Tell Tales 3

[Russellccooper]

I have had a lot of confusion recently over the appliction and installation of a telltale in an Auger cast pile. Could some one please explain to me what one would entail and how I would get any kind of result from it? I hae been told several things but have been lead to believe that it is just a piece of rebar?

 

[GeoPaveTraffic]

Russellccooper;

A telltale really is just a piece of rebar. However, it is not the material but how it is installed and used that make it a telltale. The most common application is to use the telltale to measure the deflection of the pile at a location other than the pile butt, usually the pile tip and usually during a pile load test.

To measure the deflection at the tip the telltale must be anchored to the pile grout at the tip, but isolated from the pile grout everywhere else. This is done by placing the telltale(rebar) inside a smooth plastic sleeve and sealing the ends of the sleeve around the rebar. Sometimes the annular space if filled with grease or some other compound to help prevent grout intrusion. If the rebar is not isolated from the grout by the sleeve, the telltale will not work properly.

Once installed in the pile and the pile has cured, the load test is carried out with one difference. In addition to measuring the deflection of the pile butt, the movement at the bottom of the telltale is also measured. Using the relative movement data, the total pile capacity can be divided between skin friction and tip resistance.

Hope this helps.

 

[Focht3]

A tell-tale can also be made with "small" PVC or black pipe and all-thread rod. The use of all-thread makes it easier to adjust the length of the tell-tale. And it is much easier to get a good seal at the bottom of the PVC or black pipe, since you an use washers and nuts inside and outside the end cap.

Also note that you can install multiple tell-tales in a pier/pile, which makes evaluating the load-deformation of long shafts much easier. Combining tell-tales with Mustran cells is a very powerful way to 'directly measure' the soil load transfer relationship. This is a lot better than trying to guess the proportions of skin friction and end bearing - not to mention how they respond under loading...



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"