Method and apparatus for forming cemented ground support columns
A method and apparatus for forming cemented ground support columns is disclosed. Namely, driving mandrels are provided for the efficient construction of incrementally enlarged diameter support columns. For example, the driving mandrel includes a feed tube that has a top portion and an expansion head portion. The expansion head portion further includes an expansion (or compaction) chamber and a flexible tubular egress port. Further, construction methods are provided of using the driving mandrels for the efficient construction of incrementally enlarged diameter support columns.
1. A method for constructing a support column, comprising the steps of:
providing a mandrel assembly having a feed tube operatively connected to an expansion head, wherein the expansion head comprises an expansion chamber and an egress port within the expansion chamber, the egress port being adapted for crimping;
driving the mandrel assembly into a ground surface to a prescribed initial depth with respect to the ground surface level;
adding infill material to the feed tube, wherein the infill material has sufficient mobility for advancing within the feed tube and through the egress port;
driving the mandrel assembly further into the ground surface to a prescribed driving termination depth with respect to the ground surface level;
raising the mandrel assembly above the prescribed driving termination depth;
forming a space at the bottom of the mandrel assembly;
allowing a first portion of the infill material to exit through the egress port by gravity into the expansion chamber and into the space;
forming a first placed infill material at the prescribed driving termination depth;
constructing an expanded diameter of the first places infill material, the constructing step comprising the step of re-driving the raised mandrel assembly downwards into the first placed infill material;
crimping and constricting by the egress port to prevent upward movement into the egress port by the first placed infill material and;
allowing the expansion chamber to push the first placed infill material downward and outward at a prescribed expanded diameter ground depth with respect to the ground surface level.
2. The method as recited in claim 1 , wherein the adding step is done by pumping the infill material into the feed tube.
3. The method as recited in claim 1 , wherein the infill material is mobile medium slump concrete, mobile high slump concrete, sand-cement grout, or neat cement grout.
4. The method as recited in claim 1 , further comprising the step of raising the mandrel assembly above the expanded diameter of the first placed infill material.
5. The method as recited in claim 4 , further comprising the step of allowing a second portion of the infill material to exit through the egress port by gravity into the expansion chamber.
6. The method as recited in claim 5 , further comprising the step of constructing a shaft above the expanded diameter of the first placed infill material.
7. The method as recited in claim 1 , further comprising the step of forming a second placed infill material at a different depth than the prescribed driving termination depth.
8. The method as recited in claim 1 , further comprising the step of forming a second placed infill material having a different diameter than the first placed infill material and at a different depth than the prescribed driving termination depth.
9. The method as recited in claim 1 , further comprising the step of compacting the first placed infill material to have a diameter a larger than the diameter of the expansion chamber.