Enlarged Tip Piles for Granular Soils

Enlargement of pile tip increase bearing capacity of pile. This technique is generally used in granular soils. This technique can be performed in several ways. One type of enlargement is achieved by driving a tube at the bottom with a concrete plug to the desired depth. When is added the concrete plug is forced out into the soil. After base is completed the tube is withdrawn. But this withdrawal continues while the concrete expands out at the tip of the tube. This process forms a cast-in-situ (CIS) concrete shaft.

Alternately, corrugated shell casing or a pipe is bottom-driven into the base and the tube withdrawn. This forms an annular space between pile and soil. This annular space either filled with granular filler material or else closes onto the shell. This piling work is then completed as a cast-in-place (CIP) concrete pile. In these either CIP or CIS piling techniques, the shaft is provided with steel reinforcement as requirement of the design that consider structural capacity of pile  (both axial capacity of pile and lateral capacity of pile).

In the above figure phase (1) to (3) depict the boring of gain desire depth and using expandable wings to make enlarge base and then concreting to fill the base. The phase (4) shows that the withdrawal of boring system and  the phase (5) shows lowering of cast in place pile to touch the base cast previously.

The another alternative are achieved by attaching to pile shaft a reinforced concrete base having shape like a frustum of a cone. This is very common to use a corrugated shell shaft or a pipe having thin-wall and enlarged tip base being mandrel driven to bear in generally granular subsoils. As a cast-in-place pile the shaft is completed and steel reinforcement is provided as explained earlier. Enlarge-tip base in the above explained precast form can be used with solid shafts like timber piles and it can be of sizes of wide range.