By Antonio Marinucci and Marco Chiarabelli
Drilled displacement piles (DDP) refers to a specialized technology in which a bored pile is constructed using a process in which a specially designed tool is advanced into the ground using both rotation and downward thrust (“crowd force”) to displace the in situ soil radially outward into the surrounding formation, and concrete is injected and steel reinforcement (if required) is inserted to fill the created hole and provide structural stiffness.
DDP has been used as structural foundation elements (e.g., support column loading) and for ground improvement (e.g., column-supported embankments) on both commercial and public work type projects. The maximum diameter and depth that can be achieved are directly related to the capability of the drill rig used to construct the DDP.
The Benefits of Displacement Piles:
A schematic of a representative displacement tool figure shown highlights many of the common components found on modern DDP tools. In general, modern displacement tools will contain the following common elements: (1) displacement body, which is an enlarged section near the bottom of the drill string that facilitates soil movement radially outward, thereby displacing it into the surrounding soil; (2) a drilling tip attached to the bottom of the drill string that is used to loosen the soil during the advancement of the tool (if a re-usable drilling tip is used, a pivoting gate located near the bottom of the tool or drill string is utilized for the injection of the concrete or grout; otherwise, with a sacrificial drilling tip, the concrete or grout is injected through the bottom of the drill string); (3) a hollow stem drill string with a diameter smaller than or equal to the diameter of the displacement body; (4) a lower auger segment with partial flights that moves the soil upward toward the displacement body; and (5) an upper auger segment with partial flights that moves the soil downward toward the displacement body.
- Environmentally friendly because minimal amount of drill spoils produced return to ground surface, thereby lowering both the risks associated with transport of spoils (especially contaminated material) and the cost of disposal;
- Minimal vibration induced during the construction of the displacement pile because the rotary
- drilling technique does not induce large vibrations into the soil;
- Even in loose soils, the borehole can be formed without need of steel casing and/or slurry;
- Cleanness of the working platform, lowering the risk to injury of onsite personnel;
- Compared with non-displacement bored pile techniques, the concrete overbreak is significantly lower; and
- Compared to non-displacement bored pile techniques, higher unit side friction and end bearing resistance can be achieved through the compaction of the surrounding soil, which results in a lower cost (per ton of load).
Soilmec’s hydraulic drilling rigs and patented displacement piling technique using the Traction Compaction Tool (TCT) reduces the amount of torque and crowd force required to turn the tolling and penetrate the ground.
Contact us today to learn more about our DDP technology.