Calculation of Grout Head for Auger Cast Pile

[eric1037]

I have a couple of installation questions:

1. During ACP installation, the specs require 10 feet of grout head above the auger tip. How do you calculate the volume required to maintain 10 feet of head? Do you assume the hole to be empty above the tip, or do you assume the auger and soil take up a portion of the hole? If it's the latter, what percentage of the hole is taken up by the soil and auger?

2. Once the auger tip is reaches the design tip elevation, grout is pumped to get the 10 feet of grout head. The specs require 110% of the theoretical grout volume to be pumped into the hole. Does the initial pumping of grout to attain the 10 feet of grout head count as part of the 110%?

Thanks and I look forward to your responses!

eric1037

 

[GeoPaveTraffic]

The way I have always done it is to assume that the hole is empty, therefore the number of required pumps is the number to fill 10 feet of pile.

As for the 110%, all pump strokes should be counted.

 

[eric1037]

GeoPaveTraffic:

Thanks for the reply. I agree that it should be conservative to assume that the hole is empty. However, in reality, the hole is almost entirely full. It has been some time since I have seen auger cast installed, but if I remember correctly, they screw the auger in, then start grouting, while pulling the auger up to remove the soil.

Therefore, the hole should be taken up mostly by soil and auger.

However, is the head required actually the grout in the hole or does it represent the pressure due to 10 feet of grout? Is it a pressure head or an elevation head?

If it's a pressure head, then I agree with you completely. It would be the amount of grout (and pressure) required to fill the hole if it was completely empty. However, if it's an elevation head, then whatever amount of grout causes the grout to rise 10 feet above the tip should be sufficient.

Maybe it's all academic.

The main reason I ask is that there is a dispute about how much grout actually causes 10 feet of head to develop above the tip of the auger.

 

[GeoPaveTraffic]

The purpose of the grout head is multifold. First it provides some head to help prevent the hole from caving in some soil types. Second it provides some cushion if the operator pulls the auger too fast or if the pump is not putting out quite enough grout for some reason.

All in all, it is not a significant amount of grout and the contractor should not be arguing over it.