Pile Design and Construction Practice, Fifth edition

corrected for overburden pressure when relating them to the Berezantsev or Brinch
Hansen Nqfactors.
The base resistance of open-end piles driven into sands is low compared with closed-end
piles, except when a plug of sand formed at the toe is carried down during driving. The
mechanics and effects of plug formation are discussed in Section 4.3.3.
Kulhawy(4.22)calculated the ultimate base resistance for very loose and very dense sands
in dry and saturated conditions (i.e. in the absence of groundwater and piles wholly below
groundwater level) for a range of depths down to a penetration of 30 m. Unit weights of 18.1
and 19.7 kN/m^3 were used for the dry loose and dense sands respectively. These values
shown in Figure 4.12 may be used for preliminary design purposes in uniform sand deposits.
For densities between very loose and very dense the base resistance values can be obtained
by linear interpolation.
Reduction in the rate of increase in base resistance with increase in penetration depths
is also shown by Berezantsev et al.(4.21)Their values of Nqrelated to and depth/width
ratios are shown in Figure 4.13. Ultimate base resistance values using these factors
have been calculated for a closed-end pile of 1220 mm diameter driven into loose sand
having a uniform unit submerged weight of 7.85 kN/m^3 in Figure 4.14. The angle of
shearing resistance of the sand has been assumed to decrease from 30 at the soil surface
to 28 at 30 m depth. It will be seen that the Berezantsev Nqvalues gave lower base resistance
than those of Kulhawy. In Figure 4.13 the Berezantsev factors are compared with those
of Brinch Hansen(5.4). The latter have been adopted by the American Petroleum
Institute(3.5).
A similar comparison was made for the 1 220 mm pile driven into a dense sand having a
uniform unit submerged density of 10.8 kN/m^3. The angle of shearing resistance was
assumed to decrease from 40 at the soil surface to 37 at 30 m. Figure 4.14 shows that
the Kulhawy base resistance values in this case were lower than those of Berezantsev.



Resistance of piles to compressive loads 167

Depth below ground surface (m)

01020

Saturated sand

Dry sand

Very dense

Very

loose

30 40

0

10

20

30

Ultimate base resistance (MN/m^2 )

Figure 4.12Approximate ultimate base resistance for foundations in sand (after Kulhawy(4.22)).