Reliability-based design - Risk and Reliability in Geotechnical Engineering - page 365

(a)

P H =421 kN

Deflection y (m) Moment M (kNm) Soil reaction (kN/m)

y =1 m

-200000 20000 -500 0 500

-0.05 0.00 0.05 0.10

0 0

0

seabed

seabed

e =26 m

5 5

5

water

10 10 y = 60 mm

10

z = 0

seabed

15 15

15

Stiff clay
c u =150 kPa

20 20

20

Steel pipe pile,
d =1.3 m

25 25

25

z = 23 m

(c)

(b)

1500

z =22 m

γ′= 11.8 kN/m 3
c u = 150 kN/m 2
J = 0.25
B = 1.3 m
ε = 0.01

1000

12 m

1.5

500 β =3 (bending)

c

z =0 m

1.45

0

β = 3 (deflection)

z =0 m

a

1.4

-500

b

-1000

1.35

30 32 34 36 38 40

z = 22 m

Steel wall thickness (mm)

-1500

-0.3 -0.1 0.1 0.3

y (m)

Figure 9.12 Multi-criteria reliability-based design of a laterally loaded pile in spatially autocorrelated clay: (a)
Numerical procedure for nonlinear p - y analysis of a steel tubular pile in a breasting dolphin; (b)
Matlock's nonlinear p - y curves; (c) combinations of pile external diameter and wall thickness for
reliability index β of 3.

at 26 m above the seabed can be inferred from statics once the deflection and rotation of
the pile at seabed level are known. The Matlock p-y curves for clays, as shown in Figure
9.12b , have been used. The p-y curves are nonlinear, exhibit strain softening, and vary with
depth. The calculated pile deflection ( y i ) at seabed level (where z = 0) is 0.0602 m. The pile
head deflection (at 26 m above the seabed) is, by integrating the moment-curvature equa-
tion, 0.994 m or about 1 m. Separate analysis using a specially written Fortran program to
perform the finite-element analysis using 60 equally spaced elements yielded a pile deflection
of 0.0596 m at seabed level, compared with 0.0602 m in Figure 9.12 , and practically identi-
cal shear and moment distribution along the pile length.
For reliability analysis, the 23-m embedded length of the pile was discretized into 30 seg-
ments of progressively greater length. The random variables are the lateral load P H at pile