Post grouting of drilled shafts

Considering the strain incompatibility between end bearing and side friction of drilled shafts, tip capacity is often discounted from total shaft capacity. This is due to the relatively large displacements required to mobilize the tip which often exceed service load displacement criteria.

 

To regain some of the unusable capacity of the tip, pressure-grouting the shaft tip after its construction has been successfully employed throughout the world. The process is known as Post Grouting or sometimes Base Grouting or Tip Grouting.

 

The post grouting process entails:

 

1. Installation of a grout distribution system during cage preparation that provides grout tube-access to the bottom of the shaft.

 

2. After the shaft concrete has cured, injection of high pressure grout beneath the tip of the shaft which both densifies the in-situ soil and compresses any debris left by the drilling process.

 

A major advantage of the post grouted drilled shafts is that they typically mobilize their tip capacity at lower displacements.