a bifurcated member 98. The anchor lines 60 are of neutral buoyancy to eliminate the tendency of the lines to operate as catenaries in use, i.e. they operate in straight lines. The neutral buoyancy is attained by forming the anchor lines from hollow links 60, or by covering a wire cable with a buoyant material, such as a cellular plastic, or by buoying a wire cable at intervals. To facilitate the bending of the casing 78, the upper part of the casing may be made of thin walled steel pipe, a resinous polymer, or a ductile material which bends under transverse loads.