Precast Concrete foundation piles are often driven from the surface level and then cut at the required depth after excavation of the construction pit. The excavation depth is dependent on the type of project， typically decided by underground levels for parking. This can lead to the waste of each pile of up to 10 meters. Reducing this waste does not only reduce material and installation cost， but also requires shorter pile lengths to be transported by truck.

In Holland the following method is a popular solution to this problem:

1. Install a retaining wall， preferably with sheet piles or combi-wall; alternatively an SMW or diaphragm wall can be chosen

2. Set up a steel casing with detachable base plate at ground level.

3. Drive the now closed bottom steel casing into the soil， the length of the casing should be length of pre-cast pile + excavation depth. During driving the pile， the soil is displaced and improved

4. Check to see if the tube is dry and clean

5. Lift a pre-fabricated， pre-stressed concrete pile with head reinforcement and possibly ridges for connection to a concrete floor into the casing
 

6. Pour grout into the casing to fill around the pile over the length of the bearing soil layers to improve shaft friction. Once the space between the casing and pile is filled the steel tube is ready to be withdrawn
 

7. Extract the casing by vibratory hammer， the casing is now ready to be used again

8. Excavate the construction pit by excavator or sand pump

9. Pour a concrete floor onto the floor of the pit

 

The method is suitable for complicated soil profiles and softer soils， especially those in a river delta like Shanghai.

The advantages are:

• Suitable for a wide range of pile diameter designs 

• Soil improvement achieved as the vibro-combination pile is a soil displacement method

• No risk of pile damage pre-stressed concrete piles in case of heavy piling works

• Saving pile length， no pile cutting needed

• Easier transport of (shorter) piles in city center

• No bentonite is needed， no soil is excavated

• Best solution for very weak deeper soil layers where creating a cast-in-situ pile shaft is impossible

More information about the pile:

Precast concrete piles have a large tensile force combined with the rougher wall and larger cross-section of a vibro pile， thus enhancing the tensile performance through soil friction. This type of pile is often ribbed at the top to connect well with the floor that is to be poured. The system is used for tunnels and basements， often together with an underwater concrete floor. 

Recommended equipment:

1. DRIVING: ICE Impact hammer， a noise-reducing shroud may be fitted.

2. EXTRACTING: ICE Resonance Free vibratory hammer

3. PR-90 piling rig for accurate pile positioning and high-output pile production

Special aspects

• Pre-drilling preceding the production process could considerably reduce driving time.

• Sound reductions can be realized during the production process whenever a sound shield is applied.