Tension Piles

For checking of uplift capacity of piles, Ra and Ru shall be calculated. However, Ra and Ru are not clearly defined in the Code of Practice for Foundation 2004 (for HKSAR).

In the COP, Ru is defined as "ultimate anchoring resistance of the pile" (Clause 5.1.6 and 5.3.3) while Ra is defined as "allowable anchorage resistance of the pile" (Clause 5.3.3).

As mentioned in the CODE, in general, Ra = allowable uplift resistance of the pile shaft + effective self weight of pile.

To summarize, Ra and Ru may be taken as below:
(i) Ru = the weight of soil cone near the pile
(ii) Ra = smaller value of (Bonding capacity of pile socket, Ru/ F.O.S. of 2)

Moreover, Ra is usually taken as less than 1/2 of piles' compression capacity in order to get rid of uplift test of tension pile.