Design of pile groups - Piling Engineering - page 200

Figure 5.15 Pile group analyzed in comparative study.

A detailed comparison of the results computed by the latter two programs has been
presented by Poulos and Randolph (1983) (some results obtained using PGROUP are
also included). As an illustration of the degree of agreement between the two programs,
and also to show the type of parametric study which such programs may be used for,
the effect of pile rake on a simple 3 2 pile group is presented here. The pile group

details are given in Figure 5.15, the angle of rake of the piles being denoted by

×

ψ .

A flexibility matrix for the group may be written
⎡

⎤ ⎡ ⎤ ⎡ ⎤

F wP F wH F wM

w
u
θ

P / Gr 0

⎣ ⎦ = ⎣ ⎦ ⎣ ⎦

F uP F uH F uM H / Gr 0

(5.21)

Gr 0 F

θ

F F M /

θ θ

P H M

Since the group is symmetric, the terms in F wH , F wM and F

P will be zero. Also, from θ

the reciprocal theorem, F uM must equal F

H , giving only four independent flexibility θ

coefficients.
The variation of these coefficients with the angle of rake, , is shown in Figure 5.16.

Both programs give very similar results, the largest discrepancy being 18%. The most
striking effect of varying the angle of rake of the corner piles is the change in sign
of the group rotation under horizontal loading; groups of vertical piles rotate in the
direction of loading, but the inclusion of piles raked at even modest angles can reduce
this rotation and even reverse the sense of it. The effect of double rake of the piles is
relatively small in the plane of loading.

ψ