Existing know-how
Present knowledge about time effects in clays is that the capacity may increase by 10-50% within 1-2 years after installation and to 50-200 % after 10 years.
From NGI pile tests at Haga in 1981-1983 ( )
Some past experiences are:
- old pile load test database collected by Flaate, (1966) suggested considerable time effects
- NGI's pile load test programs 1980-1990 confirmed significant time effects, and the importance of plasticity index, Ip
- NGI, in cooperation with C.J.F. Clausen have established a new worldwide database for pile capacity in clays and sands
- recent new pile tests in Iran, Minnesund (Norway) and Cowden (UK) confirm significant time effects
- documented difference between first-time testing and repeated testing (see figure).
Effect of several load tests on capacity of Haga piles
Recent examples of time effects
- Oromieh bridge in Iran (picture above) - pile that had been in the ground for 10 years (without carrying any loads) showed 2.1 times the skin friction of a new test pile installed in 2002
- Minnesund bridge - pile tested in 1992 showed an increase in capacity by a factor of 2.7 when re-tested in 2006
