Rock foundations - Geotechnical Investigation and Design Tables - page 290

Table 22.14 Shaft capacity for bored piles in rock (adapted from Seidel and Haberfield, 1995).

Adhesion Ultimate side shear resistance (MPa)

τ =

factor

ψ

(Seidel and Haberfield, 1995) Other researchers

0.5 0.1 (q u ) 0 . 5

1.0 (Lower 0.225 (q u ) 0 . 5 Lesser of 0.15 q u (Carter and Kulhawy, 1987) and

bound) 0.2 (q u ) 0 . 5 (Horvath and Keney, 1979)

Dyveman & Valsangkar, 1996

2.0 (Mean) 0.45 (q u ) 0 . 5

3.0 (Upper 0.70 (q u ) 0 . 5

bound)

22.15 Shaft resistance roughness
•

The shaft resistance is dependent on the shaft roughness.

•

The table below was developed for Sydney Sandstones and Shales.

Table 22.15 Roughness class (after Pells et al., 1980).

Roughness class Grooves

Depth Width Spacing

R1 1mm 2 mm Straight, smooth sided

< <

R2 1-4 mm

>

2 mm 50-200 mm

R3 4-10 mm 5mm

>

R4 10 mm 10 mm

> >

•

Roughness can be changed by the type of equipment and procedures used in
constructing the pile shaft in the rock.

•

Above R4 condition is used in Rowe and Armitage (1984) for a rough joint.
Therefore a universality of the above concept may be used although specific groove
numbers can be expected to vary.

22.16 Shaft resistance based on roughness class
•

The shaft resistance for Sydney Sandstones and Shales can be assessed by applying
the various formulae based on he roughness class.

•

τ = Ultimate Side Shear Resistance (MPa).

•

q u = Unconfined Compressive Strength of Intact Rock (MPa).

Table 22.16 Shaft resistance (Pells et al.,1980).

Roughness class Ultimate side shear resistance (MPa) τ =

R1 0.45 (q u ) 0 . 5

R2
R3 Intermediate

R4 0.6 (q u ) 0 . 5