Construction method for planting hollow columns in a seabed of a marine environment for supporting waterborne structures thereon

Abstract

In a construction method for planting a hollow column ( 21 ) in a seabed ( 2 ) for supporting a waterborne structure ( 11 ) thereon, a steel tube ( 101 ) is driven into the bed ( 2 ) to the founding stratum ( 5 ), with materials of the bed ( 2 ) within tube ( 101 ) excavated and any surplus steel tube ( 101 ) cut off. A first segment ( 1 A) is inserted into tube ( 101 ), then second/subsequent segments ( 2 A- 8 A) are joined tightly to its previous segment ( 1 A- 7 A) to form column ( 21 ). Pressure grouting fills gaps between the tube ( 101 ) and column ( 21 ). Upon hardening, the tube ( 101 ) and column ( 21 ) form an integral unit adapted to take loads due to a surface friction resistance present between the steel tube ( 101 ) outer surface and soil materials ( 4 ) of the seabed ( 2 ), and due to an end bearing resistance present between the base of column ( 21 ) and the founding stratum ( 5 ).

I claim: 
     
         1 . A construction method for planting a bottom-closed hollow column into a seabed beneath water of a marine environment, the hollow column adapted to support a waterborne structure thereon, comprising:
 (a) driving a steel tube having an internal diameter with a margin tolerance greater than the external diameter of the hollow column into the seabed at an installation location thereof until it reaches a founding stratum of the seabed,   (b) excavating any material of the seabed that is present inside the steel tube down to the founding stratum,   (c) lifting a bottom-closed first segment of the hollow column into the steel tube vertically so that it floats on the water, and while the first segment is held in position, lifting a second segment onto the first segment in an end to end relation, the first and second segments aligned via match cast positioning blocks and shear keys, where opposed, joining faces of the first and second segments are coated with an epoxy resin or equivalent and joined by a compression set up by a plurality of stressing bars threaded through a plurality of preformed ducts extending across the joining faces, and where the lifting and joining steps are repeated until a final segment is joined such that it is exposed above the water surface,   (d) filling up any gaps and cavities present between the steel tube and hollow column and between a base of the hollow column and founding stratum by applying a pressure grout of underwater concrete and cement, wherein after hardening the hollow column and steel tube form an integral unit adapted to take loads due to a surface friction resistance present between the steel tube outer surface and soil materials of the seabed, and due to an end bearing resistance present between the base and the founding stratum, and   (e) cutting the steel tube at a mud line level of the seabed, wherein step (e) is performed between steps (b) and (c) or alternatively after step (d).   
     
     
         2 . The method of  claim 1 , wherein the base is embodied as a bottom slab that is tapered with its apex pointing downward to serve as a lowest point of the slab, thereby allowing grout egressed from the lowest point to flow and rise so as to facilitate filling the gaps and cavities around the hollow column. 
     
     
         3 . The method of  claim 1 , further comprising backfilling a layer of sand or stone in the bottom interior of the steel tube. 
     
     
         4 . The method of  claim 1 , wherein
 the hollow column is assembled from a plurality of match cast segments, and   a reverse profile of shear keys are formed in a given match cast segment by casting against the face of the segment with shear keys of a completed match cast segment.   
     
     
         5 . The method of  claim 1 , wherein
 the hollow column is assembled from a plurality of match cast segments, and   a reverse profile of positioning blocks are formed in a given match cast segment by casting against the face with positioning blocks of a completed match cast segment.   
     
     
         6 . The method of  claim 1 , wherein uniformly distributed shear keys, such as triangle-shaped shear keys with sharp tips pointing downward, are welded to the inner face of the steel tube to increase bonding between the steel tube and the hollow column. 
     
     
         7 . The method of  claim 1 , wherein a platform of the waterborne structure includes a plurality of openings, each for insertion of a corresponding hollow column therethrough as the platform is supported on a temporary floater. 
     
     
         8 . The method of  claim 1 , wherein the waterborne structure includes a platform, with the hollow columns serving to support the platform thereon as the hollow columns are casted to corresponding platform joints. 
     
     
         9 . The method of  claim 1 , wherein space within the hollow columns are adapted for storage. 
     
     
         10 . A construction method for planting a bottom-closed hollow column into a seabed beneath water of a marine environment, the hollow column adapted to support a waterborne structure thereon, comprising:
 (a) driving a steel tube having an internal diameter with a margin tolerance greater than the external diameter of the hollow column into the seabed at an installation location thereof until it reaches a founding stratum of the seabed,   (b) excavating any material in the seabed that is present inside the steel tube down to the founding stratum,   (c) placing the entire hollow column into the steel tube vertically and ballasting it with water until it sinks to a final depth at the founding stratum,   (d) filling up any gaps and cavities between the steel tube and hollow column and between a base of the hollow column founding stratum by applying a pressure grout of underwater concrete and cement, where after hardening the hollow column and steel tube form an integral unit adapted to take loads due to a surface friction resistance present between the steel tube outer surface and soil materials of the seabed, and due to an end bearing resistance present between the base and the founding stratum, and   (e) cutting the steel tube at a mud line level of the seabed, wherein step (e) is performed between steps (b) and (c) or alternatively after step (d).