SPECIFICATIONS

File No.: FN321
Page 6
TABLE 3.2: ULTIMATE GEOTECHNICAL RESISTANCE
Depth (m)
R n
0.0 to 2.0 Nil
2.0 to 2.6 50*A s
Below 2.6
720*A p + 54*A s
Where:
R n = ΣR n 0.0 m to 2.0 m + ΣR n 2.0 m to 2.6 m + ΣR n > 2.6 m
and
A p is the area of the pile tip (m 2 ); and,
A s is the area of the pile shaft (m 2 ).
The skin friction contribution of the upper 2.0 m of pile below finished grade
should be ignored in the determination of pile capacity.
3. Construct all piles, even lightly loaded piles, with tip depths three times the
depth of seasonal frost penetration to provide sufficient pull out resistance to
potential frost jacking. The frost penetration for exterior concrete piles is
estimated at 2.5 m; therefore, the minimum pile tip depth will be 7.5 m.
4. Typically, belled piles are used to support heavier loads than straight-shaft piles.
In order to derive the design bearing capacity, the base of any belled pile must
be at least five bell diameters below finished surface, or at least 4.0 m below
ground surface in the clay till, whichever depth is greater. End bearing, belled,
cast-in-place concrete piles formed in the clay till may be designed for an
ultimate end bearing of 720 kPa. There is no skin friction contribution in
calculating the capacity of belled piles.
5. The bell base must be at least 200 mm high and the roof of the bell must be no
steeper than 60 degrees, measured from horizontal.
6. Seepage was encountered during borehole drilling so seepage or sloughing will
occur during pile excavations. Casing will be required if seepage or sloughing is