Method and apparatus for making an expanded base pier

1. A method of constructing an expanded base pier with known expanded base volume, the method comprising:

(a) providing a mandrel assembly comprising a single-wall tube portion and a tamper head, the tube portion having an exterior diameter, wherein the tube portion is connected to the tamper head at an opening thereof for allowing flowable material to flow into the tamper head, and wherein the tamper head comprises a defined lower enlarged chamber having an interior diameter greater than the exterior diameter of the tube portion and further comprising a reducing surface at an upper portion thereof and comprising a plurality of chain links for compaction and for restricting upward flow of the flowable material into the tube portion during tamping, the tamper head further sized to provide an enclosed region for allowing the flowable material to be placed therein;

(b) providing a non-moveable sealed top plate on an end of the tube portion opposite the tamper head and a separate flowable material supply tube coupled to the tube portion via a sealed connection;

(c) providing a pressure gauge for monitoring air pressure within the tube portion;

(d) driving the mandrel assembly having an initial volume of the flowable material into a ground surface to a given depth thereby forming a cavity;

(e) lifting the mandrel assembly to release the initial volume of the flowable material from the tamper head into a bottom of the cavity while adding a secondary volume of flowable material;

(f) re-driving the mandrel assembly wherein the plurality of chain compact the initial and secondary volumes of flowable material at a bottom of the cavity and to form a unitary expanded base, the expanded base having a width greater than the width of the tamper head;

(g) measuring air pressure within the tube portion during the driving, lifting, and re-driving steps to determine a pressure drop indication;

(h) calculating a unitary expanded base volume based on the pressure drop indication and initial and secondary volumes added for comparison with a design expanded base volume; and

(i) upon reaching the design expanded base volume, withdrawing the mandrel assembly while continuously discharging cementitious material from the tamper head, thereby forming, after curing, a stiff cementitious inclusion having a width substantially equal to the width of the cavity and being formed above the expanded base.

2. The method of claim 1 wherein the tamper head is filled with the initial charge of the flowable material before driving.

3. The method of claim 1 , further comprising introducing the flowable material into the enclosed region.

4. The method of claim 1 , further comprising providing the mandrel assembly with a second tube adjacent the tube portion and fluidly connected to the enlarged chamber to allow for an inspection of the flowable material during pumping.

5. The method of claim 1 further comprising an air pressure source connected to the tube portion for evacuating flowable material from the tube portion through air pressure supplied thereto.

6. The method of claim 1 wherein the flowable material comprises one or more of aggregate, concrete, grout, and cementitious material.

7. The method of claim 1 further comprising providing an air pressure release valve for reducing pressure in the tube portion.

8. The method of claim 1 further comprising providing a pressure gauge for monitoring pressure within the tube portion.