Greetings, Does anyone have experience driving pipe piles into decomposed rock for high capacities (specifically mica schist in NYC). The rock is 50 to 100+ blows per 6" penetration with a split spoon. Contractor is looking to get 150-200T design loads but is concerned with creep. Looking for actual load test experience if possible.... Thanks, Marc
The comments that follow are not based on working experience of the decomposed rock in NYC, although I have some working experience with the behaviour of mica schists in Trinidad,WI,related to slope instability where bedding planes and water play a significant role.
To afford some ideas regarding the contractor's concern of creep, it is necesarry to know the load capacities affored by shaft resistance and by toe resistance, respectively. However, this could be of some help in your assessment - One published work reports pressuremeter tests done in decomposed rock with values of creep pressure and recommended ultimate bearing pressures varying from 20 to 30 kips/ft2, 10 to 15 kips/ft2 as maximum allowable bearing pressure, and limit pressure (assumed ultimate failure pressure) approaching 60 kips/ft2. You may also find information in the Geotechical Special Publication No.100 "New Technological and Design Developments in Deep Foundations" to be of interest as well.
Poulus and Davies have provided brief info on creep settlements in their text "Pile Foundation Analysis and Design"(1980). Creep has as well many definitions. In closing, I would venture to guess in the absence of pile length, pile size and overburden soil characteristics that this phenomenon should not be a concern for the range of proposed design loads.